PalcoBios 18(2&3):21-35, September 1998
New information on the skull of the Early Permian reptile Captorhinus aguti
SEAN PATRICK MODESTO
Department of Zoology, Erindale College, University of Toronto, Mississauga, Ontario L5L 1C6 Canada
Current address: Bernard Price Institute for Palaeontology and Palaeoenvironmental Research, University of the
Witwatersrand, Johannesburg, P.O. WITS 2050, South Africa
ABSTRACT—Well preserved material of the early reptile Captorhinus aguti Cope, from the Fort Sill fissure-fill
locality, Lower Permian of Oklahoma, permits correction and emendation of earlier interpretations of its cranial
anatomy. Description of new material and reexamination of previously described specimens reveals that anterior
cristae are not present in the braincase of C. aguti, nor is there evidence for the presence of these cristae in
specimens of its sister species Captorhinus laticeps. The parasphenoid of C. aguti has broad basitubera which may
have overlain the stapedial footplates, as described for its larger relative Labidosaurikos meachami. Evidence of a
jaw-locking mechanism is lacking for both C. aguti and C. laticeps, despite such a mechanism having been proposed
originally for the latter taxon. In addition to the well-known presence of multiple rows of teeth, C. aguti is
distinguished from other captorhinids by the presence of ogival cheek teeth. The presence of ogival cheek teeth in
isolated, single-rowed elements from Fort Sill supports assertions that C. laticeps is absent from the Fort Sill fauna
and that there is a distinct stratigraphic separation between the two Captorhinus sister taxa. Similarly, single-rowed
elements with ogival teeth from the Lueders Formation of Texas are reassigned to C. aguti from C. laticeps, thereby
extending the stratigraphic range of the former species in Texas at the expense of the latter.
INTRODUCTION
The Lower Permian Fort Sill fissure-fill locality near Richards
Spur, Oklahoma, is one of the most remarkable of Paleozoic
tetrapod localities, since the vast majority of specimens
collected there are attributable to a single taxon, the mul-
tiple-tooth-rowed captorhinid reptile Captorhinus aguti
(Cope, 1882). The large amount of material collected from
the Fort Sill locality has revealed in exquisite detail the
osteology of this small reptile (Price, 1935; Fox and Bow-
man, 1966; Holmes, 1977; de Ricqles and Bolt, 1983;
Rieppel, 1993) and have made C. aguti an indispensible
taxon in recent large-scale phylogenetic studies of basal
amniotes (Gauthier et al., 1988; Laurin and Reisz, 1995;
1997).
The postcranial skeleton of C. aguti has been described
in detail in a series of recent papers (Holmes, 1977; Sumida,
1990; Rieppel, 1993). However, the most recent compre-
hensive study of the cranial anatomy of this captorhinid is
that of Fox and Bowman (1966). Although that work is no
longer considered sufficiently informative by modern stan-
dards, a more rigorous evaluation of the skull of C. aguti
has not been forthcoming. The absence of recent studies of
the cranial anatomy of this captorhinid may be attributable
to Heaton's (1979) extensive description of the skull of
Eocaptorhinus laticeps (Williston, 1909).
Heaton's (1979) work has added considerably to our
current understanding of captorhinid cranial anatomy. Un-
fortunately, by defining the genus Eocaptorhinus to include
all captorhinids "that are identical to C. aguti except for the
single tooth row" (Heaton, 1979, p. 70), he precipitated
the long-standing confusion regarding the validity of "E.
laticeps," the only species assigned to the genus (Gaffney
and McKenna,  1979).  Eocaptorhinus was ultimately de-
clared a junior synonym of Captorhinus (Gaffney, 1990),
and those single-rowed captorhinids that are otherwise
indistinguishable from C. aguti were referred to C. laticeps
(Dodick and Modesto, 1995).
Heaton's (1979) unfortunate definition of
"Eocaptorhinus also precipitated a dilemma concerning
which studies should be consulted for information on the
cranial anatomy of C. aguti; except for the obvious differ-
ence in the number of marginal tooth rows, the skeletal
designs of the two taxa appear to have been understood
tacitly by some workers to be freely interchangeable. For
example, de Ricqles and Bolt's (1983, Fig. 1) reconstruc-
tion of the skull of C. aguti in dorsal and lateral views
compares very closely with that of UE. laticeps" by Heaton
(1979, Fig. 2); their reconstruction incorporates the flawed
restoration of the jaw suspension and the inconsistency in
the length of the nasal-lacrimal suture seen in the dorsal and
lateral aspects of Heaton's (1979) restoration.
The basis of Heaton's (1979) study were several, well
preserved single-tooth-rowed skulls. (The terms "single-
tooth-rowed" and "multiple-tooth-rowed" are abbreviated
hereafter to "single-rowed" and "multiple-rowed," respec-
tively.) Unfortunately, Heaton (1979) complicated matters
greatly and compromised his description of UE. laticeps" by
using captorhinid specimens from Fort Sill to supplement
his description. Those specimens are more appropriately
referred to C. aguti, as the overwhelming majority of
tooth-bearing elements collected from the Fort Sill locality
bear multiple rows of teeth that are arranged divergently
across the tooth lamina, an autapomorphy of C. aguti
(Dodick and Modesto, 1995). Single-rowed captorhinid
jaw fragments are extremely rare at Fort Sill (Bolt and
DeMar, 1975; Modesto,  1996a), and Bolt (1980) sug-
22
PALEOBIOS, VOL. 18, NUMBERS 2&3, 1998
gested further that those specimens might be attributable
to single-rowed C. aguti. Heaton's (1979) description,
therefore, should be used with caution when investigating
the interrelationships of captorhinids.
Hundreds of new Captorhinus specimens, consisting
largely of disarticulated cranial elements and a few partial
skulls, were collected recently from the Fort Sill locality.
Close examination of these specimens, and of others
reposited in the Oklahoma Museum of Natural History
revealed the presence of several cranial apomorphies that
were not noted in previous studies (Price, 1935; Fox and
Bowman, 1966; Heaton, 1979; de Ricqles and Bolt, 1983;
Gaffney, 1990). A thorough knowledge of the anatomy of
C. aguti is important, not only for investigating the broader
aspects of basal reptile phylogeny, but also for examining
macroevolutionary phenomena such as the origin of terres-
trial vertebrate herbivory (Hotton et al., 1997). Since a
growing body of anatomical evidence suggests strongly that
the earliest reptilian herbivores were the large, multiple-
rowed captorhinids (Dodick and Modesto, 1995; Hotton
et al., 1997), a robust phylogeny of captorhinids will be
required to provide an explicit framework in order to
investigate the development of herbivory in these reptiles
and its paleoecological implications. The intent of this
study is to correct previous interpretations of the cranial
anatomy of C. aguti. The new C. aguti material is de-
scribed below and compared to that of C. laticeps.
MATERIALS
All of the Captorhinus aguti specimens described and
illustrated in this study were recovered from the Dolese
Brothers Quarry, near Richards Spur, Oklahoma ("Fort Sill"
locality of recent studies; e.g. Olson, 1991). The locality is
comprised of clay-filled fissures in Ordovician limestone, and
is assigned to the surrounding Garber Formation (Sumner
Group). The Fort Sill locality has been correlated (Heaton,
1979; Olson, 1991) with the lowermost horizons of the
Clear Fork Group of Texas (beds recognized formerly as the
"Arroyo Formation"; e.g. Romer, 1974); stratigraphic ter-
minology for Texan strata employed in this paper follows
Hentz(1988).
Specimens of C. aguti used in this study: Museum of
Comparative Zoology, Harvard University (MCZ) 1198,
an almost complete braincase preserved in association with
a partial palate and mandible; MCZ 1199, an articulated
left opisthotic and partial supraoccipital; Oklahoma Mu-
seum of Natural History, University of Oklahoma
(OMNH) 15138, a partial skull; Royal Ontario Museum
(ROM) 30096, a partial right maxilla; ROM 30097, a
partial skull table; ROM 30098, a skull roof fragment with
a nearly complete squamosal and associated braincase ele-
ments; ROM 30099, a supraoccipital; ROM 30100, a
partial right lower jaw; ROM 30101, a fragment of right
lower jaw with tooth plate; ROM 30102, middle third of
fragmentary right lower jaw; ROM 30103, posterior half of
right lower jaw; ROM 44627, a nearly complete skull.
Materials assigned to C. laticeps (formerly Eocaptorbinus
laticeps Heaton, 1979; see Dodick and Modesto, 1995 for
discussion of synonymy) were examined for comparative
purposes. These skulls were described and illustrated by
Heaton (1979): OMNH 15101, 15102, 15012, and
15022. All are from the McCann Quarry of the Wellington
Formation (Sumner Group). Additional specimens assigned
to C. laticeps hy Heaton (1979) and available for examina-
tion include: MCZ 1483, from the Petrolia Formation
(Wichita Group) in Baylor County, Texas; and MCZ 1740
and 2804, from the Waggoner Ranch Formation (Wichita
Group) of Wilbarger and Wichita counties, respectively,
Texas.
Specimens of closely related captorhinid taxa were also
examined: MCZ 8727, a nearly complete skull of
Labidosaurus hamatus (Cope, 1895), from lowermost Clear
Fork deposits of Baylor County, Texas; University of Cali-
fornia Museum of Paleontology (UCMP) 35757 and
40209, holotype and referred specimen, respectively, of
Rhiodenticulatus heatoni (Berman and Reisz, 1986), from
the Lower Permian Cutler Formation near Arroyo de Agua,
New Mexico.
Additional institutional abbreviations: AMNH, Aneri-
can Museum of Natural History, New York; FMNH, Field
Museum of Natural History, Chicago.
DESCRIPTION
Skull roof
The morphology of the lacrimal (Figure 1) is largely as
described by Fox and Bowman (1966). However, the
lacrimal also has a tongue-like suborbital process that ex-
tends posteriorly almost to the level of the orbital midpoint.
This process is appressed to the medial surface of the anterior
process of the jugal. The same condition is present in C.
laticeps specimens OMNH 15101 and 15022. This feature
is shared also with Labidosaurus hamatus, Rhiodenticulatus
heatoni,znd Labidosaurikos meachami(Dodicka.ndModcsto,
1995), but it is absent in protorothyridids and araeoscelids.
Careful preparation of specimens attributed to other
captorhinid taxa may expand the distribution of this
apomorphy within the clade.
The medial process of the jugal is positioned
dorsomedially on the anterior ramus, and its dorsal surface
is confluent with the orbital margin (Figure 1). Accord-
ingly, the base of the anterior ramus of the jugal appears
transversely broad in dorsal view. This organization of the
jugal was recognized as a synapomorphy of C. laticeps and
C. aguti by Dodick and Modesto (1995). In all other
captorhinids in which the alary process can be observed, the
process is positioned midway between the orbital and ven-
tral margins of the jugal, and the dorsal surface of the
process is not confluent with the  orbital  margin.  The
MODESTO-NEW INFORMATION ON CAPTORHINUS
23
reconstruction of this bone by Heaton (1979) illustrates
the essential features of the Captorhinus jugal. However,
due to a slightly angled medial view, and because Heaton
appears to have emphasized the facet on the medial process
receiving the pterygoid, the confluent nature of the orbital
margin and the medial process is not evident in his recon-
struction in medial aspect (Heaton, 1979, Fig. 23B).
The ventral margins of the well preserved right maxilla of
ROM 44627 (Figure 2) and the isolated maxilla, ROM
30096 (Figure 3), are relatively straight except posteriorly,
where the tip curves slightly dorsally. As the maxilla is
laterally flexed in all captorhinids (Heaton, 1979), the
upward curvature observed here might simply be an artifact
of perspective. However, lateral flexure of the maxilla can
be seen quite clearly in isolated maxillae when observed in
ventral aspect, beginning well anterior to the point where
the maxilla begins to curve dorsally (Figure 3). The poste-
rior curvature of the ventral margin is slightly more pro-
nounced in the isolated bone ROM 30096. The latter is
larger than than that of ROM 44627, which intimates an
ontogenetic role in the observed posterior curvature. Up-
ward curvature of the maxilla does not appear to have been
universally present in C. agut% since de Ricqles and Bolt
(1983) illustrated a complete, disarticulated maxilla from
Fort Sill that is comparable in size to ROM 30096, but
clearly features a straight posterior end.
The postparietal is preserved in articulation with sur-
rounding skull roof bones in ROM 30097 (Figure 4) and
ROM 30098 (Figure 5). The postparietals of both speci-
mens have a very slender dorsal contribution to the poste-
rior margin of the skull table. The dorsal exposure of the
right postparietal of ROM 30097 is even partly sculpted by
the characteristic ridge-and-pitting of the other roofing
elements. This condition is also present in C. laticeps
specimen OMNH 15101, albeit less conspicuously. Pre-
sumably this is why it is not evident in Heaton's (1979, Fig.
12) illustration of that skull. The nature of the contact
between the postparietal and parietal appears to be quite
variable in both captorhinid taxa, as Fox and Bowman
(1966) report that it is not uncommon for the parietal to
cover the dorsal portion of the postparietal completely in
C. aguti.
A nearly complete squamosal is present in ROM 30098
(Figure 5). The occipital flange of the squamosal flares
posteroventrally at approximately 130 degrees to the plane
of the temporal portion. This is in strong contrast to
previous studies (Fox and Bowman, 1966; Gaffney, 1990),
which describe the occipital flange as aligned along the
frontal plane. Heaton (1979) described and restored the
occipital flange of C. laticeps as a vertically aligned struc-
ture, but examination of OMNH 15101 reveals that it too
was directed slightly posteriorly, and would have been
visible in both dorsal and lateral views.
Palate
What is visible of the palate of ROM 44627 (Figure 2) does
not appear to differ noticeably from those palatal elements
described and illustrated by Fox and Bowman (1966), or
those seen in reconstructions by de Ricqles and Bolt (1983)
and Gaffney (1990), except in the following details. The
palatine is slightly broader and the neighboring anterior
process of the pterygoid is concomitantly narrower in ventral
aspect, and the patch of small teeth on the transverse flange
of the pterygoid clearly does not reach the lateral margin of
the flange (contra de Ricqles and Bolt, 1983).
Examination of several disarticulated quadrates indicates
that there is no distinct accessory facet located along the
posterior margin of the medial condyle, as described by
Heaton (1979) for C. laticeps. What is visible of the medial
condyle of the right quadrate of OMNH 15101 does not
support Heaton's (1979) description of an accessory facet;
the articulating surface of the quadrate appears indistin-
guishable in both taxa.
Braincase
The new C. aguti braincase material was found to differ in
several respects from the description provided by Price
(1935). Accordingly, specimens which served as the basis of
Price's (1935) study were examined in order to determine
whether the differences seen in his description and figures
were genuine. Redescription of MCZ 1198 and MCZ 1199
is provided here only to correct that of Price (1935), and,
because he did not provide specimen drawings of this
material, MCZ 1198 and 1199 are illustrated here for the
first time. Two other specimens examined by Price (1935),
AMNH 4333 and 4338, preserve very little of the braincase
and therefore are not illustrated.
The basiparasphenoid of ROM 44627 (Figure 2) is the
best preserved of the available material. Although it is
incomplete, enough is preserved to demonstrate that the
maximum relative width of the parasphenoid is much greater
than previously described: the maximum transverse width is
twice that measured across the basipterygoid processes.
This is in strong contrast to previous interpretations (Price,
1935; Clark and Carroll, 1973), which restored the
parasphenoidal wings (basitubera) as relatively narrow
flanges. The basiparasphenoids examined by Price (1935)
are too damaged to estimate correctly the full extent of the
posterolateral wings; those of MCZ 1198 are heavily dam-
aged (Figure 6), and the ventral surface of the braincase has
been spalled off completely in AMNH 4338. On the other
hand, the left parasphenoidal wing of ROM 44627 is very
well preserved except for the posterolateral corner, which
has been raised marginally above the rest of the bone by an
underlying hyoid element. The lateral edge of the wing is
gently convex, whereas the posterior margin is finely serrate
except for a small notch located laterally. Isolated
basiparasphenoids are among the most commonly encoun-
tered braincase elements in the Fort Sill material, but their
PALEOBIOS, VOL. 18, NUMBERS 2&3, 1998
1 cm
Figure 1. Captorhinus aguti, ROM 44627. Dorsal view of skull. Abbreviations: a cr, anterior crista; al, alary process of dorsum sellae;
al pr, alar process; an, angular; bo, basioccipital; bpt pr, basipterygoid process; c, coronoid; d, dentary; d ss, sutural surface for dentary;
dl pr, dorsolateral process; dm pr, dorsomedial process; dor se, dorsum sellae; eo, exoccipital; f, frontal; f int ca, foramen
intermandibularis caudalis; f int me, foramen intermandibularis medius; f int or, foramen intermandibularis oralis; fe, femur; fi, fibula;
h, hyoid element; j, jugal; j ss, sutural surface for jugal; 1, lacrimal; 1 ss, sutural svirface for lacrimal; m, maxilla; mb, membranous
labyrinth; n, nasal; op, opisthotic; p, parietal; pf, postfrontal; pi, palatine; po, postorbital; pp, postparietal; pra, prearticular;
prf, prefrontal; prm, premaxilla; pro, prootic; ps, parasphenoid; pt, pterygoid; r, rib; q, quadrate; qj, quadratojugal; s, stapes; sa,
surangular; so, supraoccipital; sp, splenial; sq, squamosal; tr, trigeminal notch; v, vomer; vi, vidian foramen; ?, unidentified element.
MODESTO-NEW INFORMATION ON CAPTORHINUS
25
basitubera are never as well preserved as in ROM 44627.
Two small denticles are present on a slightly raised area of
the ventral surface of the parasphenoid (Figure 2). Warren
(1961) and Fox and Bowman (1966) also described
parasphenoidal denticles in C. aguti material from Fort Sill,
although the denticles were positioned slightly more anteri-
orly in their specimens, between the basipterygoid pro-
cesses and even encroaching upon the base of the cultriform
process. In dorsal view, the basisphenoid portion of the
basiparasphcnoid complex clearly does not contact the
basioccipital in MCZ 1198. Since the braincase of this
specimen is much smaller than that of ROM 44627, it
almost certainly represents that of a juvenile; accordingly, it
is possible that these two endochondral bones may have
contacted one another upon maturity, although this is not
demonstrable with available adult braincase material.
A fragmentary basiparasphenoid is preserved in associa-
tion with the partial skull roof ROM 30098. The well
preserved dorsum sellae and processi sellares of ROM
30098 (Figure 5) compare closely with those of MCZ 1198
(Figure 6). However, the paired alary processes that project
posterolaterally over the trigeminal notches are relatively
larger; this may be due to younger ontogenetic age of the
former. The slightly asymmetrical nature of the alary pro-
cesses may be attributable to differential ossification of the
pila antotica. The dorsum sellae and processus sellaris are
well preserved only in L. hamatus and L. meacbami (Dodick
and Modesto, 1995) among other captorhinids where this
region is known. Alary processes appear to be absent in
both taxa, which suggests that the presence of such pro-
cesses is most likely an apomorphy of Captorhinus.
Several nearly complete, disarticulated supraoccipitals
permit emendation of Price's (1935) description of this
element. The supraoccipitals available to him were heavily
damaged: that of MCZ 1198 is missing the entire dorsal
half of the bone, while the partial supraoccipital of MCZ
1199 is preserved as two fragments that were glued to-
gether incorrectly, giving the bone an incongruous shape;
this specimen was restored here (Figure 7) by matching the
complementary edges of the fragments precisely. Since the
new supraoccipitals are more complete than Price's (1935)
material, a typical isolated supraoccipital is described first,
followed by commentary of the material used by Price
(1935).
In posterior view, the supraoccipital is remarkably plate-
like, with the main body of the bone slightly wider than it is
tall (Figure 8A-D). The paired, lateral ascending processes
project dorsolaterally well beyond the lateral margins of the
supraoccipital proper. Price (1935) restored the supraoc-
cipital incorrectly as a tranversely broad, dorso-ventrally
compressed bone with relatively short lateral ascending
processes. Due to the flawed physical restoration of MCZ
1199, he was unable to reconstruct the height of the
supraoccipital correctly. Although the supraoccipital proper
is slightly curved in horizontal section, this is not easily
apparent in complete specimens, but can be seen in MCZ
1198 in dorsal view (Figure 6). Apart from the median
ascending process, the anterodorsal margin of the bone is
relatively straight, and there are no discrete flanges that
project anteriorly from the main body of the supraoccipital
to contact the prootics. In anterior view, the membranous
labyrinth of the middle ear can be seen to traverse the entire
dorsoventral height of the area contacting the prootic.
Nutritional foramina occupy the dorsal surface of the su-
praoccipital to either side of the median ascending process.
These are usually present as relatively large openings, but
may also occur as a group of smaller, closely positioned
foramina, as seen on the left side of ROM 30099. Such
foramina are not present on the supraoccipital of L.
hamatus, the only other captorhinid in which this area of
the braincase can be examined. Lastly, the median ascend-
ing process appears to form from the fusion of three
separate dorsal projections, as evidenced by the smooth
crevices of bone seen in dorsal view between the broken
surfaces of the median process in ROM 30099. In slightly
larger (and presumably adult) specimens, the median as-
cending process is present as a single, inverted trough-like
structure. What is preserved of the supraoccipitals of MCZ
1198 and MCZ 1199 examined by Price (1935) is indistin-
guishable from the new material described here.
Mandible
The dentary (Figure 9A-E) has a deep lingual exposure
immediately posterior to the area forming the symphysis.
This appears to be true of C. laticeps as well, judging from
OMNH 15101 and 15102, although Heaton restored the
dentary (erroneously) as having a very narrow exposure
anteriorly in lingual view (Heaton, 1979, Fig. 30). The
meckelian canal (the foramen intermandibularis medius of
some authors) is open anteriorly in both captorhinid taxa. In
lateral aspect, the dentary of C. aguti overlaps the angular
slightly and the surangular more broadly (Figure 9E, F). In
contrast to the illustrations in Gaffney (1990), the dentary is
not broadly separated from the coronoid by the surangular.
The same condition is present also in C. laticeps specimens
OMNH 15101 and 15102, although Heaton (1979) erro-
neously restored the posterior end of the dentary of C.
laticepsintarposcd between the anterior ends of the surangular
and the angular.
The morphology of the splenial of C. aguti (Figure 9A-
D) is essentially as restored by de Ricqles and Bolt (1983).
Judging from what is visible in OMNH 15101 and 15102,
the splenial of C. laticeps appears indistinguishable from
that of C. aguti. In both taxa, the anterior end of the
splenial is slightly hooked in lingual view, where it forms
the ventral margin of the foramen intermandibularis medius
(Figure 9B). Heaton (1979) restored the anterior end of
this bone incorrectly for C. laticeps with an undivided
suture between the splenial and dentary.
26
PALEOBIOS, VOL. 18, NUMBERS 2&3, 1998
The coronoid was described accurately by Fox and Bow-
man (1966) as extending far anteriorly along the lingual
surface of the jaw; this is accomplished by a narrow anterior
process which extends as far as the foramen
intermandibularis oralis (Figure 9D). The coronoid of C.
laticeps exhibits the same condition in each specimen in
which the anterior end of the mandible can be examined in
lingual view (OMNH 15101, 15102, and 15022). Al-
though recognizing the the presence of the anterior process
in C. laticeps, Heaton (1979) did not realize the actual
length of the anterior process of the coronoid in that
captorhinid, and restored it falling well short of the fora-
men intermandibularis oralis (Heaton, 1979, Fig. 30).
Labidosaurus hamatus and .R. heatoni also possess elongate
anterior coronoid processes. Immediately adjacent to the
last dentary tooth, the suture with the dentary is distinctly
"stepped" in dorsal view (Figure 9C), while the
posterodorsal process of the coronoid is bifurcated posteri-
Figure 2. Captorhinus aguti, ROM 44627. Ventral view of skull. For key to abbreviations, see Figure 1.
MODESTO-NEW INFORMATION ON CAPTORHINUS
27
5mm
Figure 3. Captorhinus aguti, ROM 30096. (A) lateral and (B)
ventral views of partial right maxilla. For key to abbreviations, see
Figure 1.
orly by the surangular (Figure 9E). Both conditions are
present in C. laticeps (OMNH. 15021), L. bamatus, and L.
meachami (Dodick and Modesto, 1995). Unfortunately,
these apomorphies cannot be determined in basal
captorhinids, and so they must be regarded as ambiguous
synapomorphies of the more recently derived taxa.
The angular is slightly more elongate antero-posteriorly
than previously recognized. The anterior tip of this bone
attenuates sharply and ends at a level approximately halfway
between the two meckelian foramina (Figure 9A, B). Poste-
riorly, the angular attenuates to a sharp tip that makes only
a minor contribution to the base of the retroarticular
process (Figure 9F). The same condition is seen in C.
laticeps specimens OMNH 15101 and 15022 (contra
Heaton, 1979), whereas that of OMNH 15102 is broadly
tipped posteriorly, with a slightly deeper contribution to
the retroarticular process than that of the surangular. The
second condition appears to be more primitive of the two,
as it is seen also in basal captorhinids (Clark and Carroll,
1973).
As mentioned above, the sutural relationships of the
surangular to both the coronoid and dentary do not differ
remarkably from those of other captorhinids. The posterior
end of the surangular is slightly taller than restored in
published reconstructions of the mandible (de Ricqles and
Bolt, 1983; Gaffney, 1990), and it sheathes the dorsal two-
thirds of the lateral surface of the articular, including the
base of the retroarticular process (Figure 9F). Examination
of the McCann Quarry specimens reveals that the surangular
of C. laticeps is indistinguishable from that of C. aguti.
None of available McCann Quarry specimens supports
Heaton's (1979) description of the surangular as having an
PP    ^
5 mm
Figure4. Captorhinusaguti, ROM 30097. (A) ventral; (B) dorsal;
and (C) posterior views of partial skull table. For key to abbrevia-
tions, see Figure 1.
extensive lateral contact with the coronoid, or an acuminate
posterior end that contributes little to the retroarticular
process. Interestingly, Heaton's (1979) specimen drawings
of C. laticeps illustrate the correct morphology of the
surangular, but they are at variance with his description and
reconstructions of that element.
The new C. aguti material confirms the general descrip-
tion of the articular by Fox and Bowman (1966). There is
no "accessory articulating facet" on the posterodorsal boss
of the articular in C. aguti (Figure 9G), as described by
Heaton (1979) for C. laticeps. Furthermore, an "accessory
articulating facet" is discernible in neither OMNH 15101
nor 15102, the only specimens of C. laticeps in which the
articulating surface of the articular is adequately exposed.
Judging from the available materials of both taxa, the
articular of C. laticeps is not distinguishable from that of C.
aguti.
28
PALEOBIOS, VOL. 18, NUMBERS 2&3, 1998
Figure 5. Captorhinus aguti, ROM 30098. (A) dorso lateral and
(B) posterior views of skull roof. (C) anterior view of the
basiparasphenoid seen in B. For key to abbreviations, see Figure 1.
Dentition
The premaxillary dentition of Captorhinus aguti, well illus-
trated by de Ricqles and Bolt (1983), does not differ
noticeably from that described for C. latkeps (Heaton,
1979). However, Heaton's (1979) interepretation of lingual
wear facets on the distal tip of the teeth as wear facets is in
error, as similar excavations are present on well preserved
teeth from the single-rowed regions of the dentition of C.
aguti specimens from Fort Sill, and on the maxillary and
dentary teeth of an indeterminate basal captorhinid also from
the Fort Sill locality (Modesto, 1996a). The shallow excava-
tions accentuate anterior and posterior cutting edges present
on the distal third of anterior and lateral teeth in these
captorhinids (Modesto, 1996a). Because dentigerous
captorhinid elements collected from Fort Sill commonly bear
conspicuous, presumably premortem wear that has dulled
the cutting edges, it is understandable that Heaton (1979)
interpreted the lingual excavations as wear facets, especially
so in mechanically-prepared material. Accordingly, the hy-
pothesis of low-fibre herbivory for C. latkeps, based on the
interpretation that the lingual excavations are the result of
tooth-to-tooth occlusion and advanced recently by Hotton
et al. (1997), now appears rather tenuous. Tooth wear in
captorhinids is manifested in three ways: (1) pitting and
gouging of cheek-tooth crowns and, more rarely, conspicu-
ous facets as the result of tooth-to-tooth contact, thus far
exhibited only by the cheek teeth of many, but not in all
individuals of multiple-rowed species (Hotton et al., 1997);
(2)  a conspicuous facet on the labial surface of the first
premaxillary tooth in both Captorhinus and Labidosaurus,
attributed to grubbing action by Hotton et al. (1997); and
(3)   dulling of the anterior and posterior cutting edges
acquired presumably during normal feeding processes
(Modesto, 1996a).
The presence or absence of multiple-tooth rows in the
maxillary and dentary dentitions was the sole characteristic
used by Heaton (1979) to distinguish C. latkeps Worn C.
aguti, a diagnosis that assumes tooth morphology to be
indistinguishable in the two taxa. However, close inspec-
tion of teeth in corresponding regions of the maxilla reveals
that posterior cheek teeth of C. aguti are easily distinguish-
able from those of C. latkeps (Figure 10A, B). Those in the
latter captorhinid are relatively tall: each tooth has a length
(from base to apex) about 80 percent greater than its
mesiodistal basal diameter (Figure 10A). The distal end of
each tooth bears a triangular tip, albeit not as acute in
lateral view as in teeth of basal captorhinids (Modesto,
1996a), which gives rise to cutting edges that extend
almost halfway down to the base of the tooth, where they
become confluent with the mesial and distal surfaces of the
tooth. In anterior view the cheek teeth of C. latkeps are
seen to be distinctly triangular, with slightly sigmoidal
lingual and convex labial margins (Figure 10B).
Teeth resembling those described here for C. latkeps are
not commonly seen in the multiple-rowed regions of C.
aguti. When they are present such teeth always occupy the
first position in one of the posteriormost tooth rows. Thus,
these teeth are invariably small and never reach the absolute
size of those in equivalent positions in C. latkeps specimens
of similar skull size. In contrast to the tooth morphology
described for C. latkeps, the overwhelming majority of
teeth forming the multiple rows in C aguti are conspicu-
ously stout and slightly bulbous (Figure IOC); they are
distinctly ogival in frontal aspect, and unlike the marginal
teeth of single-rowed captorhinids, the lingual and labial
sides of the ogival teeth of C. aguti are indistinguishable
(Figure 10D). They are also relatively shorter than those of
other small captorhinids, with mesiodistal basal diameters
subequal to, or slightly greater than, their respective height.
A discrete point or tip is rarely present on the apex of an
ogival tooth (when the tooth is viewed in lateral aspect),
and the cutting edge is strictly terminal and aligned hori-
zontally.
MODESTO-NEW INFORMATION ON CAPTORHINUS
29
5mm
Figure 6. Captorhinus aguti, MCZ 1198. (A) ventral; (B) dorsal; (C) left lateral; and (D) posterior views of partial braincase. For key
to abbreviations, see Figure 1.
DISCUSSION
Functional and phylogenetic implications of the new
material
The exquisite, albeit fragmentary, preservation of the Fort
Sill material permits a more comprehensive understanding of
jaw morphology and action in a small captorhinid than was
previously possible with referred redbed material. The above
description of the lower jaw in C. aguti contrasts greatly with
recent interpretations on the sutural relationships of the
mandibular elements (Heaton, 1979; Gaffney, 1990), al-
though this may be attributed to the poorly preserved or
inadequately exposed material available to earlier workers.
Importantly, the Fort Sill material demonstrates that the
lower jaw of C. aguti does not differ notably from those of
Rhiodentkulatus, Labidosaurus, and Labidosaurikos. The
strong similarity in lower jaw morphology in such a wide
range of skull sizes highlights the remarkably conservative
nature of captorhinid morphology.
The prevailing belief in a conservative skeletal design
among captorhinid reptiles may have overshadowed an
intriguing functional hypothesis attributed to jaw action in
C. laticeps. Heaton (1979) described the presence of acces-
sory articulating facets on the quadrate and the articular of
C. laticeps, and interpreted their presence as part of a
jaw-locking mechanism. In order for the mouth to open,
Heaton (1979) postulated that the lower jaws had to be
pulled slightly posteriorly in order to disengage the facets
and permit the anteriormost dentary teeth to clear the
larger premaxillary dentition. However, the absence of
accessory articulating facets in the Fort Sill and McCann
Quarry materials does not support that hypothesis. Fur-
thermore, it is highly unlikely that the anteriormost dentary
tooth required any kind of special mechanism to clear the
larger first premaxillary tooth, whether or not the lower jaw
of Captorhinus was capable of the minor fore-and-aft trans-
lation he attributed to it: although the long axis of the first
premaxillary tooth is directed posteroventrally in the prop-
erly oriented premaxilla, the lingual edge of the tooth
(when viewed laterally) is vertical (Heaton, 1979, Fig. 7; de
Ricqles and Bolt, 1983, Fig. 2). Accordingly, there is no
"pocket" where the first dentary tooth could be "trapped."
The lower jaw therefore appears to have been able to clear
30
PALEOBIOS, VOL. 18, NUMBERS 2&3, 1998
Figure 7. Captorhinus aguti, MCZ 1199. (A) posterior and (B)
anterior views of articulated supraoccipital and left opisthotic. For
key to abbreviations, see Figure 1.
the first premaxillary tooth via simple orthal movement, as
in other early amniotes. Use of Fort Sill specimens to reject
Heaton's (1979) hypothesis of a propaliny-based
jaw-locking mechanism in C. laticeps is not unjustified,
since Heaton (1979) used Fort Sill material to supplement
his original description of the jaw suspension of C. laticeps.
Possibly the "accessory articular facets" observed by Heaton
(1979) are artifacts of poorly preserved or ill-prepared Fort
Sill specimens; as described above, no facets are present in
the McCann Quarry specimens of C. laticeps.
The descriptive work of Price (1935) and Heaton (1979)
has made the braincase of Captorhinus among the best
known among early reptiles. Accordingly, the braincase of
this captorhinid has served as a prime example of basal
amniote braincase design (Gaffney, 1990; Clack, 1993).
However, the new material reveals that some aspects of the
braincase of Captorhinus have been misinterpreted, par-
ticularly the general organization of the basiparasphenoid
and the supraoccipital.
The absence of parasphenoid wings is regarded by Laurin
and Reisz (1995) as one of several skeletal characters that
diagnose Reptilia; these authors use the term "wing" to
describe the greater posterolateral extent of the
parasphenoid basitubera seen in many basal cotylosaur taxa.
Their usage differs with that of other workers (e.g. Olson,
1947) who employ the term when referring merely to
either of the basitubera, a practice that is followed in this
paper. Indeed, maximum parasphenoid breadth in
captorhinids, when measured against the minimum breadth
of the bone (across the "neck" lying immediately posterior
to the basipterygoid processes), does not differ greatly from
that seen in synapsids and mesosaurs (Modesto, 1996b).
The presence of a broad parasphenoidal wings in C. atjuti
and other captorhinids suggests strongly that the evolution
of this character within Reptilia is more complicated than
outlined by Laurin and Reisz (1995).
The presence of laterally extensive basitubera in ROM
44627 implies that Price's (1935) and Heaton's (1979)
interpretations of the contact between the parasphenoid
and the stapes (where the stapedial footplate sits partly
within in a deep posterolateral notch of the former bone)
are incorrect. If the basiparasphenoid of ROM 44627 is
superimposed onto either braincase reconstruction, the
stapedial footplates would be deeply sheathed in ventral
view by the parasphenoidal wings. Interestingly, an over-
lapping suture is present between these two elements in the
large multiple-rowed captorhinid Labidosaurikos meachami
(Dodick and Modesto, 1995). This feature may be present
in Captorhinus, and if so, might represent a synapomorphy
that diagnoses a clade within Captorhinidac. Unfortunately,
the absence of a complete articulated braincase precludes a
detailed description of the relationship between the stapes
and braincase in Captorhinus.
Lastly, the disarticulated nature of the Fort Sill
Captorhinus material permits the reevaluation of an inter-
esting character of the reptilian braincase that has appeared
in recent phylogenetic studies: the presence of the crista
alaris (anterior crista), an anterodorsal flange formed sup-
posedly by the articulated prootic and supraoccipital
(Heaton, 1979, pp. 52-53). The anterior crista is ascribed
generally only to the supraoccipital by recent workers, the
presence of which is regarded as a reptilian synapomorphy
(Heaton and Reisz, 1986; Gauthier et al., 1988; Laurin and
Reisz, 1995). In lizards, the anterior crista is a thin vertical
flange that projects anterodorsally from the prootic portion
of the alar process, of which the latter extends dorsally well
above the anterior semicircular canal and membranous
labyrinth (Oelrich, 1956, p. 15); the alar process continues
posteriorly onto the supraoccipital, where it comprises
more than half the height of the anterior margin of this
bone (Figure 8E, F). Heaton (1979) applied the term
"crista alaris" to the anterodorsal margin of articulated
prootic and supraoccipital of captorhinids. However, the
disarticulated captorhinid supraoccipitals described here re-
veal clearly that although the anterolateral margin of the
supraoccipital is slightly thickened where it contacts the
prootic, it does not project anterodorsally as a discrete-
process. Concomitantly, the membranous labyrinth is a
large trough that runs down the entire region abutting the
prootic (Figure 8B). This arrangment is in strong contrast
to the relatively small, ventrally positioned membranous
MODESTO-NEW INFORMATION ON CAPTORHINUS
31
labyrinth of the lacertalian supraoccipital (Figure 8E). The
absence of an alar process on the supraoccipital of
Captorhinus implies that anterior cristae were not present.
In other Permo-Carboniferous reptiles this area of the
braincase is not remarkably different from the condition
seen in Captorhinus, implying that they too lack anterior
cristae. Similarly, Evans (1986; 1987) reports that neither
an alar process nor a crista alaris is present in the diapsid
taxa Toungina (Broom, 1914) and Prolacerta (Parrington,
1935). Accordingly, the presence of an alar process and/or
the crista alaris appears to be a synapomorphy of a much
less inclusive clade of reptiles.
Systematics of small captorhinids
Information provided by the new Fort Sill specimens of
Captorhinus aguti and by reexamination of previously de-
scribed materials of C. laticeps resurrects an old quandary: is
the latter binomen a junior synonym of the former? Gaffhey
and McKenna (1979) originally questioned the taxonomic
status of C. laticeps (formerly Eocaptorhinus laticeps), inti-
mating that Heaton (1979) ignored possible morphological
variation in C. aguti in order to justify the recognition of a
new genus. The taxonomic dilemma posed by Eocaptorhinus
thus appeared to be a timely example of the difficulty in
reconciling paleontological species with the biological spe-
cies concept (Gaffney and McKenna, 1979). Gaffney (1990)
later synonymized Eocaptorhinus with Captorhinus, but,
oddly, ignored the status of its only assigned species, E.
laticeps. Following a cladistic analysis of captorhinids in
which the single-rowed species redescribed by Heaton (1979)
formed a sister-group relationship with C. aguti, Dodick and
Modesto (1995) were able to recognize formally the new
combination C. laticeps. Regardless, Dodick and Modesto
(1995) did not discuss the possibility that the single-rowed
and multiple-tooth rowed forms were conspecific.
Recent advances in our knowledge of captorhinid
anatomy and phylogeny (Berman and Reisz, 1986; Dilkes
and Reisz, 1986; Sumida, 1987; 1990; Dodick and
Modesto, 1995) warrant a brief reconsideration of the
systematics of the small, non-moradisaurine captorhinids.
Captorhinus aguti has generally been recognized to have
succeeded its sister species C. laticeps both temporally and
geographically (Heaton, 1979). Attributing single-rowed
dentigerous elements from Fort Sill to C. laticeps, Heaton
(1979) believed that the two taxa co-occurred at the local-
ity, yet cautioned that there was no evidence that the two
were contemporaneous: owing to the lack of stratigraphic
control at the collecting site, he argued that it is impossible
to determine if the single-rowed and multiple-rowed speci-
mens were preserved in the same horizons in the fissures.
On the other hand, Bolt (1980) attributed all single-rowed
Fort Sill elements to C. aguti, thereby eliminating
C. laticeps from any deliberation of the Fort Sill fauna.
Considering that the number of tooth rows frequently vary
between jaws of the same individual of C. aguti and that
single-rowed elements are very rare at Fort Sill (Bolt and
DeMar, 1975), Bolt's (1980) assessment merits further
consideration. Evidence supporting Bolt (1980) comes
from the observation that the single-rowed dentary illus-
trated by Bolt and DeMar (1975) preserves ogival teeth
that are identical to those of C. aguti specimens described
in the present study. Thus, the specimen (FMNH 949)
described and illustrated by Bolt and DeMar (1975) dem-
onstrates that marginal dentition in C. aguti varied from a
al pr
5 mm
Figure 8. Reptile supraoccipitals. (A) posterior; (B) anterior; (C) dorsal; and (D) left lateral views of ROM 30099, an isolated
supraoccipital of Captorhinus aguti. (E) anterior and (F) left lateral views of the supraoccipital of Iguana iguana (private collection).
For key to abbreviations, see Figure 1.
32
PALEOBIOS, VOL. 18, NUMBERS 2&3, 1998
A
giB»'g»ia«i^|ifp'\j p
Figure 9. Captorhinus agutilowei jaw fragments. (A) lateral and (B) medial views of ROM 30100, a partial right mandible. (C) dorsal
and (D) medial views of ROM 30101, a right mandibular tooth plate. (E) lateral view of ROM 30102, the mid-section of a right mandible.
(F) lateral and (G) medial views of ROM 30103, a partial right mandible. For key to abbreviations, see Figure 1.
single row up to a maximum of eight rows (de Ricqles and
Bolt, 1983). There is, however, no evidence as yet that any
individual of C. aguti, i.e., a small captorhinid with ogival
teeth, possessed a single row of teeth in each of the four
jaws. Given the conspicuous absence of ogival teeth in the
McCann Quarry skulls and other C. laticeps specimens
examined by the author, it is unlikely that C. laticeps is
represented by the other single-rowed dentigerous ele-
ments examined by Bolt and DeMar (1975). Similarly,
several isolated, single-rowed dentaries collected by Berman
(1970) from the Lueders Formation of Texas were re-
garded by Heaton (1979) as indistinguishable from the
single-rowed Captorhinus specimens at Fort Sill. Since
these specimens (Berman, 1970, pi. 9) also possess ogival
teeth, they are hereby removed from the hypodigm of C.
laticeps and transferred to that of C. aguti; this action has
the concomitant effect of increasing slightly the strati-
graphic range of the latter species, now ranging from the
Lueders Formation through to the middle Clear Fork
Group (upper "Vale Formation" of earlier literature), at the
expense of that of its sister taxon.
Although the posterior cheek teeth of C. laticeps indeed
differ from those of single-rowed C. aguti, they appear to
display a morphology intermediate between the ogival teeth
of C. aguti on one hand and that exemplified by basal
captorhinids (Modesto, 1996a) on the other. Coupled with
the complete absence of cranial autapomorphies, the transi-
tional nature of dental morphology of C. laticeps would
appear to furnish additional evidence that this lineage might
be ancestral to C. aguti. However, the postcranial skeleton
of the former taxon has become better known since Heaton
(1979) and Heaton and Reisz (1980), and at least one
MODESTO-NEW INFORMATION ON CAPTORHINUS
33
Figure 10. Captorhinusdentition. (A) labial and (B) mesial views
of maxillary teeth 11-14 of OMNH 15101, C. laticeps. (C) lingual
and (D) distal views of posterior teeth comprising the second and
third tooth rows in the left maxilla of OMNH 15138, C. aguti.
Teeth illustrated are from the same region on the jaw in both
specimens, i.e., immediately posterior to the level of the antorbital
buttress.
autapomorphy has surfaced: the presence of overhanging
midventral "lips" on the presacral pleurocentra (Dilkes and
Reisz, 1986; Sumida, 1990). Following the tenets of the
phylogenetic species concept (Cracraft, 1983; Donoghue,
1985), the presence of a single autapomorphy allows
C. laticeps to be recognized as a valid species.
Taxonomic status remains to be validated for a number
of other small, single-rowed captorhinids. Specimens as-
signed to Proto-captorhinus pried (Clark and Carroll, 1973)
are currently being redescribed, and an undescribed
Waggoner Ranch Formation captorhinid (FMNH 183) is
undergoing formal description (S. Sumida, personal com-
munication). Hopefully these studies will resolve the rela-
tionships of those two captorhinids in particular and
strengthen captorhinid phylogeny in general. The identity
of an indeterminate basal captorhinid from Fort Sill awaits
discovery of more complete materials (Modesto, 1996a).
Two species of the early captorhinid genus Romeria
have been described. Romeria texana was erected by Price
(1937) for a single, partial skull; a more complete specimen
with a smaller skull was later referred to this taxon by Clark
and Carroll (1973). A second species, R. prima, was erected
by Clark and Carroll (1973) for a complete skull and
associated postcrania that were collected from beds slightly
older than those producing the skulls assigned to R. texana.
Neither species of Romeria is currently diagnosed by
autapomorphies, nor do they share apomorphies that may
be used to diagnose the genus itself. Romeria prima was
originally distinguished from R. texana on (meristic) mor-
phological and stratigraphic grounds by Clark and Carroll
(1973). The first premise used to separate the species
(difference in the number of marginal teeth) is no longer
compelling given that premaxillary and maxillary tooth
counts in both types are now known to vary only by a single
tooth in each bone (Heaton, 1979; contra Clark and
Carroll, 1973) and that equivalent variation is seen in other
single-rowed captorhinids (Heaton, 1979). Specific separa-
tion on stratigraphic grounds could also be considered
unjustified, considering that the distance between the old-
est and youngest stratigraphic occurrences of specimens
assigned to Romeria is probably no greater than that
known for other small captorhinids (Clark and Carroll,
1973, Fig. 22). However, the apparent absence of shared
or unique apomorphies in these specimens precludes any
formal synonymization at this time. Because the type speci-
men of R. prima preserves far more of the skeleton than
does that of R. texana, careful reexamination may reveal
autapomorphies of the former species but none in the
latter. If so, both the genus Romeria and its species R.
texana should be declared nomina dubia, and a new generic
name created to receive the holotype of R. prima.
ACKNOWLEDGMENTS
I am indebted to Dr. Robert Reisz and Ms. Heather Wilson,
who collected much of the material described herein; Dr.
Reisz also generously provided workspace and facilities for
the present study and made many helpful comments on an
early version of the paper. Muchas gracias to Dr. David
Berman for discussion of the Lueders captorhinid material.
Sincere thanks go to Mr. Bill May who provided enthusiastic
and indispensible assistance during collecting at Fort Sill.
Drs. Hans-Dieter Sues and Richard Cifelli and Mssrs. Kevin
Seymour and Charles Schaff arranged loans of specimens.
Dr. Eugene Gaffhey kindly provided photographs of Cope
Collection specimens and critiqued an earlier version of the
manuscript. Dr. Robert Carroll kindly provided comments
that improved the clarity of the study.
34
PALEOBIOS, VOL. 18, NUMBERS 2&3, 1998
LITERATURE CITED
Berman, D. S. 1970. Vertebrate fossils from the Lueders Forma-
tion, Lower Permian of north-central Texas. University of
California Publications in Geological Sciences 86, 39pp.
Berman, D. S and R. R. Rcisz. 1986. Captorhinid reptiles from
the Lower Permian of New Mexico, with description of a new
genus and species. Annals of the Carnegie Museum 55:1-28.
Bolt, J. R. 1980. New tetrapods with bicuspid teeth from the
Fort Sill locality (Lower Permian, Oklahoma). Neues Jahrbuch
fur Geologic und Palaontologie, Monatshefte 8:449-459.
Bolt, J. R. and R. E. DeMar. 1975. An explanatory model of the
evolution of multiple rows of teeth in Captorhinus aguti.
Journal of Paleontology 49:814-832.
Broom, R. 1914. A new thecodont reptile. Proceedings of the
Zoological Society of London 1914:1072-1077.
Clack, J. A. 1993. Flomologies in the fossil record: The middle
ear as a test case. Acta Biotheoretica 41:391-409.
Clark, J. and R. L. Carroll. 1973. Romeriid reptiles from the
Lower Permian. Bulletin of the Museum of Comparative
Zoology 143:321-363.
Cope, E. D. 1882. Third contribution to the history of the
Vertebrata of the Permian formation of Texas. Proceedings of
the American Philosophical Society 20:447-461.
Cope, E. D. 1895. The reptilian order Cotylosauria. Proceedings
of the American Philosophical Society 34:436-457.
Cracraft, J. 1983. Species concepts and speciation analysis, pp.
159-187 in R.F. Johnston (ed.). Current Ornithology. Ple-
num Press, New York.
Dilkes, D. W. and R. R. Reisz. 1986. The axial skeleton of the
Early Permian reptile Eocaptorhinus laticeps (Williston). Cana-
dian Journal of Earth Sciences 23:1288-1296.
Dodick, J. T. and S. P. Modesto. 1995. The cranial anatomy of
the captorhinid reptile Labidosaurikos meachami from the
Lower Permian of Oklahoma. Palaeontology 38:687-711.
Donoghue, M. J. 1985. A critique of the biological species
concept, and recommendation for a phylogenetic alternative.
The Bryologist 88:172-181.
Evans, S. E. 1986. The braincase of Prolacerta broomi (Rcptilia,
Triassic). Neues Jahrbuch fiir Geologie und Palaontologie,
Abhandlungen 73:181-200.
Evans, S. E. 1987. The braincase of Toungina capensis (Rcptilia;
Diapsida; Permian). Neues Jahrbuch fiir Geologie und
Palaontologie, Monatshefte 4:193-203.
Fox, R. C. and M. C. Bowman. 1966. Osteology and relation-
ships of Captorhinus aguti (Cope) (Reptilia:
Captorhinomorpha). University of Kansas Paleontological
Contributions, Vertebrata 11:1-79.
Gaffney, E. S. 1990. The comparative osteology of the Triassic
turtle Proganochelys. Bulletin of the American Museum of
Natural History 194:1-263.
Gaffney, E. S. and M. C. McKcnna. 1979. A Late Permian
captorhinid from Rhodesia. American Museum Novitates
2688, 15pp.
Gauthier, J. A., A. G. Kluge, and T. Rowe. 1988. The early
evolution of the Amniota. pp. 103-155 inM. J. Benton (ed.).
The Phylogeny and Classification of the Tetrapods, Volume 1.
Amphibians, Reptiles, Birds. Systematics Association Special
Volume No. 35A. Clarendon Press, Oxford.
Heaton, M. J. 1979. Cranial anatomy of primitive captorhinid
reptiles from the Late Pennsylvanian and Early Permian Okla-
homa and Texas. Oklahoma Geological Survey, Bulletin
127:1-84.
Heaton, M. J. and R. R. Reisz. 1980. A skeletal reconstruction of
the Early Permian captorhinid reptile Eocaptorhinus laticeps
(Williston). Journal of Paleontology 54:135-143.
Heaton, M. J. and R. R. Reisz. 1986. Phylogenetic relationships
of captorhinomorph reptiles. Canadian Journal of Earth Sci-
ences 23:402-418.
Hentz, T. F. 1988. Lithostratigraphy and paleoenvironments of
Upper Paleozoic continental redbeds, north-central Texas:
Bowie (new) and Wichita (revised) Groups. University of
Texas at Austin, Bureau of Economic Geology Report of
Investigations 170:1  55.
Holmes, R. B. 1977. The osteology and musculature of the
pectoral limb of small captorhinids. Journal of Morphology
152:101-140.
Hotton, N. C, III, E. C. Olson, and R. Beerbower. 1997.
Amniote origins and the discovery of herbivory. pp. 207-264
in S. S. Sumida and K. L. M. Martin (eds.). Amniote Origins:
Completing the Transition to Land. Academic Press, San
Diego.
Laurin, M. and R. R. Reisz. 1995. A reevaluation of early
amniote phylogeny. Zoological lournal of the Linncan Society
113:165-223.
Laurin, M. and R. R. Reisz. 1997. A new perspective on tetrapod
phylogeny. pp. 9-59 in S. S. Sumida and K. L. M. Martin
(eds.). Amniote Origins: Completing the Transition to Land.
Academic Press, San Diego.
Modesto, S. P. 1996a. A basal captorhinid reptile from the Fort
Sill fissures, Lower Permian of Oklahoma. Oklahoma Geology
Notes 56:4-14.
Modesto, S. P. 1996b. The anatomy, relationships, and
palacoecology of Mesosaurus tenuidens and Stereostcrnum
tumidum (Amniota: Mesosauridae) from the Lower Permian
of Gondwana. Unpublished Ph.D. thesis, University of
Toronto. 279 pp.
Oelrich, T. M. 1956. The anatomy of the head of Ctenosaura
pectinata (Iguanidae). University of Michigan, Museum of
Zoology Miscellaneous Publications 94:1-167.
Olson, E. C. 1947. The family Diadcctidae and its bearing on the
classification of reptiles. Fieldiana: Geology 11:1-53.
Olson, E. C. 1991. An eryopid (Amphibia: Labyrinthodontia)
from the Fort Sill fissures, Lower Permian, Oklahoma. Journal
ofVertebrate Paleontology 11:130-132.
Parrington, F. R. 1935. On Prolacerta broomi gen. ct sp. nov.
and the origin of lizards. Annals and Magazine of Natural
History 16:197-205.
MODESTO-NE W INFORMATION ON CAPTORHINUS
35
Price, L. I. 1935. Notes on the braincase of Captorhinus. Pro-
ceedings of the Boston Society of Natural History 40:377-
386.
Price, L. I. 1937. Two new cotylosaurs from the Permian of
Texas. Proceedings of the New England Zoological Club
16:97-102.
Ricqles, A. de and J. R. Bolt. 1983. Jaw growth and tootli
replacement in Captorhinus aguti (Reptilia:
Captorhinomorpha): A morphological and histological analy-
sis. Journal of Vertebrate Paleontology 3:7-24.
Rieppel, O. 1993. Studies on skeleton formation in reptiles. IV.
The homology of the reptilian (amniote) astragulus revisited.
Journal of Vertebrate Paleontology 13:31-47.
Romer, A. S. 1974. The stratigraphy of the Permian Wichita
redbeds of Texas. Breviora 427:1-31.
Sumida, S. S. 1987. Two different vertebral forms in the axial
column of Labidosaurus (Captorhinomorpha: Captorhinidae).
Journal of Paleontology 61:155-167.
Sumida, S. S. 1990. Vertebral morphology, alternation of neural
spine height, and structure in Permo-Carboniferous tetrapods,
and a reappraisal of primitive modes of terrestrial locomotion.
University of California Publications in Zoology 122:1-
129.Warren, J. L. 1961. The basicranial articulation of the
Early Permian cotylosaur Captorhinus. Journal of Paleontol-
ogy 35:561-563.
Williston, S. W. 1909. New or little known Permian vertebrates:
Pariotichus. Biological Bulletin 17:241-255.