The Origin And Intrarelationships Of Triassic Capitosaurid Amphibians

Abstract

ABSTRACT. The status of the temnospondyl family Capitosauridae is reviewed. Only by the inclusion of the genera Mastodonsaurus and Eocyclotosaurus can this group be considered monophyletic. This view is based on a range of robust characters which in combination constitute the most parsimonious hypothesis. The traditional view that Mastodonsaurus and Eocyclotosaurus are sister taxa of Benthosuchus is demonstrated to be based on highly variable and/or homoplastic features, whose ancestral condition is moreover uncertain. The Capitosauridae encompasses the following successive sister groups: (1) various species of Parotosuchus (which do not necessarily form a monophylum); (2) the genera Eryosuchus and Mastodonsaurus (which are probably monophyletic); and (3) a range of taxa with semi-closed or entirely closed otic notches, including the genera Wellesaurus, Kupferzellia, Eocyclotosaurus, and Cyclotosaurus. The closure of the otic notch, an oft-cited trend among capitosaurs, is most easily explained to have occurred only once, namely within the more advanced capitosaurids; the stratigraphical signi®cance of this feature is, however, very limited.KEY WORDS: Temospondyli, Stereospondyli, Capitosauridae, phylogeny. CA P I T O S A U R S form a large group of widespread and abundant Triassic temnospondyl amphibians.Their appearance is crocodile-like with a relatively very large skull, a long and¯attened trunk, and a tail of moderate length. Capitosaurs reach lengths of between two and ®ve metres, the European genus Mastodonsaurus being the largest well-known representative. Their remains have been found on every continent, and they form a major component in most Triassic tetrapod assemblages.Although capitosaur phylogeny has never been studied in great detail, there exists a generally accepted concept of a phylogenetic trend from open-notched (capitosaur) to closed-notched (cyclotosaur) forms through the Triassic (Watson 1919(Watson , 1951 Sa Ève-So Èderbergh 1935;Romer 1947; Welles and Cosgriff 1965;Ochev 1966).Capitosaur phylogeny and systematics have long suffered from two major problems: (1) the enormous quantity of fragmentary material of uncertain systematic assignment: and (2) the lack of thorough anatomical studies on representative taxa of the group. The concept of a general phylogenetic trend in capitosaur phylogeny was frequently utilized (among other sources) to correlate horizons of Triassic terrestrial sediments (Watson 1958; Welles and Cosgriff 1965;Ochev 1966; Kamphausen and Morales 1981). Capitosaurs have become a predominant component of such correlations in recent years (Ochev and Shishkin 1989;Shishkin et al. 1995;Hancox et al. 1995).The phylogeny of capitosaurs has only recently been tentatively studied on the basis of phylogenetic systematics (Ingavat and Janvier 1981;Milner 1990Milner , 1993Gubin 1997). A detailed phylogenetic analysis which relies on clear outgroup comparison, explicit character recognition, and a test of congruence is still lacking for capitosaurs in general. This is particular...

A new stereospondyl from the German Middle Triassic, and the origin of the Metoposauridae

“…Anterior palatal vacuity (character 43): The palatal vacuity of lydekkerinids, capitosauroids, brachyopoids, rhytidosteids, and plagiosaurids is unpaired, and the very similar outline of the anterior palatal depression in rhinesuchids suggests this to be the primitive condition. (In rhinesuchids the anterior palate may be perforated, but then differs from all other cases in being tiny and deeply emplaced within a much larger unpaired depression, see Schoch, 2000.) Early in the evolution of the trematosaurian clade a wide medial bridge separated the anterior palatal opening in the midline, which is retained throughout the trematosaurian clade as defined here.…”

“…the capitosauroid M. giganteus (Schoch, 1999), as representative of the capitosauroids (single exception: character 43, the derived state of which occurs in Mastodonsaurus , whereas other capitosauroids retain the plesiomorphic state, see Schoch, 2000 and Damiani, 2001),…”

“…Early in the evolution of the trematosaurian clade a wide medial bridge separated the anterior palatal opening in the midline, which is retained throughout the trematosaurian clade as defined here. In capitosauroids, such a medial subdivision evolved at least twice: once in mastodonsaurids and a second time within the cyclotosaurids (Schoch, 2000). The primitive condition for capitosauroids was a heart‐shaped unpaired opening.…”

A supertree of early tetrapods

“…We also excluded trees superseded by studies that incorporate a broader taxon and character sample (e.g. stereospondyl analyses predating Schoch (2000); Yates & Warren (2000); Damiani (2001) and Steyer (2002) …”

REVISION OF THE TYPE MATERIAL AND NOMENCLATURE OFMASTODONSAURUS GIGANTEUS(JAEGER) (TEMNOSPONDYLI) FROM THE MIDDLE TRIASSIC OF GERMANY

“…(1990), Warren and Snell (1991), Warren and Davey (1992), Kamphausen and Ortlam (1993), Milner (1994), Hancox et al . (1995), Damiani (1999, 2000, 2001, 2002), Schoch (1999, 2000, 2002 b ), Schoch and Werneburg (1999), Schoch and Wild (1999), Damiani et al . (2000), Schoch and Milner (2000), Steyer (2000), Damiani and Hancox (2003), Damiani and Rubidge (2003) and Tverdokhlebov et al .…”