Homology of fin lepidotrichia in osteichthyan fishes

Authors: Johanson, Zerina1; Burrow, Carole2; Warren, Anne3; Garvey, Jillian4

Source: Lethaia, Volume 38, Number 1, 1 March 2005 , pp. 27-36(10)

Publisher: Taylor and Francis Ltd

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Lepidotrichia are dermal elements located at the distal margin of osteichthyan fins. In sarcopterygians and actinopterygians, the term has been used to denote the most distal bony hemisegments and also the more proximal, scale-covered segments which overlie endochondral bones of the fin. In certain sarcopterygian fishes, including the Rhizodontida, these more proximal, basal segments are very long, extending at least half the length of the fin. The basal segments have a subcircular cross section, rather than the crescentic cross section of the distal lepidotrichial hemisegments, which lack a scale cover and comprise short, generally regular, elements. In rhizodonts and other sarcopterygians, e.g. Eusthenopteron , the basal elements are the first to appear during fin development, followed by the endochondral bones and then the distal lepidotrichia. This sequence contradicts the ‘clock-face model' of fin development proposed by Thorogood in which the formation of endochondral bones is followed by development of lepidotrichia. However, if elongate basal ‘lepidotrichia' are not homologous with more distal, jointed lepidotrichia and if the latter form within a distal fin-fold and the former outside this fold, then Thorogood's ‘clock-face' model remains valid. This interpretation might indicate that the fin-fold has been lost in early digited stem-tetrapods such as Acanthostega and Ichthyostega and elongate basal elements, but not true lepidotrichia, occur in the caudal fins of these taxa.

Keywords: Clock model; Eusthenopteron; Lepidotrichia; Osteichthyes; Rhizodontida; Sarcopterygii; ontogeny

Document Type: Research Article

DOI: http://dx.doi.org/10.1080/00241160510013141

Affiliations: 1: Palaeontology, Australian Museum, 6 College Street, Sydney, New South Wales, 2010, Australia, Email: zerinaj@austmus.gov.au 2: Department of Zoology and Entomology, University of Queensland, St. Lucia, Queensland, 4072, Australia, Email: C.Burrow@uq.edu.au 3: Department of Zoology, La Trobe University, Melbourne, Victoria, 3086, Australia, Email: a.warren@latrobe.edu.au 4: Department of Zoology, La Trobe University, Melbourne, Victoria, 3086, Australia, Email: j.garvey@latrobe.edu.au

Publication date: March 1, 2005

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