Oviraptorosauria: Morphology, Phylogeny, and Endocranial Evolution

Oviraptorosauria, an extinct lineage of coelurosaurian dinosaurs from the Cretaceous of Asia and North America, includes some of the most morphologically distinctive theropod taxa yet known. Their bizarre appearance and numerous skeletal similarities with extant birds instantly made oviraptorosaurs the subject of considerable interest when first discovered in the early 20th Century by the American Museum of Natural History Central Asiatic Expeditions. Subsequent discoveries have only increased the potential of the group for informing the origin of modern birds and characters that make birds distinctive among living vertebrates, including the origin of flight. The current list of shared similarities between oviraptorosaurs and modern birds includes such striking features as loss of teeth, extreme pneumatization and ornamentation of the skull, an unusual sliding jaw articulation, reduction of the tail vertebrae to form a pygostyle, feathers of modern aspect, and the behavior of brooding eggs in the same stereotypical posture. Despite such an extended period of research and popular interest, some fundamental questions regarding oviraptorosaurs remain. First, what is the phylogenetic position of Oviraptorosauria within Coelurosauria? Recent analyses produce contentious results that disagree on whether oviraptorosaurs represent a clade of bird-like, non-avian coelurosaurs or whether they actually are nested within Avialae. Obviously, these disparate topologies pose disparate models of character evolution. For example, if oviraptorsaurs are avialans they represent the first evolution of flightlessness within that clade. Second, what are the phylogenetic relationships of the taxa comprising Oviraptorosauria? And lastly, what insight would a resolved tree topology provide the study of morphological evolution, both within Oviraptorosauria specifically and more generally within Coelurosauria? I analyzed 384 morphological characters and recovered two most parsimonious trees that resolve both the position of Oviraptorosauria within Coelurosauria as well as the interrelationships of species within Oviraptorosauria. Oviraptorosauria is found to have a sister group relationship with Therizinosauria, and this entire clade is positioned as the sister taxon to the clade formed by (Paraves + Alvarezsauridae). These findings support oviraptorosaurs as non-avian coelurosaurs and thus not avialans. The implication of this topology is that many of the avian-like characteristics expressed in the group are the product of homoplastic evolution between oviraptorids (a more exclusive clade within Oviraptorosauria) and avialans. These phylogenetic hypotheses subsequently are used to elucidate the evolutionary history of endocranial morphology in Oviraptorosauria and more broadly within Coelurosauria near the origin of avian flight. Using the relatively newly employed technology of computed tomography (CT), this study provides descriptive morphology of five coelurosaur endocasts (which approximate the shape of the brain in these taxa that effectively filled the endocranial space) and evaluates shared discreet morphological characters with respect to the aforementioned phylogeny. Diagnostic morphologies are found for Oviraptorosauria and the more exclusive clades, Maniraptora, Paraves, and crown birds. This study also is the first to use CT technology to divide the endocranial casts into six neuroanatomical partitions that correspond closely to the olfactory bulbs, cerebrum, pituitary space, optic lobes, cerebellum, and brain stem. These partitions are then used to evaluate how these different regions of the "brain" are evolving. The division of the endocranial cast into partitions is a novel approach to studying endocranial morphology. Previous analyses have been limited to surveying total endocranial volume and have not been able to distinguish between regions of the brain. Those earlier analyses established that crown birds possess a much larger endocranial space with respect to body size than more distantly related groups and that there is a general transition along the coelurosaur lineage towards an increased endocranial volume. This analysis distinguishes the expansion of the cerebrum as the primary driver of volumetric change within the entire endocranium and identifies three possible expansions of the cerebrum within the maniraptoran lineage. Unique volumetric morphologies are found for both Oviraptorosauria and Paraves. Most interestingly, the volumetric proportions of Archaeopteryx lithographica illustrate that this taxon shares a plesiomorphic morphology with other paravians, suggesting that non-avialan paravians such as Microraptor zhaoianus also possessed what has previously been referred to as a "flight-ready" brain that likely supported some type of volant activity

Cranial functional specialisation for strength precedes morphological evolution in Oviraptorosauria

Oviraptorosaurians were a theropod dinosaur group that reached high diversity in the Late Cretaceous. Within oviraptorosaurians, the later diverging oviraptorids evolved distinctive crania which were extensively pneumatised, short and tall, and had a robust toothless beak, interpreted as providing a powerful bite for their herbivorous to omnivorous diet. The present study explores the ability of oviraptorid crania to resist large mechanical stresses compared with other theropods and where this adaptation originated within oviraptorosaurians. Digital 3D cranial models were constructed for the earliest diverging oviraptorosaurian, Incisivosaurus gauthieri, and three oviraptorids, Citipati osmolskae, Conchoraptor gracilis, and Khaan mckennai. Finite element analyses indicate oviraptorosaurian crania were stronger than those of other herbivorous theropods (Erlikosaurus and Ornithomimus) and were more comparable to the large, carnivorous Allosaurus. The cranial biomechanics of Incisivosaurus align with oviraptorids, indicating an early establishment of distinctive strengthened cranial biomechanics in Oviraptorosauria, even before the highly modified oviraptorid cranial morphology. Bite modelling, using estimated muscle forces, suggests oviraptorid crania may have functioned closer to structural safety limits. Low mechanical stresses around the beaks of oviraptorids suggest a convergently evolved, functionally distinct rhamphotheca, serving as a cropping/feeding tool rather than for stress reduction, when compared with other herbivorous theropods

Khaan mckennai.

77 p. : ill. (some col.) ; 26 cm.The monophyly of Oviraptoridae, a group of theropod dinosaurs, which share a uniquely bizarre morphology, has never been called into question due in large part to their unusual complex of characters. Despite a vivid recent history of discovery and broad public appeal the nature of their morphological diversity has not been explored extensively. Many previous descriptions of oviraptorid taxa are lost in the obscurity of hard-to-find journals, and many lack illustrations of what are now recognized as phylogenetically important characters. The primary goal of this paper is to provide a relatively comprehensive descriptive morphology and illustrations for one member of Oviraptoridae, namely Khaan mckennai, with an emphasis on characters that can be used to establish a phylogenetic hypothesis for the taxon and group as a whole. K. mckennai is a small-bodied, crestless oviraptorid that is known from pristine material that has been collected from the late Cretaceous sediments of Mongolia. Similar to other oviraptorids, it shares a wide number of features in common with extant birds. However, when these characters are put in the context of Oviraptorosauria, including relatively new, more basal forms like Incisivosaurus gauthieri and Caudipteryx zoui, character states such as extreme pneumatization of the skull or the reduction in the number of caudal vertebrae are found to be either homoplastic for the two groups or plesiomorphic for a more inclusive clade

Potentially Low Cost Solution to Extend Use of Early Generation Computed Tomography

In preparing a case report on Brown-Séquard syndrome for publication, we made the incidental finding that the inexpensive, commercially available three-dimensional (3D) rendering software we were using could produce high quality 3D spinal cord reconstructions from any series of two-dimensional (2D) computed tomography (CT) images. This finding raises the possibility that spinal cord imaging capabilities can be expanded where bundled 2D multi-planar reformats and 3D reconstruction software for CT are not available and in situations where magnetic resonance imaging (MRI) is either not available or appropriate (e.g. metallic implants). Given the worldwide burden of trauma and considering the limited availability of MRI and advanced generation CT scanners, we propose an alternative, potentially useful approach to imaging spinal cord that might be useful in areas where technical capabilities and support are limited

A CT-based revised description and phylogenetic analysis of the skull of the basal maniraptoran Ornitholestes hermanni Osborn 1903

Ornitholestes hermanni was one of the first small-bodiedtheropods named in the 1900s. It is known from a singlespecimen discovered during the American MuseumExpedition of 1900, at the Jurassic Morrison Formationsite known as Bone Cabin Quarry, in Wyoming. It haslong been a critical taxon in understanding the evolutionof the Coelurosauria, the clade that includestyrannosauroids, living birds, and their commonancestors. The holotype specimen comprises a nearlycomplete skull and most of a postcranial skeleton. Despitethis abundant material, its precise phylogeneticrelationships have been difficult to determine. This is inpart due to the intense mediolateral crushing of the skulland the relatively generalized postcranial anatomy. Herewe present the results of a micro- computed tomographybasedinvestigation of the cranial anatomy and subsequentincorporation of these data into a phylogenetic data matrixdesigned to test coelurosaurian interrelationships. We findrobust evidence across different optimality criteria thatOrnitholestes is the earliest-branching oviraptorosaurianspecies. Using parsimony as an optimality criterion, thisphylogenetic position is supported by 14 unambiguoussynapomorphies, including: a short frontal process of thepostorbital; short, deep, and pendant paroccipitalprocesses; a large mandibular foramen; an anterodorsallyoriented dentary symphysis; a surangular that is longerthan the dentary; short maxillary and dentary tooth rows;and procumbent dentary and premaxillary teeth. UsingBayesian fossilized birth-death models, we find highposterior probabilities (>.99) that Ornitholestes is theearliest-branching oviraptorosaurian species. Weadditionally find strong support in both analyses that thesuperficially bat-like and possibly arborealscansoriopterygids are an early branching lineage withinOviraptorosauria. This new phylogenetic position fills in apersistent ghost lineage in Oviraptorosauria and confirmsthat scansoriopterygids are basally branchingoviraptorosaurians that represent an independent origin ofaerial habits, separate from those of dromaeosaurs andavialans.Fil: Chapelle, Kimberley E.. American Museum of Natural History; Estados UnidosFil: Norell, Mark. American Museum of Natural History; Estados UnidosFil: Ford, David P.. University of the Witwatersrand; SudáfricaFil: Hendrickx, Christophe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaFil: Radermacher, Viktor J.. University of Minnesota; Estados UnidosFil: Balanoff, Amy. University Johns Hopkins; Estados UnidosFil: Zanno, Lindsay E.. North Carolina Museum of Natural Sciences; Estados UnidosFil: Choiniere, Jonah N.. University of the Witwatersrand; Sudáfrica81st Annual Meeting of the Society of Vertebrate PaleontologyMc LeanEstados UnidosSociety of Vertebrate Paleontolog

The skull roof tracks the brain during the evolution and development of reptiles including birds

Major transformations in brain size and proportions, such as the Enlargement of the brain during the evolution of birds, areaccompanied by profound modifications to the skull roof. However, the hypothesis of concerted evolution of shape between brain and skull roof over major phylogenetic transitions, and in particular of an ontogenetic relationship between specific regions of the brain and the skull roof, has never been formally tested. We performed 3D morphometric analyses to examine the deep history of brain and skull-roof morphology in Reptilia, focusing on changes during the well-documented transition from earlyreptiles through archosauromorphs, including nonavian dinosaurs, to birds. Non-avialan taxa cluster tightly together in morphospace,whereas Archaeopteryx and crown birds occupy a separate region. There is a one-to-one correspondence between the forebrain and frontal bone and the midbrain and parietal bone. Furthermore, the position of the forebrain–midbrain boundary correlates significantly with the position of the frontoparietal suture across the phylogenetic breadth of Reptilia and duringthe ontogeny of individual taxa. Conservation of position and identity in the skull roof is apparent, and there is no support for previous hypotheses that the avian parietal is a transformed postparietal. The correlation and apparent developmental link between regions of the brain and bony skull elements are likely to be ancestral to Tetrapoda and may be fundamental to all ofOsteichthyes, coeval with the origin of the dermatocranium

Variation, variability, and the origin of the avian endocranium:Insights from the anatomy of alioramus altai (theropoda: Tyrannosauroidea)

The internal braincase anatomy of the holotype of Alioramus altai, a relatively small-bodied tyrannosauroid from the Late Cretaceous of Mongolia, was studied using high-resolution computed tomography. A number of derived characters strengthen the diagnosis of this taxon as both a tyrannosauroid and a unique, new species (e.g., endocranial position of the gasserian ganglion, internal ramification of the facial nerve). Also present are features intermediate between the basal theropod and avialan conditions that optimize as the ancestral condition for Coelurosauria--a diverse group of derived theropods that includes modern birds. The expression of several primitive theropod features as derived character states within Tyrannosauroidea establishes previously unrecognized evolutionary complexity and morphological plasticity at the base of Coelurosauria. It also demonstrates the critical role heterochrony may have played in driving patterns of endocranial variability within the group and potentially reveals stages in the evolution of neuroanatomical development that could not be inferred based solely on developmental observations of the major archosaurian crown clades. We discuss the integration of paleontology with variability studies, especially as applied to the nature of morphological transformations along the phylogenetically long branches that tend to separate the crown clades of major vertebrate groups

The evolution of mammalian brain size

Relative brain size has long been considered a reflection of cognitive capacities and has played a fundamental role in developing core theories in the life sciences. Yet, the notion that relative brain size validly represents selection on brain size relies on the untested assumptions that brain-body allometry is restrained to a stable scaling relationship across species and that any deviation from this slope is due to selection on brain size. Using the largest fossil and extant dataset yet assembled, we find that shifts in allometric slope underpin major transitions in mammalian evolution and are often primarily characterized by marked changes in body size. Our results reveal that the largest-brained mammals achieved large relative brain sizes by highly divergent paths. These findings prompt a reevaluation of the traditional paradigm of relative brain size and open new opportunities to improve our understanding of the genetic and developmental mechanisms that influence brain size

Tempo and Pattern of Avian Brain Size Evolution

Relative brain sizes in birds can rival those of primates, but large-scale patterns and drivers of avian brain evolution remain elusive. Here, we explore the evolution of the fundamental brain-body scaling relationship across the origin and evolution of birds. Using a comprehensive dataset sampling> 2,000 modern birds, fossil birds, and theropod dinosaurs, we infer patterns of brain-body co-variation in deep time. Our study confirms that no significant increase in relative brain size accompanied the trend toward miniaturization or evolution of flight during the theropod-bird transition. Critically, however, theropods and basal birds show weaker integration between brain size and body size, allowing for rapid changes in the brain-body relationship that set the stage for dramatic shifts in early crown birds. We infer that major shifts occurred rapidly in the aftermath of the Cretaceous-Paleogene mass extinction within Neoaves, in which multiple clades achieved higher relative brain sizes because of a reduction in body size. Parrots and corvids achieved the largest brains observed in birds via markedly different patterns. Parrots primarily reduced their body size, whereas corvids increased body and brain size simultaneously (with rates of brain size evolution outpacing rates of body size evolution). Collectively, these patterns suggest that an early adaptive radiation in brain size laid the foundation for subsequent selection and stabilization