DOCSLIB.ORG

Three-Dimensional Tomographic Study of Dermal Armour from the Tail of the Triassic Aetosaur Stagonolepis Robertsoni

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Three-Dimensional Tomographic Study of Dermal Armour from the Tail of the Triassic Aetosaur Stagonolepis Robertsoni Downloaded from http://sjg.lyellcollection.org/ by guest on May 13, 2020 Research article Scottish Journal of Geology Published online February 14, 2020 https://doi.org/10.1144/sjg2019-026 | Vol. 56 | 2020 | pp. 55–62 Three-dimensional tomographic study of dermal armour from the tail of the Triassic aetosaur Stagonolepis robertsoni Emily Keeble and Michael J. Benton* School of Earth Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol BS8 1TQ, UK MJB, 0000-0002-4323-1824 * Correspondence: [email protected] Abstract: The aetosaur Stagonolepis robertsoni was the first reptile to be named from the Late Triassic Lossiemouth Sandstone Formation of Morayshire. Its characteristic rectangular armour plates have been reported in isolation and in association with skeletal remains. Here we present for the first time a three-dimensional reconstruction of the armour plates around the tail in association with caudal vertebrae and a chevron, to give direct evidence of the body outline. The caudal vertebral column was surrounded by eight bony osteoderms, paired paramedian dorsal and ventral plates, and a pair of lateral osteoderms on right and left. The tail shape was subcircular, broader than high. The osteoderms overlap like roofing tiles, the posterior margin of each overlapping the osteoderm following behind. The success of these scans suggests that computed tomography scanning could reveal excellent detail of all the Elgin reptiles in the future. Supplementary material: Three-dimensional models of the two fossil specimens are available at: https://doi.org/10.6084/m9. figshare.c.4824183 Received 23 September 2019; revised 24 November 2019; accepted 20 January 2020 Aetosaurs were unusual quadrupedal, highly armoured We identify the current specimens unequivocally as suchian archosaurs (Nesbitt 2011) that are known from pertaining to Stagonolepis robertsoni based on the identifi- every continent, save Australia and Antarctica, and lived cation of osteoderms and caudal vertebrae with those of that from the Carnian to Rhaetian in the Late Triassic (Heckert taxon. First, the shape and pitting of the osteoderms are and Lucas 2000; Nesbitt 2011). This was a time of great unique to Aetosauria, and Stagonolepis is the only aetosaur diversity and disparity of crurotarsans, the ‘crocodile-line’ from the Lossiemouth Sandstone Formation. In more detail, archosaurs (Nesbitt 2011; Stubbs et al. 2013), among which the osteoderms are identical in size and shape and the aetosaurs became specialized as one of the only groups of droplet-like external pitting to all previously described Triassic archosaurs to be herbivorous, though some species Stagonolepis scutes (Agassiz 1844; Walker 1961). Further, may also have been partially or fully insectivorous and better as discussed below, the caudal vertebrae in our specimens are suited to feeding on soft grubs (Desojo and Vizcaino 2009). identical to those of S. robertsoni (Walker 1961). Though phylogenetic analysis makes it clear that Aetosauria Aetosaur armour plates may occur commonly, even in must have diverged from other suchians in the Early Triassic, isolation from other skeletal elements, and this is as true of the clade is known exclusively from the Late Triassic Stagonolepis as with other genera, such as the North (Nesbitt et al. 2014). The anatomy of aetosaurs is also American forms Longosuchus (Sawin 1947), unusual, with features such as highly ornamented osteoderms Desmatosuchus (Case 1922) and Typothorax (Case 1922), and an upturned shovel-shaped rostrum that may have been whose plates may bear spines. Where they are abundant, used for digging or foraging for roots, tubers or insects aetosaur osteoderms have been used as index fossils in (Desojo et al. 2013). biochronology (Heckert et al. 1996, 2007). The ornamenta- The first aetosaur to be named anywhere in the world was tion and pitting on the dermal surface of plates may be Stagonolepis robertsoni from the Lossiemouth Sandstone diagnostic of genera or species of aetosaurs, though care Formation of Lossiemouth East Quarry, near Elgin, should be taken if using only the paramedian osteoderms, Morayshire (Walker 1961; Benton and Walker 1985). It because the lateral osteoderms may provide a stronger was described by Louis Agassiz, who, based solely on phylogenetic signal (Parker 2007). It is important to ensure drawings of the ventral dermal armour of the holotype that homologous osteoderms are used for species identifica- (ELGNM 27R), wrongly assumed it to be a fish (Agassiz tion, as their morphology changes within individuals and 1844). This was later corrected by Huxley, who reclassified species according to their position on the body, whether Stagonolepis as a reptile among the Crocodilia (Huxley dorsal, lateral or ventral, but also along the length of the body 1859, 1877). Today, Stagonolepis sits firmly within (Parker and Martz 2010; Desojo et al. 2013). Aetosauria and is considered a typical, if basal, member of Stagonolepis and other aetosaurs were encased in plates the group (Desojo et al. 2013). Stagonolepis has ventral presumably for defence against large predators such as armour and small rounded armour plates over most of the Ornithosuchus and the rauisuchians. This protective function limbs (Walker 1961). (Chen et al. 2014) was enabled by the fact that the © 2020 The Author(s). Published by The Geological Society of London for EGS and GSG. All rights reserved. For permissions: http://www.geolsoc.org.uk/ permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sjg.lyellcollection.org/ by guest on May 13, 2020 56 E. Keeble and M. J. Benton osteoderms overlapped in imbricating patterns, like slates on after blasting of the rock had taken place during small-scale a roof (Clarac et al. 2019), as is also seen in other quarrying. This very recent find shows that, despite the pseudosuchians, for example, erpetosuchids (Benton and historical nature of most Elgin specimens, the site is still Walker 2002; Ezcurra et al. 2017). However, experimental productive and it is possible that new material could be studies show that aetosaur osteoderms were weaker than uncovered in the future. There are two blocks (ELGNM those of at least some contemporaneous and modern 2018.6.1 and 2) that might come from one individual, as they crocodilomorphs and crocodilians when stresses similar to were found close together, and both represent portions of tail a predatory attack were applied to them (Clarac et al. 2019). and osteoderms from a similarly sized individual. However, All aetosaurs possessed dorsal paramedian and lateral the two sharp-edged blocks cannot be fitted together. The osteoderms, many also had ventral osteoderms, and some matrix is the typical fine-grained, well-sorted, light buff- even had appendicular osteoderms, marking them as some of coloured sandstone of the Lossiemouth Sandstone the most heavily armoured animals in the fossil record Formation. (Desojo et al. 2013; Clarac et al. 2019). ELGNM 2018.6.1 (Fig. S1A) is the larger of the two The aetosaurian dermal armour might also have played a blocks, and contains a more posterior section of the tail, role in thermoregulation (Seidel 1979; Chen et al. 2014). though it shows only the dorsal caudal paramedian plates. This is suggested by the broad surface of the osteoderm, with The internal surfaces of the osteoderm are exposed. ELGNM high vascularity, as suggested by the ornamental pattern on 2018.6.2 (Fig. S1B) likewise contains an example of the the osteoderm, which provided ample channels for cutaneous dorsal paramedian osteoderm, but also includes the corre- blood vessels to allow rapid heat transfer (Seidel 1979). sponding caudal lateral and ventral plates as well as at least Previously, the best way to study the remains of the Elgin two largely complete vertebrae and a chevron, though these reptiles was to destroy the bones, which are usually crumbly are not visible externally. and contained in a tough sandstone matrix, leaving only the mould of the fossil in the rock, from which a replica can then be CT scanning cast (Walker 1961; Benton and Walker 1981, 1985). Earlier efforts to remove the sandstone using chisels resulted in Both blocks were scanned using a Nikon XT H 225 CT damage to the soft bone, and no chemical treatment has been scanner with rotating target at the University of Bristol. found to remove the rock at all, least of all to remove the rock ELGNM 2018.6.1 was scanned at 223 kV and 399 uA using neatly and leave the bone undamaged. This all makes it difficult a 2 mm Cu filter. The gain was 24 with a 0.5 s exposure, to study the Elgin reptiles, and especially surface details such as providing 3141 projections and 4× frame averaging, resulting the unique external ornamentation of aetosaur osteoderms. in a voxel size of 0.065 mm. ELGNM 2018.6.2 was scanned Here we use computed tomography (CT) scanning to overcome at 213 kV and 179 uA with no filter. The gain was 18 and a this problem. Only two other studies have successfully 0.5 s exposure, also with 3141 projections and 4× frame attempted CT scanning of an aetosaur: Baczko et al. (2018) averaging, resulting in a voxel size of 0.0380 mm. Both scans show CT scans of the braincase of Neoaetosauroides and were run for c. 1 h 40 min each. The use of a micro-CT Hoffman et al. (2018, 2019) provide scans of scattered scanner allowed for higher resolution than a standard postcranial elements of Coahomasuchus. Parker (2018) also scanner, thus enabling a clear image, despite the difficulty attempted to CT scan the skull of S. robertsoni,buttheX-rays of scanning such a dense matrix. failed to penetrate the sandstone matrix of the specimen. Although the separation between many bones and matrix Here, we explore the imbrication of multiple armour plates was good and allowed some degree of automatic volume of an aetosaur and their relation to the underlying bones, using rendering, additional sectioning of CT scans had to be CT scanning to produce three-dimensional digital models.
Load more

Recommended publications
  • (Reptilia: Archosauria) from the Late Triassic of North America
    Journal of Vertebrate Paleontology 20(4):633±636, December 2000 q 2000 by the Society of Vertebrate Paleontology RAPID COMMUNICATION FIRST RECORD OF ERPETOSUCHUS (REPTILIA: ARCHOSAURIA) FROM THE LATE TRIASSIC OF NORTH AMERICA PAUL E. OLSEN1, HANS-DIETER SUES2, and MARK A. NORELL3 1Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964; 2Department of Palaeobiology, Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario, Canada M5S 2C6 and Department of Zoology, University of Toronto, Toronto, Ontario, Canada M5S 3G5; 3Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, New York 10024 INTRODUCTION time-scales (Gradstein et al., 1995; Kent and Olsen, 1999). Third, Lucas et al. (1998) synonymized Stegomus with Aeto- To date, few skeletal remains of tetrapods have been recov- saurus and considered the latter taxon an index fossil for con- ered from the Norian- to Rhaetian-age continental strata of the tinental strata of early to middle Norian age. As discussed else- Newark Supergroup in eastern North America. It has always where, we regard this as the weakest line of evidence (Sues et been assumed that these red clastic deposits are largely devoid al., 1999). of vertebrate fossils, and thus they have almost never been sys- tematically prospected for such remains. During a geological DESCRIPTION ®eld-trip in March 1995, P.E.O. discovered the partial skull of a small archosaurian reptile in the lower part of the New Haven The fossil from Cheshire is now housed in the collections of Formation (Norian) of the Hartford basin (Newark Supergroup; the American Museum of Natural History, where it is cata- Fig.
    [Show full text]
  • Crocodylomorpha, Neosuchia), and a Discussion on the Genus Theriosuchus
    bs_bs_banner Zoological Journal of the Linnean Society, 2015. With 5 figures The first definitive Middle Jurassic atoposaurid (Crocodylomorpha, Neosuchia), and a discussion on the genus Theriosuchus MARK T. YOUNG1,2, JONATHAN P. TENNANT3*, STEPHEN L. BRUSATTE1,4, THOMAS J. CHALLANDS1, NICHOLAS C. FRASER1,4, NEIL D. L. CLARK5 and DUGALD A. ROSS6 1School of GeoSciences, Grant Institute, The King’s Buildings, University of Edinburgh, James Hutton Road, Edinburgh EH9 3FE, UK 2School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, European Way, Southampton SO14 3ZH, UK 3Department of Earth Science and Engineering, Imperial College London, London SW6 2AZ, UK 4National Museums Scotland, Chambers Street, Edinburgh EH1 1JF, UK 5The Hunterian, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK 6Staffin Museum, 6 Ellishadder, Staffin, Isle of Skye IV51 9JE, UK Received 1 December 2014; revised 23 June 2015; accepted for publication 24 June 2015 Atoposaurids were a clade of semiaquatic crocodyliforms known from the Late Jurassic to the latest Cretaceous. Tentative remains from Europe, Morocco, and Madagascar may extend their range into the Middle Jurassic. Here we report the first unambiguous Middle Jurassic (late Bajocian–Bathonian) atoposaurid: an anterior dentary from the Isle of Skye, Scotland, UK. A comprehensive review of atoposaurid specimens demonstrates that this dentary can be referred to Theriosuchus based on several derived characters, and differs from the five previously recog- nized species within this genus. Despite several diagnostic features, we conservatively refer it to Theriosuchus sp., pending the discovery of more complete material. As the oldest known definitively diagnostic atoposaurid, this discovery indicates that the oldest members of this group were small-bodied, had heterodont dentition, and were most likely widespread components of European faunas.
    [Show full text]
  • 8. Archosaur Phylogeny and the Relationships of the Crocodylia
    8. Archosaur phylogeny and the relationships of the Crocodylia MICHAEL J. BENTON Department of Geology, The Queen's University of Belfast, Belfast, UK JAMES M. CLARK* Department of Anatomy, University of Chicago, Chicago, Illinois, USA Abstract The Archosauria include the living crocodilians and birds, as well as the fossil dinosaurs, pterosaurs, and basal 'thecodontians'. Cladograms of the basal archosaurs and of the crocodylomorphs are given in this paper. There are three primitive archosaur groups, the Proterosuchidae, the Erythrosuchidae, and the Proterochampsidae, which fall outside the crown-group (crocodilian line plus bird line), and these have been defined as plesions to a restricted Archosauria by Gauthier. The Early Triassic Euparkeria may also fall outside this crown-group, or it may lie on the bird line. The crown-group of archosaurs divides into the Ornithosuchia (the 'bird line': Orn- ithosuchidae, Lagosuchidae, Pterosauria, Dinosauria) and the Croco- dylotarsi nov. (the 'crocodilian line': Phytosauridae, Crocodylo- morpha, Stagonolepididae, Rauisuchidae, and Poposauridae). The latter three families may form a clade (Pseudosuchia s.str.), or the Poposauridae may pair off with Crocodylomorpha. The Crocodylomorpha includes all crocodilians, as well as crocodi- lian-like Triassic and Jurassic terrestrial forms. The Crocodyliformes include the traditional 'Protosuchia', 'Mesosuchia', and Eusuchia, and they are defined by a large number of synapomorphies, particularly of the braincase and occipital regions. The 'protosuchians' (mainly Early *Present address: Department of Zoology, Storer Hall, University of California, Davis, Cali- fornia, USA. The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds (ed. M.J. Benton), Systematics Association Special Volume 35A . pp. 295-338. Clarendon Press, Oxford, 1988.
    [Show full text]
  • The Origin and Early Evolution of Dinosaurs
    Biol. Rev. (2010), 85, pp. 55–110. 55 doi:10.1111/j.1469-185X.2009.00094.x The origin and early evolution of dinosaurs Max C. Langer1∗,MartinD.Ezcurra2, Jonathas S. Bittencourt1 and Fernando E. Novas2,3 1Departamento de Biologia, FFCLRP, Universidade de S˜ao Paulo; Av. Bandeirantes 3900, Ribeir˜ao Preto-SP, Brazil 2Laboratorio de Anatomia Comparada y Evoluci´on de los Vertebrados, Museo Argentino de Ciencias Naturales ‘‘Bernardino Rivadavia’’, Avda. Angel Gallardo 470, Cdad. de Buenos Aires, Argentina 3CONICET (Consejo Nacional de Investigaciones Cient´ıficas y T´ecnicas); Avda. Rivadavia 1917 - Cdad. de Buenos Aires, Argentina (Received 28 November 2008; revised 09 July 2009; accepted 14 July 2009) ABSTRACT The oldest unequivocal records of Dinosauria were unearthed from Late Triassic rocks (approximately 230 Ma) accumulated over extensional rift basins in southwestern Pangea. The better known of these are Herrerasaurus ischigualastensis, Pisanosaurus mertii, Eoraptor lunensis,andPanphagia protos from the Ischigualasto Formation, Argentina, and Staurikosaurus pricei and Saturnalia tupiniquim from the Santa Maria Formation, Brazil. No uncontroversial dinosaur body fossils are known from older strata, but the Middle Triassic origin of the lineage may be inferred from both the footprint record and its sister-group relation to Ladinian basal dinosauromorphs. These include the typical Marasuchus lilloensis, more basal forms such as Lagerpeton and Dromomeron, as well as silesaurids: a possibly monophyletic group composed of Mid-Late Triassic forms that may represent immediate sister taxa to dinosaurs. The first phylogenetic definition to fit the current understanding of Dinosauria as a node-based taxon solely composed of mutually exclusive Saurischia and Ornithischia was given as ‘‘all descendants of the most recent common ancestor of birds and Triceratops’’.
    [Show full text]
  • Late Triassic) Adrian P
    New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/56 Definition and correlation of the Lamyan: A new biochronological unit for the nonmarine Late Carnian (Late Triassic) Adrian P. Hunt, Spencer G. Lucas, and Andrew B. Heckert, 2005, pp. 357-366 in: Geology of the Chama Basin, Lucas, Spencer G.; Zeigler, Kate E.; Lueth, Virgil W.; Owen, Donald E.; [eds.], New Mexico Geological Society 56th Annual Fall Field Conference Guidebook, 456 p. This is one of many related papers that were included in the 2005 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks.
    [Show full text]
  • Tooth Enamel Microstructure of Revueltosaurus
    Palaeontologia Electronica palaeo-electronica.org Tooth enamel microstructure of Revueltosaurus and Krzyzanowskisaurus (Reptilia:Archosauria) from the Upper Triassic Chinle Group, USA: Implications for function, growth, and phylogeny Andrew B. Heckert and Jessica A. Miller-Camp ABSTRACT Tooth enamel microstructure can carry significant phylogenetic, ontogenetic, and functional information within amniotes. Here we provide the first descriptions of the tooth enamel microstructure of two Late Triassic taxa, the crurotarsan Revueltosaurus callenderi Hunt and the putative ornithischian Krzyzanowskisaurus hunti (Heckert), which some consider closely related. To test the hypotheses that enamel thickness corresponds to function and/or phylogeny we analyzed the enamel of each at various scales, measuring enamel thickness and examining microstructural features through- out both longitudinal and cross-sectional thickness using previously established tech- niques to facilitate comparisons. Both taxa possess thick (up to ~150 µm) enamel for their size (< 20 mm crown height). Enamel in R. callenderi ranged from ~5-152 µm across a premaxillary tooth in longitudinal section, and ~42-92 µm in a maxillary/den- tary tooth transverse section. K. hunti enamel thickness was ~18-155 µm longitudinally and ~29-75 µm transversely. Both also had well-developed basal unit layers (BUL) and weakly developed columnar microstructure. Well-developed lines of incremental growth (LIG) are present in both taxa, through which the columnar enamel grades into parallel crystallite enamel. Their enamel microstructure is therefore grossly similar to that of several ornithischian taxa, especially ankylosaurs, with which they are strongly convergent, and also compares well to rauisuchids and tyrannosaurids. The relatively unique combination of microstructural characteristics in the schmelzmuster of R.
    [Show full text]
  • Dinosaurs British Isles
    DINOSAURS of the BRITISH ISLES Dean R. Lomax & Nobumichi Tamura Foreword by Dr Paul M. Barrett (Natural History Museum, London) Skeletal reconstructions by Scott Hartman, Jaime A. Headden & Gregory S. Paul Life and scene reconstructions by Nobumichi Tamura & James McKay CONTENTS Foreword by Dr Paul M. Barrett.............................................................................10 Foreword by the authors........................................................................................11 Acknowledgements................................................................................................12 Museum and institutional abbreviations...............................................................13 Introduction: An age-old interest..........................................................................16 What is a dinosaur?................................................................................................18 The question of birds and the ‘extinction’ of the dinosaurs..................................25 The age of dinosaurs..............................................................................................30 Taxonomy: The naming of species.......................................................................34 Dinosaur classification...........................................................................................37 Saurischian dinosaurs............................................................................................39 Theropoda............................................................................................................39
    [Show full text]
  • University of Birmingham the Earliest Bird-Line Archosaurs and The
    University of Birmingham The earliest bird-line archosaurs and the assembly of the dinosaur body plan Nesbitt, Sterling; Butler, Richard; Ezcurra, Martin; Barrett, Paul; Stocker, Michelle; Angielczyk, Kenneth; Smith, Roger; Sidor, Christian; Niedzwiedzki, Grzegorz; Sennikov, Andrey; Charig, Alan DOI: 10.1038/nature22037 License: None: All rights reserved Document Version Peer reviewed version Citation for published version (Harvard): Nesbitt, S, Butler, R, Ezcurra, M, Barrett, P, Stocker, M, Angielczyk, K, Smith, R, Sidor, C, Niedzwiedzki, G, Sennikov, A & Charig, A 2017, 'The earliest bird-line archosaurs and the assembly of the dinosaur body plan', Nature, vol. 544, no. 7651, pp. 484-487. https://doi.org/10.1038/nature22037 Link to publication on Research at Birmingham portal Publisher Rights Statement: Checked for eligibility: 03/03/2017. General rights Unless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or the copyright holders. The express permission of the copyright holder must be obtained for any use of this material other than for purposes permitted by law. •Users may freely distribute the URL that is used to identify this publication. •Users may download and/or print one copy of the publication from the University of Birmingham research portal for the purpose of private study or non-commercial research. •User may use extracts from the document in line with the concept of ‘fair dealing’ under the Copyright, Designs and Patents Act 1988 (?) •Users may not further distribute the material nor use it for the purposes of commercial gain. Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document.
    [Show full text]
  • Gondwana Vertebrate Faunas of India: Their Diversity and Intercontinental Relationships
    438 Article 438 by Saswati Bandyopadhyay1* and Sanghamitra Ray2 Gondwana Vertebrate Faunas of India: Their Diversity and Intercontinental Relationships 1Geological Studies Unit, Indian Statistical Institute, 203 B. T. Road, Kolkata 700108, India; email: [email protected] 2Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, India; email: [email protected] *Corresponding author (Received : 23/12/2018; Revised accepted : 11/09/2019) https://doi.org/10.18814/epiiugs/2020/020028 The twelve Gondwanan stratigraphic horizons of many extant lineages, producing highly diverse terrestrial vertebrates India have yielded varied vertebrate fossils. The oldest in the vacant niches created throughout the world due to the end- Permian extinction event. Diapsids diversified rapidly by the Middle fossil record is the Endothiodon-dominated multitaxic Triassic in to many communities of continental tetrapods, whereas Kundaram fauna, which correlates the Kundaram the non-mammalian synapsids became a minor components for the Formation with several other coeval Late Permian remainder of the Mesozoic Era. The Gondwana basins of peninsular horizons of South Africa, Zambia, Tanzania, India (Fig. 1A) aptly exemplify the diverse vertebrate faunas found Mozambique, Malawi, Madagascar and Brazil. The from the Late Palaeozoic and Mesozoic. During the last few decades much emphasis was given on explorations and excavations of Permian-Triassic transition in India is marked by vertebrate fossils in these basins which have yielded many new fossil distinct taxonomic shift and faunal characteristics and vertebrates, significant both in numbers and diversity of genera, and represented by small-sized holdover fauna of the providing information on their taphonomy, taxonomy, phylogeny, Early Triassic Panchet and Kamthi fauna.
    [Show full text]
  • A Revision of the Upper Triassic Ornithischian Dinosaur Revueltosaurus, with a Description of a New Species
    Heckert, A.B" and Lucas, S.O., eds., 2002, Upper Triassic Stratigraphy and Paleontology. New Mexico Museum of Natural History & Science Bulletin No.2 J. 253 A REVISION OF THE UPPER TRIASSIC ORNITHISCHIAN DINOSAUR REVUELTOSAURUS, WITH A DESCRIPTION OF A NEW SPECIES ANDREW B. HECKERT New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, NM 87104-1375 Abstract-Ornithischian dinosaur body fossils are extremely rare in Triassic rocks worldwide, and to date the majority of such fossils consist of isolated teeth. Revueltosaurus is the most common Upper Triassic ornithischian dinosaur and is known from Chinle Group strata in New Mexico and Arizona. Historically, all large (>1 cm tall) and many small ornithischian dinosaur teeth from the Chinle have been referred to the type species, Revueltosaurus callenderi Hunt. A careful re-examination of the type and referred material of Revueltosaurus callenderi reveals that: (1) R. callenderi is a valid taxon, in spite of cladistic arguments to the contrary; (2) many teeth previously referred to R. callenderi, particularly from the Placerias quarry, instead represent other, more basal, ornithischians; and (3) teeth from the vicinity of St. Johns, Arizona, and Lamy, New Mexico previously referred to R. callenderi pertain to a new spe­ cies, named Revueltosaurus hunti here. R. hunti is more derived than R. callenderi and is one of the most derived Triassic ornithischians. However, detailed biostratigraphy indicates that R. hunti is older (Adamanian: latest Carnian) than R. callenderi (Revueltian: early-mid Norian). Both taxa have great potential as index taxa of their respective faunachrons and support existing biochronologies based on other tetrapods, megafossil plants, palynostratigraphy, and lithostratigraphy.
    [Show full text]
  • On the Presence of the Subnarial Foramen in Prestosuchus Chiniquensis (Pseudosuchia: Loricata) with Remarks on Its Phylogenetic Distribution
    Anais da Academia Brasileira de Ciências (2016) (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690 http://dx.doi.org/10.1590/0001-3765201620150456 www.scielo.br/aabc On the presence of the subnarial foramen in Prestosuchus chiniquensis (Pseudosuchia: Loricata) with remarks on its phylogenetic distribution LÚCIO ROBERTO-DA-SILVA1,2, MARCO A.G. FRANÇA3, SÉRGIO F. CABREIRA3, RODRIGO T. MÜLLER1 and SÉRGIO DIAS-DA-SILVA4 ¹Programa de Pós-Graduação em Biodiversidade Animal, Universidade Federal de Santa Maria, Av. Roraima, 1000, Bairro Camobi, 97105-900 Santa Maria, RS, Brasil ²Laboratório de Paleontologia, Universidade Luterana do Brasil, Av. Farroupilha, 8001, Bairro São José, 92425-900 Canoas, RS, Brasil ³Laboratório de Paleontologia e Evolução de Petrolina, Campus de Ciências Agrárias, Universidade Federal do Vale do São Francisco, Rodovia BR 407, Km12, Lote 543, 56300-000 Petrolina, PE, Brasil 4Centro de Apoio à Pesquisa da Quarta Colônia, Universidade Federal de Santa Maria, Rua Maximiliano Vizzotto, 598, 97230-000 São João do Polêsine, RS, Brasil Manuscript received on July 1, 2015; accepted for publication on April 15, 2016 ABSTRACT Many authors have discussed the subnarial foramen in Archosauriformes. Here presence among Archosauriformes, shape, and position of this structure is reported and its phylogenetic importance is investigated. Based on distribution and the phylogenetic tree, it probably arose independently in Erythrosuchus, Herrerasaurus, and Paracrocodylomorpha. In Paracrocodylomorpha the subnarial foramen is oval-shaped, placed in the middle height of the main body of the maxilla, and does not reach the height of ascending process. In basal loricatans from South America (Prestosuchus chiniquensis and Saurosuchus galilei) the subnarial foramen is ‘drop-like’ shaped, the subnarial foramen is located above the middle height of the main body of the maxilla, reaching the height of ascending process, a condition also present in Herrerasaurus ischigualastensis.
    [Show full text]
  • New Insights on Prestosuchus Chiniquensis Huene
    New insights on Prestosuchus chiniquensis Huene, 1942 (Pseudosuchia, Loricata) based on new specimens from the “Tree Sanga” Outcrop, Chiniqua´ Region, Rio Grande do Sul, Brazil Marcel B. Lacerda1, Bianca M. Mastrantonio1, Daniel C. Fortier2 and Cesar L. Schultz1 1 Instituto de Geocieˆncias, Laborato´rio de Paleovertebrados, Universidade Federal do Rio Grande do Sul–UFRGS, Porto Alegre, Rio Grande do Sul, Brazil 2 CHNUFPI, Campus Amı´lcar Ferreira Sobral, Universidade Federal do Piauı´, Floriano, Piauı´, Brazil ABSTRACT The ‘rauisuchians’ are a group of Triassic pseudosuchian archosaurs that displayed a near global distribution. Their problematic taxonomic resolution comes from the fact that most taxa are represented only by a few and/or mostly incomplete specimens. In the last few decades, renewed interest in early archosaur evolution has helped to clarify some of these problems, but further studies on the taxonomic and paleobiological aspects are still needed. In the present work, we describe new material attributed to the ‘rauisuchian’ taxon Prestosuchus chiniquensis, of the Dinodontosaurus Assemblage Zone, Middle Triassic (Ladinian) of the Santa Maria Supersequence of southern Brazil, based on a comparative osteologic analysis. Additionally, we present well supported evidence that these represent juvenile forms, due to differences in osteological features (i.e., a subnarial fenestra) that when compared to previously described specimens can be attributed to ontogeny and indicate variation within a single taxon of a problematic but important
    [Show full text]