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Reevaluation of the homology of bones of the cranial vault in tetrapod vertebrates
Author(s) -
Maddin Hillary,
Piekarski Nadine,
Sefton Elizabeth,
Hanken James
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.867.2
Subject(s) - cranial vault , biology , anatomy , amniote , mesoderm , parietal bone , ectoderm , cranial neural crest , tetrapod (structure) , evolutionary biology , skull , vertebrate , neural crest , paleontology , embryogenesis , genetics , embryonic stem cell , embryo , gene
Homology assessments of bones are made using one or more criteria (e.g., topology, development, phylogeny). In tetrapods, the bones of the cranial vault appear highly conserved topologically. However, recent fate maps have revealed key differences in the embryonic origin of bones of the cranial vault in representatives of two amniote lineages. In mouse, the frontal is derived from cranial neural crest (CNC) and the parietal of mesoderm, placing the CNC‐mesoderm boundary at the suture between these bones. In chicken, by contrast, this boundary is located within the frontal, which thus has a dual embryonic origin. This difference is seemingly inconsistent with the traditional assessment of homology of the avian frontal with that of mammals and other tetrapods. To elucidate this apparent conflict, we fate‐mapped CNC and mesoderm using GFP‐transgenic axolotls to reveal specific contributions to the cranial vault. The CNC‐mesoderm boundary in axolotl is located between frontal and parietal, as in mouse, but differs from that in chicken. If, however, the avian frontal is instead regarded as a fused frontal and parietal (i.e., frontoparietal) and the parietal a postparietal, then the avian cranial vault remains topologically congruent, and becomes developmentally congruent, with that of both urodeles and mammals. This hypothesis is supported by data from the fossil record: a separate frontal, parietal and postparietal is present in all stem lineages of extant taxa, including birds. Moreover, it implies that a postparietal is/was present in non‐avian archosaurs but likely fuses early in ontogeny to the parietal (or supraoccipital), as it does in many extant mammals.