IV.—The Morphology and Relationships of a Complete Therocephalian Skeleton from the Cistecephalus Zone of South Africa

Abstract

SynopsisA description is given of a new genus of mammal-like reptile, Mirotenthes, of which a remarkably complete and well-preserved skeleton was collected in 1936 by Professor Camp of the University of California, from the late Permian deposits of the South African Karroo.Unlike the majority of Permian mammal-like reptiles, Mirotenthes was an agile form of small dimensions. Many of the skeletal characters exhibit a significant approach towards the mammalian threshold. The limb structure is very advanced and the digital formula is mammalian. The differentiation of ribs to form a definite rib-cage of mammalian type is particularly noteworthy and may indicate the presence in this genus of a mammalian respiratory mechanism.The systematic study of this complete skeleton does much to bridge the gap between the primitive basal groups of mammal-like reptiles and the advanced Triassic groups from which the mammals derive. It has been known for many years that small, fast-moving carnivorous forms were present in the late Permian fauna, but the evidence has been fragmentary. The complete skeleton described in this paper throws new light on these hitherto poorly known genera.

A new skeleton of the therocephalian synapsid Olivierosuchus parringtoni from the Lower Triassic South African Karoo Basin

“…Towards the distal ends, they flare out slightly and become anteroposteriorly flattened. The thoracic ribs differ from those in Mirotenthes , which appear to have holocephalous heads (Attridge 1956).…”

“…Postcranial skeleton. To date, the postcranial elements of Cynariognathus (Cys 1967), Blattoidealestes (Boonstra, 1954), Pristerognathus (Broom, 1936), Macroscelesaurus (Haughton, 1918), Ictidosuchoides (Broom 1938), Mirotenthes (Attridge, 1956), Glanosuchus (Fourie 2001), Silpholestes (Broom, 1948), Zinnosaurus (Boonstra, 1964), Theriognathus (Boonstra, 1934; = Aneugomphius Brink, 1958), Zorillodontops (Cluver, 1969), ‘ Tetracynodon ’ (Sigogneau, 1963), Ictidosuchus (Broom 1901), Ericiolacerta (Watson, 1931; Colbert and Kitching 1981), Olivierosuchus (Brink, 1965), Regisaurus (Kemp 1978), Bauria (King 1996; Fourie 2001), Ordosia (Hou 1979), a baurioid that was tentatively identified as a regisaurid (Kemp 1986) and an unidentified bauriamorph (Watson 1931) have been described. However, Olivierosuchus is the only akidnognathid whose postcrania have undergone any form of cursory description (Brink 1965).…”

Therapsids as Mammals

“…Foramina for blood vessels and nerves, analogous to the mammalian infraorbital foramen, are present in the maxillary and sometimes also the premaxilla, lacrimal, nasal, and dentary of many and diverse therocephalians and gorgonopsians (Broom 1920(Broom , 1936aBroom and Robinson 1948;Watson 1931;von Ruene 1950;Brink 1954Brink . 1959Brink and Kitching 1953a;Crompton 1955a;Attridge 1956), and are the rule in cynodonts (e.g. Simpson 1933, Parrington 1934.…”

“…The presence of a diaphragm in some cynodonts and a therocephalian (Attridge 1956) is inferred from the great reduction of lumbar ribs (esp. Brink 1957a).…”

“…Broom 1938, Boonstra 1937, von Huene 1940, Brink 1951, Attridge 1956) and gorgonopsians (e.g. Watson 1920, Olson 1944, Romer 1956) is claimed by different authors because of different interpretations of the parallelisms involved, and the tapinocephalians are alternately grouped with the dicynodonts in the Anomodontia (Watson and Romer 1956) or with the titanosuchians in the Dinocephalia (Haughton and Brink 1954), to both of which they are manifestly related.…”