Tetrapod diversity and palaeoecology in the German Middle Triassic (Lower Keuper) documented by tooth morphotypes

摘要

Continued excavations during the last decade have yielded large quantities of tetrapod remains from the Middle Triassic (Ladinian) Erfurt Formation (Lower Keuper) in Germany. The temnospondyl dental morphotypes are highly variable but represent low taxonomic diversity. This is in contrast to the reptilian tooth morphotypes, which comprise a minimum of 26 distinct types, only some of which can be referred to taxa based on diagnostic skeletal material. The assemblage includes a taxonomically diverse range of semi-aquatic or aquatic faunivores, in addition to large terrestrial carnivores and many smaller-sized forms that may have subsisted on invertebrates and small vertebrates. With only two taxa known to date, tetrapods with dentitions suitable for oral processing of plant material form the least common faunal element. The Lower Keuper assemblages are dominated by diapsid reptiles, especially archosauriforms. Unlike in the more or less coeval tetrapod communities from Gondwana, gomphodont cynodonts are represented only by a single molariform tooth to date, whereas avemetatarsalian archosaurs are entirely absent. Most remarkable is the virtually total absence of medium- to large-sized herbivores (rhynchosaurs, dicynodont synapsids).