A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria.
Reptiles have a long history of transitioning from terrestrial to semi-aquatic or aquatic environments that stretches back at least 250 million years. Within Archosauria, both living crocodylians and birds have semi-aquatic members. Closer to the root of Archosauria and within the closest relatives of the clade, there is a growing body of evidence that early members of those clades had a semi-aquatic lifestyle. However, the morphological adaptations to a semi-aquatic environment remain equivocal in most cases. Here, we introduce a new Middle Triassic (245-235 Ma) archosauriform, Litorosuchus somnii, gen. et sp. nov., based on a nearly complete skeleton from the Zhuganpo Member (Ladinian [241-235 Ma]) of the Falang Formation, Yunnan, China. Our phylogenetic analyses suggest that Litorosuchus is a stem archosaur closely related to the aberrant Vancleavea just outside of Archosauria. The well-preserved skeleton of L. somnii bears a number of morphological characters consistent with other aquatic-adapted tetrapods including: a dorsally directed external naris, tall neural spines and elongate chevrons in an elongated tail, a short and broad scapula, webbed feet, long cervical vertebrae with long slender ribs, and an elongated rostrum with long and pointed teeth. Together these features represent one of the best-supported cases of a semi-aquatic mode of life for a stem archosaur. Together with Vancleavea campi, the discovery of L. somnii demonstrates a growing body of evidence that there was much more diversity in mode of life outside Archosauria. Furthermore, L. somnii helps interpret other possible character states consistent with a semi-aquatic mode of life for archosauriforms, including archosaurs.
Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, P. O. Box 643, Beijing, 100044, People's Republic of China. lichun@ivpp.ac.cn.
Chun
C
Li
Canadian Museum of Nature, P.O. Box 3443, Station "D", Ottawa, ON K1P 6P4, Canada. xcwu@mus-nature.ca.
Xiao-Chun
XC
Wu
Zhejiang Museum of Natural History, 6 Westlake Culture Square, Hangzhou, Zhejiang Province, 310014, China.
Li-Jun
LJ
Zhao
Department of Geosciences, Virginia Polytechnic Institute and State University, 1405 Perry Street, 4044 Derring Hall (0420), Blacksburg, VA, 24061, USA.
Sterling J
SJ
Nesbitt
Department of Geosciences, Virginia Polytechnic Institute and State University, 1405 Perry Street, 4044 Derring Hall (0420), Blacksburg, VA, 24061, USA.
Michelle R
MR
Stocker
Geological Survey of Guizhou Province, Guiyang, 550005, China.
Li-Ting
LT
Wang
D000222:Adaptation, Physiological; D000818:Animals; D059001:Aquatic Organisms / Q000145:classification*; D044822:Biodiversity; D002681:China; D005580:Fossils; D010802:Phylogeny; D012104:Reptiles / Q000033:anatomy & histology* / Q000145:classification*; D013045:Species Specificity
Adaptation; Morphology; Phylogeny; Reptile; Semi-aquatic