The position of the claws in Noasauridae (Dinosauria: Abelisauroidea) and its implications for abelisauroid manus evolution |
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Authors: | Federico L Agnolin Pablo Chiarelli |
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Institution: | 1.Laboratorio de Anatomía Comparada y Evolución de los Vertebrados,Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”,Buenos Aires,Argentina;2.Fundación de Historia Natural “Félix de Azara”, Departamento de Ciencias Naturales y Antropología,CEBBAD, Universidad Maimónides,Buenos Aires,Argentina |
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Abstract: | In this note we reassess the position of putative pedal phalanges of some South American noasaurid theropods (Abelisauroidea).
Noasaurids were considered as to be distinctive abelisauroids with a peculiar “sickle claw” on the second toe of the foot,
convergently developed with that of deinonychosaurians. Among noasaurids, the Argentinean species Noasaurus leali (latest Cretaceous) and Ligabueino andesi (Early Cretaceous) are known from incomplete specimens, including dissarticulated non-ungueal phalanges, and, in N. leali, a claw. A detailed overview of these elements indicates that the supposed raptorial claw of the second pedal digit of N. leali actually belongs to the first or second finger of the manus, and the putative pedal non-ungual phalanges of both genera also
pertain to the manus. Thus, the new interpretations of noasaurid pedal morphology blur the distinctions between Noasauridae
and Velocisauridae proposed by previous authors. Finally, we suggest, on the basis of phalangeal and metacarpal morphology,
that abelisaurids probably lost their manual claws by means of the loss of function of the HOXA11 and HOXD11 genes. Thus Noasauridae
differs from Abelisauridae in retaining plesiomorphic long forelimbs with well developed claws, as occurs plesiomorphically
in most basal theropods (e.g., Coelophysis). |
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