Janavis finalidens, gen. et sp. nov. (1 Viewer)

[Fred Ruhe]

Juan Benito, Pei Chen Kuo, Klara E. Widrig, John W. M. Jagt. Daniel J. Field, 2022

Cretaceous ornithurine supports a neognathous crown bird ancestor

Nature. 612 (7938): 100–105
doi:10.1038/s41586-022-05445-y

Abstract:

Cretaceous ornithurine supports a neognathous crown bird ancestor - Nature

A new taxon of toothed Late Cretaceous ornithurine preserving a pterygoid is reported, overturning assumptions about the nature of the ancestral crown bird skull.

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The bony palate diagnoses the two deepest clades of extant birds: Neognathae and Palaeognathae1,2,3,4,5. Neognaths exhibit unfused palate bones and generally kinetic skulls, whereas palaeognaths possess comparatively rigid skulls with the pterygoid and palatine fused into a single element, a condition long considered ancestral for crown birds (Neornithes)3,5,6,7,8. However, fossil evidence of palatal remains from taxa close to the origin of Neornithes is scarce, hindering strong inferences regarding the ancestral condition of the neornithine palate. Here we report a new taxon of toothed Late Cretaceous ornithurine bearing a pterygoid that is remarkably similar to those of the extant neognath clade Galloanserae (waterfowl + landfowl). Janavis finalidens, gen. et sp. nov., is generally similar to the well-known Mesozoic ornithurine Ichthyornis in its overall morphology, although Janavis is much larger and exhibits a substantially greater degree of postcranial pneumaticity. We recovered Janavis as the first-known well-represented member of Ichthyornithes other than Ichthyornis, clearly substantiating the persistence of the clade into the latest Cretaceous9. Janavis confirms the presence of an anatomically neognathous palate in at least some Mesozoic non-crown ornithurines10,11,12, suggesting that pterygoids similar to those of extant Galloanserae may be plesiomorphic for crown birds. Our results, combined with recent evidence on the ichthyornithine palatine12, overturn longstanding assumptions about the ancestral crown bird palate, and should prompt reevaluation of the purported galloanseran affinities of several bizarre early Cenozoic groups such as the ‘pseudotoothed birds’ (Pelagornithidae)

Enjoy,

Fred

 

[Fred Ruhe]

Systematic palaeontology

Avialae Gauthier, 1986 sensu Benito et al. 2022
Ornithurae Haeckel, 1866
Ichthyornithes Marsh, 1873b sensu Benito et al. 2022

Janavis finalidens gen. nov. sp. nov.

Etymology Janavis from the Roman god Janus and the Latin avis for bird. In Roman mythology, Janus is the god of beginnings, endings and transitions, reflecting transitional aspects of the morphology of Janavis (combining plesiomorphic features such as teeth with a neognath-like
palate) as well as its temporal provenance (deriving from the uppermost Cretaceous, making it one of the youngest non-neornithine avialan fossils in the world). The specific epithet finalidens, from the Latin finalis (adj.), meaning ending or final, and dens, for teeth, reflects the fact that the specimen is among the latest-known toothed avialans, which appear to have died out in the end-Cretaceous mass extinction shortly after Janavis lived.

Holotype Natuurhistorisch Museum Maastricht (NHMM) RD 271, a partial skeleton preserved in matrix, and associated elements extracted from the matrix by the collector, R. Dortangs, previously reported by Dyke et al.19 (Fig. 1a; see Supplementary Information for character information, measurements, additional description and discussion).
Elements preserved within the main block include six cervical and four thoracic vertebrae, six ribs, a left scapula, a nearly complete left humerus, a right manual phalanx II:1, a proximal fragment of the right femur and several unidentifiable fragments (Extended Data Figs. 1 and 2). Elements fully extracted from the matrix include an isolated tooth, the
complete left pterygoid preserved in two pieces, three thoracic vertebrae and a partial pedal phalanx (Extended Data Figs. 1 and 2). Several of these elements were left undescribed, unfigured or misidentified in the original report of the specimen19 (Fig. 1); see ‘Description’, ‘Materials’
and Supplementary Information for further details.

Locality and age CBR-Romontbos Quarry, Eben-Emael, Liège, Belgium.Valkenburg Member (67–66.9 million years ago20), Maastricht Formation, late Maastrichtian, Late Cretaceous. Additional details regarding the locality and stratigraphic setting are provided in the Supplementary Information.

Diagnosis Janavis is distinguished from other known Euornithes, and from Ichthyornis in particular, by the greater degree of pneumaticity of its thoracic vertebrae and ribs, especially the presence of large ventral pneumatic openings in the anterior thoracic vertebrae and fenestrated ventrolateral tubercles on the fifteenth presacral vertebra (Fig. 1b and Extended Data Figs. 1 and 3). It is also distinguished by the complete absence of an acromion process on the scapula21,22 (Extended Data Fig. 2d) and, most obviously, by its much larger size (maximum length of the Janavis humerus is 134.8 mm; maximum length of the longest known Ichthyornis humerus, YPM 1742, is 71.5 mm21). Additional character combinations from phylogenetic analyses that diagnose Janavis are presented in the Supplementary Information.

Fred


Fig. 1 | Skeletal reconstruction, axial pneumaticity and phylogenetic position of J. finalidens.
a, Skeletal reconstruction of J. finalidens (NHMM RD 271), including all preserved skeletal elements, compared with a composite skeleton of I. dispar illustrated at the same scale. Skeletal elements in yellow indicate previously unreported elements, and those in blue indicate elements reidentified in this study.
b, CT cross-sections illustrating the apneumatic thoracic vertebrae of Ichthyornis compared with the extensively pneumatized thoracic vertebrae of J. finalidens. The red arrowheads indicate pneumatic foramina.
c, Time-scaled phylogenetic tree showing the phylogenetic position and stratigraphic provenance of J. finalidens. The topology is simplified; see Extended Data Fig. 6 for full phylogenetic results. The orange branches denote non-ornithothoracine Avialae, the yellow branches denote Enantiornithes, the light blue branches denote paraphyletic ‘non-ornithurine Euornithes’ and the dark blue branches denote Ornithurae. The boxes at the tips of phylogenetic
branches represent the temporal range of a taxon inclusive of stratigraphic uncertainty; the triangles at the tips of phylogenetic branches represent clades comprising more than one known species, with their length indicating the
approximate temporal range of the known representatives of the collapsed clade. Illustrations of representative species for each lineage are depicted, from top to bottom: Eoconfuciusornis zhengi (Confuciusornithiformes), Eoalulavis hoyasi (Enantiornithes), Archaeorhynchus spathula, Longicrusavis houi (Hongshanornithidae), Abitusavis lii (‘Yanornithidae’), Iteravis huchzermeyeri, Gansus yumenensis, I. dispar and J. finalidens (Ichthyornithes), Brodavis varneri (Hesperornithes), Iaceornis marshi, and Asteriornis
maastrichtensis (Neornithes). Background colours mark geological stages. Camp., Campanian; Cenom., Cenomanian; Con., Coniacian; Jur., Jurassic; Ma, million years ago; Maast., Maastrichtian; Sant., Santonian. The skeletal reconstruction of Ichthyornis was modified from Benito et al.