AMER. ZOOL., 21:37-45 (1981)
Functional Analysis and the Practice of the Phylogenetic
Method as Reflected by Some Mammalian Studies1
FREDERICK S. SZALAY
Department of Anthropology, Hunter College, CUNY, 695 Park Avenue, New York, New York 10021;
Department of Vertebrate Paleontology, American Museum of Natural History,
New York, New York 10024
SYNOPSIS. The reliability of a phylogenetic hypothesis is largely dependent on the diversity
and abundance of characters. The meaning and complexity of these is furthermore a
significant factor in choosing some characters over others to reflect the relative recency
of taxa. Studying mechanical function and biological roles of character complexes yields
new characters and a more profound appreciation of the "known" ones. This growth in
available information invariably results in more convincing assembly of morphocline polarities or more clearly established homologies. This procedure of character analysis permits the construction of phylogenies which are more probable and based more securely
on the foundations of any phylogeny: biologically researched homologies. When ontogenetic, functional and adaptational studies result in equivocal veiws, as to the polarity of a
character cline, often the fossil record offers a clear and testable hypothesis on character
cline polarity.
INTRODUCTION
subscribe to the latter view and would consider all advances in phylogenetic studies
strictly dependent on new characters or
new fossils. Looking at the history of mammalian phylogenetic studies, however, this
latter view does not appear to hold true.
The so called "new characters" often represent biologically better understood character complexes, and not merely "more"
characters as the phrase would atfirstimply. Many systematists start out by attempting to understand, usually from the vantage point of mechanics and heritage, an
available character complex. Contrasted to
this procedure, which clearly gives great
importance to the biological appraisal of
features, is the post-Hennigean cladistic
approach which either disavows or actually
scorns any attempt to incorporate functional analysis into phylogenetic assessment, and rather strives for logical consistency between a list of characters (one
being considered as "good" as another)
and a cladistic {i.e., sister group) hypothesis (see Nelson [1970, 1973a, b]; Rosen
[1974]; Englemann [1977]; Tattersall and
Eldredge [1977]; and others). This school
of cladistics, therefore scorns the idea of
weighting (subsequently biological and/or
functional appraisal) as something too subjective to have place in "science" (i.e., log1
From the Symposium on Functional-Adaptive Anal- ic).
During the past decade a previously existing rift among systematists who study
phylogeny has widened as a result of the
philosophy developed by the cladistic
school. The latter has increasingly come to
campaign for a "pure," "objective," "logical," etc. approach to character analysis. A
rash of cladistic contributions has come to
eschew a preference for merely listing and
not weighting characters, in place of an
understanding of the biology, functional
meaning of the features used for phyletics,
and hence their relative value. In place of
a biological approach to character analysis
various schemes have been offered to
"test" cladograms, but not the polarity hypotheses of various character clines (Englemann, 1977; Englemann and Wiley, 1977).
These views have been recently criticized
by Bock (1977), Szalay (1977) and Naylor
(1981).
We may ask: why do systematists reevaluate phylogenetic problems as time
passes? The answer usually given is that
new data becomes available. Is this new
data always the discovery of new characters? There are many systematists who
ysis in Systematics presented at the Annual Meeting of
the American Society of Zoologists, 27-30 December
1979, at Tampa, Florida.
37
I believe that at the very heart of the
post-Hennigean cladistic approach to phy-
38
FREDERICK S. SZALAY
logeny reconstruction lies the implicit neglect for biological and functional scrutiny
of the characters employed. As a result of
this attitude the postulated homologies
chosen (the units on which phylogenies are
based) are not biologically investigated and
therefore the chances of discovering
whether these features are unique or parallel or convergent acquisitions, or whether they represent a pattern commonly attained by distant lineages because of
epigenetic factors, or because they are
rooted in a common heritage, weakens the
very foundations of such analyses. In other
words, character analysis commonly practiced in cladistics is really a semantically
masqued enumeration of characters without attempts to analyze and weight them.
What case, in light of many erudite and
extremely logical contributions in the SSZ
during the past decade, if any, can be
made for the essential importance of a
functional approach in phylogenetic analysis? The following remarks will focus not
only on the role of functional inquiry. It
is unavoidable to comment on some aspects of the purely cladistic methodology
as the extreme proponents of this view
have brought into question the relevance
of functional and adaptational inquiry to
phylogenetic analysis. Yet, recently, with
an oddly reconciliatory tone. Tattersall and
Eldredge (1977) in outlining the order in
which genealogical inquiry should proceed, noted that the first steps, according
to them, is the construction of the cladogram, then the erection of a "less precise"
tree, and then finally the nearly non-scientific, speculative, but admittedly interesting "scenario," i.e., an adaptational account of the taxa. It is not my intention to
analyze this particular statement of the cladistic method, yet comments on cladistics
will be inevitable as the role of functional
analysis is appraised. Cladogram construction before characters are biologically appraised, and the construction of various
hypotheses of adaptations, "scenarios," can
be entertained as long as we do not care
whether the characters on which we base
our cladograms are "good" or "bad" characters, i.e., we do not believe in the necessity of weighting different kinds of charac-
ters. The latter, however, is not feasible
without at least a rudimentary use of biological analysis. Furthermore, cladograms
can be constructed on a haphazard collection of allegedly shared and derived characters, but this does not ensure that thij^
particular hypothesis of cladistic genealogy
will have accounted for all of the characters in a most biologically convincing way;
this is only likely if a phylogenetic tree is
based on character analyses of the most
encompassing kind with all that this entails
in terms of developmental and physiological (mechanical) and adaptational inquiry.
Theoretically characters may be subdivisions of an organism all the way down to
its molecules. In phylogenetic analysis one
usually searches for patterns which are
uniquely, and presumably derivedly, possessed by an increasingly smaller and
smaller number of species. So ideally
speaking the characters which we should
utilize, which have the least chance of having resulted from convergent evolution,
are those which are complex and which are
the result of a specific set of selectional
forces working on the population ancestral
to a set of taxa. It is this interaction of a
specific, complex set of selectional forces
with the genetic substrate in a given instance of time which produces such unique
character combinations as bird wings,
mammal hearts, even-toed extremities on
characteristic artiodactyl carpi and tarsi, or
the tooth comb of extant strepsirhine primates. Although all of these general, descriptive conditions have been duplicated,
because of their specific details the various
characters listed are unmistakably recognized as homologous in the various taxa
which mutually possess them. So the most
reliable, "best," kind of characters for the
working systematist are unique, complex
features.
Often, however, before a unique derived character complex is recognized, an
organism (or rather its selected parts) must
be approached by the working scientist
with an attitude geared towards biological
understanding with a set of questions,
rather than just the hope of merely taking
off a list of characters onto paper with the
desire to work out a genealogy. The tra-
FUNCTIONAL AND PHYLOGENETIC METHODS IN MAMMALIAN STUDIES
ditional approach, although rarely recognized consciously, involves learning all the
systematist can about the biology of a given
region of the organism. We often want to
know, ideally, how development proceeds,
^Khat the blood and nerve supplies are,
what muscles and tendons move and restrict movements, etc. The overwhelming
majority of papers in mammalian phylogeny are based on hard parts. More often
than not these are the dental records, the
skull and occasionally the postcranium. It
appears, therefore, that systematists,
whether this point is widely acknowledged
or not, should have an overriding interest
in understanding the characters they work
with as the success of choosing, analyzing
and weighting (if they ascribe to the latter)
of these determines the phylogeny (or
cladogram) they will generate. Yet among
some systematists, the functional approach
to phyletics, to character analysis, is
scorned or considered superfluous. Clearly, these authorities will eventually produce arguments which will show that to
recognize and to determine polarity hypotheses for morphoclines one can dispense with a functional and adaptational
hypothesis.
There is often considerable risk involved
when poorly understood biological phenomena are employed as the basis for interpreting character clines. A striking example of phylogenetic speculations gone
haywire is a number of papers focusing on
primate phylogeny (e.g., Krishtalka and
Schwartz, 1979; Schwartz and Krishtalka,
1979), which based their arguments on
tooth homologies as determined by timing
and patterns of replacement, rather than
by criteria rooted in the homologies of the
various subdivisions of the dental lamina.
The basic complexity of the homology
phenomenon for structures like teeth can
be well grasped from the recent review of
Osborn (1978). Yet in another interesting
contribution, Schwartz et al. (1971) reshuffle the phylogenetic relationships of
an order of mammals based purely on
what they perceive to be the homologies of
various poorly known anterior dentitions,
simply setting aside well understood soft
anatomical and osteological characters
39
which cannot be accounted for by their
phylogenetic hypothesis.
EXAMPLES
In the following section I will briefly list
and analyze some examples, from selectively simple to increasingly more complex
features, which illustrate the importance
of even the most rudimentary functional
framework for character analysis and subsequent weighting of characters before a
phylogenetic hypothesis is synthesized.
Cranium
The cranium is a favorite area of phylogenetic research for assessing mammalian relationships. Yet in the literature of
the last fifty years one would have a difficult time finding the use of large sagittal
crests as a character signifying a particular
recency of relationships. The reason, quite
simply, is that several functionally and developmentally oriented contributions have
shown (see review by Biegert, 1963) that
the size of the crest depends on the complex relation between body size, the relative size of the temporalis, and the relative
size of the brain. The temporalis size and
conformation, of course, is dependent on
species specific masticatory requirements.
The use or non-use of a character (its
weighting), in this case, was clearly determined by functional research. It follows
that features chosen whose developmental
and functional significance, or even more
significantly, their lack of functional importance, is not known or appreciated are
risky and therefore perhaps "bad" characters, in the sense that their appearance
might be accounted for by a biological phenomenon other than a common phylogeny.
Dentition
No area of anatomy has been as influential in phylogenetic studies of mammals
as the dentition. Ironically, in spite of the
beliefs of many paleomammalogists who
are inclined to be descriptive in their accounts of dentitions and who believe that
phylogenetic analysis can easily dispense
with a mechanical appraisal of teeth, the
study of mammalian dentition is rooted in
40
FREDERICK S. SZALAY
functional and adaptational analysis. The the other hand, focused on the tarsal morbroadly and partly functionally oriented phology and articular mechanics of living
inquiries of such students as Cope, Os- tupaiids, colugos (dermopterans), priborn, Gregory, Matthew, Simpson, Butler mates and early Tertiary remains which
and others, have recently culminated in a suggest similarity to these. It should be relarge number of new studies boosted by membered that selection acts on the a u ^
both novel conceptual views (Every, 1970, mal's behavior, i.e., the mechanical solu1972) as well as new technology (Ardran tion it provides to interact with a selectional
etal, 1958; Crompton and Hiiemae, 1970; force. Although mechanical function is the
Kay, 1975; Seligsohn, 1977). Following the consequence of morphology, we are to be
literature on mammalian dentitions from reminded that often minor morphological
over a century ago makes it clear that the changes can have profound consequences,
choice of units or "characters" which often and subsequently major adaptive • signifiappear in descriptions, diagnosis, or phy- cance. Concentrating on those features of
logenetic accounts have been heavily influ- the ankle and heel bone complex which
enced by the then current conception of permit habitual inversion of the foot in the
the functional meaning of teeth. Today most primitive tupaiid, colugos, Paleocene
students of teeth as commonly speak of the primates and modern euprimates. allowed
phylogenetic significance of certain pre- us the establishment of a common formcisely delineated and understood attrition- function complex in primitive primates,
al facets as the presence or absence of "hy- dermopterans and primitive tree shrews.
pocone" (not a homologous structure in all Now clearly'these mammals are-not the
Mammalia which have it) at the beginning only ones which invert their feet, and have
of the century. Morphological analysis of characteristic functional modifications for
molar morphology often relies on func- a habitual arboreal life. In arboreal rotional approaches for the establishment of dents, viverrids, and a host of other arbohomologies of structures. Thus for exam- real mammals the substrate is utilized by
ple, the presence or absence of certain at- the foot usually assuming a habitually intritional facets may signify whether a den- verted position. To habitually face the foot
tal structure is a new acquisition or the inward during inversion the tarsals have to
transformed homologue of an existing change to accomplish this in the most enone. Homologies of lower molar cusps on ergy efficient manner—given the conan early group of primates, the Picrodon- straints of their heritage. Without going
tidae, for example, become clear only into the technical details of tarsal mechanwhen the mechanics of the occlusal pat- ics (see Szalay and Decker, 1974; Szalay,
1977, 1980) it is sufficient to state that the
terns are considered (Szalay, 1968).
complex interaction of the crus (tibia and
fibula), the seven tarsals and the rays of
Postcranium
the foot result in taxon specific modificaSeveral examples "may be cited for the tion which are simply not duplicated conextreme, perhaps essential, usefulness of vergently in living mammals, in spite of
a functional approach to character analysis essentially similar biological roles perof postcranial anatomy. I will concentrate formed by the foot of a number of arboon one example, which recently has aided real lineages. Sharing, therefore, by the
my inquiry into the relationships of a primitive members of three different orgroup of early and recent mammals, the ders of mammals a form-function complex
archontans. A number of contributors which is uniquely derived among the
have recently focused (Luckett, 1980) on Mammalia for the same mechanical purthe relationships of the living tree shrews. poses represents a unique and complex
With the exception of Szalay and Draw- character that is the base for adhering to
horn (1980) all contributors were equivo- the concept of the Archonta of Gregory
cal as to the meaning of character com- (1910). Were we to look for isolated charplexes examined, whether crania, dentition, acters on some of the tarsals, it would not
postcrania or soft anatomy. We have, on
FUNCTIONAL AND PHYLOGENETIC METHODS IN MAMMALIAN STUDIES
41
be difficult to find similar modifications in tapering nails (as in Lemur); keeled,
other groups in addition to archontans. It 'needle-claws' (Galago senegalensis); transis, however, the functioning unit, the tar- versely arched, compressed (keel-less) nails
sus, which presents us with the unique syn- (as in many ceboids and smaller catarapomorphous pattern—and this could rhines); flimsy toilet claws that are simply
Inly be gleaned after the whole has been elongate (Aotus) or strongly projecting
considered in terms of its mechanics. In this dorsad from the phalanx (Tarsius); plaqueinstance an avowedly simple functional ap- like, miniscule nails {Tarsius); and a variety
proach yielded an important character of combinations within a cheiridium (see
complex otherwise unrecognized, by which Hershkovitz, 1977) or between cheirdia."
enigmatic ordinal relationships could be
In order to illuminate the usefulness of
strongly corroborated.
a functional approach to a controversial
Another example, taken from the basket phylogenetic problem, I will approach the
of primate evolutionary problems sheds question of primate-marmoset relationinteresting, and. more complex, insight ships by first focusing on the nature of the
into the use of all biological approaches to unguae, then the digital pads underlying
character analysis in order to explain tax- these, and finally the features of the enon phylogeny.
tocuneiform-Mtl joint which faithfully
A major, if not the single most impor- mirrors the nature of grasping adaptations
tant, problem in the relationships of South of the foot. It is assumed that the extent
American primates has been the issue of to which grasping is practiced and the nawhether or not the marmosets, "clawed" ture of the ungua are closely interrelated
primates, or the remaining platyrrhines, in the development of either nails or claws
the "nailed" group, represents the ances- in primates.
tral platyrrhine and therefore probably
The thesis that marmoset claws are hoanthropoid stock. Clearly, the issue is not mologous with those of primitive mamonly "claws" vs. "nails," but these modifi- mals as claws and that they are primitive
cations of the falculae of the primitive eu- in the taxon Platyrrhini has been strongly
therians have played a very significant role supported by Cartmill (1974) and most rein the platyrrhine debate.
cently by Hershkovitz (1977). In recent
A complex terminology has grown up in years the most articulate and essentially
the literature as to the nature of the claws logicalistic arguments against the idea that
or nails, and the debate has gone on nails were the ancestral unguae in eupriwhether or not the nailed condition in pri- mates (all strepsirhines and haplorhines,
mates has evolved once or several times. but not the plesiadapiforms) were written
In other words, the question of homology by Cartmill (1974). It is best to quote his
of claws of nonprimates and marmosets, views to clarify this position. His usage of
and nails in different groups of primates the term "primate" should be interpreted
has been increasingly employed in accept- to mean euprimates. According to Cartmill
(1974, pp. 73-74):
ing or rejecting phylogenies.
It should suffice for our discussion that
Two facts contravene this interpretathe digital unguae which have been clastion. The first is that the nails of Cebus
sified as falcula (tupaiids), tegula (noncalalbifrons display in vestigal form the terlitrichine platyrrhines), ungula (cataminal matrix and deep stratum characrrhines), represent only.a part of the
teristic of true claws (Thorndike, 1968),
continuum of diverse ungual morphology
indicating that their gross morphology
in nonprimates and primates and these
represents a secondary modification of
categories are often based on different cria marmoset-like ancestral condition.
teria. To quote Rosenberger (1979, p.
382): "Biegert (1961) illustrates this variety
The second is that the same features
quite nicely. To offer an overly simplistic
persist in the grooming claws of Tarsius
(Le Gros Clark, 1936), where they must
survey, living primates may have flat nails
(as in Homo; Perodicticus); keeled, distally surely be vestigial retentions lacking any
42
FREDERICK S. SZALAY
present functional significance. We may
conclude that primitive sharp claws were
present on all digits (with the possible
exception of the first toe) of the last common ancestor of the cebids, callitrichids,
and tarsiids and that they had therefore
not been lost in the basal primates. To
assume that the basal primates lacked
claws requires that the lineage leading to
Cebus albifrons had lost its claws by the
Eocene, reacquired them during the
Oligocene, and begun to lose them again
during the later Tertiary. This is possible, but unparsimonious. It is still less
parsimonious to assume that claws have
been acquired de novo in many different
mammalian orders; it is extremely difficult on this interpretation, to account for
the presence of claws in didelphids and
other arboreal marsupials, which display
hindlimb dominated arboreal locomotion in a pronounced form. The comparative anatomical evidence indicates
that the hands and feet of the last common ancestor of the extant primates
must have resembled those of an opossum; claws have been lost independently
in four or five parallel lineages of primates.
logical or histological detail with either
gross morphology (in this case claws or
nails) or behavior. In other words, weighting either by functional considerations (in
this case) or by historical perspective, is not
utilized. It is, however, the functional aW
guments, in this case, which easily negate
distributional arguments and force one to rephrase anew parsimony-based argumentation in the light of the significance of the
characters. I perhaps redundantly emphasize that weighting should be rooted in the
biological and not merely the distributional understanding of characters. The presence of such functionally important features associated with claws as the deep
stratum and terminal matrix on some living nailed primates clearly suggests that
these features were not completely lost
when clawed forms were transformed.
The deep stratum, as Le Gros Clark (1959,
p. 173) noted, is the mechanically important part of a claw, and its presence ensures a sharp and strong point. But in developing nails, although the deep stratum
was subsequently deemphasized, it was not
functionally essential to lose it. It is therefore that hypothesis to be preferred which
takes into account the phenomenon of phylogenetic inertia, and which can explain the
Cartmill's (1974) and Hershkovitz's fact that in marmosets the claws have a) a
views could be countered on non-function- reduced deep stratum, b) a reduced flexor
al grounds. Yet, as it will become obvious, and extensor mechanism working the
the arguments would seem convincing for terminal phalanx unlike the claws in noneither side. The presence of the terminal primates (Le Gros Clark, 1936) and that
matrix and deep stratum in Cebus albifrons, c) the terminal pads are not under the
features which are well developed in distal interphalangeal joint as in clawed
clawed mammals (see above), does not nonprimates (Rosenberger, 1977). The
mean, although distribution may suggest, most parsimonious explanation, considera secondary modification from a marmoset ing the function, is that all these tried funclike condition. Cartmill's scheme of "great- tional attributes of clawed mammals are
est parsimony" asserted that if we hypoth- diminished or lost in marmosets simply
esize presence of nails in the primitive because their heritage is that of nailed platcommon ancestors to tarsiiforms and an- yrrhines.
thropoids than we must admit a lineage to
As far back as 1917, Pocock argued that
Cebus which lost its claws by the Eocene, the claws of marmosets are functionally
regained them by the Oligocene and lost correlated with their narrow hands and
them during the later Tertiary. This feet and their reduced hallux. Gregory
scheme (as that of Kay and Cartmill [1977] (1920), also argued for the derived nature
which offers an explanation of adaptations of the marmoset claw, citing the lack of
in Paleogene primates and articulates their opposability by the hand, the elongated
method of analyzing adaptations), de- metapodials, hallucial nails and the weakpends on the association of any morpho- ness of digital flexors compared to other
FUNCTIONAL AND PHYLOGENETIC METHODS IN MAMMALIAN STUDIES
living primates. Szalay (1975, p. 382) subsequently asserted that the ". . .joint morphology between Mtl and the entocuneiform leaves little doubt that the decreased
range of mobility of that joint was derived
£'om one with a much greater range, as
that displayed in . . . Saimiri or Aotus. The
clawed condition of the digits most functional in locomotion can be tied to the
characteristic molar morphology and robust incisors of the marmosets." The implication was that the gumivorous diet of
an ancestral marmoset may have precipitated the selectional forces which resulted
in the secondary evolution of claws in this
group.
As noted above, marmosets, which have
poor grasping abilities, possess a first toe
strikingly smaller than the others, and
their entocuneiform-Mtl joint allows a
much less extensive movement of Mtl than
other platyrrhine or other euprimates
(Szalay, 1975). Yet morphologically, with
the exception of the articulation between
the two bones, which is less extensive than
that of other euprimates, marmosets conform to the other groups of strepsirhine
and haplorhine primates, the entocuneiform and Mtl possessing diagnostic attributes which were derived for the ancestral
euprimate. The mechanical requirements
reflected in the joint between these two
bones serve the biological role of a powerful grasp in euprimates, equalled only
among phalangerid marsupials. Needless
to say, the morphological-mechanical solution of the entocuneiform-Mtl complex
in the latter is simply different from that
seen in primates. It is only in the marmosets that we find a drastically reduced first
toe but with an osseous morphology strikingly similar to other euprimates which
habitually grasp, but (in marmosets) accompanied by a claw clinging and climbing
habit. In living euprimates, with the exception of various modifications of the unguae
on specific cheirdia, the grasping manus
and pes have first digits which invariably
bear the flattened nails, as clearly recognized by Gregory (1922). The documented
nail bearing pollex and hallux of Notharctus (Gregory, 1920), the prevalance of distal euprimate phalanges with their char-
43
acteristic flattened distal ends in Eocene
fossil mammal quarries certainly suggest
that a nailed pollex and hallux, is primitive
at least in euprimates (Szalay, 1975; Rosenberger, 1977, 1979). Before favoring
such a hypothesis on distributional
grounds, let us further examine morphology associated and functionally interrelated with claws vs. nails, and the mechanical
attributes associated with various histologies of unguae.
Building on Le Gros Clark's (1936) rich
morphological contribution and adding interpretive insights of his own, Rosenberger
(1979) summarized some of the subsequent mechanically important differences
of the distal interphalangeal joint of euprimates from claw bearing nonprimates.
In living euprimates this joint lacks an extensor process dorsally and lacks the usual
ventral sesamoids, and has a much less developed ventral flexor process even in the
clawed marmosets. Rosenberger (1977)
made the significant discovery that in living primates the terminal volar pad, unlike
in nonprimates, lies beneath the body of
the phalanx and not below the articulation,
and as Le Gros Clark's (1936) text figure
12 dramatically illustrates, this pad is much
larger even in the claw bearing marmosets
than in clawed nonprimates. In addition,
the nail bed which underlies the claw in
marmosets is also relatively enlarged. As
Rosenberger (1977) noted, the vascular
channels identified by Le Gros Clark laterally and dorsally in the terminal phalanges of marmosets and the aye-aye, the
other genuinely clawed primate, were not
found by him in the clawed nonprimates.
It seems clear that the clawed living primates have a number of morphological attributes (the position and size of the terminal pads, reduced ventral flexor process
and osseous channels in the phalanx to
nourish the soft tissues of the hypertrophied pads), commonly found in the
nailed primates, which, have probably
evolved in close functional association with
nails. Following also Rosenberger's (1979)
synthesis, the differences between the nonprimate claws and euprimate nails, terminal pads and the interphalangeal joint area
in general depict differences in mechanical
44
FREDERICK S. SZALAY
solutions for different biological roles. In
clawed nonprimates a stable interphalangeal joint with a rigid bone between claw
and phalanx, and a thick terminal pad under the joint for shock absorption and
bracing together will serve in climbing and
securing the animal, enhancing at the
same time such functions as digging or fur
cleaning. Primates on the other hand, hypertrophied the terminal volar pad, and
moved it distally, primarily, and in this I
differ from Rosenberger's (1979) view, to
maximize the total friction surface available during grasping and grasp leaping.
According to Rosenberger (1979) perhaps
tactile efficiency was enhanced by increasing the unit area over which counterpressure is applied, and by also possibly increasing the number of sensory receptors.
To summarize these arguments, if we
consider the evidence from the entocuneiform-Mtl joint combined with the conformation of the terminal volar pad and the
interphalangeal joint, then the most convincing hypothesis which accounts for the
foregoing is that lack of grasping with the
foot and the presence of claws are secondarily acquired, derived primate conditions
in marmosets.
and splitting (sister-group ties) which is expressed by a phylogenetic tree. Organisms,
however, have numerous characters, or
fewer, but still considerably abundant
character complexes whose relative recency as shared homologies between two ( £
more taxa does not coincide from character to character. For these dilemmas the
first solution is weighting resulting from
biological analysis, the second is the arrangement of the weighted homologies
into a relative time framework. Ideally a
phylogenetic tree or a cladogram should
merely reflect this final stage of decision
making.
It is with the procedure of weighting
and temporal sorting of characters that the
insights offered by the developmental, mechanical, and adaptational analyses become the very bases of the phylogenetic
method. It is only this area of inquiry
which can be meaningfully considered as
testing procedure for a phylogenetic hypothesis. Any other approach (e.g., Englemann, 1978) for phylogeny testing, without the biological research necessary to
evaluate characters, is rooted in either consistency schemes, semantic and logicalistic
arguments, or simply a purely phenetic
approach, as the honest and unpretentious
CONCLUSION
practitioners of that latter approach to sysIt is taken as a basic tenant of the phy- tematics, the pheneticists, prefer it. Adlogenetic method that both the establish- herence to a motto of "using synapomorment of homologies and the sorting of the phies" is quite meaningless until attempts
relative usefulness of these for taxon phy- are made on biological grounds to considlogeny (weighting) depends entirely on er, test, and accept or reject a character as
sound biological (developmental, function- homologously snared and derived. Asal and adaptational) appraisal of these sumptions that certain characters are
characters or preferably character com- shared and derived, based on distributionplexes. It is maintained that mere enu- al or "out group" arguments, do not make
meration without weighting of different them so, as our knowledge of the occurkinds of characters and without attempt- rence of taxa in space and time is notoing to determine the relative time of riously poor. It is therefore the interpreshared homologies cannot result in a bio- tive schemes derived from developmental
logically (i.e., historically) meaningful tax- and mechanical studies that give special
significance and value to the characters in
on phylogeny.
living and fossil forms.
The phylogenetic method,, as Gregory
Using a developmental-functional and
(1910) called it, is essentially a historical
method. The major aim of character anal- adaptational approach to character analyysis is therefore to sort out the various sis in systematics ensures 1) that related
shared homologies between taxa into a rel- characters are pooled together and 2) recative time framework of their appearance. ognition of new characters which are of
It is the relative recency of relationships in vital significance to some function perterms of descent (ancestor-descendant ties) forming an important biological role. This
FUNCTIONAL AND PHYLOGENETIC METHODS IN MAMMALIAN STUDIES
methodological approach to phylogenetics
is the only one which allows weighting.
Without weighting, however, based on a
developmental-functional method, and
temporal sorting, in my"opinion, there is
• > meaningful attempt to.reflect evolutionary history or to test, competing phylogenetic hypotheses. '--
45
Le Gros Clark, \V. E. 1959. The antecedents of man.
Edinburgh Press.
Luckett, W. P. (ed.) 1980. Tree shrews. Plenum Press,
New York.
Naylor, B. G. 1981. A paleontological view of cladistic analysis ancestors and descendants. Syst.
Zool. (In press)
Nelson, G. J. 1970. Outline of a theory of comparative biology. Syst. Zool. 19:373-384.
Nelson, G. J. 1973a. The higher-level phylogeny of
vertebrates. Syst. Zool. 22:87-91.
REFERENCES
Nelson, G. J. 19736. Classification as an expression
Ardran, G. M., F. H. Kemp, and VT. D. L. Ride. 1958.
of phylogenetic relationships. Syst. Zool. 22:344A radiographic analysis of mastication and swal359.
. lowing in the domestic rabbit Oryctolagus canicu- Osborn,J. W. 1978. Morphogenetic gradients: Field
lus L. Proc. Zool. Soc. London 130:257-274.
versus clones. In P. M. Butler and K. A. Joysey
Biegert, J. 1961. Volarhaut der Hande und Fiisse.
(eds.), Development, function and evolution of teeth,
Handb. der Primatenkunde I I/I. Lieferung 3,
pp. 171-202. Academic Press, New York.
pp. 1-326. Karger, Basel.
Pocock, R. I. 1917. The genera of the Hapalidae
Biegert, J. 1963. The evaluation of characteristics of
(marmosets). Ann. Mag. Nat. Hist. ser. 20:247—
the skull, hands, and feet for primate taxonomy.
258.
In S. L. Washburn (ed.), Classification and human Rosen, D. 1974. Phylogeny and zoogeography of salevolution, pp. 190-203. Aldine Publ. Co., Chicago.
moniform fishes and relationships of LepidogaBock, W. J. 1977. Adaptations and the comparative
laxias salamandroides. Bull. Amer. Mus. Nat. Hist.
method. In M. K. Hecht, P. C. Goody, and B. M.
153:265-326.
Hecht (eds.), Major patterns in vertebrate evolution,Rosenberger, A. L. 1977. Xenothrix and ceboid phypp. 57-82. Plenum Press, New York.
logeny. J. Hum. Evol. 6:461^81.
Cartmill, M. 1974. Pads and claws in arboreal loco- Rosenberger, A. L. 1979. Phylogeny, evolution and
motion. In F. A. Jenkins, Jr. (ed.), Primate lococlassification of New World monkeys (Platymotion, pp. 45-84. Academic Press, New York.
rrhini, Primates). Ph.D. Diss., C.U.N.Y., New
Crompton, A. W. and K. M. Hiiemae. 1970. Molar
York.
occlusion and mandibular movements during Schwartz, J. and L. Krishtalka. 1977. Revision of
ocdusion in the American opposum, Didelphis
Picrodontidae (Primates, Plesiadapiformes):
marsupialis. J. Linn. Soc. (Zool.) 49:21-47.
Dental homologies and relationships. Ann. CarEngelmann, G. F. 1977. The logic of phylogenetic
negie Mus. 46:55—70.
analysis and the phylogeny of the Xenarthra. Schwartz, J., I. Tattersall, and N. Eldredge. 1978.
Ph.D. Diss., Columbia University.
Phylogeny and classification of the primates revisited. Yrbk. Phys. Anthrop. 21:95-133.
Englemann, G. F. and E. O. Wiley. 1977. The place
of ancestor-descendant relationships in phylog- Seligsohn, D. 1977. Analysis of species-specific molar
adaptations in strepsirhine primates. Contrib. to prieny reconstruction. Syst. Zool. 26:1-11.
matology, Vol. 11. Karger, Basel.
Every, R. G. 1970. Sharpness of teeth in man and
Szalay, F. S. 1968. The Picrodontidae, a family of
other primates. Postilla 143:1-30.
early primates. Amer. Mus. Novitates 2329:1-55.
Every, R. G. 1972. A new terminology for mammalian
Szalay, F. S. 1975. Phylogeny, adaptations and disteeth. Pegasus Press.
persal of the tarsiiform primates. In W. P. LuckGregory, W. K. 1910. Orders of mammals. Bull.
ett and F. S. Szalay (eds.), Phylogeny of the primates:
Amer. Mus. Nat. Hist. 27, Parts I and II.
A muUidisciplinary approach, pp. 357-404. Plenum
Gregory, W. K. 1920. On the structure and relations
Press, New York.
of Notharctus an American Eocene primate.
Szalay, F. S. 1977. Ancestors, descendants, sister
Mem. Am. Mus. Nat. Hist., n.s. 3:49-243.
groups and testing of phylogenetic hypotheses.
Hershkovitz, P. 1977. Living New World monkeys (PlatSyst. Zool. 26:12-18.
yrrhini) with an introduction to primates, Vol. 1.
Szalay, F. S. and R. L. Decker. 1974. Origins, evoUniv. Chicago Press, Chicago.
lution and function of the tarsus in late CretaKay, R. F. 1975. The functional adaptations of priceous eutherians and Paleocene primates. In F.
mate molar teeth. Am. J. Phys. Anthrop. 43:195A. Jenkins, Jr. (ed.), Primate locomotion, pp. 223216.
259. Academic Press, New York.
Kay, R. F. and M. Cartmill. 1977. Cranial anatomy
and adaptations of Palaechthon nacimienti and Szalay, F. S. and J. Drawhorn. 1980. Evolution and
diversification of the Archonta in an arboreal
other Paromomyidae (Plesiadapoidea, ?Primilieu. In W. P. Luckett (ed.), Tree shrews. Plemates), with a description of a new genus and
num Press, New York.
species. J. Hum. Evol. 6:19-53.
Krishtalka, L. and J. H. Schwartz. 1979. Phyloge- Tattersali, I. and N. Eldredge. 1977. Fact, theory
and fantasy in human paleontology. Amer. Sci.
netic relationships of plesiadapiform-tarsiiform
65:204-211.
primates. Ann. Carnegie Mus. Nat. Hist. 47:515540.
Thorndike, E. E. 1968. A microscopic study of the
marmoset claw and nail. Amer. Jour. Phys. AnLe Gros Clark, W. E. 1936. The problem of the claw
throp. 28:247-262.
in primates. Proc. Zool. Soc. London 1936:1-24.