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[dinosaur] Discosauriscus (Seymouriamorpha) skulls + fin-to-limb transition

Ben Creisler

New non-dino papers:

Jozef Klembara & Marika MikudÃkovà (2018)
New cranial material of Discosauriscus pulcherrimus (Seymouriamorpha, Discosauriscidae) from the Lower Permian of the Boskovice Basin (Czech Republic).
Earth and Environmental Science Transactions of The Royal Society of Edinburgh (advance online publication)
doi:Â https://doi.org/10.1017/S1755691018000798

We describe four newly discovered and three-dimensionally preserved specimens of the discosauriscid seymouriamorph Discosauriscus pulcherrimus from the Lower Permian lacustrine sediments of the Boskovice Basin (Czech Republic). Their excellent preservation revealed new cranial features that allowed us to present a new skull reconstruction of middle-sized specimens of this tetrapod. The new features include: (1) the sculpturing of the anterior wedge-like process of the parasphenoid consisting of irregular ridges, grooves, low elevations and pits; and (2) the presence of a pair of semicircular crests on the posterodorsal surface of the parasphenoidal plate. We discuss the intraspecific variability of several characters, such as the type of dermal cranial ornamentation, and the morphology of the sensory grooves, nasolacrimal canal, dentition on the pterygoids and parasphenoid. The lengths of the skulls of four new specimens range from about 18 to 31mm and represent larval ontogenetic stages.


Free pdf:

Blake V. Dickson and Stephanie E. Pierce (2018)Â
How (and why) fins turn into limbs: insights from anglerfish.
Earth and Environmental Science Transactions of The Royal Society of Edinburgh (advance online publication)

The fin-to-limb transition is heralded as one of the most important events in vertebrate evolution. Over the last few decades our understanding of how limbs evolved has significantly increased; but, hypotheses for why limbs evolved are still rather open. Fishes that engage their fins to âwalk' along substrate may provide some perspective. The charismatic frogfishes are often considered to have the most limb-like fins, yet we still know little about their underlying structure. Here we reconstruct the pectoral fin musculoskeletal anatomy of the scarlet frogfish to identify adaptations that support fin-assisted walking behaviours. The data are compared to three additional anglerfish species: the oval batfish, which represents an independent acquisition of fin-assisted walking; and two pelagic deep-sea swimmers, the triplewart seadevil and ghostly seadevil. Our results clearly show broad musculoskeletal differences between the pectoral fins of swimming and walking anglerfish species. The frogfish and batfish have longer and more robust fins; larger, differentiated muscles; and better developed joints, including a reverse ball-and-socket glenoid joint and mobile âwrist'. Further, the frogfish and batfish show finer-scale musculoskeletal differences that align with their specific locomotor ecologies. Within, we discuss the functional significance of these anatomical features in relation to walking, the recurring evolution of similar adaptations in other substrate locomoting fishes, as well as the selective pressures that may underlie the evolution of limbs.

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