Paleontologists have described a new species of pachypleurosaur from the Middle Triassic of southwestern China.
The holotype of Dianmeisaurus mutaensis from the Guanling Formation, China: (A) the skeleton in dorsal view; (B) the counterpart of (A). Scale bars – 1 cm. Image credit: Hu et al., doi: 10.1186/s13358-023-00292-4.
Dianmeisaurus mutaensis lived in what is now China during the Anisian age of the Middle Triassic epoch, around 245 million years ago.
The ancient species is a type of pachypleurosaur, a group of primitive sauropterygian reptiles from the Triassic period.
These animals resembled aquatic lizards and had small heads, long necks, paddle-like limbs, and long, deep tails.
“The Sauropterygia is the most flourishing clade among Mesozoic marine reptiles in terms of species diversity, and includes the iconic Plesiosauria from the Jurassic and Cretaceous and the stem-group Placodontia and Eosauropterygia from the Triassic,” said Dr. Jun Liu and colleagues from the Hefei University of Technology.
“Eosauropterygians were traditionally divided into three groups, the Pachypleurosauria, the Nothosauroidea, and the Pistosauroidea.”
“This traditional view holds that a monophyletic Pachypleurosauria comprises the sister group to the clade Eusauropterygia consisting of Nothosauroidea and Pistosauroidea.”
A complete and articulated skeleton of an immature Dianmeisaurus mutaensis was found in an abandoned quarry that is about 1 km northwest of Muta village in Luxi county, Yunnan province, China.
The skeleton was split into two parts during collection and prepared with pneumatic tools and needles in a paleontological lab.
“The skeleton, embedded in the dark-gray micritic limestone, consists of a part and its counterpart,” the paleontologists said.
“The specimen is well-preserved, with a total length of 99.2 mm (4 inches).”
“Adjacent to the specimen, there are scattered limb and rib bones from other individual(s), but the limited information available prevents further identification.”
An artist’s impression of the pachypleurosaur Wumengosaurus. Image credit: Nobu Tamura / CC BY-SA 4.0.
The team’s analysis recovered the new species as a sister group to Dianmeisaurus gracilis, a small pachypleurosaur from the Middle Triassic Luoping biota.
“Dianmeisaurus mutaensis exhibits several automorphic features, including the postfrontal extending posteriorly to the middle of the parietal table and being excluded from upper temporal fenestra, a stout last dorsal rib shorter than the first sacral rib, and two sacral vertebrae,” the researchers said.
“In addition, a novel data matrix was compiled to re-evaluate the interrelationships of eosauropterygians.”
“Phylogenetic analysis shows the collapse of the monophyly of Eusauropterygia,” they added.
“Pistosauroidea, Majiashanosaurus, and Hanosaurus constitute the consecutive sister groups to a monophyletic clade comprising Pachypleurosauria and Nothosauroidea.”
“Furthermore, the monophyly of Pachypleurosauria is supported by six synapomorphies.”
“Our phylogenetic results provide further evidence to the eastern Tethys origin of pachypleurosaurs,” they said.
“However, early Anisian pachypleurosaurs from the eastern Tethys region are required to test the biogeographic hypothesis.”
The findings were published in the Swiss Journal of Palaeontology.
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YW. Hu et al. 2024. A new pachypleurosaur (Reptilia: Sauropterygia) from the Middle Triassic of southwestern China and its phylogenetic and biogeographic implications. Swiss J Palaeontol 143, 1; doi: 10.1186/s13358-023-00292-4
Source : Breaking Science News