Basic Terminology and the Broader Phylogenetic and Geological Framework

Mayr, Gérald

doi:10.1007/978-3-030-87645-6_2

Cited by 1 publication

(1 citation statement)

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“…Asteriornis maastrichtensis is one of only two well-represented Mesozoic taxa that have been confidently identified as members of Neornithes (crown group birds) (Clarke et al, 2005;Clarke et al, 2016;Field et al, 2020a;Mayr, 2022a), the sole clade of birds to survive the end-Cretaceous mass extinction (Longrich et al, 2011). The holotype and only known specimen, from the latest Cretaceous Belgium, consists of fragmentary post-cranial material and a nearly complete, three-dimensionally preserved skull (Field et al, 2020a).…”

Section: Introductionmentioning

confidence: 99%

Taphonomic damage obfuscates interpretation of the retroarticular region of theAsteriornismandible

Crane

Benito

Chen

et al. 2023

Preprint

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Asteriornis maastrichtensis, from the latest Cretaceous of Belgium, is among the oldest known crown bird fossils, and its three-dimensionally preserved skull provides the most substantial insights into the cranial morphology of early crown birds to date. Phylogenetic analyses recovered Asteriornis as a total-group member of Galloanserae (the clade uniting Galliformes and Anseriformes. One important feature supporting this placement was enlargement of the retroarticular processes, which form elongate caudal extensions of the mandible in extant Galloanserae. Here, we reinterpret the jaw of Asteriornis and illustrate that the caudalmost portion of the mandibles are in fact not preserved. Instead, the caudal extremities of both the left and right mandibular rami extend to the surface of the fossil block containing the holotype skull, where they have eroded away. The originally identified retroarticular process of the right mandible - which exhibits a morphology and orientation strikingly similar to the retroarticular processes of certain extant and fossil galloanserans, including the early Palaeogene total-clade anseriforms Conflicto and Nettapterornis - instead represents a twisted and caudally displaced medial process. Nonetheless, anatomical comparisons with extant taxa reveal that we are unable to exclude the possibility that Asteriornis exhibited robust retroarticular processes comparable to those of extant Galloanserae. In light of the reinterpreted morphology of the Asteriornis mandible, we update the original anatomical character matrix used to investigate its phylogenetic relationships, and our revised phylogenetic analyses continue to support its position as a total-group galloanseran, as initially interpreted. We demonstrate additional morphological traits of the mandible supporting this phylogenetic position and provide new data on the nature and distribution of retroarticular processes among early crown birds.

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