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Ben Creisler
Recent non-dino papers:
Dorota Konietzko-Meier, Jennifer D. Werner, Tanja Wintrich & P. Martin Sander (2018)
A large temnospondyl humerus from the Rhaetian (Late Triassic) of Bonenburg (Westphalia, Germany) and its implications for temnospondyl extinction.
Journal of Iberian Geology (advance online publication)
Temnospondyls are a group of basal tetrapods that existed from the Early Carboniferous to the Early Cretaceous. They were characteristic members of Permian and Triassic continental faunas around the globe. Only one clade, the Brachyopoidea (Brachyopidae and Chigutisauridae), is found as relics in the Jurassic of eastern Asia and the Cretaceous of Australia. The other Late Triassic clades, such as Plagiosauridae, Metoposauridae, and Cyclotsauridae, are generally believed to have gone extinct gradually before the end of the Triassic and putative Rhaetian records are stratigraphically poorly constrained. Temnospondyl humeri all show a similar morphological pattern, being stout, short, with widened ends, and with a typical torsion between the proximal and distal heads. Based on these characters, a humerus found in a Rhaetic-type bonebed in unequivocally Rhaetian sediments (marine Exter Formation) in a clay pit at Bonenburg (eastern Westphalia, Germany) was identified as pertaining to the temnospondyl cf. Cyclotosaurus sp. The humeral midshaft histology also supports temnospondyl affinities and serves to exclude plesiosaurs and ichthyosaurs from consideration. This find is the geologically youngest record of a non-brachyopoid temnospondyl, indicating that cyclotosaurids survived well into the Rhaetian, likely falling victim to the end-Triassic extinction.
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April DeLaurier (2018)
Evolution and development of the fish jaw skeleton
WIREs Developmental Biology (advance online publication)
The evolution of the jaw represents a key innovation in driving the diversification of vertebrate body plans and behavior. The pharyngeal apparatus originated as gill bars separated by slits in chordate ancestors to vertebrates. Later, with the acquisition of neural crest, pharyngeal arches gave rise to branchial basket cartilages in jawless vertebrates (agnathans), and later bone and cartilage of the jaw, jaw support, and gills of jawed vertebrates (gnathostomes). Major events in the evolution of jaw structure from agnathans to gnathostomes include axial regionalization of pharyngeal elements and formation of a jaw joint. Hox genes specify the anteriorâposterior identity of arches, and edn1, dlx, hand2, Jag1bâNotch2 signaling, and Nr2f factors specify dorsalâventral identity. The formation of a jaw joint, an important step in the transition from an unâjointed pharynx in agnathans to a hinged jaw in gnathostomes involves interaction between nkx3.2, hand2, and barx1 factors. Major events in jaw patterning between fishes and reptiles include changes to elements of the second pharyngeal arch, including a loss of opercular and branchiostegal ray bones and transformation of the hyomandibula into the stapes. Further changes occurred between reptiles and mammals, including the transformation of the articular and quadrate elements of the jaw joint into the malleus and incus of the middle ear. Fossils of transitional jaw phenotypes can be analyzed from a developmental perspective, and there exists potential to use genetic manipulation techniques in extant taxa to test hypotheses about the evolution of jaw patterning in ancient vertebrates.
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