Journal Article

The cranial endoskeleton of Tiktaalik roseae

Downs, Jason P., Daeschler, Edward B., Jenkins, Farish A., Shubin, Neil H.

2008

Overview

Among the morphological changes that occurred during the ‘fish-to-tetrapod’ transition was a marked reorganization of the cranial endoskeleton. Details of this transition, including the sequence of character acquisition, have not been evident from the fossil record. Here we describe the braincase, palatoquadrate and branchial skeleton of Tiktaalik roseae , the Late Devonian sarcopterygian fish most closely related to tetrapods. Although retaining a primitive configuration in many respects, the cranial endoskeleton of T. roseae shares derived features with tetrapods such as a large basal articulation and a flat, horizontally oriented entopterygoid. Other features in T. roseae , like the short, straight hyomandibula, show morphology intermediate between the condition observed in more primitive fish and that observed in tetrapods. The combination of characters in T. roseae helps to resolve the relative timing of modifications in the cranial endoskeleton. The sequence of modifications suggests changes in head mobility and intracranial kinesis that have ramifications for the origin of vertebrate terrestriality. Fins to limbs: joining the dots Details of the morphological changes involved in the vertebrate transition to land — including the order in which they occurred — are sparse. The fossil record is too sketchy to give a feature-by-feature timeline, but by examining multiple specimens of the braincase of the Devonian fossil Tiktaalik roseae , a transitional form between fishes and tetrapods, Downs et al. have filled in some of the gaps. Although primitive in many respects, some of T. roseae' s features nod to the tetrapod state. And by reference to this new view of Tiktaalik morphology, the transition from finned to limbed fossil forms can be more readily understood. The Devonian fossil Tiktaalik roseae represents a transitional form between fishes and tetrapods. This paper presents a detailed examination of the braincase of this creature. Although primitive in many respects, some features nod to the tetrapod state.

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: Analysis / Animals / Biological Evolution / Crossopterygians / Devonian / Earth sciences / Earth, ocean, space / Ecosystem / Exact sciences and technology / Fishes - anatomy & histology / Fishes - physiology / Fossils / Gills / Humanities and Social Sciences / Models, Biological / multidisciplinary / Paleontology / Physiological aspects / Respiratory system / Science / Science (multidisciplinary) / Skull / Skull - anatomy & histology / Skull - physiology / Vertebrate paleontology / Vertebrates