The systematic relationships of taxa traditionally referred to as ‘basal ornithopods’ or ‘hypsilophodontids’ remain poorly resolved since it was discovered that these are not a monophyletic group, but rather paraphyletic set neornithischian taxa. Thus, even the known diversity has dramatically increased over past two decades, our knowledge their placement relative each other and major ornithischian subclades remained incomplete. This study employs largest phylogenetic dataset yet compiled...

New penguin fossils from the Eocene of Peru force a reevaluation previous hypotheses regarding causal role climate change in evolution. Repeatedly it has been proposed that penguins originated high southern latitudes and arrived at equatorial regions relatively recently (e.g., 4-8 million years ago), well after onset latest Eocene/Oligocene global cooling increases polar ice volume. By contrast, new discoveries middle late reveal invaded low >30 earlier than prior data suggested, during one...

Ornithischians form a large clade of globally distributed Mesozoic dinosaurs, and represent one their three major radiations. Throughout evolutionary history, exceeding 134 million years, ornithischians evolved considerable morphological disparity, expressed especially through the cranial osteodermal features most distinguishable representatives. The nearly two-century-long research history on has resulted in recognition numerous diverse lineages, many which have been named. Following...

During their long evolutionary history, neornithischian dinosaurs diverged into several clades with distinctive adaptations. However, the early evolution within Neornithischia and resolution of phylogenetic relationships taxa situated near base clade remain problematic. This is especially true for those traditionally placed at Ornithopoda, either as 'hypsilophodontids' or diverse Iguanodontia. Recent studies are improving our understanding anatomy these taxa, discoveries new...

ABSTRACT Considerable controversy surrounds the taxonomy and phylogenetic relationships of Maastrichtian basal neornithischian taxa from North America. Discovery previously unrecognized cranial material paratype specimen Thescelosaurus neglectus (USNM 7758), along with examination two new specimens that preserve nearly complete skulls mandibles, allows for reevaluation referred to material, including holotypes Bugenasaura infernalis (SDSM 7210) Parksosaurus warreni (ROM 804). A analysis was...

A small, articulated basal ornithopod skeleton from the Frenchman Formation (late Maastrichtian) of Saskatchewan (RSM P 1225.1), previously referred to taxon Thescelosaurus, differs both recognized species this (Thescelosaurus neglectus and Thescelosaurus garbanii). The differences are taxonomically informative we recognize specimen as holotype a new species, assiniboiensis sp. nov., diagnosed by presence two autapomorphies, displaying plesiomorphic traits more similar those Parksosaurus,...

Though the dinosaur Thescelosaurus neglectus was first described in 1913 and is known from relatively fossiliferous Lance Hell Creek formations Western Interior Basin of North America, cranial anatomy this species remains poorly understood. The only material confidently referred to are three fragmentary bones preserved with paratype, hindering attempts understand systematic relationships taxon within Neornithischia. Here T. fully for time based on two specimens that include well-preserved...

Theropod dinosaurs are one of the most remarkable lineages terrestrial vertebrates in Mesozoic, showing high taxonomic and ecological diversity.We investigate cranial diversity non-avian theropods some basal birds, using geometric morphometrics to obtain insights into evolutionary modifications skull.Theropod skulls mostly vary shape snout length postorbital region (principal component [PC] 1), with further variation orbit shape, depth region, position jaw joint (PC 2 PC 3).These results...

Crocodyliforms serve as important taphonomic agents, accumulating and modifying vertebrate remains. Previous discussions of Mesozoic crocodyliform feeding in terrestrial riverine ecosystems have often focused on larger taxa their interactions with equally large dinosaurian prey. However, recent evidence suggests that the impact smaller crocodyliforms environments should not be discounted. Here we present direct by a small juvenile specimens ‘hypsilophodontid’ dinosaur from Upper Cretaceous...

Improvements in the perceived completeness of fossil record may be driven both by new discoveries and reinterpretation known fossils, but disentangling relative effects these processes can difficult. Here, we propose a methodology for evaluating historical trends record, demonstrate its implementation using freely available software ASCC (version 4.0.0), present an example crown-group birds (Aves). Dates discovery recognition oldest representatives 75 major lineages were collected period...

Knowledge regarding the early evolution within dinosaurian clade Ankylopollexia drastically increased over past two decades, in part because of an increase described taxa from Early Cretaceous North America. These advances motivated recent completion extensive preparation and conservation work on holotype only known specimen Dakotadon lakotaensis , a basal ankylopollexian Lakota Formation South Dakota. That (SDSM 8656) preserves partial skull, lower jaws, single dorsal vertebra, caudal...

The stratigraphic record of first appearances provides an independent source data for evaluating and comparing phylogenetic hypotheses that include taxa with fossil histories. However, no standardized method exists calculating these metrics polytomous phylogenies, restricting their applicability. Previously proposed methods insufficiently deal this problem because they skew or restrict the resulting scores. To resolve issue, we propose a treating polytomies when metrics: Comprehensive...

Removal or protection from biostratinomic agents of decomposition, such as predators and scavengers, is widely seen a requirement for high-quality preservation soft tissues in the fossil record. In this context, extremely rapid burial an oft-cited mechanism shielding remains degradation, but not all fossils fit nicely into paradigm. Dinosaurian mummies particular seemingly require two mutually exclusive taphonomic processes to preserve under that framework: desiccation burial. Here we...

Improvements in the perceived completeness of fossil record may be driven both by new discoveries and reinterpretation known fossils, but disentangling relative effects these processes can difficult. Here, we propose a methodology for evaluating historical trends record, demonstrate its implementation using freely available software ASCC (version 4.0.0), present an example crown-group birds (Aves). Dates discovery recognition oldest representatives 75 major lineages were collected period...

Approaches quantifying the relative congruence, or incongruence, of molecular divergence estimates and fossil record have been limited. Previously proposed methods are largely node specific, assessing incongruence at particular nodes for which both data available. These existing metrics, other that quantify across topologies including entirely extinct clades, so far not taken into account uncertainty surrounding ages fossils. They also treated younger than previously assessed minimum clade...

Avian remains are rare from Paleogene sediments in the Great Plains region of North America, especially those that can be identified taxonomically. Here, we describe avian eggshell fragments Fitterer Ranch locality within Oligocene Brule Formation Dakota and assign them to ootaxonomy. The specimen examined (NDGS 1934) exhibits low tubercles form undulating surface ornamentation; 650–900-µm-thick composed three structural layers calcite; abrupt transition between mammillary continuous layers;...

Gaining a detailed understanding of the geographic and temporal variations between Lancian mammalian faunas within Western Interior Basin requires specimens to be associated with precise stratigraphic data, but only few mammal-producing localities are documented in such detail from Hell Creek Formation southwestern North Dakota. Recent work at two sites Dakota resulted discovery additional mammal previously for which position is precisely recorded. The most productive site situated 12.07 m...

Crocodyliforms serve as important taphonomic agents, accumulating and modifying vertebrate remains. Previousdiscussions of Mesozoic crocodyliform feeding in terrestrial riverine ecosystems have often focused on larger taxa their interactions with equally large dinosaurian prey. However, recent evidence suggests that the impact smaller crocodyliforms environments should not be discounted. Here we present direct by a small juvenile specimens ‘hypsilophodontid’ dinosaur from Upper Cretaceous...

An exquisitely preserved male skeleton of an early arctoid, Eoarctos vorax new genus and species, provides a unique window into the origin divergence Carnivora. Recovered from Fitterer Ranch locality in Oligocene (Orellan to Whitneyan North American Land Mammal ages) Brule Formation southwestern Dakota (∼32 Ma), arctoid offers opportunity evaluate fundamental relationships caniform (dog-like) carnivorans. possesses suite plesiomorphic characters inherited its miacid ancestors, making it...

Korth, William W., Robert J. Emry, Clint A. Boyd, and Jeff Person. Rodents (Mammalia) from Fitterer Ranch, Brule Formation (Oligocene), North Dakota. Smithsonian Contributions to Paleobiology, number 103, vi + 45 pages, 17 figures, 15 tables, 1 appendix, 2019.—Eighteen rodent species are recognized the Ranch fauna of Dakota on basis more than a thousand collected specimens. Of recognized, four new: prosciurine aplodontiids Prosciurus hogansoni Altasciurus leonardi, heliscomyid Heliscomys...

Mosasaurs are large, carnivorous aquatic lizards with a global distribution that lived during the Late Cretaceous. After 200 years of scientific study, new mosasaur species still being discovered as localities explored and specimens collected long ago reevaluated using modern standards delimitation. Even so, phylogenetic positions many key taxa unresolved therefore our understanding macroevolution is muddled. Here, we describe genus mosasaurine comprising partial skull skeleton from Pembina...