The Phylogeny of Basal Coelurosaurian Theropods (Archosauria: Dinosauria) and Patterns of Morphological Evolution during the Dinosaur-Bird Transition

Theropod dinosaurs are an iconic and familiar group of extinct species that include predators such as Tyrannosaurus and Velociraptor, as well as an array of other Mesozoic taxa. Carnivorous theropods are the evolutionary ancestors of birds, and the evolutionary transition between theropods and birds is a textbook example of a major evolutionary transformation in the history of life. Despite a flurry of research on early birds and their dinosaurian relatives, however, several questions still remain. First, the anatomy of some major theropod groups has yet to be described in detail. Second, there is little consensus on the phylogenetic relationships of the basal members of a theropod subgroup called Coelurosauria: the clade of birds and their closest relatives (defined as all taxa closer to birds than to Allosaurus). Third, there has been little synthetic work on large-scale macroevolutionary patterns during theropod evolution. This dissertation includes three chapters that touches on these three major issues. Chapter 1 is a detailed description of the Late Cretaceous tyrannosaurid theropod Alioramus altai, based on its holotype specimen from the Tsaagan Khuushu locality in the Maastrichtian Nemegt Formation of Mongolia. This monographic description provides further evidence that Alioramus is an unusual long-snouted, gracile, and slender-limbed taxon with an unpredecented degree of cranial ornamentation among tyrannosaurids and an extremely pneumatized skeleton. Anatomical comparisons indicate that the long skull of Alioramus is an autapomorphic feature that is proportionally longer (relative to femur length) than in any other known tyrannosaurid specimen, including juveniles, and that Alioramus is morphologically distinctive relative to similarly-sized individuals of the contemporary and sympatric Tarbosaurus. The coexistence of the long-snouted Alioramus and robust and deep-snouted Tarbosaurus, which are found together at the Tsaagan Khuushu locality, demonstrate that multiple large tyrannosaurids were able to live in sympatry, likely because of niche partitioning due to differences in craniofacial morphology and functional behavior. Chapter 2 presents a comprehensive new phylogenetic analysis of coelurosaurian theropods, which is an updated version (and thus the latest iteration) of the long-standing Theropod Working Group (TWiG) analysis. The new analysis incoroporates a wealth of new taxa and character data into the TWiG matrix for the first time, most of which is relevant to basal (non-maniraptoran) coelurosaurs such as tyrannosauroids and ornithomimosaurs, which had previously been the subject of only cursory character and taxon sampling in TWiG studies. The full dataset was analyzed under parsimony, and the resulting phylogeny includes several well supported relationships and agrees with previous analyses in many aspects. As a result, it is argued that a consensus view of basal coelurosaurian relationships has emerged, including: 1) the monophyly of major subclades such as Tyrannosauroidea, Compsognathidae, and Ornithomimosauria; 2) the position of the singleton genera Bicentenaria, Zuolong, and Tugulusaurus near the base of Coelurosauria; 3) the placement of Tyrannosauroidea as the most basal major coelurosaurian subclade; 4) the inclusion of Guanlong, Dilong, and Proceratosaurus within Tyrannosauroidea; 5) the existence of a derived maniraptoran clade that includes alvarezsauroids, therizinosauroids, oviraptorosaurs, and paravians to the exclusion of ornithomimosaurs and tyrannosauroids. Remaining areas of uncertainty include the phylogenetic position of Compsognathidae and the singleton genus Ornitholestes, and relationships at the base of the Ornithomimosauria + Maniraptora clade and Maniraptora itself. The phylogeny indicates that much of the early history of Coelurosauria has yet to be sampled in the fossil record, that coelurosaurs originated at small body size, and that the evolution of the iconic Tyrannosaurus-like bauplan occurred only towards the end of the Cretaceous. Chapter 3 presents a geometric morphometric analysis that is used to study broad patterns in theropod skull shape variation and compare the distribution of taxa in cranial morphospace (form) to both phylogeny and quantitative metrics of biting behaviour (function). The analysis finds that theropod skulls primarily differ in relative anteroposterior length and snout depth and to a lesser extent in orbit size and depth of the cheek region, and that oviraptorosaurs deviate most strongly from the "typical" and ancestral theropod morphologies. Noncarnivorous taxa generally fall out in distinct regions of morphospace and exhibit greater overall disparity than carnivorous taxa, whereas large-bodied carnivores independently converge on the same region of morphospace. The distribution of taxa in morphospace is strongly correlated with phylogeny but only weakly correlated with functional biting behaviour. These results imply that phylogeny, not biting function, was the major determinant of theropod skull shape

Filling the Corallian gap: new information on Late Jurassic marine reptile faunas from England

Two of the best known Mesozoic marine reptile assemblages can be found in units deposited in the Jurassic Sub-Boreal Seaway of the UK: the late Middle Jurassic Oxford Clay Formation (OCF) and Late Jurassic Kimmeridge Clay Formation (KCF). They record two very differently structured faunas, but understanding the turnover between them is hampered by a gap in the fossil record that spans much of the Oxfordian, the so-called “Corallian gap”. We provide a comprehensive review of specimens from the Corallian Group (CG) of the UK, which includes the first descriptions of several fossils, particularly teeth. We demonstrate that there is a severe reduction in observed marine reptile diversity during the Oxfordian, with several Callovian taxa well known from the OCF not persisting into the Corallian strata, including small-to-mid-sized pliosaurids and longirostrine teleosaurids. We do, however, find evidence that at least one member of each key OCF lineage (plesiosauroids, pliosaurids, ichthyosaurs, and thalattosuchians) survived into the Corallian interval, and that one keystone KCF lineage (the Torvoneustes line of metriorhynchid thalattosuchians) was present during this time, indicating an earlier radiation of this group than previously thought. We suggest that faunal turnover between the OCF and KCF may have been driven by environmental perturbations during the Oxfordian, which selectively removed small bodied pliosaurids and longirostrine teleosaurids from the Jurassic Sub-Boreal Seaway, but less affected metriorhynchids, plesiosauroids, and ophthalmosaurid ichthyosaurs. The preferential removal of taxa from the sub-Boreal realm may have helped facilitate the radiation of lineages that became dominant during the Late Jurassic

New Specimens of the Rare Taeniodont Wortmania (Mammalia: Eutheria) from the San Juan Basin of New Mexico and Comments on the Phylogeny and Functional Morphology of “Archaic” Mammals

Background: Taeniodonta is a clade of Late Cretaceous – Paleogene mammals remarkable for their relatively extreme cranial, dental, and postcranial adaptations and notable for being among the first mammals to achieve relatively large size following the Cretaceous-Paleogene mass extinction. Previous workers have hypothesized that taeniodonts can be divided into two clades: Conoryctidae, a group of small-bodied taeniodonts with supposedly “generalized” postcranial skeletons, and Stylinodontidae, a group of large-bodied, robust animals with massive forelimbs and claws adapted for scratch-digging. However, many taeniodont taxa are poorly known and few are represented by postcranial material, leaving many details about their anatomy, biology, and evolution ambiguous. Methodology/Principal Findings: In this paper, we describe three new specimens of the rare taxon Wortmania otariidens from the early Paleocene (Puercan) of New Mexico. Among these specimens is one that includes remarkably complete cranial and dental material, including associated upper and lower teeth, and another that consists of partial forelimbs. These specimens allow for an updated anatomical description of this unusual taxon, supply new data for phylogenetic analyses, and enable a more constrained discussion of taeniodont biology and functional morphology. Conclusions/Significance: The new specimen of Wortmania that includes associated upper and lower teeth indicates that previous interpretations of the upper dentition of this taxon were not accurate and the taxon Robertschochia sullivani is a junior synonym of W. otariidens. New specimens that include partial forelimbs indicate that Wortmania is very similar to later, large-bodied taeniodonts, with marked and distinctive adaptations for scratch-digging. Comparisons with other taeniodont taxa that include postcranial material suggest that all taeniodonts may have had scratch-digging adaptations. A phylogenetic analysis shows that Schowalteria and Onychodectes are basal taeniodonts, Stylinodontidae (including Wortmania) is monophyletic, and a monophyletic Conoryctidae (but not including Onychodectes) is only recovered when certain characters are ordered

Comparative functional morphology indicates niche partitioning among sympatric marine reptiles

Mesozoic marine ecosystems were dominated by diverse lineages of aquatic tetrapods. For over 50 Ma in the Jurassic until the Early Cretaceous, plesiosaurians, ichthyosaurians and thalattosuchian crocodylomorphs coexisted at the top levels of trophic food webs. We created a functional dataset of continuous craniomandibular and dental characters known from neontological studies to be functionally significant in modern aquatic tetrapods. We analysed this dataset with multivariate ordination and inferential statistics to assess functional similarities and differences in the marine reptile faunas of two well-sampled Jurassic ecosystems deposited in the same seaway: the Oxford Clay Formation (OCF, Callovian–early Oxfordian, Middle–Late Jurassic) and the Kimmeridge Clay Formation (KCF, Kimmeridgian–Tithonian, Late Jurassic) of the UK. Lower jaw-based macroevolutionary trends are similar to those of tooth-based diversity studies. Closely related species cluster together, with minimal overlaps in the morphospace. Marine reptile lineages were characterized by the distinctive combinations of features, but we reveal multiple instances of morphofunctional convergence among different groups. We quantitatively corroborate previous observations that the ecosystems in the OCF and KCF were markedly distinct in faunal composition and structure. Morphofunctional differentiation may have enabled specialization and was an important factor facilitating the coexistence of diverse marine reptile assemblages in deep time

THE OSTEOLOGY OF ALIORAMUS, A GRACILE AND LONG-SNOUTED TYRANNOSAURID (DINOSAURIA: THEROPODA) FROM THE LATE CRETACEOUS OF MONGOLIA

Fig. 68: Closeup of right ilium of the holotype specimen of Alioramus altai (IGM 100/1844) in lateral view. Scale bar 5 5 cm. Abbreviations as in figure 66.Published as part of Brusatte, Stephen L., Carr, Thomas D. & Norell, Mark A., 2012, The Osteology Of Alioramus, A Gracile And Long-Snouted Tyrannosaurid (Dinosauria: Theropoda) From The Late Cretaceous Of Mongolia, pp. 1-197 in Bulletin of the American Museum of Natural History 2012 (366) on page 149, DOI: 10.1206/770.1, http://zenodo.org/record/539926

A new taeniolabidoid multituberculate (Mammalia) from the middle Puercan of the Nacimiento Formation, New Mexico, and a revision of taeniolabidoid systematics and phylogeny

Multituberculates were amongst the most abundant and taxonomically diverse mammals of the late Mesozoic and the Paleocene, reaching their zenith in diversity and body size in the Paleocene. Taeniolabidoidea, the topic of this paper, includes the largest known multituberculates, which possess highly complex cheek teeth adapted for herbivory. A new specimen from the early Paleocene (middle Puercan; biochron Pu2) of the Nacimiento Formation, New Mexico represents a new large-bodied taeniolabidoid genus and species, Kimbetopsalis simmonsae. A phylogenetic analysis to examine the relationships within Taeniolabidoidea that includes new information from Kimbetopsalis gen. et sp. nov. and gen. nov. and from new specimens of Catopsalis fissidens, first described here, and data from all other described North American and Asian taeniolabidoids. This analysis indicates that Catopsalis is nonmonophyletic and justifies our transfer of the basal-most taeniolabidoid ‘Catopsalis’ joyneri to a new genus, Valenopsalis. Kimbetopsalis and Taeniolabis form a clade (Taeniolabididae), as do the Asian Lambdopsalis, Sphenopsalis, and possibly also Prionessus (Lambdopsalidae). Taeniolabidoids underwent a modest taxonomic radiation during the early Paleocene of North America and underwent a dramatic increase in body size, with Taeniolabis taoensis possibly exceeding 100 kg. Taeniolabidoids appear to have gone extinct in North America by the late Paleocene but the appearance of lambdopsalids in the late Paleocene of Asia suggests that they dispersed from North America in the early to middle Paleocene

A new tyrannosaurine specimen (Theropoda: Tyrannosauroidea) with insect borings from the Upper Cretaceous Honglishan Formation of Northwestern China

A large theropod ilium was recently collected from the Upper Cretaceous Honglishan Formation in the Sangequan area of the northern Junggar Basin, Xinjiang, China, which represents the first officially reported dinosaur fossil from this formation. Several morphological features, including robust supracetabular ridge, reduced supracetabular crest, concave anterior margin of the pubic peduncle, ventral flange on the pubic peduncle, converging dorsal surface of the iliac blades, laterally visible cuppedicus shelf, and ventral flange on the posterior surface of pubic peduncle, suggest that this specimen can be referred to Tyrannosaurinae, and furthermore, a few differences between this specimen and other tyrannosaurines in particular the contemporary Asian tyrannosaurine Tarbosaurus suggest that IVPP V22757 may represent a new tyrannosaurine species. However, in the absence of extensive data that would make it possible to properly evaluate these differences, we refrain from naming a new taxon based on this specimen. Some insect borings are also identified in this specimen, and are referable to the ichnogenus Cubiculum, which is interpreted as the insect pupichnia. This new fossil documents the presence of a gigantic theropod in the Upper Cretaceous of Junggar Basin, adding new information on its poorly studied ecosystems

The ecological diversification and evolution of Teleosauroidea (Crocodylomorpha, Thalattosuchia), with insights into their mandibular biomechanics

Throughout the Jurassic, a plethora of marine reptiles dominated ocean waters, including ichthyosaurs, plesiosaurs and thalattosuchian crocodylomorphs. These Jurassic ecosystems were characterized by high niche partitioning and spatial variation in dietary ecology. However, while the ecological diversity of many marine reptile lineages is well known, the overall ecological diversification of Teleosauroidea (one of the two major groups within thalattosuchian crocodylomorphs) has never been explored. Teleosauroids were previously deemed to have a morphologically conservative body plan; however, they were in actuality morphofunctionally more diverse than previously thought. Here we investigate the ecology and feeding specializations of teleosauroids, using morphological and functional cranio‐dental characteristics. We assembled the most comprehensive dataset to date of teleosauroid taxa (approximately 20 species) and ran a series of principal component analyses (PC) to categorize them into various feeding ecomorphotypes based on 17 dental characteristics (38 specimens) and 16 functionally significant mandibular characters (18 specimens). The results were examined in conjunction with a comprehensive thalattosuchian phylogeny (153 taxa and 502 characters) to evaluate macroevolutionary patterns and significant ecological shifts. Machimosaurids display a well‐developed ecological shift from: (1) slender, pointed tooth apices and an elongate gracile mandible; to (2) more robust, pointed teeth with a slightly deeper mandible; and finally, (3) rounded teeth and a deep‐set, shortened mandible with enlarged musculature. Overall, there is limited mandibular functional variability in teleosaurids and machimosaurids, despite differing cranial morphologies and habitat preferences in certain taxa. This suggests a narrow feeding ecological divide between teleosaurids and machimosaurids. Resource partitioning was primarily related to snout and skull length as well as habitat; only twice did teleosauroids manage to make a major evolutionary leap to feed distinctly differently, with only the derived machimosaurines successfully radiating into new feeding ecologies