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[dinosaur] Plesiosaur long necks bent downward + Slavoia, stem-amphisbaenian + Baurubatrachus, hyperossified frog

Ben Creisler

Some recent non-dino papers:

Free pdf:

Leslie F. Noè, Michael A. Taylor, and Marcela Gómez-Pérez (2017)
An integrated approach to understanding the role of the long neck in plesiosaurs.
Acta Palaeontologica Polonica 62 (1): 137-162 

The evolution and function of the long neck in plesiosaurs, and how the problems associated with stiffness or flexibility were overcome during feeding, or rapid swimming during predator avoidance, are explored, and a new interpretation for the function of the plesiosaur neck is presented. Based on the anatomy of the articular faces of contiguous cervical vertebral centra, neural arches, and cervical ribs, the plesiosaur neck was mainly adapted for ventral bending, with dorsal, lateral and rotational movements all relatively restricted. Predominant ventral bending indicates the neck was adapted for use beneath the body, suggesting feeding in the water column, close to the sea floor, or within soft sediments on the sea floor. A new model is proposed for the plesiosaur bauplan, comprising the head as a filter, straining, sieve feeding or sediment raking apparatus, mounted on a neck which acted as a stiff but ventrally flexible feeding tube, attached to the body which acted as a highly mobile feeding platform. Numerous features of plesiosaurs, including cranial and dental form, cervical vertebral morphology, body shape and limb-based propulsion, conform to this model. Comparative data from modern organisms support this novel explanation for the structure and function of the plesiosaur long neck. This integrative analysis offers an explanation for the evolution of the plesiosaur long neck as a key evolutionary novelty, and why this apparently enigmatic feature remained a prominent feature of plesiosaurs. 


Free pdf:

Mateusz Tałanda (2017)
Evolution of postcranial skeleton in worm lizards inferred from its status in the Cretaceous stem-amphisbaenian Slavoia darevskii.
Acta Palaeontologica Polonica 62 (1): 9-23 

Amphisbaenians are one of the most derived fossorial groups among Squamata. Studies of their evolution were hampered by their specialized limbless morphology and unrecognized early fossil record. This study presents a detailed description of the postcranial anatomy of the oldest known stem-amphisbaenian Slavoia darevskii. The skeleton shows an incipient adaptation to the fossorial mode of life, expressed in the early stages of limb reduction and elongation of the trunk, typical aspects of modern worm lizards. The forelimbs show a hyperphalangy of the first digit. They were probably strengthened this way to support the head in burrowing. Such an anatomy of the most ancient amphisbaenians implies that the forelimbs were lost multiple times in the amphisbaenians to be retained only in the Bipedidae. The hindlimb reduction was initiated early (before the split into modern families) but may have been completed independently. Despite these changes, S. darevskii still had the plesiomorphic 26 presacral vertebrae but the neck region was shorter, as shown by the ribs morphology and position.


Ana María Báez & Raúl Orencio Gómez (2017)
Dealing with homoplasy: osteology and phylogenetic relationships of the bizarre neobatrachian frog Baurubatrachus pricei from the Upper Cretaceous of Brazil.
Journal of Systematic Palaeontology (advance online publication)

The hyperossified frog Baurubatrachus pricei Báez & Peri 1989 from the Maastrichtian Serra da Galga Member of the Marília Formation is described in detail, as preparation of the type and only known specimen revealed significant features, particularly of the pectoral and pelvic girdles. This species is rediagnosed on the basis of the combination of plesiomorphic and derived character states, including two unique traits: cranial roof with round openings that might have contained the tympanic membrane completely circumscribed by ornamented dermal bone, and scapula bearing a conspicuous crest deflected ventrally to form a deep basin on its leading edge. Since its discovery it was suggested that Baurubatrachus might be a relative of the South American ceratophryids, a phylogenetic placement endorsed by recent analyses. In order to test this hypothesis considering all the available information, we conducted several maximum parsimony analyses under different weighting schemes and topological constraints, scoring 143 characters for 71 extant and extinct anuran taxa. Our taxonomic sampling included species with well-ossified dermatocrania as well as less ossified members of main neobatrachian clades to explore the impact of hyperossification, which frequently drives groupings based on homoplastic features. We also assessed the phylogenetic signal provided by cranial and postcranial partitions. Although we recovered a monophyletic Ceratophryidae repeatedly, Baurubatrachus was not related with this nobleobatrachian group but associated with the calyptocephalellid australobatrachians, although with weak support. Other possible phylogenetic placements are also discussed, as well as microhabitat and habits, taking into account both anatomical and geological data.