An official website of the United States government
Abstract Silesaurids (Archosauria: Dinosauriformes) are found in Middle to Upper Triassic deposits across Pangea, but few stratigraphic sections record the evolution of the group in one geographic area over millions of years. Here, we describe silesaurid remains from the oldest of the Upper Triassic stratigraphic sequence from the base of the Dockum Group, from the type locality of the Otischalkian faunachronozone. Isolated limb bones diagnostic of silesaurids include humeri, femora, and tibiae of a seemingly uniqueSilesaurus‐like taxon from the same locality (Otis Chalk Quarry 3). The femora consist of four specimens of different lengths that sample the variation of character states associated with ontogeny, also sampled previously in both silesaurids (e.g.,Asilisaurus kongweandSilesaurus opolensis) and within neotheropods within Dinosauria (e.g.,Coelophysis bauri). Our observations of the variation in the silesaurid sample further reinforce the interpretation of high variation of morphological features common in dinosauriforms. Furthermore, we show that overpreparation of bone surfaces has hidden some of this variation in previous interpretations. The tibia growth series shows that the fibular crest of the tibia develops during ontogeny, yet another phylogenetically informative character for dinosaurs and their kin that is at least ontogenetically variable in silesaurids. The presence of silesaurids at the base of the Dockum Group (late Carnian or early Norian) conclusively shows that the group was present near the onset of deposition of Upper Triassic rocks and survived for millions of years in the same geographic area at low latitudes throughout the Late Triassic.
more »
« less
The osteology of Shuvosaurus inexpectatus , a shuvosaurid pseudosuchian from the Upper Triassic Post Quarry, Dockum Group of Texas, USA
Abstract A vast array of pseudosuchian body plans evolved during the diversification of the group in the Triassic Period, but few can compare to the toothless, long‐necked, and bipedal shuvosaurids. Members of this clade possess theropod‐like character states mapped on top of more plesiomorphic pseudosuchian character states, complicating our understanding of the evolutionary history of the skeleton. One taxon in this clade,Shuvosaurus inexpectatushas been assigned to various theropod dinosaur groups based on a partial skull and referred material and its postcranium was assigned to a different taxon in Pseudosuchia. After the discovery of a skeleton of a shuvosaurid with aShuvosaurus‐like skull and a pseudosuchian postcranial skeleton, it became clearShuvosaurus inexpectatuswas a pseudosuchian. Nevertheless, a number of questions have arisen about what skeletal elements belonged toShuvosaurus inexpectatus, the identification of skull bones, and the resulting implication for pseudosuchian evolution. Here, we detail the anatomy of the skeletonShuvosaurus inexpectatusthrough a critical lens, parse out the bones that belong to the taxon or those that clearly do not or may not belong to the taxon, rediagnose the taxon based on these revisions, and compare the taxon to other archosaurs. We find thatShuvosaurus inexpectatuspossesses similar anatomy to other shuvosaurids but parts of the skeleton of the taxon clarifies the anatomy of the group given that they are preserved inShuvosaurus inexpectatusbut not in others.Shuvosaurus inexpectatusis represented by at least 14 individuals from the West Texas Post Quarry (Adamanian holochronozone) and allShuvosaurus inexpectatusskeletal material from the locality pertains to skeletally immature individuals. All of the skeletons are missing most of the neural arches, ribs, and most of the forelimb. We only recognizeShuvosaurus inexpectatusfrom the Post Quarry and all other material assigned to the taxon previously is better assigned to the broader group Shuvosauridae.
more »
« less
- Award ID(s):
- 1943286
- PAR ID:
- 10525218
- Publisher / Repository:
- Anatomical Record
- Date Published:
- Journal Name:
- The Anatomical Record
- Volume:
- 307
- Issue:
- 4
- ISSN:
- 1932-8486
- Page Range / eLocation ID:
- 1175 to 1238
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Denazinemys nodosais a Late Cretaceous representative of the North American turtle clade Baenidae diagnosed, among others, by a shell surface texture consisting of raised welts. We provide a detailed description of a partial skeleton from the late Campanian Kaiparowits Formation of Utah, USA, including bone-by-bone analysis of its cranium based on images obtained using micro-computed tomography. A revised phylogenetic analysis confirms placement ofDenazinemys nodosaclose toEubaena cephalicaandBoremysspp. within the clade Eubaeninae. Comparison with a second skull from the Kaiparowits Formation previously assigned toDenazinemys nodosaquestions its referral to this taxon. An assortment of specimens from the Early to Late Campanian of Mexico and the USA had previously been referred toDenazinemys nodosabased on shell surface texture alone, even though this characteristic is known to occur in other baenids. Our review of all available material concludes thatDenazinemys nodosais currently only known from the Late Campanian of New Mexico and Utah.more » « less
-
Abstract Eopneumatosuchus colbertiCrompton and Smith, 1980, known from a single partial skull, is an enigmatic crocodylomorph from the Lower Jurassic Kayenta Formation. In spite of its unique morphology, an exceptionally pneumatic braincase, and presence during a critical time period of crocodylomorph evolution, relatively little is known about this taxon. Here, we redescribe the external cranial morphology ofE.colberti, present novel information on its endocranial anatomy, evaluate its phylogenetic position among early crocodylomorphs, and seek to better characterize its ecology. Our examination clarifies key aspects of cranial suture paths and braincase anatomy. Comparisons with related taxa (e.g.,Protosuchus haughtoni) demonstrate that extreme pneumaticity of the braincase may be more widespread in protosuchids than previously appreciated. Computed tomography scans reveal an endocranial morphology that resembles that of other early crocodylomorphs, in particular the noncrocodyliform crocodylomorphAlmadasuchus figarii. There are, however, key differences in olfactory bulb and cerebral hemisphere morphology, which demonstrate the endocranium of crocodylomorphs is not as conserved as previously hypothesized. Our phylogenetic analysis recoversE.colbertias a close relative ofProtosuchus richardsoniandEdentosuchus tienshanensis, contrasting with previous hypotheses of a sister group relationship with Thalattosuchia. Previous work suggested the inner ear has some similarities to semi‐aquatic crocodyliforms, but the phylogenetic placement ofE.colbertiamong protosuchids with a terrestrial postcranial skeletal morphology complicates paleoecological interpretation.more » « less
-
Abstract Ancestors of the Antarctic icefishes (family Channichthyidae) were benthic and had no swim bladder, making it energetically expensive to rise from the ocean floor. To exploit the water column, benthopelagic icefishes were hypothesized to have evolved a skeleton with “reduced bone,” which gross anatomical data supported. Here, we tested the hypothesis that changes to icefish bones also occurred below the level of gross anatomy. Histology and micro‐CT imaging of representative craniofacial bones (i.e., ceratohyal, frontal, dentary, and articular) of extant Antarctic fish species specifically evaluated two features that might cause the appearance of “reduced bone”: bone microstructure (e.g., bone volume fraction and structure linear density) and bone mineral density (BMD, or mass of mineral per volume of bone). Measures of bone microstructure were not consistently different in bones from the icefishesChaenocephalus aceratusandChampsocephalus gunnari, compared to the related benthic notothenioidsNotothenia coriicepsandGobionotothen gibberifrons. Some quantitative measures, such as bone volume fraction and structure linear density, were significantly increased in some icefish bones compared to homologous bones of non‐icefish. However, such differences were rare, and no microstructural measures were consistently different in icefishes across all bones and species analyzed. Furthermore, BMD was similar among homologous bones of icefish and non‐icefish Antarctic notothenioids. In summary, “reduced bone” in icefishes was not due to systemic changes in bone microstructure or BMD, raising the prospect that “reduced bone” in icefish occurs only at the gross anatomic level (i.e., smaller or fewer bones). Given that icefishes exhibit delayed skeletal development compared to non‐icefish Antarctic fishes, combining these phenotypic data with genomic data might clarify genetic changes driving skeletal heterochrony.more » « less
-
Cretaceous dinosaurs were first reported from the Indian subcontinent in the late 1800s, and titanosaur sauropod and abelisauroid theropod remains are now known from central, western, and southern parts of India and from central western Pakistan. Although dinosaur remains are abundant, associated or articulated specimens are extremely rare, and so are complex skeletal elements such as cranial bones and presacral vertebrae. The historical pattern of sampling and collecting has limited the inferences about patterns of diversity, phylogenetic affinity, and paleobiogeographic relationships of Indian dinosaurs. Here we report on three titanosaur vertebrae representing regions of the skeleton that are complex and otherwise poorly represented in the Indian record, including two anterior dorsal vertebrae pertaining to a single individual from Rahioli, in Gujarat State (western India), and an anterior caudal neural arch from Bara Simla, in Madhya Pradesh State (central India). Phylogenetic analysis places the two individuals within Titanosauria, but further resolution of their affinities is precluded by their incompleteness and that of titanosaur vertebral columns in general, lack of coding of character data for titanosaur presacral and anterior caudal vertebrae, and relatively coarse understanding of the evolutionary relationships of titanosaurs. Comparisons with contemporaneous and spatially proximal titanosaurs from Indo-Pakistan, Madagascar, and South America provide insights into their affinities. The dorsal vertebrae share close affinity with Isisaurus from India and Mendozasaurus from Argentina. Few local comparisons are available for the anterior caudal vertebra, which shares characteristics with Tengrisaurus from the Early Cretaceous of Russia.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/ar.25376
