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The hyomandibulae of rhizodontids (Sarcopterygii, Stem-Tetrapoda)
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Physiology and Developmental Biology, Evolutionary Organism Biology.
2008 (English)In: Journal of morphology (1931. Print), ISSN 0362-2525, Vol. 269, no 6, 654-665 p.Article in journal (Refereed) Published
Abstract [en]

Despite its important role in the study of the evolution of tetrapods, the hyomandibular bone (the homologue of the stapes in crown-group tetrapods) is known for only a few of the fish-like members of the tetrapod stem-group. The best-known example, that of the tristichopterid Eusthenopteron, has been used as an exemplar of fish-like stem-tetrapod hyomandibula morphology, but in truth the conditions at the base of the tetrapod radiation remain obscure. We report, here, four hyomandibulae, from three separate localities, which are referable to the Rhizodontida, the most basal clade of stem-tetrapods. These specimens share a number of characteristics, and are appreciably different from the small number of hyomandibulae reported for other fishlike stem-tetrapods. While it is unclear if these characteristics represent synapomorphies or symplesiomorphies, they highlight the morphological diversity of hyomandibulae within the early evolution of the tetrapod total-group. Well-preserved muscle scarring on some of these hyomandibulae permit more robust inferences of hyoid arch musculature in stem-tetrapods.

Place, publisher, year, edition, pages
2008. Vol. 269, no 6, 654-665 p.
Keyword [en]
Sarcopterygii, Rhizodontida, stem-tetrapod, hyomandibula, stapes, fossils
National Category
Biological Sciences
URN: urn:nbn:se:uu:diva-97739DOI: 10.1002/jmor.10609ISI: 000256598300003OAI: oai:DiVA.org:uu-97739DiVA: diva2:172792
Available from: 2008-10-29 Created: 2008-10-29 Last updated: 2009-11-02Bibliographically approved
In thesis
1. Endocranial Morphology and Phylogeny of Palaeozoic Gnathostomes (Jawed Vertebrates)
Open this publication in new window or tab >>Endocranial Morphology and Phylogeny of Palaeozoic Gnathostomes (Jawed Vertebrates)
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gnathostomes, or jawed vertebrates, make up the overwhelming majority of modern vertebrate diversity. Among living vertebrates, they comprise the chondrichthyans (“cartilaginous fishes” such as sharks, skates, rays, chimaeras) and the osteichthyans (“bony fishes” or bony vertebrates, inclusive of tetrapods). Gnathostomes appear to have originated in the early Palaeozoic Era, but their early fossil record is fairly scant. The best fossils appear first in the Late Silurian and Devonian periods. Much of gnathostome diversity owes to unique adaptations in the internal skeleton of their head (the endocranium). The endocranium is composed of the braincase, jaws, hyoid arch, and branchial arches, which sometimes fossilise when they are composed of bone or calcified cartilage.

The purpose of this thesis is to describe and compare the fossilised cranial endoskeletons of a variety of different Palaeozoic gnathostomes. The objective is to test current conceptions of gnathostome interrelationships (i.e. phylogeny) and infer aspects of key morphological transformations that took place during the evolution of Palaeozoic members of this group. Two key areas are examined: the morphology and interrelationships of Palaeozoic gnathostomes and the morphology of the visceral arches in sarcopterygian fishes.

New data on the visceral arches are described from the stem tetrapods Panderichthys and rhizodontids. These provide insight into the sequence of character acquisition leading to the tetrapod middle ear. Panderichthys shows key features of the tetrapod middle ear chamber were established prior to the origin fo digited limbs. New morphological data are described from the “acanthodian” fish Ptomacanthus. Ptomacanthus provides only the second example of a well-preserved braincase from any member of this group. It shows dramatic differences from that of its counterpart, Acanthodes, providing new evidence for acanthodian paraphyly. New interpretations of basal gnathostome and osteichthyan phylogeny are presented, challenging or enriching existing views of these problems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 50 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 570
systematics, palaeontology, anatomy, evolution
National Category
urn:nbn:se:uu:diva-9360 (URN)978-91-554-7330-3 (ISBN)
Public defence
2008-11-21, Lindahlsalen, Evolutionary Biology Centre, Norbyvägen 18A, Uppsala, Sweden, 09:00 (English)
Available from: 2008-10-29 Created: 2008-10-29 Last updated: 2009-04-03Bibliographically approved

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