Steven E Jasinski | State Museum of Pennsylvania (original) (raw)

Papers by Steven E Jasinski

Research paper thumbnail of Late Cretaceous Dinosaur Biogeography and Endemism in the Western Interior Basin, North America: A Critical Re-Evaluation

North-south provinciality among Campanian and/or Maastrichtian vertebrates, especially dinosaurs,... more North-south provinciality among Campanian and/or Maastrichtian vertebrates, especially dinosaurs, in the Western Interior basin of North America (specifically, between West Texas and southern Alberta, Canada) has been accepted by many vertebrate paleontologists for about 30 years. However, a critical review indicates that the case for provinciality based on non-dinosaurian vertebrates is weak to nonexistent, and that the case based on dinosaurs is problematic, resting solely on a few taxa of dinosaurs, most notably the chasmosaurine ceratopsids, which have also been used to identify extreme dinosaur endemism. Paleobiogeographic provinces can be rejected because of: (1) problems and biases in sampling; (2) the lack of topographic barriers in the Western Interior basin that would divide provinces; (3) the lack of significant climatic or vegetational differences and/or gradients to provincialize vertebrates; (4) how taxonomic (largely cladotaxonomic) decisions have been intimately invo...

Research paper thumbnail of A softshell turtle (Testudines: Trionychidae: Plastomeninae) from the uppermost Cretaceous (Maastrichtian) Hell Creek Formation, North Dakota, USA, with implications for the evolutionary relationships of plastomenines and other trionychids

Cretaceous Research, 2022

Research paper thumbnail of Biomechanical Modeling of Coelophysis Bauri: Possible Feeding Methods and Behavior of a Late Triassic Theropod

Research paper thumbnail of No definitive evidence of Paleocene dinosaurs in the San Juan Basin

Paleontologia Electronica, 2009

In a recent article in this journal, Fassett (2009) concludes that dinosaur fossils of Paleocene ... more In a recent article in this journal, Fassett (2009) concludes that dinosaur fossils of Paleocene age are present in the San Juan Basin of New Mexico-Colorado. However, we argue that, based on existing data, Fassett has failed to produce compelling evidence to support this conclusion. In the San Juan Basin, only one arguably reworked dinosaur bone (an isolated hadrosaur femur) is stratigraphically above undisputed Paleocene pollen, so palynology does not demonstrate Paleocene dinosaurs in the San Juan Basin. Nor does ...

Research paper thumbnail of Complete specimens of the Eocene testudinoid turtles Echmatemys and Hadrianus and the North American origin of tortoises

Bulletin of the New Mexico Museum of Natural History and Science, 2021

Newly described specimens of North American Eocene turtles provide valuable information on their ... more Newly described specimens of North American Eocene turtles provide valuable information on their morphology and, more specifically, variation, both intraspecific and ontogenetic. We describe several complete and nearly complete testudinoid (Testudinoidea) specimens, including juvenile specimens of Hadrianus corsoni, H. majusculus, Echmatemys haydeni and E. naomi. These specimens help us determine that the oldest and most basal tortoises are from the western United States, suggesting Testudinidae evolved in North America from one of the geoemydid-like forms in the genus Echmatemys, which have their lowest stratigraphic occurrence in the earliest Wasatchian North American land-mammal “age” (early Eocene, Ypresian, ~53 Ma).

Research paper thumbnail of New dromaeosaurid dinosaur (Theropoda, Dromaeosauridae) from New Mexico and biodiversity of dromaeosaurids at the end of the Cretaceous

Scientific Reports, 2020

Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse f... more Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse fossil record, particularly at the time of their extinction near the Cretaceous-Paleogene boundary. Here we report on a new dromaeosaurid, Dineobellator notohesperus, gen. and sp. nov., consisting of a partial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, the first diagnostic dromaeosaurid to be recovered from the latest Cretaceous of the southern United States (southern Laramidia). The holotype includes elements of the skull, axial, and appendicular skeleton. The specimen reveals a host of morphologies that shed light on new behavioral attributes for these feathered dinosaurs. Unique features on its forelimbs suggest greater strength capabilities in flexion than the normal dromaeosaurid condition, in conjunction with a relatively tighter grip strength in the manual claws. Aspects of the caudal vertebrae suggest greater movement near the tail base, aiding in agility and predation. Phylogenetic analysis places Dineobellator within Velociraptorinae. Its phylogenetic position, along with that of other Maastrichtian taxa (Acheroraptor and Dakotaraptor), suggests dromaeosaurids were still diversifying at the end of the Cretaceous. Furthermore, its recovery as a second North American Maastrichtian velociraptorine suggests vicariance of North American velociraptorines after a dispersal event during the Campanian-Maastrichtian from Asia. Features of Dineobellator also imply that dromaeosaurids were active predators that occupied discrete ecological niches while living in the shadow of Tyrannosaurus rex, until the end of the dinosaurs’ reign.

Research paper thumbnail of So different, yet so alike: North American slider turtles (Trachemys scripta)

Vertebrate Zoology, 2020

We studied for the first time the molecular differentiation of all three currently recognized sub... more We studied for the first time the molecular differentiation of all three currently recognized subspecies of Trachemys scripta, including the morphologically distinct western populations of T. s. elegans (‘western red-eared sliders’), using mitochondrial and nuclear DNA sequences (up to 3,236 bp and 2,738 bp, respectively) and 14 microsatellite loci. We found that only the quickly evolving microsatellite loci discriminated T. s. troostii and the western red-eared slider from the remaining two subspecies, while T. s. elegans and T. s. scripta were not distinct in any marker system. Our findings challenge the current intraspecific systematics of T. scripta and suggest that the conspicuous differences in coloration and pattern reflect population-specific, rather than taxonomic, differentiation. We abstain from synonymizing any subspecies because, for traditionalists and conservationists, abandoning the well-established and morphologically distinct subspecies of T. scripta is not desirable. However, if subspecies of T. scripta continue to be recognized, the current taxonomy with three subspecies is difficult to justify. Western red-eared sliders are morphologically distinct and differ from T. s. elegans and T. s. scripta, with respect to microsatellites, as much as T. s. troostii does. In view of this morphological and genetic evidence, subspecies status should be considered for western red-eared sliders.

Research paper thumbnail of Baenid (Baenidae: Testudines) lower jaws from the Late Cretaceous and Paleocene of the San Juan Basin, New Mexico

Bulletin of the New Mexico Museum of Natural History and Science, 2018

Two isolated lower jaws belonging to different baenid turtles are identified as cf. Boremys grand... more Two isolated lower jaws belonging to different baenid turtles are identified as cf. Boremys grandis from the upper Campanian (Late Cretaceous) Kirtland Formation (De-na-zin Member) and cf. Neurankylus torrejonensis from the Paleocene Nacimiento Formation (Puercan). Cf. Boremys grandis is the first lower jaw of a baenid to be documented from the Late Cretaceous (Kirtlandian) of New Mexico and may represent a temporal extension for this taxon. Cf. Neurankylus torrejonensis may be the oldest record of this taxon, which may suggest evidence for anagenesis. As turtle skull material, including lower jaw and cranial remains, are rare from the Cretaceous and Paleocene of New Mexico, these specimens provide new morphological information and potential extensions of the respective biostratigraphic ranges of these turtles. They also help us further understand the composition of turtle faunas during the Cretaceous/Paleogene transition in New Mexico and the southern United States. Durophagy may not have been as important to survival of the baenid turtles at the end-Cretaceous extinction as previously thought, at least in the southern United States, because durophagous turtles appear to be absent during the Late Cretaceous in this region. In addition, the percentage of nondurophagous turtle genera in the Paleocene of North America is larger than previously believed. Turtle paleoecology was obviously distinct in northern and southern North America during the Late Cretaceous, at least regarding the major niches held by turtles. This paleoecological separation became less distinct following the Cretaceous-Paleogene extinction event, with durophagous taxa present, potentially through migration or evolutionary events, to the south.

Research paper thumbnail of A new slider turtle (Testudines: Emydidae: Deirochelyinae: Trachemys) from the late Hemphillian (late Miocene/early Pliocene) of eastern Tennessee and the evolution of the deirochelyines

PeerJ, 2018

Trachemys (Testudines: Emydidae) represents one of the most well-known turtle genera today. The e... more Trachemys (Testudines: Emydidae) represents one of the most well-known turtle genera today. The evolution of Trachemys, while being heavily documented with fossil representatives, is not well understood. Numerous fossils from the late Hemphillian Gray Fossil Site (GFS) in northeastern Tennessee help to elucidate its evolution. The fossil Trachemys at the GFS represent a new species. The new taxon, Trachemys haugrudi, is described, and currently represents the most thoroughly described fossil emydid species known. A phylogenetic analysis, including 31 species, focusing on the subfamily Deirochelyinae is performed that includes the new fossil species, along with numerous other modern and fossil deirochelyine species, representing the first phylogenetic analysis published that includes several fossil deirochelyines. The phylogenetic analysis, utilizing morphological evidence, provides monophyletic clades of all modern deirochelyines, including Chrysemys, Deirochelys, Pseudemys, Malaclemys, Graptemys, and Trachemys. A strict consensus tree finds the recently described fossil species Graptemys kerneri to be part of a clade of Graptemys + Malaclemys. Three fossil taxa, including one previously referred to Pseudemys (Pseudemys caelata) and two to Deirochelys (Deirochelys carri and Deirochelys floridana) are found to form a clade with modern Deirochelys reticularia reticularia, with D. floridana sister to the other members of the clade. Chrysemys is found to be part of a basal polytomy with Deirochelys in relation to other deirochelyine taxa. Two fossil taxa previously referred to Chrysemys (Chrysemys timida and Chrysemys williamsi) form a paraphyly with the modern Chrysemys picta picta and Deirochelys, and may be referable to distinct genera. Additionally, fossil taxa previously attributed to Trachemys (Trachemys hillii, Trachemys idahoensis, Trachemys inflata, and Trachemys platymarginata) and T. haugrudi are found to form a clade separate from clades of northern and southern Trachemys species, potentially suggesting a distinct lineage of Trachemys with no modern survivors. Hypotheses of phylogenetic relationships mostly agree between the present study and previous ones, although the inclusion of fossil taxa provides further clues to the evolution of parts of the Deirochelyinae. The inclusion of more fossil taxa and characters may help resolve the placement of some taxa, and further elucidate the evolution of these New World turtles.

Research paper thumbnail of First occurrence of a tyrannosauroid dinosaur from the lower Campanian Merchantville Formation of Delaware, USA

Memoir of the Fukui Prefectural Dinosaur Museum, 2017

This study provides a detailed osteological description of an isolated proximal caudal centrum an... more This study provides a detailed osteological description of an isolated proximal caudal centrum and two nearly complete isolated metatarsals II and IV of the left foot of a gracile theropod dinosaur from the Lower Campanian of the Merchantville Formation in northern Delaware, USA. The caudal centrum and the metatarsals are referred to Tyrannosauroidea. The centrum is not well preserved, and thus not diagnostic; however, both metatarsals are diagnostic. The referral to Tyrannosauroidea is supported by several morphological features, including extensive surfaces on metatarsals II and IV for the articulation with metatarsal III, and a characteristic low, slightly convex muscle scar on metatarsal IV developed as a thin low ridge located on the posterior surface between the M. gastrocnemius pars lateralis insertion scar and the metatarsal III articular surface. This ridge has been previously interpreted as the plantar ridge, which is present in some derived Late Campanian tyrannosauroid taxa. Additionally, metatarsal IV has a deep medial notch for the accommodation of an “L”– shaped proximal articulation of metatarsal III, and a “U”– shaped proximal articular end. The Merchantville Formation tyrannosauroid exhibits arctometatarsalian metatarsals, as do tyrannosaurids. The Merchantville Formation tyrannosauroid is differentiated from other known basal and derived tyrannosaurids by having a characteristically shaped proximal articular surface of metatarsal II in which the proximal and posterior ends lie on the long axis of the proximal articular surface. However, the posterior proximal articular surface of metatarsal II is not as strongly angled laterally as in more derived tyrannosauroids. The Merchantville Formation tyrannosauroid adds to the record of Appalachian tyrannosauroid, evolution and paleostratigraphic position, and provides new morphological information about the metatarsal anatomy of these iconic theropods.

Research paper thumbnail of Late Hemphillian colubrid snakes (Serpentes, Colubridae) from the Gray Fossil Site of northeastern Tennessee

Journal of Herpetology, 2017

The Gray Fossil Site (GFS) of northeastern Tennessee is a late Hemphillian fossil locality in the... more The Gray Fossil Site (GFS) of northeastern Tennessee is a late Hemphillian fossil locality in the southern Appalachian mountain region of eastern North America with a diverse vertebrate fauna. Snakes make up a substantial microfossil portion of the GFS herpetofauna, particularly the Colubridae, comprised of members of the Colubrinae and Natricinae. Seven colubrid taxa have been identified from the site so far, including three natricines (cf. Neonatrix, Nerodia, Thamnophis) and at least four colubrines (Coluber/ Masticophis, Pantherophis, Pituophis, gen. et sp. nov.). Indeed, cf. Neonatrix and the new genus (and species) are the only extinct genera identified. Although Neonatrix is tentatively identified for the first time east of Nebraska, the new species represents a distinct taxon. In addition, the oldest reported definitive occurrence of Masticophis is presented herein. Some of the snakes suggest a pond or other aquatic habitat at GFS, particularly cf. Neonatrix and Nerodia, whereas others, such as Masticophis and Pituophis, tend to prefer more open forested habitats. The GFS represents a poorly understood region of North America at a crucial time period in snake evolution, and its study may help us further understand the modern snake fauna present today in midcontinental and eastern North America.

Research paper thumbnail of First record of fossil chelydrid and trionychid turtles (Testudines) from the Pleistocene of Sonora, Mexico

Bulletin of the New Mexico Museum of Natural History and Science, 2016

The late Pleistocene of northern Mexico is relatively poorly understood, and represented by only ... more The late Pleistocene of northern Mexico is relatively poorly understood, and represented by only a few fossil localities. One such locality is Térapa, located in east-central Sonora. The deposit dates to between 43,000 and 40,000 years old (Rancholabrean) and yields a rich fossil fauna of over 60 identified taxa, dominated by birds and large mammals. Geologic evidence at the site indicates a marshland with permanent sources of calm freshwater, which is supported by the presence of fossil remains of freshwater invertebrates, fishes, frogs, crocodilians and turtles. Previous studies have reported fossil turtles representing two families: Emydidae and Kinosternidae. Both of these families are represented in the extant fauna of Sonora. Here, we present the remains of two additional families of turtles from Térapa, Chelydridae and Trionychidae, both of which are absent today in the naturally-occurring fauna of Sonora. The extralimital presence of these families at Térapa indicates a significant biogeographical shift between the late Pleistocene and the present day. Previous studies have noted the similarly unusual discovery of crocodilians at Térapa, and proposed that its presence might be the result of dispersal into Sonora via coastal and riparian routes. We suggest a similar migration pattern might explain the presence of chelydrids and trionychids at the site, with the turtles dispersing into Sonora either from the north or from the south, and we discuss evidence for both scenarios.

Research paper thumbnail of The validity of the Late Cretaceous pachycephalosaurid Stegoceras novomexicanum (Dinosauria: Pachycephalosauridae)

Bulletin of the New Mexico Museum of Natural History and Science, 2016

In light of a recent paper, we review, and reassess, the validity of the pachycephalosaurid dinos... more In light of a recent paper, we review, and reassess, the validity of the pachycephalosaurid dinosaur Stegoceras novomexicanum (Dinosauria: Ornithischia: Pachycephalosauridae). Specimens that are referred to Stegoceras novomexicanum are all late Campanian (early Kirtlandian) in age and are not only from a restricted stratigraphic horizon at the Fruitland/Kirtland transition, but also from a small geographic area of the San Juan Basin, New Mexico. While some of the characters initially used in diagnosing this taxon may be representative of an earlier (sub-adult) ontogenetic stage, such as the reduction of the size of the posteromedial extension of the parietal and the size of the supratemporal fenestrae, several other characters confirm its validity. These include the shape of the posteromedial extension of the parietal, the relative position of the supratemporal fenestrae, the shape and degree of inflation of the nasal boss, morphology of the prefrontal-frontal suture, curvature of the frontal-parietal suture, and its relative overall size and gracile form relative to the type (lectotype) of Stegoceras validum from the Judithian of Alberta, Canada. Although the holotype of Stegoceras novomexicanum may represent a sub-adult individual, it also possesses some diagnostic features that are indicative of an adult. This combination of features may indicate heterochrony for Stegoceras novomexicanum within the Pachycephalosauridae. Recently recovered small-bodied, high-domed pachycephalosaurid specimens from the Fruitland-Kirtland transition further support our interpretation that this taxon represents a distinct, small-bodied adult pachycephalosaurid in New Mexico. The previously described paratypes, and newly collected specimens, are conservatively assigned to cf. Stegoceras novomexicanum, as all this material comes from a very restricted stratigraphic interval and geographic area.

Research paper thumbnail of Late Cretaceous dinosaur biogeography and endemism in the Western Interior Basin, North America: A critical re-evaluation

Bulletin of the New Mexico Museum of Natural History and Science, 2016

North-south provinciality among Campanian and/or Maastrichtian vertebrates, especially dinosaurs,... more North-south provinciality among Campanian and/or Maastrichtian vertebrates, especially dinosaurs, in the Western Interior basin of North America (specifically, between West Texas and southern Alberta, Canada) has been accepted by many vertebrate paleontologists for about 30 years. However, a critical review indicates that the case for provinciality based on non-dinosaurian vertebrates is weak to nonexistent, and that the case based on dinosaurs is problematic, resting solely on a few taxa of dinosaurs, most notably the chasmosaurine ceratopsids, which have also been used to identify extreme dinosaur endemism. Paleobiogeographic provinces can be rejected because of: (1) problems and biases in sampling; (2) the lack of topographic barriers in the Western Interior basin that would divide provinces; (3) the lack of significant climatic or vegetational differences and/or gradients to provincialize vertebrates; (4) how taxonomic (largely cladotaxonomic) decisions have been intimately involved in the perception of endemism and provinciality; (5) how the demonstrable diachroneity of most fossil assemblages undermines the ability to include them in biogeographic analyses; and (6) how the non-uniformitarian conclusions of those who argue for dinosaur provinciality and endemism undermine their own arguments. Not only do we demonstrate the biological and geological implausibility of dinosaur-based biogeographic provinces and high degrees of endemism in the Western Interior basin during the Late Cretaceous, but the arguments and analyses that have been marshalled to support such concepts are questionable. Consequently, there is no compelling evidence that there was any discrete biogeographic separation of the Campanian (or Maastrichtian) dinosaur-dominated vertebrate assemblages from north to south beteen Texas and Alberta in the Western Interior basin. Also, there is no compelling evidence of high degrees of dinosaur endemism in the Western Interior basin during the Campanian.

Research paper thumbnail of A borophagine canid (Carnivora: Canidae: Borophaginae) from the middle Miocene Chesapeake Group of eastern North America

Journal of Paleontology, 2015

A tooth recovered from the middle Miocene Choptank Formation (Chesapeake Group) of Maryland is id... more A tooth recovered from the middle Miocene Choptank Formation (Chesapeake Group) of Maryland is identified as a new cynarctin borophagine (Canidae: Borophaginae: Cynarctina), here called Cynarctus wangi n. sp. The tooth, identified as a right upper second molar, represents the first carnivoran material reported from the Choptank Formation and part of a limited record of borophagine canids from eastern North America. As ?Cynarctus marylandica (Berry, 1938), another cynarctin borophagine from the older Calvert Formation, is known only from lower dentition, its generic affinities are uncertain. However, features of this new material are compared to features of ?C. marylandica through occlusal relationships, allowing for referral to a distinct species. Even so, the Choptank Formation material still offers two possible scenarios regarding its identification. In one, its geographic and stratigraphic provenance could imply that it belongs to ?C. marylandica. If this were correct, then the generic placement of ?C. marylandica would be correct and the taxon would be more derived than some other Cynarctus species in regard to hypocarnivory, and less derived than others. The second possibility, and the one believed to be most probable, is that a distinct cynarctin borophagine is present in the Chesapeake Group in strata younger than the type specimen of ?C. marylandica. This new borophagine canid expands the sparse fossil record of this group in northeastern North America and furthers our knowledge of the fossil record of terrestrial taxa in this region.

Research paper thumbnail of Theropod bite marks on dinosaur bones: Indications of a scavenger, predator or both?; and their taphonomic implications

Bulletin of the New Mexico Museum of Natural History and Science Bulletin, 2015

Three nearly complete, isolated vertebrae, and a right humerus of a sub-adult hadrosaurine (Ornit... more Three nearly complete, isolated vertebrae, and a right humerus of a sub-adult hadrosaurine (Ornithopoda: Hadrosaurinae), all from separate individuals and from the Late Cretaceous (late Campanian) Hunter Wash local fauna (Fruitland Formation [Fossil Forest Member] and Kirtland Formation [Hunter Wash Member]), San Juan Basin, New Mexico, bear distinctive bite marks. These bite marks vary in size and shape, suggesting that different species of theropods, or possibly different ontogenetic individuals of a single species, were feeding on the carcasses pertaining to these individual elements. The isolated vertebrae suggest post-mortem bites, probably from scavenging behavior, whereas the bite marks on the humerus may have been inflicted during predation. Based on the bite mark traces, it appears that all bite marks were made by tyrannosauroids of different ontogenetic stages and/or different species.

Research paper thumbnail of Middle Miocene Carnivora of New Mexico (Tesuque Formation): Species patterns, richness, and faunal turnover

Bulletin of the New Mexico Museum of Natural History and Science, 2015

Recent field work and research call for a new look at the carnivorans from the middle Miocene of ... more Recent field work and research call for a new look at the carnivorans from the middle Miocene of New Mexico. Here changes in carnivoran guilds through time within the Tesuque Formation as well as the carnivoran diversity in each member are described. The Tesuque Formation in New Mexico contains fossiliferous layers of strata that span the late Hemingfordian through the Clarendonian (and potentially into the earliest early Hemphillian). Borophagines were the dominant carnivorans, and presumably the dominant predators, during the middle Miocene in New Mexico. However, when borophagines become less abundant, canines become more abundant, showing an inverse relationship and perhaps leading to instances where members of these groups utilize similar niches. Hesperocyonines are only present in the early Barstovian, while the large amphicyonids are found only in the late Barstovian, potentially filling an open niche left by the hesperocyonines. While carnivoran diversity drops after the Barstovian, mustelids persist in the early Clarendonian. Felids tend to become less numerous through time, perhaps allowing mustelids to fill the role of the small predators in place of Pseudaelurus (among others), and these may have in turn been replaced by small canines. In addition, this study records the first occurrences of several carnivorans in distinct members, or in the Tesuque Formation as a whole, including the first occurrence of mustelids (non-mephitine mustelids) in the formation. While the carnivoran fauna from the middle Miocene of North America is more diverse, it is noted that the Tesuque carnivoran fauna has a higher percentage of canids, and a lower percentage of mustelids and procyonids. Statistical analyses show each carnivoran group is found in most of the members and so do not cluster differently with the exception of Hesperocyoninae. The Barstovian Skull Ridge and Pojoaque members are the most statistically similar in terms of their carnivoran diversity.

Research paper thumbnail of A new dromaeosaurid (Theropoda: Dromaeosauridae) from the Late Cretaceous of New Mexico

Bulletin of the New Mexico Museum of Natural History and Science, 2015

A left frontal from the Upper Cretaceous Kirtland Formation (De-na-zin Member), San Juan Basin, N... more A left frontal from the Upper Cretaceous Kirtland Formation (De-na-zin Member), San Juan Basin, New Mexico, is diagnosed as Saurornitholestes sullivani n. sp., a new species of dromaeosaurid (Theropoda: Dromaeosauridae). The frontal is similar to Saurornitholestes langstoni in being triangular in shape, not basined between the median suture and the orbital rim, and having the caudal portion of the frontal well-rounded and slightly inflated, without evidence of a frontoparietal crest. It is distinct from S. langstoni in being more constricted anteriorly, possessing less prominent nasal facets, possessing a less prominent anterior projection between the nasal and lacrimal facet regions, having a deeper and less strongly demarcated orbital rim, possessing a deeper and more prominent olfactory bulb surface, possessing a more pronounced and longer ventrally-directed ridge between the olfactory bulb surface and the cerebral hemisphere surface, possessing a more robust frontal-frontal sutural surface, and while being slightly smaller in overall size, still being more robust than S. langstoni. The enlarged olfactory bulb surface is believed to convey a greater olfactory sense in this dinosaur, in particular in comparison to S. langstoni, and may have been important for its predatory behavior. Saurornitholestes sullivani represents the only known dromaeosaurid from the Late Cretaceous of southern Laramidia, and specifically the San Juan Basin of New Mexico, and shows geographic and temporal differences between the two currently recognized species of Saurornitholestes.

Research paper thumbnail of Investigation into the paleobiology of Dasypus bellus using geometric morphometrics and variation of the calcaneus

Journal of Mammalian Evolution, 2014

The extinct taxon Dasypus bellus has long been considered identical to the extant Dasypus novemci... more The extinct taxon Dasypus bellus has long been considered identical to the extant Dasypus novemcinctus osteologically when disregarding allometric differences. In this study, we undertake a preliminary investigation into this extinct taxon and an extant relative D. novemcinctus, by comparing the calcanea of these two dasypodids. Clear osteological differences are observed including a mediolaterally-reduced facet region, an anteriorly-shortened calcaneal head, a reduced peroneal process, and a curved and dorsoventrally-shortened calcaneal foot in D. bellus. Such characters are not allometric and likely correlate to distinct behavioral differences. Specifically, we suggest that D. novemcinctus maintains a more fossorial lifestyle, while the larger D. bellus was likely more terrestrial, with potentially little digging behavior. Such lifestyle differences could not only explain the osteological differences present, but also why fossils of D. bellus have been recovered farther north than the present range of D. novemcinctus. Fossils of Dasypus may need to be re-evaluated to determine how these two taxa relate temporally and geographically, which may have further implications regarding some past interpretations and provide new details on the behavior and potential relationships between these (and other) xenarthrans.

Research paper thumbnail of An undercover hellbender: Unique artificial shelter use by an endangered and threatened amphibian, the Eastern hellbender (Cryptobranchus alleganiensis alleganiensis)

Collinsorum: The Journal of Kansas Herpetology, 2014

This article discusses the use of artificial shelter, in this sense human refuse. This is an impo... more This article discusses the use of artificial shelter, in this sense human refuse. This is an important occurrence for the endangered large cryptobranchid amphibian Cryptobranchus alleganiensis alleganiensis (Eastern hellbender), and may have implications for its conservation, along with other endangered amphibians and other animals.

Research paper thumbnail of Late Cretaceous Dinosaur Biogeography and Endemism in the Western Interior Basin, North America: A Critical Re-Evaluation

North-south provinciality among Campanian and/or Maastrichtian vertebrates, especially dinosaurs,... more North-south provinciality among Campanian and/or Maastrichtian vertebrates, especially dinosaurs, in the Western Interior basin of North America (specifically, between West Texas and southern Alberta, Canada) has been accepted by many vertebrate paleontologists for about 30 years. However, a critical review indicates that the case for provinciality based on non-dinosaurian vertebrates is weak to nonexistent, and that the case based on dinosaurs is problematic, resting solely on a few taxa of dinosaurs, most notably the chasmosaurine ceratopsids, which have also been used to identify extreme dinosaur endemism. Paleobiogeographic provinces can be rejected because of: (1) problems and biases in sampling; (2) the lack of topographic barriers in the Western Interior basin that would divide provinces; (3) the lack of significant climatic or vegetational differences and/or gradients to provincialize vertebrates; (4) how taxonomic (largely cladotaxonomic) decisions have been intimately invo...

Research paper thumbnail of A softshell turtle (Testudines: Trionychidae: Plastomeninae) from the uppermost Cretaceous (Maastrichtian) Hell Creek Formation, North Dakota, USA, with implications for the evolutionary relationships of plastomenines and other trionychids

Cretaceous Research, 2022

Research paper thumbnail of Biomechanical Modeling of Coelophysis Bauri: Possible Feeding Methods and Behavior of a Late Triassic Theropod

Research paper thumbnail of No definitive evidence of Paleocene dinosaurs in the San Juan Basin

Paleontologia Electronica, 2009

In a recent article in this journal, Fassett (2009) concludes that dinosaur fossils of Paleocene ... more In a recent article in this journal, Fassett (2009) concludes that dinosaur fossils of Paleocene age are present in the San Juan Basin of New Mexico-Colorado. However, we argue that, based on existing data, Fassett has failed to produce compelling evidence to support this conclusion. In the San Juan Basin, only one arguably reworked dinosaur bone (an isolated hadrosaur femur) is stratigraphically above undisputed Paleocene pollen, so palynology does not demonstrate Paleocene dinosaurs in the San Juan Basin. Nor does ...

Research paper thumbnail of Complete specimens of the Eocene testudinoid turtles Echmatemys and Hadrianus and the North American origin of tortoises

Bulletin of the New Mexico Museum of Natural History and Science, 2021

Newly described specimens of North American Eocene turtles provide valuable information on their ... more Newly described specimens of North American Eocene turtles provide valuable information on their morphology and, more specifically, variation, both intraspecific and ontogenetic. We describe several complete and nearly complete testudinoid (Testudinoidea) specimens, including juvenile specimens of Hadrianus corsoni, H. majusculus, Echmatemys haydeni and E. naomi. These specimens help us determine that the oldest and most basal tortoises are from the western United States, suggesting Testudinidae evolved in North America from one of the geoemydid-like forms in the genus Echmatemys, which have their lowest stratigraphic occurrence in the earliest Wasatchian North American land-mammal “age” (early Eocene, Ypresian, ~53 Ma).

Research paper thumbnail of New dromaeosaurid dinosaur (Theropoda, Dromaeosauridae) from New Mexico and biodiversity of dromaeosaurids at the end of the Cretaceous

Scientific Reports, 2020

Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse f... more Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse fossil record, particularly at the time of their extinction near the Cretaceous-Paleogene boundary. Here we report on a new dromaeosaurid, Dineobellator notohesperus, gen. and sp. nov., consisting of a partial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, the first diagnostic dromaeosaurid to be recovered from the latest Cretaceous of the southern United States (southern Laramidia). The holotype includes elements of the skull, axial, and appendicular skeleton. The specimen reveals a host of morphologies that shed light on new behavioral attributes for these feathered dinosaurs. Unique features on its forelimbs suggest greater strength capabilities in flexion than the normal dromaeosaurid condition, in conjunction with a relatively tighter grip strength in the manual claws. Aspects of the caudal vertebrae suggest greater movement near the tail base, aiding in agility and predation. Phylogenetic analysis places Dineobellator within Velociraptorinae. Its phylogenetic position, along with that of other Maastrichtian taxa (Acheroraptor and Dakotaraptor), suggests dromaeosaurids were still diversifying at the end of the Cretaceous. Furthermore, its recovery as a second North American Maastrichtian velociraptorine suggests vicariance of North American velociraptorines after a dispersal event during the Campanian-Maastrichtian from Asia. Features of Dineobellator also imply that dromaeosaurids were active predators that occupied discrete ecological niches while living in the shadow of Tyrannosaurus rex, until the end of the dinosaurs’ reign.

Research paper thumbnail of So different, yet so alike: North American slider turtles (Trachemys scripta)

Vertebrate Zoology, 2020

We studied for the first time the molecular differentiation of all three currently recognized sub... more We studied for the first time the molecular differentiation of all three currently recognized subspecies of Trachemys scripta, including the morphologically distinct western populations of T. s. elegans (‘western red-eared sliders’), using mitochondrial and nuclear DNA sequences (up to 3,236 bp and 2,738 bp, respectively) and 14 microsatellite loci. We found that only the quickly evolving microsatellite loci discriminated T. s. troostii and the western red-eared slider from the remaining two subspecies, while T. s. elegans and T. s. scripta were not distinct in any marker system. Our findings challenge the current intraspecific systematics of T. scripta and suggest that the conspicuous differences in coloration and pattern reflect population-specific, rather than taxonomic, differentiation. We abstain from synonymizing any subspecies because, for traditionalists and conservationists, abandoning the well-established and morphologically distinct subspecies of T. scripta is not desirable. However, if subspecies of T. scripta continue to be recognized, the current taxonomy with three subspecies is difficult to justify. Western red-eared sliders are morphologically distinct and differ from T. s. elegans and T. s. scripta, with respect to microsatellites, as much as T. s. troostii does. In view of this morphological and genetic evidence, subspecies status should be considered for western red-eared sliders.

Research paper thumbnail of Baenid (Baenidae: Testudines) lower jaws from the Late Cretaceous and Paleocene of the San Juan Basin, New Mexico

Bulletin of the New Mexico Museum of Natural History and Science, 2018

Two isolated lower jaws belonging to different baenid turtles are identified as cf. Boremys grand... more Two isolated lower jaws belonging to different baenid turtles are identified as cf. Boremys grandis from the upper Campanian (Late Cretaceous) Kirtland Formation (De-na-zin Member) and cf. Neurankylus torrejonensis from the Paleocene Nacimiento Formation (Puercan). Cf. Boremys grandis is the first lower jaw of a baenid to be documented from the Late Cretaceous (Kirtlandian) of New Mexico and may represent a temporal extension for this taxon. Cf. Neurankylus torrejonensis may be the oldest record of this taxon, which may suggest evidence for anagenesis. As turtle skull material, including lower jaw and cranial remains, are rare from the Cretaceous and Paleocene of New Mexico, these specimens provide new morphological information and potential extensions of the respective biostratigraphic ranges of these turtles. They also help us further understand the composition of turtle faunas during the Cretaceous/Paleogene transition in New Mexico and the southern United States. Durophagy may not have been as important to survival of the baenid turtles at the end-Cretaceous extinction as previously thought, at least in the southern United States, because durophagous turtles appear to be absent during the Late Cretaceous in this region. In addition, the percentage of nondurophagous turtle genera in the Paleocene of North America is larger than previously believed. Turtle paleoecology was obviously distinct in northern and southern North America during the Late Cretaceous, at least regarding the major niches held by turtles. This paleoecological separation became less distinct following the Cretaceous-Paleogene extinction event, with durophagous taxa present, potentially through migration or evolutionary events, to the south.

Research paper thumbnail of A new slider turtle (Testudines: Emydidae: Deirochelyinae: Trachemys) from the late Hemphillian (late Miocene/early Pliocene) of eastern Tennessee and the evolution of the deirochelyines

PeerJ, 2018

Trachemys (Testudines: Emydidae) represents one of the most well-known turtle genera today. The e... more Trachemys (Testudines: Emydidae) represents one of the most well-known turtle genera today. The evolution of Trachemys, while being heavily documented with fossil representatives, is not well understood. Numerous fossils from the late Hemphillian Gray Fossil Site (GFS) in northeastern Tennessee help to elucidate its evolution. The fossil Trachemys at the GFS represent a new species. The new taxon, Trachemys haugrudi, is described, and currently represents the most thoroughly described fossil emydid species known. A phylogenetic analysis, including 31 species, focusing on the subfamily Deirochelyinae is performed that includes the new fossil species, along with numerous other modern and fossil deirochelyine species, representing the first phylogenetic analysis published that includes several fossil deirochelyines. The phylogenetic analysis, utilizing morphological evidence, provides monophyletic clades of all modern deirochelyines, including Chrysemys, Deirochelys, Pseudemys, Malaclemys, Graptemys, and Trachemys. A strict consensus tree finds the recently described fossil species Graptemys kerneri to be part of a clade of Graptemys + Malaclemys. Three fossil taxa, including one previously referred to Pseudemys (Pseudemys caelata) and two to Deirochelys (Deirochelys carri and Deirochelys floridana) are found to form a clade with modern Deirochelys reticularia reticularia, with D. floridana sister to the other members of the clade. Chrysemys is found to be part of a basal polytomy with Deirochelys in relation to other deirochelyine taxa. Two fossil taxa previously referred to Chrysemys (Chrysemys timida and Chrysemys williamsi) form a paraphyly with the modern Chrysemys picta picta and Deirochelys, and may be referable to distinct genera. Additionally, fossil taxa previously attributed to Trachemys (Trachemys hillii, Trachemys idahoensis, Trachemys inflata, and Trachemys platymarginata) and T. haugrudi are found to form a clade separate from clades of northern and southern Trachemys species, potentially suggesting a distinct lineage of Trachemys with no modern survivors. Hypotheses of phylogenetic relationships mostly agree between the present study and previous ones, although the inclusion of fossil taxa provides further clues to the evolution of parts of the Deirochelyinae. The inclusion of more fossil taxa and characters may help resolve the placement of some taxa, and further elucidate the evolution of these New World turtles.

Research paper thumbnail of First occurrence of a tyrannosauroid dinosaur from the lower Campanian Merchantville Formation of Delaware, USA

Memoir of the Fukui Prefectural Dinosaur Museum, 2017

This study provides a detailed osteological description of an isolated proximal caudal centrum an... more This study provides a detailed osteological description of an isolated proximal caudal centrum and two nearly complete isolated metatarsals II and IV of the left foot of a gracile theropod dinosaur from the Lower Campanian of the Merchantville Formation in northern Delaware, USA. The caudal centrum and the metatarsals are referred to Tyrannosauroidea. The centrum is not well preserved, and thus not diagnostic; however, both metatarsals are diagnostic. The referral to Tyrannosauroidea is supported by several morphological features, including extensive surfaces on metatarsals II and IV for the articulation with metatarsal III, and a characteristic low, slightly convex muscle scar on metatarsal IV developed as a thin low ridge located on the posterior surface between the M. gastrocnemius pars lateralis insertion scar and the metatarsal III articular surface. This ridge has been previously interpreted as the plantar ridge, which is present in some derived Late Campanian tyrannosauroid taxa. Additionally, metatarsal IV has a deep medial notch for the accommodation of an “L”– shaped proximal articulation of metatarsal III, and a “U”– shaped proximal articular end. The Merchantville Formation tyrannosauroid exhibits arctometatarsalian metatarsals, as do tyrannosaurids. The Merchantville Formation tyrannosauroid is differentiated from other known basal and derived tyrannosaurids by having a characteristically shaped proximal articular surface of metatarsal II in which the proximal and posterior ends lie on the long axis of the proximal articular surface. However, the posterior proximal articular surface of metatarsal II is not as strongly angled laterally as in more derived tyrannosauroids. The Merchantville Formation tyrannosauroid adds to the record of Appalachian tyrannosauroid, evolution and paleostratigraphic position, and provides new morphological information about the metatarsal anatomy of these iconic theropods.

Research paper thumbnail of Late Hemphillian colubrid snakes (Serpentes, Colubridae) from the Gray Fossil Site of northeastern Tennessee

Journal of Herpetology, 2017

The Gray Fossil Site (GFS) of northeastern Tennessee is a late Hemphillian fossil locality in the... more The Gray Fossil Site (GFS) of northeastern Tennessee is a late Hemphillian fossil locality in the southern Appalachian mountain region of eastern North America with a diverse vertebrate fauna. Snakes make up a substantial microfossil portion of the GFS herpetofauna, particularly the Colubridae, comprised of members of the Colubrinae and Natricinae. Seven colubrid taxa have been identified from the site so far, including three natricines (cf. Neonatrix, Nerodia, Thamnophis) and at least four colubrines (Coluber/ Masticophis, Pantherophis, Pituophis, gen. et sp. nov.). Indeed, cf. Neonatrix and the new genus (and species) are the only extinct genera identified. Although Neonatrix is tentatively identified for the first time east of Nebraska, the new species represents a distinct taxon. In addition, the oldest reported definitive occurrence of Masticophis is presented herein. Some of the snakes suggest a pond or other aquatic habitat at GFS, particularly cf. Neonatrix and Nerodia, whereas others, such as Masticophis and Pituophis, tend to prefer more open forested habitats. The GFS represents a poorly understood region of North America at a crucial time period in snake evolution, and its study may help us further understand the modern snake fauna present today in midcontinental and eastern North America.

Research paper thumbnail of First record of fossil chelydrid and trionychid turtles (Testudines) from the Pleistocene of Sonora, Mexico

Bulletin of the New Mexico Museum of Natural History and Science, 2016

The late Pleistocene of northern Mexico is relatively poorly understood, and represented by only ... more The late Pleistocene of northern Mexico is relatively poorly understood, and represented by only a few fossil localities. One such locality is Térapa, located in east-central Sonora. The deposit dates to between 43,000 and 40,000 years old (Rancholabrean) and yields a rich fossil fauna of over 60 identified taxa, dominated by birds and large mammals. Geologic evidence at the site indicates a marshland with permanent sources of calm freshwater, which is supported by the presence of fossil remains of freshwater invertebrates, fishes, frogs, crocodilians and turtles. Previous studies have reported fossil turtles representing two families: Emydidae and Kinosternidae. Both of these families are represented in the extant fauna of Sonora. Here, we present the remains of two additional families of turtles from Térapa, Chelydridae and Trionychidae, both of which are absent today in the naturally-occurring fauna of Sonora. The extralimital presence of these families at Térapa indicates a significant biogeographical shift between the late Pleistocene and the present day. Previous studies have noted the similarly unusual discovery of crocodilians at Térapa, and proposed that its presence might be the result of dispersal into Sonora via coastal and riparian routes. We suggest a similar migration pattern might explain the presence of chelydrids and trionychids at the site, with the turtles dispersing into Sonora either from the north or from the south, and we discuss evidence for both scenarios.

Research paper thumbnail of The validity of the Late Cretaceous pachycephalosaurid Stegoceras novomexicanum (Dinosauria: Pachycephalosauridae)

Bulletin of the New Mexico Museum of Natural History and Science, 2016

In light of a recent paper, we review, and reassess, the validity of the pachycephalosaurid dinos... more In light of a recent paper, we review, and reassess, the validity of the pachycephalosaurid dinosaur Stegoceras novomexicanum (Dinosauria: Ornithischia: Pachycephalosauridae). Specimens that are referred to Stegoceras novomexicanum are all late Campanian (early Kirtlandian) in age and are not only from a restricted stratigraphic horizon at the Fruitland/Kirtland transition, but also from a small geographic area of the San Juan Basin, New Mexico. While some of the characters initially used in diagnosing this taxon may be representative of an earlier (sub-adult) ontogenetic stage, such as the reduction of the size of the posteromedial extension of the parietal and the size of the supratemporal fenestrae, several other characters confirm its validity. These include the shape of the posteromedial extension of the parietal, the relative position of the supratemporal fenestrae, the shape and degree of inflation of the nasal boss, morphology of the prefrontal-frontal suture, curvature of the frontal-parietal suture, and its relative overall size and gracile form relative to the type (lectotype) of Stegoceras validum from the Judithian of Alberta, Canada. Although the holotype of Stegoceras novomexicanum may represent a sub-adult individual, it also possesses some diagnostic features that are indicative of an adult. This combination of features may indicate heterochrony for Stegoceras novomexicanum within the Pachycephalosauridae. Recently recovered small-bodied, high-domed pachycephalosaurid specimens from the Fruitland-Kirtland transition further support our interpretation that this taxon represents a distinct, small-bodied adult pachycephalosaurid in New Mexico. The previously described paratypes, and newly collected specimens, are conservatively assigned to cf. Stegoceras novomexicanum, as all this material comes from a very restricted stratigraphic interval and geographic area.

Research paper thumbnail of Late Cretaceous dinosaur biogeography and endemism in the Western Interior Basin, North America: A critical re-evaluation

Bulletin of the New Mexico Museum of Natural History and Science, 2016

North-south provinciality among Campanian and/or Maastrichtian vertebrates, especially dinosaurs,... more North-south provinciality among Campanian and/or Maastrichtian vertebrates, especially dinosaurs, in the Western Interior basin of North America (specifically, between West Texas and southern Alberta, Canada) has been accepted by many vertebrate paleontologists for about 30 years. However, a critical review indicates that the case for provinciality based on non-dinosaurian vertebrates is weak to nonexistent, and that the case based on dinosaurs is problematic, resting solely on a few taxa of dinosaurs, most notably the chasmosaurine ceratopsids, which have also been used to identify extreme dinosaur endemism. Paleobiogeographic provinces can be rejected because of: (1) problems and biases in sampling; (2) the lack of topographic barriers in the Western Interior basin that would divide provinces; (3) the lack of significant climatic or vegetational differences and/or gradients to provincialize vertebrates; (4) how taxonomic (largely cladotaxonomic) decisions have been intimately involved in the perception of endemism and provinciality; (5) how the demonstrable diachroneity of most fossil assemblages undermines the ability to include them in biogeographic analyses; and (6) how the non-uniformitarian conclusions of those who argue for dinosaur provinciality and endemism undermine their own arguments. Not only do we demonstrate the biological and geological implausibility of dinosaur-based biogeographic provinces and high degrees of endemism in the Western Interior basin during the Late Cretaceous, but the arguments and analyses that have been marshalled to support such concepts are questionable. Consequently, there is no compelling evidence that there was any discrete biogeographic separation of the Campanian (or Maastrichtian) dinosaur-dominated vertebrate assemblages from north to south beteen Texas and Alberta in the Western Interior basin. Also, there is no compelling evidence of high degrees of dinosaur endemism in the Western Interior basin during the Campanian.

Research paper thumbnail of A borophagine canid (Carnivora: Canidae: Borophaginae) from the middle Miocene Chesapeake Group of eastern North America

Journal of Paleontology, 2015

A tooth recovered from the middle Miocene Choptank Formation (Chesapeake Group) of Maryland is id... more A tooth recovered from the middle Miocene Choptank Formation (Chesapeake Group) of Maryland is identified as a new cynarctin borophagine (Canidae: Borophaginae: Cynarctina), here called Cynarctus wangi n. sp. The tooth, identified as a right upper second molar, represents the first carnivoran material reported from the Choptank Formation and part of a limited record of borophagine canids from eastern North America. As ?Cynarctus marylandica (Berry, 1938), another cynarctin borophagine from the older Calvert Formation, is known only from lower dentition, its generic affinities are uncertain. However, features of this new material are compared to features of ?C. marylandica through occlusal relationships, allowing for referral to a distinct species. Even so, the Choptank Formation material still offers two possible scenarios regarding its identification. In one, its geographic and stratigraphic provenance could imply that it belongs to ?C. marylandica. If this were correct, then the generic placement of ?C. marylandica would be correct and the taxon would be more derived than some other Cynarctus species in regard to hypocarnivory, and less derived than others. The second possibility, and the one believed to be most probable, is that a distinct cynarctin borophagine is present in the Chesapeake Group in strata younger than the type specimen of ?C. marylandica. This new borophagine canid expands the sparse fossil record of this group in northeastern North America and furthers our knowledge of the fossil record of terrestrial taxa in this region.

Research paper thumbnail of Theropod bite marks on dinosaur bones: Indications of a scavenger, predator or both?; and their taphonomic implications

Bulletin of the New Mexico Museum of Natural History and Science Bulletin, 2015

Three nearly complete, isolated vertebrae, and a right humerus of a sub-adult hadrosaurine (Ornit... more Three nearly complete, isolated vertebrae, and a right humerus of a sub-adult hadrosaurine (Ornithopoda: Hadrosaurinae), all from separate individuals and from the Late Cretaceous (late Campanian) Hunter Wash local fauna (Fruitland Formation [Fossil Forest Member] and Kirtland Formation [Hunter Wash Member]), San Juan Basin, New Mexico, bear distinctive bite marks. These bite marks vary in size and shape, suggesting that different species of theropods, or possibly different ontogenetic individuals of a single species, were feeding on the carcasses pertaining to these individual elements. The isolated vertebrae suggest post-mortem bites, probably from scavenging behavior, whereas the bite marks on the humerus may have been inflicted during predation. Based on the bite mark traces, it appears that all bite marks were made by tyrannosauroids of different ontogenetic stages and/or different species.

Research paper thumbnail of Middle Miocene Carnivora of New Mexico (Tesuque Formation): Species patterns, richness, and faunal turnover

Bulletin of the New Mexico Museum of Natural History and Science, 2015

Recent field work and research call for a new look at the carnivorans from the middle Miocene of ... more Recent field work and research call for a new look at the carnivorans from the middle Miocene of New Mexico. Here changes in carnivoran guilds through time within the Tesuque Formation as well as the carnivoran diversity in each member are described. The Tesuque Formation in New Mexico contains fossiliferous layers of strata that span the late Hemingfordian through the Clarendonian (and potentially into the earliest early Hemphillian). Borophagines were the dominant carnivorans, and presumably the dominant predators, during the middle Miocene in New Mexico. However, when borophagines become less abundant, canines become more abundant, showing an inverse relationship and perhaps leading to instances where members of these groups utilize similar niches. Hesperocyonines are only present in the early Barstovian, while the large amphicyonids are found only in the late Barstovian, potentially filling an open niche left by the hesperocyonines. While carnivoran diversity drops after the Barstovian, mustelids persist in the early Clarendonian. Felids tend to become less numerous through time, perhaps allowing mustelids to fill the role of the small predators in place of Pseudaelurus (among others), and these may have in turn been replaced by small canines. In addition, this study records the first occurrences of several carnivorans in distinct members, or in the Tesuque Formation as a whole, including the first occurrence of mustelids (non-mephitine mustelids) in the formation. While the carnivoran fauna from the middle Miocene of North America is more diverse, it is noted that the Tesuque carnivoran fauna has a higher percentage of canids, and a lower percentage of mustelids and procyonids. Statistical analyses show each carnivoran group is found in most of the members and so do not cluster differently with the exception of Hesperocyoninae. The Barstovian Skull Ridge and Pojoaque members are the most statistically similar in terms of their carnivoran diversity.

Research paper thumbnail of A new dromaeosaurid (Theropoda: Dromaeosauridae) from the Late Cretaceous of New Mexico

Bulletin of the New Mexico Museum of Natural History and Science, 2015

A left frontal from the Upper Cretaceous Kirtland Formation (De-na-zin Member), San Juan Basin, N... more A left frontal from the Upper Cretaceous Kirtland Formation (De-na-zin Member), San Juan Basin, New Mexico, is diagnosed as Saurornitholestes sullivani n. sp., a new species of dromaeosaurid (Theropoda: Dromaeosauridae). The frontal is similar to Saurornitholestes langstoni in being triangular in shape, not basined between the median suture and the orbital rim, and having the caudal portion of the frontal well-rounded and slightly inflated, without evidence of a frontoparietal crest. It is distinct from S. langstoni in being more constricted anteriorly, possessing less prominent nasal facets, possessing a less prominent anterior projection between the nasal and lacrimal facet regions, having a deeper and less strongly demarcated orbital rim, possessing a deeper and more prominent olfactory bulb surface, possessing a more pronounced and longer ventrally-directed ridge between the olfactory bulb surface and the cerebral hemisphere surface, possessing a more robust frontal-frontal sutural surface, and while being slightly smaller in overall size, still being more robust than S. langstoni. The enlarged olfactory bulb surface is believed to convey a greater olfactory sense in this dinosaur, in particular in comparison to S. langstoni, and may have been important for its predatory behavior. Saurornitholestes sullivani represents the only known dromaeosaurid from the Late Cretaceous of southern Laramidia, and specifically the San Juan Basin of New Mexico, and shows geographic and temporal differences between the two currently recognized species of Saurornitholestes.

Research paper thumbnail of Investigation into the paleobiology of Dasypus bellus using geometric morphometrics and variation of the calcaneus

Journal of Mammalian Evolution, 2014

The extinct taxon Dasypus bellus has long been considered identical to the extant Dasypus novemci... more The extinct taxon Dasypus bellus has long been considered identical to the extant Dasypus novemcinctus osteologically when disregarding allometric differences. In this study, we undertake a preliminary investigation into this extinct taxon and an extant relative D. novemcinctus, by comparing the calcanea of these two dasypodids. Clear osteological differences are observed including a mediolaterally-reduced facet region, an anteriorly-shortened calcaneal head, a reduced peroneal process, and a curved and dorsoventrally-shortened calcaneal foot in D. bellus. Such characters are not allometric and likely correlate to distinct behavioral differences. Specifically, we suggest that D. novemcinctus maintains a more fossorial lifestyle, while the larger D. bellus was likely more terrestrial, with potentially little digging behavior. Such lifestyle differences could not only explain the osteological differences present, but also why fossils of D. bellus have been recovered farther north than the present range of D. novemcinctus. Fossils of Dasypus may need to be re-evaluated to determine how these two taxa relate temporally and geographically, which may have further implications regarding some past interpretations and provide new details on the behavior and potential relationships between these (and other) xenarthrans.

Research paper thumbnail of An undercover hellbender: Unique artificial shelter use by an endangered and threatened amphibian, the Eastern hellbender (Cryptobranchus alleganiensis alleganiensis)

Collinsorum: The Journal of Kansas Herpetology, 2014

This article discusses the use of artificial shelter, in this sense human refuse. This is an impo... more This article discusses the use of artificial shelter, in this sense human refuse. This is an important occurrence for the endangered large cryptobranchid amphibian Cryptobranchus alleganiensis alleganiensis (Eastern hellbender), and may have implications for its conservation, along with other endangered amphibians and other animals.