Alexander Kuznetsov & Aleksandra Panyutina (2018)
First paleoichnological evidence for baby-riding in early mammals.
Ameghiniana (advance online publication)
doi: 10.5710/AMGH.19.09.2018.3184
It is not yet known how old parental care in mammals is. One fossil trackway ascribed to Ameghinichnus patagonicus Casamiquela, 1961 of a mouse-sized primitive mammal from the Middle Jurassic of Patagonia, Argentina, almost 170 Myr in age, shows deviation from the usual bilateral symmetry: the left forelimb digits were dragging in the swing phase, and the tail was bent to the right and dragged over the right footprints. However, the footprints are evenly spaced, indicating that the animal was not limping. The opposition of the tail and the forelimb dragging marks could possibly be explained by a heavy load carried on the left side. The hypothesis is supported by experiments on laboratory rats. A plausible load would be babies riding on a milk-producing mother, as they do in extant opossums and many other mammals. Baby-riding is an underestimated possible feature of basal mammals, which could logically integrate evolutionary acquisition of such profound mammalian features as milk-feeding, endothermy, hairs, and limb parasagittalism.
Evangelos Vlachos, Enrique Randolfe, Juliana Sterli & Juan M. Leardi (2018)
Changes in the diversity of turtles (Testudinata) in South America from the Late Triassic to the present.
Ameghiniana (advance online publication)
doi: 10.5710/AMGH.18.09.2018.3226
Recent advances in the fossil record, anatomy, and evolutionary history of South American turtles allow a thorough analysis of their changes in diversity, as well as to identify several major extinction events. The history of turtles in South America starts with stem turtles surviving in the southwestern margin of the Pangea. With the onset of the breakup of Pangea in the Middle Jurassic, turtles begin to diversify, giving rise to the main South American turtle clades, some of which survive until present. The first peak of diversity was achieved in the Early Cretaceous, given by basal members of Pelomedusoides, Pan-Chelidae, and Meiolaniformes. A first extinction event is recognized in the end of the Early Cretaceous, affecting mainly the pelomedusoids in northern latitudes and coinciding with the final separation of South America from Africa. Although a general trend of diversification was obtained for most of the Mesozoic, pan-chelids registered extintion events during the middle to Late Cretaceous, and posteriorly the clade is only represented by its crown group members. The K-Pg boundary mass extinction affected the thriving turtle communities deeply in South America by reducing their diversity in half. The effect of this extinction is noted in all clades and latitudes, although turtles with their distributions more extended towards the north (e.g., Pelomedusoides) were more affected. Reduction of diversity continued on the aftermath of the K-Pg extinction, roughly until the middle Eocene and the final isolation of South America from Antarctica. In this ânewâ continent, the surviving turtles continued to decrease on their diversity, up to an injection of biodiversity from Africa, with the arrival of tortoises, which helped to recover the diversity levels to higher values. The Andean uplift in Late Oligocene-Early Miocene and the associated climate and habitat changes posed new problems for the turtles and tortoises of the continent, but they continued to rise and expand. New injections of biodiversity took place at the end of the Neogene with the Great American Biotic Interchange, as novel clades reached South America from the North. The modern biodiversity of South American turtles took its final shape only during the last million years.
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Robert E. Weems (2018)
Crocodilians of the Calvert Cliffs.
in Stephen J. Godfrey (ed.) The Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA. Smithsonian Contributions to Paleobiology 100: 213--240Â
doi: 10.5479/si.1943-6688.100
Crocodilian remains from the Calvert Cliffs are referable to the tomistomine
genus Thecachampsa. The closest living relative is Tomistoma schlegelii, the false
gharial of Southeast Asia. Two species are present: Thecachampsa sericodon Cope and
Thecachampsa antiquus (Leidy). The type specimen of the Florida tomistomine Gavialosuchus americanus is referable to T. sericodon, and some other specimens previously
referred to G. americanus belong to T. antiquus. These tomistomine species are found
in shallow marine coastal deposits, indicating that they habitually inhabited coastal marine
waters as do the modern saltwater crocodile (Crocodylus porosus) and American
crocodile (C. acutus). Tomistomine remains are fairly common in the Miocene coastal
marine deposits of North America, South America, Europe, Africa, and southern Asia.
By the Pliocene, however, tomistomines had become restricted to Southeast Asia. Today,
Tomistoma schlegelii, the sole surviving tomistomine species, is found only in freshwater.
A few crocodilian osteoderms from the Calvert Formation in Delaware do not pertain to
Thecachampsa. They may pertain to Alligator olseni White and indicate that a strictly
freshwater crocodilian was also present during Calvert time. Its remains should eventually
be found along the Calvert Cliffs.
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Sergio A. BalagueraâReina, Miryam VenegasâAnaya, Valeria BeltrÃnâLÃpez, Alejandra Cristancho & Llewellyn D. Densmore (2018)
Food habits and ontogenetic dietary partitioning of American crocodiles in a tropical Pacific Island in Central America
Ecosphere 9(9): Article e02393
Studies on food habits are fundamental to understanding the ecology of a species and its interactions with the community to which it belongs. Among crocodylians, diet affects a variety of biological, physiological, and behavioral characteristics. However, despite having one of the largest distributions across the Americas, some aspects of Crocodylus acutusâ natural history remain poorly studied, particularly in insular areas. We characterized American crocodilesâ food habits in Coiba Island, Panama, assessing ontogenetic dietary variation and dietary overlap by age group and size. We captured and collected stomach content samples from 49 individuals from four transects from March to December 2013. From these samples, we could taxonomically identify three phyla, four subphyla, eight classes, 11 orders, 17 families, 14 genera, and 12 species as prey items. However, not all samples could be identified to the lowest taxon (species), having most of them identified only to family level. Large juveniles had the largest proportion of prey items and subadults the largest proportion of gastroliths and vegetal content. Percent occurrence per major categories (insects, arachnids, crustaceans, fish, reptiles, birds, and mammals) showed crustaceans and insects as the most prominent groups of prey items on this island. Overlapping group analysis showed a reduction in the consumption of invertebrates (crustaceans and insects) as individuals aged. However, these items were the most common throughout all American crocodiles sampled. Dietary overlap analyses showed a likely ontogenetic dietary partitioning with high overlap (>60%) between small and large juveniles and low overlap (<30%) among small juveniles, subadults, and adults. To date, 71 species have been reported as prey items for American crocodiles. However, relying on prey items identified only to genus, we had at least 97 prey items. Thus, C. acutus can be defined as generalist with a broad spectrum of prey inhabiting all types of habitats and having all types of consumption classifications. Overall, American crocodiles inhabiting coastal areas present some differences in both dietary composition and structure with those dwelling inland and freshwater habitats as well as an interindividual diet variation, which reflects the plasticity and adaptability of C. acutus to a variety of conditions.
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Nathan A. Jud, Michael D. DâEmic, Scott A. Williams, Josh C. Mathews, Katie M. Tremaine and Janok Bhattacharya (2018)
A new fossil assemblage shows that large angiosperm trees grew in North America by the Turonian (Late Cretaceous).
Science Advances 4(9): eaar8568
DOI: 10.1126/sciadv.aar8568
The diversification of flowering plants and marked turnover in vertebrate faunas during the mid-Cretaceous transformed terrestrial communities, but the transition is obscured by reduced terrestrial deposition attributable to high sea levels. We report a new fossil assemblage from multiple localities in the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in Utah. The fossils date to the Turonian, a severely underrepresented interval in the terrestrial fossil record of North America. A large silicified log (maximum preserved diameter, 1.8 m; estimated height, ca. 50 m) is assigned to the genus Paraphyllanthoxylon; it is the largest known pre-Campanian angiosperm and the earliest documented occurrence of an angiosperm tree more than 1.0 m in diameter. Foliage and palynomorphs of ferns, conifers, and angiosperms confirm the presence of mixed forest or woodland vegetation. Previously known terrestrial vertebrate remains from the Ferron Sandstone Member include fish teeth, two short dinosaur trackways, and a pterosaur; we report the first turtle and crocodilian remains and an ornithopod sacrum. Previous studies indicate that angiosperm trees were present by the Cenomanian, but this discovery demonstrates that angiosperm trees approaching 2 m in diameter were part of the forest canopies across southern North America by the Turonian (~92 million years ago), nearly 15 million years earlier than previously thought.
News:
Researchers add surprising finds to the fossil record