{"scopus_import":"1","date_published":"2014-01-01T00:00:00Z","_id":"2248","abstract":[{"text":"Avian forelimb digit homology remains one of the standard themes in comparative biology and EvoDevo research. In order to resolve the apparent contradictions between embryological and paleontological evidence a variety of hypotheses have been presented in recent years. The proposals range from excluding birds from the dinosaur clade, to assignments of homology by different criteria, or even assuming a hexadactyl tetrapod limb ground state. At present two approaches prevail: the frame shift hypothesis and the pyramid reduction hypothesis. While the former postulates a homeotic shift of digit identities, the latter argues for a gradual bilateral reduction of phalanges and digits. Here we present a new model that integrates elements from both hypotheses with the existing experimental and fossil evidence. We start from the main feature common to both earlier concepts, the initiating ontogenetic event: reduction and loss of the anterior-most digit. It is proposed that a concerted mechanism of molecular regulation and developmental mechanics is capable of shifting the boundaries of hoxD expression in embryonic forelimb buds as well as changing the digit phenotypes. Based on a distinction between positional (topological) and compositional (phenotypic) homology criteria, we argue that the identity of the avian digits is II, III, IV, despite a partially altered phenotype. Finally, we introduce an alternative digit reduction scheme that reconciles the current fossil evidence with the presented molecular-morphogenetic model. Our approach identifies specific experiments that allow to test whether gene expression can be shifted and digit phenotypes can be altered by induced digit loss or digit gain.","lang":"eng"}],"department":[{"_id":"CaHe"}],"article_processing_charge":"No","year":"2014","intvolume":"       322","publication_identifier":{"issn":["1552-5007"]},"publisher":"Wiley-Blackwell","volume":322,"title":"Thumbs down: A molecular-morphogenetic approach to avian digit homology","type":"journal_article","publication":"Journal of Experimental Zoology Part B: Molecular and Developmental Evolution","author":[{"full_name":"Capek, Daniel","orcid":"0000-0001-5199-9940","first_name":"Daniel","last_name":"Capek","id":"31C42484-F248-11E8-B48F-1D18A9856A87"},{"last_name":"Metscher","full_name":"Metscher, Brian","first_name":"Brian"},{"first_name":"Gerd","full_name":"Müller, Gerd","last_name":"Müller"}],"date_created":"2018-12-11T11:56:33Z","status":"public","page":"1 - 12","publist_id":"4701","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","publication_status":"published","month":"01","quality_controlled":"1","issue":"1","date_updated":"2025-04-17T16:21:35Z","language":[{"iso":"eng"}],"doi":"10.1002/jez.b.22545","day":"01","oa_version":"None"}