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1 February 2013 A New Species of Auk (Charadriiformes, Pan-Alcidae) from the Miocene of Mexico
N. Adam Smith
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A fossil from the Middle Miocene Rosarito Beach Formation of Baja California represents a previously undescribed, auklet-sized species of wing-propelled diving Pan-Alcidae (Aves, Charadriiformes). This new taxon, Divisulcus demerei, is recognized from the presence of a bifurcated scapulotricipital sulcus of the distal end of the humerus, a potentially neomorphic character within Aves. Additionally, the degree of compression of the humeral shaft of this new species is less than that of other pan-alcids. These characters may represent retention of ancestral character states that are associated with the transition to wing-propelled diving from nondiving Charadriiformes. This discovery provides further information regarding paleodiversity in this clade, extends the geographic range of Miocene pan-alcids, and may represent the oldest record of the clade from the Pacific Ocean basin, as previously reported unambiguous records are from Late Miocene or younger deposits (∼10–1.6 Ma). Moreover, the age of this new pan-alcid (14–16 Ma) corresponds with the timing of the Middle Miocene climatic optimum, a time for which previous records of Pacific Ocean basin pan-alcids were lacking. Because of the relative incompleteness of the specimen, the systematic position of this new taxon within the Pan-Alcidae from a phylogenetic analysis is not strongly supported. Until additional remains of D. demerei are recovered that can provide additional character data, the affinities of this new taxon within the Pan-Alcidae are uncertain.

© 2013 by The Cooper Ornithological Society. All rights reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press's Rights and Permissions website,
N. Adam Smith "A New Species of Auk (Charadriiformes, Pan-Alcidae) from the Miocene of Mexico," The Condor 115(1), 77-83, (1 February 2013).
Received: 11 April 2012; Accepted: 1 August 2012; Published: 1 February 2013
Divisulcus demerei
fossil seabird
wingpropelled divers.
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