Lorenzo Marchetti, Matteo Belvedere, Sebastian Voigt, Hendrik Klein, Diego Castanera, Ignacio DÃaz-MartÃnez, Daniel Marty, Lida Xing, Silverio Feola, Ricardo N. Melchor & James O.Farlow (2019)
Defining the morphological quality of fossil footprints. Problems and principles of preservation in tetrapod ichnology with examples from the Palaeozoic to the present.
The morphology of fossil footprints is the basis of vertebrate footprint ichnology. However, the processes acting during and after trace fossil registration which are responsible for the final morphology have never been precisely defined, resulting in a dearth of nomenclature. Therefore, we discuss the concepts of ichnotaphonomy, ichnostratinomy, taphonomy, biostratinomy, registration and diagenesis and describe the processes acting on footprint morphology. In order to evaluate the morphological quality of tetrapod footprints, we introduce the concept of morphological preservation, which is related to the morphological quality of footprints (M-preservation, acronym MP), and distinguish it from physical preservation (P-preservation, acronym PP), which characterizes whether or not a track is eliminated by taphonomic and diagenetic processes. M-preservation includes all the morphological features produced during and after track registration prior to its study, and may be divided into substages (ichnostratinomic, registrational, taphonomic, stratinomic, diagenetic). Moreover, we propose an updated numerical preservation scale for M-preservation. It ranges from 0.0 (worst preservation) to 3.0 (best preservation); intermediate values may be used and specific features may be indicated by letters. In vertebrate footprint ichnotaxonomy, we regard the anatomy-consistent morphology and to a lesser extent the trackway pattern as the only acceptable ichnotaxobases. Only footprints showing a good morphological preservation (grade 2.0â3.0) are useful in ichnotaxonomy, whereas ichnotaxa based on poor morphological preservation (grade 0.0â1.5) are considered ichnotaphotaxa (nomina dubia) characterized by extramorphologies. We applied the preservation scale on examples from the Palaeozoic to the present time, including three ichnotaphotaxa and 18 anatomy-consistent ichnotaxa/morphotypes attributed to several vertebrate footprint producers. Results indicate the utility, feasibility and suitability of this method for the entire vertebrate footprint record in any lithofacies, strongly recommending its use in future ichnotaxonomic studies.
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David A. D. Parry, R. D. Bruce Fraser, Lorenzo Alibardi, Kim M. Rutherford & Neil Gemmell (2019)
Molecular structure of sauropsid Î-keratins from tuatara (Sphenodon punctatus).
Journal of Structural Biology (advance online publication)
Highlights
Although the molecular structure of Î-keratins from the Archosaurs (birds, crocodiles, turtles) and squamates (lizards and snakes) has been studied for more than 50 years and the key parameters established by X-ray diffraction, infrared spectroscopy and sequence analysis, the research has lacked data on the Rhynchocephalia, the last branch of the lepidosaurs in the phylogenetic map. This paper represents the culmination of the very considerable efforts that have been made over many years by a diverse group from New Zealand, Australia, Italy and the UK to collect and analyse the beta-keratin sequence data from tuatara, the sole representative of the Rhynchocephalia. Also described is the X-ray diffraction pattern from tuatara claw and this is compared with those from other Î-keratins. In so doing this research advances the Î-keratin story structure-wise for the sauropsids in general (birds and reptiles). Now, at last, we have a totally consistent structural model across all members of the sauropsids.
Abstract
The birds and reptiles, collectively known as the sauropsids, can be subdivided phylogenetically into the archosaurs (birds, crocodiles), the testudines (turtles), the squamates (lizards, snakes) and the rhynchocephalia (tuatara). The structural framework of the epidermal appendages from the sauropsids, which include feathers, claws and scales, has previously been characterised by electron microscopy, infrared spectroscopy and X-ray diffraction analyses, as well as by studies of the amino acid sequences of the constituent Î-keratin proteins (also referred to as the corneous Î-proteins). An important omission in this work, however, was the lack of sequence and structural data relating to the epidermal appendages of the rhynchocephalia (tuatara), one of the two branches of the lepidosaurs. Considerable effort has gone into sequencing the tuatara genome and while this is not yet complete, there are now sufficient sequence data for conclusions to be drawn on the similarity of the Î-keratins from the tuatara to those of other members of the sauropsids. These results, together with a comparison of the X-ray diffraction pattern of tuatara claw with those from seagull feather and goanna claw, confirm that there is a common structural plan in the Î-keratins of all of the sauropsids, and not just those that comprise the archosaurs (birds and crocodiles), the testudines (turtles) and the squamates (lizards and snakes).
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Michael C. Granatosky, Eric J. McElroy, Myra F. Laird, Jose Iriarte-Diaz, Stephen M. Reilly, Andrea B. Taylor, Callum F. Ross (2019)
Joint angular excursions during cyclical behaviors differ between tetrapod feeding and locomotor systems.
Journal of Experimental Biology : jeb.200451Â
doi: 10.1242/jeb.200451Â
Tetrapod musculoskeletal diversity is usually studied separately in feeding and locomotor systems. However, comparisons between these systems promise important insight into how natural selection deploys the same basic musculoskeletal toolkitâconnective tissues, bones, nerves and skeletal muscleâto meet the differing performance criteria of feeding and locomotion. In this study, we compare average joint angular excursions during cyclic behaviorsâ chewing, walking and runningâin a phylogenetic context to explore differences in the optimality criteria of these two systems. Across 111 tetrapod species, average limb-joint angular excursions during cyclic locomotion are greater and more evolutionarily labile than those of the jaw joint during cyclic chewing. We argue that these findings reflect fundamental functional dichotomies between tetrapod locomotor and feeding systems. Tetrapod chewing systems are optimized for precise application of force over a narrower, more controlled and predictable range of displacements, the principal aim being to fracture the substrate, the size and mechanical properties of which are controlled at ingestion and further reduced and homogenized (respectively) by the chewing process. In contrast, tetrapod limbed locomotor systems are optimized for fast and energetically efficient application of force over a wider and less predictable range of displacements, the principal aim being to move the organism at varying speeds relative to a substrate whose geometry and mechanical properties need not become more homogenous as locomotion proceeds. Hence, the evolution of tetrapod locomotor systems has been accompanied by an increasing diversity of limb-joint excursions, as tetrapods have expanded across a range of locomotor substrates and environments.
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Stephan Handschuh, Nikolay Natchev, Stefan Kummer, Christian J. Beisser, Patrick Lemell, Anthony Herrel &Â Vladislav Vergilov (2019)
Cranial kinesis in the miniaturised lizard Ablepharus kitaibelii (Squamata: Scincidae)
Journal of Experimental Biology: jeb.198291Â
doi: 10.1242/jeb.198291Â
Cranial kinesis refers to intracranial movements in the vertebrate skull that do not concern the jaw joint, the middle ear, or the hypobranchial skeleton. Different kinds of cranial kinesis have been reported for lizards, including mesokinesis, metakinesis, amphikinesis (simultaneous meso- and metakinesis), and streptostyly. Streptostyly is considered relatively widespread within lizards, while mesokinesis has been documented only for geckos, varanids, and anguids. The present study investigates cranial kinesis in the miniaturised scincid Ablepharus kitaibelii by integrating morphological and experimental data. Based on microCT, we provide a description of skull osteology. Cranial joints were studied with histology, which results in the first detailed description of cranial joint histology for a member of the Scincidae. Taken together, morphological data indicates a high potential for amphikinesis and streptostyly, which was also corroborated by skull manipulations. High-speed cinematography demonstrated that mesokinesis occurs during food uptake, processing, and intraoral transport cycles. Bite force measurements showed prolonged and reasonably hard biting even at large gape. Based on this data we formulate a model of the amphikinetic Ablepharus skull mechanism, which provides an extension of Frazzetta's quadric-crank model by placing a special emphasis on metakinesis. According to this model, we hypothesize that metakinetic intracranial movements may provide a means for reducing strain in jaw adductor muscles. Presented hypotheses can be addressed and tested in future studies.
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M. Vasilopoulou-Kampitsi, J. Goyens, R. Van Damme & P. Aerts (2019)
The ecological signal on the shape of the lacertid vestibular system: simple versus complex microhabitats.
Biological Journal of the Linnean Society: blz022
Shape variation in the vestibular system is often linked to microhabitat structure and locomotor performance. Highly circular and orthogonal semicircular canal pairs are linked to higher motion sensitivity. Here, we use 3D geometric morphometrics to investigate shape variation in the vestibular system within lacertid lizards and its relationship to balance control. We found that lacertids living in complex microhabitats possess narrow but longer vestibular systems, an S-shaped anterior canal, a straightened lateral canal and a short common crus. However, lacertids specialized for simple microhabitats (open areas) possess wider but shorter vestibular systems, more circular anterior and lateral canals, and a longer common crus. Contrary to our expectations, species living in simple microhabitats possess more anatomical adaptations that enhance the sensitivity of their vestibular system. This suggests that species inhabiting open areas may benefit from increased sensitivity given that they are potentially more visibile to predators and have lower shelter availability. Finally, the wider shape of the vestibular system of the open area species may be linked to a wider and potentially flattened skull, which may be related to sand-diving or prey hardness.