Jaw anatomy of Vegavis iaai (1 Viewer)

[Fred Ruhe]

Gerardo P. Álvarez-Herrera, Sebastián Rozadilla, Federico L. Agnolín & Fernando E. Novas, 2024

Jaw anatomy of Vegavis iaai (Clarke et al., 2005) from the Late Cretaceous Antarctica, and its phylogenetic implications

Geobios, Volume 83, April 2024, Pages 11-20

Abstract​

Vegavis iaai is without any doubt the most complete and well-known Mesozoic bird from Antarctica. In spite of being known by several specimens, its highly specialized postcranial anatomy has obscured the recognition of its phylogenetic affinities. Skull material from Vegavis is scarce, and the lower jaw is known by a relatively well-preserved articular region of a partially articulated specimen (MACN-PV 19.748). The aim of the present contribution is to describe this articular region and to analyze its potential phylogenetic information. The articular region of Vegavis shows a unique combination of characters that separates it from most Mesozoic lineages. On the contrary, its anatomy is congruent with that of neornithine birds, and particularly from the neoavian clade Aequorlitornithes. Detailed comparisons led to the recognition of several shared features, including a well-developed transverse crest posterior to the articular cotyles, that bears a well-developed lateral tubercle; a short and ventrally deflected retroarticular process; a dorsally exposed posterior fossa; tree cotyles for jaw articulation, with a well-developed caudal cotyle fused to the medial cotyle; and lateral crest anteriorly projected with respect to the lateral cotyle. The three-cotyle articulation of the jaw of Vegavis invited us to review skull anatomy of its close kin Polarornis. A review of the bones of Polarornis indicates that the element previously identified as a quadrate is an uncertain bone, and thus, skull-jaw articulation of this taxon remains unknown. In contrast with previous contributions, we were not able to find diagnostic features of the Galloanserae clade on Vegavis jaw. The neoavian-like jaw of Vegavis contrasts with the anseriform signature of its postcranium, suggesting that this bird held some kind of morphological mosaicism on its skeleton.

Enjoy,

Fred

 

[Fred Ruhe]

Systematic paleontology

Aves Linnaeus, 1758
Ornithurae Haeckel, 1866
Neornithes Gadow, 1893
Vegaviidae Agnolín et al., 2017
Vegavis iaai Clarke et al., 2005

Emended diagnosis (based on Clarke et al., 2005, 2016; Agnolín
et al., 2017; Acosta-Hospitaleche and Worthy, 2021; present
study): Vegavis iaai shows the following unique combination of
apomorphies: (i) mandible with dorsoventrally high transverse
crest, with an anteriorly deflected lateral tubercle and a concave
anterior surface; (ii) lateral crest of mandible reaches the level of
the dorsal margin of the tomial crest, and both are separated by
a wide and deep longitudinal fossa; (iii) retroarticular process with
a thick and laterally emarginated posterolateral rim; (iv) a subcircular depression on the proximal femur.

Fred


Fig. 1. Mandible of Vegavis iaai (MACN-PV 19.748) in medial (A, A’), lateral (B, B’), dorsal (C, C’), ventral (D, D’), and posterior (E, E’) views. B is modified from Clarke et al. (2016). Abbreviations: ds, dorsal sulcus; lc, lateral cotyle; lcr, lateral crest; lt, lateral tubercle; pf, posterior fossa; pmc, posterior mandibular cotyle; rap, retroarticular process; tocr, tomial crest; trcr, transversal crest. Scale bar: 1 cm.