JOURNAL OF CRUSTACEAN BIOLOGY, 21(1): 49–55, 2001
A NEW SPECIES OF ANOSTRACAN FROM THE MIOCENE OF CALIFORNIA
Denton Belk and Frederick R. Schram
(DB) Dept. of Biology, Our Lady of the Lake University, 411 SW 24th St., San Antonio, Texas 78207–4666,
U.S.A.; (FRS) Zoological Museum, University of Amsterdam, Post Box 94766, 1090 GT Amsterdam,
The Netherlands (corresponding author e-mail: [email protected]).
A B S T R A C T
We have restudied some of the material of a fossil anostracan originally discussed and illustrated by Palmer from the Middle Miocene, Barstow Formation, near Yermo, California, and we
now recognize it as a new species, Branchinecta barstowensis. It is the best-preserved fossil anostracan known to date. The closest affinities of this species are with B. pollicifera Harding, 1940,
collected from the mountains of Peru and Bolivia around Lake Titicaca.
named Silurian specimen mentioned above.
One of our reviewers believes these fossils
are anostracans with eight pairs of thoracic
limbs, which, if so, would make it unique
among Anostraca. Clearly this species warrants a special study.
The best anostracan fossils remain the material discussed and illustrated by Palmer
(1957) from the Middle Miocene, Barstow
Formation, in the Calico Mountains, near
Yermo, in San Bernardino County, California (see also Jenkins, 1986). Palmer recorded
this species as among the three most abundant (some 3,000 specimens) in an arthropod
fauna composed of mostly insects and arachnids. Despite the “remarkable” quality of
preservation of these fossils, Palmer declined
to describe and name a new species. We re-examined Palmer’s original material with SEM
and concluded that these specimens represent
a new species of the genus Branchinecta.
Anostracans, or fairy shrimp, because of
the delicate nature of their exoskeleton, do
not occur commonly as fossils. Indeed, only
a handful have made their way into the literature, and most of these have an ambiguous
status.
Schram (1986: 376, fig. 30–10) mentioned
and illustrated a possible anostracan from the
Silurian of Indiana, but did not attempt to describe it. Van Straelen (1943) described a
form from the Devonian Hunsrück Shale,
Gilsonicaris rhenanus, but Rolfe (1967) recognized this as a possible young stage of an
arthropleurid myriapod from this same fauna,
Bundenbachiellus minor Broili (1930). Goldenberg (1873) described a purported anostracan, Branchipusites anthracinus, from the
Upper Carboniferous of Germany, but we
suggest this might actually prove to be an insect nymph as Rolfe (1967) suggested for
Rochdalia parkeri Woodward, 1913. Guthörl
(1934), however, interpreted Branchipusites
as an Arthropleura limb, and indeed Goldenberg described this species from a fauna
that includes several species of Arthropleura
among what he termed the “Phyllopoda.”
Whatever its affinities, this Paleozoic
Branchipusites, from its description and illustration, clearly is not an anostracan.
Jell and Duncan (1986) briefly mention and
illustrate an anostracan from the Lower Cretaceous of Victoria, Australia.
Woodward (1879) described Branchipodites vectensis from the Oligocene of the Isle
of Wight. Rolfe (1967) was inclined to accept
this as an anostracan, and it resembles in
some ways the outline features of the un-
SYSTEMATICS
Order Anostraca G.O. Sars, 1867
Family Branchinectidae Daday, 1910
Branchinecta Verrill, 1869
Diagnosis.—Eleven pairs of trunk limbs (thoracopods), each with one proximal epipodite.
Male antennae 2-segmented and clearly separate from each other; basal segments often
with processes, spines, pad-like structures
covered with minute spines (pulvilli), welts,
and other outgrowths, but lacking frontal and
antennal appendages. Female antennae unsegmented and generally cylindrical. Second
49
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 1, 2001
Fig. 1. Brachinecta barstowensis new species. A, Ventral view of m holotype, USNM 561976a; genital region distorted and abdomen missing, × 32. B, Ventral view of female; antennae, and frontal and dorsal parts of the head missing in specimen; brood pouch similar to that of B. pollicifera (see figs. 3 and 4 in Harding, 1940); photograph courtesy of John E. Jenkins, × 52. bp = brood pouch with cysts; e = compound eyes; gr = genital region; mn = mandible.
maxillae uniquely robust and well developed
in both sexes with 5–30 terminal setae, and
3–5 soft setae near center projecting forward
from anterior margin of medial surface. Male
genital segments not swollen; linguiform outgrowth extending from posterior edge of second genital segment just under medial side of
basal part of each penis. Penes protrude ventrolaterally, far apart, visible in dorsal view.
Basal part of each penis rigid with posterior
directed extension having 1, rarely 2, medial
outgrowths of variable form. Each retractile
apical part of penis bears 2 dentate warts of
variable appearance located toward distal end,
not found in other genera. No clearly defined
seminal vesicles. Females often with variously
placed and shaped processes on dorsal half
of thoracic and genital segments. Brood pouch
with elongate posterior portion extending beyond genital segments. Resting eggs (cysts)
spherical with variously textured surfaces.
Branchinecta barstowensis, new species
Figs. 1–3
Material.—Holotype USNM 561976a (Fig.
1A), a male, largely complete. The distal end
of the right antenna of the type specimen used
in our figures was broken off inadvertently.
However, we saw the specimen before it was
damaged, and the distal segment terminated
as figured by Palmer (1957).
Although literally thousands of specimens
of the Barstow anostracan exist in the fossil
invertebrate collections of the Smithsonian
Institution National Museum of Natural History, the San Bernadino County Museum, and
the San Diego Natural History Museum, these
are almost all fragmentary. Thus, we confine
ourselves here to illustrating the two most
complete specimens, one each for male and
female.
Diagnosis.—Male (Fig. 1A): Antennal basal
segment with wart-like bumps on anterior
surface extending from about center to near
proximal end, and finger-like process projecting medially from posteromedial region
near proximal end. Finger-like process with
numerous cone-shaped spines scattered over
its surface. Distal segment curved medially
and tapering to rounded point. Maxilla robust,
with 3 forwardly directed soft setae inserted
near center on anteromedial surface. Female
BELK AND SCHRAM: NEW ANOSTRACAN FROM CALIFORNIAN MIOCENE
51
Fig. 2. Brachinecta barstowensis new species, USNM 561976a. A, Ventral aspect of head region of holotype including view of anterior and median surface of right antenna, × 115. B, Close-up of right antenna with wart-like bumps
near distal end of basal segment and unique finger-like process, × 265. C, Close-up of finger-like process with coneshaped spines on surface, × 455. D, Ventral view of mouth region, × 300. A2 = antenna; cs = cone spines; fp = finger-like process; g = gnathobases of first thoracopods; l = labrum; (r)mn = (right) mandible; rm1 = setae on right
maxillule; lm2 = left maxilla; pg = paragnath; ss = anteriorly directed, proximal soft setae of maxillae; w = wart-like
processes.
(Fig. 1B): Brood pouch pear-shaped with
short posterior end.
Stratum.—Lower Nodule Zone, Barstow Formation, Middle (?) Miocene.
Locality.—The holotype comes from USGS
locality 19057, described by Palmer (1957)
as occupying the tip of small hill in a badlands area, at 2,420 feet, SW1/4 NE1/4
SW1/4 SW1/4 sec. 24, T.10S., R.1E. However, ten other localities for the Barstow
arthropod fauna occur in the immediate area,
either as distinct sites or stratigraphic horizons at particular sites. Branchinecta
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 1, 2001
Fig. 3. Brachinecta barstowensis new species, USNM 561976a. A, Close-up of maxillary region, × 700. Β, Closeup of anterior thoracopods with gnathobase and adjacent endites labeled and numbered, × 220. A2 = antenna; ds =
bases of distal, dense setae on remnant of shaft of left maxilla; g = gnathobases of third thoracopod; pg = paragnath;
rm1 = setae on right maxillule; ss = anteriorly directed, proximal soft setae of maxillae.
barstowensis remains one of two species that
occur at all these sites and horizons, matched
in frequency only by the dipteran Dasyhelea
australis antiqua Palmer, 1957.
Description.—A distinctive finger-like process projects medially from the posteromedial surface of the basal segment of the antenna of the male near its distal end (Fig. 2A,
C). This process has numerous cone-shaped
spines scattered over its surface (Fig. 2C).
There is a pattern of wart-like bumps on the
anterior surface of the basal segment of the
male antenna (Fig. 2A, B). The distal segments of the antennae taper to a rounded point
(see Palmer, 1957).
The first maxilla bears a comb of spines directed anteriorly towards the mouth (Figs.
2D, 3A). The second maxilla is robust and
columnar, with three soft setae projecting forward from near the center of its anteromedial surface (Fig. 3A), and it appears that the
distal portion of the maxilla was well developed with dense setae (Fig. 3A).
The 11 thoracic appendages (Figs. 1A, 3B)
preserve the well-developed gnathobases,
consisting of the continuously setose, fused
first and second endites. Four additional, se-
tose endites can be clearly distinguished lateral to the gnathobases.
Little structural detail of the male genital
region is apparent (Fig. 1A). Nevertheless,
this implies that there were no hard, basal
structures on the penes (as would be expected
in a chirocephalid). This in turn suggests a
basally flexible penis typical of Branchinecta.
The female brood pouch of B. barstowensis
has a short posterior terminus (Fig. 1B).
Remarks.—The Barstow fossils occur in nodules of calcium carbonate, which sometimes
contain intercalated layers of silica. Preparation of the fossils typically involves immersion of the concretions in acetic acid combined with frequent washing and sorting of
the residual concentrate. Palmer records that
some of the nodules have layers composed
of short rods that he believes may represent
anostracan fecal pellets. The fossils that
emerge from these concretions contain one or
more distinctive replacement minerals, most
commonly quartz and that largely as fibrous
bundles of chalcedony. In addition to the silica, some replacement in individual instances
occurred with crystalline forms of celestite,
gypsum, bassanite, and analcite.
BELK AND SCHRAM: NEW ANOSTRACAN FROM CALIFORNIAN MIOCENE
The exact age of these beds remains difficult to assess. The arthropods do not correlate stratigraphically with any similar fossils
elsewhere. Vertebrate beds within the
Barstow Formation are conformable with or
slightly younger than those that contain the
arthropods, and they date apparently from either late Middle or early Late Miocene time.
The associated arthropod fauna in the
Barstow beds contains both aquatic and terrestrial components. Aquatic forms include
dytiscid beetle larvae, larvae of water mites,
and pupae of the dipterans Dasyhelea and
Culicoides. Except for the fairy shrimp, the
aquatic portion of the fauna contains only larval forms. The associated terrestrial fauna
contains more species, but with fewer individuals. These include a spider, a mite, a
grasshopper, thrips, a wide array of hemipterans, some beetles, and adult dipterans. Such
a combination of species typically characterizes lakes or ponds in early spring or late winter. In addition, the minerals that replace the
original organic material seem to indicate that
the Barstow habitat probably was highly alkaline.
DISCUSSION
Branchinecta barstowensis is by far the
best-preserved fossil anostracan discovered to
date. Rarely does one get a chance to make
detailed comparisons of fossil forms to Recent relatives. The preservation is evocative
of the remarkable preservations seen in the
phosphatized faunas collected from the Cambrian Orsten (e.g., see Walossek, 1999).
The extant species most similar to B.
barstowensis is B. pollicifera Harding, 1940.
Both taxa have a distinctive finger-like
process projecting medially from the posteromedial region of the basal segment of the
male antenna near its distal end (Figs. 2A,
4A; see also Harding, 1940: figure 1). This
process is an apomorphic feature and is the
single most convincing piece of evidence supporting our assignment of the Barstow anostracan to the genus Branchinecta. In both B.
barstowensis and B. pollicifera, the fingerlike antennal process has numerous coneshaped spines scattered over its surface (Figs.
2C, 4B).
The antennae of the males reveal speciesspecific differences between the living and
fossil animals. At the proximal end of the
basal segment of the antenna of B. pollicifera
53
there is a swollen area with a rough surface
distal to which there is a rough-surfaced,
rounded knob on a pedestal (Fig. 4A, B),
which B. barstowensis lacks. The distal antennal segment of B. pollicifera has a low, triangular ledge near the proximal end on its anteromedial edge that is not present in B.
barstowensis (compare Fig. 2A with Harding,
1940: figure 1). The paratype male of B. pollicifera (see Fig. 4A, B) exhibits a small
process distal to the finger-like process not
discussed or figured by Harding (1940). This
small process does not occur on B.
barstowensis. The distal segments of the antennae in both species taper to a rounded
point (Fig. 4A) (see also Palmer, 1957, and
Harding, 1940).
It is unfortunate that we do not know what
the female antennae of B. barstowensis look
like because females of B. pollicifera possess a medially directed, thumb-like process
or spur similar to that seen on only one other
congener, B. cornigera Lynch, 1958.
Linder (1941) considers the maxillae of
Branchinecta sufficiently different from those
of all other genera of Anostraca as to be an
important defining characteristic of the genus:
the second maxillae being developed as a robust columnar structure that bears 3–5 soft setae that project forward from the anterior margin of its medial surface (Fig. 3A) and from
5 to 30 stiff setae at the distal end. The forward-projecting soft setae are typical of anostracans in general (Fryer, 1983). It is the robustness of the maxillae and their strong development distal to the soft setae that are
unique to the genus (Cannon and Leak, 1932).
On paratype material of B. pollicifera, we
counted five setae at the distal end of each
maxilla. Unfortunately, the distal setae and
much of the distal ends and outer edges of
both maxillae are missing from the type specimen of B. barstowensis (Fig. 3A). Palmer
(1957) mistook the soft setae for terminal setae and his drawing of a maxilla in figure 86c
is erroneous. What he refers to as a “diskshaped” protuberance is in fact the distal end
of the maxilla.
The brood pouch of B. barstowensis, with
its short terminal end, is similar to that of B.
pollicifera (compare Fig. 1B to Harding,
1940: figures 3, 4).
Palmer (1957), in reviewing the biogeographic affinities of the Barstow fauna, took
great care to point out that he perceived no
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JOURNAL OF CRUSTACEAN BIOLOGY, VOL. 21, NO. 1, 2001
Fig. 4. Branchinecta pollicifera Harding, 1940, m paratype from the Natural History Museum, London, 1941.5.21.1–5.
A, Posterior view of cephalic region of male, × 34. Β, Close-up of basal structures on second antenna, × 220. A2 =
second antenna; ds = distal segment of antenna; e = compound eyes; fp = finger-like process with cone shaped
spines; kp = knob-like pedestal; sp = small process.
BELK AND SCHRAM: NEW ANOSTRACAN FROM CALIFORNIAN MIOCENE
links to Central or South America. This, he
believed, constituted a singular and distinct
exception to the idea that prevailed in the paleobiogeographic literature of that time (e.g.,
see Darlington, 1948) that postulated such
north-south connections for the Tertiary faunas of North America. It is therefore of considerable interest that the Barstow anostracan
shows its closest relationship with a species
from the Bolivian and Peruvian shores of
Lake Titicaca in the Andes, B. pollicifera.
ACKNOWLEDGEMENTS
We wish to express our thanks to Dr. Conrad Labandeira, National Museum of Natural History, the Smithsonian Institution, for his assistance in setting up access
to the Palmer material and arranging time on the museum SEM. Special thanks go to Susann Braden who took
the SEM photos for us. She was very helpful in showing
us the things we asked to see and working with us to get
the best possible photographs of this difficult material.
We also extend special thanks to Prof. Geoffrey Boxshall,
Natural History Museum, London, for loan of type material of B. pollicifera, and Mr. John E. Jenkins, San
Bernardino County Museum, for use of his photo of the
fossil female Branchinecta. Dr. Michael Fugate, The
Claremont Colleges, shared with us his extensive knowledge of modern Branchinecta, and Stephen Keable of
the Australian Museum helped track down some literature on fossil Anostraca. Prof. Dieter Walossek and another anonymous reviewer offered valuable comments
that improved the text.
Arthur Humes made a noteworthy contribution to
anostracan studies by skillfully attending to the editorial
needs of some 50 papers treating these crustaceans published in Journal of Crustacean Biology during his tenure
as editor. For this reason, and especially in appreciation
of the good spirited way he worked with both of us during our service to The Crustacean Society, we are pleased
to contribute an anostracan paper to this volume in his
memory.
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RECEIVED: 16 July 1999.
ACCEPTED: 14 October 1999.