Browsing by Author "Bhullar, Bhart-Anjan S."
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Item New diminutive Eocene lizard reveals high K-Pg survivorship and taxonomic diversity of stem xenosaurs in North America (American Museum novitates, no. 3986)(American Museum of Natural History., 2022-02-16) Smith, Krister T.; Bhullar, Bhart-Anjan S.; Bloch, Jonathan I.We describe a new diminutive early Eocene lizard, Blutwurstia oliviae, gen. et sp. nov., on the basis of associated cranial and postcranial remains from the Clarks Fork Basin of Wyoming. Results from phylogenetic analyses suggest that B. oliviae is on the stem of knob-scaled lizards (Xenosaurus), a relict extant clade of specialized, stenotopic crevice-dwellers from Mexico and Central America. Results further suggest that B. oliviae is basal to all other previously described pan-xenosaurs (members of Pan-Xenosaurus, the total clade of Xenosaurus) except species of Entomophontes, to which it is closely related. Given that B. oliviae and Entomophontes are known from a limited fossil record, with only one recovered element (the maxilla) in common, the level of support for this relationship is surprisingly high. We use a posteriori time-calibrated trees and ghost lineages (maximum parsimony) and divergence time estimates under the fossilized birth-death process (Bayesian inference) to infer patterns of extinction across the Cretaceous-Paleogene (K-Pg) boundary in Pan-Xenosaurus, including those consistent with pseudoextinction. Whereas the fossil record documents a single lineage in the latest Cretaceous, results from analyses using these analytical methods suggest that three or more species existed, with high survivorship across the K-Pg boundary. The surviving lineages were apparently present at proximal to intermediate distance from the Chicxulub impact site, thought to have a causal relationship with extinctions across the K-Pg boundary. The premaxilla and dorsal vertebrae of E. incrustatus and B. oliviae, respectively, independently suggest that each of these taxa had a depressed body form consistent with extant crevice-dwelling squamates, which may have played a role in the high survivorship of pan-xenosaur lineages across the K-Pg boundary.Item A new dromaeosaurid (Dinosauria: Coelurosauria) from Khulsan, Central Mongolia (American Museum novitates, no. 3982)(American Museum of Natural History., 2021-11-08) Napoli, James G.; Ruebenstahl, Alexander; Bhullar, Bhart-Anjan S.; Turner, Alan H. (Alan Hamilton); Norell, MarkDromaeosaurid theropods represent a rare but important clade of nonavialan dinosaurs. Their close evolutionary relationship to modern birds has placed them at the center of paleontological research for the last several decades. Herein we describe a new species of dromaeosaurid—Kuru kulla, gen. et sp. nov.—based on a partial skeleton from the Late Cretaceous Khulsan locality (Barun Goyot Formation) of Mongolia. This species is diagnosed by several autapomorphies within Dromaeosauridae, including a sharp groove anterior and ventral to the narial fossa on the premaxilla, a posterolaterally directed hornlet on the posterodorsal process of the lacrimal, a deep surangular bearing two surangular foramina, and anteriorly displaced pleurocoels on the dorsal centra. The taxon is further characterized by a unique combination of characters, including a mediolaterally narrow metatarsal II, serrations on both carinae of the dentary teeth, hyposphenes that are widely separated but joined by a web of bone, and a lacrimal with a poorly developed boss on its lateral surface. Phylogenetic analysis finds Kuru kulla to be the sister taxon of Adasaurus mongoliensis, from the slightly later Nemegt Formation, with which it is united by three synapomorphies: a posterior surangular foramen that is ~30% the depth of the surangular, absence of a fourth trochanter of the femur, and thoracic centra that are markedly longer than their midpoint widths. The recognition of this taxon has important implications for common assumptions of Mesozoic terrestrial ecosystem structure and adds new data to a recently recognized pattern in dromaeosaurid faunal composition among Late Cretaceous localities in Mongolia and Inner Mongolia (Nei Mongol Autonomous Region, China).