437
MIOCENE PRIMATES FROM KENYA
Miocene Primates from Kcnya. By A. TINDELL
HOPWOOD,
D.Sc., F.L.S.,
Department of Geology, British Museum (Natural History).
(PLATE
6)
[Read 26 October 19331
I. INTRODUCTION.
Several years ago, Mr. E. J. Wayland, Director of the Geological Survey
of Uganda, sent to the Geological Department of the British Museum a small
collection of fossils which he had received from Dr. H. L. Gordon of Koru,
Kenya Colony. Dr. Gordon had found them on the surface of a kopje which
he was quarrying for agricultural lime. -4mong them was a nodule which
revealed the tip of a canine tooth. On development the enclosed fossil proved
to be the left maxilla of a large anthropoid ape with the cheek-teeth almost
unworn. Since the fossils were weathering out of beds presumed to be of
Lower Miocene age, this specimen was obviously of great interest and importance. I n view of the possibility of obtaining more fossils, it seemed better
t o refrain from publication in the hope that later consignments might contain
additional specimens of Primates.
These hopes were not realised until August 1931, when I visited Koru on
behalf of the Trustees of the British Museum. During the five weeks that
I was in camp nine more fragments of primate dentitions, as well as a rich
and varied fauna of lower mammals, were recovered. All the bones had
been broken before burial, and gnawed by rodents as they lay on the surface.
The fauna consists of two or three genera, which may prove to be lemuroids,
Dimtheriuna hobleyi, three genera of Creodonts, an amphicyonine carnivore,
several Rodents, two Insectivores-one very close t o Potamogale,-as well as
small pigs and ruminants.
The remains of higher primates are referred t o three new genera of Simiidae,
one of which is regarded as ancestral t o the Chimpanzee. Both the others
have become extinct.
11. SYSTEMATIC
DESCRIPTION.
All the specimens are in the Department of Geology, British Museum
(Natural History). The registered numbers refer t o the departmental registers
of fossil mammals.
Suborder CATARRHINA.
2
1
2
3
DIAGNOSIS.-P~missing. Dental formula I - , c - , P - ,M-2
1
2
3
.
Tympanic
forming a bony external auditory meatus. NO tympanic bulla.
Generally
31
WNN. JOURN,-&OOLOaY,
VOL. X,sXVIq
438
DR. A . TINDELL HOPWOOD ON
with a squamoso-frontal suture owing t o the preponderance of the frontal
and alisphenoid in the formation of the orbital plate. Orbito-temporal foramen
s m a l l . . . . (Weber, 1904, p. 783).
Family SIMIIDAE.
DIAaNosm-Upper and lower molars quadritubercular, labial and lingual
cusps alternating. Lower molars usually with a third labial cusp or 8 fifth
cusp on the posterior margin. I n the upper molars the labial cusps are more
or less closely connected with the anterior lingual cusp ; posterior lingual
cusp usually smaller than the anterior. Premolars bicuspid, wider than
long. (Adapted from Schlosser, 1923, p. 651.)
Genu 8 LIMNOPI
THRCI :r Hopwood.
1933. Ann. & Mag. Nat. Hist. (10) xi, p. 97.
DIAaNosIs.-Gibbon-like Simiidae with very low-crowned cheek-tceth in
the lower jaw. Length-breadth index of lower molars exceeding 90. Lower
molars with distinct external cingulum between the cusps.
GENoTuPE.-Limno~ithecuslegetet Hopwood.
LIMNOPITHECUS
LEGRTET Hopwood. (PI.6. figs. 1, 2.)
1933. Ann. t Mag. Nat. Hist. (10) xi, p. 97.
DIAQNOSIS.-AS
for the genus.
HOLOTYPE.-Afragment of the right mandibular ramus with the first and
second molars partly worn. Regd. M 14079.
PARATYPE.-Apiece of the left mandibular ramus with the two deciduous
cheek-teeth, and with the left lateral incisor still in the crypt. Regd. M 14080.
DIMENSIONS.-
-
.-
Dm3 :Length . . . . . . . . . . .
Breadth . . . . . . . . . .
Height. .........
..
Index . . . . . . . . . . . .
4.5
3.4
2.8
75.6
Dm4 : Length . . . . . . . . . . .
Breadth . . . . . . . . . .
Height. . . . . . . . . . . .
Index . . . . . . . . . . . .
-
5
4.2
2-1
84
-~
._
.~
~
..
..
..
..
..
..
..
..
-
..
3.8
2.6
2.4
68.4
..
..
..
..
4.6
3.5
2.4
..
..
..
~-- -
78.1
__~~
~~~
439
MIOCENE PRIMATES FROM KENYA
.
.
.
.
.
.
.
.
............
M 1 : Length . . . . . . . . .
Breadth . . . . . . . .
Height. . . . . . . . . .
Index . . . . . . . . . .
4.9
2.8
92.5
M 2 : Length . . . . . . . . .
Breadth ........
Height. . . . . . . . . .
Index . . . . . . . . . .
6.2ost.
6.0
2.8
96.8 est.
5.3
~
..
..
..
___.~
7.8
5.7
6.0
4.6
..
4.2
76.9
2.7
80.6
..
9.8
..
..
6.5
4.5
66.3
6.2
5.1
3.2
82.3
..
~
5.4
4.3
3
79.6
..
..
..
..
DEs(*mPTION.-The holotype will be described first.
The body of the mandible has undergone extensive post-mortem deformation,
with the result that the second molar is now about 3 mm. below the first.
This gives the second molar the appearance of rising from the crypt to replace
a lost deciduous tooth. But such is not the case, and, since the occl~sal
surface of the crown is worn, it is quite certain that the tooth has been displaced
after death.
Each tooth is built on the same general plan of a basin with five cusps on the
periphery, a basal cingulum between each CUSP, wihh the possible exception
of the two lingual cusps of the damaged first molar, and a small fovea anterior.
The hypoconulid is median. Each cusp is low, blunt, rounded, and slightly
worn a t the top, so that the dentine is just exposed. The metaconid of the
first molar and the protoconid and metaconid of the second molar have lost
the peripheral enamel. Hence the teeth have a false appearance of an
anterior narrowing.
The paratype is in perfect condition. It is deeper and heavier, but otherwise
agrees fairly well with the corresponding region in a young female Hylobates
Zeuciscus (B.M. Zool. Dept. 9.1.5.2). The symphysis extended back t o the
level of Dp3 ; the mental foramen is below the same tooth. Held with the
alveolar margin horizontal, the bone narrows from in front backwards. The
depth a t the anterior end of Dp3 is 12 mm. ; a t the posterior end of Dp4
it is 10 mm. ; the thickness is 5.5 mm. and 5 mm. a t the same places.
The third dcciduous premolar is not very compressed. It has a distinct
metaconid separated from the protoconid by a deep notch representing
the antero-posterior sulcus. The sharp antero-internal cingulum bounds a
relatively large trigonid basin, or fovea anterior, The talonid basin is
wide and deep.
3 1*
440
DR. A. TINDELL HOPWOOD ON
The succeeding tooth (Dp4) is quinquecuspidate, wider behind than in
front, and has anterior buccal and posterior basal cingula between the cusps.
There is a definite crista transversa anterior, which, together with the anterior
cingulum, bounds the fovea anterior. The hypoconulid resembles those of
the second dentition in being central. When the tooth is viewed from the
buccal or lingua1 aspects the trigonid and talonid are seen t o be of equal
height.
DIscussIoN.-There are two fossil forms with which this species may be
compared, namely, Pliopithecus antiquus Gervais and Prohylobates tandyi
Fourteau. The former hss a definite cingulum, the latter none a t a l l ;
Limnopithecus has a slight cingulum which causes small foveae between all
the ciisps except the metaconid and entoconid. I n this respect, therefore,
the new species i s intermediate between the European and Egyptian species.
On the other httnd, it agrees with Prohylobates and certain specimens of
Pliopithecus (Mayet & Lecointre, 1909, p. 63 ; Remane, 1921, p. 151) in the
median position of the hypoconulid.
Tn the genera which are still living, Symphalangus and Hylobates, there
is no cingulum, except anteriorly, and the hypoconulid has become slightly
buccal in position. I n Symphalangm the metaconid Rhowu a bifid tip. Moreover, the fossil has a greater breadth index :-M1.
...........
Lirnnopithecw,
Hylobatea ...............
Symphalangua ...........
92.5
80.6
16.9
M2.
90.8 eat.
82.3
06.3
This proves that Hylobates and Limnopithecus both differ from SymphaEangus
in having the second molar wider than the first-possibly, but not certainly,
a sign of greater specialisation.
I n its milk-dentition the fossil is more advanced than Hylobdea. This
is reflected in the well-marked metaconid of Dp3, the five cusps of Dp4 compared
with the four found in Hylobates, and in the relative heights of the talonid
and trigonid of Dp4, which are equal in Limnopithecus and unequal in Hytobates.
Hence there can be no doubt that Limnopithecus and Hylobates are distinct
genera.
Similarly, Limnopithecus and Symphalangus are distinct if t o the differences
previously mentioned be added the structure of the metaconid, which is simple
in the former and bifid in the latter.
Pliopithecw and Hylobates are so much alike that Hoffmann (1893) united
them. He showed that they agree, not only in the characters of the adults,
but that the milk-dentitions are also alike in the absence of a hypoconulid
on the posterior deciduous premolar. In this respect, therefore, Limnopithecus is distinct from Pliopithecus.
Other reasons for keeping the three fossil genera apart are the vS;rious
ages of the deposits in which they are found and their widely separated
441
JMIOCENE PRIMATES FROM KENYA
localities. Apart from convenience, neither reason is particularly sound,
but, when dealing with species founded on such fragmentary remains as those
of Prohylobates tandyi and Limnopithecus legetet there is much t o be said in its
favour. Prohylobates is from beds which Fourteau (1920) ascribed t o the
Burdigalian ; Pliopithecus begins in the Aquitanian of Sansan and passes up to
the top of the Miocene ; but Limnopithecus occurs in beds of which the age is
not definitelyknown. These beds are a t present termed Lower Miocene, because
they contain Dinotheriuni hobleyi. This species was first described from Karungu
on the shore of Lake Victoria, and by analogy with European faunas the beds
in which i t was found were termed Lower Miocene (Andrews, 19 14). Experience
shows that European standards are apt to be misleading when applied to
Africa, and that the age must be judged, not by survivors from the past such
as the creodonts, nor by the presence of Ilinotherium, but by the lakest most
advanced members of the fauna. Hence, apart from zoo1ogical considerations,
i t is convenient t o give these fossils from Kenya a separate generic name.
The trivial name is that, of the hill on whose slopes I had my camp, and
in whose shadow the specimens were found.
Genus XENOPITHE’C~
s Hopwood.
1933. Ann. & Mag. Nat. Hist. (10) xi, p. 97.
I)rAGNosIs.-Simiidae in which ridges connect the protocone t o the paracone,
metacone, and hypocone ; a fourth ridge connects the paracone and metacone.
Cusps of trigon crowded, subequal in size. Hypocone large, but somewhat
less than the cusps of the trigon. Anterior and posterior cjiigula distinct,
internal cingulum massive. Enamel on lingual surface of the protocones
wrinkled ; elsewhere it is smooth.
GENoTYPE.-Xenopithec us koruensis Hopwood.
X E x o P I T f f E c u . 3 mRc%:\srs
Hopwood. (P1. 6. figs. 3, 4.)
1933. Ann. & Mag. Nat. Hist. (10) xi, p. 97.
DIAGNOSIS.-ASfor the genus.
HOLOTYPE.-A fragment of the left maxilla with the partly worn first and
second molars. Regd. M 14081.
PARATYPE.-Aright upper posterior deciduous molar. Regd. M 14082.
MAmmIAL.-In addition t o the holotype and paratype, a broken mandibular symphysis with worn left third premolar. Regd. M 14083.
DIMENSIONS
.Dp4.
Length .............
5.7
Breadth ............
6.6
Height ..............
3.4
Breadth index ...... 115.8
MI.
6.8
8.3
2;5+
122.1
M2.
7.4
9.4
3;lf
127
DEscRIPTIoN.-The first molar is of a rounded quadrangular outline,
somewhat broader than long. The three cusps of the trigon are close t o each
other and joined by a ridge between each pair of cusps. A large hypocone
442
DR. A. TINDELL HOPWOOD ON
abuts on the protocone ; a ridge joins them. Wear has exposed the dentine
of each of the four cusps, as well as of tho ridge between the paracone and
metacone.
The protocone is a stout cusp in connection with six ridges. It is difficult
to decide which of these bclong t o the protocone and which belong t o the
three remaining cusps. Two a t least are free from doubt. They a m a t the
anterior and posterior extremities of the lingual surface of the cusp. The one
in front forms the anterior border of the fissure between the internal cingulum
and thc protocone and hypocone, but the hinder one divides the same fissure
into two subequ:el parts. Passing clockwise from the antero-internal ridge,
we come to what appears t o he a double antero-external ridge. This is made
up of two independent structures. One of them, the anterior, belongs t o the
protocone. This is definitely proved by a n extension of the dentine lake
where the enamel on the crest of the ridge has been worn away. The other,
posterior one belongs t o the paracone, though in this ease the indication is not
so distinct. Chntinuing in the same direction, the next ridge is that which
connocts the protocone and metacoiie. Here, owing t o the Khapes of the
rcqwctivc lakes of dentine, there is no doubt that the ridge is madti u p of
two parts, one t o each cusp. The sixth, and last, of these ridges is that joining
tht. protocone and hypocone. This is :In offshoot of the latter, since there
is a corresponding emhayment of thcl dentine of the hypocone; only, and not
of the. protocone. Hence, we may conclude that the protocorie is provitletl
with four ridges, which are antcro-internal, ctntero-external, postero-external,
and poatero-internal in position.
The paracone has lost some of thc enamel on its antero-external surface.
Allowing for this, the cusp is seen to bc a low rounded cone only less stout
than the protocone. It has two ridges, one antero-internal and one posteromedian. The latter connects it with the mctacone.
Thr metacone is of approximately the same size as the paracone. It has
the aame characters, and only differs from that, cusp in the two ridges, which
are antero-median and internal in position.
The hypocone is almost equal to the two previous ones in size and stoutness,
but it has, in addition t o the antero-median ridge already mentioned, a faint
medio-external ridge in the fovea posterior.
There are a5 least traces of a cingulum on all four sides of the tooth. That
on the lingual side is a massive, fiilly-developed, basal ridgc, almost wide
enough to be termed a shelf. It begins at the antcro-internal ridge of the
protooone, dies out when it reaches the hypocone, arid has the summit strongly
beaded. From its internal surface, just in front of the postero-internal ridge
of thcb protocone, tt spur passeti inwards t o meet the protocone. The anterior
cingulum is, naturally, a more delicate structure. I t begins at the mteroiiiternai ridge of the protocone, passes across the front, of the tooth, and ends
in the centre of the anterior face of the paracone. Any beading of the summit
has been destroyed by wear. To say that the anterior cingulum begins a t
MIOCENE PBIMATES FROM KENYA
443
the antero-internal ridge of the protocone is a matter of convenience, for it is
absolutely continuous with the internal cingulum. The external cingulum
is a minute ridge joining the bases of the paracone and metacone ; it resembles
the posterior cingulum in its isolation from its neighbours. The latter joins
the metacone and hypocone, and dies away on their posterior faces.
Since the cingulum closes all the gaps between the cusps, it follows that
there are four foveae. Ridges from the cusps affect these in varying degree.
The fovea exterior is a minute dimple between the paracone and metacone :
it has no unusual features. The fovea interior is a large irregularly triangular
hollow, or fissure, interrupted by two ridges, one from the cingulum and one
from the protocone. These divide it into three parts. The anterior and
posterior are deep pits of nearly the same size, whereas the median section is
a very small cleft between the two ridges. Similarly, the fovea anterior
is divided into two deep, but narrow, fissures by the antero-external ridge
of the protocone, which passes downwards and outwards from the summit of'
the cusp t o merge in the anterior cingulum.
The second molar agrees with the first in all essential features, so that only
the differences need consideration. Some of these, such as the very definite
simple wrinkling of the enamel on the lingual surface of the protocone, doubtless
have their origin in the fact that the tooth is less worn than its fellow. Others,
which are structural, concern the ridges and cingulum.
The postero-internal ridge of the protocone is absent, and the antero-internal
much reduced. The external cingulum and the ridge passing in from the
internal cingulum to the protocone are both missing. Hence there is no
fovea exterior and the fovea interior is simplc and undivided. This tooth
has three roots, one internal and two external. The arch of the external
roots is wide but pointed above. The internal root measures 6 mm. antero.
posteriorlyaad about 7.5 mm. from above downwards. It has a shallow
vertical groove on the lingual surface.
The last upper deciduous premolar is nearly square. Whereas the buccal
arid anterior margins are straight, the lingual and posterior margins are curved.
The interior, lingual, and posterior cinguln are strong ; the buccal cingulum
is obsolete. The buccal cusps are sharp and pointed: the lingual blunter
and more depressed. As in the adult, ridges connect all three cusps of the
trigon.
Four ridges pass down from the summit of the protocone. The first forms
part of the ridge connecting with the hypocone ; the second of that connecting
with the metacone ; the third passes down into the trigon basin ; the fourth
joins a long ridge from the paracone, and proceeds past it t o merge into the
anterior cingulum. The enamel on the surface of the protocone is strongl-v
wrinkled.
The hypocone is iii contact with a bifurcating ridge from the metacone.
From it one ridge passes in t o join the ridge connecting protocone and metacone, a i d one to join a ridge from the protocone.
444
DR. A. TINDELL HOPWOOD ON
The metacone, which is relatively high and pointed, has strong anterior and
posterior ridges in addition t o those mentioned in connection with the hypocone.
Hence it has four ridges in all. Three are simple and one is bifurcate.
The paracone is about the same size as the metacone. It has a strong
posterior and a weak anterior ridge. The longest and strongest of the thrco
ridges is that which joins the paracone to the protocone.
The external cingulum is a rounded swollen ridge ; it is only slight. The
remaining cingula are sharp and somewhat crenulatd a t the summit. The
snterior, posterior, and internal foveae are well marked, though the anterior
is only a deep cleft.
The symphysis is assigned to this species on account of its size. It is too
big and massive for Limnopithecus, but yet not big enough for Proconsul.
A worn left anterior premolar is retained with part of the tooth behind it.
In front the crowns of the left canine and incisors have been broken OR.
Part of the alveolus of the right central incisor remains ; the rest of the jaw
is lost,
An extended surface of occlusion with the upper canine passes from the
summit of the one-cusped premolar down on t o the anterior root ; any enamel
there may have been on the root had long since disappeared, and the surface
of the root been worn flat before the animal died. This leaves no doubt that
the syniphysis is that of a fully grown adult. The incisor roots have the buccolingual diameter longer than the transverse. The canine root (7x5 mm.) is
relatively small, but there is nothing to show the nature of the crown.
In cross-section the symphysis is stouter than any of those figured by Woodward (1914, fig. l), and very much stouter than that of Dryopithecus pilgrimi
(Gregory & Hellman, 1926, fig. 16). The fossa for the insertion of the geniohyoid and geniohyoglossus muscles has two very deep pits a t its base. The
digastric fossa is not so definite as in Dryopithecus, and, to judge from the
scar which show8 where it was broken off during preparation, the digastric
tubercle was small. The inferior margin was not produced backwards to form
a simian shelf.
DIscvssIoN.-This curious form, at once primitive and specialised in its
characters, is included among the Simiidae largely as the result of a process
of elimination.
The upper molars of the Cercopithecidae have four cusps arranged in two
pairs, so that the crown is divided into two nearly equal parts. Each tooth
usually bears high transverse ridges joining its cusps, and the toeth have
a strong tendency to bilophodonty. These features also oharacterise the fossil
forms. Even what is perhaps the oldest of them, Mesopithecus pentelici from
the Europian Pontian, has this bilophodont character well marked. Oreopithecus agrees in this respect, although owing to its curious ridges it is often
placed in a separate family, the Oreopithecidae. Xenopithecus differs, since
the cusps are not paired, nor are the teeth bilophodont. Hence i t is not one
of the Cercopithecidae.
MIOCENE PRIMATES JTROM KENYA
445
If Oreopithecus be regarded as belonging to a separate family, that family
cannot include the present genus. I n Xenopithecus protocone and hypocone
are joined by a ridge ; whereas in Oreopithecus they are not so joined, but a
ridge from the hypocone passes forwards and outwards to join the crista obliqua.
This difference in structure is of great importance.
The Gibbons and Xenopithecus agree in having a single internal root to the
upper molars, though this root is larger in the fossil, but they differ in the size
of the hypocone. This is not much more than a rudiment in the Gibbons,
whereas in the fossil it is very large.
It is obvious that Xenopithecus is not one of the Hominidae, but it may well
be included among the Simiidae. The strong paracone-metacone and protoconehypocone ridges are unusual, but they are developed to some extent among
certain members of the group. The cingulum may be matched in Proconsul
and the trigon in Dryopithecus and some Chimpanzees. Even the paracone
and metacone are connected in Dryopithecus darwinii. Thus Glaessner say^,
‘ Zwischen Para- und Metacon findet sich ein verhaltnismiissig kraftige Randleiste ’ (1931, p. 18) ; whilst Remane (1921 b, p. 158)says of D. rhenanus, ‘ Der
Hypoconus ist durch Eandleisten mit dem Protoconus ziemlich eng verbunden.’ If the cingula of Xenopithecus were suppressed, the ridges which
join the cusps would become ‘ Randleisten.’ Thus, the various features occur
singly among other species of this group.
Probably Xenopithecus is an aberrant form of Anthropoid adapted for a
different mode of life, in much the same way that Alouatta differs from the rest
of the Cebidae through having teeth adapted for its diet of leaves rather than
fruit.
Genus lUIlocosst L Hopwood.
1833. Ann. & Mag. Nat. Hist. (10) xi, p. 98.
I)IAGNosIS.-Simiidae
approximating to the Chimpanzes in sizc. h e molars bicuspid ; protocone from 130 to 160 per cent the height of the deuterocone ; posterior cingulum well marked. First and second molars quadrate ;
trigon very distinct ; proto- para-, and meta-cones of about the same size ;
hypocone equal to the protocone, or slightly larger, Third molar reduced,
eubcircular ; protocone larger than paracone ; metacone and hypocone very
much reduced. lnternal cingulum of molar teeth strong, external cingulum
weak. Enamel wrinkles increase in strength from the first t o the third molar.
Lower molars showing the Dryopithecus pattern. Hypoconulid central in
first and second, buccal in third molars. Third molar with definite anterior
transverse crest and strong cingula.
G ~ ~ o ~ ~ ~ ~ . - - P r o caforicanus
n s u l Hopwood.
PBOCONSUL
-4FRJCAA’CS Hopwood. (P1. 6. figs. 5-10.)
1933. Ann. & Mag. Nat. Hist. (10) xi, p. 98.
DIAGNOSIS.-ASfor the genus.
HOLOTYPE.-Aleft maxilla with C‘-RI13 slightly worn. Regd. M 14084.
446
DR. A. TINDELL HOPWOOD ON
MATmIfi.-ln addition t o the holotype, a broken mandible lacking the
incisors and canines, the whole of the left third molar, and the posterior part
of the right, regd. M 14086 ; a right first upper molar, regd. M 14085 ; a n
almost unworn, but weathered orown of a third right lower molar, regd.
M 14087.
DIMENSIONS.a'
'0
i
.$
'-
s
$6
-!2
3,
Tooth diinsnsion.
_ _ -
.
.
-
Upper Dentition.
C::
Length .........
Breadth
Height (bucc.) ...
Hoight (ling.) . . .
Index . . . . . . . . . .
........
YY : Length
1'4:
1
gs
.........
a,
.
1:
;
- a
$6.
.-
ge6-s
2:g
da
8s
4
zGLip1
k__ - u.-
-
11.3
9.1
15
13.5
81
..
..
..
7.3
0.4
..
7.5
8.0
8.1
..
..
..
6.6
Breadth . . . . . . . .
Height (buw.) ...
Height (ling.) . . .
lndex ..........
12'3
Length .........
Breadth ........
Height (bucc.) . . .
Height (ling.) . . .
Index ..........
5.8
8.9
6.4
4.8
152
50
7.9
M l : Length .........
9.6
Breadth ........
5.2
Height (bucc.) ...
4.3
Height (ling.) . . .
Index .......... 122
..
..
..
11.6
X.6
14.6
13.4
74
4.9
107
..
6.5
..
..
..
5.5
5.2
..
9.6
148
7.8
9.0
9.4
10.6
4.8
4.2
116
5.2
5.2
113
9.2
M 2 : Length. ........
11.3
Breadth ........
5.4
Hoight (bucc.) . . .
4.5
Height (ling.) ...
Index . . . . . . . . . . 123
..
..
..
..
8-8
10.3
5.1
6.1
117
7.8
MY: Length . . . . . . . . .
Breadth ........ 10.3
4.9
Height (bucc.) ...
4.4
Height (ling.) ...
Index .......... 130
..
8.4
..
..
..
..
9.8
3.9
6.1
116
447
MIOCXNE PRIMATES FROM KENYA
DIMENSIONS
(conk).-
Tooth dimension.
-__-
Lower Dentitioit.
C:
Length ....
8*9(root)
Breadth ....
13.7 (root)
Index ...... 154 (est).
P3:
Length. ....
Breadth ....
Index ......
12.5
7.1
56.8
8.9 (root)
13-2 (root)
148 (est.)
12.6
7.4
58.8
P4 : Length . . . . .
7.4 (est.)
Breadth . . . .
8.9 (est.)
Index ...... 120 (est.)
7.3
8.9 (est.)
122 (est.)
Ill1 : Length .....
Breadth ....
Index ......
99
9.5 (est.)
9.5 (est.)
100 (est.)
M2 : Length .....
Breadth ....
Index
11 (est.)
10.8
91
11-7
10.8
92
M3 : Length .....
Breadth ....
Index ......
11.6 (root)
8.9 (root)
77 (est.)
10.2 (est.)
......
9.5
9.4
..
..
_____
..
..
..
..
..
..
..
..
..
..
~ _ _ _ _ _
11.6
10.0
86.2
8. 3
8.8
103.5
8.3
8.6
103.6
..
..
..
..
..
..
..
..
..
..
..
11.1
9.8
88.3
..
..
..
..
11.1
10.1
91
114
9.0
85
11.9
9.4
79
10.8
10.1
94
12.6
10.4
83
I
.
Additional measurements :External depth of mandible between P 3 and P4 .........................
External depth of mandible at M3 ......................................
Length of symphysis .................................................
Distance of mental foramen from alveolar border .........................
Maximum diameter of mental foramen ..................................
Minimum diameter of mental foramen ..................................
Length of left inferior series P 3 to M3 ..................................
..
36
31.4
28.5
17.6
4.3
3.0
53
The following measurements were taken in a straight line from the crown of the arch
between the two roots to the tips o f the roots themselves. No account is taken of the
curvature of the roots :Anterior root.
Posterior root
Shape of arch
.......
.......
.......
Direction of roots. ...
Separation of‘ roots . .
c.
17
..
..
Vertical.
..
P4.
M1.
M2.
1\13.
15
10
12
10
13
13
14
15
Cleft, but wider Rounded. Point. Point.
than P3.
Vertical.
Vertical.
+-Down and back.-+
Well sep.
f- -----Pronounced.--+
P3.
17
16
Cleft.
448
hScRiPTIoN.-Tho
DR. A. TINDEW HOPWOOD ON
upper and lower dentitions are described separately.
Upper Dentition.
'I'he holotypo has undergone post-mortem deformation, which has caused
the tooth-row to bend inwards. The tip of the canine has been displaced
downwards and inwards. A fracture passing through the alveolus of P4 has
changed the relative positions of the two pieces, and P4 itself has moved out
into the wide crack to a position internal to that which it should properly
occupy. Apart from these accidents after death, the palate is straight-sided.
The incisor-teeth are missing, only oblique sections of the roots remain.
Between the roots the bony alveolar plates are about 2.9 mm. thick, from whirh
it is deduced that t'he crowns were fairly large and square. A gap of 4 nim.
separatos tho lateral incisor from the canine.
The canine is a stout pointed tooth with a strong cingulum on the lingual
surface. For descriptivo purposes it may bo regarded as a rough four-sided
pyramid, which has two lingual and two buccal faces. The proximo-buccal
surfaco is a scalene triangle, slightly convex transversely. It passes into the
disto-buccal face through an increase in the convexity of its surface. Tho
latter face is of similar nature, but narrower. Both the lingual surfaces are
1nore complex than the buccal. The proximo-lingual is triangular ; it is concave
from tip to neck, the concavity is most marked a t the neck, and convex transversely ; it is the most extoiisive of the four faces. The disto-lingual face is
more corroctly a distal face which has a slightly lingual position. It is very
narrow and curved lingually. At the bas0 there is a doop groove, which
becomes shallower as it passes towards the summit and dies out after covering
about two-thirds the height of the tooth.
The third premolar is of the biscupid type usually occurring in anthropoid
apes ; it has a high sharp-pointed protocone, a lower and blunter deuterocone,
and a distinct posterior cingulum. The protocone is roughly pentagonal in
cross-section. There is an anterior and a posterior ridge, or keel, on the
lingual surface. Thero are also antero-internal and median ridges which pass
down towards the deuterocone, with whicsh the former connects, and divide
the surface into throe unequitl parts. A division of the buccal surface into
two faces, of which the antero-external is slightly the smaller. is effected by
a strong submedian convexity.
The deuterocone is little more than half tho height of tho protocone and
bluntly rounded ; its real shape is obscured by :t posterior facet due to wear.
A slight ridge on the buccal surface connects with the antero-internal ridge
of the protocone.
A well-definod posterior cingulum connects the posterior keel of the protocone with the postero-lingual surfaco of the deuterocone. The portion nearest
the protocone, about one-third of the whole, is unworn and slightly roughened.
The remainder is worn m o o t h by use ; its msxirnuni width, 1 mm., is a t t h e
floor of the valley between the two cones. The buccal termination is somewhat
stout and rounded so as to form an incipient style.
MIOCENE PRlMATES FROM KENYA
449
The fourth premolar is a smaller tooth than the former, from which it differs
in that the protocone is not so tall and pointed, and also in that it has both
anterior and posterior cingula. The protocone has a strong keel in front and
behind, as well as an antero-lingual ridge which forms a connection with the
anterior keel of the deuterocone. There are three subdivisions of the buccal
surface of the protocone ; a strong central convex rib is flanked on either side
by much smaller, almost plane areas bounded by the cingulum and the central
rib, and which mainly consist of the keel. The lingual surface shows a similar
division, which is rendered more distinct by the antero- and postero-lingual
ridges. The latter is almost obsolete.
There is a tendency for the deuterocone to form anterior and posterior keels
after the manner of the protocone. The anterior keel sends down a ridge from
its junction with the cingulum to connect with the antero-lingual ridge of the
protocone. Compared with the third premolar, the deuterocone is much smaller
in proportion to the protocone ; if the height of the protocone be taken as
100 in each tooth, then the height of the deuterocone in the fourth premolar
is 75, compared with not quite 62 in the third.
The anterior cingulum is not so strong as the posterior, and is practically
confined t o the protocone ; a t its buccal end it forms a style as strong as that
formed by the posterior cingulum. The latter begins a t the posterior keel
of the protocone and passes inwards t o a point just short of the centre of the
lingual face of the deuterocone. Where it forms the boundary of the posterior
fossa of the occlusal surface it is worn smooth ; elsewhere it is slightly
beaded.
The first molar is somewhat rhomboidal in outline. Owing t o the backward
extension and large size of the hypocone, the lingual side is longer than the
buccal. The crown of the tooth is surrounded by a beaded cingulum, which is
discontinuous a t each of the angles except the antero-internal. The primary
trigon is very distinct with strong ridges joining the protocone to the paracone
and metacone, and a deep fissure between the two last. The cusps are low
and practically of equal height ; the height of the lingual surface is 83 per cent.
of that of the buccal. Both paracone and metacone have anterior and posterior
keels, but the posterior keel of the metacone is nearly obsolete. The enamel
is smooth and almost devoid of wrinkles, the only ones being where the ridges
join the cusps.
The isolated first upper mokw agrees with that just described in every
essential, even though it differs in points of detail. For example, the valley
between the hypocone and protocone is wider than in the holotype, and the
ridges on the cusps are somewhat stronger and better defined. Probably the
most striking difference is to be found in the cingulum, which is discontinuous
only a t the antero- and postero-buccal corners for a short distance. It is
very much stronger and more distinctly beaded in this tooth than it is in the
holotype.
The second molar tooth is larger, stouter, and more wrinkled than the &st,
which it resembles in its outline and general structure, Owing to the posterior
450
DR. A . TINDELL HOPWOOD ON
extension and large size of the hypocone, the tooth has a rhomboidal outline.
The trigon is distinct, but the ridges joining the protocone t o the paracone
and metacone are not so strong as in the first molar, and that between the protocone and metacone is divided by a definite cleft. All four cusps are of approximately the same height. Owing to the fact that there is practically no difference
in height between the internal and external cingula, there is only a slight
difference in height between the buccal and lingual surfaces. There are
anterior and posterior keels to both paracone and metacone, and this tooth
differs from the first molar in that the posterior keel of the metacone is more
distinct than it is in that tooth. Both the cingula are more distinct than they
are in the fist molar ; the beading is more sharply defined. The internal
cingulum is carried round the back of the tooth t o terminate on the posterior
face of the hypocone, so that, except for two small gaps (one posterior and one
antero-external), the cingulum encircles the tooth.
The wrinkling of the enamel is very distinct. On the buccal surface of the
hypocone are three wide, deep, slightly sinuous grooves, whereas on the
corresponding surface of the protocone there are only two grooves of the same
simple unbranched type. Passing inwards from the anterior surface of the
protocone, to the lingual and thence to the posterior surface, there arc nine
small but clear indentations of the enamel a t the base of the cone.
The third molar is much reduced, subcircular, and almost bicuspid from t8he
diminution in size of the metacone and hypocone. The protocone and paracone are as large as in the second molar, but more depressed. They are joined
by a ridge which is bent anteriorly, and which forms a slight node where it
joins the anterior cingulum. The enamel of these two cusps is wrinkled;
that of the protocone has furrows on the buccal surface and pits round the
base of the lingual surface, whereas the paracone is wrinkled on the lingual
surface. None of the wrinkling is as regular as in the second molar.
Although the metacone is small and mis-shapen it is a distinct cusp, but tho
hypocone, which is itlmofit worn away, is little more than a superficial feature
in the enamel of a broad shelf-like cingulum. The cingulum appears t o he
continuous all round the tooth; it is beaded, and on the lingual side the
beading is coarser than in either the first or second molars.
Lower Dentition.
The lower dentition of this species is not so well known as the upper
because the teeth are either broken off level with the mandible, incisors, and
canines, or else SO worn that the interpretation of their structure becomes
a matter of extreme difficulty and doubt. Only the third premolar and an
isolated third molar can be described in detail.
The roots of the two median and right lateral incisors are preserved in the
right mandibular fragment. Each tooth is produced in a bucco-lingual direction,
compressed transversely, and has a single wide shallow groove on the interstitial fiurfaces. The lateral root is larger and stouter than the median, and
MIOCENE PRIMATES FROM KENYA
451
in this root alone there is a satisfactory section of the pulp-cavity, which shows
as an elongate narrow canal, about 2 mm. long in a bucco-lingual direction
and 0.5 mm. in its greatest width. It is nearer the buccal surface, and is
rounded a t that end, whereas its lingual end appears to be pointed.
The canine-root is separated from that of the lateral incisor by a gap of from
2 to 3 millimetres. It is inserted obliquely across the mandible, is a rounded
oblong in cross-section, and has an oval pulp-cavity which is 3 mm. long
and 1 mm. wide. The antero-internal and postero-external angles are more
rounded than the other two, which are almost right angles. The interstitial
surfaces are almost flat, only the proximal having a slight indication of the
groove seen on the incisor-roots.
The anterior premolar (P3) is a large, subcaniniform, twin-rooted tooth,
set obliquely in the jaw. It consists of a single massive cone, with a basinshaped heel and a slight antero-internal cingulum. The tooth itself presents
four faces for description, namely, two anterior and two posterior. Of these
the antero-external is possibly a more or less arbitrary selection, for it consists
of the occlusal surface where this tooth is worn against the upper canine.
The antero-external or occlusal face is 10.6 mm. long and 2 mm. wide.
It extends from the apex of the tooth down the whole extent of the enamel,
which is produced down on t o the anterior root. Passing downwards and
forwards it soon changes direction t o pass downwards and outwards. The
postero-external face is an irregular triangle which is gently convex from
above downwards, and rather more convex from side to side. Between them
these two faces form the buccal surface of the tooth.
The antero-internal face consists of two parts-a larger anterior portion
which is concave from above downwards as well as from side to side and a
smaller posterior portion which is convex in both directions. This face is
separated from the postero-internal one by a very sharp angle due to a change
of direction through which the latter is almost wholly posterior in position.
Both this angle and that separating the postero-internal and postero-external
faces are worn by occlusion with the upper dentition. The postero-internal
face is triangular and concave, the concavity passing downwards into the
bashed talonid.
There is an almost obsolete internal cingulum, and the convex posterior
portion of the antero-internal face has something of a flattened buttress, the
metaconid, closely pressed against the lingual surface of the tooth. All this
is indefinite, but the talonid is well marked and, by combining the observations made on either tooth, it is seen to have incipient buccal and lingual
cusps which show as minute lakes of dentine.
The fourth lower premolar is so worn and damaged that certain features
have been wholly destroyed ; chief of these are all those dependent on the
enamel of the lingual surface, which has entirely disappeared. The tooth
itself is bicuspid with a large bashed heel on which stand two cusps. Apparently
there was a small fovea anterior.
452
DR. A. TINDELL HOPWOOD ON
Both first lower molars are so damaged that it is impossible to say whether
they had a hypoconulid or not, although analogy with the second molars,
as with the isolated third molar, makes it probable that they had. The dentine
lakes are transverse and, in the left tooth, not yet confluent throughout their
length, whence one deduces more or less of a division into anterior and posterior
ridges, the protolophid and metalophid. The tooth is wider behind (9-5 mm.)
than in front (8.6 mm.). No signs of a cingulum remain.
The right second molar has received no damage other than that due t o wear ;
hence the position and number of the cusps is not in doubt. This tooth shows
the typical Dryopithecus pattern of five cusps with the metaconid and hypoconid in contact. The hypoconulid is noteworthy for its position in the centre
of the posterior end of the tooth. Owing t o wear, each cusp has a central
lako of dentine ; of these, the hypoconid is the largest and is confluent with
that of the hypoconulid, the next largest. Then follow in order the lakes of the
protoconid, entoconid, and metaconid respectively. This proves that the
greatest amount of wear came on the postero-external part of the crown.
There is no definite cingulum preserved, although the general appearanre
of tho tooth conveys the impression that there may have been a partial cingulum
on the labial side a t least, and possibly on the lingual side as well. This impression is strengthened on examination of the isolated lower third molar.
The third lower molar is known from an isolated crown of an almost unworn,
though somewhat weathered, tooth from the right side. Its outstanding
features are the arrangement of the three external and two internal cusps in
two pdrallel rows, the large size of the fovea anterior and fovea posterior, the
relatively strong ridge connecting the two anterior cusps, and the marked
cingula. All the cusps are low and obtuse,
The protoconid has four strong crests-an anterior, a posterior, a mediobuccal, and a medio-lingual. These give the cusp a pyramidal appearanco.
The metaconid has only one ridge, medio-buccal in position, which joins the
corresponding ridge of the protoconid and the two form a low, but distinct
protolophid. The hypoconid is so damaged through weathering that i t is
not safe to make any detailed statements concerning its construction. It
appears to have five crests-one anterior, one posterior, one buccal, and two
lingual. Of these the anterior and posterior seem to be shorter than the other
three. Damage, too, has obscured the characters of the hypoconulid, which
i R in the same line as the protoconid and hypoconid. So far as can be seen,
it is much smaller than the three previous cusps, and has the enamel heavily
wrinkled. A crest on the lingual surface passes forwards and inwards t o j o b
one from the entoconid. This last cusp is of about the same size as the hypoconulid, but more slender, pointed, and better defined. Its posterior face is
deeply concave, and a postero-buccal crest passes downwards and backwards
to meet that coming from the hypoconulid.
The anterior cingulum is very strong. It forms the anterior wall of the deep
fovea anterior, of which the posterior wall is formed by the ridge connecting
453
MIOCENE PRIMATES FROM KEYNA
the protoconid to the metaconid. It has the beaded character seen in the
upper molars, and the whole of the enamel lining the fovea anterior is wrinkled
by simple, straight, unbranched furrows, which pass down to the deep transverse
cleft at the bottom. The anterior ridge of the protocone interrupts the cingulum, but the space between that ridge and the medio-buccal ridge is occupied
by an almost equally strong cingulum similarly beaded. After this latter
interruption the cingulum appears to continue right along the buccal and
posterior margins of the tooth, and to follow along the lingual margin t o the
posterior surface of the entoconid, where it finally ceases. That part of it
which bounds the fovea posterior shows the same kind of wrinkling of the
enamel as that seen in the fovea anterior.
Most of the wrinkles in the enamel occur in the foveae a t either end of the
tooth, and are described above, but there are others which pass down into the
central basin of the crown. One comes down from the protoconid ; one is
between the protoconid and the hypoconid ; three are between the entoconid
and metaconid ; and two are on the posterior face of the protolophid. An
additional wrinkle between the hypoconid and hypoconulid is the longest.
This is complicated by the presence of four tributary wrinkles which pass into
it from the hypoconulid and the crista obliqua, which connects that cusp to
the entoconid.
The tooth just described is broken off a t the roots. There were two of these,
an anterior and a posterior. The former expanded transversely. It supported
the two anterior cusps. The latter, which was massive, supported the remainder
of the crown. A similar arrangement is seen in the corresponding tooth of
the left mandibular ramus which is broken away, leaving the roots still in
the jaw.
The third molar of the right ramus is broken across obliquely, so that the
anterior cusps alone remain. All the jaw behind the fracture has been lost,
nor could i t be found after the most careful search. That portion of the tooth
which remains is very worn, and adds nothing to the description already given.
All the wrinkles are obliterated, the anterior fovea has disappeared, and the
dentine of the protoconid is exposed in a large depression.
The inner surface of the left mandibular ramus was dissected away so as
to expose the roots of the premolar and molar teeth, as well as the posterior
surface of the canine-root. This last is single, very stout, and vertical or nearly
so. I n its position it differs from all the anthropoids quoted by Gregory and
Hellman (1926, Table xlii), but agrees with the human canine. The roots
of the third premolar are directed downwards and very slightly forwards.
They are both very thick, but the posterior root is thicker, shorter, and situated
more t o the lingual surface of the jaw than the anterior root. I n contrast
to the third premolar, the fourth has the most slender roots of all the cheekteeth. They are quite straight, and are 4.5 mm. apart a t their tips. All the
molars have the roots more or less curved backwards. I n the first and third
LINN. J0URN.-ZOOLOGY,
VOL. XXXVIII
32
454
DR. A . TINDELL HOPWOOD ON
molars the posterior root is larger and straighter than the anterior, but in the
second molar the anterior root is the larger.
Owing to heavy impregnation with mineral matter the specimens are almost
opaque to X-rays ; nevertheless, working with a Coolidge Universal Tube a t
30 inches, with a current of 30 milliamps a t a pressure of 90 kilo-volts, satisfactory images of the dissected left ramus were obtained with an exposure
of 10 seconds.
The photographs show the nerve-canals in the posterior roots of the third
and fourth premolars t o have a maximum diameter of 0.6 and 0-8 mm.
respectively ; their junction with the pulp-cavity is not shown. The pulpcavity of the left first molar is visible only in the posterior root-shadow and
the hinder half of the crown. The canal in the root is of approximately the
same diameter as the height of the cavity in the centre of the crown, but th0
cavity increases in size a t its junction with the canal from the root, and at this
point the width of the shadow is just over half a millimetre. I n no other
crown is the pulp-cavity visible.
8
Osteology.
Owing to post-mortem deformation the maxillary fragment is confusing
in its osteological characters. Seen from in front, or in profile, the chief
feature is the pronounced slope of the subnasal area, indicating a notable
degree of prognathism. Another prominent feature in the anterior region is
the manner in which the canine and anterior premolar are inserted into the
jaw. They carry on the slope of the facial surface, and project a t an angle
of approximately 45" to the vertical. Tho root of the zygomatic process of the
maxilla has its origin very close to the alveolar border, and extends forward
to come into line with the anterior margin of the first molar. Seen from below,
the most prominent feature is the very shallow dome of the palate.
Despite its broken condition, the mandible affords valuable information
as to its characters. It is very massive and deep, with a long symphysis
which does not retreat as much as in the Chimpanzee. The outer surface
below the premolars and first molar bears a wide but shallow depression, due,
in part, to the everted inferior border of the bone. The mental foramen is
single and situatod under the anterior root of the third premolar. On the
inner surface a low rounded ridge continues the line of the symphysis backwards
and upwards along the jaw towards the ascending ramus. Between this ridge
and the alveolar border the bone is hollowed out in a shallow depression. At
the level of the first molar the ridge seems t o bifurcate, sending an indistinct
branch towards the angle of the jaw. The area in the fork is also excavated.
Ono very important character is the almost plane surface of the inner aspect
of the jaw below the third molar.
COMPARISONS.-AS these remains were found in Africa, the obvious
comparisons are with the Gorilla and Chimpanzee. Similarly, the Miocene
age of the beds in which they were found suggests a comparison with the
455
MTOCENE PRIMATES FROM KENYA
Eurasiatic ' genus ' Dryopithecus. It is also evident from the foregoing
description that comparisons with the Orang Utan and Palaeosimia are more
or less academic, since the relationship is remote.
Comparisons with Dryopithecas are complicated by the rarity of specimens
of the upper dentition of that genus and by the worn state of the lower dentition
of this species. Gregory (1922) records six species of Dryopithecus, viz.,
D. chinjiensis Pilgr., D. punjabicus Pilgr., D. giganteus Pilgr., D. fontani Lartet,
D . rhenanus (Pohlig.), and D. darwini Abel. Of these six, two only, D. punjabicus and D. rhenanus, are represented by upper teeth ; the first by a maxilla
with the premolars and first and second molars, and the second by two isolated
molars. Our knowledge of the remainder is limited to the lower dentition,
and in some cases to single teeth. The three species described by Brown,
Gregory, and Hellman (1924) are also founded on portions of lower jaws.
From this it follows that the remains of Proconsul africanus, unsatisfactory
though they be in certain respects, are a t present unique in affording a relatively
complete picture of the upper and lower dentition of a Miocene anthropoid ape.
The outstanding characters of the upper cheek-teeth of this species are :(1) The tall, sharp-pointed buccal cusps of the premolars
(2) The quadrate outline of the molars.
(3) The prominent trigon.
(4) The very strong cingulum.
(5) The prominent hypocone.
(6) The rounded, reduced third molar.
Of these the third and fourth are primitive characters, whereas the remainder
are specialised. This indicates a mixture of characters, and clossr examination
proves that this mixture pervades the entire upper dentition, For example,
the premolars are specialised in their high outer cusps which, in the third premolar especially, are so marked as almost t o make the teeth caniniform. At the
same time their great breadth is t o be accounted a primitive character, persisting
from very early times when the ancestral anthropoids all had the anterior
teeth so crowded that any increase in size had to take place transversely.
Similarly, the first and second molars are very primitive in their marked tritubercular pattern and strong cingula, but they are equally specialised in
their large hypocones, quadrate contours, and in the greater length of the
lingual compared with the buccal surface.
The upper dentition has many resemblances to that of Dryopithecus, so far
as the latter is known t o us, but the differences are no less important. Points
of resemblance are :(a) The two-cusped premolars.
( b ) The four-cusped molars.
( c ) The marked trigon.
(d) The quadrangular contour.
32 *
.
456
DR. A . TINDELL HOPWOOD ON
But the teeth differ from those of Dryopithecw in :-
(a) Their smaller size.
(b) Their strong cingula.
Their hypocones, which are much larger than those of either D. punjabicus or D. rhemnus.
( d ) The disparity of size between the buccal and lingual cusps of the
premolars when compared with the corresponding cusps in D. punjabicus.
( e ) The relatively shorter antero-posterior diameter of the cheek-teeth
when compared with D. punjabicus ; this is not so marked when
comparison is made with D. rhenanus.
(c)
Taken together, these appear to me suacient to exclude the African fossils
from the ‘ genus ’ Dryopithecw. Even though (a) and ( e ) might be regarded
as individual or specific characters, the remainder are, in the sum, differences
which separate genera rather than species.
The main points in which the teeth of P. afriwnus differ from those of the
Gorilla are :-
( a ) Their smaller size.
(b) The greater width and smaller length of the premolars.
( d ) The greatly reduced M3.
( e ) The pronounced cingula.
(f) The stronger crista transversa anterior and crista obliqua.
In this instance also, these differences, together with others which are
not 80 ifimediately obvious, have a value which must be accorded generic
rank.
It is not so easy t o separate the upper dentition of P. africanus from that
of the Chimpanzee. The teeth of the latter are so extraordinarily variable
in their size, shape, and occlusal relationships that it is difficult t o know what
is the normal dentition. I n this connection the general description given by
Prof. W. K. Gregory (1922, pp. 343-344) may be quoted in full. He says :‘The upper molars clearly retain the sharp V-like ridges of the primitive
tritubercular pattern, but they add thereto a poorly developed posterior ridge,
runnng from the enlarged hypocone to the metacone. There is a decided
tendency to divide the internal root into an anterior and posterior moiety,
or, rather, the formerly distinct roots may be in course of coalescing . . The
third upper and lower molars are somewhat reduced in size and degenerate in
form. . . . The molar crown0 are coarsely wrinkled, the cusps being lower
than in the Gorilla.. The upper premolars are comparatively small and are
prominently bicuspid. . . . The canines form stout tusks.’ All this can be
upplied almost equally well t o the fossil teeth under consideration, but there
..
MIOCENE PRIMATES FROM KENYA
457
are characters in the fossil which are not present in the recent species, and
vice versa. Chief of these characters are :--
(a) The anterior premolar is more caniniform in the fossil.
( 6 ) The premolars, especially P4,are shorter in the fossil.
(c) The fossil molars have a very prominent cingulum.
(d) The ridge joining the metacone and hypocone is present in the fossil
only in the first molar, and that tooth alone has a definite fovea
posterior.
(e) The Chimpanzee has the enamel more wrinkled than it is in P. africanus.
(f) The entire premolar-molar series is cut a t about the same time in
Proconsul, whereas in the Chimpanzee the first molar erupts in the
sixth year, and the third not before the fifteenth year (Zuckerman,
1928).
Hence it would seem that the dentition of Proconsul is more primitive than
that of the Chimpanzee, and for that reason I have placed it in a separate
genus.
There is no insuperable difficulty in the way of deriving the recent from the
fossil dentition. The main requirements are a slight lengthening of the muzzle
with a corresponding increase in the length of the tooth-row, a reduction
of the cingulum, and a reduction in size of the buccal cusps of the premolars.
The last upper molar of the Chimpanzee has a larger metacone than that of
P . africanus, but a lengthening of the upper jaw would allow the reduced
nietacone t o increase in size and so give rise to the condition found in the
Chimpanzee.
The lower teeth were compared with the same three forms as before, beginning
with Dryopithecus. Here we are handicapped, not only by lack of material
for comparison, but also by the extremely worn and damaged condition of the
main material of P. africanus. Indeed, if this species were represented only
by the lower jaw, to separate it from Dryopithecus would be difficult.
The only Miocene ape from Africa with which it can be compared is Dryopithecus mogharensis (Fourteau, 1920, p. 95). That species is not well figured,
and the exiguous description leaves much to be desired. Remane (1924) has
already discussed Fourteau’s work. He says, ‘ Nur bei Wiirdigung der kiinstlichen Gattung Dryopithecus kann Dr. mogharensis in dieser bleiben, in Wirklichkeit bleibt es noch unsicher, ob es um einen Hylobatiden oder Simiiden
handelt . . . . ’. Pending re-examination of the specimens, the matter may
well rest there. At present the Egyptian specimens are of no use in making
critical comparisons.
The metaconid of the third premolar of P . africanws is indicated by a faint
triangular area on the labial surface of the tooth, the antero-posterior sulcus
is equally faint. I n both these respects it is a t least as primitive as D. pilgrimi,
and more primitive than any other species of Dryopithecus in which this tooth
is known. The anterior premolar is also narrower than any of the corresponding
458
DH.. A . TINDELL HOPWOOD ON
teeth of Dryopithecus quoted by Gregory and Hellman (1926), and SO might be
regarded as primitive in that respect also were it not for Remane’s demonstration (1921) that the breadth index is not a reliable criterion. Another marked
difference lies in the extension of the enamel on to the anterior root of the tooth
of Proconsul. This is a distinctly simian character not seon in any species of
Dryopithecus.
The fourth premolar agrees with those of the Irldian spocios of Dryopithecus
in being broader than long, and so differs from D. fontani. The agreement is
also with the Indian rathor than the European in that the external cinguluni
is absent or obsolete. I n the larger talonid basin and very distinct hypoconid
and metaconid, P. africanus appears to be more advanced than any species
of Dryopithecus, with the possible exception of D. frickae. The trigonid would
bo higher than the talonid in the unworn tooth, but probably the relative
height would be no grei~terthan it is in Dryopithecus.
The first rnolar is so worn as to render comparisons impossible.
The length, breadth, broadth index, and talonid index (85.5) of the second
lower molar are all well within the limits of variation of ‘ Dryopithecus ’. It
agroes with D.rautleyi and D. frickae in the more central position of the hypoc*onulid,and differs in this respect from all the other species. This relationship
is reversed when the external cingulum between the protoconid and hypoconid
is considered. The relatively flat occlusal surface, ospecially on the buccal
side, agree8 with U ,frickae, cautleyi, pilgrimi, and punjabicus. If the isolated
third lower molar is a safe guide, the crown must have been lower and flatter
than it is in Dryopithecus.
The third lower molar differs from all t8hosein the specimens of Dryopithecus
hitherto doscribed because the buccal margin consists of three cusps (protoconid,
hypoconid, Ltnd hypoconulid) arranged in a perfectly straight line. The maximum height, too, is very much less than in any known species of Dryopithecus.
There are other differences also, such as the small size of the hypoconulid and
entoconid when compared with the remaining cusps, the very large fovea
posterior, and the relatively strong ridge which joins the hypoconulid t o the
entoconid. The labial margin has well-defined grooves behind the two cusps
which cause it t o have a serrated appearance resombling that described by
Pilgrim in D. punjabicus. The cingulum is stronger than any found among
the various species of Dryopithecus, most of which have lost this feature
altogether.
When comparison iu made with the Chimpanzee, the disparity between the
mandibular rami and the rough general agreement betweon the cheek-teeth
are at once evident. I n addition to the more massive mandible, P. africanus
has the mental foramen iinder the anterior root of the third premolar, and thus
farther forward than in the Chirupansoe, which usually has the foramen under
the fourth premolar. On the other hand, the symphysis of the Chimpanzee
does not extend any farther backwards than that of Proconsul. What value
ctttaches to this observation is not clet~r,€or in d l genera of Anthropoid apes
the backward extension of the m:Lndible appears to vary within wide limits,
MIOCENE PRIMATES FROM KENYA
459
and, so far as I have been able to trace, apart from one paper by Woodward
(1914), very little work has been done on that region of the lower jaw.
I n its general form and structure, the third lower premolar of P. africanus
comes within the limits of variation of the corresponding tooth in the Chimpanzee,
nor does there appear t o be any definite criterion whereby the teeth may be
separated. Speaking of the metaconid of the Chimpanzee, Remane (1921,
p. 60) says :-' Es finden sich alle Uebergange von vollstandigem Fehlen bis
zu relativ starker Entwicklung.' Examination of the series in the British
Museum led to the same conclusion. For what it may be worth, one may
point out that the roots in the fossil appear to be stronger than they are in the
Chimpanzee.
The fourth premolar and first molar of the Chimpanzee and Proconsul
are scarcely comparable owing to damage and wear, but if specimens of
both in the same state of wear are placed side by side they are practically
indistinguishable.
The only feature which can be said t o separate the second lower molars of
Proconsul from equally worn specimens of the Chimpanzee is the central position
of the hypoconulid, though according to Gregory and Hellman (1926, Table
xliv) the position of this cusp in the Chimpanzee varies from lateral to central
(rarely) and hence would afford no distinction.
The isolated third lower molar of Proconsul is a t once separated from that
of the Chimpanzee by its much lower crown, the peculiar arrangement of the
buccal cusps, the strong cingula, and the blunt rounded tops of all the cusps.
It is also much narrower than any quoted by Remane, or by Gregory and
Hellman.
Taking the Gorilla as our standard of comparison, we find that the third
lower premolar of Proconsul is :
(a) Smaller.
( 6 ) Narrower ; the index varies from 56.8 to 58.8, whereas the minimum
value quoted by Gregory and Hellman (op. cit. p. 44) is 66.4 and the
average 86.2.
( c ) Shallower in the talonid basin.
( d ) Even less developed as regards the metaconid, although the Gorilla
itself is backward in this feature.
Similarly, the third molar of Proconsul differs from that of the Gorilla in its :
( a ) Size, which is less.
( b ) Low depressed cusps.
( c ) Strongly developed cingula.
But it agrees with the Gorilla, as well as with the Chimpanzee, in having
ridges between the protoconid and metaconid, and between entoconid and
hypoconulid.
The mandible is much deeper than it is in the Gorilla. If the external
depth of the jaw a t the front of M3 be expressed as a percentage of the length
460
DR. A . TINDELL HOPWOOD ON
of the premolar-molar series, the resultant for Proconsul is 60 per cent, for the
Gorilla, 50 per cent, whereas in two Chimpanzees taken a t random it varied
between 48 and 58 per cent. On the other hand, the mandible is about as
thick as those of the Gorilla and Chimpanzee. The ratio employed by Gregory
and Hellman (op. cit. Table i) is the thickness of tho jaw across the anterior
moiety of the third molar expressed as a, percentage of the outside depth of the
jaw a t the same place. They give the value for the Gorilla as 54.76 per cent
and for the Chimpanzee 53.85 per cent, The ratio in Procowul is 54-1per cent.
Discussion.-This paper was nearly finished when Dr. L. S. B. Leakcy submitted some remains of anthropoids, both originals and casts, to Sir Arthur
Keith, P.R.S. These specimens were obtained from the Lower Miocene of
Rusinga Island in the Kavirondo Gulf, about one hundred and sixty miles
Wcst of Koru. Sir Arthur generously allowed me to examine them with him,
m d to make comparisons with my own material. To his courtesy and consideration I am much indebted, and I wish to express my thanks for the
privilege thus extended to me.
It had d l along boen evidont that, oven allowing for the post-mortem
deformation of the maxilla, the upper and lower teeth from Koru could never
have been made to occlude, and that the upper teeth represented a smaller
animal than the lower. Among Dr. Leakey’s material is a cast of a mandihiilar
ramus which occludes perfectly with the holotype of P. africanus, whereas
his maxillary specimens, which are from larger animals, occliidc with the
mandiblo from Koru.
Until tho nowly discovcrccl matcrial is described and made available it is
not permissible to comment on it, though Dr. Leekey is to he congratulated
on his good fortune. At present there is no reason for separating the mandible
and maxilla described in this paper. Not only has individual variation to
be taken into account, but also variation between the sexes. The results
of this double variation arc familiar to anyone who has studied a long series of
anthropoid skulls, and enjoins caution when dealing with a few specimens.
It has been pointcd out above that there is a marked general resemblance
between Proconsul and the Chimpanzoo, and that Gregory’s description of the
latter is almost equally applicable to the former. Indeed, the main difference
between the two is the more primitive character of the fossil. I n its anterior
mandibular premolar, which has the enamel produced down on to the anterior
root, Proconsul is more simian than Dryopithecus, and more specialised than
many Chimpanzees. On the other hand, there areno great difficulties in the way
of deriving the dentition of the Chimpanzee from that of Proconsul, and I regard
the latter as ancestral to the Chimpanzee.
This new genus has no closc connection with the South African form Australopithecus. The first molars of that genus are much more like those of the Gorilla
than either the Chimpanzee or Proconsul. Indeed, there is very little difference
between the Gorilla and Australopithecus, which appears to be a precocioiis
offshoot of the gorilline lineage.
461
MIOCENE PRIMATES FR03'I KEh-YA
111. AFRICAAND
THE EVOLUTION OF
ANTHROPOIDS.
Including those described in this paper, there are seven genera of fossil
anthropoids known from Africa. Their localities and horizons are :Egypt (Fayiim)
.......
Egypt (Maragha) . . . . . . Burdigalian
Kenya
...............
........ Propliopithecus.
............ Prohylobates.
' Dryopithecus. '
Lower Oligocene
Lower Miocene !
Union of South Africa . Upper Pliocene :1
........
Limnopithecus.
Xenopithecus.
. . . . . . . . Australopithecus.
Schlosser (1911) pointed out that Propliopithecus is structurally the primitive
stage from which evolved the dentitions of the later anthropoids and man.
This view is supported by Gregory (1916, 1922), who extends it by placing the
genus in a central position leading to the Hylobatidae on the one hand and to
the Simiidae on the other. Remane (1921), basing his opinion on the reduction
of the trigonid, includes Propliopithecus among the Hylobatidae and separates
it from the Simiidae.
Fourteau (1920) describes Prohylobates as a direct ancestor of Hylobates, but,
as Remane (1924) showed, it is more specialised than, and hence not ancestral
to, Hylobates. His suggestion that it is a specialised descendant of Propliopithecus unconnected with higher forms is, apparently, well founded.
Limnopithecus is not ancestral to Hylobates ; it has a more specialised milkdentition. The permanent teeth differ from those of Prohylobates in the presence
of a small cingulum, but agree with them in the variation of the breadth index
between 90 and 100. This genus, too, is probably a specialised member of the
Propliopithecus lineage.
Xenopithecus is an unsolved problem : that it is a descendant of one of the
FayQm primates is only a guess incapable of proof until comparable material
is found. Either the lower dentition of this genus or the upper dentition
of one of the FayQm genera is needed.
Dryopithecus mogharensis has not yet been discussed, except by Remane
(1924)) who regards it as indeterminate on the material at present available,
but expresses the opinion that it may be another derivative of Propliopithecus.
Proconsul is definitely more primitive in its dentition than any fossil member
of the Chimpanzee-Gorilla group hitherto described. The lower dentition
is not yet known in sufficient detail for a critical opinion t o be based on it.
The genus is related to Dryopithecus and ancestral to the Chimpanzee.
This wealth of fossil anthropoids from the middle Tertiary beds of Central
Africa sheds new light on the problem of the dispersal of the higher Primates.
Hitherto all such remains have been found in Europe or in Asia ; the theories
of their origin and dispersal have alternated between African and Asiatic
centres. The present discoveries suggest that the former may eventually
prove to be correct, and that the course of events may have been similar t o
462
IlR. A. TINUELL HOPWOOD ON
the outline sketched, in the following paragraphs. It should be made quite
clear from the outset that this outline is tentative. The total number of fossil
spocimens of the higher Primates is too small to justify a dogmatic statement
about their evolution, and this skutch should be taken for what it is meant
to be, namely, a personal interpretation of the known facts, an interpretation
which may well be proved false as our knowledge increases.
Yropliopithecus, or something olosely resembling it, appears to provide a
stimting-point from which more advanced animals arose. Its descendants,
radiating from N.E. Africa or Arabia, entered Europe and Asia, and pressed
southwards farther into Africa. Wherever they went, they continued to evolve,
some in ono direction and some in another, but all of them were restrained by
the limitations of their nature. They began as primitive anthropoids, and their
evolution was governed by that fact. If they had met with identical conditions
in all three directions, their evolution would have been along identical lines ;
the conditions were not identical, nor was the course of their evolution. Nevertheless, parallel evolution could and did occur-for example, there are three
Chimpanzee-like forms, namely, D . rhenanus in Europe, D. punjabicus in India,
;tnd Proconsul in Africa.
Those forms which went south gave rise to the modern African anthropoids.
Their stock also provided the unprogressive Lirnnopithecus, the aberrant
Xenopithecw, and the precocious Australopithecus, but these Itranches from
the main stem lead nowhere.
The European descendants paralleled the African in their evolution ; hence
the gorilline features of Dryopithecus fontani and the resemblances between
tho Chimpanzee and D. rhenanus. They are of importance ; for, from a complex
centred round D. rhemnus the human line may have had its origin.
The branch which wandered into Asia also paralleled the African ChimpanzeeGorilla group fairly closely, but there were certain influences a t work which
prevented this parallelism proceeding as far as in the European species. The
effect of theso influences is clear. ‘ On the whole the lndian Dryopithecus ”
seems to be allied rather with the orang than with the gorilla-chimpanzee-man
group, the former constituting an eastern, the latter a western division of the
family Simiidae ’ (Grogory & Hellman, 1928, p. 84).
Despite the probability that the higher primates had their origin in Arabia
or North-Eastern Africa, it does not follow that Africa is the continent in which
the final transition from ape to man was effected. At present there is practically
no evidence in support of such a view, but much can be said for the Central
Asian origin of man.
A branch of the Dryopithecus rhenanus complex travelling eastwards penotrated to Central Asia after the Himalayan uplift had progressed so far as to
constitute a barrier t o the northward migration of the Indian genera with their
Orang-utan affinities. There further evolution resulted in man, and from
thence human beings spread over tho face of the eart,h. I n other words, the
primary centre of dispersal of the anthropoids was in or near Northern Africa.
‘ I
HOP WOOD
JOURN. LINN. SOC., ZOOL.VOL.XXXVII1. PL.6
MIOUENE PRIMATES FROM EENYA
463
and a branch of the western group wandered through Europe to Central Asia,
where it gave rise to man.
IV.
ACKNOWLEDGMENTS.
1 have t o express my grateful thanks to Professors G. Elliot Smith, F.R.S.,
and H. A. Harris, M.D., D.Sc., who provided me with the X-ray photographs,
as well as to Mr. J. Melville, t o whose skill as radiographer I am indebted for
the technical excellence of the photographs themselves.
I am no less obliged to E. J. Wayland, Esq., t o Dr. Gordon, and E. Cooper, Esq.,
the former and present owners of Legetet Farm, and to A. S. Kerton, Esq.,
of Koru, for their manifold help both in East Africa and a t home. To them,
too, I tender my thanks.
LISTOF WOBKSCONSULTED.
ANDREWS,C. W. 1914. Quart. Jorrrn. Geol. Soc. lxx, pp. 163-186, pls. xxvii-xxix.
BROWN,
B., GREGORY, Mi. K., & HELLMAN,
M. 1924. Amer. Mus. Novitates, No. 130.
POURTEAU,
B. 1920. Contribution a 1’Etudecles Vcrtebrbs Miocbnes de 1’Egypte. Survey
Dcpartment, Cairo.
M. 1931. Ann. naturhist. Mus. Wien, xlvi, pp. 15-27, pl. ii.
GLAESSNEX,
GREQORY,
W. K. 1916. Bull. Amer. Mus. Nat. Hist. xxxv, pp. 239-355, pl. i.
- 1922. The Origin and Evolution of the Human Dentition, pp. xviii, 548, pls. i-xv.
8vo. Baltimore.
C HELLMAN,
M. 1926. Amer. Mu.Xat. Hkt., Anthrop. Papers, xxviii, pt. 1.
HOFFBIAN,
A. 1893. Abhand. k.-k.geol. Iteichs. xv, Heft 6.
HOPWOOD,
A. TINDELL. 1933. Ann. & Mag. Nat. Hist. ( l o ) , xi, pp. 96-98.
MAYET, L., & LECOINTRE,Ctsse P. 1909. l h d e Sommaire des Mammifbres Fossils
de la Touraine. Ann. Univ. Lyon, n.s. Paso. 26.
PILGRIM,
G. E. 1915. Rec. Geol. Surv. India, xlv, pp. 1-74, pls. i-iv.
1932. The Fossil Carnivora of India. Palaeont. Indica, n.8. xviii.
A. 1921 a. Centraibi. Min. GeoI. Paiaont. Jahrg. 1921, pp. 336-339.
REMANE,
1921 6 . Arch. Naturges. lxxxvii, Abt. A, Heft 11, pp. 1-179.
- 1924. Centralbl. Min. Geol. Palaont. Jahrg. 1924, pp. 220-223.
SCHLOSSER,
M. 1911. Beitr. Palaont. Geol. 0est.-Ung. xxiv, pp. 51-167, pls. ix-xvi.
__ 1923. See ZITTEL,K. A. VON.
WEBER,M. 1904. Die Saugetiere, pp. xii, 866, 8vo. Jena.
WOODWARD,
A. S. 1914. Quart. Journ. Geol. Soc. lxx, pp. 316-320, pl. xliv.
ZITTEL,K. A. VON. 1923. Grundziige der Palaontologie, ii, pp. v, 706, ed. 4. 8vo. Miinchen.
(Mammals revised by Max Schlosser.)
L_
-
EXPLANATION O F PLATE 6.
Fig. 1. Limnopithecus legetet Hopw. First and second right lower molars; occlusal
aspect, X 2. HoEotype, regd. M 14079.
Fig. 2. L. Zegetet Hopw. Part of the left mandibular ramus with deciduous dentition ;
occlusal aspect, x 2. Paratype, regd. M 14080.
Fig. 3. Xenopithecus koruensis Hopw. First and second left upper molars; occlusal
aspect, X 2. Holotype, regd. M 14081.
Yig. 4. S.Fzorueusis Hopw. Posterior right upper deciduous molar ; occlusal aspect, x 2.
Pczrcitype, regd. h1 14081.
464
MIOUENE PRIMATES BROM KENYA
Fig. 5. Proconsul africanus Hopw. Left maxilla ; ocolusal aspeot, x 1. Holotgpe, regd.
M 14084.
Fig. 6. The same ; labial aspect, x 1.
Pig. 7. P. africanus Hopw. s i g h t mandibular ramus; internal aspect, X 1. Hegd.
M 14086.
Pig. X. P. africanus Hopw. Left mandibular ramua; internal aspect dissected t o display the roots of the teeth, x 1. Regd. M 14086.
Pig. 9. P. africanw Hopw. First right upper molar; occlusal aspect, X 2. Hegd.
M 14085.
Pig. 10. P. africaiaus Hopw. Third right lower molar; occlusal aspect, X 2. Eegd.
M 14087.
[The registor-numbers are those of the Department of Geology of the British Museum
(Natural History). Figures 1, 2, 4 were drawn by Miss Barbara Hopkin8.J