Osteology and relationships of the Late Triassic giant dicynodont Lisowicia

Abstract

Unexpectedly abundant remains of herbivorous therapsids in the Late Triassic strata of southern Poland have significantly supplemented knowledge of their evolution. The skeletal morphology of the Late Norian (or Rhaetian) dicynodont Lisowicia bojani supports its close relationship to the Carnian Woznikella, both known from the Polish part of the Germanic Basin. Three evolutionary lineages of dicynodonts—Laurasian–Gondwanan Rhadiodromus klimovi → Jachaleria candelariensis lineage, Laurasian lineage Shaanbeikannemeyeria xilougouensis → Lisowicia bojani, and the Gondwanan lineage Kannemeyeria simocephalus → Dinodontosaurus brevirostris—are distinguished based on characters of cranial and postcranial elements. In the lineages characterized by the parietal oval in cross-section and the two distinct articulations on the sternum, there is a tendency to exclude the frontal from the orbital margin and to reduce the number of sacral vertebrae. In the lineage with the parietal narrow and triangular in cross-section, the frontal forms part of the orbit margin, there is a single joint on the sternum, and there is a tendency towards flattening the skull roof. In both lineages the shoulder girdle is convergently modified, the acromion process decreased, and joints on the sternum moved posteriorly.