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Sunday, January 14th, 2024
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| 8:22a | [Paleontology • 2024] Tyrannosaurus mcraeensis • A Giant tyrannosaur from the Campanian–Maastrichtian of southern North America and the Evolution of tyrannosaurid gigantism
Abstract Tyrannosaurid dinosaurs dominated as predators in the Late Cretaceous of Laurasia, culminating in the evolution of the giant Tyrannosaurus rex, both the last and largest tyrannosaurid. Where and when Tyrannosaurini (T. rex and kin) originated remains unclear. Competing hypotheses place tyrannosaurin origins in Asia, or western North America (Laramidia). We report a new tyrannosaurin, Tyrannosaurus mcraeensis, from the Campanian–Maastrichtian Hall Lake Formation of New Mexico, based on a fossil previously referred to T. rex. T. mcraeensis predates T. rex by ~ 6–7 million years, yet rivaled it in size. Phylogenetic analysis recovers T. mcraeensis as sister to T. rex and suggests Tyrannosaurini originated in southern Laramidia. Evolution of giant tyrannosaurs in southern North America, alongside giant ceratopsians, hadrosaurs, and titanosaurs suggests large-bodied dinosaurs evolved at low latitudes in North America.
Dinosauria Owen, 1842. Theropoda Marsh, 1881. Tetanurae Gauthier, 1986. Coelurosauria von Huene, 1914. Tyrannosauridae Osborn, 1905. Tyrannosaurinae Currie, 2003. Tyrannosaurini Olshevsky, 1995. (Tyrannosaurini is here defined as the last common ancestor of Tarbosaurus baatar and Tyrannosaurus rex and all its descendants). Tyrannosaurus mcraeensis sp. nov. Diagnosis: Large tyrannosaurin distinguished from Tyrannosaurus rex (Fig. 4; SI) by the following characters (*autapomorphies): postorbital with low, posteriorly positioned cornual process; postorbital with anteriorly projecting prefrontal/frontal articular surfaces; squamosal with ventrally projecting quadratojugal process; squamosal with a concave medial margin; strong ridge bounding the anterior margin of the squamosal ventral pneumatic fossa; dentary very shallow posteriorly and with a convex posteroventral margin*; splenial with anteriorly positioned apex*; splenial with shelf-like dentary overlap*, splenial with deep, posteriorly directed angular process; prearticular weakly bowed*; small ventral prearticular-angular contact; articular T-shaped in dorsal/ventral view; retroarticular process deep and quadrangular in posterior view. Holotype: NMMNH P-3698, partial skull including right postorbital and squamosal (Fig. 2), left palatine, fragment of maxilla, and lower jaws (Fig. 3) including left dentary, right splenial, prearticular, angular and articular, isolated teeth and associated chevrons. Horizon and locality: Uppermost Campanian or lower Maastrichtian of the Hall Lake Formation, McRae Group, NMMNH locality 343, near Kettle Top Butte, Sierra County, New Mexico21 (Fig. 1A). The site lies 43 m above the base of the Hall Lake Formation. A tuff 33 m below the tyrannosaur site has a U/Pb age of 73.2 ± 0.7 Ma22 (Fig. 1B). Etymology: The species name, mcraeensis, refers to the McRae Group of western New Mexico.
Sebastian G. Dalman, Mark A. Loewen, R. Alexander Pyron, Steven E. Jasinski, D. Edward Malinzak, Spencer G. Lucas, Anthony R. Fiorillo, Philip J. Currie and Nicholas R. Longrich. 2024. A Giant tyrannosaur from the Campanian–Maastrichtian of southern North America and the Evolution of tyrannosaurid gigantism. Scientific Reports. 13: 22124. DOI: 10.1038/s41598-023-47011-0 | ||||||||
| 9:47a | [Herpetology • 2024] Amolops dafangensis • A New Species of Amolops (Anura: Ranidae) from Guizhou Province, China
Abstract The Torrent frogs of the genus Amolops are widely distributed in Nepal and northern India eastwards to southern China and southwards to Malaysia. The genus currently contains 84 species. Previous studies indicated underestimated species diversity in the genus. In the context, a new species occurring from the mountains in the northwestern Guizhou Province, China is found and described based on morphological comparisons and molecular phylogenetic analyses, Amolops dafangensis sp. nov. Phylogenetic analyses based on DNA sequences of the mitochondrial 16S rRNA and COI genes supported the new species as an independent lineage. The uncorrected genetic distances between the 16S rRNA and COI genes in the new species and its closest congener were 0.7% and 2.6%, respectively, which are higher than or at the same level as those among many pairs of congeners. Morphologically, the new species can be distinguished from its congeners by a combination of the following characters: body size moderate (SVL 43.2–46.8 mm in males); head length larger than head width slightly; tympanum distinct, oval; vocal sacs absent; vomerine teeth present; dorsolateral folds weak formed by series of glands; nuptial pads present on the base of finger I; heels overlapping when thighs are positioned at right angles to the body; tibiotarsal articulation reaching the level far beyond the tip of the snout when leg stretched forward. Key words: Mitochondrial gene, taxonomy
Amolops dafangensis sp. nov. Diagnosis: Amolops dafangensis sp. nov. resembles members of the A. mantzorum group in the absence of true dorsolateral folds and the presence of a circum-marginal groove on the disc of the first finger. The tarsal fold and tarsal glands are absent, and a nuptial pad is present on the first finger in males (Jiang et al. 2021). Amolops dafangensis sp. nov. can be distinguished from other congeners by the following characters: (1) body size moderate (SVL 43.2 – 46.8 mm in males); (2) head length larger than head width slightly; (3) tympanum distinct, oval; (4) vocal sacs absent; (5) vomerine teeth present; (6) dorsolateral folds weak formed by series of glands; (7) nuptial pads present on base of finger I; (8) heels overlapping when thighs are positioned at right angles to the body; tibiotarsal articulation reaching the level far beyond the tip of the snout when leg stretched forward. Etymology: The specific epithet dafangensis refers to the distribution of this species, Dafang County, Guizhou Province, China. We propose the common English name “Dafang Cascade Frogs” for this species and Chinese name as “Da Fang Tuan Wa (大方湍蛙)”. Shi-Ze Li, Jing Liu, Xiao-Cong Ke, Gang Cheng and Bin Wang. 2024. A New Species of Amolops (Amphibia, Anura, Ranidae) from Guizhou Province, China. ZooKeys. 1189: 33-54. DOI: 10.3897/zookeys.1189.115621 |
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