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ANNALS OF THE SOUTH AFRICAN MUSEUM

ANNALE VAN DIE SUID-AFRIKAANSE MUSEUM

Volume 69 Band

June 1976 Junie

Part 10 #£Deel

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TRESS

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NOTES ON THE ADDUCTOR JAW MUSCULATURE

OF VENJUKOVIA, A PRIMITIVE ANOMODONT

THERAPSID FROM THE PERMIAN OF THE USS.S.R.

HERBERT R. BARGHUSEN

Cape Town Kaapstad

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NOTES ON THE ADDUCTOR JAW MUSCULATURE OF VENJUKOVIA,

A PRIMITIVE ANOMODONT THERAPSID FROM THE PERMIAN

OF THE U.S.S.R.

HERBERT R. BARGHUSEN

Departments of Anatomy and Oral Anatomy, University of Illinois Medical

Center, Chicago, Illinois 60680

(With 4 figures)

[MS accepted 9 March 1976]

ABSTRACT

The primitive anomodont Venjukovia, from Zone II of the Russian Permian, has been

thought to bridge the morphological gap between dinocephalians and dicynodonts. Much

of the pattern of adductor jaw musculature in Venjukovia conforms closely to that found in

dicynodonts and is thereby consistent with the hypothesis that these are closely related forms.

The most important similarity is the probable presence in Venjukovia of a distinctive lateral

division of the external adductor. The presence of this division is a derived character previously

known only in dicynodonts. However, as far as can be determined, similarities between

Venjukovia and dinocephalians only involve joint possession of a primitive therapsid arrange-

ment of various other parts of the jaw musculature. Therefore, the muscle pattern does not

provide evidence of a closer relationship with dinocephalians than with other primitive

therapsid groups. Moreover, in contrast to primitive dinocephalians (brithopodids), Venju-

kovia lacks an extensive area of origin of the external adductor from the dorsal surface of the

temporal roof. The absence of this specialized area of origin suggests (tentatively) that Venju-

kovia retained the primitive therapsid condition of the temporal roof and that the lines leading

to Venjukovia and dicynodonts on the one hand and to dinocephalians on the other diverged

before the primitive dinocephalian condition was achieved.

CONTENTS

PAGE

linyigoyatienoml 6 op 4 @ a o « 2)

IWENEEIL 6 5 6 6 oo op a vo,» Ail)

Adductorjaw musculature . . . 252

Conclusions# en nee

Acknowledgements . . . . . 259

References iS ope Re Se OY)

Abbreviations Peete, Ot Le ee Wht ete 9).

INTRODUCTION

The Russian anomodont Venjukovia has long attracted attention because

it shows structural resemblances to tapinocephalid dinocephalians on the

one hand (Efremov 1940) and to dicynodonts on the other (Watson 1942,

1948). Efremov noted general resemblances between Venjukovia and tapino-

cephalids in the structure of the teeth, face and palate. Watson agreed. but

also noted that the lower jaw of Venjukovia shows many features which are,

in essence, identical with those in dicynodonts. Romer (1956) regarded Venju-

kovia as seeming to bridge the morphological gap between dinocephalians

249

Ann. S. Afr. Mus. 69 (10), 1976: 249-260, 4 figs.

250 ANNALS OF THE SOUTH AFRICAN MUSEUM

and dicynodonts. It is not the purpose of this paper to extensively analyse

the phylogenetic position of Venjukovia; the issues involved are complex

and demand a thorough phylogenetic analysis of therapsids in general which

is the subject of a paper in preparation. However, the present study, which

involves a partial reconstruction of adductor jaw musculature in Venjukovia,

has obvious potential for defining character states useful in such an analysis.

In addition, some general but very tentative conclusions concerning the possible

relationships between Venjukovia, dinocephalians and dicynodonts can be

advanced based on a comparison of their patterns of adductor jaw musculature.

Accordingly, such comparisons will be made in so far as it is possible to do

so in this paper.

A rationale for jaw muscle reconstruction in synapsid reptiles and a

reconstruction of this musculature (based on a reptilian model) in the pelycosaur

Dimetrodon has already been provided (Barghusen 1973). The evaluation of

direct evidence of muscle attachment as well as the arguments concerning the

distribution of individual jaw muscles presented for Dimetrodon also apply

to the reconstructions made here. For this reason, the reader is referred to

Barghusen (1973) for clarification of the issues involved. In addition, by virtue

of the phylogenetic position of Dimetrodon within the pelycosaur family from

which therapsids were derived, the pattern of jaw musculature which it shows

constitutes the pattern primitive to the evolution of this musculature in therapsid

reptiles. Therefore, comparisons of the reconstructed musculature in Venju-

kovia will also be made with that of Dimetrodon exemplifying the pre-therapsid

arrangement from which the musculature of Venjukovia was derived.

MATERIAL

The reconstruction of adductor jaw musculature presented here for Venju-

kovia is based on information gained from a skull of V. prima (PIN 2793/1)

and three lower jaws of V. invisa (PIN 157/1111, 157/1112, 157/5) housed in

the Palaeontological Institute, U.S.S.R. Academy of Sciences, Moscow. The

skull is exceptionally well-preserved except posteriorly where much of the bone

forming the posterior margin of the lateral temporal fenestra, the posterior

root of the zygomatic arch, and the occiput has flaked from the matrix. Never-

theless, the bone which is present, and impressions of bone in the matrix,

clearly indicate that the outlines of the lateral temporal fenestra, temporal

fossa, zygomatic arch, and the position of the quadrate correspond to that

shown in Figures 1A and 1C. Matrix has not been cleared from the temporal

fossae or the orbits. For this reason it is impossible to estimate the area of

origin of m. adductor mandibulae internus pseudotemporalis, m. adductor

posterior, and, if present, m. adductor mandibulae internus pterygoideus

anterior. Consequently, these muscles will not be considered in this recon-

struction. However, the medial surface of the lower jaw (Fig. 1D) has not

departed sufficiently from that of Dimetrodon to suggest that the general areas

NOTES-ON THE ADDUCTOR JAW MUSCULATURE OF VENJUKOVIA Dik

Fig. 1. Reconstruction of the skull and lower jaw of Venjukovia.

A. Dorsal view of skull. B. Ventral view of skull with left lower jaw in place. C. Lateral view

of skull and lower jaw. D. Medial view of lower jaw. The areas of origin and insertion of the

external adductor and posterior pterygoideus jaw musculature are indicated by parallel

lines. The outline of the posterior margin of the skull and the position of the quadrate were

determined from bone impressions in the matrix. (Skull reconstructed from PIN 2793/1;

lower jaw reconstructed from PIN 157/1111, 157/1112, 157/5.)

of insertion of these muscles were significantly different from those in

Dimetrodon.

The reconstruction of brithopodid jaw musculature is also based on

specimens housed in the Palaeontological Institute, Moscow. These include an

exceptionally well-preserved skull and lower jaw of Titanophoneus potens

(PIN 157/1). Details of the temporal fossa were also gained from Notosyodon

gusevi (PIN 2505/1).

Much of the information upon which the reconstruction of musculature

in Lystrosaurus is based was collected in 1965 at Yale University from an

acid-prepared skull (SAM-4325). Unfortunately this skull was subsequently

D572 ANNALS OF THE SOUTH AFRICAN MUSEUM

destroyed in transit. More recently, information has also been gained from

acid-prepared material examined while the author visited the South African

Museum, Cape Town. This material included a skull and lower jaw of

L. declivis (Nat. Mus. C 403).

ADDUCTOR JAW MUSCULATURE

M. ADDUCTOR MANDIBULAE EXTERNUS

The temporal region of Venjukovia exhibits the posterodorsal enlargement

of both the lateral temporal fenestra and temporal fossa which is characteristic

of most therapsids as opposed to sphenacodontid pelycosaurs (cf. Figs 2A, C).

In dorsal view (Fig. 1A) the temporal fossa is broadly exposed due to the

extensive but as yet incomplete reduction in the width of the temporal roof.

The degree of reduction is comparable to that seen in some dicynodonts (cf.

Emydops, Crompton & Hotton 1967, Fig. 1B) but not as extensive as that

found, for example, in Lystrosaurus (Fig. 3A). The presence of a temporal

crest (Fig. 1A, temp cr) in Venjukovia provides direct evidence that the external

adductor took origin from the lateral face of that part of the postorbital forming

A B

MAME (lat) MAME (lat)

Fig. 2. Lateral views of the skull and lower jaw of Dimetrodon, A, hypothetical condition,

B, Venjukovia, C, and Lystrosaurus, D, forming a morphological series which illustrates

stages in the development of the lateral division of the external adductor jaw musculature

characteristic of dicynodonts. In A the zygomatic arch is positioned close to the adducted

lower jaw. In B the zygomatic arch is dorsally displaced creating an access route for that

part of the external adductor originating from the anterior face of the quadratojugal and

quadrate to invade the lateral surface of the squamosal. In C and D the arch is further dis-

placed and the invasion, creating the lateral division of the external adductor, has taken

place; in addition, an area of insertion for the lateral division is established on the dorsolateral

surface of the lower jaw. (A after Romer and Price.)

NOTES ON THE ADDUCTOR JAW MUSCULATURE OF VENJUKOVIA 253

a —

——

(med) =:

att apon

Fig. 3. The skull and lower jaw of Lystrosaurus.

A. Dorsal view of skull. B. Ventral view of skull with left lower jaw in place. C. Lateral view

of skull and lower jaw. The areas of origin and insertion of the external adductor and posterior

pterygoideus muscles are indicated by parallel lines.

the lateral margin of the temporal roof. The establishment of muscle origin

here probably represents an invasion of muscle attachment from the anterior

face of that part of the squamosal forming the posterior wall of the temporal

fossa. This condition, which is a distinct departure from that found in sphena-

codontids, was probably common among primitive therapsids as it is also

found in gorgonopsids, Biarmosuchus, and Eotitanosuchus (personal observa-

tions). The extent of this muscle attachment on the postorbital also approaches

that seen in dicynodonts (e.g. Lystrosaurus, Fig. 3A; also see Crompton &

Hotton 1967; Cluver 1975). Venjukovia, however, does not achieve the special-

ized condition seen in brithopodids, the most primitive known dinocephalians.

In brithopodids, the external adductor took extensive origin from the dorsal

surface of the temporal roof (Fig. 4A; also see Watson 1948; Olson 1962;

Boonstra 1963; Barghusen 1973). The condition in brithopodids contrasts

254 ANNALS OF THE SOUTH AFRICAN MUSEUM

sharply with that found in other primitive therapsids (i.e. gorgonopsids, Eotita-

nosuchus, Biarmosuchus, and ictidorhinids) as well as in Venjukovia. All these

animals retain the sphenacodontid arrangement, in which no adductor jaw

musculature attaches to the dorsal surface of the temporal roof. In contrast

to more primitive dinocephalians, many tapinocephalid dinocephalians (e.g.

Moschops) reverted back to the primitive therapsid and sphenacodontid arrange-

ment in the sense that the attachment of the external adductor to the dorsal

surface of the temporal roof was eliminated. Evidence strongly suggests that

this reversal in tapinocephalids was related to the development of head-butting

behaviour in these animals (Barghusen 1975). Conceivably a reversal may also

have taken place in the ancestry of Venjukovia. However, Venjukovia does not

exhibit any of the specializations for use of the dorsal surface of the head in

butting which are displayed by tapinocephalids and which, if present in Venju-

kovia, would suggest tapinocephalid relationships. At the moment it seems

more likely, therefore, that the condition manifested by Venjukovia is a retention

of the primitive therapsid and pelycosaur condition as there are no obvious

functional reasons to suggest that the absence of muscle attachment to the

dorsal surface of the temporal roof was secondarily derived. If so, Venjukovia

reflects a morphological stage, with regard to the attachment of part of the

adductor musculature, resembling that which must have been antecedent to

the stage reached by the most primitive known dinocephalians. Such a con-

clusion appears to be implicit in Boonstra’s (1963) remarks to the effect that

when the dinocephalian and dicynodont lines diverged, the intertemporal skull

table was broad and the origin of the adductor muscles showed a fairly primi-

tive condition. This conclusion runs counter to suggestions (Efremov 1940)

that Venjukovia was derived from tapinocephalids.

Preparation of the temporal fossa is not complete in the skull of Venjukovia.

However, there are reasons to believe that the undersurface of much of the

retained portion of the temporal roof served for the attachment of the external

adductor. This is expected from the distribution of the attachment of this

muscle in living reptiles. In addition, a depression on the undersurface of the

roof indicates that this was the case in Dimetrodon (see Barghusen 1973) and

a similar scar or depression has been found in all therapsids examined in which

the temporal region was sufficiently prepared and which showed a degree of

development of the temporal roof similar to that of Venjukovia. These therapsids

include Titanophoneus (see Orlov 1958, fig. 21) and Notosyodon among the

dinocephalians and Leontocephalus (see Kemp 1969, fig. 5) among the gor-

gonopsids. This evidence clearly suggests that such an arrangement of muscle

attachment was present prior to and during the evolution of those therapsids

that did not completely eliminate the temporal roof. It is also expected (Barg-

husen 1973) that the dorsal and ventrolateral parts of the posterior wall of

the temporal fossa, including the squamosal and quadrate, served as an area

of origin of the external adductor muscle in Venjukovia. The squamosal portion

of this area of attachment to the posterior wall of the fossa would have served

NOTES ON THE ADDUCTOR JAW MUSCULATURE OF VENJUKOVIA PI)

att apon

Fig. 4. The skull and lower jaw of Titanophoneus.

A. Dorsal view of skull. B. Ventral view of skull. C. Lateral view of skull and lower jaw.

The areas of origin of the external adductor and posterior pterygoideus muscles are indicated

by parallel lines. (Outlines after Orlov.)

as the original site from which the invasion of muscle attachment onto the

lateral surface of the postorbital in therapsids, including Venjukovia, took

place.

The posterodorsal tip of the dentary, forming the apex of the coronoid

eminence in Venjukovia, marks the probable site of attachment of a bodenapo-

neurosis (Fig. 1D, att apon) serving for the insertion of much of that part of

the external adductor described above. This function for the coronoid eminence

is indicated by comparisons with living reptiles (Barghusen 1973) and is con-

sistent with direct evidence of tendon attachment in Dimetrodon (Barghusen

1968) and theriodont therapsids. A similar insertion would also have been

present in all dinocephalians (Fig. 4C, att apon) and, as Cluver (1975) has

256 ANNALS OF THE SOUTH AFRICAN MUSEUM

recently pointed out, in dicynodonts, in which the posterodorsal tip of the

dentary marks a site of tendinous attachment (Fig. 3C, att apon) identical in

position to that in Venjukovia.

By far the most important question concerning the external adductor in

Venjukovia is whether or not a lateral division was present comparable to that

found in dicynodonts (Figs 2D, 3B, C). The external adductor jaw musculature

independently established an extensive area of attachment on the zygomatic

arch and exposed lateral surface of the lower jaw at least twice and probably

three times in therapsid history. This definitely occurred in cynodonts (Barg-

husen 1968) and dicynodonts (Watson 1948; Crompton & Hotton 1967;

Cluver 1975) and probably occurred in gorgonopsids (Barghusen 1968; Kemp

1969). In each group the manner in which this muscular modification occurred

is highly distinctive. In cynodonts a laterally bowed zygomatic arch created a

channel through which developing masseter musculature descended from the

temporal fossa to insert on the lateral surface of the dentary; subsequent

events led to the establishment of muscular origin on the entire zygomatic

arch. An invasion also occurred in gorgonopsids but in this case the muscle

attachments were confined to the lateral surface of the angular and the posterior

root of the zygomatic arch. In dicynodants, a channel was created for the

invasion of musculature from the confines of the temporal fossa through the

dorsal displacement of the zygomatic arch relative to the dorsal surface of the

lower jaw (Crompton & Hotton 1967). This invasion resulted in a newly added

lateral division of the external adductor originating from the arch and expanded

lateral surface of the squamosal and inserting on a distinctive lateral shelf of

the dentary (Crompton & Hotton 1967; also see Figs 3B-C). This muscular

development is a dicynodont hallmark, as is the developing masseter muscle

for cynodonts.

Despite the limitations of incomplete preservation posteriorly, the mor-

phology of Venjukovia indicates that this animal closely conforms to, and may

reflect, an initial stage in the development of the condition seen in dicynodonts.

The zygomatic arch is dorsally displaced relative to the jaw articulation. This

created the necessary condition whereby external adductor musculature origi-

nating on the ventrolateral part of the posterior wall of the temporal fossa

(the quadratojugal and quadrate as reconstructed in Dimetrodon (Barghusen

1973)) had free access to invade the lateral surface of the squamosal by a route

passing inferior to the level of the zygomatic arch (Fig. 2). It is also apparent

(Fig. 2) that the zygomatic arch of Venjukovia and dicynodonts was dorsally

displaced to the level of the inferior margin (Fig. 2A, inf mar) of the attachment

of the external adductor to the inner surface of the cheek as reconstructed in

Dimetrodon on the basis of stretch capabilities of muscle (see Barghusen 1968).

This suggests that much of the length of the inferior and medial surfaces of the

arch could have served for the origin of musculature with sufficient fibre length

to allow for a substantial gape (also see Watson’s 1948 discussion of gape in

dicynodonts). Finally, this displacement removes the zygomatic arch from

NOTES ON THE ADDUCTOR JAW MUSCULATURE OF VENJUKOVIA DSi

immediate proximity to the lateral surface of the lower jaw which, thereby,

becomes a potential site of muscle insertion.

The extent of invasion of muscle attachment onto the lateral surface of

the squamosal is impossible to determine in Venjukovia due to insufficient

preservation of the posterior root of the zygomatic arch. However, the presence

of a fossa (Fig. 1C, fossa) excavated into the lateral surface of the surangular

and most posterior part of the dentary, as a departure from the primitive

therapsid condition, strongly suggests that such invasion did take place. The

fossa indicates the incipient development of muscle attachment to the dorso-

lateral surface of the jaw corresponding to the insertion of the lateral division

of the external adductor in dicynodonts (Fig. 3C); the insertion has merely

expanded anteriorly in dicynodonts to include more of the dentary. The fossa

thus indicates the presence of a laterally placed muscle whose area of origin

may well have included the lateral surface of the squamosal. If so, the impression

of the squamosal left on the matrix suggests that the posterior root of the

zygomatic arch was shaped as in Figure IC and capable of supporting an area

of origin from its lateral surface as is illustrated.

M. ADDUCTOR MANDIBULAE INTERNUS PTERYGOIDEUS (POSTERIOR)

The area of origin of the posterior pterygoid muscle in Venjukovia is

clearly very similar to that reconstructed in Dimetrodon (Barghusen 1973).

A boss on the distal end of the transverse process of the pterygoid as well as

indications of a medial pterygoid crest (Fig. 1B, m pt cr) provide direct evidence

of tendinous attachment in the manner of sphenacodontids, theriodonts, and

brithopodids (Fig. 4B), as well as many living reptiles. The ventral surface of

the quadrate ramus of the pterygoid is also expected to have served as an area

of origin for this muscle mass (Fig. 1B, MAMIPt (post)). The major difference

in area of origin of the posterior pterygoid muscle between Venjukovia, on the

one hand, and Dimetrodon and brithopodids, on the other, is that the transverse

process is less massive and projects anterolaterally in Venjukovia (cf. Figs 1B,

4B). The anterolateral projection approaches (but by no means achieves) the

condition in dicynodonts, in which the transverse process has lost its role in

bracing and controlling the movements of the lower jaw and projects almost

straight forward (Fig. 3B, tp). In this regard, Venjukovia resembles a morpho-

logical stage which was probably antecedent to the condition in dicynodonts.

It is generally assumed that the transverse process of the pterygoid is either

reduced (Romer 1956) or entirely eliminated (Watson 1948; Crompton &

Hotton 1967) in dicynodonts. It appears, however, that this structure is merely

redirected forward and in many cases is well developed. The structure labelled

as the transverse process in Figure 3B has the same general topographic rela-

tionships to the subtemporal fossa and the ectopterygoid (when the latter is

present) as does the structure which is clearly the transverse process in Venju-

kovia. Moreover, direct evidence in one acid-prepared specimen (SAM-4325)

of Lystrosaurus indicates that the relationship to the posterior pterygoid muscle

258 ANNALS OF THE SOUTH AFRICAN MUSEUM

is also the same. The ventral surface of the distal portion of the process is

slightly rugose and striated, suggesting tendon attachment. In addition, a line

of parallel striations (Fig. 3B, str) extends posteromedially from the ventral

edge of the anteriorly directed process to terminate near the level of the basi-

pterygoid joint. The position of this line corresponds to that of the medial

pterygoid crest and also provides direct evidence of probable tendon attachment.

The area of insertion of the posterior pterygoid muscle in Venjukovia

(Fig. 1B) is expected to have included the ventromedial surface of the articular

and probably the anteromedial face of the retroarticular process. This recon-

struction contrasts with many made in the past in which it was assumed that

pterygoideus musculature ran beneath the jaw to insert on the lateral surface

of the main body of the angular medial and posterior to the reflected lamina.

This has been thought to have been the case in sphenacodontid pelycosaurs

and in therapsids in general (see Barghusen 1968, 1973; Crompton & Hotton

1967; Watson 1948). The muscle involved has been given various names and

reconstructed with a number of different areas of origin; however, it is the

posterior pterygoid muscle as reconstructed by Barghusen (1973). While an

insertion on the lateral surface of the angular appears to be valid for sphena-

codontids, its validity is questionable in most therapsids. As pointed out by

Allin (1975), the very close relationship between the reflected lamina and the

lateral surface of the main body of the angular in the vast majority of therapsids,

including brithopodids, Venjukovia, and dicynodonts, argues against the inter-

vention of musculature between these structures. The confinement of muscu-

lature within such a narrow space would cause functional inefficiency since

the amount of muscle is necessarily very small and, as Allin remarks, the

muscle ‘would be unable to shorten without bulging against its skeletal confines

as well as constricting off its own blood supply, although an associated venous

plexus might provide volumetric compensation’. It may be added that if a

venous plexus were present in the space between the lamina and main body

of the angular, the amount of musculature present would have been negligible.

It is more reasonable, as persuasively argued by Allin, to regard this space as

housing an air-filled chamber existing as a tympanic or pharyngeal diverti-

culum and functioning in sound reception.

CONCLUSIONS

The pattern of adductor jaw musculature reconstructed for Venjukovia

Suggests that this animal is closely related to dicynodonts—perhaps more

closely related to dicynodonts than to any other known therapsid group.

A close relationship is indicated by: 1. the probable presence of a similar

lateral division of the external adductor in both groups in contrast to the

condition in other therapsids; and 2. the fact that the structure of the area of

origin of the posterior pterygoid in Venjukovia is consistent with the structure

postulated for a theoretical morphological stage transitional to the dicynodont

condition. The muscular morphology of Venjukovia contrasts with that of

NOTES ON THE ADDUCTOR JAW MUSCULATURE OF VENJUKOVIA 259

primitive dinocephalians in that there is no specialized origin of the external

adductor from the dorsal surface of the temporal roof in Venjukovia. Unless

a reversal (i.e. secondary elimination of this area of origin) is postulated,

animals which would be classified as dinocephalians were not involved in the

ancestry of Venjukovia. At the moment, there is no evidence which suggests

that such a reversal took place. The therapsid ancestry of Venjukovia is, the

author believes, an open question.

ACKNOWLEDGEMENTS

I am indebted to the following individuals and institutions for making

fossil material in their care available for study: Dr Peter K. Chudinov of the

Palaeontological Institute, U.S.S.R. Academy of Science, Moscow; Dr Michael

A. Cluver of the South African Museum, Cape Town; and Dr A. W. Crompton,

formerly of Yale University, New Haven, Connecticut. Thanks are also due

to Dr James Hopson for critical commentary on the manuscript.

This research was supported by NSF grant GB-40061.

REFERENCES

ALLIN, E. F. 1975. Evolution of the mammalian ear.—J. Morph. 147: 403-438.

BARGHUSEN, H. R. 1968. The lower jaw of cynodonts (Reptilia, Therapsida) and the evolu-

tionary origin of mammal-like adductor jaw musculature. —Postilla 116: 1-49.

BARGHUSEN, H. R. 1973. The adductor jaw musculature of Dimetrodon (Reptilia, Pelyco-

sauria).—J. Paleont. 47: 823-834.

BARGHUSEN, H. R. 1975. A review of fighting adaptations in dinocephalians (Reptilia, Therap-

sida). — Paleobiology 1: 295-311.

Boonstra, L. D. 1963. Early dichotomies in the therapsids.—S. Afr. J. Sci. 59: 176-195.

CLuverR, M. A. 1975. A new dicynodont reptile from the Tapinocephalus Zone (Karoo System,

Beaufort Series) of South Africa, with evidence of the jaw adductor musculature. — Ann.

S. Afr. Mus: 67: 7-23.

Crompton, A. W. & Hotton, N. 1967. Functional morphology of the masticatory apparatus

“of two dicynodonts (Reptilia, Therapsida).—Postilla 109: 1-51.

Erremoy, I. A. 1940. Preliminary description of new Permian and Triassic terrestrial verte-

brates from the U.S.S.R.—Trudy paleon. Inst. 10: 1-140.

Kemp, T. S. 1969. On the functional morphology of the gorgonopsid skull.— Phil. Trans. R.

Soc. (B) 256: 1-83.

Otson, E. C. 1962. Late Permian terrestrial vertebrates, U.S.A. and U.S.S.R.—Am. phil.

Soc. Trans. 52: 1-224.

Or.ov, J. A. 1958. Predatory dinocephalians from the fauna of Isheyevo (Titanosuchia).—

Trudy Paleon. Inst. Akad. Nauk. 72: 1-114.

Romer, A. S. 1956. Osteology of the reptiles. Chicago: University of Chicago Press.

Watson, D. M. S. 1942. On Permian and Triassic tetrapods.— Geol. Mag. 79: 81-116.

Watson, D. M. S. 1948. Dicynodon and its allies.—Proc. Zool. Soc. Lond. 118: 823-877.

ABBREVIATIONS

an angular

art articular

att apon attachment of the bodenaponeurosis

bo basioccipital

260 ANNALS OF THE SOUTH AFRICAN MUSEUM

bs basisphenoid

d dentary

ect ectopterygoid

f frontal

inf mar inferior margin of the origin of the external adductor from the inner surface

of the cheek

} jugal

] lacrimal

m maxilla

MAME external adductor muscle

MAME (lat) lateral division of the external adductor muscle

MAME (med) medial division of the external adductor muscle

MAMIPt (post) posterior pterygoid muscle

m pt cr medial pterygoid crest

n nasal

p parietal

pal palatine

par paroccipital process

part prearticular

pf postfrontal

pm premaxilla

po postorbital

prf prefrontal

pt pterygoid

q quadrate

sa surangular

sm septomaxilla

sp splenial

sq squamosal

str striations

temp cr temporal crest

tp transverse process of the pterygoid

Vv vomer

Nat. Mus. National Museum, Bloemfontein, South Africa.

PIN Palaeontological Institute, Moscow, U.S.S.R.

SAM South African Museum, Cape Town, South Africa.

- - a a ae es a 7

MY = = - “, 7 * { = = pe = aay = ~ is

— > : U = p Se ; € = D

= _- = E 2

~ ;. = a = : 5 = a : = : :

~ 7 = - s E = . = = i

: 4 ; = 1 v

er ¢ a 2 =

= = z ae . iH By

i ; ; ee

) - ‘ ‘ 7 -

* :

‘

aan i

= *s =e sy ; oa i)

cs P — : er me = . : x

= ; 28

, <

6. SYSTEMATIC papers must conform with the International code of zoological nomenclature

(particularly Articles 22 and 51).

Names of new taxa, combinations, synonyms, etc., when used for the first time, must be

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Family Nuculanidae

Nuculana (Lembulus) bicuspidata (Gould, 1845)

Figs 14-15A

Nucula (Leda) bicuspidata Gould, 1845: 37.

Leda plicifera A. Adams, 1856: 50.

Laeda bicuspidata Hanley, 1859: 118, pl. 228 (fig. 73). Sowerby, 1871: pl. 2 (figs 8a—b).

Nucula largillierti Philippi, 1861:

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Note standard form of writing South African Museum registration numbers, date and geographical positions.

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