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Adriel R. Gentil & MartÃn D. Ezcurra (2018)
A new rhynchosaur maxillary tooth plate morphotype expands the disparity of the group in the Ischigualasto Formation (Late Triassic) of Northwestern Argentina.
Historical Biology (advance online publication)
doi:Â https://doi.org/10.1080/08912963.2018.1438425ÂÂ
http://www.tandfonline.com/doi/full/10.1080/08912963.2018.1438425
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Rhynchosaurs are a clade of quadruped, herbivorous stem-archosaur diapsids restricted to the Triassic Period. The group became globally distributed and the numerically dominant tetrapods of several terrestrial ecosystems before their extinction. Derived rhynchosaurs are characterized by a specialized masticatory apparatus, composed of a blade-and-groove occlusion with multiple longitudinal maxillary tooth rows. The morphology of the maxillary tooth plate has shown to be taxonomically and phylogenetically informative. So far, two rhynchosaur maxillary tooth plate morphotypes are known in Argentina, one belonging to an unnamed stenaulorhynchine from the ChaÃares Formation and the other to the hyperodapedontine Hyperodapedon sanjuanensis, the single rhynchosaur species currently name for the Ischigualasto Formation. Here we describe a new rhynchosaur maxillary tooth plate morphotype based on an indeterminate hyperodapedontine specimen from the Ischigualasto Formation. This maxillary tooth plate (PVL 2728) possesses a single longitudinal groove that divides symmetric lateral and medial tooth-bearing areas with relatively large tooth crowns, which is an uncommon combination of features among hyperodapedontines. These qualitative observations in addition to quantitative analyses show that the morphology of PVL 2728 differs from that of, at least, other sampled South American rhynchosaurs. Therefore, this specimen expands the morphological disparity of rhynchosaurs in northwest Argentina and southwestern Pangaea.
=====Krzysztof Kolenda, Anna Najbar, Beata Rozenblut-KoÅcisty, Ewa Serwa & Tomasz SkawiÅski (2018)
Common occurrence of Sharpeyâs fibres in amphibian phalanges.
Zoomorphology (advance online publication)
DOI: https://doi.org/10.1007/s00435-018-0400-4
https://link.springer.com/article/10.1007%2Fs00435-018-0400-4
https://link.springer.com/content/pdf/10.1007%2Fs00435-018-0400-4.pdf
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Sharpeyâs fibres are known mainly as providing anchorage between tooth and the periodontal ligament but they occur also in other types of bones. In the postcranial skeleton these fibres are usually present at the muscle or tendon attachment sites. They were reported in all major groups of extant vertebrates, as well as in putative lissamphibian ancestorsâtemnospondyls and lepospondyls. However, it was recently stated that their presence was very rarely described in extant amphibians. In limbs, they were reported predominantly from proximal bones. They have not yet been reported from phalanges, which are the most commonly sectioned amphibian bones. Here, we describe phalangeal histology of nine species representing most major clades of lissamphibians. These results show that Sharpeyâs fibres occur commonly in lissamphibian phalanges. In shaft, they are radially oriented and occur in the periosteal bone, at sites of tendon attachment. They can also occur in the metaphysis and contact the cartilage. This may provide a basis for foot muscle reconstructions in fossil amphibians.