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The braincase and inner ear of Placodus gigas(Sauropterygia, Placodontia) — a new reconstruction based on micro-computed tomographic data


Neenan, James M; Scheyer, Torsten M (2012). The braincase and inner ear of Placodus gigas(Sauropterygia, Placodontia) — a new reconstruction based on micro-computed tomographic data. Journal of Vertebrate Paleontology, 32(6):1350-1357.

Abstract

Placodus gigas is an unarmored placodont marine reptile (Diapsida, Sauropterygia) known from the Middle Triassic of Europe, most commonly found in the shallow marine carbonate facies of the German Muschelkalk (lower Anisian to middle Ladinian, approximately 243–235 Ma). Generally, the morphology of the skull is well understood, with the exception of the braincase, which is partially obscured by dermatocranial bone. Two skulls that display well-preserved and intact chondrocranial elements were scanned using industrial micro-computed tomography (μCT), thus revealing parts of the braincase that were previously obscured and allowing a new three-dimensional reconstruction of the region to be constructed. This includes a complete osteological description, the first reconstruction of a sauropterygian vestibular apparatus, and a new virtual cranial endocast. The morphology of the braincase and sphenoid region has been revised, revealing the position of the hypophyseal pit. The enigmatic ‘alisphenoid bridge’ has been reinterpreted as being a dorsally extended dorsum sellae. The vestibular apparatus is shown to have strongly dorsoventrally compressed vertical semicircular canals, a commonly observed morphology of other marine reptiles, and an ‘alert’ head position of about 20°, indicating a highly aquatic lifestyle. Because placodonts are the sister group to all other sauropterygians, these new data are of great comparative and phylogenetic significance, providing insight into some of the morphological and functional changes that occurred on the stem leading to the more derived sauropterygians.

Abstract

Placodus gigas is an unarmored placodont marine reptile (Diapsida, Sauropterygia) known from the Middle Triassic of Europe, most commonly found in the shallow marine carbonate facies of the German Muschelkalk (lower Anisian to middle Ladinian, approximately 243–235 Ma). Generally, the morphology of the skull is well understood, with the exception of the braincase, which is partially obscured by dermatocranial bone. Two skulls that display well-preserved and intact chondrocranial elements were scanned using industrial micro-computed tomography (μCT), thus revealing parts of the braincase that were previously obscured and allowing a new three-dimensional reconstruction of the region to be constructed. This includes a complete osteological description, the first reconstruction of a sauropterygian vestibular apparatus, and a new virtual cranial endocast. The morphology of the braincase and sphenoid region has been revised, revealing the position of the hypophyseal pit. The enigmatic ‘alisphenoid bridge’ has been reinterpreted as being a dorsally extended dorsum sellae. The vestibular apparatus is shown to have strongly dorsoventrally compressed vertical semicircular canals, a commonly observed morphology of other marine reptiles, and an ‘alert’ head position of about 20°, indicating a highly aquatic lifestyle. Because placodonts are the sister group to all other sauropterygians, these new data are of great comparative and phylogenetic significance, providing insight into some of the morphological and functional changes that occurred on the stem leading to the more derived sauropterygians.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Paleontological Institute and Museum
Dewey Decimal Classification:560 Fossils & prehistoric life
Language:English
Date:2012
Deposited On:01 Nov 2012 08:35
Last Modified:05 Apr 2016 16:03
Publisher:Taylor & Francis
ISSN:0272-4634
Publisher DOI:https://doi.org/10.1080/02724634.2012.695241

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