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

Figures & data

Table 1. Preserved skull elements, damage and taphonomic distortion in recently recovered Genyornis newtoni skull material from Lake Callabonna. Note that all of these specimens are also associated with post-cranial material not described here.

Specimen Number	Preserved element(s)	Brief description
SAMA P59516	Articulated skull: cranium, rostrum, mandible, quadrates, pterygoids, paraglossum, basihyal, ceratobranchials, atlas, axis	Extensive deformation to the skull: some lateral compression, left side displaced caudally relative to right; the mandible and quadrates are shifted and rotated caudally relative to the cranium, but the quadrates remain articulated in the quadratic fossa; the cranium is tilted rostroventrally, underlapping the caudally displaced rostrum; the right mandibular ramus is heavily damaged on the lateral side; fragmentary pterygoids are disarticulated caudally on either side of the cranium; the paraglossum is displaced rostrally and crushed between the palatines and the medial side of the right mandibular rami; the basihyal and ceratobranchials are disarticulated; and the atlas and axis are together articulated but disarticulated from the skull.
NMV P256893	Cranium, quadrate, mandible	Skull fragments include a mediolaterally compressed partial left caudal skull, separate right quadrate, parts of a left ceratobranchial and mandible. The articulated left quadrate is fragmented; the disarticulated right quadrate lacks the processus orbitalis and has sustained damage to the lateral side and the medial apex of the condylus mandibularis lateralis. A fragment of the rostral mandible preserves part of the left ramus mandibulae and pars symphysialis, the fragmented articulated caudal mandible preserves the processus medialis mandibulae and associated cotyla medialis.
SAMA P53830	Cranium, quadrate	Only preserves the fragmented partial condylus occipitalis (occipital condyle) and partial right quadrate. Of the quadrate, only the pars otica is without significant damage, although a fragment of the orbital region is also retained.
SAMA P59517	Rostrum, mandible	Disarticulated elements. Near-complete rostrum but mediolaterally flattened, the height of the rostrum and key features are still assessable, e.g. right palatinum largely intact. There are two mandible fragments which represent the right and left ramus mandibulae, partes intermedialis et caudalis. The right ramus has suffered much damage with the processus medialis mandibulae and cotyla medialis poorly preserved. The opposite ramus is completely eroded dorsally. Two fragments of shaft from one ceratobranchial, no ends preserved.
SAMA P59521	Rostrum	Disarticulated and disassociated rostrum. Near complete specimen with only slight bilateral compression mid-way along the flattened lateral plates of the praemaxillaria, and thus, forms the main basis of the G. newtoni rostrum descriptions herein.
SAMA P59520	Cranium, quadrate, mandible	Fragmented section of the left side of the caudal skull. Preserves the osseus meatus acusticus externus and processus paroccipitalis, and a partial left quadrate remains in articulation; the pars otica is well preserved, pars mandibularis is heavily abraded, and the articulatory region of the mandible, is crushed. A fragment of the right ramus mandibulae, pars symphysialis, is also preserved.

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.

Figure 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.

Figure 4. Soft-tissue attachment sites on the cranium of a dromornithid, illustrated using a digitally modified representation of Ilbandornis woodburnei (QMV 2000:gfv:20) due to the relative lack of deformation in this skull and the conservative nature of dromornithid skull morphology: A. Rostral aspect; B. Caudal aspect; C. Ventral aspect; D. Right lateral aspect; E. Oblique (rostrolateral) aspect. Abbreviations: ap.art., origin site of aponeurosis articularis; ap.dep.m., an aponeurotic site of origin of m. depressor mandibulae; ap.med.sup., origin site of aponeurosis mediosuperficialis; ap.sup., origin site of aponeurosis superficialis; ap.zyg., origin site of aponeurosis zygomatica (muscle fibres of m. AME profundus, pars zygomaticus, and m. AME profundus, pars superficialis, originate from the medial and lateral surfaces of this aponeurosis, respectively); lig.oc.mand., attachment area corresponding to the origin of ligamentum occipitomandibulare, continuous with that of membrana postmeatica; lig.post.orb., attachment area of origin of ligamentum postorbitale; m.AME.prof.cor., origin area of m. AME profundus, pars coronoideus; m.AME.sup., origin area of m. AME superficialis; m.biv.cerv., insertion area of m. biventer cervicis; m.c.c., origin area of m. cucullaris capitis; m.comp., insertion area of m. complexus; m.dep.mand., origin area of m. depressor mandibulae; m.pro.pter.quad., origin area of m. protractor pterygoidei et quadrati; m.ps.tem.s., origin area of m. pseudotemporalis superficialis; m.rec.cap.dors., insertion areas for slips of m. rectus capitis dorsalis; m.rec.cap.lat., insertion area of m. rectus capitis lateralis; m.rec.cap.vent.lat., area for aponeurosis of insertion of m. rectus capitis ventralis, pars lateralis; m.rec.cap.vent.med., insertion area of m. rectus capitis ventralis, pars medialis; m.spl.cap., insertion area of m. splenius capitis; mem.at.oc.dors., attachment area of membrana atlantooccipitalis dorsalis; mem.at.oc.vent., attachment area of membrana atlantooccipitalis ventralis; mem.pm., attachment site of membrana postmeatica, which incorporates and is not separatable with respect to the more ventromedial ligamentum occipitomandibulare. Scale bar: 50 mm. Illustrated attachment areas on the cranium are non-extensive estimates; only the sites corresponding to selected muscles, aponeuroses, membranes and ligaments are indicated.

Figure 5. Caudal and ventral views of the cranium of Genyornis newtoni, digitally cropped from the images of the entire skull: A. SAMA P59516 image and annotated outline in caudal view; B. SAMA P59516 fossa parabasalis and associated foramina for nerves, focus region outlined in A.; C. Complete ventral view of SAMA P59516 with box indicating region featured in D.; D. Ventral cranium, SAMA P59516 image and annotated outline, rotated anti-clockwise from C. Annotations: can., canal tentatively identified as canalis orbitalis (see Baumel and Witmer 1993: annot. 95); cfp., crista fossae parabasalis; coe., ostium canalis ophthalmici externi; cond.oc., condylus occipitalis; cr.bas.lat., crista basilaris lateralis; cr.nu.trans., crista nuchalis transversus; cr.ven., crista ventralis; f.para., fossa parabasalis; fng., foramen n. glossopharyngealis (IX); fnh., foramen n. hypoglossi (XII); fnv., foramen n. vagi (X); inc.mc., incisura mediana condyli; for.mag., foramen magnum; i.para., lamina parasphenoidalis; m.rec., insertion for musculus rectus capitis dorsalis; occ., ostium canalis carotici and branch of nerve VII; pr.basi., processus basipterygoideus; pr.par., processus paroccipitalis; prom.ex., prominentia exoccipitalis; r.para., rostrum parasphenoidalis (basis rostri parasphenoidalis); s.int., septum interorbitale; tu.au., tuba auditiva communis; tubc.bas., tuberculum basilare. Scale bars: A., D. 20 mm, B. 10 mm, C. 40 mm. Dark grey shading indicates regions where damage precludes morphological assessment, and light grey indicates foramen and fossae. Dotted lines in D. indicate the alignment and distortion of the sagittal plane of each region.

Figure 6. Genyornis newtoni right quadrate, NMV P256893: A. Lateral view, image and annotated outline; B. Medial view, image and annotated outline; C. Dorsal view; D. Ventral view; E. Rostral view; F. Caudal view. Annotations: cap.s-o., capitulum squamoso-oticum; cond.l., condylus mandibularis lateralis; cond.m., condylus mandibularis medialis; con.pt., condylus pterygoideus including facies articularis pterygoidei; cr.med., crista medialis; cr.tymp., crista tympanica; d.caud., depressio caudomedialis; d.rost., depressio rostromedialis; d.sup., depressio supracondylaris; for.rost., foramen pneumaticum rostromediale; f.basi., fossa basiorbitalis; fov.q., fovea quadratojugalis; musc., tubercles for insertion of m. protractor pterygoidei et quadrati; o.cap., otic part of capitulum squamoso-oticum; p.oti., pars otica; p.sub., prominentia submeatica; s.cap., squamosal part of capitulum squamoso-oticum; t.sub., tuberculum subcapitulare; v.inco., vallecular intercotylaris. Scale bars: 10 mm. Dark grey shading indicates regions where damage precludes morphological assessment, and light grey indicates the foramen pneumaticum rostromediale.

Figure 7. Genyornis newtoni rostrum, lateral views: A. SAMA P59521 left lateral view image and annotated outline; B. SAMA P59521 right lateral view; C. SAMA P59517 left and right lateral views. Annotations: ang., angulus tomialis; ca., casque; cr.tom., crista tomialis; fov., foveae corpusculorum nervosorum; lac., lacrimal ; margo.lat., margo lateralis palatini; nas., apertura nasi ossea; pala., palatinum; p.o.l., processus orbitalis of lacrimale; pr.jug., processus jugalis of the maxillare; pr.max., processus maxillopalatinus of the maxillare; pr.n.m., processus nasalis of the maxillare; sul.para., sulcus paratomialis. Scale bars: 20 mm. Dark grey shading indicates regions where damage precludes morphological assessment, and light grey indicates fenestrae, foveae, and aperturae.

Figure 8. Dromornis planei rostrum, specimen NTM P932–2, shows distortion and cavitation on the surface of the bone: A. Right side; B. Left side; C. Close-up image of the distortion on the rostrodorsal-most part of the left side of the rostrum. Annotations: ar.jug., arcus jugalis; cr.tom., crista tomialis; fen., fenestra; lac., lacrimal; p.o.l., processus orbitalis of lacrimal. Scale bars: A., B. 50 mm and C. 20 mm.

Figure 9. Genyornis newtoni rostrum, specimen SAMA P59521, and comparison of palatine and jugal arch morphology: A. Ventral/Palatal view image and annotated outline; B. Dorsal view image and annotated outline; C. Caudal view image and annotated outline; D. Hypothetical reconstruction of the palatines of Genyornis newtoni (pale orange), pars lateralis palatini (dark orange), and the jugal arch (brown) from specimen SAMA P59521; E. the galliform condition, Ortalis canicollis (see Zusi and Livezey 2006: fig. 7A); F. the anseriform condition, Anser albifrons (see Zelenkov and Stidham 2018: fig. 2A). Annotations: ang., angulus tomialis; bulb., bulbous regions largely associated with each palatine including complete synostosis with the processus maxillopalatinus of the maxillare, the processus rostralis of the palatines, and the processus palatinus of the praemaxillary; ca., casque; cho.na., choana nasalis ossea; cr., craniorostral hinge; cr.tom., crista tomialis; cul., culmen; fen.pal., fenestrae palatina; fos.cho., fossa choanalis palatini; fov., foveae corpusculorum nervosorum; lac. – lacrimal; iam.d. – lamella dorsalis, pars choanalis palatini; margo.lat., margo lateralis palatini; os.pal., ossa palatina; pal., palatum osseum; pons.mj. – pons maxillaro-jugalis; pr.cho. – processus choanalis palatini; pr.jug., processus jugalis of the maxillare; pr.max., processus maxillopalatinus; sep.na., septum nasale osseum; sn.pl., supranarial plate (of processus maxillopalatinus); sul.para., sulcus paratomialis and associated depression; sut.Vm., sutura vomeromaxillaris; vom., vomer. Scale bars: 20 mm, D.-F. not to scale. Dark grey shading indicates regions where damage precludes morphological assessment, light grey indicates sulci, fenestrae, foveae, and aperturae, dotted lines follow the rostral continuation of the sulcus paratomialis, and the white arrows in B and C indicate the lateral articular ‘condyles’ (internal processes of the nasolacrimals, sensu Murray and Vickers-Rich 2004).

Figure 10. Genyornis newtoni mandible morphology: A. Caudal view of skull part NMV P256893, partially preserving ramus mandibulae, pars caudalis ventrally, which retains the medial process of the mandible; B. Image and annotated outline of SAMA P59516 in right lateral view, digitally removed from the image of the entire skull; C. Ventral view of the symphysial region of mandible specimen SAMA P59516; D. Caudal view of symphysial part of mandible specimen NMV P256893; E. Dorsal view of symphysial part of mandible specimen NMV P256893; F. Proposed arrangement of insertions of the adductor muscle complex on the lateral side of the mandible for dromornithids (drawn from specimen NTM P2774–2 of Ilbandornis sp. due to the limited distortion and conservative nature of dromornithid skull morphology) compared with re-drawn examples of extant galloanserans, Anseres – Anas platyrhynchos (Davids 1952a: fig. 3b), Anhimidae – Anhima cornuta (NMV B12574), Megapodiidae – Aepypodius arfakianus (Weber 1996: fig. 2a) and Phasianidae – Gallus gallus (Fujioka 1963: fig. 7). Annotations: c.lat., cotyla lateralis.; cr.par., crista paracoronoidea rostralis and crista paracoronoidea caudalis.; ADM, angulus dorsalis mandibulae; AVM, angulus ventralis mandibulae; exc., excavation associated with the region of recessus conicalis in anatids; f.neur., foramen neurovascularis.; m.AMEPc, m. AME profundus, pars coronoideus; m.AMEs, m. AME superficialis; m.AMEPs, m. AME profundus, pars superficialis; m.AMEPz, m. AME profundus, pars zygomaticus; m.AMP, m. adductor mandibulae posterior; m.ps., abraded prominence and approximate area for insertion of m. pseudotemporalis profundus; pr.cor., processus coronoideus (approximate position indicated, not visible as it is obscured by associated cranium); pr.lat.m., processus lateralis mandibulae; pr.med.m., processus medialis mandibulae; pr.ret., processus retroarticularis; sym., pars symphysialis, rostrum mandibulae; tom., crista tomialis; Scale bars: A., C.-E. 10 mm, B. 20 mm, F. not to scale. Dark grey shading indicates regions where damage precludes morphological assessment, and light grey indicates fenestra.

Figure 11. The hyoid elements of Genyornis newtoni specimen SAMA P59516: A. Complete specimen SAMA P59516 in ventral view; B. paraglossum, arrows for orientation (dorsal, ventral); C. Right lateral view of the basihyal and both left and right ceratobranchials in situ, image rotated 90 degrees clockwise from A.; D. Annotated outline of hyoid elements, arrow for orientation of basihyal only (clockwise: dorsal, rostral, ventral, caudal). Annotations: a.cb., damaged region just rostral of the articulatio ceratobasihyalis; a.pb., surface corresponding to articulatio paraglosso-basihyalis; bh., basihyal; cb., ceratobranchials; cor., cornua (processus paraglossus caudalis); for., central foramen. Scale bars: A. 40 mm, B. 10 mm, C., D. 20 mm.

Figure 12. Galloanseran consensus trees derived from skull characters to assess the relationships of dromornithids: A. Parsimony strict consensus tree cladogram of 2 MPTs (length = 786, corresponding phylograms are displayed in SI 5), bootstrap support values are displayed below each corresponding branch; B. the consensus tree phylogram based on Bayesian inference (majority-rule, undated). The scale bar in B. relates to degree of morphological change across branch lengths. Posterior Probability values are specified next to respective nodes. The suborders Anhimae and Anseres are indicated, as is the superfamily Phasianoidea. Branches are differentially coloured corresponding to Galliformes (green) and Anseriformes (blue). The additional colour gradient across branches is indicative of support values in both consensus trees displayed (bootstrap values and posterior probabilities, respectively). Fossil taxa are shown in bold.

Figure 13. An artistic reconstruction of the skull of Genyornis newtoni, based on all available fossil material, left lateral view. Illustration by Jacob C. Blokland. Scale bar is equal to 50 mm.

Figure 14. Two select morphological features which show variation across Galloanserae, and, in isolation as single character studies, indicate different phylogenetic hypotheses for the evolutionary placement of the Dromornithidae: A. the presence of either the rostromedial or caudomedial foramen (dark orange) in relation to the crista medialis (light orange) on the quadrate, in medial view; B. the relationship between the aponeurosis zygomatica and processus postorbitalis, in addition to the presence of an ossified portion (dark orange) of the aponeurosis zygomatica (light orange). Dotted and dashed branches in B. illustrate alternative hypotheses discussed in text; the unresolved position illustrated by the dotted line denotes the uncertainty of the order of divergence between the anhimids and dromornithids. Positions of Conflicto antarcticus and the Presbyornithidae are based on Tambussi et al. (2019: fig. 14) and Houde et al. (2023: fig. 9B). Nodes do not correlate with time. Not all families within Galloanserae are displayed. Morphologies drawn from photos and figures in literature: A.: Anseres – Anseranas semipalmata (see Elzanowski and Stidham 2010: fig. 5C), Anhimidae – Anhima cornuta (see Elzanowski and Stidham 2010: fig. 8B), Presbyornithidae – (see Elzanowski and Stidham 2010: fig. 5B), Conflicto antarcticus – (Tambussi et al. 2019: fig. 6A), Dromornithidae – Genyornis newtoni (NMV P256893), Megapodiidae – Megapodius freycinet (see Elzanowski and Stidham 2010: fig. 5A), Phasianidae – Gallus gallus (FUR 119); B.: Anseres – Sarkidiornis melanotos (see Zusi and Livezey 2000: figs. 6D, 7D), Dromornithidae – Genyornis newtoni (SAMA P59516), Anhimidae – Chauna torquata (see Zusi and Livezey 2000: figs. 6C, 7B), Megapodiidae – Alectura lathami (SAMA B2439), Phasianidae – Meleagris gallopavo (see Zusi and Livezey 2000: fig. 4 G). Silhouettes (designed by PLM) are illustrative representations of species in the same family or appropriate clade, as indicated. Images are not to scale.

Figure A1. SAMA P 10838, Stirling (1913) original skull of Genyornis newtoni as it is currently: A. lateral view of the skull; B. dorsal view of the skull, showing the block in which the skull has been set. Annotations: ap.zyg.oss., aponeurosis zygomatica ossificans; cond.oc, condylus occipitalis; cr.or., crista orbitalis; pr.post., processus postorbitalis. Image a credit: Mahala Fergusen. Scale bar: 2 cm.

Figure A2. Laterally compressed rostrum, specimen SAMA P59517, transected by a fault in the clay matrix which has offset the caudal part from that more rostral: A. right lateral; B. left lateral; C. dorsal; D. ventral. Annotations: ang.cl., angulus caudolateralis; ca., casque; cr.tom., crista tomialis; cul., culmen; margo.lat., margo lateralis; nas., apertura nasi ossea; pala., os palatinum. Scale bars: 20 mm.

Figure A3. Additional skull specimens of Genyornis newtoni: A. NMV P256893, partial dorsal calvaria in dorsal and ventral views; B. SAMA P53830 jugal arch, right side, medial, lateral, and dorsal views; C. SAMA P53830, right quadrate; D. SAMA P53830 partial condylus occipitalis and occipital region of the cranium; E. SAMA P59520, ramus mandibulae, pars symphysialis, right side, dorsal and ventral views; F. SAMA P59520, partial left lateral cranium in medial (left) and lateral (right) views. Annotations: an.tymp., annulus tympanicus; c. quad, condylus quadratica; cap.s-o., capitulum squamoso-otica; cond.oc., condylus occipitalis; cr.med., crista medialis; cra., cranium; d.rost., depressio rostromedialis; m.a.e., osseous meatus acusticus externus; mand., mandible; quad., quadrate. Scale bars: 10 mm.

Figure A4. Additional specimens of Genyornis newtoni: A. NMV P256893 partial left skull medial view; B. – G. SAMA P59517, fragmentary mandibular rami, B. right ramus mandibulae, pars caudalis and pars intermedia in lateral view; C. and medial view; D. left ramus mandibulae, pars caudalis et intermedius, lateral view; E. and medial view; F. fragmentary right ramus mandibulae, pars caudalis, dorsal view; G. and rostral view. Abbreviations: c.med., cotyla medialis mandibulae; cer., ceratobranchial; d.rost., depressio rostromedialis; imp.cor., impressio m. AME profundus, pars coronoideus; m.pt.dor., insertion area of m. pterygoideus dorsalis; p.lat., processus lateralis mandibulae; p.med., processus medialis mandibulae; t.prae., tuberculum praearticulare. Scale bar: 10 mm.

Table A1. Genyornis newtoni skull measurements. Rounded to the first decimal point.

Element and Measurements	Specimens (mm)
Cranium	SAMA P59516	NMV P256893/SAMA P53830
Total rostrocaudal skull length, including both the cranium and rostrum. Note: This is a minimum estimate of skull length considering the displacement of the cranium relative to the rostrum which has resulted in the rostrum overlapping the most rostral part of the cranium.	296	–/–
Width of lateral side: from prominentia exoccipitalis to rostral margin of processus postorbitalis at ventral base of crista orbitalis, in horizontal alignment. Note: For specimen SAMA P59516, measured on left side of the cranium.	61.6	59.3/–
Height of caudal cranium: from ventral point of processes paroccipitalis to most dorsal point on crista nuchalis transversus.	126.8	–/–
Dorsoventral height of caudal cranium along the mediolateral midline.	83.9	–/–
Fossa pseudotemporalis: mediolateral width and dorsoventral height (W/H).	–	9.8/6.6
Processus paroccipitalis: maximum length from ventral base of osseous meatus acusticus externus.	55.1	52.5/–
Width of caudal side, occipital region: mediolateral width in alignment with the condylus occipitalis.	88.6	–/–
Osseous meatus acusticus externus: mediolateral width and dorsoventral height (W/H).	10.6/12.1	14.4/12.7
Condylus occipitalis: mediolateral width and dorsoventral height (W/H).	16.4/16.1	–/17.3
Foramen magnum: width and height (W/H).	16.9/24.4	–/–
Individual tuberculum basilare: mediolateral width and dorsoventral height (W/H). Note: For specimen SAMA P59516, measurements from left tubercle.	12.6/15.3	–/–
Processus basipterygoideus: rostrocaudal length of the articular surface.	15.2	–/–
Quadrate	NMV P256893	SAMA P53830
Maximum height from rostrocaudal midpoint of the ventral margin of pars mandibularis to dorsal-most point on pars otica.	47.2	–
Pars otica: Height from dorsal margin of fovea quadratojugalis to dorsal-most point on pars otica.	28.1	31.0
Capitulum squamoso-otica: mediolateral width/rostrocaudal length.	12.8/12.8	–
Depressio rostromedialis: dorsoventral height.	12.5	–
Foramen pneumaticum rostromediale: dorsoventral height.	6.3	–
Pars mandibularis: maximum length of long axis including both articular surfaces.	26.2	–
Rostrum	SAMA P59521	SAMA P59517
Rostrocaudal length of the rostrum from the centre of the craniorostral hinge to rostral apex.	212.4	237.1
Maximum dorsoventral height of the fused praemaxillare/maxillare plates, from the caudal end of the culmen, just rostral of the casque, ventrally to the tomial surface.	72.9 (34.3% length)	81.2 (34.2% height)
Maximum mediolateral width of the rostrum between left and right margo tomialis.	76.05	NA
Rostrocaudal length of casque.	51.4	59.1
Mediolateral width of the casque.	76.3	N/A
Rostrocaudal length of the ventral rostrum, not including the vomer and palatines.	129.4	162.6
Dorsoventral height of the caudal post narial bar, not inclusive of the casque.	32.4	39
Os palatinum: maximum dorsoventral height from point of interaction with the os maxillare near the angulus tomialis to the ventral-most extent of the palatinum.	42.8	45.1
Mandible	SAMA P59516 Note: all measurements from right side of specimen.	NMV P256893
Rostrocaudal length of mandible: caudal end of processus retroarticularis to rostral tip of ramus mandibulae, pars symphysialis.	293	N/A
Depth of mandible: dorsoventral height from highest point on the angulus dorsalis mandibulae to the immediately ventral point on ventral side. This is approximately the rostral-most point of the angulus ventralis mandibulae.	61.5	N/A
Rostrocaudal length of processus retroarticularis from its caudal extent to the caudal margin of processus lateralis mandibulae.	39.7	N/A
Ramus mandibulae, pars symphysialis, rostrocaudal length.	44.2	N/A
Maximum mediolateral width of mandible at processus medialis mandibulae.	N/A	25.5
Rostrocaudal length of angulus ventralis mandibulae where it is entirely distinct ventrally with respect to the rest of the ventral mandible margin.	81.8	N/A

Table A2. (Part 1) Homological correlations for the terminology associated with musculus adductor mandibulae across examples of relevant literature.

Part 1

Holliday and Witmer (2007) ^+

Matsuoka et al. (2008)

Dzerzhinsky and Grintsevichene (2002)

Zusi and Livezey (2000)

Weber (1996) ^+

Vanden Berge and Zweers (1993)

Dzerzhinsky and Potapova (1974)

Zweers (1974)

Musculus adductor mandibulae externus

Musculus adductor mandibulae externus superficialis

Musculus adductor mandibulae externus superficialis, A-portion

Musculus adductor mandibulae externus profundus caudalis (Aec)

Musculus adductor mandibulae externus, pars articularis, caput externa

Musculus adductor mandibulae externus, pars articularis

Musculus adductor mandibulae externus, pars profunda [caudalis]^1

Musculus adductor mandibulae externus profundus, pars caudalis (Aec)

Musculus adductor mandibulae externus, pars caudolateralis (ACL)

Musculus adductor mandibulae externus profundus, pars superficialis

Musculus adductor mandibulae externus superficialis, C-portion

Musculus adductor mandibulae externus superficialis (Aes: also see Dzerzhinsky and Potapova 1974; Dzerzhinsky 1982) ^

Musculus adductor mandibulae externus, pars superficialis

Musculus adductor mandibulae externus, pars zygomatica

Musculus adductor mandibulae externus, pars ventralis^3

Musculus adductor mandibulae externus superficialis (Aes)

Musculus adductor mandibulae externus, pars rostromedialis (ARM)

Musculus adductor mandibulae externus profundus, pars zygomaticus

Musculus adductor mandibulae externus superficialis, B-portion

Musculus adductor mandibulae externus medialis (Aem)

Musculus adductor mandibulae externus, pars zygomatica + musculus adductor mandibulae externus, pars articularis, caput externa (in part)

Musculus adductor mandibulae externus, pars zygomatica

Musculus adductor mandibulae externus, pars ventralis

Musculus adductor mandibulae externus medialis (Aem)

Associated with aponeurosis 2a (ap.2a)

Musculus adductor mandibulae externus profundus, pars coronoideus

Musculus adductor mandibulae externus medialis

Musculus adductor mandibulae externus profundus rostralis (Aer)

Musculus adductor mandibulae externus, pars coronoidea

Musculus adductor mandibulae externus, pars coronoidea

Musculus adductor mandibulae externus, pars rostralis [temporalis] *

Musculus adductor mandibulae externus profundus, pars rostralis (Aer)

Associated with aponeurosis 4a (ap.4a)

Musculus adductor mandibulae internus

Musculus pterygoideus dorsalis

Musculus pterygoideus dorsalis medialis

Musculus pterygoideus

—

Musculus pterygoideus dorsalis

Musculus pterygoideus (various subdivisions reviewed)

Musculus pterygoideus dorsalis medialis

Musculus pterygoideus dorsalis medialis

Part 1

Holliday and Witmer (2007) +

Matsuoka et al. (2008)

Dzerzhinsky and Grintsevichene (2002)

Zusi and Livezey (2000)

Weber (1996) +

Vanden Berge and Zweers (1993)

Dzerzhinsky and Potapova (1974)

Zweers (1974)

Musculus pterygoideus ventralis

Musculus pterygoideus ventralis lateralis + musculus pterygoideus dorsalis lateralis; musculus pterygoideus ventralis medialis

Musculus pterygoideus

—

Musculus pterygoideus ventralis lateralis; musculus pterygoideus ventralis medialis; musculus pterygoideus ventralis caudalis

Musculus pterygoideus (various subdivisions reviewed)

Musculus pterygoideus ventralis lateralis; musculus pterygoideus dorsalis lateralis + musculus pterygoideus ventralis medialis + musculus pterygoideus caudalis

Musculus pterygoideus ventralis lateralis + musculus pterygoideus dorsalis lateralis; musculus pterygoideus ventralis medialis

Musculus pseudotemporalis superficialis

Musculuspseudotemporalis superficialis

Musculus pseudotemporalis superficialis (Pss: also see Dzerzhinsky and Potapova 1974; Dzerzhinsky 1982) ^

—

Musculuspseudotemporalis superficialis

Musculuspseudotemporalis superficialis

Musculuspseudotemporalis superficialis (Pss)

Musculus pseudotemporalis superficialis

Musculus pseudotemporalis profundus

Musculus pseudotemporalis profundus

—

—

Musculuspseudotemporalis profundus

Musculus pseudotemporalis profundus/musculus adductor mandibulae caudalis

Musculuspseudotemporalis profundus (Psp)

Musculus pseudotemporalis profundus

Musculus adductor mandibulae posterior ^†

Musculus adductor mandibulae posterior lateralis

Musculus adductor mandibulae externus profundus

Fibres of musculus adductor mandibulae externus profundus caudalis, attached to musculus adductor mandibulae posterior (Aec*)

Musculus adductor mandibulae externus, pars articularis, caput interna

Musculus adductor mandibulae caudalis^2

Musculus adductor mandibulae ossis quadrati [caudalis]^†

Musculus adductor mandibulae posterior (Ap), possibly in association with their mandibular aponeurosis posterior insertionis

Musculus adductor mandibulae externus profundus (AEP)

Musculus adductor mandibulae posterior medialis

Musculus adductor mandibulae posterior

Musculus adductor mandibulae posterior (Ap)

Musculus adductor mandibulae posterior

Musculus adductor mandibulae caudalis^2

Musculus adductor mandibulae ossis quadrati [caudalis]

Musculus adductor mandibulae posterior (Ap), from aponeurosis posterior quadratica (apq)

Musculus adductor mandibulae posterior (AMP)

Part 2

Holliday and Witmer (2007)

Dzerzhinsky and Belokurova (1972)

Zusi and Storer (1969)

Fujioka (1963)

Goodman and Fisher (1962)

Davids (1952a, b, c)

Hofer (1950)

Lakjer (1926)

Musculus adductor mandibulae externus

Musculus adductor mandibulae externus superficialis

Musculus adductor mandibulae externus, pars profunda caudalis (Aec)

Musculus adductor mandibulae externus, part 2

Musculus masseter medius (5B)

Musculus adductor mandibulae externus, superficialis, Ia portion

Musculus adductor mandibulae externus (m. add. ext)

Musculus adductormandibulae externus, pars superficialis

Musculus adductor mandibulae externus profundus (III kaud.)

Musculus adductor mandibulae externus profundus, pars superficialis

Musculus adductor mandibulae externus, pars superficialis (Aes)

Musculus adductor mandibulae externus, part 1

Musculus masseter superficialis (5A)

Musculus adductor mandibulae externus, superficialis, Ic portion

Musculus adductor mandibulae externus (m. add. ext)

Musculus adductor mandibulae externus, pars occipitalis

Musculus adductor mandibulae externus superficialis (I)

Musculus adductor mandibulae externus profundus, pars zygomaticus

Musculus adductor mandibulae externus, pars medialis (Aem)

Musculus adductor mandibulae externus, part 2

Musculus masseter superficialis (5A)

Musculus adductor mandibulae externus, superficialis, Ib portion

Musculus adductor mandibulae externus (m. add. ext)

Musculus adductor mandibulae externus, pars medialis

Musculus adductor mandibulae externus medialis (II)

Musculus adductor mandibulae externus profundus, pars coronoideus

Musculus adductor mandibulae externus, pars profunda rostralis (Aer)

Musculus adductor mandibulae externus, part 3

Musculus masseter profundus (6)

Musculus adductor mandibulae externus, medialis (M. II)

Musculus adductor mandibulae externus (m. add. ext)

Musculus adductor mandibulae externus temporalis

Musculus adductor mandibulae externus profundus (III rost.)

Musculus adductor mandibulae internus

Musculus pterygoideus dorsalis

Musculus pterygoideus, pars dorsalis medialis

Musculus pterygoideus, pars dorsalis, lateral branch

Musculus pterygoideus dorsalis medialis (11Ab)

Musculus pterygoideus dorsalis, medial part

Musculus pterygoideus dorsalis medialis

Musculuspterygoideus, pars dorsalis medialis

Musculus pterygoideus, pars dorsalis medialis

Musculus pterygoideus ventralis

Musculus pterygoideus, pars ventralis lateralis; musculus pterygoideus, pars dorsalis lateralis + musculus pterygoideus, pars ventralis medialis + musculus pterygoideus, pars dorsalis caudalis

Musculus pterygoideus, pars lateralis, dorsolateral branch + musculus pterygoideus, pars lateralis, ventromedial branch + musculus pterygoideus, pars dorsalis, medial branch

Musculus pterygoideus dorsalis lateralis (11B) + musculus pterygoideus ventralis medialis (9A); musculus pterygoideus ventralis lateralis (9B) + pterygoideus dorsalis medialis (11Aa)

Musculus pterygoideus ventralis, lateral part + musculus pterygoideus dorsalis, lateral part; musculus pterygoideus ventralis, medial part

Musculus pterygoideus ventralis lateralis + musculus pterygoideus dorsalis lateralis; musculus pterygoideus ventralis medialis

Musculuspterygoideus, pars ventralis lateralis + musculus pterygoideus, pars dorsalis lateralis; musculus pterygoideus, pars ventralis medialis; musculus pterygoideus, pars caudalis

Musculus pterygoideus, pars ventralis lateralis + musculus pterygoideus, pars dorsalis lateralis; musculus pterygoideus, pars ventralis medialis; musculus pterygoideus, pars dorsalis 1

Musculuspseudotemporalis superficialis

Musculuspseudotemporalis superficialis (Pss)

Musculus pseudotemporalis superficialis

Musculus temporalis (7)

Musculus pseudotemporalis superficialis

Musculus pseudotemporalis superficialis (m. pseudo. sup.)

—

Musculus pseudotemporalis superficialis

Musculus pseudotemporalis profundus

Musculus pseudotemporalis profundus (Psp)

Musculus pseudotemporalis profundus

Musculus quadratomandibularis (10C)

Musculus pseudotemporalis profundus

Musculus pseudotemporalis profundus (m. pseudo. prof.)

—

Musculus pseudotemporalis profundus

Part 2

Holliday and Witmer (2007)

Dzerzhinsky and Belokurova (1972)

Zusi and Storer (1969)

Fujioka (1963)

Goodman and Fisher (1962)

Davids (1952a, b, c)

Hofer (1950)

Lakjer (1926)

Musculus adductor mandibulae posterior ^†

Musculus adductor mandibulae posterior lateralis

Musculus adductor mandibulae posterior (Ap), to aponeurosis a.11

Musculus adductor mandibulae posterior

Musculus quadratomandibularis (10A)

Musculus adductor mandibulae externus, profundus (M. III)

Musculus adductor mandibulae externus profundus (m. add. ext. prof.)

Musculus adductor mandibulae externus, pars profunda

—

Musculus adductor mandibulae posterior medialis

Musculus adductor mandibulae posterior (Ap), from superficial aponeurosis a.12

Musculus adductor mandibulae posterior

Musculus quadratomandibularis (10B)

Musculus adductor mandibulae posterior (‘a’ and ‘b’ parts in Mergus merganser)

Musculus adductor mandibulae posterior (m. add. post.)

Superficial musculus adductor mandibulae externus, pars profunda

—

— not treated in the particular study.

Notes.

+While we follow Holliday and Witmer (2007) for all muscles included here in general, the homologies of more specific parts of musculus pterygoideus, not addressed in-depth by these authors, are associated in this study herein following the relationships inferred by Weber (1996), namely musculus pterygoideus ventralis lateralis, musculus pterygoideus ventralis medialis, musculus pterygoideus ventralis caudalis, and musculus pterygoideus dorsalis. Also see Weber (1996), Tab. 11.

¹Because of the ambiguity in the displayed figure by Vanden Berge and Zweers (1993: fig. 6.5) corresponding to the insertions of musculus adductor mandibulae externus, pars profunda [caudalis], and musculus adductor mandibulae externus, pars ventralis, the muscle synonymous with musculus adductor mandibulae externus superficialis (sensu Holliday and Witmer 2007) may be predominately equable to musculus adductor mandibulae externus, pars profunda [caudalis], but may also relate to musculus adductor mandibulae externus, pars ventralis, in part.

²While Weber (1996, p. 57) recognised that there is some differentiation in the exact insertion area of fibres relating to their musculus adductor mandibulae caudalis (to the aponeurosis paracoronoidea interna, and rostrad of the articulatio quadrato-mandibularis), likely representative of parts recognised in other studies, beyond this mention there is no differentiation of these parts.

³Vanden Berge and Zweers (1993: annot. 18) described part of the musculus adductor mandibulae externus, pars ventralis, as originating on the processus postorbitalis, but then erroneously or accidentally displayed this part originating upon the caudal orbit on the diagram (fig. 6.5) of Podilymbus podiceps that was adapted from Zusi and Storer (1969: Figure 6). Instead, this area corresponds to the origin of musculus pseudotemporalis superficialis (part 2) of the latter authors’ study.

*Zusi and Livezey (2000) suggested that their musculus adductor mandibulae externus, pars coronoidea, is synonymous with musculus adductor mandibulae externus, pars rostralis [temporalis], of Vanden Berge and Zweers (1993). However, Holliday and Witmer (2007) suggested that their musculus adductor mandibulae profundus (and included parts) is equivalent to musculus adductor mandibulae externus pars ventralis of Vanden Berge and Zweers (1993) and interpret musculus adductor mandibulae externus, pars coronoidea, of Zusi and Livezey (2000) as part of their musculus adductor mandibulae profundus. Musculus adductor mandibulae externus, pars rostralis [temporalis], of Vanden Berge and Zweers (1993) was also considered synonymous to musculus adductor mandibulae externus superficialis (Holliday and Witmer 2007: Table 2). Based on the origins and insertions illustrated and described in Zusi and Storer (1969), and those of the derivative adaptive diagram and annotations of Vanden Berge and Zweers (1993), it is revealed that musculus adductor mandibulae externus, pars rostralis [temporalis], of Vanden Berge and Zweers (1993) is comparable to musculus adductor mandibulae externus profundus, pars coronoideus, of Holliday and Witmer (2007), and not equivalent to musculus adductor mandibulae externus superficialis, contrary to the latter study. This is supported by reporting that the terminal insertion of musculus adductor mandibulae externus, pars rostralis [temporalis], of Vanden Berge and Zweers (1993) relates to processus coronoideus (sensu stricto, see Baumel and Witmer 1993: annot. 44), which is comparable to musculus adductor mandibulae externus profundus, pars coronoideus, of Holliday and Witmer (2007), and can be compared with muscles that insert on this feature in other studies (e.g. musculus adductor mandibulae externus profundus, pars rostralis, sensu Dzerzhinsky 1982, and others).

†Musculus adductor mandibulae externus, pars profunda [caudalis], of Vanden Berge and Zweers (1993) was interpreted as synonymous with musculus adductor mandibulae externus, pars articularis (likely caput externa) by Zusi and Livezey (2000). The latter name was considered equivalent to musculus adductor mandibulae externus superficialis, while the former is considered synonymous with musculus adductor mandibulae posterior by Holliday and Witmer (2007: Table 2), and thus there appears to be a conflict in this assignment of synonymy. An overarching issue is that musculus adductor mandibulae posterior may not exist in two separate parts in some birds but may do (as medial and lateral parts) in some Galloanserae and Neoaves (see Zusi and Storer 1969; Holliday and Witmer 2007, p. 467). Musculus adductor mandibulae posterior was not divided into parts by Zusi and Storer (1969) and was hence not labelled in separate parts on this same diagram that was adapted by Vanden Berge and Zweers (1993: fig. 6.5).

Vanden Berge and Zweers (1993: annot. 18) categorised their musculus adductor mandibulae, pars profunda [caudalis], as an external adductor muscle, and stated that it acts independently of the musculus adductor mandibulae ossis quadrati [caudalis]. They did not explicitly say that their musculus adductor mandibulae, pars profunda [caudalis], originates on the neurocranium in part, while the associated diagram of Vanden Berge and Zweers (1993: fig. 6.5), adapted from Zusi and Storer (1969: fig. 6), shows part of the origin in this region. The insertion displayed in this figure as labelled by Vanden Berge and Zweers (1993: fig. 6.5) leaves ambiguity with regards to whether it is better associated with the musculus adductor mandibulae externus or the musculus adductor mandibulae posterior (sensu Holliday and Witmer 2007). However, the original figure and related description of the muscle illustrated by Zusi and Storer (1969) would also imply this corresponds to part of the external adductor musculature. Furthermore, the annotation given by Vanden Berge and Zweers (1993: annot. 18) describes this muscle as deriving solely from the quadrate, which when their subsequent figure labels their musculus adductor mandibulae, pars profunda [caudalis], as inserting on the caudal mandible in an area comparable to where part of musculus adductor mandibulae posterior may insert in some taxa, it can be interpreted ambiguously, however, and may be considered as synonymous with part of musculus adductor mandibulae posterior, therefore (as per Holliday and Witmer 2007: table 2).

Holliday and Witmer (2007: 467) equated musculus adductor mandibulae posterior with only musculus adductor mandibulae ossis quadrati [caudalis] of Vanden Berge and Zweers (1993) in text but associated both this muscle and musculus adductor mandibulae externus, pars profunda [caudalis], with musculus adductor mandibulae posterior in their related table (table 2). Considering Holliday and Witmer’s (2007) interpretation that musculus adductor mandibulae posterior lateralis is synonymous with musculus adductor mandibulae externus, pars articularis, caput interna (of Zusi and Livezey 2000), combined with the suggestion by Zusi and Livezey (2000) that their pars articularis is equivalent to musculus adductor mandibulae externus, pars profunda [caudalis], while the latter authors’ musculus adductor mandibulae posterior is the same as musculus adductor mandibulae ossis quadrati [caudalis] of Vanden Berge and Zweers (1993), it makes sense that musculus adductor mandibulae externus, pars articularis, caput externa of Zusi and Livezey (2000) would then correspond well with musculus adductor mandibulae externus, pars profunda [caudalis], of Vanden Berge and Zweers (1993), and thus an external adductor muscle (musculus adductor mandibulae externus superficialis, sensu Holliday and Witmer 2007). In contrast, Holliday and Witmer’s (2007) musculus adductor posterior medialis can be considered the same as musculus adductor mandibulae posterior (sensu Zusi and Livezey 2000, when musculus adductor mandibulae externus, pars articularis, caput interna is present), and the same as musculus adductor mandibulae ossis quadrati [caudalis] of Vanden Berge and Zweers (1993).

We thus consider musculus adductor mandibulae externus, pars profunda [caudalis], of Vanden Berge and Zweers (1993) as inequivalent to part of the musculus adductor mandibulae posterior, and instead associate it with the musculus adductor mandibulae externus superficialis. It should be noted that this assigned correlation is dubious and the area labelled as associated with this muscle by Vanden Berge and Zweers (1993: fig. 6.5) may receive fibres from both musculus adductor mandibulae posterior and musculus adductor mandibulae externus superficialis.

^ Specific term not mentioned in the particular study; non-abbreviated terminology derived from closely related studies using the same labelled acronym (cited)

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Data availability statement

All data generated or analysed during this study are included in this published article, the appendices and supplementary information files.