Título:
The ontogenetic transformation of the mesosaurid tarsus: a contribution to the origin of the primitive amniotic astragalus
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Autor:
Piñeiro Martínez, Graciela H.
Núñez Demarco, Pablo Andrés
Meneghel Morena, Melitta D.
Núñez Demarco, Pablo Andrés
Meneghel Morena, Melitta D.
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Artículo
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Palabras clave:
Mesosaur ontogeny
Astragalus formation
Evolutionary studies
Navicular origin
Implicated groups
Amniotes
Non Amniotes
Astragalus formation
Evolutionary studies
Navicular origin
Implicated groups
Amniotes
Non Amniotes
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Año de publicación:
2016
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Resumen:
The hypotheses about the origin of the primitive amniotic tarsus are very speculative.
Early studies argued that the origin of the astragalus, one of the largest proximal bones in
the tarsus of basal amniotes, was produced by either the fusion of two, three, or even four
of the original tarsal bones, the intermedium, the tibiale and the proximal centralia (c4
and c3), or that the intermedium alone transforms into the primitive astragalus. More
recent studies have shown that the structure of the tarsus in Captorhinus supports the
former hypothesis about a fusion of the intermedium, the tibiale, the proximal centrale
(c4) and eventually c3, producing a purportedly multipartite structure of the amniotic
astragalus, but the issue remained contentious. Very well preserved tarsi of the Early
Permian aquatic amniote Mesosaurus tenuidens Gervais, 1864 1865, which represent
the most complete ontogenetic succession known for a basal amniote (the other
exceptional one is provided by the Late Permian diapsid Hovasaurus boulei Piveteau,
1926), suggest that there is more than one ossification center for the astragalus and
that these fuse during late embryonic stages or maybe early after birth. A non-hatched
Mesosaurus in an advanced stage of development shows that the tarsus is represented by
a single bone, most probably the astragalus, which seems to be formed by the suturing
of three bones, here interpreted as being the intermedium, the tibiale, probably already
integrated to the c4 in an earlier stage of the development, and the c3. An amniote-like
tarsal structure is observed in very basal Carboniferous and Permian tetrapods such as
Proterogyrinus, Gephyrostegus, the diadectids Diadectes and Orobates, some microsaurs
like Tuditanus and Pantylus and possibly Westlothiana, taxa that were all considered as
true amniotes in their original descriptions. Therefore, the structure of the amniotic
tarsus, including the configuration of the proximal series formed by the astragalus and
the calcaneum, typically a pair of enlarged bones, could have been established well
before the first recognized amniote walked on Earth. Accordingly, the tarsus of these
taxa does not constitute specialized convergences that appeared in unrelated groups,
they might be instead, part of a transformation series that involves taxa closely related
to the early amniotes as some hypotheses have suggested.
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PeerJ Inc
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PeerJ, 2016, (4 ), e2036
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Citación:
Piñeiro, G., Núñez, P., Meneghel, M. "The ontogenetic transformation of the mesosaurid tarsus: a contribution to the origin of the primitive amniotic astragalus". PeerJ [en línea]. 2016 (4 ), e2036. doi: 10.7717/peerj.2036
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2167-8359
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Licencia Creative Commons Atribución (CC - By 4.0)
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| Ficheros | Descripción | Tamaño | Formato | ||
|---|---|---|---|---|---|
| 107717peerj2036.pdf | — | 73.92 MB | Adobe PDF |