An examination of non-mammalian cynodont cranial endocasts

Du Plessis, Dewald

An examination of non-mammalian cynodont cranial endocasts

dc.contributor.advisor	Botha-Brink, J.
dc.contributor.advisor	Butler, H. J. B.
dc.contributor.author	Du Plessis, Dewald
dc.date.accessioned	2018-01-19T07:09:04Z
dc.date.available	2018-01-19T07:09:04Z
dc.date.issued	2010-09
dc.description.abstract	English: The palaeoneurology (study of the nervous system of extinct animals) of nonmammalian cynodonts, which were the ancestors of mammals, is poorly understood. It is thought that the relative brain size of cynodonts increased with time, and that this change significantly affected their physiology and behaviour. Forty-four cynodont skulls belonging to eleven genera from Permian, Triassic and Jurassic strata were scanned and analysed using neutron computerized tomography (NCT), at the SAFARI-1 Nuclear Research Reactor of the Nuclear Energy Corporation of South Africa (Necsa). Data concerning the endocranial casts was hereby obtained in a non-destructive manner. Four specimens, namely Galesaurus, Platycraniellus, Langbergia and Tritylodon produced successful scans and were used for further study. Measurements of the cranial material were used to calculate the size of the brain endocasts and the approximate body masses were determined from an equation using skull length. The encephalization quotient (EO), a measure of brain size relative to body size, was determined for each specimen using brain volume and body mass. Changes in the position of the brain inside the skull, and an overall increase in size of the brain in the more derived cynodonts indicate some development towards the mammalian condition. Taxonomic variation regarding the shape and size of the olfactory bulbs and other parts of the brain endocasts is discussed and related to differences in ecology or behaviour. The relatively deep and large olfactory bulbs in some cynodonts may be an adaptation to either nocturnal behaviour, dietary or habitat preferences. Relatively large cranial endocasts in Galesaurus, Platycraniellus, Massetognathus, Tritylodon, Chiniquodon and the tritheledonts may be related to habitat preference or social behaviour. The basal epicynodonts Galesaurus and Platycraniellus have the largest cranial endocasts of all the cynodonts studied. Their large cranial endocasts may be related to behavioural or ecological preferences, but the results require confirmation from a larger sample size. The present study provides an important foundation from which further cranial endocast studies on cynodonts can be developed.	en_ZA
dc.description.abstract	Afrikaans: Min is bekend oor die palaeoneurologie (studie van die senuweestelsel van uitgestorwe diere) van nie-soogdieragtige Cynodontia, wat die voorouers van soogdiere is. Daar word vermoed dat die relatiewe breingrootte van Cynodontia oor tyd toegeneem het, en dat hierdie verandering hulle fisiologie en gedrag aansienlik beïnvloed het. Vier-en-veertig Cynodontia-skedels, wat tot elf genera behoort en uit Permiese, Triassiese en Jurassiese aardlae afkomstig is, is met behulp van neutron gerekenariseerde tomografie (NCT), by die SAFARI-1 Kernnavorsingsreaktor van die Suid-Afrikaanse Kernkragkorperasie (Necsa) geskandeer en ontleed. Inligting rakende die binneskedelvormafdrukke is hierdeur op 'n nie-vernietigende wyse bekom. Vier eksemplare, naamlik Galesaurus, Platycraniellus, Langbergia en Tritylodon, het suksesvolle skanderings geproduseer en is vir verdere studie gebruik. Afmetings van die skedelmateriaal is gebruik om die grootte van die breinafgietsels te bereken en die benaderde liggaamsmassa is bepaal uit 'n vergelyking wat van skedellengte gebruik maak. Die ensefalisasiekwosiënt (EK), 'n maatstaf van breingrootte relatief tot liggaamsgrootte, vir elke eksemplaar is bepaal deur breinvolume en liggaamsmassa te gebruik. Veranderinge in die ligging van die brein binne die skedel, en 'n algehele toename in grootte van die brein in die meer gevorderde Cynodontia dui op 'n neiging van ontwikkeling in die rigting van 'n meer soogdieragtige toestand. Taksonomiese variasie rakende die olfaktoriese lobbe en ander dele van die breinafgietsels is bespreek en verbind met verskille in ekologie of gedrag. Die relatief diep en groot olfaktoriese lobbe by sommige Cynodontia is dalk 'n aanpassing vir naglewende gedrag, dieet- of habitatsvoorkeure. Relatiewe groot breinafgietsels in Galesaurus, Platycraniellus, Massetognathus, Tritylodon, Chiniquodon en die Tritheledonta word toegeskryf aan habitatvoorkeur of sosiale gedrag. Die basale Epicynodontia Galesaurus en Platycraniellus het die grootste breinafgietsels van al die Cynodontia wat bestudeer is. Hulle groot breinafgietsels hou dalk verband met gedrags- of ekologiese voorkeure, maar die resultate benodig bevestiging van 'n groter monstergrootte. 'n Belangrike fondering word deur hierdie studie gebied, waaruit verdere breinafgietselstudies by Cynodontia ontwikkel kan word.	af
dc.description.sponsorship	National Research Foundation (NRF)	en_ZA
dc.identifier.uri	http://hdl.handle.net/11660/7631
dc.language.iso	en	en_ZA
dc.publisher	University of the Free State	en_ZA
dc.rights.holder	University of the Free State	en_ZA
dc.subject	Computerised tomography	en_ZA
dc.subject	Cynodontia	en_ZA
dc.subject	Encephalization	en_ZA
dc.subject	Palaeoneurology	en_ZA
dc.subject	Paleontology, Triassic	en_ZA
dc.subject	Reptiles, Fossil	en_ZA
dc.subject	Therapsida	en_ZA
dc.subject	Fossils -- Morphology	en_ZA
dc.subject	Tomography	en_ZA
dc.subject	Dissertation (M.Sc. (Zoology and Entomology))--University of the Free State, 2010	en_ZA
dc.title	An examination of non-mammalian cynodont cranial endocasts	en_ZA
dc.type	Dissertation	en_ZA