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Odp: [dinosaur] Gunakadeit, new thalattosauroid from Late Triassic of Alaska (free pdf)

"Our newly assembled and expanded phylogenetic dataset reveals the new taxon to occupy a basal position within Thalattosauria, while representing the stratigraphically youngest record of the clade in North America."
"Gunakadeit joseeae is recovered as the basalmost member of Thalattosauroidea."
"Despite this stratigraphic incongruence, Gunakadeit exhibits a mosaic of features consistent with its relatively basal position among thalattosauroids."

Just a philosophical question - are these statements accurate? I understand that _Gunakadeit_ is currently the most early-branching taxon of thalattosauroideans, and it's supposedly the most plesiomorphic. I am not sure, however, if I like the idea that of the two sister taxa, the more basal is the one with lesser species described. Suppose, in the future, we will find more taxa on the _Gunakadeit_ side of the dichotomy, some of them highly derived/apomorphic, and even of Jurassic age. The current topology might as well remain unchanged (except the addition of the new taxa), but it will be the Thalattosaurus-Xinpusaurus clade considered more basal.

Dnia 4 lutego 2020 17:44 Ben Creisler <bcreisler@gmail.com> napisaÅ(a):


Ben Creisler

A new paper with free pdf:

Gunakadeit joseeae gen. et sp. nov.

Patrick S. Druckenmiller, Neil P. Kelley, Eric T. Metz & James Baichtal (2020)
An articulated Late Triassic (Norian) thalattosauroid from Alaska and ecomorphology and extinction of Thalattosauria.
Scientific Reports 10, Article number: 1746
doi: https://doi.org/10.1038/s41598-020-57939-2
https://www.nature.com/articles/s41598-020-57939-2


Thalattosaurians are a cosmopolitan clade of secondarily aquatic tetrapods that inhabited low-latitude, nearshore environments during the Triassic. Despite their low taxic diversity, thalattosaurians exhibit remarkable morphological disparity, particularly with respect to rostral and dental morphology. However, a paucity of well-preserved material, especially leading up to their extinction, has hampered efforts to develop a robust picture of their evolutionary trajectories during a time of profound marine ecological change. Here, we describe a new taxon based on an articulated and nearly complete skeleton from Norian sediments of southeastern Alaska, USA. The holotype is the most complete North American thalattosaurian yet described and one of the youngest occurrences of the clade worldwide. We present a new hypothesis of interrelationships for Thalattosauria and investigate potential feeding modes in the Alaskan taxon. An integrated view suggests that the absence of pelagic lifestyles and restricted ecological roles may have contributed to thalattosaursâ eventual extinction.

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