150 



C.A. MARSICANO AND A. WARREN 



pmx 



Fig. 3 Trucheosaurus major, holotype MMF 1 2697a. Diagram of skull 

 from Fig. 1 . Scale bar represents 20 mm. m?, possible mandibular 

 fragment. 



Fig. 5 Trucheosaurus major. Drawing of the skull incorporating only 

 those parts preserved on MMF 12697 and BMNH R3728. No attempt 

 has been made to correct probable flattening of the skull or to speculate 

 on the original shape of the occiput. It is unlikely that the paroccipital 

 process of the tabular and exoccipital protrudes posteriorly in the 

 undistorted specimen. Scale bar represents 20 mm. f, frontal; j, jugal; 

 mx, maxilla; n. nasal; p. parietal; pf. prefrontal; pmx, premaxilla; po, 

 postorbital; pof. postfrontal; pp, postparietal; qj, quadratojugal; sq, 

 squamosal; st, supratemporal; t, tabular. 



PHYLOGENETIC ANALYSIS 



Fig. 4 Trucheosaurus major, holotype BMNH R3728. Diagram of skull 

 from Fig. 2. Scale bar represents 20 mm. 



The family Rhytidosteidae was erected by Huene (1920) for 

 Rhytidosteus and Peltostega. Later, Cosgriff (1965) created the 

 superfamily Rhytidosteoidea for the Rhytidosteidae and the 

 monogeneric family Laidleridae (Kitching 1957). Subsequently, 

 Cosgriff & Zawiskie (1979) removed the Laidleridae and erected a 

 new rhytidosteid family, the Indobrachyopidae, for those members 

 of the Rhytidosteidae with rounded, as opposed to triangular, skulls. 

 Because they were unable to distinguish the families Rhytidosteidae 

 and Indobrachyopidae except on the basis of skull outline, Warren & 

 Black (1985) returned the members of the Indobrachyopidae to the 

 Rhytidosteidae. Shishkin (1994) re-erected the Rhytidosteoidea. 

 including in it the Rhytidosteidae and Peltostegidae. More recently, 

 Warren ( 1998) restricted the superfamily to the Rhytidosteidae and 

 Laidleridae. 



The purpose of this preliminary analysis is to provide a hypothesis 

 for the relationships among rhytidosteids and determine whether 

 more than one monophyletic group is represented. Nearly all those 

 characters used in the different revisions mentioned above were 

 considered. Nevertheless, the triangular shape of the skull, although 

 it was used in all previous diagnoses of the family, was not included 

 as it was not possible to define discrete states for this character, 

 especially in the case of incomplete material. 



The following rhytidosteid taxa were used in the analysis: 

 Rhytidosteus capensis (Owen 1884, Cosgriff 1965), Peltostega sp. 

 (Nilsson 1946), Laidleria gracilis (Kitching 1957, Warren 1998), 

 lndobrachyops panchetensis (Heune & Sahni 1958, Cosgriff & 

 Zawiskie 1979), Deltasaurus kimberleyensis (Cosgriff 1965), 

 Rewana quadricuneata (Howie 1 972), Derwentia warreni (Cosgriff 

 1974), Arcadia myriadens (Warren & Black 1985), Boreopelta 

 vavilovi (Shishkin & Vavilov 1985), Mahavisaurus sp. (Lehman 



