===
Lene L. Delsett, Patrick S. Druckenmiller, Ãyvind Hammer, Krzysztof Hryniewicz, Espen M. Knutsen, Maayke J. Koevoet,s Hans A. Nakrem, Aubrey J. Roberts & JÃrn H. Hurum (2019)
Mesozoic marine reptiles from Spitsbergen and their ecosystems.
Geology Today 35(1): 20-25
In the Mesozoic seas, the apex predators were reptiles. From the Arctic archipelago of Svalbard, the Spitsbergen Mesozoic Research Group has excavated numerous well preserved marine reptile skeletons in order to understand the biology of these animals and the environment they lived in. The work of eleven field seasons has made this one of the largest and most productive palaeontological research projects in the high Arctic worldâwide. The initial eight seasons focused on one of the richest occurrences of Late Jurassic-earliest Cretaceous (c. 150â139 Ma) marine reptiles in the world, and nearly sixty specimens have been collected, together with a diverse assemblage of invertebrates, some of which are associated with methane seeps. The last three seasons were spent investigating events further back in time, as Spitsbergen preserves the remains from some of the first marine reptile radiations in the wake of the most devastating extinction in the history of the Earth, at the Permian-Triassic boundary (c. 252 Ma).
=====
Free pdf:
Bryan M. Gee, Joseph J. Bevitt, Ulf Garbe & Robert R. Reisz (2019)
New material of the 'microsaur' Llistrofus from the cave deposits of Richards Spur, Oklahoma and the paleoecology of the Hapsidopareiidae.Â
PeerJ 7:e6327Â
Free pdf:
The Hapsidopareiidae is a group of "microsaurs" characterized by a substantial reduction of several elements in the cheek region that results in a prominent, enlarged temporal emargination. The clade comprises two markedly similar taxa from the early Permian of Oklahoma, Hapsidopareion lepton and Llistrofus pricei, which have been suggested to be synonymous by past workers. Llistrofus was previously known solely from the holotype found near Richards Spur, which consists of a dorsoventrally compressed skull in which the internal structures are difficult to characterize. Here, we present data from two new specimens of Llistrofus. This includes data collected through the use of neutron tomography, which revealed important new details of the palate and the neurocranium. Important questions within "Microsauria" related to the evolutionary transformations that likely occurred as part of the acquisition of the highly modified recumbirostran morphology for a fossorial ecology justify detailed reexamination of less well-studied taxa, such as Llistrofus. Although this study eliminates all but one of the previous features that differentiated Llistrofus and Hapsidopareion, the new data and redescription identify new features that justify the maintained separation of the two hapsidopareiids. Llistrofus possesses some of the adaptations for a fossorial lifestyle that have been identified in recumbirostrans but with a lesser degree of modification (e.g., reduced neurocranial ossification and mandibular modification). Incorporating the new data for Llistrofus into an existing phylogenetic matrix maintains the Hapsidopareiidaeâs (Llistrofus + Hapsidopareion) position as the sister group to Recumbirostra. Given its phylogenetic position, we contextualize Llistrofus within the broader "microsaur" framework. Specifically, we propose that Llistrofus may have been fossorial but was probably incapable of active burrowing in the fashion of recumbirostrans, which had more consolidated and reinforced skulls. Llistrofus may represent an earlier stage in the step-wise acquisition of the derived recumbirostran morphology and paleoecology, furthering our understanding of the evolutionary history of "âmicrosaurs."
====
====
Chapters from new book:
Janine M. Ziermann, Raul E. Diaz Jr & Rui Diogo (2019)
Heads, Jaws, and Muscles
Anatomical, Functional, and Developmental Diversity in Chordate Evolution
***
Daniel Smith-Paredes & Bhart-Anjan S. Bhullar (2019)
The Skull and Head Muscles of Archosauria.
Heads, Jaws, and Muscles: 229-251
Archosaurs is the clade composed by birds (Aves) and crocodiles, alligators, and the gharial (Crocodylia). This relatedness is not obvious and for a long time was not taken into account, as birds were seen as a group separate even from the rest of reptiles. Both avians and crocodylians are morphologically very distinct and in many aspects different from each other and from the ancestral forms within Archosauria. The skulls of birds are composed of thin and light bones, many fused to each other, and others articulating in mobile joints allowing the beak to move and bend with respect to the rest of the skull. In crocodylians the skulls are massive and heavy, a solid akinetic structure built to crush prey. The accompanying muscle system, attaching onto and responsible for the movement of the head, jaws, eyes, or tongue, is equally distinct. As a result of the striking differences and the relatively recent realization of crocodylians and avians being closely related, the comparison of their anatomy has never been very straightforward. This chapterâs goal is to provide a review of archosaur anatomy and to give at least some sense of the similarities and differences between archosaur musculature.
======
Gabriel S. Ferreira & Ingmar Werneburg (2019)
Evolution, Diversity, and Development of the Craniocervical System in Turtles with Special Reference to Jaw Musculature.
Heads, Jaws, and Muscles: 171-206Â
Turtles are one of the most enigmatic groups of vertebrates with their highly modified âbody planâ and, as such, attracted the attention of researchers for a long time. Aside from the unusual turtle shell, the skull in this group shows great changes in comparison to that of other amniote groups. Because the skull has been considered one of most important body regions when analyzing the phylogenetic relationships of amniotes, the distinct turtle skull morphology is one of the key features in defining their position among reptiles. Here, we review the current knowledge of the turtle head, summarizing the general morphology of the skull and neck as well as the different anatomical modifications characteristic of the main lineages of extant and extinct turtles. We explore the main questions that have been raised while studying those issues, for instance, the origin and diversity of the temporal emarginations (dermal bone reductions), the different neck retraction mechanisms and their influence on the shape of the skull, and the anatomy and development of the jaw adductor musculature and its relation to some characteristic features of the turtle skull, such as akinesis and the divergent trochlear mechanisms in cryptodires and pleurodires. Based on 3D reconstructions, we propose a hypothetical model for ancestral states and gross morphology of the jaw adductor musculature in Proganochelys quenstedti (the earliest turtle with a complete shell), an important step toward the understanding of the evolution of those muscles in turtles. Finally, we suggest that more integrative approaches that consider anatomical, developmental, and paleontological data and that employ modern techniques in morphological and functional anatomic analyses (such as ÎCT scanning and finite element analysis) have a greater potential to answer the still numerous open questions about the evolution of the turtle head.
====