The newly-described saurosphargid reptile Prosaurosphargis yingzishanensis represents the earliest known occurrence of its clade.
Life reconstruction of Prosaurosphargis yingzishanensis depicted in the Early Triassic shallow marine environment of the Nanzhang-Yuan’an region, Hubei Province, South China. Image credit: Wolniewicz et al., doi: 10.7554/eLife.83163.
Prosaurosphargis yingzishanensis lived in what is now South China during the Early Triassic epoch, some 247 million years ago.
“Several groups of reptiles invaded the marine realm in the aftermath of the end-Permian mass extinction, the largest extinction event in Earth’s history,” said Hefei University of Technology paleontologist Jun Liu and colleagues from Germany, Poland, and China.
“This phenomenon was likely a result of the scarcity of marine competitors and predators caused by the extinction event and high productivity in the incipient shallow marine environment.”
“Triassic marine reptiles, including the iconic Ichthyosauromorpha and Sauropterygia, as well as some other smaller and lesser known groups, achieved high taxonomic and ecological diversity rapidly after their emergence in the Late Early Triassic and played a pivotal role in the reorganization of marine food webs following the end-Permian extinction.”
“Because Mesozoic marine reptiles represent likely several independent transitions from a terrestrial to an aquatic lifestyle, they also provide an ideal system to analyze the roles of function and constraint in determining evolutionary pathways.”
Prosaurosphargis yingzishanensis was approximately 1.5 m (5 feet) in total body length and was covered by a heavy dermal armor composed of osteoderms.
The ancient species belonged to Saurosphargidae, a small group of aquatic reptiles within the large clade Sauropterygia.
“Sauropterygia was a diverse clade of Mesozoic marine reptiles that first appeared in the Late Early Triassic and its members remained important predators in marine ecosystems until their extinction at the end of the Late Cretaceous,” the paleontologists said.
“Sauropterygia is traditionally divided into two major lineages, representing two markedly different body plans: the Placodontia and the Eosauropterygia.”
“Saurosphargids are a small clade of Mesozoic marine reptiles characterized by the presence of body armor comprising broadened dorsal ribs, forming a closed ‘rib-basket,’ and a moderately- to well-developed osteoderm covering.”
“They are known from the Middle Triassic of Europe and South China, although recent evidence suggests they could have survived as late as the Late Triassic.”
“Saurosphargids are one of the reptile groups proposed as the sister-group of sauropterygians, but some recent phylogenetic analyses have suggested their placement within sauropterygians instead, as either the sister-group to placodonts or eosauropterygians.”
Holotype of Prosaurosphargis yingzishanensis (A) and skeletal reconstruction with known elements highlighted in white (B). Image credit: Wolniewicz et al., doi: 10.7554/eLife.83163.
The partial postcranial skeleton of Prosaurosphargis yingzishanensis was found in Yingzishan quarry, part of the Jialingjiang Formation, in China.
The specimen is now housed in the Geological Museum of the Hefei University of Technology.
“The specimen represents the Early Triassic Nanzhang-Yuan’an fauna and originates from the upper part of the third member of the Jialingjiang Formation,” the researchers said.
Prosaurosphargis yingzishanensis represents the earliest recorded occurrence of saurosphargids, extending their fossil record back by approximately 4.5 million years from the Middle to the Early Triassic epoch.
“Saurosphargids are thus the fourth major marine reptile lineage known from the Early Triassic Nanzhang-Yuan’an fauna, which also includes as many as seven species of hupehsuchians, one species of ichthyosauriforms, and four taxa representing the sauropterygian lineage leading to Eosauropterygia,” the scientists said.
“Prosaurosphargis yingzishanensis is one of the largest marine reptiles known from this ecosystem.”
“The presence in the Nazhang-Yuan’an fauna of several predatory reptiles representing a broad range of body sizes (0.25 to 4 m, or 0.8 to 13 feet) and displaying various ecomorphological adaptations supports the view of a rapid diversification of predators in the immediate aftermath of the end-Permian mass extinction and high predation pressure in shallow marine ecosystems in the Early Triassic,” they concluded.
The study was published online in the journal eLife.
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Andrzej S. Wolniewicz et al. 2023. An armoured marine reptile from the Early Triassic of South China and its phylogenetic and evolutionary implications. eLife 12: e83163; doi: 10.7554/eLife.83163
