The rhamphotheca of the Eocene pseudo-toothed birds from Antarctica

ABSTRACT

The Pelagornithidae are an extinct group of soaring birds that lived all over the world between the early Palaeocene and the Pliocene-Pleistocene and are characterised by the presence of hollow denticles along the tomial edges formed by the expansion of the premaxillary, maxillary, and dentary bones. The presence of distinctive sulci in the upper and lower jaws together with the absence of wearing signs on the denticles, attributable to the handling of the prey, indicates the development of a resistant and compound rhamphotheca. To reconstruct it, we turned to the evidence provided by extant representatives with similar configurations and the osteological correlates of the beak. As a result, we propose a model for the middle-latest Eocene Antarctic Pelagornithidae, in which the rhamphotheca would have been formed by thick horny plates. The culminicorn was separated from the laternicorn by an extense sulcus nasi that continuous caudally to the apertura nasi ossea, a sturdy and hooked unguis maxillaris covering the rostrum, with small nares opening at the cranial end of the apertura nasi ossea, dorsal and ventral ramicorns, and a thick unguis mandibularis with a pseudomental fold and a sulcus on the mandible.

GRAPHICAL ABSTRACT

KEYWORDS:

• Pelagornithidae
• James Ross Basin
• beak morphology
• Paleogene
• Antarctic Peninsula

Acknowledgments

We thank to Mariana Picasso and Diego Montalti (MLP), Yolanda Davies (MACN), Sergio Bogan (Fundación Azara), and David Rubilar-Rogers (Museo Nacional de Historia Natural) for the access to the collections. To Universidad Nacional de La Plata and Consejo Nacional de Investigaciones Científicas y Tecnológicas for partial support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/08912963.2023.2230584.

Additional information

Funding

This work was partially supported by the Consejo Nacional de Investigaciones Científicas y Tecnológicas PIP 0096; Universidad Nacional de La Plata PID N955, and Agencia Nacional de Promoción Científica y Tecnológica PICT 2017 0607.