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[dinosaur] Early Cretaceous dinosaur tracks of southwestern China + new Colobomycter (Parareptilia) species + more





Ben Creisler
bcreisler@gmail.com


A number of new papers:

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Lida Xing &, Martin G. Lockley (2016)
Early Cretaceous dinosaur and other tetrapod tracks of southwestern China.
Science Bulletin (advance online publication)
DOI: 10.1007/s11434-016-1093-z
http://link.springer.com/article/10.1007/s11434-016-1093-z

In recent years the Lower Cretaceous red beds of southwestern China have yielded more than 20 significant dinosaur-dominated tracksites. More than half occur in the Jiaguan Formation with the remainder in the Feitianshan and Xiaoba formations. Collectively these sites provide evidence of at least 13 distinct dinosaurian trackmaker morphotypes, in addition to two avian theropod (bird) morphotypes and pterosaur and turtle tracks. Together these total 17 morphotypes provide a data base of 479 potential trackmakers, probably representing the same number of individuals. Such an ichnological database provides a useful proxy paleoecological census of tetrapod communities in the area during the Early Cretaceous, and is especially significant given the complete absence or scarcity of skeletal remains reported from these formations. The composition of ichnofaunas in all three formations is heavily saurischian (theropod and sauropod) dominated with a high diversity of distinctive theropod morphotypes, mostly assignable to known ichnogenera. Moreover, ichnofaunal data from multiple sites are generally consistent between sites and an indication of the reliability and repeatability of track census data. Such regionally-widespread data are rapidly superseding the information available from the skeletal record in the corresponding area, and must therefore be considered of high paleontological value.

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Ryosuke Motani (2016)
Palaeobiology: Born and Gone in Global Warming.
Current Biology 26(11): R466–R468
doi:10.1016/j.cub.2016.04.014
http://www.sciencedirect.com/science/article/pii/S0960982216303360
http://www.cell.com/current-biology/fulltext/S0960-9822(16)30336-0

Summary

Why ichthyosaurs — marine Mesozoic reptiles — disappeared before the dinosaur extinction has remained a mystery. New research suggests they may have gone extinct stepwise, during one of the most extreme greenhouse periods in the history of complex life-forms.


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Colobomycter vaughni

Mark J. MacDougall, Sean P. Modesto & Robert R. Reisz (2016)
A new reptile from the Richards Spur Locality, Oklahoma, USA, and patterns of Early Permian parareptile diversification.
Journal of Vertebrate Paleontology (advance online publication) 
DOI: 10.1080/02724634.2016.1179641
http://www.tandfonline.com/doi/full/10.1080/02724634.2016.1179641



The Lower Permian Richards Spur locality is the most speciose Paleozoic continental vertebrate assemblage currently known, and a significant proportion of the tetrapod diversity found at the locality is made up of parareptiles. The first Richards Spur parareptile to be described was Colobomycter pholeter. It has been characterized by its enlarged premaxillary tooth and paired enlarged maxillary teeth, unique dentition that grants it an appearance quite distinct from other parareptiles at Richards Spur. Here we describe new cranial material from Richards Spur that is referable to Colobomycter. This new material differs from that of C. pholeter in that it possesses at least three more teeth on its maxilla, the enlarged premaxillary and maxillary teeth are more gracile than those in C. pholeter, and the lacrimal is restricted externally to the orbital margin and does not exhibit an extra lateral exposure. We infer that these differences merit specific distinction and assign the new fossil to Colobomycter vaughni, sp. nov. The discovery of C. vaughni at Richards Spur is important, because it reveals the presence of another member of the clade Lanthanosuchoidea in Oklahoma, making it the sixth to be found in the state. The large number of taxa from this clade found in Oklahoma suggests that during the Early Permian, this area of western Laurasia was the center of a radiation of small, predatory lanthanosuchoids.

http://zoobank.org/urn:lsid:zoobank.org:pub:149450CF-4CB8-4099-B037-7E371A5AB286

SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

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Joel D. Hutson & Kelda N. Hutson (2016)
An Investigation of the Locomotor Function of Therian Forearm Pronation Provides Renewed Support for an Arboreal, Chameleon-like Evolutionary Stage.
Journal of Mammalian Evolution (advance online publication)
DOI: 10.1007/s10914-016-9341-1
http://link.springer.com/article/10.1007/s10914-016-9341-1

Although investigations of forelimb characteristics are central to therian evolutionary studies, the functional origins of forearm pronation are neglected. However, recent research based on bipedal manipulations strongly suggests that proximal radioulnar joint mobility is highly conserved in tetrapods. This new information calls for a replication of previously published physical simulations of forearm bone movements, to investigate whether active therian pronation/supination evolved from the plesiomorphic mechanism via which locomotor-induced torsion is passively alleviated during forelimb retraction. Preliminary results using representative extant and extinct tetrapod forelimb elements are supportive, and also offer insight into why another overlooked forearm trait, osteological full pronation (mechanically aligned elbow and wrist/finger joints), evolved only in therians and chameleons. During forelimb retraction in tetrapods with unfused radii/ulnae, the radius unexpectedly remains fixed in place as a functional complex with the firmly planted manus/carpus, which the ulnar complex (ulna/humerus) displaces relative to. Therefore, the highly conserved functional morphology of the tetrapod forearm indicates that enhanced therian manual dexterity, which emphasizes isolated radial movements bipedally, was preceded by the locomotor evolution of ulnar supination relative to the radius quadrupedally. This counterintuitive information indicates that the traditional hypothesis, that therian pronation/supination evolved arboreally to amplify radial mobility, requires modification. The authors propose that proximal long-axis rotations of the therian ulnar complex co-evolved with osteological full pronation during a period of arboreal, chameleon-like locomotion, to continue allowing torsion at a reinforced proximal radioulnar joint. These adaptations were later or simultaneously co-opted for object manipulation using active radioulnar pronation/supination.