Domenic C. DâAmore, Megan Harmon, Stephanie K. Drumheller & Jason J. Testin (2019)
Quantitative heterodonty in Crocodylia: assessing size and shape across modern and extinct taxa.Â
Heterodonty in Crocodylia and closely related taxa has not been defined quantitatively, as the teeth rarely have been measured. This has resulted in a range of qualitative descriptors, with little consensus on the condition of dental morphology in the clade. The purpose of this study is to present a method for the quantification of both size- and shape-heterodonty in members of Crocodylia. Data were collected from dry skeletal and fossil specimens of 34 crown crocodylians and one crocodyliform, resulting in 21 species total. Digital photographs were taken of each tooth and the skull, and the margins of both were converted into landmarks and semilandmarks. We expressed heterodonty through Footeâs morphological disparity, and a principal components analysis quantified shape variance. All specimens sampled were heterodont to varying degrees, with the majority of the shape variance represented by a âcaniniformâ to âmolariformâ transition. Heterodonty varied significantly between positions; size undulated whereas shape was significantly linear from mesial to distal. Size and shape appeared to be primarily decoupled. Skull shape correlated significantly with tooth shape. High size-heterodonty often correlated with relatively large caniniform teeth, reflecting a prioritization of securing prey. Large, highly molariform, distal teeth may be a consequence of high-frequency durophagy combined with prey size. The slender-snouted skull shape correlated with a caniniform arcade with low heterodonty. This was reminiscent of other underwater-feeding tetrapods, as they often focus on small prey that requires minimal processing. Several extinct taxa were very molariform, which was associated with low heterodonty. The terrestrial peirosaurid shared similarities with large modern crocodylian taxa, but may have processed prey differently. Disparity measures can be inflated or deflated if certain teeth are absent from the tooth row, and regression analysis may not best apply to strongly slender-snouted taxa. Nevertheless, when these methods are used in tandem they can give a complete picture of crocodylian heterodonty. Future researchers may apply our proposed method to most crocodylian specimens with an intact enough tooth row regardless of age, species, or rearing conditions, as this will add rigor to many life history studies of the clade.
Tomasz Szczygielski, Dawid DrÃÅdÅ, Dawid Surmik, Agnieszka KapuÅciÅska & Bruce M. Rothschild (2019)
New tomographic contribution to characterizing mesosaurid congenital scoliosis.Â
PLoS ONE 14(2): e0212416
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The presence of a pathology in the vertebral column of the early Permian mesosaurid specimen ZPAL R VII/1, being one of the oldest amniotic occurrences of congenital scoliosis caused by a hemivertebra, was recently recognized. Here we provide CT data to further characterize the phenomenon. The affected hemivertebra is wedged (incarcerated) between the preceding and succeeding vertebrae. The neural canal is misshapen but continuous and the number of dorsal ribs on each side of the specimen corresponds with the number of the vertebrae, documenting its congenital (homeobox-related) derivation.
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Ralf Werneburg, Florian Witzmann & Joerg W. Schneider (2019)
The oldest known tetrapod (Temnospondyli) from Germany (Early Carboniferous, VisÃan)
PalZ (advance online publication)
A unique skull roof fragment of a relatively large-sized tetrapod of VisÃan age from Chemnitz-GlÃsa, Saxony, is described. The specimen consists of three bones, an elongated supratemporal with a radially arranged dermal sculpture and the sulcus of the otical part of the infraorbital line, the medial portion of the squamosal which is sutured with the anterolateral supratemporal, and a small, strip-like tabular bone. A deep âotic notchâ is indicated. This new tetrapod was predominantly aquatic, as indicated by the deep and relatively broad lateral line sulcus. The type of dermal sculpture and the configuration of the bones indicate that the specimen is probably an adult temnospondyl, with the course of the lateral lines resembling those of dvinosaurians. Together with Balanerpeton from Scotland, this is the geologically oldest temnospondyl and the oldest known tetrapod record in Germany up to now.
FranÃois Druelle, Jana Goyens, Menelia Vasilopoulou-Kampitsi & Peter Aerts (2019)
Compliant legs enable lizards to maintain high running speeds on complex terrains.
Journal of Experimental Biology : jeb.195511Â
doi: 10.1242/jeb.195511Â
Substrate variations are likely to compel animal performance in natural environments, as running over complex terrains challenges the dynamic stability of the body differently in each step. Yet, being able to negotiate complex terrains at top speed is a strong advantage for animals that have to deal with predators and evasive prey. Only little is known on how animals negotiate such terrain variability at high speed. We investigated this in fast running Acanthodactylus boskianus lizards, by measuring their 3D kinematics using four synchronized high-speed video cameras (325Hz) on an adaptable racetrack. This racetrack was covered with four different substrates, representing increasing levels of terrain complexity. We found that the lizards deal with this complexity gradient by gradually adopting more erect parasagittal leg postures. More erected legs enable, in turn, more compliant legs use which are highly adjustable on complex terrains. Additionally, the lizards stabilise their head, which facilitates vestibular and visual perception. Together, compliant legs and head stabilisation enable the lizards to minimise movements of the body centre of mass, even when running on highly irregular terrains. This suggests that the head and the centre of mass are the priority targets for running on uneven terrains. As a result, running performance (mean forward speed) decreases only slightly, and only on the most challenging substrate under investigation.
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Rasha E. Abo-Eleneen, Sarah I. Othman, Hanan M. Al-Harbi, Ahmed M. Abdeen & Ahmed A. Allam (2018)
Anatomical study of the skull of amphisbaenian Diplometopon zarudnyi (Squamata, Amphisbaenia).
Saudi Journal of Biological Sciences 26(3): 503-513
This study investigates the amphisbaenian species skull which includes cranium, lower jaw and hyoid apparatus. The medial dorsal bones comprise the premaxilla, nasal, frontal and parietal. The premaxilla carries a large medial tooth and two lateral ones. The nasals are paired bones and separated by longitudinal suture. Bones of circumorbital series are frontal, orbitosphenoid and maxilla. The occipital ring consists of basioccipital, supraoccipital and exooccipital. Supraoccipital and basioccipital are single bones while the exo-occipitals are paired. The bones of the palate comprise premaxilla, maxilla, septomaxilla, palatine, pterygoid, ectopterygoid, basisphenoid, parasphenoid, orbitosphenoid and laterosphenoid. Prevomer and pterygoid teeth are absent. Palatine represent by two separate bones. The temporal bones are clearly visible. The lower jaw consists of the dentary, articular, coronoid, supra-angular, angular and splenial. The hyoid apparatus is represented by a Y-shaped structure. The mandible is long and is suspended from the braincase via relatively short quadrate. There is an extensive contact between the long angular and the large triangular coronoid. Thus inter-mandibular joint is bridged completely by the angular and consequently, the lower jaws are relatively rigid and kinetic. The maxillae are suspended from the braincase largely by ligaments and muscles rather than through bony articulation. In conclusion, the skull shape affects feeding strategy in Diplometopon zarudnyi. The prey is ingested and transported via a rapid maxillary raking mechanism.
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Paulina Jimenez-Huidobro and Michael W. Caldwell (2019)
A new hypothesis of the phylogenetic relationships of the Tylosaurinae (SQUAMATA: MOSASAUROIDEA).
Frontiers in Earth Science (advance online publication)
doi: 10.3389/feart.2019.00047
Tylosaurinae Williston, 1897, is reconstructed in most analyses as the sister group of the Plioplatecarpinae Dollo, 1884. The most distinctive characteristic of the group is an elongate edentulous rostrum on the premaxilla. Members of the tylosaurine subfamily are divided into two genera: Tylosaurus Marsh, 1872, and Taniwhasaurus Hector, 1874. When all arguably valid tylosaurine species are included in a single phylogenetic analysis, some clades are well supported, i.e., the clade formed by T. proriger (Cope, 1869) + T. bernardi (Dollo, 1885), or the clade T. pembinensis (Nicholls, 1988) + T. saskatchewanensis. In contrast, clade relationships for other species are unresolved, i.e., T. gaudryi (Thevenin, 1896), T. nepaeolicus (Cope, 1874), and the several species within the genus Taniwhasaurus. When T. gaudryi (ThÃvenin, 1896), Ta. âmikasaensisâ Caldwell et al., 2008, and âTâ. capensis ' Broom, 1912 were removed from the analysis, T. nepaeolicus appeared as the basal member of the genus. The relationships within the genus Taniwhasaurus are unresolved; however, when the problematic taxa are removed, the genus is monophyletic, with Ta. oweni as the sister group of Ta. antarcticus. Based on morphological characters present in the holotype of âTâ. capensis Broom, 1912, we suggest a re-assignation to the genus Taniwhasaurus, based on the flutes and facets in the crown of the two preserved replacement teeth. The lack of a clear diagnosis of Hainosaurus/Tylosaurus neumilleri leaves this taxon as nomen dubium; the few characters visible on the specimen show strong similarities to both T. pembinensis and T. saskatchewanensis; therefore the specimen cannot be identified beyond Tylosaurus sp. Reassessment of the known materials of the Japanese species Ta. âmikasaensisâ suggests that the various specimens do not display sufficient diagnostic characters to support âmikasaensisâ as distinct from Taniwhasaurus oweni. The hypothesis for a North Atlantic Circle Basin distribution for species of the genus Tylosaurus from the Coniacian to the Maatrichtian is supported, and a more cosmopolitan distribution is suggested for the genus Taniwhasaurus (Santonian to Maastrichtian) with species present along the margins of the Pacific, Indian and Antarctic Ocean Basins.