Topic
Terminonatator
About: Terminonatator is a research topic. Over the lifetime, 2 publications have been published within this topic receiving 121 citations.
Papers
TL;DR: A new elasmosaur, Terminonatator ponteixensis, gen. et al. as mentioned in this paper, from the Upper Campanian Bearpaw Formation of southwestern Saskatchewan, Canada, is one of the few plesiosaurs for which detailed osteology of both skull and postcrania is available.
Abstract: A new elasmosaur, Terminonatator ponteixensis, gen. et sp. nov., from the Upper Campanian Bearpaw Formation of southwestern Saskatchewan, Canada, is one of the youngest plesiosaurs from the Western Interior, and one of the few plesiosaurs for which detailed osteology of both skull and postcrania is available. The skull includes the upper side of the inner ear cavity and a median portion of the roof of the braincase. This taxon is distinguished from other elasmosaurs by a combination of several osteological characters variable among elasmosaurs, as well as the unique feature of a high and pointed coronoid process. Anomalous ossification is seen in the fused or pronged gastralia, development of tubercules in metacarpals, and healed fracture of the limb. The dorsal portion of the braincase is compared with other plesiosaurs, showing a variation in plesiosaur braincase morphology. Identity of carpal and tarsal elements is examined based on recent debates on the homology of mesopodials.
TL;DR: This research recognizes the ‘Cimoliasauridae’ (nomen dubium) as a paraphyletic group but informative of a plesiomorphic cervical vertebral morphology of elasmosaurids which was persistent throughout the whole Cretaceous and from whom aristonectines, styxosaurines and Thalassomedon and close relatives are derived.
Abstract: Two extremely-long necked elasmosaurids, AMNH 1495, holotype of Hydralmosaurus serpentinus, and AMNH 5835, previously referred to H. serpentinus, are here reviewed in detail. Unique features of the cervical vertebrae, which are only present on elasmosaurids from the Western Interior Seaway, are recognized based on these specimens and by comparison with penecontemporaneous taxa with biogeographic affinities. Phylogenetic analysis, bivariate graphic analysis of cervical vertebrae proportions, comparisons of different cervical vertebral types, paleobiogeographic distribution and study of the elasmosaurid axial evolution throughout the Cretaceous are here integrated. As a result, at least two separate lineages within the Elasmosauridae are identified by independently acquired extremely-long necks (over 60 cervical vertebrae). First, a still scarcely known lineage is so far represented by the lower Cenomanian Thalassomedon haningtoni, the Turonian Libonectes morgani and close relatives. A second lineage is here defined as a new clade, the Styxosaurinae, which groups the Campanian genera Terminonatator, Styxosaurus (='Hydralmosaurus'), Albertonectes and Elasmosaurus, the two latter forming a derived branch that includes the most extreme amniote necks known to date (more than 70 cervical vertebrae). Phylogenetic analysis supports AMNH 1495 and AMNH 5835 as being closely related to Styxosaurus snowii. Therefore, the species Styxosaurus browni is re-validated, while AMNH 1495 is here referred to Styxosaurus sp. This research also recognizes the 'Cimoliasauridae' (nomen dubium) as a paraphyletic group but informative of a plesiomorphic cervical vertebral morphology of elasmosaurids which was persistent throughout the whole Cretaceous and from whom aristonectines, styxosaurines and Thalassomedon and close relatives are derived. The genus Hydralmosaurus is recommended for being abandoned.
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2016 | 1 |
| 2003 | 1 |