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Cretaceous ornithurine supports a neognathous crown bird ancestor

Nature volume 612, pages 100–105 (2022)Cite this article

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Abstract

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)13,14,15.

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Fig. 1: Skeletal reconstruction, axial pneumaticity and phylogenetic position of J. finalidens.
Fig. 2: Comparative pterygoid and palatal morphology of J. finalidens and representatives of the main neornithine lineages.
Fig. 3: Three-dimensional geometric morphospace of avian pterygoid morphology.

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Data availability

Scan data and surface meshes of all preserved elements of Janavis are housed on MorphoSource (https://www.morphosource.org/projects/000444955?locale=en; project ID 000444955), along with surface meshes of comparative taxa (https://www.morphosource.org/projects/000444956?locale=en; project ID 000444956). See Supplementary Information for a complete list of skeletal models and relevant links. Phylogenetic matrices and morphometric landmark coordinates are provided at Zenodo (zenodo.org; https://doi.org/10.5281/zenodo.6591303). The Life Science Identifier for Janavis is urn:lsid:zoobank.org:act:E02F4DBF-35EC-4194-AD70-8CADDB01CE2E.

Code availability

The code underpinning our morphometric analyses is provided at Zenodo (zenodo.org; https://doi.org/10.5281/zenodo.6591303).

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Acknowledgements

We thank R. Dortangs for collecting the specimen, K. Smithson for scanning support, M. Lowe for collections assistance, B. Creisler for etymological information, S. Finney for preparation assistance, G. Navalón for assistance with morphometric methods, A. Chen and L. Steell for proofreading and discussion, and R. Olivé for permission to use his artwork. J.B. acknowledges support from the Hesse Award from the American Ornithological Society and grants from the Jurassic Foundation and Paleontological Society. This work was funded by UKRI grant MR/S032177/1 to D.J.F. For the purpose of open access, the authors have applied a Creative Commons Attribution (CC-BY) license to any Author Accepted Manuscript version arising.

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Authors and Affiliations

  1. Department of Earth Sciences, University of Cambridge, Cambridge, UK

    Juan Benito, Pei-Chen Kuo, Klara E. Widrig & Daniel J. Field

  2. Natuurhistorisch Museum Maastricht, Maastricht, The Netherlands

    John W. M. Jagt

  3. Museum of Zoology, University of Cambridge, Cambridge, UK

    Daniel J. Field

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  1. Juan Benito
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Contributions

D.J.F. and J.B. conceived and designed the project. D.J.F. supervised the project. J.W.M.J. facilitated sample access and provided provenance data. J.B., K.E.W. and P.-C.K. segmented CT scans. J.B. and D.J.F. identified the pterygoid. J.B. and P.-C.K. performed analyses. The manuscript was written by J.B. and D.J.F., with input from all of the authors.

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Correspondence to Juan Benito or Daniel J. Field.

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Extended data figures and tables

Extended Data Fig. 1 Best-preserved cervical and thoracic vertebrae of Janavis finalidens.

(a) 6th or 7th cervical vertebra; (b) 7th or 8th cervical vertebra; (c) 1st thoracic vertebra (12th presacral); (d) 2nd thoracic vertebra (13th presacral); (e) 3rd thoracic vertebra (14th presacral); (f) 4th thoracic vertebra (15th presacral); (g) indeterminate mid-thoracic vertebra; (h) fragmentary indeterminate mid-thoracic vertebra. Scale bar equals 10 mm.

Extended Data Fig. 2 Additional non-vertebral skeletal elements of Janavis finalidens and comparative elements of Ichthyornis.

All elements belong to Janavis unless otherwise specified. (a) Isolated tooth; (b) left pterygoid; (c) left scapula; (d) detailed view of omal end of left scapula; (e) thoracic ribs; (f) ribcage (previously identified as lower jaws and portion of the zygoma; Dyke et al.19), with the five ribs coloured orange, green, yellow, and red, and the two thoracic vertebrae in blue and purple; (g) Cross sections of omal end of Janavis and Ichthyornis scapulae, showing the well preserved bone surface around the acromion region of Janavis; left, Janavis scapula with cross-sectional planes 1-4 indicated; top, cross-sections through Janavis scapula (including surrounding rock matrix); bottom, cross-sections through Ichthyornis scapula at equivalent positions (FHSM VP-18702, mirrored); (h) reconstructed left humerus; (i) distorted left humerus as preserved; (j) mirrored right humerus of Ichthyornis specimen KUVP 119673; (k) right manual phalanx II:1; (l) right manual phalanx II:1 of Ichthyornis specimen ALMNH PV93.2.133; (m) proximal portion of right femur; (n) fragmentary pedal phalanx. Ichthyornis specimen figures (I and K) modified from Benito et al.22. All scale bars equal 10 mm.

Extended Data Fig. 3 CT-cross sections and additional views illustrating pneumaticity of the thoracic vertebrae of Janavis finalidens and the apneumatic condition of Ichthyornis.

(a) 15th vertebra of Janavis; (b) 15th vertebra of Ichthyornis; (c) indeterminate mid-thoracic vertebra of Janavis; (d) indeterminate mid-thoracic vertebra of Ichthyornis. Position of cross-sections 1-6 shown on the left for each specimen. (e) Additional views of Janavis vertebrae illustrating the position and extent of pneumatic foramina; left to right: indeterminate mid-thoracic vertebra in caudolateral view, indeterminate mid-thoracic vertebra from (c) in dorsolateral (left) and caudolateral (right) views, and 15th vertebra from (b) in caudolateral view. Small red arrows in (a) and (c) indicate pneumatic foramina situated within the pleurocoels, and large red arrow in (a) corresponds to the large ventral pneumatic opening. Scale bars equal 10 mm.

Extended Data Fig. 4 Detailed pterygoid morphology of Janavis finalidens and selected neornithines.

All are left pterygoids except those of Anatalavis, Anas, Megapodius and Lophophorus, which are mirrored right pterygoids. BPC, contact with basipterygoid process; PC, contact with palatine (or hemipterygoid); PF, pneumatic foramen; QAS, quadrate articular surface; RP, rostral process. All scale bars equal 2.5 mm.

Extended Data Fig. 5 Detailed pterygoid morphology of selected neornithines.

Illustrated pterygoids from right side, except that of Pelecanus, which is a mirrored left pterygoid. BPC, contact with basipterygoid process; PC, contact with palatine (or hemipterygoid); PF, pneumatic foramen; QAS, quadrate articular surface. All scale bars equal 2.5 mm.

Extended Data Fig. 6 Phylogenetic position of Janavis finalidens.

(a) topology recovered from Bayesian analysis of a modified version of the morphological matrix from Wang et al.50 and Benito et al.22; (b) topology recovered from Bayesian analysis of a modified version of the morphological matrix from Torres et al.12 and Benito et al.22. Node values indicate Bayesian posterior probabilities. Genus names in white indicate taxa illustrated on the right side of the figure, with corresponding illustrations indicated by superscript numbers (illustrations not to scale). Branches in white indicate the position of Janavis, the focal taxon of this study. Illustrations are courtesy of R. Olivé, used with permission.

Extended Data Fig. 7 Landmarking scheme for ornithurine pterygoids.

Taxa shown exemplify the range of variation of the principal morphological structures within our sample. (a) pseudo-landmark curve delimiting the quadrate contact of the pterygoid in caudal view; (b) pseudo-landmark curve delimiting the hemipterygoid-palatine contact of the pterygoid in rostral view; (c) pseudo-landmark curve characterizing the shape of the “dorsal crest” of the pterygoid in dorsal view; (d) pseudo-landmark curve characterizing the shape of the “medial crest” of the pterygoid, which includes the rostral process in those taxa which possess one, in medial view; (e) pseudo-landmark curve characterizing the shape of the “ventral crest” of the pterygoid in ventral view; (f) pseudo-landmark curve delimiting the shape of the basipterygoid process contact of the pterygoid.

Extended Data Fig. 8 Bivariate morphospaces of three-dimensional avian pterygoid geometry.

Plots illustrate morphospace distribution on the three first principal component axes; proportion of geometric variance explained by each principal component indicated on axis labels. (a) PC1 vs PC2; (b) PC1 vs PC3; and (c) PC2 vs PC3. Colours indicate the phylogenetic affinities of the included taxa: Palaeognathae (yellow), Galliformes (burgundy), Anseriformes (pink), Neoaves (blue); fossil taxa indicated in grey and numbered (1 – Janavis, 2 – Dasornis, 3 – Anatalavis).

Extended Data Fig. 9 Geometric similarity among avialan pterygoids summarized using total Procrustes distance.

(a) heatmap of total Procrustes distance. All taxa included in our morphometric analyses are illustrated. Strong geometric similarity is indicated by blue portions of the heatmap (low Procrustes distances), weak geometric similarity is indicated by red portions of the heatmap (high Procrustes distances), and intermediate degrees of geometric similarity are indicated by shades of yellow. Heatmap illustrates strong geometric similarity between Janavis and Anseriformes, Galliformes, and Dasornis, weak geometric similarity with Palaeognathae, and limited similarity with Neoaves. Cladogram beneath the heatmap illustrates the phylogenetic relationships of all taxa included in the analyses (Dasornis is illustrated as an early stem anseriform, though this is only one of several potentially viable phylogenetic placements for Pelagornithidae; see main text). (b) summarized Procrustes distance values from Janavis to major neornithine clades, showing the minimum, maximum and mean distances between Janavis and representatives of Galliformes, Anseriformes, Neoaves and Palaeognathae. Distances are lowest between Janavis and members of Galliformes and Anseriformes; cell background colours correspond to the heatmap colour scale from (a). (c) Box plots illustrating the Procrustes distance distribution between Janavis and major neornithine clades. PD = Procrustes Distance. n = 32 independent taxa compared with Janavis (Dasornis excluded due to its uncertain phylogenetic position); Galliformes: mean = 0.29, median = 0.29, minimum = 0.24, 1st quartile (25th percentile) = 0.26, 3rd quartile (75th percentile) = 0.32, maximum = 0.34; Anseriformes: mean = 0.37, median = 0.36, minimum = 0.32, 1st quartile (25th percentile) = 0.33, 3rd quartile (75th percentile) = 0.41, maximum = 0.44; Neoaves: mean = 0.44, median = 0.44, minimum = 0.35, 1st quartile (25th percentile) = 0.38, 3rd quartile (75th percentile) = 0.49, maximum = 0.55; Palaeognathae: mean = 0.78, median = 0.79, minimum = 0.70, 1st quartile (25th percentile) = 0.72, 3rd quartile (75th percentile) = 0.83, maximum = 0.84.

Extended Data Fig. 10 Reconstructed ichthyornithine palatal morphology and comparative neornithine taxa.

(a) Skulls in palatal view, from left to right: composite Ichthyornithes skull reconstruction (see main text), Lophophorus impejanus, and Struthio camelus. Ichthyornithes palatal reconstruction produced using Ichthyornis dispar skull model from Field et al.24; the quadrate is a composite of I. dispar specimens BHI 6421 and AMNH FARB 32773 (yellow), palatine and hemipterygoid of I. dispar AMNH FARB 32773 (green, from Torres et al.11), and pterygoid from Janavis finalidens at 50% scale (blue). (b) Isolated views of composite Ichthyornithes palate morphology from A; (c) focused views of the quadrate-pterygoid contact (top) and the pterygoid-hemipterygoid/palatine contact (bottom) in anatomical connection and separated, in approximately ventral view, showing the close match between the contacts of the Ichthyornis quadrate and palatine-hemipterygoid and the Janavis pterygoid at 50% scale. Janavis pterygoid in (a) illustrated at 100%; Ichthyornis skull components in (a) illustrated at 200%. Scale bars equal 10 mm.

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Merged PDF including table of contents, additional background/provenance data, further detail on phylogenetic analyses, further detail on geometric morphometric analyses, morphological variation in the pterygoid and basisphenoid, additional morphological description and discussion, institutional abbreviations, scan parameters, specimens included in the morphometric analyses, other comparative specimens, morphometric character descriptions, synapomorphies diagnosing key clades, morphological character descriptions, MorphoSource links, supplementary references.

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Benito, J., Kuo, PC., Widrig, K.E. et al. Cretaceous ornithurine supports a neognathous crown bird ancestor. Nature 612, 100–105 (2022). https://doi.org/10.1038/s41586-022-05445-y

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