Skull morphology of Genyornis (1 Viewer)

[albertonykus]

McInerney, P.L., J.C. Blokland, and T.H. Worthy (2024)
Skull morphology of the enigmatic Genyornis newtoni Stirling and Zeitz, 1896 (Aves, Dromornithidae), with implications for functional morphology, ecology, and evolution in the context of Galloanserae
Historical Biology 36: 1093-1165
doi: 10.1080/08912963.2024.2308212

The presence of Dromornithidae in the Australian Cenozoic fossil record was first reported in 1872, yet although eight species and hundreds of specimens are known, key information on their morphology remains elusive. This is especially so for their skulls, which contributes to a lack of resolution regarding their relationships within Galloanserae. The skull of the Pleistocene dromornithid, Genyornis newtoni, was initially described in 1913. Additional fossils of this species have since been discovered and understanding of avian skull osteology, arthrology, and myological correlates has greatly advanced. Here we present a complete redescription of the skull of Genyornis newtoni, updating knowledge on its morphology, soft-tissue correlates, and palaeobiology. We explore the diversity within Dromornithidae and make comprehensive comparisons to fossil and extant galloanserans. Furthermore, we expand on the homologies of skull muscles, especially regarding the jaw adductors and address the conflicting and unstable placement of dromornithids within Galloanserae. Findings support generic distinction of Genyornis newtoni, and do not support the close association of Dromornithidae and Gastornithidae. We thus recommend removal of the dromornithids from the Gastornithiformes. Considering character polarities, the results of our phylogenetic analyses, and palaeogeography, our findings instead support the alternative hypotheses, of dromornithids within, or close to, the Suborder Anhimae with Anseriformes.

 

[Fred Ruhe]

Systematic palaeontology

AVES Linnaeus, 1758
NEORNITHES Gadow, 1892
NEOGNATHAE Pycraft, 1900
GALLOANSERAE Sibley, Ahlquist and Monroe, 1988
DROMORNITHIDAE Fürbringer, 1888
GENYORNIS Stirling and Zietz, 1896
GENYORNIS NEWTONI Stirling and Zietz, 1896

Phylogenetic analyses

To qualitatively assess some of the hypotheses present herein, and to precede future, more extensive analyses assessing the phylogeny of Dromornithidae and their relationships to other galloanseran families, we only present preliminary analyses using a limited character and taxon sample. Our ingroup includes 22 modern species from across the Galloanserae radiation and 12 relevant fossil taxa that are hypothesised to have galloanseran or near-galloanseran affinities, while the outgroup consists of three palaeognaths (Eudromia elegans, Dromaius novaehollandiae and Casuarius casuarius) and four neoavians (Antigone rubicunda, Fulmarus glacialoides, Accipiter fasciatus and Colius striatus). We have reassessed and added to the characters of Worthy et al. (2017b; see Appendix Four) and produced a character matrix comprising characters of the skull only. These 100 morphological/standard discrete characters address variation across the complete skull (3), cranium (28), lacrimal (3), quadrate (22), mandible (29), and rostrum (15). Of these characters, 51 are ordered. Missing data was coded as ‘?’, and no gaps (‘-’) were coded. See SI 3 and 4 for the ing NEXUS files that were used in phylogenetic analyses. These analyses are summarised below. In consideration of the likely extensive convergence in postcranial material and the tions derived from the giant, flightless nature of the nithids, a reassessment of dromornithid postcranial morphology is required to inform on the characters and methods used in a more complete analysis. This is beyond the scope of this study which specifically focuses on testing the phylogenetic tion pertaining to the skull.
Currently, a lack of directly comparable skull elements for some dromornithid species (resulting in missing data) and our exclusion of postcranial material from these analyses, restrict quantitative assessment of intrafamilial dromornithid relation ships. These phylogenetic analyses are thus focused on testing the interfamilial relationships in the context of Galloanserae. All analyses in the present study were constrained to cular-based topological relationships for modern taxa ing a combination of Wang et al. (2013), Burleigh et al. (2015), Prum et al. (2015), and Kimball et al. (2019), and appropriated to the taxon-selection herein at specific or
eric levels. Molecular-based constraints for Anatidae were relaxed following Worthy et al. (2022).
Parsimony analyses were conducted using PAUP* v. 4.0a169 (Swofford 2003). The search for optimal trees involved a heuristic approach, with 10,000 replicates of random stepwise taxon addition using the tree-bisection- reconnection (TBR) branch-swapping algorithm, holding 10 trees at each step, and saving no more than 100 trees of a length greater than or equal to 1 in each replicate. Subsequent bootstrapping involved 10,000 bootstrap replicates with the following parameters: 100 random-addition sequence replicates per bootstrap replicate; no more than 1,000 trees at a score equal to or greater than 1 saved per bootstrap
cate; holding 10 trees each step; and TBR branch swapping implemented. Multistate characters were treated as uncertainty.
An undated Bayesian analysis of the morphological data was also performed using MrBayes v. 3.2.7 (Ronquist and Huelsenbeck 2003), appropriating the same character and taxon selection, ordering settings, and molecular-based topo
logical constraints as the parsimony analysis. The Mk model (Lewis 2001) was used to apply maximum likelihood
geny inference to the variable, discrete morphological dataset (coding = variable). Evolutionary rate variability was
ted according to gamma parameter (rates = gamma). Four independent analyses were simultaneously run for a total of 50,000,000 generations, and sampled every 5,000 generations, to confirm convergence. The heating parameter was set as 0.1, and four chains per analysis, one cold and three incrementally heated, were used to better explore the tree topology space. The first 20% of sampled trees from all runs were discarded as relative burn-in, and the remaining samples combined to produce a consensus tree.

Fred


Figure 1. Figure 1. The near-complete, articulated skull of Genyornis newtoni (SAMA P59516): A. Left lateral view; B. Left lateral view outlined with major parts distinguished; C. Right
lateral view; D. Right lateral view outlined with major parts distinguished; E. Dorsal view; F. Caudal view; G. Ventral view; H. Rostral view. Annotations: cb., ceratobranchial; cr., cranium; ma., mandible; or., orbit; pt., pterygoid; ro., rostrum; qu., quadrate; ve., articulated vertebrae. Scale bars: 50 mm, E. to G. all to same scale.

Figure 2. Genyornis newtoni caudal orbit, NMV P256893, rostral view showing the caudal orbit and quadrate articulation with the skull and mandible: A. Image; B. Annotated outline. Annotations: ap.zyg.oss., aponeurosis zygomatica ossificans; cr.or., crista supraorbitalis; f.pseu., fossa pseudotemporalis; mand., mandible; m.lev., origin for m. levator palpebrae dorsalis; n.for., foramen neurovasculare; quad., quadrate. Scale bar: 10 mm. Dark grey shading indicates regions where damage precludes morphological assessment, and light grey indicates foramina and fossae. Dotted lines provide approximate region corresponding to labelled area, and do not indicate exact boundaries.


igure 3. Lateral view of the left side of the cranium of Genyornis newtoni: A. SAMA P59516 with shaded indication of focus region; B. SAMA P59516 image and annotated outline, digitally removed from the image of the entire skull; C. NMV P256893 image (includes part of the mandible and quadrate ventrally) and annotated outline; D. Left rostrolateral view of Anhima cornuta specimen NMV B12574, box denotes region of focus in E., Quadrate disarticulated; E. Rostrolateral view of the left lateral cranium of Anhima cornuta specimen NMV B12574. Annotations: an.tymp., annulus tympanicus; ap.dep.m., an aponeurotic site of origin of m. depressor mandibulae; ap.zyg.oss., aponeurosis zygomatica ossificans; cr.zyg., crista zygomatica; cr.nu.trans., crista nuchalis transversa; cr.or., crista supraorbitalis; cr.art., crista aponeurosis articularis; f.pseu., fossa pseudotemporalis; imp.dm., impressio m. depressor mandibulae; imp.sup., impressio m. AME superficialis; jug., jugal arch; mand., mandible; m.a.e., osseous meatus acusticus externus; pr.par., processus paroccipitalis; pr.post., processus postorbitalis; pr.sup., processus suprameaticus; quad., quadrate; t.pseu., tubercle for m. pseudotemporalis (specifically aponeurosis pseudotemporalis superficialis). Scale bars: A. 50 mm, B., C. 20 mm, D., E. 10 mm. Dark grey shading indicates regions
where damage precludes confident morphological assessment, and light grey indicates foramina and fossae. Dotted lines provide approximate regions corresponding to labelled areas, and do not represent accurate boundaries.