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Abstract
The extinct Odontopterygiformes are the sole birds known to possess strong and sharp bony pseudoteeth, the shape and location of which are closely mimetic of real teeth. The structure of the pseudoteeth is investigated here in a late Pliocene/early Pleistocene species, Pelagornis mauretanicus, using X-ray microtomography and thin sections. The results are interpreted with regard to the pseudotooth mode of growth, and have implications concerning aspects of Pelagornis ecology. The larger pseudoteeth are hollow and approximately cone-shaped, and the smaller ones are rostro-caudally constricted. The walls of pseudoteeth are composed of bone tissue of the fibro-lamellar type, which is intensively remodeled by Haversian substitution. The jaw bones display the same structure as the pseudoteeth, but their vascular canals are oriented parallel to the long axis of the bones, whereas they are perpendicular to this direction in the pseudoteeth. There is no hiatus or evidence of a fusion between the pseudoteeth and the jaw bones. Two possible models for pseudotooth growth are derived from the histological data. The most plausible model is that pseudotooth growth began after the completion of jaw bone growth, as a simple local protraction of periosteal osteogenic activity. Pseudotooth development thus occurred relatively late during ontogeny. The highly vascularized structure and the relative abundance of parallel-fibered bone tissue in the pseudoteeth suggest poor mechanical capabilities. The pseudoteeth were most likely covered and protected by the hardened, keratinized rhamphotheca in the adult during life. The late development of the pseudoteeth would involve a similarly late and/or partial hardening of the rhamphotheca, as displayed by extant Anseriformes, Apterygiformes and some Charadriiformes. This would add support to the hypothesis of a close phylogenetic relationship between Odontopterygiformes and Anseriformes. The late maturation of the Pelagornis feeding apparatus, and hence the delayed capability for efficient prey catching, suggests that Pelagornis was altricial.
Highlights
All living birds (Neornithes, approximately 9900 species) are toothless, and they represent 94% of all edentulous living tetrapods [1,2]
The pseudoteeth are made of a bone tissue intensely remodeled by the Haversian process, and housing numerous vascular canals that open at the cortical surface
The interpretive sketch of a thin section provided in Howard ([3]: fig. 5), shows ‘‘circumferential lamellae’’ that are observed neither on the jaw bones nor on the pseudoteeth of our P. mauretanicus specimens
Summary
All living birds (Neornithes, approximately 9900 species) are toothless, and they represent 94% of all edentulous living tetrapods [1,2]. It is all the more surprising that a single, distinctive extinct avian clade, the Odontopterygiformes, developed bony pseudoteeth [3] resembling true teeth, a character most likely derived subsequent to neornithine edentulism [2]. This pseudodentition has peculiar characteristics, and displays an original distribution pattern with pseudoteeth of uneven sizes arranged in regular ‘‘waves’’ [3,4,5,6,7,8,9]. The only other bird clade displaying a series of bony odontoids, albeit much less developed and sharp than in the Ondontopterygiformes, were some of the recently extinct ‘goose-like’ moa-nalos of the Hawaiian Islands [16]
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