Mesozoic birds display considerable diversity in size, flight adaptations and feather organization, but exhibit relatively conserved patterns of beak shape and development. Although Neornithine (that is, crown group) birds also exhibit constraint on facial development, they have comparatively diverse beak morphologies associated with a range of feeding and behavioural ecologies, in contrast to Mesozoic birds. Here we describe a crow-sized stem bird, Falcatakely forsterae gen. et sp. nov., from the Late Cretaceous epoch of Madagascar that possesses a long and deep rostrum, an expression of beak morphology that was previously unknown among Mesozoic birds and is superficially similar to that of a variety of crown-group birds (for example, toucans). The rostrum of Falcatakely is composed of an expansive edentulous maxilla and a small tooth-bearing premaxilla. Morphometric analyses of individual bony elements and three-dimensional  rostrum shape reveal the development of a neornithine-like facial anatomy despite the retention of a maxilla–premaxilla organization that is similar to that of  nonavialan theropods. The patterning and increased height of the rostrum in Falcatakely reveals a degree of developmental lability and increased morphological disparity that was previously unknown in early branching avialans. Expression of this phenotype (and presumed ecology) in a stem bird underscores that consolidation to the neornithine-like, premaxilla-dominated rostrum was not an evolutionary prerequisite for beak enlargement.

See supplementary file (PDF) for methods used in this paper.

1. O'Connor et al Supplementary File: Supplementary tables/appendices: 3D coordinate changes related to digital reconstructions, landmark identification for geometric morphometric analyses, list of phylogenetic characters, list of supplementary figure captions, etc.

2. TWIG_primary: Nexus File, with executable fxs for Bayesian analysis conducted in paper based on modified matrix from the Theropod Working Group (TWIG) iterations of Turner et al. (2012) and Brusatte et al. (2014). [A. Turner]

3. TWIG_primary_MRC. Tree file (Majority Rule Consensus) of the Bayesian analysis using the TWIG matrix. [A. Turner]

4. Falcatakely_SS_analyses: Nexus File, with executable fxs for Bayesian analysis conducted in paper based on modified matrix from the Theropod Working Group (TWIG) iterations of Turner et al. (2012) and Brusatte et al. (2014); used in stepping stone analysis and alternative hypothesis testing for the position of Falcatakely [A. Turner]

5. TWIG_primary_apomorphies.txt. Listing of node-specific support information based on the TWIG analysis. [A. Turner]

6. WEA2019_primary: Nexus File, with executable fxs for Bayesian analysis conducted in paper and based on modified matrix from Wang and Zhou (2019), with modifications from Field et al. (2018). [A. Turner]

7. WEA_primary_MRC. Tree file (Majority Rule Consensus) of the Bayesian analysis using the Wang and Zhou (2019) WEA matrix. [A. Turner]

8. WEA_partitioned: Nexus File, with executable fxs for Bayesian analysis conducted in paper and based on modified matrix from Wang and Zhou (2019), with modifications from Field et al. (2018); partitioning reflects cranial versus postcranial character data [A. Turner]

9. WEA_sensitivity_archaeopteryx: Nexus File, with executable fxs for Bayesian analysis conducted in paper and based on modified matrix from Wang and Zhou (2019), with modifications from Field et al. (2018); sensitivity reflects coding Archaeopteryx for just cranial data [A. Turner]

10. WEA_sensitivity_sapeornis: Nexus File, with executable fxs for Bayesian analysis conducted in paper and based on modified matrix from Wang and Zhou (2019), with modifications from Field et al. (2018); sensitivity reflects coding Sapeornis for just cranial data [A. Turner]

11. WEA_primary_apomorphies.txt. Listing of node-specific support information based on the Wang and Zhou (2019), with modifications from Field et al. (2018), analysis. [A. Turner]

12. Falcatakely_Interactive morphospace plot of 3D rostrum shape. HTML file.  Plot of first two principal components of 3D landmark analysis of rostrum of Falcatakely forsterae and extant avian taxa. Hovering over data points reveals species name and order. Supraordinal groups can be toggled on/off by clicking on the legend.This is an .html document that can be viewed in standard web browsers. [R. Felice]

13. 3D PDF S1. Polygon surface models (from CT data) for in-situ reconstruction. [Groenke]

14. 3D PDF S2. Polygon surface models (from CT data) for Beauchêne-style reconstruction. [Groenke]