Upper Permian

zoological journal ofthe Linnean So&& (1 996), 117: I 15- 139. With 15 figures

A primitive anomodont therapsid &om the base of-the Beaufort Group (Upper Permian) of South Africa BRUCE S. RUBIDGE Bernard Price Institutefor Palaeontological Research, Universip Bag 3, P.O. Wits, 2050, South A h c a

of the Witwatersrand, Rivate

AND JAMES A. HOPSON

Department of Organha1 Biologv and Anatomy, Universig Street, Chicago, IL 60637, USA.

of Chicago, 1025 East 57th

Received Sephber 1994, accepkd for publicatinn AM7 1995

Patranomodon nyaphulii, known from a nearly complete skull, lower jaw and partial postcranial skeleton, is morphologically the most primitive anomodont therapsid yet discovered. It is from the Eoditynodon Assemblage Zone, the lowest biozone of the Beaufort Group of South Africa, which has a primitive therapsid fauna comparable with that of the Russian Zone I. Patranaomodon is primitive with respect to other anornodonts in having short palatal exposure of the premaxilla, an unreduced tabular, a slit-like interpterygoidal vacuity, a screw-shaped jaw articulation (which precludes fore-aft sliding of the lower jaw), and only three sacral vertebrae. The poorly-known Galechincr and GarCpur from the younger Cirtecephalur Assemblage Zone appear to be at a comparably primitive evolutionary grade, and the three genera are tentatively united in the family Galechiridae. The taxon Dromasauria is shown to be paraphyletic and therefore should be discarded. 01996 The Linnean Socirty of London

ADDITIONAL KEY WORDS:-Therapsida

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Anomodontia

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Patranomodon

Permian.

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Karoo

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Upper

CONTENTS Introduction . . . . Material and methods . Abbreviations . . . . Geological background SkuU description . . . Skull . . . . . Lower jaw . . . Postcranial skeleton . .

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Correspondence to Bruce Rubidge. 0024-4082/96/060115

+ 25 $18.00/0

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01996 The h e a n Society of London

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B. S. RUBIDGE AND J. A. HOPSON Cervical vertebrae and ribs . . . . . . . . . . . . . . . . . . . . Dorsal vertebrae and ribs . . . . . . . . . . . . . . . . . . . . Sacral vertebrae and ribs . . . . . . . . . . . . . . . . . . . . Forelimb . . . . . . . . . . . . . . . . . . . . . . . . . Pelvic girdle and femur . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of Palranornodon with Galcchinu and Galepur . . . . . . . . . . . . Comparison with Galechinu . . . . . . . . . . . . . . . . . . . . Comparison with Ga& . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . .

127 128 129 130 133 136 137 137 137 138 138 138

INTRODUCTION

The Anomondontia are a major subgroup of the Therapsida (mammal-likereptiles and mammals) and were the principal tetrapod herbivores of the late Permian and early Triassic. This group includes the abundant and diverse Dicynodontia, the Venjukoviamorpha from Russia (Tchudinov, 1983; Hopson & Barghusen, 1986) and the Dromasauria from South Africa (Brinkman, 1981). Until the discovery of a well preserved skull and partial skeleton of a small non-dicynodont anomodont from the lowermost rocks of the Beaufort Group in South Africa, the inter-relationships of the non-dicynodont anomodonts were poorly understood. This creature, named Patranornodon nyaphulii has been identified as the most primitive known anomodont (Rubidge & Hopson, 1990). Because the skull of Patranornodon is so complete and well preserved, and so primitive in morphology, it has been usell in determining more precisely the relationships of the various non-dicynodont anomodont genera to each other as well as to the Dicynodontia. It led Rubidge and Hopson (1990) to conclude that the Dromasauria and Venjukoviamorpha are paraphyletic groups and that these names should therefore be discarded. As the skull and postcranium of this most important primitive anomodont have not yet been fully described, this paper aims to fulfill this need. Furthermore, the postcranial elements are unique in that they are the only described postcranial bones of non-dicynodont anomodonts that are not preserved as natural moulds and can therefore be studied in three-dimensions.

MATERIAL AND METHODS

The specimen (NMQR 3000) was collected in 1986 by Mr John Nyaphuli on the farm Combrinkskraal in the Prince Albert district, South Africa and is housed in the Karoo fossil collection of the National Museum, Bloemfontein, South Africa. It consists of a skull and lower jaw (which were tightly articulated when found) as well as several postcranial elements preserved in five small calcareous nodules. These nodules came from a small bone-bearing ‘pocket’ in a laterally continuous bed of brown-weathering calcareous nodules considered to have been of pedogenic origin (McPherson & Germs, 1979; Smith, 1980, 1990).Although the postcranial elements were not all preserved in a single nodule, the fact that they were very closely associated and are all in the same size range, lead us to believe that they belong to the same individual.

PRIMITIVE SOUTH AFRICAN ANOMODONT

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ABBREVIATIONS

Institutions AMNH American Museum of Natural History, New York, USA. Bernard Price Institute for Palaeontological Research, Johannesburg, BP/ 1 South Africa. NMQR National Museum, Bloemfontein, South Africa. South Africa Museum, Cape Town, South Africa. SAM Figures ang art ax

bo bs bX

cap cc ce cer cor

dc den eam ec

ex f lie fm icf ic if il is

j

jf

k

lar Ic ICO

IPt mc mro mec rnx n nsP OP Pa

angular articular axis basioccipital basisphenoid basioccipital capitulum carotid canal rentrum cervical rib coronoid distal carpal dentary external auditory neatus ectopterygoid exoccipital frontal femur foramen magnum internal carotid foramen intercrntrum intervertebral foramen ilium ischiurn jugal jugular foramen keel lachrymal lateral centrale lateral condyle of femur lateral process of pterygoid medial centrale medial condyle of femur rnrtacarpal maxilla nasal neural spine opisthotic parietal

pabs Pal Par Phl pm P'n PO POf POP plX Pra

Prf

P" Prp PIX PI Ptf q

si

wt r

ra ral rl sa sar so

SP sq St

t tem tp ul un V

vc vg

parabasisphenoid palatine paroccipital process phalange premaxilla pineal foramen postorbital postfrontal postparietal postzygapophysis prearticular prefrontal prootic preparietal prezygapophysis pterygoid posttemporal foramen quadrate quadratojugal quadrate ramus of pterygoid rib radius radiale reflected lamina of angular surangular sacral rib articulation supraoccipital splenial squamosal stapes tabular temporal crest transverse process ulnare ungual phalanx vomer vidian canal videan groove

GEOLOGICAL BACKGROUND

Specimen NMQR 3000 was collected in rocks of the Late Permian Eodicynodon Assemblage Zone (Rubidge, 1990a, 1995), the oldest vertebrate biozone of the Beaufort Group. Therapsid fossils from this biozone include Eodicynodon (the most primitive true dicynodont known) (Rubidge, 1990b), Tupinocuninus (the most primitive tapinocephaline dinocephalian known) (Rubidge, 199 l), Austrulosyodon a primitive anteosaurid dinocephalian (Rubidge, 1993, 1994), scylacosaurid therocephalians (Rubidge, Kitching & ven den Heever, 1983), and gorgonopsians.

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SKULL DESCRIPTION

Skull The skull is nearly complete (Figs Id), lacking only the tip of t.e snout and a part of the left naris, the right stapes and portions of the braincase. The lower jaw is lacking only the left articular region and anteriormost part of the symphyseal region. The anterior portion of the premaxilla is weathered, but it is apparent that it forms the entire anterior, and portion of the anteroventral border of the external naris. In ventral view (Fig. 1) the premaxillae form the anterior ends of the internal nares from which short grooves extend forward. Medial to the nares, paired processes of the premaxillae extend back to underlie the anterior ends of the vomers in a W-shaped contact. Although the anterior part of the snout is missing, it appears that the amount of premaxillary expansion on the palatal surface was small, unlike that of most latter anomodonts. The number of premaxillary teeth is unknown, but we presume that,

Figure 1. Ventral view of skull of Patranomodon nyuphuli (NMQR 3000). Scale bar = 10 mm.


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as in Guhchims, at least three incisors were present. Laterally, the premaxilla appears to form an elongate process which extends back to a point between the third and fourth maxillary teeth. The maxilla forms most of the ventral and posterior borders of the external naris. Posteriorly it extends back below the lacrimal and jugal as a tapering zygomatic process terminating below the middle of the orbit. The maxilla decreases in height on the lingual side of the tooth row, so a greater amount of tooth crown is visible lingually than labially. Internal to the teeth the maxilla forms a slight shelf which contacts the anterolateral process of the palatine medial to the last tooth. Seven conical teeth are preserved in the right maxilla and five on the left. All teeth point forward relative to the maxillary border, and are more-or-less the same size, with the exception of the last tooth on the right side which is smaller. The crowns are slightly recurved and enamel on the labial sides is smooth but that on the lingual side has vertical ridges and grooves. The nasal forms the dorsal border of the external naris and extends back to meet the frontal at the level of the anterior border of the orbit. A septomaxilla cannot be identified on the rim of either narial opening. The lachrymal forms a relatively short segment of the anteroventral rim of the orbit. It has a short dorsal contact with the prefrontal, and a longer anterior and ventral contact with the maxilla. Posteroventrally it has a short contact with the jugal, thus excluding the maxilla from the orbital rim. Dorsal to the lachrymal the prefrontal is a large bone forming the anterior border of the orbit. The frontal has a long exposure on the orbit margin and forms much

Figure 2. Lateral view of skull of Patranmodon nyaphulii (NMQR 3000). Scale bar = 10mm.

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B. S . RUBIDGE AND J. A. HOPSON

of the skull roof between the orbits (Fig. 3). It meets the prefrontal anterolaterally and has a short contact with the postfrontal posterolaterally. Medial to the postfrontal it has a deeply interdigitating suture with the parietal and contacts the preparietal more medially. The preparietal of Patranornodon is a prominent element which forms the anterior border of the parietal foramen. This bone is an unexpected element in a primitive anomodont, although it is present in the Dicynodontia. Broom (1914: 13) reports a preparietal in Galepus but this cannot be verified because the sutures to which Broom referred have since been obliterated (Brinkman, 1981: 20). The known specimens of Galeops do not preserve this region of the skull roof. A preparietal is not present in Otsheria and Vmjhvia. The parietal (Fig. 3) forms the greater part of the intertemporal roof, including the lateral and posterior borders of the parietal foramen, and the dorsal third of the occipital surface. Laterally, it contacts the postfrontal, postorbital, and squamosal and, posterolaterally sends a long, thin lappet between the squamosal and tabular.

Figure 3. Dorsal view of skull of Pubanornodon nyuphulii (NMQR 3000). Scale bar = 10 mm.


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On the occipital surface (Fig. 4) the parietal is overlapped by the tabular and postparietal. The postfrontal (Fig. 3) is a roughly triangular element forming the posterodorsal margin of the orbit. It has a long slender anterior process which extends along the orbital rim and contacts the frontal and parietal on the medial site. Laterally, the postfrontal extends onto the anterior part of the postorbital bar as a slender tapering process. The postorbital forms nearly all of the slender postorbital bar. On the skull roof it contacts the parietal medially and the postfrontal anteriorly, and sends a short process back along the medial rim of the temporal fenestra to contact the squamosal. A faint temporal crest, extending from the suture with the squamosal forward on to the posterior surface of the postorbital bar, is the only evidence for attachment of adductor jaw musculature to the margin of the temporal fenestra. The jugal extends nearly the full length of the zygomatic arch (Fig. 2). In palatal view (Fig. 1) it extends medial to the maxilla to contact the ectopterygoid and perhaps the palatine. It has a short postorbital process situated medial to the postorbital bone. The temporal portion of the zygomatic arch is formed by the jugal below and the squamosal above. The squamosal is a complex bone which forms the ventral, posterior, and posterodorsal margins of the temporal fenestra (Fig. 3). The posterodorsal border of the temporal fenestra is not folded backwards as it is in dicynodonts, indicating that the external adductor jaw musculature did not take origin from the dorsal or posterior surfaces of the squamosal. This is considered to be a retention of the primitive therapsid condition seen in biarmosuchians (Hopson, 1991). In occipital view (Fig. 4)the squamosal is convexly rounded on the dorsal and lateral sides. More medially it forms a triangular concave area, the external auditory meatus, which widens ventrally. On its ventrolateral margin it forms a slender ventral projection, which extends to a level of the lateral condyle of the quadrate. The zygomatic process of the squamosal is slender, it overlies the jugal dorsolaterally and terminates anteriorly at the level of the postorbital bar. In the palate (Fig. 1) the vomers are paired, separated by a midline suture along their entire length. They form a broad bar, concave ventrally, between the elongate choanae; behind the choanae they expand laterally to underlie the palatines and contact the pterygoids posteriorly. The palatine is a complex bone which contacts the maxilla, vomer, pterygoid, ectopterygoid and perhaps the jugal. The palatine sends a short process forward along the medial surface of the maxilla to form the posterolateral border of the choana. Lateral to the anterior end of the pterygoid, each palatine ridge expands to form a rugose, pitted boss similar to the toothed palatine bosses of biarmosuchians, primitive dinocephalians, and gorgonopsids. The pits on the bosses of Patranomodon resemble alveoli, but a diligent search has failed to yield the remains of teeth. Behind the bosses, the palatines extend back a short distance as broad ridges which converge towards the midline and continue onto the pterygoids as narrow crests. The poorly preserved ectopterygoid is a narrow element, bounded anteromedially by the palatine and posteromedially and posteriorly by the pterygoid. It forms the anterolateral surface of the pterygoid flange and contacts the jugal on the anterior border of the subtemporal fossa. Paired pterygoids form the entire posterior part of the palate. Anterior processes of the pterygoid contact the vomers in the roof of the choanal trough. The most

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Figure 4. Occipital view of skull of Patranornodon nyaphulii (NMQR 3000). Scale bar = 10 mm.

prominent feature of the pterygoid is the transverse flange of which the ventral border does not descend below the level of the palate, unlike the condition in nonanomodont therapsids. The outer face of the flange forms a flat triangular surface, which fits close to the medial surface of the mandible. Behind the transverse flanges, the lateral borders of the pterygoids curve inward to form a constriction just anterior to the quadrate rami. Parasagittal ridges continue posteriorly from the palatines extending back nearly to the basipterygoid joint. The interpterygoid vacuity is long and narrow and is bounded entirely by the pterygoids. Posteromedial to the pterygoid flange is a narrow vertical ridge which extends back on to the quadrate ramus of the ptergyoid. The outer surface of this ridge forms a ventrolaterally-facing depression which was probably an area of origin for pterygoideus musculature (Barghusen, 1976). The quadrate ramus is a slender process which nearly reaches a short pterygoid process on the quadrate. The unpaired postparietal (Fig. 4) is roughly rectangular with a short dorsal midline projection overlapping the parietals and a somewhat longer and broader ventral projection overlapping the supraoccipital. The tabular is a large sheet-like element covering the dorso-lateral part of the occiput. On the lateral margin of the occiput the tabular extends down to form the doriolateral margin of the posttemporal foramen. The large size and great ventrolateral extent of the tabular, which broadly overlaps the lateral margin of the supraoccipital and thereby hides its possible contact with the squamosal, represents the primitive therapsid condition, which is modified in all more derived anomodonts (King, 1988). Parasphenoid and basisphenoid are indistinguishably fused (Fig. 1). Just behind the narrowest part of the bone, circular carotid canals pass vertically upward on


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either side of the parasphenoid keel. A short groove, the vidian canal, which transmitted the palatine ramus of the facial nerve, extends forward from each carotid opening and beneath the parabasisphenoid and the pterygoid. Behind the carotid foramina the parasphenoid keel bifurcates to form laterally-directed ridges which form the anterior margin of a deep backwardly-directed pocket, which was presumably an attachment area for ventral cervical musculature. The separation between basioccipital and parabasisphenoid is not clear but appears to be represented by a change in texture of the bone where the pocket for neck musculature meets the flatter surface behind it. Lateral to this the parabasisphenoid forms ‘the medial border of the fenestra ovalis. The exoccipitals (Fig. 4)form the paired lateral condyles of the occipital condyle and are separated ventrally by a thin wedge of basioccipital. Midway up the lateral margin of the foramen, the exoccipitals contact the supraoccipital. The supraoccipital is very broad, extending nearly across the entire occiput. It borders the upper half of the foramen magnum and the dorsomedial margin of the posttemporal foramen. Dorsally it is overlain by the postparietal and dorsolaterally and laterally by the tabular. Ventrolaterally it contacts the opisthotic and the exoccipital ventromedially. The bones of the otic capsule cannot be separated, so the opisthotic and prootic are treated together. The paroccipital process extends laterally at the level of the occipital condyle, and forms the ventral border of the posttemporal foramen. Its posterior surface is indented by a sulcus which begins just lateral to the jugular foramen, increases in height and depth distally and terminates at a small anterolaterally-directed foramen. The ventral part of the paroccipital process bends backwards and its distal end is drawn out into a prominent ventrolaterally directed process. A similar process has been described in the dicynodont fingoria by Cox (1959), who interpreted it as an attachment area for a tympanum. The prootic portion of the otic capsule is not well exposed. Anteromedial to the post-temporal foramen, the prootic forms a bulge which probably marks the position of the underlying anterior vertical semicircular canal. The quadrate has the shape of an inverted ‘T’with the horizontal bar forming the articular area while the vertical bar is the ascending process which lies against the anterior surface of the squamosal. The articular surface consists of a lateral and medial condyle separated by an oblique sulcus. The lateral condyle is more transverse in orientation and narrower anteroposteriorly than the medial condyle. The articular surface has the primitive screw-shape characteristic of carnivorous therapsids (anteosaurids, Orlov, 1958; gorgonopsians, Kemp, 1969; therocephalians Kemp 1972; early cynodonts, Crompton, 1972) in which the articular surface of the lower jaw must slide laterally as the jaw opened (Parrington, 1955). Fore-aft sliding of the articular on the quadrate is not possible in such a jaw joint, unlike the highly specializedjaw joint of dicynodonts. The ascending process of the quadrate (Fig. 2) is curved both mediolaterally and dorsoventrally, with a concave anterior surface. The left quadrate appears to have a small pterygoid process which extends toward the quadrate ramus of the pterygoid but is separated from it by a short gap. The quadrate of Guleops whuits’ also has, according to Brinkman (1981: 8-9), “an anteriorly directed flange that meets the pterygoid.” The quudrutojugul is a tall, anteroposteriorly flattened bone with the inner margin expanding dorsomedially and passing behind the quadrate. The lower end of the quadratojugal forms an expanded foot-like process which grips the dorsal surface of

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the lateral quadrate condyle. A left stapes is preserved in nearly natural position, although the footplate may have shifted slightly forward. The body of the stapes, which lacks a stapedial foramen, slopes ventrolaterally and posteriorly to meet the medial condyle of the quadrate on its dorsomedial surface. A slender dorsal process extends from the posterolateral surface of the stapes to contact the paroccipital process. The stapes is unknown in all other non-dicynodont anomodonts. Brinkman (1981) notes than in Galeops whaitsi the fenestra ovalis is located well above the level of the stapedial pit on the medial surface of the quadrate, indicating that the stapes sloped ventrolaterally (as it does in Patranomodon). He also notes that this differs from the condition in dicynodonts, in which the stapes is nearly horizontal. In dicynodonts, the bones forming the rim of the fenestra ovalis are elongated ventrally so as to place the fenestra nearly opposite the lower end of the quadrate. The fenestra ovalis of Patranomodon is located below the level of the occipital condyle, resembling the condition in dicynodonts and differing from the condition in other therapsid groups (see Orlov, 1958, for primitive dinocephalians; Sigogneau-Russell, 1989, for biarmosuchians and gorgonopsians).

Lower jaw The dentary (Figs 5 , 6) forms the anterior half of the lower jaw. It is uncertain whether the two dentaries are fused because, although a median line of matrix is visible on its lower half, the upper half of the symphysis appears to be continuously ossified across the midline. In Galechinu, the lower jaws are separated anteriorly and the symphyseal surface of the right ramus is displaced anteromedially so that it is exposed immediately in front of the left ramus (see Brinkman, 1981,fig 10; the right symphyseal region is the unlabelled elongate structure contacting the anterior end of the left dentary). The missing anterior part of the dentary in Patranomodon is restored on the basis of the dentary of Galechinu. The anterior half of the dentary has a slightly convex lateral surface which is heavily pitted, as in Galechinu and Galeops (Brinkman 198l), whereas the surface of the posterior half is slightly depressed below the out-turned dorsal border and lacks pitting. Similar pitting of the dentary and facial part of the skull in dicynodonts is interpreted as indicating the presence of a cornified integument (horny beak). It is therefore possible that the non-dicynodont anomodonts also possessed a cornified jaw covering. Brinkman (1981: 24) suggests that in Galechinu adductor jaw muscles inserted on a similarly depressed area of the dentary. This is unlikely, as such musculature would be oriented at such a low angle as to be a very ineffective adductor of the mandible. It could not function as a retractor of the mandible, as a similarly-placed muscle would in dicynodonts, because the jaw articulation in Patranomodon, and presumably in Galechinu,was not a slidingjoint. Posterodorsally the dentary extends slightly above the level of the surangular as a low coronoid eminence. Five teeth and one empty alveolus are preserved in the left dentary. As in the maxilla, the alveoli lie medial to and below the dorsal margin of the jaw. Probably no more than two additional teeth lay in the missing anterior part of each ramus. The teeth are all damaged to some extent and do not preserve the longitudinal ridges and grooves seen in the upper dentition. The splenial covers the lower half of the medial surface of the dentary and


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anteriorly enters into the symphysis. Above its posterior end, immediately behind the last tooth and just in front of the mandibular fenestra, is a small, flat, inconspicuous element lying against the dentary. On the right side, its posterior half is slightly raised from the surface of the dentary and its dorsal and posterior suture with the dentary is clearer than on the left. Its surface lacks the longitudinal striations seen immediately above it on the dentary. The dorsal edge of this element lies at the level of the upper border of the mandibular fenestra and it has a short posterior prong which extends above the anterior end of the fenestra. The remainder of the bone extends anteroventrally medial to the splenial. We have identified this element in Patranomodon as a coronoid bone. The coronoid has been lost in dicynodonts and is also supposed to be absent in other anomodonts (Watson & Romer, 1956; King, 1988). However, a small coronoid has been reported in Vmzhziu (Hopson, 1991) and we have identified a probable coronoid in the type specimen of Galeops whaitsi (A.M.N.H.5536).Thus, although the coronoid has been lost in dicynodonts, a small coronoid appears to have been retained in the non-dicynodont anomodonts. Behind the dentary the surangular forms the entire dorsal margin of the mandible and immediately posterior to the level of the jaw articulation, it extends to the lateral surface of the retroarticular process of the articular. It also contacts the prearticular on the lateral surface of the jaw below the rear of the angular. The descending posterior part of the surangular forms a vertical wall which masks the articular

pm

d

Figure 5. Lateral view of lower jaw of Palranornodon y ~ p h u l i (NMQR i 3000). Scale bar = 10 rnrn.

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Figure 6. Medio-dorsal view of lower jaw of Pahanomodon nyaphulii (NMQR 3000). Scale bar = I0 mm.

glenoid from lateral view. This corresponds with the condition in other nondicynodont anomodonts and contrasts with that of dicynodonts where lateral wall is absent and the articular surface is exposed laterally. The angular forms the entire lower border of the mandibular fenestra behind which it is dominated by a large reflected lamina; Posterior to the reflected lamina, the ventral edge of the angular extends posterodorsally, leaving uncovered a triangular area which in most therapsids is overlain by the angular, but here exposes the prearticular. A similar lateral exposure of prearticular is described in Caleops (Brinkman, 1981). The prearticular is a long, slender element underlying the jaw articulation posteriorly and extending forward below the adductor fossa, of which it forms the medial border, to contact the dentary and splenial. The articular surface of the articular closely matches that described for the quadrate. As the lower jaw opened, the obliquely-oriented matching surfaces caused the articular to slip laterally on the quadrate. POSTCRANIAL SKELETON

Postcranial elements were preserved in five nodules found with the skull. Three of the nodules contained six cervical vertebrae, four dorsal vertebrae, and three fused sacral vertebrae, all with associated ribs. A fourth contained the distal portions of a radius and ulna and a nearly complete manus, and a fifth parts of the pelvis and femur.


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Figure 7. Lateral view of cervical vertebrae or Patranmodon nyaphulii (NMQR 3000). Scale bar = 10mm.

Cm'cal vertebrae and ribs The cervical series is represented by five complete vertebrae and the posterior zygapophyses of a more anterior vertebra (Figs 7, 8). These vertebrae are considered to be cervicals because an intercentrum is preserved between the first two complete vertebrae and the ventral surfaces between the remaining centra are bevelled, indicating the presence of intercentra in life; the zygapophyses are further apart than in trunk vertebrae; the ribs are short and sutured to the transverse processes. If the last vertebra in this articulated series is a cervical, as we believe it is, then the first, fragmentary vertebra is the axis and the last is the seventh cervical. The rest of this description assumes that at least portions of all cervicals except the atlas are preserved. The cervical centra are relatively short compared to their widths, unlike in Galechinu where they are as long as they are wide (Brinkman, 1981). A low longitudinal midventral ridge is present on the second complete vertebra (cervical 4), but on none of the others. This also contrasts with Galechinu in which all of the preserved cervicals have a prominent midventral ridge. The neural spines are inclined slightly forward, though their dorsal ends are slightly recurved. The neural arch is positioned over the anterior two-thirds of the centrum and the prezygapophyses extend forward over the posterior third of the preceding centrum. The postzygapophyses, therefore, extend only slightly over the succeeding centrum. An oval intervertebral foramen is formed above the posterior third of each centrum. At the level of the dorsal margin of the last four cervical centra are short horizontal transverse processes to which are sutured the dorsal heads of short doubleheaded ribs. The narrower ventral heads contact the anterior margin of the centrum near its ventral border, just lateral to the facet of the intercentrum. An anteroposteriorly-directed foramen passes between the two rib heads on cervicals 5-7. A foramen associated with the fourth cervical is uncertain. On the third cervical, the rib is very short and its capitulum is attached higher on the centrum and is merged with the tuberculum, so that a foramen between them is absent.

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Dorsal vertebrae and ribs Two complete and two partial dorsal vertebrae are preserved, some with associated ribs (Figs 9, 10). The centra are about as wide as the cervical centra but are longer. Ventral surfaces of the centra are flat and lateral surfaces concave. The neural arches are positioned near the anterior ends of the centrae, and neural spines lie above the posterior two-thirds. These are at least twice as high as they are anteroposteriorly long, and curve slightly posteriorly. The prezygapophyses lie anterior to the neural spines but, unlike those in the cervical series, overhang the preceding centrum only slightly. The postzygapophyses, therefore, extend well behind the neural spine to overhang the succeeding centrum. They appear to be more deeply separated from one another than in the cervicals. A short transverse

Figure 8. Cervical vertebrae of Pafranomodon yaphulii (NMQR3000);A, ventral view; B, dorsal view. Scale bar = 1Omm.


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Figure 9. Lateral view of dorsal vertebrae of Pahanomodon nyaphulii (NMQR 3000). Scale bar = IOrnrn.

process lies near the base of the neural arch below which the lateral surface of the arch is slightly excavated. The ribs are all disarticulated. They are single-headed, with a long ventral process and a short dorsal process which together form a single continuous articulation with the vertebra. A series of slender rib fragments lie on each side on the ventral surface of the nodule (Fig. 10A). They appear to be longitudinally splintered with free segments which are extremely slender and needle-like resembling the supposed gastralia described in Galechim (Brinkman, 1981: fig. 10). Needle-like rib fragments also occur in the type specimen of Galepusjouberti (Brinkman, 1981, fig. 1 l), and an undescribed ‘dromasaur’ (SAM unnumbered specimen). We suggest that the presumed gastralia of Galechinu (SAM 1068), which have been described as unique among therapsids (Romer 1956) are such fragmentary distal ends of ribs, oriented in a similar fashion to those described here in Patranomodon.

Sacral vertebrae and ribs The sacral vertebra with fused ribs are preserved in articulation (Fig. 1 1). They are very fragmentary, lacking centra and most of the neural spines and zygapophyses. The first sacral vertebra preserves the postzygapophyses in articulation with the prezygapophyses of the second vertebra and in the second and third vertebrae only bases of the neural spines are preserved. The sacral ribs of the right side provide a good idea of the nature of the sacral articulation. Their interpretation has been aided by comparison with the unnumbered S.A.M. ‘dromasaur’, which is the only primitive anomodont specimen with the sacroiliac joint preserved. The short shafts of all sacral ribs are inclined slightly dorsolaterally and decrease in basal (anteroposterior) length from first to third. The first sacral rib is incomplete anteriorly and curves back to contact the

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distally expanded second rib. The shaft of the third rib is oriented slightly anteriorly and its expanded distal end broadly overlaps the lateral surface of the second rib to almost contact the first rib.

Forelimb The distal portions of the left radius and ulna are preserved in articulation with a nearly complete manus, though the proximodorsal part of the wrist and adjacent distal crus are incomplete due to weathering. Assuming the portions of the crus to be as in Galechinu, the radius is missing about half its length. The manus (Fig. 12) which is exposed in dorsal view is complete except for the

Figure 10. Dorsal vertebrae of Putranmodon nyaphulii (NMQR 3000);A, ventral view; B, dorsal view. Scale bar = 1Omm.


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absence of the intermedium and pisiform, the proximal part of the ulnare, and parts of terminal phalanges I and 11. The carpus is very similar to that of Gulechim, although the individual elements are more completely ossified and consequently form a more compact unit. The radiale is roughly rectangular, about twice as long. The medial centrale is a proximodistally compressed rectangular element which contacts the entire distal surface of the radiale. It has two distinct distal facets for articulation with distal carpals 1 and 2. The lateral centrale is roughly quadrangular, has a long contact with the medial centrale, a short contact with the radiale, and proximally would have contacted with the medial centrale, a short contact with the radiale, and proximally would have contacted the intermedium. It has a long lateral contact with the ulnare and, at its distolateral corner, just touches the fourth distal carpal. The lateral centrale in Gulechim has a much greater contact with distal carpal

Figure 1 1. Sacral vertebrae of Putranornodon nyaphulii (NMQR 3000); A, lateral view; B, dorsal view. Scale bar = IOmm.

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4.The ulnare is the largest carpal element, and though damaged proximally appears to be slightly longer than wide. It has the shape of a parallelogram, with parallel proximal and distal surfaces and sides which are inclined ventromedially. It contacts the lateral centrale (and intermedium)medially, the pisiform (not preserved) laterally, and distal carpals 4 and 5 distally. The first distal carpal is a large element that contacts the medial centrale and distal carpal 2, and extends distomedially beyond the other carpals. Second and third distal carpals are about equal in size and are essentially mirror images of one another. The second has a curved proximomedial surface in contact with distal carpal 1 and the medial centrale, and a flat lateral surface contacting a matching surface on distal carpal 3. The latter has a curved proximolateral surface contacting the lateral centrale and fourth distal carpal. The large distal carpal 4 is about the same size as the first. Its anteroproximal face turns outward as a prominent lip contacting the ulnare. It also has a short contact with the lateral centrale above distal carpal 3, which it partially overlies. Laterally, it contacts distal carpal 5, a small but wellossified rectangular element which contacts the ulnare proximally. The Mth distal carpal is variably present in anomodonts, also being present in the holotype of Galechinu scholtri, but absent in the referred specimen of G. scholtri and in dicynodonts (Brinkman, 1981; King, 1988; Hopson, 1991). The metacarpals increase in length from first to fourth, with the fifth being about the length of the second. The first metacarpal has a rounded proximal end. This

n

3

Figure 12. Dorsal view of manus of Pahanomodon y@hulii (NMQR 3000).Scale bar = 1 O m m .


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contrasts with the divided, more flattened proximal facets seen in Galechinu (Brinkman, 1981: fig. 10). The proximal articular facets in metacarpals 2 4 appear to be flat, suggesting little movement on the carpus, whereas metacarpal 1 may have been able to abduct and adduct. In addition to their main contacts with their own distal carpals, metacarpal 3 has a small contact with distal carpal 4, as has metacarpal 4 with distal carpal 5. The fifth metacarpal has a distinctive proximal end; it is wider than in the others and only its medial half is in contact with the fifth distal carpal. Its lateral half extends proximally as a distinct process external to distal carpal 5. The shafts of the metacarpals are about equal in diameter. The distal ends of the second through fourth metacarpals are more expanded than the proximal ends. The phalangeal formula, as in all other anomodonts, is 2-3-3-3-3. The ungual phalanges, transversely narrow and slightly curved, are extremely long and although similar in shape, are relatively longer than those of Galechinu. Pelvic girdle and fmur

A partial left pelvic girdle (posterior part of the ilium and much of the ischium) and incomplete femur were prepared from a single nodule (Figs 13, 14). Only the posterior half of the head and a small proximal part of the shaft of the femur are preserved, as well as the dorsal part of the distal end as a separate fragment. The ilium of non-dicynodont anomodonts is inadequately known. Incomplete ilia have been described only in Galepusjouberti and the referred specimen of Galechinu scholtzi (Brinkman, 1981: figs 9 , l l ) and a partial ilium is also preserved in an undescribed and unnumbered ‘dromasaur’ specimen in the South African Museum. Comparison with these specimens indicates that less than half of the ilium is preserved. The restored anterior part (Figs 13,14) includes a very small anterodorsal process, also seen in Galepus. The restored diameter of the supra-acetabular constriction is about 14-15mm7 of which only 6.6mm is preserved. O n this interpretation, the preserved portion includes a large part of the dorsal blade of the ilium, the entire posterior process, and a small portion of the acetabulum. In the unnumbered S.A.M. specimen, which is preserved in dorsal view, the ilium is vertical and oriented parasagitally. The pelvis of Patranomodon is described below as though the ilium had the same orientation. The dorsal blade of the ilium extends above a well developed supra-acetabular buttress as a very thin plate, slightly concave laterally and convex medially. As preserved, it has a nearly straight dorsal border above the acetabulum. The short posterior process comes to a blunt point and has a slightly thickened border. On the supra-acetabular constriction, internal to the supra-acetabular buttress, is a shallow circular depression surrounded by a thickened rim (Fig. 14). Comparison with the undescribed S.A.M. specimen indicates that the depression is the articular surface for the third sacral rib. The sacral articulation is also recognizable in Galepus as a longitudinal trough of roughened bone bounded above and below by low ridges. The intact ilium of Patranomodon would have had additional depressions for the anterior two ribs. Below the sacral articulation, a short, medially-curving extension forms the dorsomedial buttress of the acetabulum and meets the acetabular process of the ischium. The very low position of the sacral articulation is primitive for therapsids

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B.S. RUBIDGE AND J. A. HOPSON

and contrasts with the more dorsal position on the iliac blade in dicynodonts (King, 1988: fig. 40G). The ischium is a long, broad element, consisting of a thickened anterolateral acetabular process which contributes to the acetabulum, and a long plate which extends posteromedially. The medial edge of the ischial plate is damaged, but presumably met the opposite ischium in a long horizontal midline symphysis, as in Galepus and Galechinu (Brinkman, 1981: figs 9,lO). Not enough of the femur is preserved to determine whether the head is inflected medially or tilted upward relative to the shaft. The posterior border of the femur is compressed dorsoventrally. On the underside, about 5 mm from the proximal end, is a deep teardrop-shaped depression bounded front and back by low ridges which converge distally. At the distal end of the depression is a prominent ventral projection. Because the more anterior and distal parts of the femoral shaft are missing, it is uncertain whether this ventral projection continued distally as the lower border of the shaft or whether it was a distinct process. An undescribed ‘dromosaur’ specimen (BP\ 1\2468) preserves the proximal half of the femur and shows that at a comparable distance from the head the posterior part of the shaft shows a similar

Figure 13. Lateral view of pelvis of PatrmMmodon nyaphulii (NMQR 3000). Scale bar = 1 O m m .


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increase in dorsoventral diameter. This suggests that the thickness of the entire femur distal to the head is increasing in Patranomodon. Comparison of the femur of Patranomodon with that of Eodicynodon, the most primitive dicynodont known, shows a similar deepening posterodistal to the head, though that of Eodicynodon lies closer to the head. In the latter, this thickened region resembles the trochanter major of other dicynodonts (Boonstra, 1966). In Patranomodon, a distinct trochanter major is absent. In Galepus, the rear border of the femur, just behind and distal to the rounded head, has a rugose slightly raised ridge which undoubtedly represents the trochanter major. A comparable ridge is absent in Patranornodon. The shaft of the femur gradually widens distally into the paired condyles (Fig. 15) which are separated by a prominent groove extending on to the dorsal surface. The lateral border of the shaft is slightly convex and the medial border slightly concave.

Figure 14. Medial view of pelvis of Palranomdon nyaphulii (NMQR 3000). Scale bar = 10mm.

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Figure 15. Dorsal view of distal end of femur of Putrunornodon "yuphulii (NMQR 3000). Scale bar = I O m m .

DISCUSSION

Hopson & Barghusen (1986) listed ten synapomorphies of Anomodontia, but in their preliminary description of Patranomodon, Rubidge & Hopson (1990) noted that only 4 of these occur in their new genus. We now find the following features characterize the Anomodontia:

(1) Zygomatic arch displaced dorsally well above tooth row, basicraniurn, and jaw articulation. (2) Squamosal with long vertical flange behind quadrate and quadratojugal. (3) Facial region short (about one-third total skull length). (4) Septomaxilla lacking elongated posterodorsal process between nasal and maxilla. (5)Fenestra in lower jaw between dentary, angular, and surangular. (6) Coronoid bone very reduced in size (absent in dicynodonts). (7)Dentition homodont, no enlarged canines (secondarily upper caniniform tooth in VenjukoOVia and dicynodonts). (8)Palatal teeth absent. (9) Fenestra ovalis lying below level of occipital condyle. (10)Heavy pitting on anterior part of dentary, perhaps indicating presence of cornified integument. (11) Manus (and pes) with phalangeal formula of 2-3-3-3-3. Patranomodon is primitive in morphology with respect to other anomodonts (except for Galechinu and Galepus) in the following features: (1) Palatal exposure of premaxilla short, premaxilla not closely approaching palatine medial to the maxilla. (2) Tabular extending ventrally to level of posttemporal foramen, covering contact of supraoccipital with squamosal. (3) Interpterygoidal vacuity an elongate slit between ventral ridges of pterygoids (rather than oval as in more derived forms).


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(4)Screw-shaped articular surface between quadrate and articular, precluding

fore-aft sliding movement of articular on quadrate (articular and quadrate unknown in Ohheria). (5)A possible fifth feature is the presence of only three sacral vertebrae in Patranomodon, (dicynodontshave five); however the number is unknown in other non-dicynodont anomodonts. COMPARISON OF PATM.NOMODOJV WITH GALECHIRUS AND W P U S

When assessing the relationship of Patranomodon to other primitive anomodonts, Rubidge and Hopson (1990) considered its skull to resemble those of Galechinu and Galepus from the Cisttxephalw Assemblage Zone, but to differ sufficiently from both to justifjr its placement in a new genus. They provisionally placed Patranomodon in the family Galechidue of Broom (1912, non King, 1988). However, the skulls of Galechinu and Galepus are very incomplete so that extensive comparison with the excellent skull of Patranomodon is not possible. However, further study of the skull and postcranial skeleton of Patranomodon has yielded additional features which separate this genus from Gakchirus and Galepus.

Comparison with Galechirus The only significant difference between the skulls of Patranomodon and Galechinu is that the premaxilla is more than twice as deep (6 mm vs. 2.5 mm) below the narial opening in Patranomodon than in Galechinu. Even when the greater size of the former is taken into account, the subnarial dimension is still twice as great in Patranomodon. In the postcranial skeleton the post-axis cervical centra (third and fourth) in Galechinu have sharp ventral keels whereas in Patranomodon a low ventral ridge is present on the fourth cervical vertebra but not on succeeding vertebrae. The preserved trunk vertebrae of Galechinu possess low keels but those of Patranomodon have flat ventral surfaces, although information is lacking on possible regional variation in the dorsal series. In the manus, the lateral centrale of Patranomodon has a slight contact with distal carpal 4, whereas in Galechinu this contact is more extensive. Also, the proximal end of the first metacarpal is rounded in Patranomodon but is partially divided, with flat articular facets, in Galechinu. The manual unguals of Patranomodon are proportionally longer than those of Galechinu. In the former they are equal to or greater than the lengths of the two proximal phalanges combined; in Galechinu, the unguals are only a little longer than a single more proximal phalanx. Comparison with Galepus An internal impression is the only part of the skull preserved in Galebus. The few preserved postcranial elements common to both genera do not assist in differentiating Galepus and Patranomodon. However, Galepus has two features which are lacking in Patranomodon. The premaxilla of Galepus forms an incipient secondary

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palate, and there is an edentulous region present anterior to the tooth row (Brinkman, 1981).

CONCLUSIONS

Because Patranomodon lacks several apomorphic characters present in all other nondicynodont anomodonts, with the possible exception of Galechinu and Gahpus, it is considered to be the most primitive known anomodont. It is unique among primitive anomodonts in being represented by a very well preserved skull, the interpretation of which has led to a greater understanding of the phylogenetic relationships of the most primitive anomodonts to each other and to the dicynodonts (Rubidge & Hopson, 1990; Hopson & Rubidge, in prep.). All described ‘dromasaur’ material is preserved as natural moulds with the result that in the past it has been possible to glean knowledge of only a small part of the skull or skeleton. Furthermore, with such incompletely preserved material, it was not always possible to compare one specimen with another for taxonomic assessment. It is now evident that Galeops is more derived in the direction of dicynodonts than the genera placed in the Galechiridae, so that the ‘dromasaurs’from South Africa form a paraphyletic series. Inasmuch as it does not constitute a natural group, the name Dromasauria should be discarded. The discovery of an anomodont in South Africa even more primitive than Otsheria and VmjhVia from Russia, previously considered the most primitive anomodonts (Hopson & Barghusen, 1986; King, 1988), is of great palaeobiogeographic importance. In the past it was considered that the earliest therapsid fauna was known only from Russian Zone I deposits at Ocher, and that the South African therapsids resulted from a migration of elements from the northern hemisphere (Sigogneau & Tchudinov, 1972). With the discovery of Patranomodon and a Syodon-like dinocephalian (Rubidge, 1993, 1994) which closely resemble counterparts from the oldest therapsid fauna from Russia, it is evident that comparably primitive therapsid faunas are present in both South Africa and Russia.

ACKNOWLEDGEMENTS

The authors are indebted to John Nyaphuli for meticulous preparation of the specimen. Chris Engelbrecht and Johann Welman of the National Museum, Bloemfontein, are thanked for permission to work on the material described, and Gillian King and Roger Smith of the South African Museum, Cape Town for the loan of ‘dromasaur’ material in their care. We are indebted to Gillian King and Barry Cox for reviewing the manuscript and for very useful comments. The foundation for Research Development and National Science Foundation (Research Grant BSR-8906619) are acknowledged for financial assistance to Rubidge and Hopson respectively.

REFERENCES

Barghusen HR. 1976. Notes on the adductor jaw musculature of VmjhVia, a primitive anomodont therapsid from the Permian of the U.S.S.R. Ann& ofthe South A~hcanMuseum 68: 249-260.


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Boonstra LD. 1966. The girdles and limbs of the Dicynodontia of the Tapinocephalur Zone. Annals ofthe South Afiean Museum 50: 1-1 I . Brinkman D. 1981. The structure and relationships of the dromasaurs (Reptilia: Therapsida). Brm'ora 465: 1-34. Broom R. 1912. On some new fossil reptiles from the Permian and Triassic beds of South Africa. Proceedings ofthe