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[dinosaur] Ecological Radiations of Early Mammals + Peltosaurus

Ben Creisler

Recent non-dino papers:

David M. Grossnickle, Stephanie M. Smith & Gregory P. Wilson (2019)
Untangling the Multiple Ecological Radiations of Early Mammals.
Trends in Ecology & Evolution (advance online publication)
doi: https://doi.org/10.1016/j.tree.2019.05.008


Multiple stem and early mammal groups experienced large-scale ecological radiations, including Jurassic mammaliaforms, Late Cretaceous multituberculates, Late Cretaceous metatherians, and Paleogene placentals.

Small insectivores or omnivores are the progenitors of each ecological radiation, which involve rapid diversifications of diets and modes of locomotion.

There are three main periods of ecological diversification (EarlyâMiddle Jurassic, Late Cretaceous, and Paleogene), each involving radiations of multiple mammalian groups. The Late Cretaceous radiations may have been triggered by the KTR and the Paleogene radiations were to have been likely catalyzed by the end-Cretaceous mass extinction event.

Phylogenetic context and paleontological data are critical for examining ecological radiations in deep time, especially because many radiations involve stem lineages of modern clades that do not have living representatives.


The ecological diversification of early mammals is one of the most globally transformative events in Earthâs history and the Cretaceous Terrestrial Revolution (KTR) and end-Cretaceous mass extinction are commonly hailed as catalysts. However, a confounding issue when examining this diversification is that it comprised nested radiations of mammalian subclades within the broader scope of mammalian evolution. In the past 200 million years, various independent groups experienced large-scale radiations, each involving ecological diversification from ancestral lineages of small insectivores; examples include Jurassic mammaliaforms, Late Cretaceous metatherians, and Cenozoic placentals. Here, we review these ecological radiations, highlighting the nuanced complexity of early mammal evolution, the value of ecomorphological fossil data, and the importance of phylogenetic context in macroevolutionary studies.


Simon G. Scarpetta (2019)
Peltosaurus granulosus (Squamata, Anguidae) from the middle Oligocene of Sharps Corner, South Dakota, and the youngest known chronostratigraphic occurrence of Glyptosaurinae.
Journal of Vertebrate Paleontology Article: e1622129
doi: Âhttps://doi.org/10.1080/02724634.2019.1622129 Â

Glyptosaurinae is an extinct group of anguid lizards commonly found in the Cretaceous and Paleogene fossil record of North America and Eurasia. Glyptosaurines are well documented up until the middle Oligocene, but the temporal extent of the group was never constrained precisely. Here, I document the youngest known record of glyptosaurine lizards. I describe 10 fossils of the glyptosaurine Peltosaurus granulosus from the Monroe Creek and upper Sharps formations of Sharps Corner, South Dakota. The youngest known occurrence of Peltosaurus and Glyptosaurinae is between 27.4 and 26.4 Ma, based on a correlation of the magnetozone of the Monroe Creek Formation with chron C9n. Those dates are in the age range of a hypothesized middleâlate Oligocene warming event. I review relevant morphological characteristics previously described for Peltosaurus and provide images of the holotypes of Peltosaurus abbotti and Peltosaurus granulosus, as well as two relatively complete specimens of Peltosaurus granulosus. I also establish an apomorphy of Peltosaurus on the frontal bone. Additionally, I correct an error in the literature pertaining to the original description of Peltosaurus.

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