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Anatomy of the temporal bone in early anthropoids with remarks on the problem of anthropoid origins.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 56:3-21 (1981)
Anatomy of the Temporal Bone in Early Anthropoids,
With Remarks on the Problem of Anthropoid Origins
M. CARTMILL, R.D.E. MAcPHEE, AND E.L. SIMONS
Department of Anatomy (M.C.,R.D.E.M.,E.L.S.),Department of
Anthmpology (M.C.,E.L.S.), and Center for the Study of Primate Biology and
History (E.L.S.),Duke University, Durham, North Carolina 27710
KEY WORDS
Parapithecidae
Ear region, Primates, Fayum, Oligocene, Pongidae,
ABSTRACT
New and previously undescribed specimens of the petrous, squamous, and tympanic parts of the temporal bones of anthropoid primates from the
Oligocene of Egypt display a general morphological resemblance to the equivalent parts of Recent ceboid skulls. Like that of ceboids, the ectotympanic bone of
Fayum anthropoids is a simple anulus, fused to the squamosal at both its extremities. The petrosal's bullar contribution appears to bear transverse septa running laterally from promontory to ectotympanic; similar septa are seen in callitrichids and some prosimians. The definitive stylomastoid foramen is in a position
characteristic for ceboids but not found among adult catarrhines. As far as can
currently be determined, pneumatization of the petrous and squamous temporal
is specifically anthropoid-like in pattern and extent, but exhibits no special resemblances to that found in any particular anthropoid taxon. On the other hand,
Fayum anthropoids appear to resemble other catarrhines and to differ from most
extant ceboids in lacking a vascular canal leading from the subarcuate fossa to
the sigmoid venous sinus. Vascular impressions on a squamosal fragment tentatively assigned to Aegyptopithecus zeuxis show that the petrosquamous and cranio-orbital venous sinuses were persistently large, as in prosimians. A squamosal
fragment previously attributed to Apidium phiomense, and adduced as evidence
for a lemuriform ancestry of Anthropoidea, is probably that of a hyaenodontid
creodont. I t is certainly not that of a primate. The ceboid-like morphology of the
early catarrhine ear region is probably primitive for anthropoids, and in any case
it does not argue for an Old World origin of ceboids -but it emphatically suggests
that Anthropoidea is a strictly monophyletic taxon.
With the possible exceptions of Branisella
boliuiana and the enigmatic Burmese Eocene
primates Pondaungia and Amphipithecus
(Hoffstetter, 1969; Szalay, 1970;Simons, 1971;
Ba et al., 1979; Ciochon and Savage, 1979; Szalay and Delson, 1979),the earliest anthropoids
known are those recovered from Oligocene sediments of the Fayum Province, Egypt. Since
1907, when the first Fayum primates were recovered by Richard Markgraf, those sediments
have yielded over 500 specimens of early anthropoids belonging to the families Pongidae
(sensu lato) and Parapithecidae. Most of the
identifiably anthropoid remains consist of
0002-9483/81/5601-0003$05.50 0 1981 ALAN R. LISS, INC.
teeth and mandibular fragments, predominantly those of parapithecids. However, postcranial bones attributable to anthropoids of
both families are also numerous in collections
from the Fayum, and provide us with our sole
source of information about the locomotor adaptations of early anthropoids (Fleagle et d.,
1975; Conroy, 1976; Fleagle and Simons, 1978,
1979).
The Fayum primates have also furnished the
only direct evidence we have concerning the
cranial morphology of early anthropoids. AlReceived November 11, 1980 accepted April 16,1981
4
M. CARTMILL. R.D.E. MacPHEE. AND E.L. SIMONS
most all of the diagnostic peculiarities that distinguish extant anthropoids from extant prosimians are features of the cranial skeleton.
These peculiarities include an enlarged neurocranium, an almost complete postorbital septum, a fused mandibular symphysis, absence
of the stapedial artery and its bony canal, and
an internal carotid artery which enters an anteriorly positioned carotid foramen and traverses a canal in a bony septum between 1)the
tympanic cavity proper and 2) the anterior accessory cavity, a trabeculated chamber pneumatizing the apex and adjacent parts of the
petrous temporal (Gingerich, 1973; Szalay,
1975a; Gingerich and Schoeninger, 1977;Cartmill and Kay, 1978; Cartmill, 1980; MacPhee
and Cartmill, 1981).
Apart from numerous maxillae and mandibles, and the nearly complete skull of the primitive pongid Aegyptopithecus zeuxis found by
G.E. Meyer in the 1966-67 field season (Simons, 1967, 1969,1972), only a handful of cranial fragments of Fayum anthropoids have
been recovered, and few of these have been described. Various facial elements and teeth attributable to the parapithecid Apidium phiomense were assembled by Simons (1972)into a
composite reconstruction of a rather marmoset-like facial region. Fragmentary frontals
and parietals referred to A . zeuxis were used
by Radinsky (1973)in reconstructing the endocast of the braincase from the 1966 skull. Gingerich (1973) described two bony fragments
found in association with A. phiomense teeth,
interpreting those fragments as remains of a
right temporal bone of that species.
From these few, mostly provisional studies
of the scanty remains available, much has been
learned. Like modern anthropoids, the pongids
and parapithecids from the Fayum exhibit
complete fusion of the mandibular symphysis.
The postorbital septum of Aegyptopithecus
was at least as well developed as that of some
extant ceboids; and maxillary and frontal fragments of Apidium suggest that the septum of
parapithecids was ceboid-like (Simons, 1959;
R.F. Kay, pers. comm.). However, the brain of
Aegyptopithecus did not exceed that of extant
Malagasy lemurs in relative size (Gingerich,
1977; Kay and Simons, 1980), which implies
that the marked brain enlargement characteristic of modern anthropoids was acquired
independently in more than one anthropoid
lineage.
The only published study of the ear region of
the Fayum catarrhines is that of Gingerich
(1973).This controversial study represents the
first investigation of the possible phyletic implications of the anular ectotympanic of these
primates. Immediately prior to Gingerichs
study, Simons (1972)had briefly described the
narrow ectotympanic of Aegyptopithecus and
likened it to that of ceboids. Gingerich, however, argued that in a fossil he identified as Apidium the ectotympanic was not only anular but
“free and intrabullar,” like that of adapids and
Malagasy lemurs. From this and other resemblances between adapids and early anthropoids, Gingerich drew the conclusion that anthropoids and lemurs alike were derived from
Eocene adapids, whereas Tarsius and its Eocene relatives were derived from Paleocene plesiadapiforms. These conclusions have been assailed by other investigators who, for various
reasons, prefer to think that anthropoids originated from Eocene tarsioids, and dismiss
Gingerichs analysis of the supposed Apidium
squamosal on the grounds that (inter alia) the
fragments in question either differ significantly from the temporals of lemurs and adapids, or
do not differ significantly from those of tarsioids and ceboids in the respects alleged, or
both (Hoffstetter, 1974a; Hershkovitz, 1974;
Cartmill, 1975; Szalay, 1975a; Cartmill and
Kay, 1978).
In addition to the specimens described by
Gingerich and the still imperfectly described
ear region of the Aegyptopithecus skull, the
temporal bone of Fayum anthropoids is known
from three petrosals collected by Yale University expeditions in 1964 and 1966, and by a
squamosal fragment collected by the 1977
Duke University expedition to the Fayum. We
here offer descriptions of these fossils and a reexamination of the assemblage (Yale Peabody
Mus. No. 23968)from which Gingerich extracted the material he described. We hope thereby
to arrive at a more precise understanding of
the morphology of the ear region in the skull of
early catarrhines.
PETROSAL
Four isolated petrosals (Figs. 1,3,4) from
Yale Quarry I in the Upper Fossil Wood Zone
(Jebel el Qatrani Formation, Fayum Province)
are attributable to anthropoids. One of these
(YPM 25972) is larger than the other three
(YPM 25973,25974, and 23968). Although differential breakage of these specimens makes it
impossible to quantify this difference precisely, the few homologous measurements that can
be taken or estimated suggest that YPM
25972 is about 25% larger than the smaller
ones (which are essentially identical in size).
5
EARLY ANTHROPOID TEMPORAL BONES
a
.I
,
fossa for tensor tympani
hiatus can. n. pet ma/::,
faciaJ cma/
fen. vestibuli
carotid conal
stylomastoid foramen
groove for tympanic n.
medaJ wall of bu/Ja
fenestra cochleae
transbullor septum
Fig. 1 Ventrolateral view (a,b)of isolated left petrosal of
Fayum catarrhine (YPM 25972).Large arrow points anteriorly, small arrow laterally. Scale = 1 rnm. This specimen
nreserves
r-- - - a small Dortion of the posteromedial segment of
the medial buliar wall, inciuding a part of the
ectotympanic’sposterior crus. One transbullar septum, connecting the promontory with the ectotympanic fragment, is
also preserved. Arrow indicates pyramidal eminence (for m.
stapedius). Hachure shows probable extent of remaining
portion of ectotympanic.
6
M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS
The large petrosal is comparable in size to that
of a squirrel monkey (Saimizf).Since the parapithecid Apidium phiomense is the only Quarry I anthropoid that resembles Saimin in body
size (Kay and Simons, 1980), it is possible that
all four specimens represent remains of that
species. If so, the three smaller petrosals may
represent female or juvenile specimens of
Apidium. Apidium phiomense occurs in the
Quarry I fauna with greater frequency than
other anthropoids, and juvenile specimens are
common (R.F. Kay, pers. comm.). Contravening this interpretation is the fact that pneumatization is more extensive in the three smaller
specimens than in the larger -just the reverse
of what would be expected if the size difference
were due to degree of maturity or to sexual dimorphism. A few other minor features, noted
below, also suggest that the petrosal sample
may include at least two species. We cannot
rule out the possibility that the large petrosal
represents one of the other Quarry I anthro-
poids: Parapithecus grangeri, Propliopithecus
chirobates, or even Aegyptopithecus zeuxis.
The smaller anthropoid petrosals, on the basis
of size alone, can most parsimoniously be
assigned to Apidium phiomense.
The preserved parts of the petrosal in all four
specimens comprise most of the extremely
dense bone surrounding the otic capsule’s labyrinth, together with various remnants of the
more fragile cortical bone delimiting the pneumatic cavities of the middle ear. Although almost nothing remains of the auditory bulla and
tegmen tympani in any single specimen,
enough of the accessory pneumatic cavities
and carotid canal has been preserved in one or
another fragment to stamp them all unmistakably as anthropoid petrosals.
Tympanic cavity
Small sections of the medial wall of the tympanic cavity proper are preserved on YPM
Fig.2. Left ear region of Cullithriz sp. seen from ventral posterolateralaspect, with portions of bulla and ectotympanic
removed to display transbullar septa (asterisks).Scale = 1 mm.
EARLY ANTHROPOID TEMPORAL BONES
23968 and 25972; the latter is especially interesting, because the rearmost parts of the petrosal plate and ectotympanic are still in place. In
this specimen, the remaining portion of the
plate is that which rims the sinus tympani (diverticulum D, of Saban 119631 and other authors). As may be seen in Figure 1,this sinus is
deeply excavated and is bounded by small
crests (transbullar septa), which run downward and backward to converge on a thick
ridge descending from the external aspect of
the facial canal. If, as we suspect, this ridge is a
small remnant of the ectotympanic’s posterior
crus (see below), then the intratympanic surface of the petrosal plate bore subtympanic
transbullar septa running from the promontory and fossular area to the ectotympanic.
Among living small anthropoids, such septa
are best developed in callitrichids (Fig. 2), although they occur widely among prosimians
(Allocebus, Necrolemur, Rooneyia, Plesiadupis; cf. Cartmill and Kay, 1978).
Because of extensive damage, the pattern of
middle-ear pneumatization exhibited by the
Fayum anthropoids cannot be ascertained precisely. However, there are sufficient clues to
demonstrate that pneumatization was substantial and not at all lemur-like. Small cellules, delimited by worn crests representing
the bases of broken septa and trabeculae, surround the auditory capsule on its medial, superior, anterior, and posterior aspects. By analogy with extant anthropoids, these can be divided into two major complexes; a posterior,
mastoid group and an anterior, apical group.
Mastoid group. The network of crests and
depressions on the posterior surfaces of the
Fayum petrosal (cf. Fig. 4)represents what remains of the mastoid antrum and its ramifying
diverticula. The mastoid group of cellules was
unquestionably a large one. As we reconstruct
it, this group extended from the antrum (and
epitympanic recess) around the gyri of the
semicircular canals and into the floor of the
subarcuate (parafloccular) fossa. The fossa’s
floor did not, therefore, contribute to the side
wall of the skull in the mastoid region (as it
does in Tarsius and Malagasy lemurs), but was
instead separated from it by air-filled spaces
(as it is in extant anthropoids and lorisiforms).
Although mastoid pneumatization penetrated
the petrosal crest to a slight extent, it did not
extend past the level of the hiatus canalis nervi
facialis.
Apical group. Little can be said about the degree of pneumatization of the anterior end of
the otic capsule, although persistent traces of
7
cellules and septa suggest that it must have
been extensive (cf. Fig. 3). Medially, the apical
group’ penetrated the bone of the petrosal
plate a t least as far as the posterior carotid foramen. Anterodorsally, it excavated the petrosal apex in front of the anterior wall of the internal acoustic meatus. The anterior portion of
the petrosal crest was also slightly inflated by
the apical group of air cells.
I t is certain that in life the mastoid and apical groups communicated via the tympanic
cavity proper, into which they opened. In extant anthropoids, mastoid and apical air-cell
complexes sometimes develop secondary connections through their conjoint inflation of 1)
the entire petrosal crest and 2), more frequently, the medial wall of the bulla. The first sort of
connection is demonstrably absent in YPM
25972; the second sort appears to be present in
the smaller petrosals, although breakage
renders this uncertain. I t is clear at any rate
that pneumatic spaces separate the posteroinferior end of the carotid canal from the
auditory capsule in the smaller petrosals, but
not in the large one.
Vascular channels
Arteries. The carotid channel is preserved to
some extent in all four specimens, and is more
complete in YPM 23968 than in the other three
(Fig. 4).The internal carotid entered the bulla
at a point anterior to the coronal plane of the
fenestra vestibuli and considerably medial to
the fenestra cochleae, curved upward and forward along the anteromedial side of the promontory, and apparently left the middle ear cavity after passing through some portion of the
apical complex of air cells. Like that of Tarsius,
but unlike that of all other known extinct and
extant nonanthropoid primates (Szalay,
1975a),the internal carotid canal of the Fayum
IThe apical complex of anthropoids is sometimes referred to as the
hypotympanic sinus or cavity (e.g.. by Hershkovitz,1977).This term
appears to have been introduced into the English literature by Gregory (1920).who in turn adopted it from van Kampen 11905).It was originally intended to refer b a quite-improbableventrad expansion of
the primitive mammalian middle ear cavity whereby a supposedlydistinct space (the hypotympanicsinus) was gradually incorporatedinto
the true tympanic cavity. In addition to its application to any volume
subjacent to the tympanic cavity proper (which surrounds the auditory ossicles and windows),in primatology the term “hypotympanic
sinus”has also been used to refer to the medial chamber of the lorisiform bulla (Saban,1963;Cartmill. 1975)and to the anteriorchamber of
the tarsiiform bulla (Saban, 1963; Szalay, 1975% Szalay and Delson,
19’79).This scattershot application of one name to several different
cavities that can be shown to be nonhomologous on developmental
grounds (MacPhee,1981) is inappropriate. The term “hypotympanic
sinus”has lost what little intelligiblemeaning it had in the first place,
and it should be withdrawn from scientific usage.
M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS
8
Fig. 3. Isolated right petrosal of Fayum catarrhine
(YPM 25973), ventral view; direction arrows as in Figure 1.
Scale = 1 mm. This specimen preserves some of the petrosal‘s highly pneumatized apex, although almost all of the
mastoid air cells are lost. The pointer identifies the entrance
to the fenestra cochleae, which is hidden in this view by the
basal turn of the cochlea. Key: a, apex of the petrosal; ac. air
cell (member of the mastoid group, penetrating the
petrosal’s dorsal surface);ag, air cells of the apical group; cc,
carotid canal; fca, facial canal; ftt, fossa for tensor tympank
fv, fenestra vestibuli; lsc, lateral semicircular canal; ms,
mastoid region; pr, promontory.
sulcus for internal carotid n.
tegmen tympani (br.)
hiatus can.
n. pet. maj.
transverse septum
fossa for tensor tym.
medial wall of bulla
“denticulate”septum
fenestra cochleae
facial canal (bd
lat semicircular can.
groove for tympanic n.
\
U
Fig. 4. Isolated right petrosal of Fayum catarrhine
(YPM 239681, ventral view; anterior is toward top of page,
lateral toward left. Scale = 1mm. This petrosal, referred to
Apidium by Gingerich (1973). is the only specimen with a
moderately complete carotid canal. The ridge of bone forming the posterior border of the sinus tympani may be a
transbullar septum (cf. Fig. l a , b); so may the “denticulate”
septum (cf. Gingerich, 1973). although its original orienta-
floor of subarcuate
fossa (br.1
tion seems to have been horizontal rather than vertical. The
mastoid and apical groups apparently met medially in the
region of the carotid canal, within the substance of the petrosal component of the bulla. The arrow identifies a shallow
sulcus, which may have held part of the tympanic plexus or
caroticotympanic artery. Broken surfaces indicated by
“(br.)”.
EARLY ANTHROPOID TEMPORAL BONES
anthropoid petrosals traverses only a small
portion of the promontorium and does not
shield the fenestra cochleae from ventral view.
The size and relations of the carotid canal
constitute the principal reason why these
specimens can be unequivocally identified as
anthropoid. As Gingerich (1973) noted, the
YPM 23968 specimen resembles anthropoids
and differs from early tarsioids and most other
prosimians in lacking a stapedial artery, although certain grooves running from the carotid canal across the promontory’s ventral surface may have contained caroticotympanic arteries (see below),one of which may represent a
vestige of the stapedial stem.
Veins. A deep jugular fossa is well preserved
on the ventral surface of YPM 25972 and
25973. The slitlike aperture of the cochlear canaliculus opens into the top of this fossa. A
shallow but well-defined sulcus running medially backward behind this fossa toward the region of the rather large fossula for the saccus
endolymphaticus probably represents the terminal end of the indentation for the sigmoid sinus. No other major venous impressions are
well enough preserved to warrant description.
Examination of a representative sample of
45 anthropoids1indicates that in nonateline ceboids, a patent canal leads from the depths of
the subarcuate fossa caudally and medially to
an opening in the channel of the sigmoid sinus,
behind and below the aperture (fossula sacci
endolymphatici) of the vestibular aqueduct.
The only other mammal known to possess such
a canal is the colugo (Cynocephulus uoluns),in
which the canal is occupied by a vein (Cartmill
and MacPhee, 1980); we have found a dried
vessel in this position in one Suguinus skull.
Small pits occur in a similar position on the
wall of the sigmoid sinus in some juvenile pongids and cercopithecids, but we have found
none that is demonstrably connected by a canal to the subarcuate fossa. No such canal occurs in prosimians, in human fetuses (Padget,
1957), in adults of extant catarrhines, or in any
of the Fayum petrosals.
Neural channels
The canal of the facial nerve is broken to
varying extents in all specimens, but it was
definitely a complete bony tube in the living
animals. The entire intrapetrosal course of the
nerve is discernible on YPM 25972 (Fig. 1)as a
result of breakage. A small foramen situated
behind the (damaged) stylomastoid foramen
opens into the facial canal; it presumably
9
transmitted the auricular ramus of the vagus.
(Theexternal aperture of this vagal canaliculus
is hidden in Figure 1 by the projecting frag
ment of the ectotympanic.) Owing to breakage
of the mastoid air cells, the stylomastoid foramen is not preserved intact on any of the specimens, but it is clear that it lay high up on the
posterior side of the bulla’s meatal rim, a position not seen in modern catarrhines but typical
of New World monkeys generally. This difference between extant New and Old World anthropoids is probably largely or wholly interpretable as a secondary effect of their differences in length of the bony meatal tube and degree of mastoid inflation.
The sympathetic and glossopharyngeal
roots of the tympanic plexus are traceable in
the fossils, and were described in part by Gingerich (1973). The tympanic canaliculus
through which the tympanic branch of nerve
IX enters the bulla is preserved only in the
large petrosal (YPM 25972), where its inferior
orifice lies posterior and lateral to the jugular
fossa. The nerve emerges into the tympanic
cavity within the sinus tympani in YPM
25972, under cover of a transbullar septum. In
that specimen (Fig. 1) and in YPM 25974 and
23968, a sulcus leads anteriorly upward from
the tympanic canaliculus past the posterior upper corner of the fenestra cochleae to a point
below the vestibular window; in YPM 23968, it
continues through a short bony tunnel into the
fossa for the tensor tympani, whence it cannot
be further traced.
In YPM 23968, a minute foramen can be discerned within the carotid canal, on its posterior
aspect, a t about the point where that canal
comes into contact with the promontory. Farther up, on the medial wall of the semicanal for
the auditory tube, another small foramen
opens into a deep sulcus that runs upward and
forward in parallel with the posterior edge of
the carotid canal (Fig. 4). We infer that the two
foramina are connected, and that they and the
sulcus represent the course of a caroticotympanic branch of the sympathetic carotid nerve
or plexus within the carotid canal. The foramina and sulcus may have contained a caroti’Anthropoids examined for presence of subarcuate canal (sample
sizes in parentheses):Cebuellapygmaea (2). Callithrix jacchus (2),Saguinus oedipus (3), Leontopithecus msalia il), Callimico goeldii (1).
Aotus trivirgatus (21, Cacajao melnnocephalus (11. Pithecia monacha
(1). Callicebus moloch (3),Cebus albifmns (11, Cebus capucinus (1). Alouatta sp. (2). Ateles geoffmyi (1).Ateles fusciceps ( l ) ,Lagothrix lagotricha 111. CercoDithecur talaooin 12). CercoDithecusDetaurista(l1. Cep
cocebus torquatus 12). Macaca sp. (11,Papw anubis (2),Colobus guereza (21. Presbytzs cristatus (2),Hylobutes lar ( 2 ) ,Hylobates moloch (21.
Pongo pygmaeus (2),Pan tmglodytes (4). Total = 45.
10
M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS
cess, a ventrally facing concavity in the squamosal represents the upper half of the external
acoustic meatus. The postglenoid foramen lies
just posterior to the medial end of the postglenoid process; it retains the primitive large
diameter seen in lemurs and some ceboids
(Conroy, 1980b).On the endocranial surface of
the specimen, a sulcus representing the squamosal surface of the petrosquamous venous siIntratympanic muscles
nus runs forward and downward to terminate
On the smaller petrosals, the lower edge of in the postglenoid foramen. The foramen has
the fossa for m. tensor tympani is delimited by the form of a short bony canal, about as long as
a crest that runs forward and slightly upward it is wide, which in life surrounded the terminal
from the anterior border of the fossula fenes- end of the venous sinus (See note, p. 21).
In typical prosimians, as in primitive euthertrae vestibuli (Fig. 4).The corresponding fossa
on the large petrosal (Fig. 1)has no definite ians generally, venous blood entering the
lower edge. This is another slight morphologi- transverse sinus drains laterally and leaves the
cal difference suggesting that the three braincase through two parallel outflow chansmaller petrosals represent one anthropoid nels: 1)the sigmoid sinus, which empties into
species and the large petrosal another.
the internal jugular vein, and 2) the petrosquaIn YPM 25972 only, enough of the rear of the mous sinus, which runs forward in a channel
tympanic cavity is preserved to permit identi- wholly enclosed by the petrosal and squamosal
fication of the pyramidal eminence or osseous (hence its name) and becomes the external jugchamber that held the origin and belly of the
ular vein after traversing the postglenoid forastapedius. A tiny perforation in the pyramids men. The distal part of the petrosquamous siapex represents the aperture through which nus also receives a major venous channel runthis muscle's tendon entered the tympanic cav- ning backward from the orbit through the cranio-orbital foramen in company with the ramus
ity (Fig. 1).
superior of the stapedial artery. This cranio-orSQUAMOSAL AND ECTOTYMPANIC
bital venous sinus drains the meningeal veins
The isolated right squamosal, Duke Univer- of the side wall of the braincase. I t is representsity No. 1065, which was recovered from Quar- ed on dried skulls by a broad straight sulcus,
ry I in 1977, is similar in known parts to the usually referred to as the sinus canal. In ansquamosal of Aegyptopithecus zeuxis (Fig. 5). thropoids, the sigmoid drainage is emphasized
and may have come from a female or other at the expense of the petrosquamous system;
small individual of that species. The specimen the postglenoid foramen is reduced or absent,
preserves the glenoid fossa, the postglenoid the bony petrosquamous canal becomes a shalforamen, the posterior root of the zygomatic low sulcus (persistently roofed over in some cearch, and the inferior part of the temporal boids), and the cranio-orbital sinus is greatly
squama, together with the lateral half of the reduced in conjunction with the loss of the stamastoid process of the petrosal, with which the pedial ramus superior and the capture of its
squamosal is completely fused. The mastoid branches by branches of the maxillary and lacprocess exhibits pneumatization of a sort typi- rimal arteries. In Homo and many other catarcal for anthropoids, with cellules extending in- rhines, all these elements of the petrosquato the temporal squama. The anterior surface
of the postglenoid process has spalled off, but
the process is otherwise intact and appears to
have been feebly developed. Except for having
Fig. 5. Ventral views of glenoid region in Fayum antbroa relatively gracile postglenoid process, the en- poids: a) isolated right squamosal DU 1065; b) correspondregion of basicranium of Aegyptopithecus zeuxis (Cairo
tire fragment resembles the corresponding ing
Geol. Mus. 40237; photograph courtesy of Dr. R.F. Kay). Inparts of a small Alouatta skull. The formation set on u, postglenoid region with oblique lighting to emphaof the medial wall of the glenoid fossa by a size contours of anterior CNS of ectotympanic. Key: b, bulla;
stout downward expansion of the squamosal e, ectotympanic (apex of anterior crus);ep. entoglenoidproof squamosal;gf,glenoid fossa: mg, mastoid group; ms,
(an entoglenoid process) is a particularly strik- cess
mastoid region; pcf, posterior carotid foramen; pgf, posting resemblance to Alouatta
glenoid foramen: pgp, postglenoid process; zp, zygomatic
Immediately behind the postglenoid pro- process of squamosal.
cotympanic branch of the internal carotid artery as well; if present, the caroticotympanic
artery would have occupied the faint groove indicated by an arrow in Figure 4. Since the facial canal is perforated for most of its length in
this specimen, the place where the chorda tympani escaped into the tympanic cavity can no
longer be identified.
EARLY ANTHROPOID TEMPORAL BONES
11
12
M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS
Fig. 6. Dorsal view of isolated anthropoid right squamosal DU 1065, showing impressions of petrosquamous sinus
(pss) and cranio-orbital sinus (cos). Direction arrows as in
mous system are normally absent in the adult.
The Fayum squamosal retains a prosimian-like
petrosquamous system, in which the petrosquamous sinus and postglenoid foramen are
relatively as large as those of the most primitive of living anthropoids, and the cranio-orbital sinus is represented by a broad, straight
sulcus resembling that of Lemur or Tarsius
(Fig. 6 ) .Whether the petrosquamous sinus lay
in a complete bony canal or an open sulcus
cannot be determined from the available
fossils.
The tip of the anterior crus of the ectotympanic anulus remains attached to the Fayum
squamosal; it is discernible as a flat, expanded
lamina immediately behind the postglenoid
foramen, of which it forms the posterior edge
(Fig. 5a). A broken surface posteromedial to
the foramen represents the plane along which
the anulus fractured when the squamosal was
separated from the lost bulla. The occurrence
and position of this break demonstrate what is
also inferrable from the appearance of the
edges of the terminal lamina: the anterior crus
of the ectotympanic was solidly fused to the
squamosal in the living animal. Had a joint
Figure 1. Asterisk indicates “bristle”drawn as if traversing
postglenoid foramen. Key: ac, air eellules;z, zygomatic process of squamosal.
persisted between the two bones, the tip of the
anterior crus would have been lost with the
rest of the ectotympanic.
A portion of the ectotympanic’s posterior
crus is seemingly preserved on the YPM 25972
specimen, but it is battered and broken beyond
easy recognition. Our identification is hesitant, and is largely influenced by what we have
found in our survey of extant primates. There
are two morphological justifications for thinking that the area shaded in Figure 1 is ectotympanic in origin: 1)In all ceboids, but especially
in medium- and small-sizedones, the definitive
stylomastoid foramen is situated immediately
behind the margin of the posterior crus, close
to its apical end; 2) In those ceboids that exhibit small ridges or transbullar septa on the
floor of the sinus tympani (i.e,, callitrichids
other than Saguinus, and some cebids), the
system of ridges extends as far as the petroectotympanic suture, but no further; they end
flush with the ectotympanic’s posterior crus.
Since the foramen and at least one transbullar
septum are partly preserved in YPM 25972,
the rear of the tympanic cavity in Fayum anthropoids may be directly compared with the
EARLY ANTHROPOID TEMPORAL BONES
13
corresponding region in modern ceboids. We
feel that the morphological correspondences
are sufficientlydetailed to warrant the identification of the thick ridge (see above)as the ectotympanic. This ridge, or ectotympanic fragment, is not demarcated from adjacent bone by
a suture; complete synostosis of the anulus
and petrosal plate evidently occurred here in
Fayum anthropoids as it does in other fossil
and modern primates. Neither end of the ectotympanic, as we identify it on the Fayum fossils, differs significantly from the equivalent
parts of the ectotympanic in platyrrhines.
THE YPM 23968 ASSEMBLAGE
The material catalogued with the accession
number 23968 in the Yale Peabody Museum is
an assemblage of ten items which were found
closely associated with each other at Quarry I.
Two of these-the petrosal and the supposed
Apidium squamosal- were described by Gingerich (1973). The remaining eight items comprise a fragment of a small anthropoid frontal,
a second petrosal, and six teeth. One of the
teeth is caniniform, with a short crown and a
long, thick root; it may be a lower canine of
Apidium phiomense, but it lacks diagnostic
features that would enable us to identify it confidently.
The other five teeth in the assemblage are
cheek teeth of Apidium phiomense. With the
kind assistance of our colleague R.F. Kay, we
have identified them as follows: 1)a very badly
2) an unworn left P4(orposworn right P3or P4;
sibly P3);3) an almost unworn left M', plus surrounding alveolar bone including part of the
M3 socket; 4) a heavily worn right M'; 5) a very
badly worn small cheek tooth, either a somewhat ill-formed M3or an upper premolar.
It is obvious that more than one individual of
Apidium is represented in the YPM 23968 assemblage. Of the two petrosals included in this
assemblage, one is anthropoid and was described in some detail by Gingerich (1973).The
other (Fig.7),which was not mentioned by Gingerich, differs considerably from the first. Although this particular specimen is poorly preserved, the most recent Duke Fayum expedition (November 1980) collected several more
petrosals of the same type. There can be no
question that these elements came from anonprimate mammal species. This is evinced by
the broad, uninflated mastoid region, the anteroposteriorly short endocranial surface, the
anteriorly positioned parafloccular fossa, and
the absence of any arterial grooves or canals on
the promontory. A pronounced vascular
Fig. 7. Isolated left petrosal from YPM 23968 assemblage; ventral view. Direction arrows as in Figure 1.Scale =
1 mm. This specimen lacks any sign of a petrosal tympanic
process and is clearly nonprimate. The internal carotid may
have been accommodated in the vascular groove on the medial side of the petrosal, a position typical for carnivores.
The basal turn of the cochlea (asterisk)is fully exposed, o w
ing to loss of the bone forming the fenestra cochleae. Key:
fca, facial canal; fv,fenestra vestibuli; lsc, lateral semicircular canal; pr. promontory; vg, vascular groove (probably for
the internal carotid artery).
groove running anteroposteriorly along the
petrosal's medial and inferior edge may have
held a medially positioned internal carotid artery like that of a carnivore or rodent. The medial and anterior edges of these specimens are
smooth and unbroken, indicating that the petrosal was separated from the surrounding basicranial bones by unossified tissues and so became detached easily from the skull base after
death. In no case is there a trace of a bony bulla; the bulla, if osseous, was apparently not
formed by the petrosal. In all these respects,
these petrosals differ from those of primates
and resemble those of early carnivorous placentals, either creodonts or primitive carnivoranS.
Because the YPM 23968 assemblage contains disparate elements secondarily brought
together from more than one individual of
Apidium (as shown by the dental-wear distribution) and from more than one order of mam-
14
M. CARTMILL, R.D.E. MacPHEE. AND E.L. SIMONS
mals (as shown by the second petrosal), the association of the supposed Apidium squamosal
with teeth of A. phiomense provides no warrant for attributing it to that species. The identification of this squamosal must be based exclusively on its morphology.
We have made extensive comparisons of the
supposed Apidium squamosal (Fig. 8)with reptilian, avian, and mammalian cranial and postcranial material in the osteological collections
of the American and U.S. National Museums
of Natural History. After successively trying
and failing to persuade each other that the specimen represents a carnivore atlas, a turtle atlas, a primate zygomatic, and a lizard articular,
we are convinced that Gingerichs identification of it as a mammalian squamosal is correct.
However, we are also convinced that the squa-
mosal is not that of a primate, for the following
reasons:
1. The articular surface of the glenoid is
hemicylindrical in form, suggesting a uniaxial
pattern of rotation like that of a carnivoran.
2. The postglenoid foramen is located far
behind the postglenoid process, rather than at
its posteromedial edge, where it lies in primates that retain this foramen (cf. Figs. 5 and
Fig. 8. a)Isolated squamosal (YPM239681, probably of a
small creodont; ventrolateral view. Large arrow points anteriorly: small arrow dorsally. Scale = 1mm. b) Same specimen and scale, dorsal anterolateral view. Pointers in a identify a projecting ridge of bone beneath the posttympanic
process, identified as the ectotympanic’sposterior CNS by
Gingerich (1973).Key: d, cancellous tissue exposed through
breakage of zygomatic process; gf,glenoid fossa; pgf, postglenoid foramen: pgp, postglenoid process: ptp, posttympanic process: tf, floor of temporal fossa (betweentemporal squama and posterior end of zygomatic arch);zp, zygomatic process of the squamosal. Asterisk in b identifies cancellous tissue exposed on medial side of specimen as a result
of loss of temporal squama.
9).
3. The postglenoid foramen is the lower terminus of a vertical canal, about nine times as
long as the foramen’s diameter.
4. The posterior root of the zygomatic arch
is deeply excavated on its superior aspect. This
excavation, which represents the floor of the
posterior temporal fossa, becomes shallower
but wider posteriorly (Fig. 8b), indicating that
Fig. 9. Three views (ventral,ventrolateral, and dorsal anterolateral) of temporal bone anatomy in the Eocene Bridgerian creodont Limnocyon verus (USNM No. 299722). Key:
gf,glenoid fossa; pgf, postglenoid foramen;pgp, postglenoid
process; pr, promontory; ptp, posttympanic process; s, sulcus for chorda tympani and associated vessels; tf. floor of
temporal fossa. The photographs are reversed for comparison with Figure 8% b. Fig 9a approx. natural size.
16
M. CARTMILL, R.D.E. MacPHEE. AND E.L. SIMONS
the posterior part of the braincase was small
relative to the adjoining part of the temporal
fossa.
5. The process identified by Gingerich as
the posterior crus of the ectotympanic juts
from the lateral edge of this posterior expansion at an angle of about 45”.Our mental reconstruction of the remainder of the “ectotympanic“places the greater part of the bone lateral to the side wall of the skull. Since such a positioning is never encountered in mammals, we
conclude that the feature in question is simply
a projecting part of the squamosal-probably
the posttympanic process.
In all these respects, the YPM 23968 squamosal differs from those of known primates.
The large postglenoid process rules out attributing this specimen to Rodentia. However,
there are resemblances to creodonts and miacids (Matthew, 1909) in the posterior expansion of the temporal fossa, the form of the glenoid, the positioning of the postglenoid foramen, and other features. A shallow groove running anteriorly around the medial end of the
postglenoid process (and notching it in passing)precisely resembles the sulcus for the chorda tympani and associated vessels in primitive
fissipede Carnivora (Petter, 1966). In this and
other details, the YPM 23968 squamosal is
similar to that of a small hyaenodontid creodont like Limnocyon uerus from the Bridger
Eocene (Fig. 9),which differs principally in features associated with its larger size-e.g., the
greater saliency of the postglenoid process.
Fissipede carnivorans first appear in Africa
in the Miocene (Savage, 1978).The YPM 23968
squamosal is therefore more likely to represent
a small creodont than a miacid. The only creodont previously described from the Upper Fossil Wood Zone is Metasinopa fraasi (Osborn,
1909), which is too large an animal to be the
source of the YPM 23968 squamosal. However, Duke University expeditions have in the
last three field seasons uncovered several mandibles of a small creodont at Quarry I, in the
very same zone that yielded the disputed squamosal. Preliminary studies suggest that these
represent a species of the genus Masrasector.
The sole named species of this genus, M.
a e g y p t i c ~ s is
~ , based on type material from
Quarry G in the middle of the Qatrani Formation, slightly earlier than the level from which
the YPM 23968 assemblage was recovered.
Masrasector aegypticus was a fox-sized animal; the creodont mandibles from Quarry I are
somewhat smaller in size, but show no other
obvious differences from the Quarry G Masrasector material. The question of their taxonom-
ic distinctiveness is currently under study; it is
sufficient for our purposes to note that they
represent a likely source for the YPM 23968
squamosal. We tentatively attribute that
squamosal to an undetermined species of
Masrasector, or another proviverrine hyaenodontid of similar size, and accordingly conclude that the specimen has no relevance to the
problem of anthropoid origins.
DISCUSSION
In every anatomical feature, the ear region of
Fayum catarrhines more closely resembles
those of Recent anthropoids than it does those
of any prosimians. It follows that virtually all
of the important events in the evolution of the
anthropoid temporal bone must have preceded
the early Oligocene. Though the Fayum catarrhine basicranium is more primitive in some respects than that of any extant catarrhine, its
differences from modern catarrhines all represent resemblances to platyrrhines. Because of
these facts, the temporal bones of Fayum anthropoids shed very little new light on the
problem of identifying the prosimian ancestors
of the Anthropoidea. I t is now abundantly
clear that the Fayum anthropoids exhibit no
apomorphous features of the ear region that
are shared with adapids or other “lemuroids”
(in the broad sense). Lemurs, ceboids, and Fayum anthropoids resemble adapids, but differ
from all tarsioids, in lacking a bony meatal
tube extending laterally past the recessus.
However, absence of this tube is probably a retention from the ancestral primate stock, and
within-family differences among modern mammals strongly suggest that meatal elongation
is highly labile. No exclusive resemblances between adapids and anthropoids in ectotympanic-squamosal relations, the pattern of carotid
circulation, middle-ear pneumatization, or any
other fundamental aspect of the organization
of the otic region appear to exist. The hypothesis that anthropoids evolved from adapids now
rests entirely on the evidence provided by the
teeth and jaws (Gingerich and Schoeninger,
1977).
The more popular hypothesis that anthropoids were derived from omomyids sensu lato,
most persuasively urged in recent years by
Szalay (197513,1976; Szalay and Delson, 197%
also finds little or no support in the anatomy of
the ear region. Rooneyia and Necrolemur, the
only early tarsioids whose ear regions are ade’The original species name, aegypticum (Simons and Gingerich,
1974). is here emended to aegypticus in accord with Article 30aW of
the International Code of Zoological Nomenclature.
EARLY ANTHROPOID TEMPORAL BONES
quately known, exhibit no striking otic specializations (with the possible exception of the
bony meatal tube), but remain in most respects
persistently primitive. The posteromedial position of the posterior carotid foramen, which
Szalay and others (e.g., Cartmill and Kay,
1978)have identified as a synapomorphy of an
omomyid-tarsier-anthropoid clade, may well
be a primitive primate feature. The posterolateral position of this foramen has been regarded
as primitive for primates because it characterizes Plesiadapis, adapids, and some Malagasy
lemurs. However, the posteromedial position
is found in lorisiforms and omomyids (sensulato),and is also characteristic of most of the possible outgroups of Primates, including tree
shrews, elephant shrews, and lipotyphlous Insectivora. In fetal Malagasy lemurs, the internal carotid artery enters the bulla from the medial side, exactly as in fetal lorises, and shifts
laterally later in development; the degree of
lateral displacement (maximal in most lemurids and indriids, minimal in cheirogaleids) is
correlated with, and is probably an effect of,
differences in the extent and pattern of pneumatization in the rear part of the petrosal plate
(MacPhee, 1981).If the posteromedial position
precedes the more lateral position in primate
17
phylogeny as well as ontogeny, as the insectivore evidence suggests, then the posteromedial position cannot be a shared derived feature of omomyids and anthropoids. However,
the more lateral position of the foramen (and
the associated pattern of pneumatization) in
Malagasy lemurs might represent evidence for
phyletic affinities between lemurs and adapids.
Unlike anthropoids and Tarsius, known omomyids lack a transverse partition separating
the tympanic cavity proper from a large anterior (or apical) accessory cavity. The latter cavity, as a separate entity, appears to be wholly
unrepresented in Necrolemur, Rooneyia, and
Tetonius (although we are not certain of this,
because we have not studied the fossil material
of Rooneyia, and because the poor condition of
the only skull of Tetonius precludes a definite
conclusion).These early Tertiary tarsioids also
exhibit a transpromontorial carotid routing
that is in most respects primitive for primates,
whereas anthropoids from the Oligoceneto the
Recent display a perbullar carotid pathway
that is not presaged in any ancient tarsioid.
The distinctive features of these two types of
pathway are summarized in Table 1.The single
feature of the ear region of Fayum anthropoids
TABLE 1. Internal carotid pathways
Transuromontorial uathwav
Perbullar uathwav
-1. The IClPA traverses the entire ventral or
1. The IClPA travels over only a small part
ventrolateral surface of the promontory.
of the promontory and in any event does
not cross the latter’s ventrolateral surface.
2. From its entry point in the bulla’s
posterior wall, the IC travels on or
near the ventral lip of the cochlear
window, where it divides into the PA and SA.
2. The IC does not travel near the cochlear
window, but always well anterior to it.
3. The PA is never enclosed by material
from the petrosal plate and is always
situated lateral to the bullar medial
Wall.
3. The IClPA is enclosed in a complete canal
that is derived from the petrosal plate,
and therefore it is morphologically
situated “within”the bullar wall.
4. The IClPA is situated entirely within the
4. The IC/PA bypasses the tympanic cavity
tympanic cavity proper until it leaves the
middle ear.
5. The SC travels only a short distance from
its origin to the obturator foramen of the
stapes; among Recent forms, the SA is present
throughout life (except when the entire internal
carotid system is reduced, as in lorises and
dwarf lemurs).
and passes out of the middle ear after
traveling through the anterior accessory cavity.
5. The SC, when present, begins beneath
the anterior pole of the promontory,
and travels backward along the
length of the promontory in order to
reach the stapes; among Recent forms
the SA normally involutes perinatally,
usually in its entirety.
The transpromontorial pathway is found in living strepsirhines and all fossil nonanthropoid primates (so far as this can be determinedfrom existing evidence).The perbullarpathway is distinctive of Oligocene-Recentanthropoids,and a very similar routing is found in contemporary Tar
sius. Of the two, the transpromontorial pathway is clearly the more primitive;it is frequently encountered in Eutheria and may be primitive for
that infraclass. Omomyids consistently group with adapids and plesiadapoids for traits 1-5. although they may differ in other respects (e.g..in
having a larger promontory canal). Tarsius differs from anthropoidsin retaining a stapedial canal (trait 5). which, however, contains only a fibrous remnant of the stapedial artery in the adult stage. Key: IC, internal carotid stem; PA, promontory artery; ICIPA, internal carotid stem and
promontory artery considered together; SC. stapedial canal.
18
M. CARTMILL, R.D.E. MacPHEE. AND E.L. SIMONS
that suggests a possible derivation from omomyids is the apparent presence, as in Rooneyia, Necrolemur, and most callitrichids (Fig. 2),
of small transbullar septa or “struts”running
across the tympanic surface of the petrosal
plate to the ectotympanic. The occurrence of
similar septa in Plesiadapis and Allocebus
(Gingerich, 1975a, 1976; Cartmill and Kay,
1978), and the dubious identification and uncertain distribution of these septa in the
Fayum anthropoids, render the significance of
this resemblance unclear.
Arterial canals in the middle ear have been
invoked in arguments both for and against the
notion that anthropoids evolved from omomyids. Szalay (1975a)proposed that a canal for
the promontory artery larger than that for the
stapedial artery may represent a shared derived feature linking tarsiers, omomyids, and
anthropoids. Gingerich (1973)suggested that a
relatively large promontory artery may also be
found in some specimens of Notharctus, and
that an enlarged promontory artery is therefore not necessarily a sign of omomyid affinities. We are inclined to believe that the relative
proportions of these two arteries typically
found in these several taxa do tend to support
Szalay’sposition: but the support they provide
is feeble, because the canals for these two arteries are subequal in size in Necrolemur (Szalay,
1975a), some extant strepsirhines exhibit
marked reduction of the stapedial artery (Saban, 1963),and the presence of an arterial canal
does not in any case imply the presence of a
corresponding artery (Conroy and Wible,
1978).Gingerich (1973),assuming that it does,
asserted that the YPM 23968 petrosal resembles that of extant anthropoids and differs
from those of omomyids and Tarsius in lacking
a stapedial artery. In fact, a stapedial canal is
present in adult tarsiers, but the proximal part
of the stapedial artery of Tarsius degenerates
and becomes a mere fibrous cord early in fetal
life (Hill, 1953;Wunsch, 1975).Whether the artery was equally regressive in any omomyids is
impossible to say.
Cartmill and Kay (1978), following Simons
(1974)in refusing to lump omomyids together
with anthropoids and Tarsius as a suborder
Haplorhini, nevertheless proposed that Tarsius is the phyletic sister group of the Anthropoidea, and that tarsiers are more closely related
to anthropoids than any early Tertiary prosimians are. In support of this hypothesis, they
noted that in Tarsius and anthropoids, but in
no other primates, the internal carotid artery’s
pathway is what we have here called perbullar,
as opposed to transpromontorial. A similar observation had been made a half-century earlier
by F. Wood Jones, who remarked that in tarsiers, as in anthropoids, “the internal carotid artery enters through the bulla, not by perforation of its posterior wall” (Jones, 1929, p. 151).
The partitioning-off of an anterior accessory
cavity of the middle ear, remarked on above,
was cited by Cartmill and Kay as a second otic
similarity between Tarsius and anthropoids
which is not shared by omomyids. A third such
similarity may be the prenatal loss of a functional stapedial artery, although widespread
parallel evolution of this trait makes it an unreliable indicator of phyletic affinities, and its
distribution among extinct primates cannot be
ascertained in any case.
Whether or not the Cartmill-Kay hypothesis
holds up in the long run, it is clear that the ear
region of Oligocene anthropoids differs radically, not only from those of extant strepsirhines,
but also from those of Paleogene prosimians.
All early prosimians for which the ear region is
known resemble each other, and differ from anthropoids, in possessing a subtympanic extension of the tympanic cavity and a partial or
complete bony tube enclosing the “intrabullar”
recessus meatus (Stehlin, 1912; Szalay, 1975a;
Cartmill, 1975; Gingerich, 1976; Conroy,
1980a),as well as in having a transpromontorial carotid pathway and in lacking a transverse
septum delimiting an anterior accessory cavity of the middle ear. The anthropoid states of
the characters in question (Fig. 10, Table l), taken together, define an otic complex distinctive of higher primates. Stratophenetic considerations (sensuGingerich)as well as considerations of parsimony imply that in all these respects, the Fayum anthropoids are more derived than any other Paleogene primates so far
known. Since no fossil prosimians appear, in
these same respects, to be suitable anthropoid
antecedents, and since the distinctive and
highly specialized anthropoid otic complex
was already fully evinced in catarrhines from
the early Oligoceneof the Fayum, it seems likely that anthropoids were derived from a group
of Eocene prosimians that is currently unknown (or a t least not known from basicranial
remains). We find it impossible to believe that
the anthropoid otic complex could have
evolved independently in the Old and New
Worlds, no matter whether we postulate a last
common ancestor that resembled known adapids or known omomyids in the morphology of
the ear region. The hypothesis that separate
lineages of New and Old World prosimians,
EARLY ANTHROPOID TEMPORAL BONES
19
I
A
Fig. 10. Idealized schemata of the cut-open hullae of Paleogene primates. In early prosimians of modem aspect (A),
the part of the ectotympanic that frames the eardrum is
aphaneric or intrabullar (1);there is a partial or complete
bony anular bridge (“ossified anulus membrane”)(2); a canal
for the stapedial artery is present (3);and the internal carotid artery enters the bullar posteriorly (4) and courses across
the ventrolateral surface of the promontory (5).In Oligocene
and later anthropoids (B),the ectotympanic is phaneric or
“extrabullar” (6), and the petrosal apex is inflated by a tra-
beculated anterior accessory cavity (7). The internal carotid
artery of anthropoids (8)enters the bulla through an anteriorly placed carotid foramen (9) and traverses the septum
(asterisk)between the tympanic cavity and anterior accessory cavity; as a result, the fenestra cochleae (10)is directly
visible from the ventral aspect. The position of the auditory
tube is indicated by white arrows; the shorter white arrow in
(B)shows the aperture through which the anterior accessory
cavity communicates with the rest of the middle ear.
whether omomyids sensu lato (Gregory, 1951,
vol.1, p. 473; Gazin, 1958; Romer, 1968,p. 185),
adapids (Gingerich, 1975b),or unspecified but
presumably different prosimian stocks (Cachel, 1976, 1979), gave rise independently to
Platyrrhini and Catarrhini, seems wholly untenable. Platyrrhines and catarrhines evidently had a last common ancestor that could not
have been ancestral to any other known primates.
When and where did that common ancestor
live? The ceboid-like features of the ear region
of the Fayum anthropoids, together with the
persistence of three premolars in the Parapithecidae, have been invoked by Hoffstetter
(1971,1972,1974b, 1977a, b) as support for his
hypothesis that the last common ancestor of
the Old and New World anthropoids inhabited
Africa in the Eocene, and that the primates of
South America are descended from a parapithecid-like form that managed to cross the
South Atlantic by rafting. Our reasons for rejecting this hypothesis are those presented by
Simons (1976). Other hypothetical South Atlantic connections, involving a common anthropoid ancestry in Gondwanaland prior to
the separation of Africa and South America
(Hershkovitz, 1977)or an invasion of Africa by
early platyrrhines, again by rafting (Szalay,
1975b),seem equally implausible. In any case,
there is no reason for believing that the few features of the platyrrhine ear region (anularecto-
20
M. CARTMILL, R.D.E. MacPHEE, AND E.L. SIMONS
tympanic, more medial carotid foramen, less
ventral stylomastoid foramen, etc.) which distinguish platyrrhines from modern catarrhines
represent anything but primitive anthropoid
features lost in post-Oligocene catarrhines.
Although the earliest undoubted anthropoids are those of the Fayum, there are sound
if not conclusive reasons for thinking that anthropoids were present at about the same time
in South America (Branisella)and slightly earlier in Burma (Pondaungia; perhaps Amphipithecus). The intermediate spatial position
and antecedent temporal position of the
Burmese fossils suggest that the ancestral anthropoid was a mid-Eocene or earlier inhabitant of either eastern Asia (Conroy and Bown,
1974; Conroy, 1978)or western North America
(Szalay and Delson, 1979), and that dispersal
of anthropoids from one hemisphere to the other may have occurred via Beringia. Discovery
of the ear region of Chumashius or other omomyids from the west coast of North America
might well shed new light on the problem of anthropoid origins.
ACKNOWLEDGMENTS
We thank Drs. S. Anderson, E. Delson, R.
Emry, M.C. McKenna, and R.W. Thorington,
Jr., and Mr. D.H. Russell and other members
of the staffs of the National and American Museums of Natural History for their invaluable
help. We are grateful to Drs. R.F. Kay and J.G.
Fleagle for their comments on the manuscript,
and to Dr. Kay for his aid in identifying the
Apidium teeth in the YPM 23968 assemblage
and for allowing us to reproduce his stereophotograph of the Aegyptopithecus skull (Fig. 5 ) .
The Fayum material used in this study has
been recovered by expeditions under the third
author’s direction from 1960 to 1980, made
possible by grants BNS-77-20104 and
BNS-80-16206 from the National Science
Foundation and Smithsonian Foreign
Currency Awards 23 and 809479. The first
author’s research was supported by a Research
Career Development Award (K04-HD00083)
from NIH. Some phases of the second author’s
research were supported by a grant from the
Duke University Medical School Research
Fund.
We thank Susan Gurganus for preparing the
manuscript, and Veronica Mahanger-MacPhee
for editorial assistance.
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~~
NOTE ADDED IN PROOF
Additional cleaning of the skull of Aegyptopithecus reuxis (CGM 40237) has demonstrated that the supposed postglenoid foramen
(labelled "pgf" in Fig. 5) is a blind pit; the
foramen is bilaterally absent in this skull. The
DU 1065 anthropoid squamosal, which has a
large postglenoid foramen, is therefore
probably not attributable to A. zeuxis. It may
represent a large parapithecid.
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