Ricardo Araújo

Bringing Dicynodonts Back to Life: Paleobiology and Anatomy of a New Emydopoid Genus from the Upper Permian of Mozambique

Dicynodontia represent the most diverse tetrapod group during the Late Permian. They survived the Permo-Triassic extinction and are central to understanding Permo-Triassic terrestrial ecosystems. Although extensively studied, several aspects of dicynodont paleobiology such as, neuroanatomy, inner ear morphology and internal cranial anatomy remain obscure. Here we describe a new dicynodont (Therapsida, Anomodontia) from northern Mozambique: Niassodon mfumukasi gen. et sp. nov. The holotype ML1620 was collected from the Late Permian K5 formation, Metangula Graben, Niassa Province northern Mozambique, an almost completely unexplored basin and country for vertebrate paleontology. Synchrotron radiation based micro-computed tomography (SRµCT), combined with a phylogenetic analysis, demonstrates a set of characters shared with Emydopoidea. All individual bones were digitally segmented allowing a 3D visualization of each element. In addition, we reconstructed the osseous labyrinth, endocast, cranial nerves and vasculature. The brain is narrow and the cerebellum is broader than the forebrain, resembling the conservative, “reptilian-grade” morphology of other non-mammalian therapsids, but the enlarged paraflocculi occupy the same relative volume as in birds. The orientation of the horizontal semicircular canals indicates a slightly more dorsally tilted head posture than previously assumed in other dicynodonts. In addition, synchrotron data shows a secondary center of ossification in the femur. Thus ML1620 represents, to our knowledge, the oldest fossil evidence of a secondary center of ossification, pushing back the evolutionary origins of this feature. The fact that the specimen represents a new species indicates that the Late Permian tetrapod fauna of east Africa is still incompletely known.

A proposed terminology of theropod teeth (Dinosauria, Saurischia)

ABSTRACT Theropod teeth are typically not described in detail, yet these abundant vertebrate fossils are not only frequently reported in the literature, but also preserve extensive anatomical information. Often in descriptions, important characters of the crown and ornamentations are omitted, and in many instances, authors do not include a description of theropod dentition at all. The paucity of information makes identification of isolated teeth difficult and taxonomic assignments uncertain. Therefore, we here propose a standardization of the anatomical and morphometric terms for tooth anatomical subunits, as well as a methodology to describe isolated teeth comprehensively. As a corollary, this study exposes the importance of detailed anatomical descriptions with the utilitarian purpose of clarifying taxonomy and identifying isolated theropod teeth.

The dentition of megalosaurid theropods

Theropod teeth are particularly abundant in the fossil record and frequently reported in the literature. Yet, the dentition of many theropods has not been described comprehensively, omitting details on the denticle shape, crown ornamentations and enamel texture. This paucity of information has been particularly striking in basal clades, thus making identification of isolated teeth difficult, and taxonomic assignments uncertain. We here provide a detailed description of the dentition of Megalosauridae, and a comparison to and distinction from superficially similar teeth of all major theropod clades. Megalosaurid dinosaurs are characterized by a mesial carina facing mesiolabially in mesial teeth, centrally positioned carinae on both mesial and lateral crowns, a mesial carina terminating above the cervix, and short to well-developed interdenticular sulci between distal denticles. A discriminant analysis performed on a dataset of numerical data collected on the teeth of 62 theropod taxa reveals that megalosaurid teeth are hardly distinguishable from other theropod clades with ziphodont dentition. This study highlights the importance of detailing anatomical descriptions and providing additional morphometric data on teeth with the purpose of helping to identify isolated theropod teeth in the future.

A new plesiosauroid from the Toarcian (Lower Jurassic) of Alhadas, Portugal

A partial plesiosauroid skull from the São Gião Formation (Toarcian, Lower Jurassic) of Alhadas, Portugal is re-evaluated and described as a new taxon, Lusonectes sauvagei gen. et sp. nov. It has a single autapomorphy, a broad triangular parasphenoid cultriform process that is as long as the posterior interpterygoid vacuities, and also a unique character combination, including a jugal that contacts the orbital margin, a distinct parasphenoid—basisphenoid suture exposed between the posterior interpterygoid vacuities, lack of an anterior interpterygoid vacuity, and striations on the ventral surface of the pterygoids. Phylogenetic analysis of Jurassic plesiosauroids places Lusonectes as outgroup to “microcleidid elasmosaurs”, equivalent to the clade Plesiosauridae. Lusonectes sauvagei is the only diagnostic plesiosaur from Portugal, and the westernmost occurrence of any plesiosaurian in Europe.

Two new theropod egg sites from the Late Jurassic Lourinhã Formation, Portugal

Two new Late Jurassic (uppermost Late Kimmeridgian) dinosaur eggshell sites are described, Casal da Rola and Porto das Barcas, both near Lourinhã, central-west Portugal. Casal da Rola yields eggshells with an obliquiprismatic morphotype comparable to those from a nest with the associated fossil embryos from Paimogo, tentatively assigned to the theropod Lourinhanosaurus antunesi. The Porto das Barcas eggshells have a dendrospherulitic morphotype with a prolatocanaliculate pore system. This morphotype was also recognised in eggshells from a clutch with associated Torvosaurus embryos at the Porto das Barcas locality. A preliminary cladistic analysis of eggshell morphology suggests theropod affinities for the Casal da Rola eggs, but is unable to resolve the phylogenetic position of the Porto das Barcas eggs. The eggshells at both sites are preserved in distal flood plain mudstones and siltstones. Carbonate concretions within the deposits indicate paleosol development.

THE ALFRED LEEDS FOSSIL VERTEBRATE COLLECTION OF THE NATIONAL MUSEUM OF IRELAND—NATURAL HISTORY

Alfred nicholson Leeds (1847–1917) is famous among vertebrate palaeontologists for amassing an invaluable collection of fossil vertebrates from the Middle Jurassic aged ‘Oxford Clay’ deposits of the Peterborough district in the UK, throughout the late nineteenth and early twentieth centuries. Part of his collection was acquired by the national Museum of Ireland— natural History in november 1893 but has not previously been described. This fossil material includes a suite of Jurassic marine reptiles: crocodiles, plesiosaurs and ichthyosaurs. There are no examples, however, of the giant fish Leedsichthys; the remains of which are commonly found among the fauna of the Oxford Clay Formation. Despite representing only a very small fraction of the total Leeds Collection, the specimens in Ireland are significant historically, and have scientific value in their own right. For the first time, in this paper, a historical review of the Dublin Leeds Collection is presented, the fossil specimens described and a long-lost piece of important documentation is presented.

A biomechanical analysis of the skull and adductor chamber muscles in the Late Cretaceous Plesiosaur Libonectes

Plesiosaurs were a diverse clade of marine reptiles that spanned nearly threequarters of the Mesozoic (earliest Jurassic to latest Cretaceous). They exhibit variation in head and neck morphology that presumably relates to functional differences in feeding habits. However, from a biomechanical standpoint, these marine creatures have a cranial organization shared with few reptile clades: the neodiapsid condition. Nevertheless, basic structural features in some derived clades, such as elasmosaurids, remain poorly understood, namely the presence of large supratemporal fenestrae, tall temporal bars, and high parietal crests. These features present biomechanical compromises with paleobiological implications for feeding habits. Here we test specific hypotheses regarding skull structure and mechanics in the elasmosaurid plesiosaur Libonectes morgani from the Late Cretaceous of Texas (USA). Using finite element analysis and loadings based on a detailed reconstruction of adductor chamber musculature, we provide estimates of stress and strain distributions for the Libonectes skull. We also digitally morphed different anatomical variants of the Libonectes skull, in order to assess the role of those traits in skull’s mechanical performance (e.g., height of the temporal bar). Our results show that a larger physiological cross-section of the adductor muscles is achieved by an enlarged supratemporal fenestra which although it reduces mechanical performance of the skull, it is offset by increased strength of a taller parietal crest and temporal bar, given the loading is largely symmetrical, the lateral components are offsetting yielding a vertical force vector. This arrangement also increases the length of the adductor musculature and thus the total muscle mass. We propose that the reduced pterygoid flange indicates a diminished role for the pterygoideus muscle, reflecting a shift of the majority of the bite force to the adductor mandibulae externus, pseudotemporalis, and adductor mandibulae posterior muscles. Reduction of the pterygoideus falsifies the dual adductor system hypothesis, in which kinetic inertia and static pressure coexist. Ricardo Araújo. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA, rmaraujo@smu.edu and Museu da Lourinhã, Rua João Luís de Moura, 95, 2530-158 Lourinhã, Portugal Michael J. Polcyn. Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA mpolcyn@smu.edu ARAÚJO AND POLCYN: PLESIOSAUR MASTICATION 2

Plesiosaur pectoral myology

Plesiosaurians are highly derived secondarily-adapted organisms (if fishes are primarily-adapted) with a long evolutionary history, and they are closely related with basal eosauropterygians. Attempts to reconstruct soft-tissue anatomy can be complicated due to the lack of extant closely-related species, thus various lines of evidence must be considered. This study aims to reconstruct the pectoral girdle myology of eosauropterygians. Information derived from the extant phylogenetic bracket method was not sufficient to clarify muscle attachments in the pectoral girdle of plesiosaurians. To correctly infer muscle homologies, the extant phylogenetic bracket information had to be complemented with developmental and osteological information, and osteological transformations had to be traced back to Permian basal neodiapsids. The reconstructed pectoral girdle musculature presented here is, thus, significantly different from previous attempts. As in secondarily-adapted aquatic modern analogues, several muscles atrophied (e.g., pectoralis, episternocleidomastoideus) and others specialized (e.g., coracobrachialis, clavodeltoideus) in order to attain a more influential role to the stringent conditions of subaquatic locomotion. The subcoracoscapularis, scapulodeltoideus, scapulohumeralis and supracoracoideus are inferred to be glenohumeral stabilizers. The clavodeltoideus acted as the main protractor muscle and the coracobrachialis as a major retractor muscle, possibly in conjunction with the latissimus dorsi. Several heads of the triceps possibly atrophied, as in whales, serving mainly as a cubital joint stabilizer. The trapezius, serratus and levator scapulae served as pectoral girdle stabilizers. PE Article Number: 18.1.8A Copyright: Society for Vertebrate Paleontology March 2015 Submission: 29 November 2013. Acceptance: 31 January 2015 Araújo, Ricardo and Correia, Fernando. 2015. Soft-tissue anatomy of the Plesiosaur pectoral girdle inferred from basal Eosauropterygia taxa and the extant phylogenetic bracket. Palaeontologia Electronica 18.1.8A: 1-32. palaeo-electronica.org/content/2015/1062-plesiosaur-pectoral-myology ARAÚJO AND CORREIA: PLESIOSAUR PECTORAL MYOLOGY Ricardo Araújo. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, USA; Museu da Lourinhã, Rua João de Luís de Moura, 95, 2530-158 Lourinhã, Portugal; Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal and Museum für Naturkunde, Berlin, Germany. rmaraujo@smu.edu Fernando Correia. Departamento de Biologia, Universidade de Aveiro, Campus Santiago, 3810-193 Aveiro, Portugal. fjorgescorreia@sapo.pt