Symposium

学术报告会

 

Title：Phenotypic Potential of the Avian Hand Elucidates Dinosaur Digit Homology

Reporter: Josef Stiegler (Department of Biology, The George Washington University)

Host: Shuo Wang  (Laboratory of Vertebrate Evolution)

Time：9:00 am, March 28^th, 2018

Room：理科楼430

 

Introduction：

Embryological evidence shows that the avian carpometacarpus is primarily derived from the middle three (II-IV) of the five tetrapod manual digits (I-V), while the paleontological consensus has long been that the digits of non-avian theropod dinosaurs correspond to digit positions I-III. Paleontologists and embryologists have proposed a series of hypotheses to resolve this conflict, each centered on a homeotic shift in digit identities from positions I-III to II-IV.

While some have adopted reference to the three functional digits of tetanuran theropod dinosaurs as II-IV and paleornithologists often use avian specific nomenclature (e.g. os metacarpale alulare, etc.), most paleontologists continue to refer to these digits as I-III, as the phylogenetic location of the proposed frame shift is not well understood. New evidence regarding the range of metacarpal phenotypes in extant birds informs this debate, and is evaluated in combination with common phenotypes of the manus in disparate non-avian theropod lineages.

The three functional digits present in coelurosaurs are most parsimoniously interpreted as being derived from positions II, III, and IV, and this hypothesis can be extended to earlier-diverging nodes within Tetanurae depending on the phylogenetic position of Megaraptora and the nature of the homeotic shift in digit identities (abrupt and complete vs. gradual and piecemeal). Three viable evolutionary developmental hypotheses (frame shift, limited frame shift, and lateral shift) are reviewed, and a path forward for paleontologists and embryologists to test hypotheses is discussed.

 

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