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The Morphology and Relationships of Youngina Capensis Broom and Prolacerta Broomi Parrington

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The Morphology and Relationships of Youngina Capensis Broom and Prolacerta Broomi Parrington 89 Palaeont. afr., 18, 89- 131 (1975) THE MORPHOLOGY AND RELATIONSHIPS OF YOUNGINA CAPENSIS BROOM AND PROLACERTA BROOMI PARRINGTON by C. E. Gow ABSTRACT Comprchcnsive descriptions o f the osteology of Youngina capensis Broom and Prolacerla broomi P<llTinglon arc presenled. New det<lil s of the braincase of Prolerosuchus Jergusi Broom are given as these became necessary for comparative purposes. It is suggested that the initial radiation of sauropsid reptiles was a Permian event as yet poorly documented. The phylogenetic position of Yo III/gil/a bOlh forward and backward in time cannot be narrowly defin ed , though certain charae!crs sccm spccific<lll y to preclude it from lizard ancestry. Proiacerla, on th e basis of tooth implanlalion. braincase morphology and postcra nial anatomy is shown to be closest to the prolcrosllchia n Ihecodonts. It is very definitely not concerned with lizard origins, but would on <lvailablc cvidcncc seem to be a perfectly good ancestor for the middle Triassic fo rms M aOWI/1'1I/1IS and TrlnV.llro/lheus, which latter must cease to be regarded as li za rd ancestors. We have herc a ralher distinct reptilian lineage which branched off from common ancestral stock .illsl prior 10 Ih e advcnt of archosaurs. CONTENTS Page INTRODUCTION .... 89 YOUNG INA M<llerial and Methods 90 OSleology 90 Fllne! ion . 97 Relalionships 98 Synonymy and diagnosis PROLACERTA Review of literature and material 99 Ma terial and Methods 99 Osteology 100 Prolerosuckus braincase III Flllle! iOIl 112 Ecologv ..... 116 Rela I io'nships 116 Synonymy and diagnosis 118 DISCUSS ION 118 SU MMARY 123 REFE RENCES 123 LIST OF ABBR EV IATIO NS 131 INTRODUCTION are notas generalised as has until now been believed. The Eosuchia are an order within the Subclass The Permian eosuchians, typified by Youngina, are Lepidosauria and in the light ofthe present study must generally considered the hub oflater diapsid reptilian be added to Romer's (1956 ) otherwise satisfactory diversification (e .g. Romer, 1956 ). definition that dorsal dermal armour was present. The Youngina is relatively poorly known ; thus part of the genera comprising Romer's family Younginidae are a present study will describe the anatomy of this animal reasonably homogeneous group, with the exception in detail. To begin with it will be necessary to decide of Noteosuchus, which shows rhynchocephalian af­ just what we mean by Eosuchia and to try to decide finities (Carroll, pers. com.). Of the rest the best what is to be understood as comprising the genus material in existence is that of Youngina (with its tax­ You ngina. Here it is necessary to be very explicit as it is onomic variants), and these with their smooth peg­ becoming clear that the Upper Permian was a crucial like marginal dentition can be distinguished from period in sauropsid evolution and that relationships H eleosaurus (Carroll, in press) which has serrated 90 marginal dentition and certain other features which Material referable to Youngina capensis Broom 1914. put it more closely in line with the Archosaurs. A.M. N.H. 5561: Younginacapensis Broom 1914. Skull Broom (1914 et seq.) was responsible for the three and vertebrae, in American Museum of Natural generic and five specific names with which what is History. mani festly one form (Youngina capensis) is presently en­ Locality: New Bethesda, Graaff- Reinet. cumbered. This string of names is misleading; all the Collected: R. Broom. specimens come from the same horizon, differing only u.c. 1528: Youngoides romeri Olson and Broom 1937. in size, state of preservation and preparation, and Skull in University of Chicago. nature of deformation, which factors adequately ac­ Locality:Towerwater, Murraysburg. count for all supposed taxonomic differences. One R. C. 90: Y oungopsis rubidgei Broom and Robinson can have no doubts about synonymising them all un­ 1948. Very good skull. der Youngina capensis to stress the probability that this Locality: Doornkloof, Graaff- Reinet. was a single monospecific genus. This work will pre­ Collected:J. W. Kitching, 1939. sent a detailed description of this animal based on all R. C. 91: Youngoides minor Broomand Robinson 1948. useful material. A poor partial skull. A second undescribed Pro lacerta (Parrington, 1935), on the basis of its in­ specimen with the same number is also Youngina. complete lower temporal bar, has been considered to Locality: New Bethesda, Graaff- Reinet. represent a stage between the Eosuchia and the Collected: Kitching Bros., 1940. Squamata, but this concept must be reject~d. Acritical T.M. 1490: Youngopsis kitchingi Broom 1937. A very re-examination of the true position of Prolacerta is poor skull. necessary. Until now Pro lacerta (which includes Pricea) Locality: New Bethesda, Graaff- Reinet. has been known from a few skulls and some cervical Collected:J. W. Kitching. vertebrae. Largely on the basis ofan incomplete lower T.M. 200: Younginacapensis Broom 1922. Fragments of temporal bar it has been regarded as ancestral to the postcranial skeleton, now even fewer than when Squamata. The present study describes the whole described by Broom, but certainly ofYoung ina. skeleton and the animal is shown to be Archosaurian Locality: New Bethesda, Graaff- Reinet. in almost every respect. Collected: I. Venter, circa 1920. The braincase ofProterosuchus is here re-described in T.M. 3603: Posterior half of a large skull, now acid some detail for comparative purposes. prepared. No catalogue data. R. C. 625 and 626: Two poorly preserved skulls. YOUNGINA Locality : Well wood , Graaff- Reinet. Collected: S. H. Rubidge, 1936 -45. MATERIAL AND METHODS R.C. 714: Incomplete skull. The descriptions of Youngina are based on Locality: Ganora, New Bethesda, Graaff-Reinet. material in the Bernard Price Institute (BPI) and one Collected: S. H. Rubidge, 1940. partial skull from the Transvaal Museum (TM). The K. 106: Badly flattened skull in the collections of the several specimens in the Rubidge Collection (RC) Geological Survey, Pretoria. - were examined. Professor Crompton kindly provid­ Locality: Blaaukranz. ed copies of his unpublished drawings of Youngina Collected: A. W. Keyser. rubidgei; these, though useful, have not been used B.P.1.375:Skull. here, and there are one or two points where we Locality: von der Waltzhoek, Graaff- Reinet. differ. These points of difference are those which it Collected:J. W. Kitching, 1946. has been possible to prepare more fully. A cast and B.P.1.2459: Small flattened partial skull. photographs of the Chicago specimen (Youngoides Locality: Klipplaat, Richmond. romeri ) were made available to the author. Collected:J. W. Kitching, 1951. All Youngina material comes from the Dap­ B.P.1.2871 : Skull. tocephalus zone of the Karroo. The state of preserva­ tion is rather different from that of the millerettids Locality: Beeldhouersfontein, Murraysburg. (Gow, 1972) of the same age, which might imply Collected:J. W. Kitching, 1958. some ecological differences in life. While the B. P.1. 2859: Skull and skeleton. millercttids are articulated and distortion free, the Locality: Doornplaas, Graaff- Reinet. younginids are disarticulated and the skulls are dis­ Collected:J. W. Kitching, 1964. torted. Most of the Youngina material has in the past been OSTEOLOGY OF YOUNGINA subjected to mechanical preparation which had caused some damage and also restricted the scope of The Skull further work. Fortunately it was possible to prepare Dnma/ bonf'1 of the skull roof a good braincase and skeleton in formic acid; other details were pieced together from mechanical PTf'1llaxil/a (Figures 1 and 6). The premaxilla is preparation of selected areas of different skulls. fairly well represented only in B.P.I. 2871. There 91 N ------t. 2cm Figure I. Youngina capensis B.P.I. 287 J. appear to have been three premaxillary teeth. The Parietal (Figures 2, 4, 5 and 6). The parietals enclose a important feature of the premaxilla is its medial ex­ large pineal opening and send out posterolaterally tent in the palate: the premaxillae run well back in­ directed wings. The area bordering the upper tem­ side the maxillae in a strong contact and meet in the poral opening is deep and has a shallow pocket in the midline. posterior corner affording a strong area of origin for Maxilla (Most Figures). The maxilla sheaths most of the part of the jaw adductor muscle complex. The wings slender, rather shallow snout, and has an extensive are joined by a slight ridge between skull table and oc­ contact with the palatine. The teeth are conical, sharply ciput. Each lateral wing forms important at­ pointed and not serrated; they thicken lingually at the tachments; anteriorly there is an extensive firm con­ base much as described for Milleretta (Cow , 1972); they are tact with the squamosal (Figures 4 and 6): applied to sub-thecodont and become firmly ankylosed in deep pi ts. the posterior surface are a post-parietal and tabular, An exact count is not possible but there are about30 tooth while the tip is sheathed by a supratemporal whose ex­ positions with alternate replacement so that one gets a act relationships will be discussed separately. The count of about 20 functional teeth of different ages. An lateral wings roof large post-temporal fossae and important aspect of the maxillary tooth row is that it there is no firm contactwith the supraoccipital. extends back to below the postorbital bar (c.f. Postfrontal. The postfrontal is firmly sutured Proterosuchus Cruickshank, 1972, and crocodilians, but between frontal and postorbital. not lizards) . Postorbital. The postorbital is overlapped above by SeptomaxiLla. Detailsofthis bone are totally lacking. the post-frontal (this region, the anterior border of Nasal (Figures 1 and 6). The relationships of the th e upper temporal opening, is deep); ventrally it has a nasals are clear except anteriorly where there is some rigid sloping contact with the jugal, and posteriorly a doubt as to the exact position of the sutures with the broad flat sheet has an extensive overlap onto th e premaxillae, but this is oflittle consequence.
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