MONJUROSUCHIDAE, AS A MONOPHYLETIC

Gao, Ke-Qin & Fox, Richard C., 2005, A new choristodere (Reptilia: Diapsida) from the Lower Cretaceous of western Liaoning Province, China, and phylogenetic relationships of Monjurosuchidae, Zoological Journal of the Linnean Society 145 (3), pp. 427-444 : 438

MONJUROSUCHIDAE AS A MONOPHYLETIC FAMILY

Two genera and species are currently classified in the family Monjurosuchidae : the type species Monjurosuchus splendens from the Yixian Formation exposed near Lingyuan, and Philydrosaurus proseilus gen. et sp. nov. described here from the Chiufotang Formation exposed near Chaoyang. With inclusion of these two taxa in a revised data set (Appendix 2), a parsimony analysis revealed that the monophyly of the family is supported by the following synapomorphies: dorsal process of squamosal absent (13-2; unknown for Hyphalosaurus and Shokawa ); supratemporal fenestra smaller than orbit (14-0; character reversal); infratemporal fenestra closed (15-1; homoplastic in Lazarussuchus , see Evans & Klembara, 2005); post-temporal fenestra absent (47-1; also in Simoedosauridae ); posterior process of ischium strongly developed (75-1; uniquely diagnostic for the family Monjurosuchidae ).

A POSSIBLE MONJUROSUCHIDAE –HYPHALOSAURIDAE CLADE

Hyphalosaurus and Shokawa are two morphologically peculiar, long-necked choristoderes known from the Lower Cretaceous of China and Japan ( Evans & Manabe, 1999; Gao, Tang & Wang, 1999). Both MPTs ( Fig. 6 ) recognize a Hyphalosaurus – Shokawa clade, for which the name Hyphalosauridae (fam. nov.) is proposed here. The grouping of the two forms in the family Hyphalosauridae is unambiguously supported by two uniquely derived character states of the two genera of the family: cervical vertebral count more than 16 (67-1); and caudal neural spines tall and narrow (72-1). Because the skull morphology is either poorly known or entirely unknown for the two forms, the diagnosis of the family would be enhanced by further study of the known material and discovery of new material.

Within the phylogenetic framework of the Choristodera , both Monjurosuchidae and Hyphalosauridae are recognized as robust familial groups outside the neochoristoderan clade; however, the two MPTs differ from one another in placing the two families as either successive sister groups with the Neochoristodera ( Fig. 6A ), or grouped together as the sister group with the Neochoristodera ( Fig. 6B ). The grouping of Monjurosuchidae with Hyphalosauridae as sister groups is weakly supported by the following two character states: lateral borders of frontals strongly constricted (3-1; unknown for Shokawa ); and orbit large and dorsally orientated (11-1; unknown for Shokawa ). Because the current data matrix contains a large amount of missing data for the basic taxa of the two families, the robustness of the possible Monjurosuchidae– Hyphalosauridae clade must be tested further when new data become available.

Figures

Figure 6. Comparison of the two equally parsimonious trees (TL = 123 steps; CI = 0.85; RI = 0.87) derived from analysis of data presented in Appendices 1 and 2.