DOCSLIB.ORG

Evolution and Development of the Skull

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Evolution and Development of the Skull evolution and development of the skull modules and networks modular development and evolution when and how during development and evolution? • increase in brain size • decrease in facial size human “candidate genes” • FOXP2 [forkhead box P2] (Lai et al. 01) – some alleles associated with speech and language disorder – humans have specific allele, different from great apes – “human” allele also in Neanderthals (Krause et al. 07) • MYH [myosin heavy chain expression] (Stedman et al. 04) – less expressed in humans (MYH16 inactivation) compared to great apes • ASPM [abnormal spindle-like microcephaly-assoc.] (Mekel Bobrov et al. 05) MCPH1 [microcephalin] (Evans et al. 05) – some alleles involved in primary microcephaly – some alleles show signs of recent selective sweeps in humans, but they are not related to brain size skull: development, evolution, function ear ossicles Meckel’s cartilage desmocranium: intramembranous (desmal) neurocranium chondrocranium: enchondral (cartilaginous) splanchnocranium human neonate skull (CT reconstruction) developmental modules or developmental network? skull development and evolution branchial (pharyngeal) arch transformation Reichert's theory eye stapes nasal bones squa- incus mosum maxilla malleus proc. styl. mandibula hyoid larynx MC: Meckel's cartilage PQ: palatoquadratum TR: trabeculae Reichert's theory synapsid (mammal-like reptile) angular mammal Liem et al. 04 branchial arches and circulation Liem et al. 04 branchial arches and circulation internal (dorsal) carotid external (ventral) carotid Liemal.04 et frog human carotid pathways ce/ci: carotis ext./int. s: a. stapedia p: a. promontorii pa: a. pharyngea ascendens most cheirogaleids tarsiers lemuriforms loriforms anthropoids Geissmann, 03 Gray’s Anatomy branchial arches and human anatomy arch" skeletal elements" muscles" arteries" cranial nerves" 1" maxilla, mandible, incus, mastication" -" V trigeminus" malleus" 2" stapes, styloid process, " facial expression" -" VII facialis" body and lesser horns of hyoid" 3" body and greater horns stylopharyngeus" int. IX glossopharyngeus" of hyoid " carotis" 4-6" laryngeal cartilages" palatine, 4: aorta, " X vagus + acc.cran." pharyngeal, subclavia" XI acc.spin." laryngeal, 5,6: -" trapezius, sternomastoid" gene expression patterns during early head development Kuratani 04 genetics of craniofacial development Santagati & Rijli,03 congenital malformations Franceschetti (Treacher-Collins) syndrome Apert/Crouzon (1st branchial arch) syndrome skull evo-devo and human craniofacial malformations FGFR-2 gene mutations lead to congenital malformations of head and limbs: „1st+2nd branchial arch disorders“ •! e.g. Apert syndrome (acrocephalo-syndactyly) –! craniosynostoses –! underdevelopment of maxilla –! low position of ears –! syndactyly •! e.g. Franceschetti (Treacher Collins) syndrome –! underdevelopment of mandible, zygomatic bones and external/middle ears developmental reorganization during evolution •! heterotopy: spatial reorganization –! deposition vs. resorption –! size, shape, arrangement of dep. and res. fields •! heterochrony: temporal reorganization –! sequence of growth events (onset - duration - offset) –! local rates of growth and development speciation and development heterochrony, heterotopy, allometry definitions •! ontogeny: structural (form) change from conception to death •! form: size and shape •! growth: change in size •! development: change in shape •! allometry: size-related change (or variation) in shape speciation through ontogenetic reorganization •! heterotopy: spatial reorganization of ontogeny, change in directions of growth and development –! e.g. migration patterns of NCC –! e.g. nr. and arrangement of dental cusps –! e.g. spatial arrangement of depository and resorptive bone growth fields •! heterochrony: temporal reorganization of ontogeny, change in rates of growth and development –! e.g. proliferation rates of NCC –! e.g. onset, duration, and offset of dental cusp formation –! e.g. local rates of bone resorption and deposition heterochrony example: humans and chimps cranial size human chimp dental age neurocranial size splanchnocranial size dental age dental age birth adult birth adult heterochrony example: humans and chimps cranial shape: splanchno/neuro size chimp human dental age birth adult log (cranial shape) adult ontogenetic allometry birth log (cranial size) heterochrony: adult descendant similar in shape paedomorphosis to juvenile ancestor phenotype juvenile ancestor adult descendant developmental time heterochrony: juvenile descendant similar in shape peramorphosis to adult ancestor phenotype adult ancestor juvenile descendant developmental time heterochrony: pattern and process •! different heterochronic processes can result in similar heterochronic patterns •! example: paedomorphy of the human head can result from –! delayed facial growth –! decelerated facial growth –! early cessation of facial growth –! advanced brain growth –! accelerated brain growth –! long duration of brain growth –! … or a combination of these processes è all result in small-faced, large-brained heads .
Load more

Recommended publications
  • Redalyc.Ontogeny of the Cranial Bones of the Giant Amazon River
    Acta Scientiarum. Biological Sciences ISSN: 1679-9283 [email protected] Universidade Estadual de Maringá Brasil Gonçalves Vieira, Lucélia; Quagliatto Santos, André Luiz; Campos Lima, Fabiano Ontogeny of the cranial bones of the giant amazon river turtle Podocnemis expansa Schweigger, 1812 (Testudines, Podocnemididae) Acta Scientiarum. Biological Sciences, vol. 32, núm. 2, 2010, pp. 181-188 Universidade Estadual de Maringá .png, Brasil Available in: http://www.redalyc.org/articulo.oa?id=187114387012 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative DOI: 10.4025/actascibiolsci.v32i2.5777 Ontogeny of the cranial bones of the giant amazon river turtle Podocnemis expansa Schweigger, 1812 (Testudines, Podocnemididae) Lucélia Gonçalves Vieira*, André Luiz Quagliatto Santos and Fabiano Campos Lima Laboratório de Pesquisas em Animais Silvestres, Universidade Federal de Uberlândia, Av. João Naves De Avila, 2121, 38408-100, Uberlandia, Minas Gerais, Brazil. *Author for correspondence. E-mail: [email protected] ABSTRACT. In order to determine the normal stages of formation in the sequence of ossification of the cranium of Podocnemis expansa in its various stages of development, embryos were collected starting on the 18th day of natural incubation and were subjected to bone diaphanization and staining. In the neurocranium, the basisphenoid and basioccipital bones present ossification centers in stage 19, the supraoccipital and opisthotic in stage 20, the exoccipital in stage 21, and lastly the prooptic in stage 24. Dermatocranium: the squamosal, pterygoid and maxilla are the first elements to begin the ossification process, which occurs in stage 16.
    [Show full text]
  • Skull – Ii Dermatocranium
    BIOLOGY 524 ADVANCED VERTEBRTE MORPHOLOGY -OSTEOLOGY- SKULL – II DERMATOCRANIUM S. S. SUMIDA INTRODUCTION RECALL: SPLANCHNOCRANIUM – The splanchnocranium (sometimes called the viscerocranium) is the phylogenetically most ancient part of the skull. It arose even before vertebrates themselves to support the pharyngeal gill slits of protochordates. Within the vertebrates, it supports gill structures or their evolutionary derivatives. The cartilagenous or bony components are derived from neural crest, and form endochondrally. Components of the upper and lower jaw are derived from this. CHONDROCRANIUM – The chondrocranium is a cradle that supports the underside of the brain itself. Its components form endochondrally, and can be derived from either mesoderm or neural crest. The chondrocranium is derived from multiple individual structures that fuse to become this cradle. Not all components ossify, with some remaining as cartilage. DERMATOCRANIUM – The dermatocranium is slightly later in development and makes up the outer casing of the skull. It protects the brain above, and protects the entire braincase from below as the plate. Embryology of the Dermatocranium All components of the vertebrate dermatocranium form intramembranously from neural crest cells. In fact, it is unfortunate, as this type of formation used to be known as “dermal bone formation” (because of the proximity of the ne to the skin. However, even though we no longer use the term dermal formation, we still use the term dermatocranium. Notably, whereas the entire dermatocranium is derived from neural crest forms intramembranously, it is not the only part of the skeleton derived from neural crest (also the splanchnocranium, which forms endochondrally), and it is not the only part of the skeleton that forms intramembranously (also significant parts of the pectoral girdle, which is derived from mesoderm).
    [Show full text]
  • Jaw Suspension
    JAW SUSPENSION Jaw suspension means attachment of the lower jaw with the upper jaw or the skull for efficient biting and chewing. There are different ways in which these attachments are attained depending upon the modifications in visceral arches in vertebrates. AMPHISTYLIC In primitive elasmobranchs there is no modification of visceral arches and they are made of cartilage. Pterygoqadrate makes the upper jaw and meckel’s cartilage makes lower jaw and they are highly flexible. Hyoid arch is also unchanged. Lower jaw is attached to both pterygoqadrate and hyoid arch and hence it is called amphistylic. AUTODIASTYLIC Upper jaw is attached with the skull and lower jaw is directly attached to the upper jaw. The second arch is a branchial arch and does not take part in jaw suspension. HYOSTYLIC In modern sharks, lower jaw is attached to pterygoquadrate which is in turn attached to hyomandibular cartilage of the 2nd arch. It is the hyoid arch which braces the jaw by ligament attachment and hence it is called hyostylic. HYOSTYLIC (=METHYSTYLIC) In bony fishes pterygoquadrate is broken into epipterygoid, metapterygoid and quadrate, which become part of the skull. Meckel’s cartilage is modified as articular bone of the lower jaw, through which the lower jaw articulates with quadrate and then with symplectic bone of the hyoid arch to the skull. This is a modified hyostylic jaw suspension that is more advanced. AUTOSTYLIC (=AUTOSYSTYLIC) Pterygoquadrate is modified to form epipterygoid and quadrate, the latter braces the lower jaw with the skull. Hyomandibular of the second arch transforms into columella bone of the middle ear cavity and hence not available for jaw suspension.
    [Show full text]
  • Covariation of the Endocranium and Splanchnocranium During Great Ape Ontogeny
    RESEARCH ARTICLE Covariation of the endocranium and splanchnocranium during great ape ontogeny 1,2 1 1 1 Nadia A. ScottID *, Andre Strauss , Jean-Jacques Hublin , Philipp Gunz , 1 Simon NeubauerID 1 Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz, Leipzig, Germany, 2 Konrad Lorenz Institute for Evolution and Cognition Research, Martinstrasse, Klosterneuburg, Austria * [email protected] a1111111111 a1111111111 a1111111111 a1111111111 Abstract a1111111111 That great ape endocranial shape development persists into adolescence indicates that the splanchnocranium succeeds brain growth in driving endocranial development. However, the extent of this splanchnocranial influence is unknown. We applied two-block partial least squares analyses of Procrustes shape variables on an ontogenetic series of great ape cra- OPEN ACCESS nia to explore the covariation of the endocranium (the internal braincase) and splanchnocra- Citation: Scott NA, Strauss A, Hublin J-J, Gunz P, nium (face, or viscerocranium). We hypothesized that a transition between brain growth and Neubauer S (2018) Covariation of the endocranium splanchnocranial development in the establishment of final endocranial form would be mani- and splanchnocranium during great ape ontogeny. PLoS ONE 13(12): e0208999. https://doi.org/ fest as a change in the pattern of shape covariation between early and adolescent ontogeny. 10.1371/journal.pone.0208999 Our results revealed a strong pattern of covariation between endocranium and splanchno- Editor: Carlo Meloro, Liverpool John Moores cranium, indicating that chimpanzees, gorillas, and orangutans share a common tempo and University, UNITED KINGDOM mode of morphological integration from the eruption of the deciduous dentition onwards to Received: February 12, 2018 adulthood: a reflection of elongating endocranial shape and continuing splanchnocranial prognathism.
    [Show full text]
  • Developmental and Evolutionary Significance of the Zygomatic Bone Yann Heuzé, Kazuhiko Kawasaki, Tobias Schwarz, Jeffrey Schoenebeck, Joan Richtsmeier
    Developmental and Evolutionary Significance of the Zygomatic Bone Yann Heuzé, Kazuhiko Kawasaki, Tobias Schwarz, Jeffrey Schoenebeck, Joan Richtsmeier To cite this version: Yann Heuzé, Kazuhiko Kawasaki, Tobias Schwarz, Jeffrey Schoenebeck, Joan Richtsmeier. Develop- mental and Evolutionary Significance of the Zygomatic Bone. THE ANATOMICAL RECORD, 2016, 299 (12), pp.1616-1630. 10.1002/ar.23449. hal-02322527 HAL Id: hal-02322527 https://hal.archives-ouvertes.fr/hal-02322527 Submitted on 11 Jan 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. THE ANATOMICAL RECORD 299:1616–1630 (2016) Developmental and Evolutionary Significance of the Zygomatic Bone YANN HEUZE, 1 KAZUHIKO KAWASAKI,2 TOBIAS SCHWARZ,3 4† 2† JEFFREY J. SCHOENEBECK, AND JOAN T. RICHTSMEIER * 1UMR5199 PACEA, Bordeaux Archaeological Sciences Cluster of Excellence, Universite De Bordeaux 2Department of Anthropology, Pennsylvania State University, University Park, PA 3Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Centre, Roslin, Midlothian, UK 4Division of Genetics and Genomics, The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Midlothian, UK ABSTRACT The zygomatic bone is derived evolutionarily from the orbital series.
    [Show full text]
  • Introduction
    click for previous page Sharks of the World, Vol. 2 1 1. INTRODUCTION his is the second volume of an extensively rewritten, cousins to elasmobranchs within the Chondrichthyes, and revised, and updated version of the original FAO Catalogue may find a higher profile as silver sharks or ghost sharks. Tof Sharks of the World (Compagno, 1984). It covers all the Considering them as ‘sharks’ brings batoids and described species of living sharks of the orders chimaeroids out of the perceptual dark. The batoids and Heterodontiformes, Lamniformes, and Orectolobiformes, chimaeras tend to receive far less attention than nonbatoid including their synonyms as well as certain well-established but sharks in most places. Some of the batoids currently are as currently undescribed species (primarily Australian species important for fisheries or more so than nonbatoid sharks or mentioned by Last and Stevens, 1994). It includes species of chimaeroids, and some are under severe threat from major, moderate, minor, and minimal importance to fisheries overexploitation and habitat modification (i.e. sawfishes, (Compagno, 1990c) as well as those of doubtful or potential use freshwater stingrays). The batoid sharks will hopefully be to fisheries. It also covers those species that have a research, the subject of a forthcoming and much overdue FAO recreational, educational, and aesthetic importance, as well as Catalogue of Batoids of the World; likewise for the those species that occasionally bite and threaten people in the chimaeroids. water and the far more numerous species that are ‘bitten’ and threatened by people through exploitation and habitat modification. The Catalogue is intended to form part of a comprehensive review of shark-like fishes of the world in a form accessible to fisheries workers as well as researchers on shark systematics, biodiversity, distribution, and general biology.
    [Show full text]
  • Overview of Structure of the Adult Skull the Developing Skull Has Three Component Origins
    Biology 223 Human Anatomy for Biology Majors Week 8; Lecture 1; Monday Dr. Stuart S. Sumida Overview of Structure of the Adult Skull The developing skull has three component origins: •Condrocranium (base of skull / braincase) •Dermatocranium (flat bones of skull) •Splanchnocranium (bones derived from gill arch elements) Mode of Germ Layer Formation Origin Condrocranium Endochondral Mesoderm Dermatocranium Dermal Neural Crest Splanchnocranium Endochondral Neural Crest CHONDROCRANIUM: Bones of the base of the skull. •Most major cranial nerves escape the skull through these. •Endochondral •Mesodermal •Include: ethmoid, sphenoid (part), occipital (part) right and left temporal (parts). Flat bones of skull: DERMATOCRANIUM (These and others.) Gill slit bones: become SPLANCHNOCRANIUM Mandible (Lower Jaw) Skull – Anterior View Anterior Frontal Inferior Ethmoid superior lateral Bones of the Orbit Skull – Lateral View Maxilla: Lateral View External Parietal Internal Temporal Internal External Neonatal Temporal Bone Skull – Superior View Skull – Posterior View Inferior Occipital Internal Skull – Inferior View Hard Palate Infratemporal Region Skull – Internal View Sphenoid Occipital Major Ligaments Near Jaw Joint Major Ligaments Near Jaw Joint: Stylomandibular Sphenomandibular Bones of the Basicranium Ethmoid Sphenoid Temporal Occipital Anterior Sphenoid Posterior Dermal Roofing Bones Nasals Frontal Parietals Dermal Facial Bones Maxilla Zygomatic Lacrimal Maxilla: Lateral View Bones of the Orbit Dermal Palatal Bones Maxilla Palatine Vomer Hard Palate Bones of Splanchnopleure Sphenoid Greater Wing Temporal Styloid Process Middle Ear Ossicles Middle Ear Ossicles Malleus Incus Stapes Malleus Incus Stapes .
    [Show full text]
  • Neurocranium
    NEUROCRANIUM Andrea Heinzlmann University of Veterinary Medicine Department of Anatomy and Histology 8th October 2019 THE SKULL (CRANIUM) FUNCTIONS OF THE SKULL: • forms the bony framework of the head • houses the barin and meninges • houses the higher sense organs • houses the parts of the respiratory system • houses the parts of the digestive system • provides attachments for the facial muscles bo • provides attachments for the mastications muscles http://raab.moovr.fr/cow-skull-diagram.html ca eq http://www.nhc.ed.ac.uk/index.php?page=493.172 https://www.horsetalk.co.nz/2017/09/28/b ridle-fit-important-horse-saddle-fitting/ SHAPE OF THE SKULL - differs from species to species - the viscerocranium (splanchnocranium) is larger than the neurocranium a. NEUROCRANIUM: forms a protective case around the brain b. VISCEROCRANIUM: form the skeleton of the face as well as parts of the jaw BONES OF THE SKULL • flat consist of: 1. LAMINA EXTERNA Lamina externa 2. SPONGY MIDDLE LAYER – DIPLOE 3. LAMINA INTERNA diploe Lamina interna https://news.psu.edu/photo/483082/2017/09/18/brain-magnets-diploe https://www2.aofoundation.org/wps/portal/!ut/p/a1/04_Sj9CPykssy0xPLMnMz0vMAfGjzOKN_A0M3D2D Dbz9_UMMDRyDXQ3dw9wMDAzMjYEKIvEocDQnTr8BDuBoQEh_QW5oKAD4ENaS/dl5/d5/L2dJQSEvUUt3 QS80SmlFL1o2XzJPMDBHSVMwS09PVDEwQVNFMUdWRjAwMDcz/?bone=CMF&segment=Cranium&sho wPage=A&contentUrl=srg/popup/additional_material/93/X40-Harvest-bone-graft.jsp PNEUMATIC BONES OF THE SKULL • lined by respiratory mucous epithel • contain air • connected to the nasal cavity • known as paranasal sinuses (sinus paranasales) • the diploe disappear • the lamina ext. et int. fused http://vanat.cvm.umn.edu/ungDissect/Lab18/Img18-9.html https://www.semanticscholar.org/paper/Disorders-of-the-Paranasal-Sinuses-Tremaine-Freeman/b9dc638997799bb89577bf771f4a3a0a2f96f6a6/figure/11 BONES OF THE NEUROCRANIUM UNPAIRED BONES: 1.
    [Show full text]
  • The Mandibular and Hyoid Arches—From Molecular Patterning to Shaping Bone and Cartilage
    International Journal of Molecular Sciences Review The Mandibular and Hyoid Arches—From Molecular Patterning to Shaping Bone and Cartilage Jaroslav Fabik 1,2, Viktorie Psutkova 1,2 and Ondrej Machon 1,* 1 Department of Developmental Biology, Institute of Experimental Medicine of the Czech Academy of Sciences, 14220 Prague, Czech Republic; [email protected] (J.F.); [email protected] (V.P.) 2 Department of Cell Biology, Faculty of Science, Charles University, 12800 Prague, Czech Republic * Correspondence: [email protected] Abstract: The mandibular and hyoid arches collectively make up the facial skeleton, also known as the viscerocranium. Although all three germ layers come together to assemble the pharyngeal arches, the majority of tissue within viscerocranial skeletal components differentiates from the neural crest. Since nearly one third of all birth defects in humans affect the craniofacial region, it is important to understand how signalling pathways and transcription factors govern the embryogenesis and skele- togenesis of the viscerocranium. This review focuses on mouse and zebrafish models of craniofacial development. We highlight gene regulatory networks directing the patterning and osteochondrogen- esis of the mandibular and hyoid arches that are actually conserved among all gnathostomes. The first part of this review describes the anatomy and development of mandibular and hyoid arches in both species. The second part analyses cell signalling and transcription factors that ensure the specificity of individual structures along the anatomical axes. The third part discusses the genes and molecules that control the formation of bone and cartilage within mandibular and hyoid arches and how dysregulation of molecular signalling influences the development of skeletal components of the Citation: Fabik, J.; Psutkova, V.; viscerocranium.
    [Show full text]
  • Osteology-‐ Skull
    BIOLOGY 524 ADVANCED VERTEBRTE MORPHOLOGY -OSTEOLOGY- SKULL – III SPLANCHNOCRANIUM S. S. SUMIDA INTRODUCTION RECALL: The splanchnocranium (sometimes called the viscerocranium) is the phylogenetically most ancient part of the skull. It arose even before vertebrates themselves to support the pharyngeal gill slits of protochordates. Within the vertebrates, it supports gill structures or their evolutionary derivatives. The cartilagenous or bony components are derived from neural crest, and form endochondrally. Components of the upper and loWer jaw are derived from this. Gills Gills of fishes are openings from the pharynx, through the body Wall, to the outside of the body, alloWing Water to pass over the gills but leave the gut tube before heading to the remainder of the gut tube. 1 Embryology of the Spanchnocranium All components of the vertebrate splanchnocranium form endochndrally from neural crest cells. Notably, Whereas the entire splanchnoocranium is derived from neural crest and forms endochondrally, it is not the only part of the skeleton derived from neural crest (also the dermatocranium, Which forms intramembranously), and it is not the only part of the skeleton that forms endochondrally (also almost all of the postcranial skeleton, and parts of the parts of the chondrocranium, Which are derived from mesoderm). Primitive Splanchnocranium The splanchnocranium is generally considered the most primitive part of the skull skeleton. The splanchnocranium is the skeleton of the gill structures, and gills, or gill-like structures are more broadly distributed amongst chordates, so the skeleton accompanying it presumably Was in place at or near the origin of vertebrates. BRIEF (PARTIAL) SURVEY OF SPLANCHNOCRANIUM OF JAWLESS VERTEBRATES In the most primitive jawless vertebrates, the head region is dominated by the gill apparatus.
    [Show full text]
  • Introduction to Fish Biology and Ecology
    1 INTRODUCTION TO FISH BIOLOGY AND ECOLOGY 1.1. FISH BIOLOGY- INTRODUCTION: Fish have great significance in the life of mankind, being an important natural source of protein and providing certain other useful products as well as eco- nomic sustenance to many nations. The gradual erosion of commercial fish stocks due to over -exploitation and alteration of the habitat is one reason why the science fish biology came into existence (Royce, 1972). It is a well known fact that the knowledge on fish biology particularly on mor- phometry, length-weight relationship, condition factor, reproduction, food and feeding habit, etc. is of utmost important not only to fill up the lacuna of our present day academic knowledge but also in the utility of the knowledge in increasing the technological efficiencies of the fishery entrepreneurs for evolving judicious pisciculture management. For developing fishery, it is necessary to understand their population dynamics- how fast they grow and reproduce, the size and age at which they spawn; their mortality rates and its causes, on what they prey upon along with other biological processes. There are many isolated disciplines in fish biology, of which the study of mor- phology is inseparably related to study of the mode of life of the organism. It fact, the size and shape are fundamental to the analysis of variation in living or- ganisms ( Grant and Spain, 1977) and morphological variations even in the same species most often related to the varied environmental factors. 2 Fish Biology and Ecology 1.1. General characters of a fish Fishes are the first vertebrates with Jaws.
    [Show full text]
  • ARAV Master Classes
    Section 23 ARAV Master Classes Tim Tristan, DVM; David Hannon, DVM, DABVP (Avian) Moderators Clinical Approach to Tortoises and Turtles Stephen J Divers, BVetMed, DZooMed, Dipl ACZM, Dipl ECZM (Herpetology), Dipl ECZM (Zoo Health Management), FRCVS Session #081 Affiliation: From the Department of Small Animal Medicine and Surgery (Zoological Medicine), College of Veterinary Medicine, University of Georgia, 2200 College Station Road, Athens, GA 30602, USA. Abstract: Chelonians remain one of the most popular types of reptiles kept in captivity, whether it be as a companion animal or a zoo/wildlife exhibit. Their characteristic shell can be a hindrance to veterinary evaluation and medical/surgical intervention. This masterclass focuses on the veterinary approach to these interesting animals and includes an introduction to the species, relevant anatomy and physiology, physical examination, sedation and anesthesia, diagnostic imaging, diagnostic sample collection and therapeutic routes for drug delivery including central line placement. Introduction Tortoises, turtles and terrapins are vertebrates with similar organ systems to mammals. However, they are ecto- thermic and rely on environmental temperature and behavior to control their core body temperature. They possess both renal and hepatic portal circulations, and predominantly excrete ammonia, urea, or uric acid depending upon their evolutionary adaptations (Table 1). They possess nucleated red blood cells and their metabolic rates are lower than those of mammals. Like all reptiles they exhibit ecdysis – a normal process by which the outer integu- ment is periodically shed throughout life. Most are diurnal but may be crepuscular and secretive in their habits. The species require broad spectrum light for psychological and, in the case of UVB (290-300 nm), vitamin D3 synthesis and calcium homeostasis.
    [Show full text]