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[dinosaur] Juvenile Deinosuchus + Cloverly Formation stratigraphy




Ben Creisler
bcreisler@gmail.com


Recent papers not yet mentioned:


Chase Doran Brownstein (2019)
First Record of a Small Juvenile Giant Crocodyliform and its Ontogenetic and Biogeographic Implications.
Bulletin of the Peabody Museum of Natural History 60(1): 81-90
doi: https://doi.org/10.3374/014.060.0104
https://bioone.org/journals/Bulletin-of-the-Peabody-Museum-of-Natural-History/volume-60/issue-1/014.060.0104/First-Record-of-a-Small-Juvenile-Giant-Crocodyliform-and-its/10.3374/014.060.0104.short

Deinosuchus is a genus of large crocodylian that inhabited North America during the Late Cretaceous. This massive predator has become one of the most well-known prehistoric organisms, with a considerable amount of literature on its biogeography, ecology, and evolution published. However, ontogenetic changes of Deinosuchus and other species of extinct large, predatory crocodyliforms have remained poorly understood because of a lack of remains known from juvenile individuals and issues surrounding the ability of histological analysis of adult material to provide information on yearly growth. Here, I describe a tooth from a juvenile Deinosuchus estimated at less than 1m in total body length. As the first reported specimen of a juvenile Deinosuchus, to the author's knowledge, in the literature, the new fossil evinces the extremely small size of young individuals of this taxon compared to adults more than 8 m and 3,500 kg. Furthermore, the tooth shows that some morphological discrepancies existed between the dentition of juvenile and adult Deinosuchus individuals, including the size of the nutritive region. In addition to being the first specimen of Deinosuchus from northeastern North America described in detail, the tooth emphasizes the biological extremes of attaining large body size in Deinosuchus and may add support to the hypothesis that the ontogeny of gigantic crocodyliforms was characterized by extended periods of juvenile growth.

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Michael D. D'Emic, Brady Z. Foreman, Nathan A. Jud, Brooks B. Britt, Mark Schmitz, James L. Crowley (2019)
Chronostratigraphic Revision of the Cloverly Formation (Lower Cretaceous, Western Interior, USA).
Bulletin of the Peabody Museum of Natural History 60(1): 3-40Â
doi: https://doi.org/10.3374/014.060.0101
https://bioone.org/journals/Bulletin-of-the-Peabody-Museum-of-Natural-History/volume-60/issue-1/014.060.0101/Chronostratigraphic-Revision-of-the-Cloverly-Formation-Lower-Cretaceous-Western-Interior/10.3374/014.060.0101.short


The Cloverly Formation is an important geologic unit for understanding the development of North American terrestrial landscapes and ecosystems, but the age of this unit is poorly constrained. We report UâPb radiometric dates determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and chemical abrasion thermal ionization mass spectrometry (CA-TIMS) from euhedral zircons derived from fluvial sandstone and bentonitic claystone. We reanalyzed published biostratigraphic, paleomagnetic, and radiometric datasets, which have generally disregarded younger (late AlbianâCenomanian) ages for the formation. New data reported in this study suggest that deposition of the Cloverly Formation spanned the ValanginianâCenomanian stages (ca. 140 Maâ98 Ma), a longer time interval than the commonly cited AptianâAlbian depositional timeframe. The lowest member of the Cloverly Formation, the Pryor Conglomerate, was deposited ca. 140â130 Ma in response to the onset of the Sevier Orogeny shedding sediment from the west. The overlying Little Sheep Mudstone Member was deposited ca. 124â109 Ma in a time of low sediment supply. In the midâlate Albian to early Cenomanian (ca. 109â98 Ma), sediment sourced from the east was deposited as the Himes Member and Greybull Sandstone. Following this, the Sykes Mountain Formation began nearshore deposition as the Western Interior Seaway transgressed from the north. Our revised chronostratigraphic framework for the Cloverly Formation is congruent with tectonic subsidence analysis showing a rapid increase in accommodation space in the mid-Albian. We hypothesize that more intensive sampling may yield multiple fossil assemblages within the formation, paralleling its correlates to the south. Furthermore, we hypothesize that some poorly represented taxa will be synonymized with taxa from those same units now that their temporal equivalence has been demonstrated.


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