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Home , Lycorhinus, Ornithischia, Palpebral (bone), Pes (anatomy), Tatisaurus

Acta P al a eontologica P ol on ica Vol. 30 No. 3-4 pp. 137-150 Warszawa, 1985

TERESA MARYANSKA and HALS ZKA OSMOLSKA

ON ORNITHISCI-IIAN P HYLOGENY

MARYANSKA, T. a n d OSMOLSKA, B .: On ornithischian phylogen y. Ac ta Palaeont. Polonica, 30, 3-4, 137-150, 1985. (is sued 1986). The ornithischian d inosaurs a r e analysed usin g t he cl adistic methodology. The preferr ed hypothesis (se e fig. 1) Is that : 1. a re m onophyletic, 2. Ankylosaur ia a re sister group of a ll othe r or n it hi schians , 3. P achyceph a lo­ saurla + are monophyletic unit s hari ng co m mon char a c te rs not found in other ornlthischians. Quadrupeda li ty is considered as primitive ornithischlan condition.

Key W 0 r d s : d in os a u rs, O rnithischia , cl adistics.

Ter esa M aryansk a . Muze um z tem t, Po!sk a Akademia N auk. c t. Na S kar p ie 20/26, 00-488 W arszaw a ; H a! szka Osm6! sk a. Z a k la d P a! e o b io! o gii , P o!sk a A k ad em i a Nauk, a!. Z WiT k i i W i gury 93, 02-089 W arsza w a . P ol and. R ecei v ed : June. 1985

I NTRODUCTION

Th e mutual relationships of different ornithischian groups ha ve often been discussed. It has been suggested that are the central group (e.g. Galton 1978) from which mos t other ornit hischians deri ved , although recently (e.g. Santa Luca 1984; Sereno 1984) ornit hopods have been removed from the ornithischian ancestry. We (Maryanska and Os­ m6lska 1974) excluded pachycephalosaurs from ornithopods , establishing for them a new suborder - the P achycephalosauria, deriving, however, that suborder traditionally from an ornithopod family - the Hypsilo­ phodontidae. In our other paper (Maryanska and Osmolska 1975) we also followed the traditional opinion that the Ceratopsia evolved from the Ornithopoda. We removed, however, the Psittacosairridae fr om the Orni­ thopoda and considered them as tr ue representatives of the Ceratopsi a, at the same time arguing against psittacosaur anc estry to the remaining Ceratopsia. More recent papers (Coombs 1979; Santa Luca 1980, 1984; Nor ma n 198!a) drew attention to the fact that the ornithopod ischium is unique in possessing an obturator process and this derived character may 138 TERESA MA RYANSKA & HA LSZ KA OSMOLSKA discredit the idea of ornithopod ancestr y to and Certopsia, the represen tatives of which hav e an ischium without the process. In this situation, a question of origins of these two groups remains still open. In fact, the origin of , and their re­ lationship with other ornithischians, are also still unclear (comp. Ma­ ryanska 1977; Coombs 1978a, 1979). For the ab ove reasons, we try in the present paper to test the re­ lationships among ornithischian taxa by means of cladistic methodology. Accordingly, we present below our preferred hypothesis (fig. 1) which in our opinion is more parsimonious than others. The present hypothesis is very clos e to the one which we have outlined earlier (Maryanska and Osm6lska 1984a); some minor differences are discussed here in the res­ pective chapte rs.

PHYLOGENETIC HYPOTHESIS

Ornithischia. - Using as the outgroup the traditionally called Thecodontia I ) we state tha t ornithischians (Group A) share a large number of derived characters, among which we discuss five of those most commonly recognized . They are: predentary (1), quadratojugal with long axis vertical (2), bones (3), pelvis with caudally di rected pubis and an terior prepubic process (4), ossifie d associa­ ted with the vertebral column (5). These synapomorphies support the opinion that Ornithischia are monophyl etic, a view which has never been seriously questioned . Some authors quoted additional characters, Sereno (1984) for instance, listed 15 ornithischian synapomorphies, many of which are acc eptable. Two of these characters cannot be considered synapomorphies: "premaxilla exte nded posterodorsally on the lateral aspect of the face, excluding the m axilla from the border of the external nares" and "pes digit V loses last phalanx" (Sereno 1984: 222). The first of the two is also quoted as a synapomorphy by Charig (1982), and the second by Norman (1984b) . Although it is generally true that pre­ maxilla extends laterally ba ckwards in most ornithischians, resulting , in the exclusion of maxilla from the external naris, the character is already present in many thecodonts (e.g., Chasmatosaurus, Euparkeria) and some other archosaurs (e.g. in some prosauropods), and may be a plesi omorphy in ornithischians. The second character, the reduction of fifth digit, is often obs erved as a derived condition in representatives of every group.

I) The di scu ssion whe ther Dinosauria are mon ophyletic is out of the scop e of th is paper. Some evidence was present ed (Bakker and Ga lton 1974; Seren o 19841 in favor of the close rela tion ships between Or ni t hischia and Prosauropoda and dino saur monophyly. We considere d this hypothesis as premature. O NO RNITHISCHIAN PHYLO GENY 139

Norman (1984b) considers absen ce of the anterior pubic process as an ornithischian synapomor phy. However, the process (= pre pubis) is present in all known ornithischians, although in some it is very short. It should be thus acc epted that the process was already present in a common ornithischian ancestor. First dichotomy - Ankylosauria. - Within the Ornithischia, the an­ kylosaurs differ from all other groups by having the following syna­ pomorphies: closing of supratemporal fen estra (6), closing of antorbital fe nestra (7), development of postocul ar shelf on the postorbital (8), very shor t olfactor y stalks (9), laterally twisted ili ac blad e with very long preacetabular process (10), situated mainly on the ventral surface of ilium (11), exte nsive ar mor (12). We consider the imperforate acetabulum, an outstanding ankylosaur character, a plesiomorphy, in which we follow Maryanska (1977) and Coombs (1979). It is possible that ankylosaurs realized the vertical posture of their hind limbs independently from other ornithischians without developing of the in turned, set-off femoral head and without perforation of the acetabulum , simply by the lateral twist of the ilium (10). It caused a change in the position of the acetabulum which bec ame placed primarily on the ventral surface of ilium. One can suppose that this way to achieve the vertica l (or near-vertical) posture of the fe mur in ankylosaurs parallels a similar de velopment in rauisuchid thecodonts (Bonapar te 1981, 1984). The closed supratemporal and antor bital fenestrae (6, 7) are considered by us as ankylosaur synapomorphies. These characters are found spora­ dically among other ornithischians, often as individual features or in the progressive represen tatives of a given group. For that reason one can consider that these characters appeared con vergently in some non­ ankylosaur ornithischians. Contrary to our earlier hypothesis (Maryanska and Osm6lska 1984a), we do not consider now that the system of cranial sinuses is synapo­ morphic for Ankylosauria, as it is lacking in the . According to our preferred hypothesis (fig . 1), the Ankylosauria constitute a sister-group to all other Ornithischia (Group B); the latest common ancestor of the latter had at least one derived character­ a perforated acetabulum (13) However, if the hypothesis of the dinosaur monophyly is corroborated (comp. foot-note on p. 138) our hypothesis would be falsified in this point. . - Two of most widely known synapomorphies of Ste­ gosauria, the unit which we include in the Group B. are: the double row of plates, or spikes, along the backbone (14) and the very broad and short ischium (15). If, as it appears , stegosaurs were de void of the ossified tendons associated with the vertebral column, the lack of ossi­ fication might be also considered as a derived charact er of that group. A, Ornithischia 8 C o

F·Ceratopsia I

Fig. 1. Clad ogram showing preferred hypot hesis of phylogenetic relationsh ip s w it hi n Ornithischi a . Numbe rs r efer to synapom orph ic or autapomorphic characters. 1 - pre dentary , 2 - qua dra to jugal w it h the long axis ver tical, 3 - palpebra l bones, 4 - p ubis directed caudally, prepubis develop ed, 5 - ossified s a ssociate d wi th ve rtebral column, 6 - closure of supratempo ral fe nestra, 7 - closur e of antor­ bita l fenestra, 8 - postocular shelf on postor bi tal, 9 - ve ry sho rt olfactory stalks, 10 - ilium twiste d laterally w it h long p reacetabular process, 11 - acetabulum pl aced on ventr al sur face of ilium, 12 - extensive ar m or, 13 - pe rforate acetab ulum, 14 ­ do uble r ow of plates or sp ikes al ong backbone, 15 - broad a nd sho rt ischiu m, 16 ­ medially t urned femor al head, 17 - greater trocha nter expanded anteroposteriorly, separ ated from femoral head, le sse r trochanter separated from t he greater. 18 - obturator process on ischi um, 19 - mo re t han twenty-three p resacr a l vertebr ae , 20 - parietals an d squarnosals extended posteriorly over han ging occiput, 21 - vomera in pal atal aspect contacting m axillae anter ior ly. 22 - reduced, shor t and slende r p ubis, 23 - acetabula r po rtions of opposing ilia m ore di stant than the dor sa l ones, 24 - thickened sk ull r oof bones, 25 - su rface of skull r oof bo nes textured, 26 - ossif ication of an te ro medin l orb ital wall, or bit separated fro m n asal cavity, 27 - high occi put, 28 - basicranium se pa­ rated from pa latal and subor bital regions by extended q uadr ate and pterygoid and by junction of basisphenoid and pro otic wi th quadrate w ing of pte rygoid. 29 ­ an te rior por tion of preacet abular process of ili um h or izontal, me dial flange on illium, 30 - pubis peduncle of ischium long, contacting p ubis peduncle of illium, 31 - forelim b about a fourt h of hind limb length, 32 - tozuc-and-gro ovc art icula­ tion between trunk vertebrae zygapophyses, 33 - baske l -- like structure around CCiU­ daIs formed of S- sh aped ossified tendons, 34 - ro stral bon e, 35 - w idenin g of skull across [ugals, 36 - nasa l horn core, 37 - p arietosqua rnosa l fri ll , 38 - sharply pointed and compressed predentary, 39 - three a nter ior cervicals coos sified, 40­ small, highly placed n ar is, -ll - external m anus digit s reduced: fifth entirely lost, fourth wi t h but one p halanx.

(14)/ ON ORNITHISCHIAN PHYLOGENY 141

Th e Scelidosauridae have been traditionally assigned to the Stegosauria, although Romer (1968) considered them as ankylosaurs and Thulborn (1977) as ornithopods. According to our opinion, scelidosaurids are neither ankylosau rs (they have, among other characters, the perforated aceta­ bulum) nor ornithopods (they lack the ornithopod synapomorphy - the obturator process to the ischium). Whether they are stegosaurs is diffi­ cult to decide as long as the entire scelidosaurid material is not re­ examined. Our conclusion concerning phylogenetic position of stegosaurs is similar to that proposed by Norman (1984b) although we wo uld not accept all his synapomorphies. We consider the presence of palpebraIs as an ornithischian synapomorphy, and their incorporation in the orbital margin is found in such non-ankylosaurian and non-stegosaurian or nithischians as most pachycephalosaurs and some ornithopods. Norman proposes a common ancestor to ankylosaurs, stegosaurs, and scelidosaurids; our conclusion in that matter is more r eserved (see above) although Nor­ man's view may be acceptable. We do not agree with Sereno's (1984) phylogenetic hypothesis sug­ gesting a common ancestry to ankylosaurs, stegosaurs and pachyce ­ phalosaurs + ceratopsians. We consider the synapomorphies quoted by this author in his point 11 as doubtful. Th e reduction of the inter­ pterygoid vacuity, caused by medial extension of pterygoids is a com­ mon trend within archosaurs (as well as gen erally in many r eptiles); in pachycephalosaurs this character is also very variable: from a narrow, long vacuity in through vacuity separated into two portions (the anterior and the posterior) in , to medially connected pterygoids with very restricted vacuity visible only in posterior view in . A very similar pattern of development of the pterygoids is observed in ceratopsians which is completely different from that found in the ankylosaurs. The vomera do not extend to the posterior margin of the tooth row in Bagaceratops and in any pachycephalosaur in which the region is known. The degree of reduction of the retroarticular process in the three pachycephalosaurs in which the mandible is known (Stego­ ceras, and ) is ab out the same as in some ornithopods (e.g., , ), which makes it pro­ babl e that reduction of retroarticular process was realized independently several times in ornithischian groups. The another character in the poin t 11 of Ser eno (1984) - reduction of distal carpals to two - cannot be investiga te d in pachycephalosaurs, because the is unknown in these . In our opinion, the number of distal carpals does not constitute a good character for considering phylogen y of dinosaur groups, because these small bones are very often missing and there is often doubt about how many ossified carpals were, in fact, present in a given sp ecies. 142 T ERESA MARYANSKA & HALSZKA OSMOLSKA

Heterodontosauridae. - A femur with a distinctly medially turned head and very prominent 4-th trochanter (16) is a synapomorphy of Group C (the sister-group of Stegosauria). Within that group, the Hete­ rodontosauridae constitute, according to our hypothesis, a sister-group to the remaining ornithischians (Group D), the latter sharing as a syna­ pomorphy the greater trochanter anteroposteriorly expanded, clearly separated from the femoral head, and the lesser trochanter well separated from the greater (17). Only one completely preserved heterodontosaurid is presently known - tucki. However, only its post­ cranial skeleton has been described (Santa Luca 1980); its skull is so far preliminarily characterized (Crompton and Charig 1962; Charig and Crompton 1974). In this situation it is difficult to recognize cranial synapomorphies of that family (for the derived characters of H. tucki see Santa Luca 1980). were earlier considered by us (Maryanska and Osmolska 1984a) as a sister- group of Pachycephalosauria + Ceratopsia, the opinion which we regard now untenable. Sereno (1984) included the Heterodontosauridae to Ornithopoda on the basis, among others, of the "asymmetrical enamel thickness" occurring in the representatives of these dinosaur groups. Consequently, he had to exclude from the ornithopods. We consider Lesothosaurus rather a "good" ornithopod. To us , it seems probable that such a cha­ racter as the asymmetric enamel might be quite often developed conver­ gently several times (and it was at least twice: in the and Ornithopoda). The convergent development of the obturator process on the ischium should be hypothesized in L esothosaurus and ornithopods in the case if the assymetry of ename l is considered a synapomorphy of heterodontosaurids and ornithopods. In our opinion, this is less probable taking into account that, aside of the presence of the obturator process, the entire structure of pelvis is ver y similar in Lesothosaurus and the ornithopods. Ornithopoda. - In Group D, the Ornithopoda (including Lesotho­ saurus) sh are the obturator process to the ischium (18) and a variable number of presacral vertebrae but greater than twenty three (19). As Santa Luca (1980) has noted, the common ornithischian ancestor either had, or had not, an obturator process. Assuming the first possibility, reduction of the process in all non-ornithopod ornithischians should be rega rded as a derived state, acc epting the second possibility it should be considered a primitive one. However, hypothesis considering presence of the obturator process an ornithopod synapomorphy, which appeared after the basal ornithischian divergence had taken place, is more parsimonious. More than 23 presacral vertebrae is found also in stego­ saurids; w e assume here that this character might appear convergently in the latter group. O N ORNITHISCHIAN PHYLO GENY 143

Pachycephalosauria + Ceratopsia. - Ornithopods constit ute a sister group to the Group E, formed of the Pachycephalosauria and Ceratopsia. In agreement with Sereno (1984), we hypothesize the Pachycephalosauria as the sister-group of the Ceratopsia. According to our hypothesis, the shared derived characters of the Group E are: post erior expansion of the parietals and squamosals , all of which overhang the occiput (20), the vomer anteriorly con tacting the maxillae within palate (21), reduced, short and narrow pubis (22), distance between acetabular portions of the ilia much larger than that between the dorsal portions (23). Reduction of the pubis, even complet e, is found also in the ankylosaurs. The pelvic structure is, however, so entire ly different in these groups that the atrophy of the pubis has to be a convergent character. The bending out of the acetabular iliac portions (23) enlarges the effect of a generall y broad spacing of the ilia wi thin the entire group E, and con sequently of the hind limbs. Sereno (1984) mentions nine synapomorphies for pachycephalosaurs and ceratopsians. Two of the above listed derived characters (21, 22) are the same as those of Sereno. His two other characters, these con­ cerning configuration of the jugal are acc eptable to us . We cannot agree, however , with Sereno's opinion that "long, slender pos tacetabular process on the ilium" is a synapomorphy of that group: the process is by no means slender in pachycephalosaurs having a broad medial horizontal extension in form of a medial flange. Th e tooth characters considered by Sereno as synapomorphies are eit he r plesiomorphy or homoplasy. Unique pachycephalosaur characters include: thickening of the skull roof bones (24), their textured nature (25), complet e ossification of the anterior an d medial wall of orbit forming a bony separation between the orbit and the nasal cavity (26), high occiput (27), separation of the basicranium from the palatal and suborbital regions by an extension of the quadrate and pterygoid and by junction of the basisphenoid and prootic wi th quadrate wing of the pterygoid (28), broad, horizontal an­ terior portion of preacet abular process of the ilium and the medial flan ge of ilium (29), pubic peduncle of the ischium long, contacting pubic pe­ duncle of the ilium (30), forelimb reduction to about a fourth of the hind limb length (31), tongue-and-groove articulation be tween the zygapo­ physes of trunk vertebrae (32), basket-like structure formed of the S-shaped ossified tendons around caudal ve r te brae (33). The tongu e- and-gr oove articulation between zygap ophyses (32) was mentioned by Brown and Schlaikijer (1943) also in andrewsi Gran ger et Gregory; the character is evidently absent in all other ceratopsians, and its presence in Protoceratops andrewsi is highly doubtful. The Ceratopsia (Group F) share as deri ved cha racters : the rostral 144 TE RESA MA RYANSKA & HALSZKA OSMOLSKA bone (34) and wi de ning of the skull acr oss the jugals (35). Testing t he thr ee units constituti ng t he Ceratopsia - P sittacosauridae, Protoce­ r atopsidae and Ceratopsidae - w e foun d that the two latter share several derived character s n ot found in t he Psittacosauridae w hich indicates that the Protoceratopsidae and Ceratopsidae share a comm on ancestor , w hich n either had in common with the Psittacosauridae. These synapom orphies are: nasal horn core (36), exte ns ive parietosquamosal frill (37), sharply pointed and com press ed pr edentary (38), three anterior cervicals coossi­ fie d (39). These of the Psittacosauridae are: exte rnal nares small and highly pl aced (40), r eduction of external digits in the manus, the fifth being completely lost , w hile the fourth having but one ve stigial phalanx (41). Formerly, we (Ma ryanska and Osm6lska 1975) r eported the presence of the nas al horn core also in the psittacosaurs. L ately , we were able to state t hat this is not true and t here is no horn core in any psittacosa­ urid known. Conclusions. Our pref erred hypothesis maintains our former sepa­ r ation of the P achyc ephalosauria and the Psittacos auridae from the Ornithopoda, as w ell as the assignment of the Psittacosaur idae to the Ceratopsia as the siste r -g r oup to the Protoceratopsidae plus Ceratopsidae. These opinions are n ow almost ge nerally accepted (Santa Luca 1980, Coombs 1982 , Sues and Galton 1982). However , our ear lie r hypothesis concerning the hypsilophodontid ancestry to the P achyce phalosauria and to the Cer atopsia has been here fa lsified . The Ornithopoda constitute the sister-group to the P achyc ephal osauria plus Cer atopsia, the two la tter sharing an ancesto r in com mo n which neither has in com mon with the Ornithopoda. We do not create in this paper new categorical r anks or n ew n ames for taxa which w ould result from our cladogram (fig. 1). We believe t hat pro lif er ati on of r anks and names would lead to a confusion. So the mor e that to our knowledge, ou rs is the t hir d hypothesis (com p.: Nor­ man 1984 ; Sereno 1984) concerning ornithisc hia n inter-r elationships published wi thin t wo last years (1984-1985). For the same reason, we do not foll ow Zhao (1983) who united Ceratopsia (sensu Maryanska and Osm6lska 1975 ) and Pachyc ephal osaur ia in on e suborder P achycephalo­ , altho ug h we arrived to a similar conclusion that both groups are m ore closely related to ea ch other than to t he remaining ones.

REMAR KS ONORN ITHI SCHIAN EVOLUT ION

The first ornithischian radiation took place towards the end of the , because in t he Lower de posits representatives of hete­ ro dontosaur ids, fa brosaurids and scelidosaurids a re al ready known.Ac­ cor ding to the hypothesis here proposed, it star ted w ith the first m ajor dichotomy , separati ng the Ankylosa uria from an ancestor of all othe r ON ORNITHISCHIAN PHYLOGENY 145 ornithischians. This opinion is supported by a great morphological distance between ankylosaurs and the remaining ornithischians. Among t he most peculiar characters emphasizing that distance should be men­ tioned: universal absence of supratemporal and antorbital fenestrae, w hich are present, at least primitively, in all other ornithischian groups, as w ell as the occurrence of the "tabulars" in the posterior portion of the skull roof, bones which are never found in any advanced (comp. Maryanska 1971: 48). Lately Toumanova (1981) has also drawn the attention to the morphological uniqueness of the Ankylosauria. We should, however, admit that at the moment paleontological record does not confirm such an early separation of the ankylosaurs: their first known presence is from the Callovian of the Northern Hemisphere (). From the Southern Hemisphere () ankylosaurs are reported (Molnar 1980) still later, their only unquestionable represen­ tative, Minmi Molnar, being known fro m the Aptian; assignment of Lametasaurus Matley and Brachypodosaurus Ch akravar ti to the Ankylo­ sauria is doubtful (comp. Galt on 1981). Similarl y as for ankylosaurs, the paleontological record of Stego­ sauria is non-existing in the Triassic; their first occurrence is from the Bathonian of the Northern Hemisphere, where they survived until Neocomian. In Gondwana, however, stegosaurs have their latest record still in the , and may be even in the Maastrichtian (Galton 1981). Early divergence of Stegosauria from . the line leading to other non-anyklosaur ornithischians is supported , in our opinion, by still not fully open acetabulum. Presence of several primitive characters in that g roup (see: Galton 1980: 832) also speaks in favor of early separation. Dong et al. (1983: 145) considered stegosaurs and ankylosaurs as the descendants of a late Triassic heterodontosaurid. We think that the present knowledge of heterodontosaurids does not corroborate the hypo­ t hesis of the close relationships between these dinosaurs. The unquestionable Heterodontosauridae are known only from the of the Souther n Hemisphere (Elliot and Clarens for ma­ tions, southern Africa: Olsen and Galt on 1984; Kitching and Raath 1984). In the Northern Hemisphere, Simmons an d Dianchun­ gosauru s Young are repor ted fro m Lufeng in Chi na (You ng 1982); the assignment of these gene ra to Heterodontosauridae is doubtful. Although the only well known representative of that family, the Early Jurassic Heterodontosaurus tucki Crompton et Charig, was already sp ecialized in some respects (Santa Luca 1980), it still displays several primitive ornithischian characters, which may, in our opinion, indicate that it was close to a common ancestor of all other ornithischians, excluding ankylo ­ saurs and stegosaurs. Such characters include: the long fJrelimbs wi th a large pentadactyl manus, the continuous lesser and greater trochanters on femur (comp. Santa Luca 1980).

3 Acta Palaeontologic a Polonic a Nr 3-4185 146 TERESA MARYANSKA & HALSZKA OSMOLSKA

The ornithischians which are most differentiated and have the most extensive stratigraphic and geographic record are the Ornithopoda, which range from the Lower Jurassic to the end of ; the representatives of almost all ornithopod families are present on both hemispheres. They derived very early: their earliest well known re­ presentative, Early Jurassic Lesothosaurus diagnosticus Galton, may no t necessary be close to the ancestor of the later ornithopods (see below). The ornithopods were evidently the most successful ornithischians. The Pachycephalosauria and Ceratopsia have their earliest records in the Lower Cretaceous, thus their divergence might have taken place in the Late Jurassic. Also still in the Late Jurassic, the Psittacosauridae probably separated from the line ancestral to the remaining ceratopsians: the Protoceratopsidae and Ceratopsidae. These two latter families have their records in the Upper Cretaceous, the earliest protoceratopsids somewhat preceding ceratopsids. It seems reasonable to accept that their divergence started in the Early Cretaceous. Ceratopsia so far seem restricted to the Laurasia (the only ceratopsian recorded from Gond­ wana Notoceratops Tapia has been questioned by some authors), while within the Pachycephalosauia one representative (Majungatholus atopus Sues et Taquet 1979) is known from the Campanian of Gondwana (Mada­ gascar). In our earlier papers (Maryanska and Osm6lska 1974, 1975) we de­ rived both Pachycephalosauria and Ceratopsia from the Hypsilophodon­ tidae. Galton (1978) considered the Fabrosauridae as a basal ornithischian family. Presently, we agree with Santa Luca (1980), that no ornithopod can be considered a possible ancestor to any other ornithischian group. Galton (1978) suggested that an archetypal ornithischian was close to bipedal Lesothosaurus. In contrast, we argue that the first ornithischian was rather a quadruped, or at best only a facultativ biped (we agree in this respect with Coomb's opinion expressed in 1979), with: somewhat shortened forelimbs, a presacral count of vertebrae lower than 24, ossified tendons, closed acetabulum, short prepubis, rather long, post­ eriorly directed pubis, straight ischium without obturator process, small predentary, unspecialized, leaf-like cheek tooth crowns and canine-like premaxillary dentition, slender mandible with low coronoid process and retroarticular process well developed. During a subsequent , one observes gradual improvements of the hip joint preventing the instability of the erect limb during parasagittal motion (characters 13, 16) and establishing the capability for the transverse adjustment of the footfall (character 17; compo Hotton 1980). It is evident that efficient ornithischian bipedality could be achie­ ved only after the hip joint had been adequately modified. The obligatory bipedality within Ornithischia occurred unquestiona- ON ORN ITH IS CII IA N PHYLO GENY 147

bly only in two groups: in some (at least) fabrosaurids (Lesothosaurus) and in all known pachycephalosaurs in which the weakne ss and shortness of the forelimbs excluded any poss ibility of quadrupedal progression. In all other ornithischians for which the obligatory bipedality was tradi­ tionally pos tulated, it was not unequivocally proved, and often the evi­ dence quoted in favor of bipedality sp eaks rather for the cursoriality (comp. Coombs 1978b ). Recen tl y some authors rejected the idea of obliga tory bipedality in man y ornithischians. For instance: it was sugge­ sted by Santa Luca (1980: 200) that "heterodontosaurids... have quadru­ pedal as well as bipedal capabiliti es"; Norman (1980) considered Mantell and Tenontosaur us Ostrom as capable of quadrupedal locomo­ tion; we (Maryanska and Osm6lska 1983, 1984b) considered that in some circumstances hadrosaurs might be quadrupeds, although we share the traditional opinion that they were habitual bipeds because the structure of their manus was unsuited for progression on a hard ground. Our recent inspection of new psittacosaur material in Ulan Bator (presently under elaboration by Dr. A. Perle) has convinced us that the structure of the for elimb, particularly an exceptionally strong deltopectoral crest, as well as the natural curvature of the ver tebral column, speak in favor of the quadrupedal abilities of the psittacosaurs. Microceratops Bohlin was once considered by us (Maryanska and Osmolska 1975) as secon­ darily adapted to quadrupedal progression. It seems, however, equally possible that quadrupedality in that protoceratopsid was the retained, primitive condition and that Microceratops (as the only protoceratopsid) was bipedal during fas t progression. If one excludes ornithopods from the ornithischian ancestry, as we propose in the present paper , it is no longer necess ary to assume that bipedality was primitive for ornithischians. Accordingly, we presume that such ornithischians as: ankylosaurs, stegosaurs and ceratopsians were not secondary, but primar y quadrupeds, while pachycephalosaurs were secondary bipeds. Heterodontosaurids may be regarded as qua­ drupeds which achieved a certain degree of bipedal faculty. The strong curvature of the ver tebral column in the naturally (?) arranged skeleton of H. tucki (Santa Luca 1980: fig . 3) agrees well with the suggested quadrupedality of that . What concerns the ornithopod lineage, a tendency to quadrupedality observed in some forms may be explained either as a retention of primiti ve ornithischian faculties, or as a secondary condition. If the former is true, as we suppose, fabrosaurids would be the ornithopods which achieved very earl y a high degr ee of bipedality and thus could not give rise to any other ornithopod family. Lastly, is should be men tioned here that ornithopods were the only ornithischians which attained large sizes being still able to progress bipedally. On e may suppose that it was possible on ly due to the presence of obturator process which in a way preadap ted the pelvis to support the increasing weights. 148 TERESA MA RYANSKA & HA LSZKA OSM OL SKA

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a nd - 1983. So me im plications of hadrosa urian postc rani cal a natomy. - Act a Palaeont. Polon ica, 28, 1-2, 205-207. and - 1984a. Phylogenetic classification of ornithischia n dinosaurs. I n : Ab­ stracts of 27th Internation al Geol ogical Congress, 1, 286- 287. Nauka Press, Moscou. and - 1984b. P ost cranial a natom y of Saurol ophu s angustiro st r i s with com­ ments on ot her hadrosaurs. In: Z Kielan-Jaworcwsk a (ed.), Resu lt s P ol.­ Mong. P alaeont. Expeds., X .- Palaeont. Polonica, 46, 119-141. MOLNAR, R. E. 1980. An a n kylosaur (Ornithischia: . Rep tilia) from the Lower Cretace ou s of Southern Queensland. - M em. Qd. Mus., 20, 1, 77- 87. NORMAN, D. B. 1980. On the or ni thischian d in osaur I guanod on berni ssart ensi s of Bernissart (Belgium). - M em. Roy. Sci. N at. Be lgique, 178, 1-105. 1984a. On the cranial morphology and evolution of ornithop od d in osa urs. ­ Symp. Z ool. Soc. Lond., 52, 521-547. 1984b . A systemati c reappraisal of the r eptile or de r Ornithischia. Short paps., Third Syrnp. Mesozoi c Terrestrial Ec osyst ems, T tib ingen, 157-162. OLSEN, P . E. an d G ALTON, P . M. 1984. A review of the r eptile a nd amp hi bian assemblages from the Stro m ber g of Southern Africa w ith special emphasis on the footprints a nd the age of the Stormberg. - P al aeon t . Afri cana, 25, 87-110. ROMER, A. S. 1968. No tes a nd commen ts on paleontology 1-304. Univ . Chicago Press. Chicag o, London. SANTA LUCA, A. P . 1980. The p ost cranial ske le ton of H et er odontosauru s tucki (Reptil ia, Ornithischia) from the Stormberg of S outh Afr ica. - Ann. S. Afr. Mus., 79, 7, 159-21l. 1984. P ost cranial r ema in s of F abrosaurid ae (Rep tilia : Ornithischia ) from the Stormberg of So uthern Africa. Palaeon t. Afri cana, 25, 151-180. SERENO, P . C. 1984. The phylogeny of th e Ornithischi a , a reappra isal. S ho rt paps., Third Symp. Mesozoic Terrestrial Ecosy stems, Ttibirige n , 219-226. SU ES, H . D. a nd GALTON, P . M. 1982. The sy stema tic position of. v al densis (Reptilia : Ornithischia) from the Wealden of Northwest ern Ger­ m any. - Palaeontograph ica, A , 178, 4-6, 183-190. a nd TAQUET, P . 1979. A p achycephalosaurid dinosaur from Madagascar and Laurasia- G ondw ana connec tion in the Cretaceou s. - Natur e, 279, 633-635. THULBORN, R. A. 1977. Relationsh ip s of t he Low er J urassic din osa ur Sceliilo­ saurus harrisoni . - J. Paleont ., 51, 4, 725-739. [T OUMA NOVA, T. A .] TYMAHOBA, T. A. 1981. 0 MOPcPO JIOTWqecKOM cnoeofipaa mi aHKJ1JI03aBpoB. - IIaAeo1£ToAb lK., 3, 124-128. (YOUNG, C. C.) YA NG , Z. 1982. On a new genus of din osa ur from Luf'eng. Yunan. In: Z. Min gzh en (ed .), S ele ct ed w orks of Yang Zhungj ian. (In Chi­ nese) 38-42. P ekin. ZHAO, X. 1983. Phylogeny and evolutionary stages of D in osauria, A cta Pa lae ont. Polonica, 28, 1-2, 295-306. 150 TERESA M A RYANSKA & H AL SZKA OSMOLSKA

T ERE SA MARY ANSKA i H ALSZKA OSMOLSKA

o FILOGENEZIE DINOZAUROW PTASIOMIEDNICZYCH (ORN ITHI SCHIA)

,St reszczenie

Dokon ano kl adysty cznej analizy pokrewieilstw miedzy rozny rni gruparni din o­ zaurow ptasiomiedniczych (Ornit hischia). Preferow an a hipote za (fig. 1) po stuluje, i.e: dino zaury ptasiomiednicze sa grupa mon ofiletycznq ; dinozaury pancerne (An­ kylosauria) sa grupa siost rzana w szy stkich pozostalych ptasiom iedniczych; dino­ za ury gruboglowe (Pachycephalosauria) + dinozaury rogate (Ceratopsia) sa jed­ nostka monofiletycznq . Zd aniem autorek, nie ma do ty chczas dostatecznych dowo­ dow pozw al ajacych utrzyrnywac poglad , i.e pi erwotna cecha din ozaurow ptasio­ miedniczych jest dwunozn osc. W chwili obec nej bardziej prawdopodobne wydaje sie, i.e przod ek ptasiomi edniczych byl czworo noi.ny. Praca zostala wyko nana w r amach problemu MR II 6.