Has the importance of the amniote egg been overstated?

Authors
Citation
J. Skulan, Has the importance of the amniote egg been overstated?, ZOOL J LINN, 130(2), 2000, pp. 235-261
Citations number
136
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Animal Sciences
Journal title
ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY
ISSN journal
0024-4082 → ACNP
Volume
130
Issue
2
Year of publication
2000
Pages
235 - 261
Database
ISI
SICI code
0024-4082(200010)130:2<235:HTIOTA>2.0.ZU;2-8
Abstract
The evolution of the amniote egg is commonly regarded as an important miles tone in the history of the vertebrates, an innovation that completed the tr ansition from aquatic to fully terrestrial existence by permitting eggs to be laid away from standing water. This view dern es ultimately from the rec apitulationist theories of Haeckel, and rests on the assumption that extant frogs and salamanders are good models for the reproductive habits of early tetrapods and the ancestors of the amniotes. It also assumes that it is mo re difficult to lay eggs on land than in water, and that the amniote egg is an adaptation to the physical rigours that eggs encounter in terrestrial e nvironments. Taken together, these assumptions comprise what may be termed the 'Haeckelian framework' for the origin of vertebrate terrestriality. Sev eral independent. lines of evidence suggest chat the assumptions of the Hae ckelian Framework are false. There appear to be no theoretical reasons to a ssume that the evolution of terrestrial egg-laying was difficult, or requir ed a structure as elaborate as the anmiote egg. The physical conditions egg s encounter in the terrestrial environments where they are actually laid ar e quite mild. Land may in fact be an easier place to lay eggs than water. I n addition, analysis of the distribution of key reproductive character stat es among vertebrates provides no evidence that the 'typical amphibian' repr oductive mode is primitive for tetrapos. Amniotes are as likely as frogs or salamanders to retain primitive reproductive character stales. (C) 2000 Th e Linnean Society or London.