Ben Creisler
Some recent non-dino papers:
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Free pdf:
Tomaz P. Melo, Ana Maria Ribeiro, AgustÃn G. Martinelli & Marina Bento Soares (2019)
Early evidence of molariform hypsodonty in a Triassic stem-mammal.
Nature Communications 10, Article number: 2841
DOI:
https://doi.org/10.1038/s41467-019-10719-7
Free pdf:
https://www.nature.com/articles/s41467-019-10719-7.pdfHypsodonty, the occurrence of high-crowned teeth, is widespread among mammals with diets rich in abrasive material, such as plants or soil, because it increases the durability of dentitions against wear. Hypsodont postcanine teeth evolved independently in multiple mammalian lineages and in the closely related mammaliaforms since the Jurassic period. Here, we report the oldest record, to our knowledge, of hypsodont postcanines in the non-mammaliaform stem-mammal, Menadon besairiei, from the early Late Triassic. The postcanines are long and columnar, with open roots. They were not replaced in older individuals and remained functional after the total wear of the crown enamel. Dental histology suggests that, convergently to hypsodont mammals, wear was compensated by the prolonged growth of each postcanine, resulting in dentine hypsodont teeth most similar to extant xenarthran mammals. These findings highlight the constraints imposed by limited tooth replacement and tooth wear in the evolutionary trajectories of herbivorous mammals and stem-mammals.
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Multiple limb bones of different Middle Triassic capitosaurs from India including Cherninia denwai and Paracyclotosaurus crookshanki were examined to reveal differences in palaeobiology and lifestyle adaptations. Limb bone anatomy of Cherninia is characterized by distinct torsion and its absence in the fore and hindlimb bones, respectively. Substantial torsion is seen in all the limb bones of P. crookshanki. Woven fibred bone tissue, a very rapidly deposited tissue mostly seen in the embryos and very young individuals of higher vertebrates, is reported for the first time in a juvenile temnospondyl. Predominance of incipient fibrolamellar bone tissue is seen in a large bodied Middle Triassic temnospondyl suggesting that such tissues in nonâamniotes helped in achieving large body sizes rapidly. Highly vascularized woven fibred bone tissue in the early ontogeny, transforming to a more stable incipient fibrolamellar bone tissue associated with growth marks later in ontogeny characterizes C. denwai. This suggests rapid sustained growth slowed down and became punctuated later in ontogeny. A continuous slow growth throughout ontogeny is suggested for P. crookshanki as parallel fibred bone and azonal lamellar bone tissue are seen in all the examined limb bones. The growth of C. denwai and P. crookshanki had variable susceptibility to seasonal fluctuations. The onset of sexual maturity was at 55% adult size for Cherninia as implied from the change in tissue type. Cherninia inhabited the bottom of the water column and acted as a passive benthic predator whereas Paracyclotosaurus was a shallow water predator that retained a high level of terrestriality.
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Free pdf:
All available data on the Jurassic and Cretaceous climates of Siberia, based on isotope, palaeontological and lithological markers are summarized. Late Pliensbachian cooling, early Toarcian warming, followed by late Toarcian to Middle Jurassic cooling and long-term Late Jurassic warming are well-recognized. Gradual cooling started since the late Ryazanian and continued during the whole Early Cretaceous except the short early Aptian warming event. At the beginning of the Late Cretaceous climate became warmer with warming peak at the Cenomanian-Turonian transition. During the middle and late Turonian climate became colder. During the Coniacian-Campanian time interval climate became warmer, but at the end of the Campanian new cooling event occurred. New records of marine reptiles from the Toarcian, Kimmeridgian, Volgian and SantonianâCampanian of the north of Eastern Siberia are described. All data concerning marine reptile occurrences in the Jurassic and Cretaceous of Siberia are reviewed; these records (from 51 localities) are mostly located at high palaeolatitudes. The analysis has revealed that most of the localities containing fossil reptile remains were located in the Transpolar palaeolatitudes (70Â-87Â). There are no direct relationship between climate oscillations and distribution of these animals. Taking into account recent data arguing that nearly all groups of the Jurassic and Cretaceous big marine reptiles were able to maintain constant body temperature and also were capable make long-range seasonal migrations, any conclusions concerning usage of these animals as markers of warm climate should be treated with a caution.