Alida M Bailleul, John R Horner, and Casey M Holliday (2017)
Tyrannosaurus rex Shows Histological Evidence For Avian-Style Cranial Kinesis.
FASEB Journal 31 no. 1 Supplement: 251.1
Modern avian cranial kinesis played a significant role in the adaptive radiation of birds as they evolved flexible skulls from their presumably less kinetic, non-avian theropod ancestors. Avian cranial kinesis is partly mediated by novel synovial joints, which differ from those of other extant sauropsids in that they form secondary articular cartilage on dermatocranial elements. This tissue is different from the primary articular cartilage that is ubiquitous among the endochondral elements of all vertebrates. The evolutionary origin of secondary cartilage among the dinosaurian line still remains unclear, consequently limiting inferences of cranial kinesis in dinosaurs and other extinct taxa.
For the first time, we investigate the presence of secondary articular cartilage in the cranial joints of a non-avian theropod dinosaur, Tyrannosaurus rex (MOR 1125), by comparing microanatomical features of a reference synovial joint, the jaw joint, and the lesser understood otic joint, which is responsible for streptostylic movements in the avian feeding apparatus. Five extracted fragments of these joint articular surfaces from the surangular, quadrate and squamosal were microCT-scanned, and then serially sectioned via histological techniques to identify secondary cartilage. Complementary histological data from two extant archosaurs (Anas platyrhynchos and Alligator mississippiensis) were also examined.
The membranous squamosal and surangular of T. rex possess a thin layer of mineralized, secondary articular cartilage above their subchondral bone. The quadrate fragments possess primary articular cartilage, but no clear histological differences between primary and secondary cartilage were identified. These results suggest that the jaw and otic joints of T. rex were synovial and identical in structure to those of modern birds, but substantively different from those of A. mississippiensis. This study provides for the first time clear paleohistological evidence for a synovial otic joint, which bolsters hypotheses of avian-style streptostyly in a theropod dinosaur, and that birds inherited this tissue from their dinosaurian ancestors. This study has significant implications for our understanding of the origins of avian cranial kinesis, for inferences of kinesis in theropod dinosaurs, and increases our knowledge of the evolution of cranial skeletal tissues in vertebrates.
Noell Carrillo, Ashley VanZant, and Merrilee Guenther (2017)
Large hadrosaurid dinosaur from the San Juan Basin, New Mexico.
FASEB Journal 31 no. 1 Supplement: lb35
Hadrosaurid dinosaur diversity in the San Juan Basin of New Mexico has been difficult to determine due, in part, to poor preservation of specimens compared to those found in northern North America. A reexamination of a collection of hadrosaurid material from the Hunter Wash Member of the Kirtland Formation in San Juan County, New Mexico, excavated in 1922 by Charles H. Sternberg, has revealed some well-preserved specimens. Among these specimens is a large hadrosaurid humerus that is 860 millimeters in length, with a humeral shaft diameter of 176 millimeters. The proportional size of the deltopectoral crest in relation to the humeral shaft indicates that the humerus comes from a saurolophine hadrosaur.
Previously recognized hadrosaurid diversity in the lower Kirtland Formation has been restricted to the lambeosaurine, Parasaurolophus cyrtocristatus, and the saurolophine, Kritosaurus navajovius. Recent studies of hadrosaurid elements in this Sternberg collection have indicated that there are additional, as yet unnamed, saurolophine taxa in the San Juan Basin with strong affinities to the Kritosaurini, but distinct from K. navajovius. The large humerus is significantly larger than that of any of the previously known hadrosaurid taxa from the lower Kirtland Formation, including the newly described kritosaurine material. Morphometric analysis of the humerus suggests an element with proportions similar to those of Shantungosaurus, one of the largest hadrosaurs, and dissimilar to any of the previously known San Juan Basin hadrosaurid taxa. The robust construction of the humeral shaft is reflected by a shaft volume to humeral length ratio that greatly exceeds most other hadrosaurid taxa, resulting in a humerus with greater loading capacity. Though it is an isolated element, this humerus provides evidence that there were large hadrosaurids, potentially from a new species, living in the San Juan Basin, expanding the diversity of the San Juan Basin hadrosaurid dinosaur fauna.
William Ruger Porter and Lawrence M Witmer (2017)
Restoring dinosaur cephalic vascular anatomy and thermophysiology using osteological correlates and anastomotic connections.
FASEB Journal 31 no. 1 Supplement: 579.2
The restoration of dinosaur cephalic blood vessels is critical to understanding physiological thermoregulatory strategies in dinosaurs. Cephalic blood vessels of extant diapsids are known to support physiological thermoregulatory capabilities that modulate head and neurosensory tissue temperatures. Given their close phylogenetic relationship to extant diapsids, dinosaurs are hypothesized to have had similar vascular arrangements and physiological abilities. To test this hypothesis, the cephalic vascular anatomy of extant diapsids (turtles, squamates, crocodilians, and birds) was investigated using CT-scanning, vascular injection, and gross dissection with special attention given to blood vessels within known sites of thermal exchange (oral, nasal, and orbital regions). Vascular osteological evidence in skull bones of both extant and extinct specimens was collected to test hypotheses of vascular anatomy within the heads of dinosaurs. CT data were segmented in Avizo and vascular restorations were made using Maya. The large blood vessels that supply and drain diapsid heads displayed a conserved branching pattern, as the common carotid artery reliably bifurcates into internal and external carotid arteries. Further evidence for the subsequent branching patterns of these blood vessels adds support for a highly conserved diapsid vascular pattern. An important detail for identifying not only the blood vessels forming osteological correlates, but also identifying the blood vessels that passed between soft-tissues, is the anastomotic connections that each blood vessel shared. For example, within the orbit, evidence for anastomoses between the supraorbital, ophthalmotemporal and branches of the cerebral carotid arteries was found in all three extant clades sampled. This evidence indicates the location of each participating artery and subsequently highlights the course of all three blood vessels back to their parent vessel. Within the narial region, near the maxilla-premaxilla suture, evidence for anastomotic connections between the maxillary and nasal vessels was found. This anastomosis often included the palatal vessels, indicated by a canal that opened onto the palate. The connection between these vessels would have allowed blood to pass from the palate to the nasal region, or vice-versa, serving as a potential collateral blood flow pathway to both of these regions. Additionally, some of the blood vessels to the nasal region are branches of the cerebral carotid arteries, which in large dinosaurs do not appear to be emphasized and seem inadequately sized to supply a large nasal region. This indicates that collateral blood flow was important for supplying emphasized sites of thermal exchange in large dinosaurs. When several dinosaur taxa were compared, different foramina sizes highlighted not only the potential diameter of blood vessels supplying sites of thermal exchange, but also which blood vessels supplied a majority of the blood to physiologically relevant regions of the head. Enabled by an understanding of the vascular anatomy of dinosaurs, we can begin to investigate the physiology of sites of thermal exchange and what important role they served in dinosaur thermoregulatory strategies.
Mary Higby Schweitzer and Wenxia Zheng (2017)
Soft Tissue and Protein Preservation in Dinosaur Fossils: Evidence, Criteria and Implications.
FASEB Journal 31 no. 1 Supplement: 243.3
Evolutionary change first occurs in the genes or the proteins they encode; thus molecular investigations of extant organisms have transformed our understanding of evolutionary biology. DNA and protein sequence data have been used to test hypotheses of evolutionary relationships, paleobiogeographic trends, rates of molecular change, population mixing, and timing of dispersals. Molecular data have provided insight into population bottlenecks that place species at risk for extinction, and have shed light on species origins, radiations and extinctions, as well as organismal response to climate change at the molecular level. However, the extension of these investigations into deep time is extremely limited; estimates of rate and direction of molecular evolution are currently based upon data derived from living organisms and extrapolated to extinct ones, not directly derived. Remnants of these molecules in fossils allow observation of molecular evolution and diversity across deep time and can reveal molecular traits contributing to adaptation and resilience in the face of these challenges.
We present evidence that proteins are preserved in at least two dinosaur specimens that also evidenced still-soft tissues, discuss the need for rigorous criteria for accepting the identity of biomolecules in deep time, and briefly discuss what these data may mean to our understanding of molecular evolution, species relationships and molecular adaptability over time.
Gregory M Erickson, Stephen M Kuhn-Hendricks, and Brandon A Krick (2017)
Fracture Property Experimentation On Hadrosaurid Dinosaur Wavy Enamel Reveals Energy-Robbing Crack Deflection and Channeling To Localize Damage: A Rare Case of Mammalian-Like Dental Sophistication In Reptiles.
FASEB Journal 31 no. 1 Supplement: 251.5
Reptiles rarely approached the biomechanical sophistication of feeding or dietary diversity seen in mammals. Their teeth are typically non-occluding, semi-conical structures with simplistic parallel-crystalite enamel surrounding an orthodentine core. Conversely, most mammals possess multi-cusped teeth that are drawn across one another during mastication and self-wear to their functional morphology. Mammalian enamel is complex -- a fiberglass-like composite composed of bundles of hydroxyapatite crystals known as prims, surrounded by compliant proteinacous sheaths. Among the most sophisticated prism architectures is the modified radial enamel (MRE) of grazing ungulates whose coarse tooth surfaces enable grinding of tough, abrasive-laden plant matter. MRE conveys exceptional fracture toughness and controlled fracture propagation minimizing damage to the brittle enamel crests. Hadrosaurid (duck-billed dinosaurs) are notable in independently evolving self-wearing grinding dentitions and complex wavy enamel (WE) composed of folded layers of hydroxyapatite crystals whose biomechanical import is unknown. We tested the hypothesis that WE served an analogous role to ungulate MRE by: 1) tribologically modeling the effects on hadrosaurid occlusal surfaces should a section of enamel become fractured; 2) introducing enamel fractures to the teeth of hadrosaurids, outgroups lacking WE, and horses and bison using Vickers-tipped indenters; 3) testing for controlled-crack propagation using Watson’s Two-Sample Test of Homogeneity; and 4) contrasting the results in comparative ecological contexts. Removal of enamel sections leads to aberrant self-wear to hadrosaurid chewing pavements (= “wave mouth” in equine veterinary science) inhibiting functionality. Non-WE enamels show isotropic fracturing and catastrophic damage to the enamel shells. WE and MRE three-dimensionally limit damage in enamel crests through energy-robbing crack deflection at kinks in the enamel fabrics or prism boundaries and channeling perpendicular to the enamel-dentine junction. Hadrosaurid WE represents an alternative reptilian solution for damage resistance in grazing taxa, one that evolved millions of years earlier than in mammalian ungulates. Our findings add to a growing body of evidence that material properties are preserved in fossil teeth and can be used to explore dental form and function throughout the fossil record and to develop biologically-inspired industrial materials.
Casey M Holliday, Cheryl A Hill, Julian L Davis, Lawrence M Witmer, and Kevin M Middleton (2017)
Inside Dinosaurs: A Broader Impacts Program for Research, Teaching and Public Education Through Dinosaur Biology, Physics and Evolution.
FASEB Journal 31 no. 1 Supplement: 734.8
Inside Dinosaurs is a NSF-funded, multi-pronged broader impacts program that immerses undergraduate research interns, secondary-school science teachers, and the public in evolution, biomechanics and avian origins through a series of parallel and complementary activities. It incorporates STEM disciplines and offers opportunities for graduate and undergraduate lab members to interact with the local public and grade 6–12 teachers through science communication and outreach activities. Besides annual REU lines for University of Missouri undergraduates, we host two undergraduates from other institutions each summer to learn new experimental, modeling and anatomical techniques. Additionally, we recruit a local teacher each summer who, while embedded in the lab, conducts research and helps translate our discoveries into secondary school- level learning activities that fit within the Next Generation Science Standards. Together, the PIs, students, and teachers are developing and testing new classroom activities that are disseminated to interested Missouri teachers through a series of workshops. Besides these intense, lab-based interactions, Inside Dinosaurs sponsors the Dinosaurs and Cavemen Science Expo, a pop-up natural history museum exhibit that hosts two dozen activities put on by over thirty faculty and students and experiences crowds from 500–1000 people each year. These synergistic activities among faculty, teachers and visiting students help design and develop more specific learning activities to help bring paleontology, biomechanics, and anatomy to Central Missouri and the rest of the country.
Ashley Caroline Morhardt, Ryan Ridgely, and Lawrence M Witmer (2017)
Gross Anatomical Brain Region Approximation (GABRA): a new landmark-based approach for estimating brain regions in dinosaurs and other archosaurs.
FASEB Journal 31 no. 1 Supplement: 251.2
Studying brain evolution in extinct taxa can be challenging due to a lack of close correspondence between the morphology of the endocranial cavity and that of the underlying brain. Cranial endocasts may be faithful brain proxies in certain groups (mammals, birds) due to relatively complete filling of the cavity with neural tissue in life. However, the brain does not fill the endocranial cavity in many adult non-avian archosaurs, making their endocasts less reliable indicators of brain size and shape. As such, previous studies of relative brain size and evolution in archosaurs relied on untested assumptions about brain-endocast fidelity. We propose a new approach known as Gross Anatomical Brain Region Approximation (GABRA), which involves importing a digital endocast, derived from CT scanning and 3D visualization software, into modeling software (Maya). In Maya, brain regions underlying the endocast are modeled as 3D polygons. Discernable osteological correlates for soft-tissue structures (e.g., neurovascular canals, dural sinuses, fossae formed by the brain itself) present on the endocast serve as anatomical landmarks that inform the location and size of the modeled general brain regions (e.g., cerebral hemispheres, cerebellum, optic lobes, olfactory bulbs). Together, the anatomical landmarks form a set of explicit criteria used to assess endocasts and model brain regions. GABRA criteria and resulting brain models were validated in extant diapsids (lizards, snakes, alligators, birds) via literature review, gross dissection, CT scanning of iodine-stained specimens, and MRI studies. Therefore, GABRA models produced for extinct archosaurs are credible. Credible GABRA models for extinct dinosaurs provided volumetric estimates for general brain regions, which, when summed, offer a whole-brain estimate. Such data from several dinosaurs have permitted analyses using modern comparative methods of relative brain-size evolution (e.g., encephalization quotient), with results indicating that brain sizes for many dinosaurs were previously underestimated. Additionally, analyses of GABRA data show a mix of concerted and mosaic patterns of brain evolution, wherein the pituitary and olfactory bulbs emerge as evolving independently from the rest of the brain. In sum, GABRA provides insight into how brains evolved across dinosaur lineages. Future studies will examine within-lineage changes, offering greater insight into how and why dinosaur brains evolved.
Ali Nabavizadeh (2017)
Extreme Muzzles of Mastication: Craniofacial Muscular Support Systems of Large Herbivores (Dinosaurs, Mammals, and More)
FASEB Journal 31 no. 1 Supplement: 86.3
Herbivory has evolved countless times independently throughout vertebrate evolution. Among extant amniotes, it is seen in various mammals as well as some reptiles and birds and the fossil record greatly extends this diversity to non-mammalian synapsids (e.g., dicynodonts and pelycosaurs), non-avian dinosaurs (e.g., horned ceratopsians, duck-billed hadrosaurs, armored ankylosaurs and stegosaurs, and long-necked sauropods), parareptiles, and others. This study explores (through dissections, osteological correlates, and literature review) the vast functional diversity of cranial musculature acting as massive functional support systems in the muzzles of the largest herbivores over millions of years. Trigeminal jaw muscle anatomy has changed drastically throughout amniote evolution and the anatomical constraints that have been placed on individual subclades has dictated how they accommodate for a transition to an herbivorous lifestyle. These anatomical variations have modified to adapt to withstanding feeding forces in various grinding feeding motions in both browsing and grazing. Jaw motions include orthal (i.e., vertical closure of oral cavity), transverse, wishboning, proal (i.e., rostrally oriented), and palinal (i.e., caudally oriented) feeding strokes. For instance, the diversity in dinosaur jaw muscle anatomy suggests how, in accordance with various joint morphologies, muscles adapt to different feeding strategies, such as orthal feeding with slight bilateral long-axis rotation of the dentaries (e.g., in basal ornithischians, stegosaurs, and pachycephalosaurs), palinal feeding with more pronounced bilateral long-axis rotation of the dentaries (e.g., in hadrosaurs and ankylosaurs), and strictly orthopalinal feeders (e.g., ceratopsians). These variations are seen, in large part, with the extent of rostral insertion of adductor musculature providing greater mechanical advantage as well as the stability and support needed for the more complex feeding motions observed in tooth wear. This rostral muscle elongation is also seen in herbivorous synapsids, such as dicynodonts and edaphosaurid pelycosaurs, also accommodating palinal motion. Conversely, large herbivorous mammals are adapted to perform various transverse feeding motions, with few exceptions, such as in elephants which are proal feeders. The masseter muscle is especially attached farther forward on the zygomatic arch in some large herbivorous mammals, lateral to the tooth row to a certain extent, also accommodating mechanical advantage and support for more complex feeding motions. Lastly, another major factor in the mammalian line of cranial musculature is the presence of muscles of facial _expression_, which have taken many forms for different feeding habits, such as the proboscis in elephants and the tendon-bearing musculature seen in ungulates such as rhinoceroses, hippopotamuses, bovids, and horses. These cranial muscle support systems are ideal for withstanding the most powerful browsing and grazing habits and this study aims to show the remarkable diversity of these magnificent terrestrial beasts.