PMC

Pygoscelis papua, macrophotographs of the disarticulated bones of Maxilla and the small bones with which it articulates caudally (specimen G2). The rostral portion of Maxilla was unable to be imaged in any penguin and thus we were reliant on cleaned specimens for illustration; however, these are subject to distortion by cleaning (burial in soil). Os nasale sinistrum, left lateral view: (a) Processus premaxillaris. (b) Processus maxillaris. (c) Processus frontalis. Os premaxillare (an unpaired bone), left lateral view: (d) Rostrum maxillae. (e) Processus frontalis. (f) Processus maxillaris. Note the distortion of Processus frontalis and Processus maxillaris caused by cleaning; in intact specimens both are straight. Os jugale sinistrum, left lateral view: We could not identify Os quadratojugale in this specimen nor on micro‐CT in G1. Os maxillare dextrum, ventral view: (g) Processus maxillopalatinus, (h) Processus premaxillaris, (i) Processus jugalis, (j) The groove in which Processus maxillaris ossis palatini sits. Os palatinum sinistrum, left lateral view: (k) Processus maxillaris (syn. Processus premaxillaris), (l) Processus rostralis, and (m) Processus pterygoideus

Lateral view (a), ventral view (without lower jaw) (b), caudal view (c) and dorsal view (d) of the skull of adult 1, and lateral view (e), ventral view (f), medial view (g) and dorsal view (h) of the left ramus of the lower jaw of adult 1. Note that the cristae and processes have become more developed. cond.caud., condylus caudalis; cond.lat., condylus lateralis; cond.occ., condylus occipitalis; cr.temp., crista temporalis; cr.nuch.transv., crista nuchalis transversa; f.temp., fossa temporalis; for.magn., foramen magnum; pars caud., pars caudalis; pars dent., pars dentalis; pes pter., pes pterygoidei; proc.antorb., processus antorbitalis; proc.cor., processus coronoideus; proc.mand.lat., processus mandibulae lateralis; proc.mand.med., processus mandibulae madialis; proc.orb., processus orbitalis; proc.ot.qd., processus oticus quadrati; proc.parocc., processus paroccipitalis; proc.postorb., processus postorbitalis; proc.suprameat., processus suprameaticus; proc.transpal., processus transpalatinus; proc.zyg., processus zygomaticus; sept.in.orb., septum interobitalis; sept.nas., septum nasalis; ses. 1, large sesamoid bone; ses. 2, small sesamoid bone; ses., sesamoid bones; symph.mand., symphysis mandibulae; t.ps.temp., tuberculum pseudotemporalis; z.flex.arc.cr.fac., zona flexoria arcus cranio facialis; z.flex.arc.jug., zona flexoria arcus jugalis; z.flex.pal., zona flexoria palatina.

Osteology. Lateral view of the left side of the skull of Geospiza fortis (a) and Padda oryzivora (b). Note that the crista temporalis and the processus antorbitalis are much more prominent in G. fortis. The beaks, however, have more or less the same shape. cond.qd.jug., condylus quadrati jugalis; cr.nuch.transv., crista nuchalis transversa; cr.temp., crista temporalis; cr.tom., crista tomialis; fen.mand.caud., fenestra mandibulae caudalis; f.temp., fossa temporalis; os pal., os palatinum; os pter., os pterygoideum; os qd., os quadratum; os vo., os vomer; pars caud.mand., pars caudalis mandibulae; pars dent.mand., pars dentalis mandibulae; pes pter., pes pterygoidei; proc.antorb., processus antorbitalis; proc.max.praemax., processus maxillaris praemaxillae; proc.orb.qd., processus orbitalis quadrati; proc.pal.praemax., processus palatinus praemaxillae; proc.parocc., processus paroccipitalis; proc.postorb., processus postorbitalis; proc.praemax.pal., processus praemaxillaris palatini; proc.sup.meat., processus suprameaticus; proc.zyg., processus zygomaticus; sept.interorb., septum interorbitalis; ses. 1, first sesamoid bone; ses. 2, second sesamoid bone; tub.sq., tuberculum squamosum.

Lateral view (a), ventral view (without lower jaw) (b), caudal view (c) and dorsal view (d) of the skull of embryo 1, and lateral view (e), ventral view (f), medial view (g) and dorsal view (h) of the left ramus of the lower jaw of embryo 1. Note that all the bones of the lower and upper jaw are present, but only two bones of the braincase have started to ossify. The beak of this specimen is broken and bent ventrolaterally. cond.qd.jug., condylus quadrati jugalis; for.caud.mand., foramen caudalis mandibulae; os ang., os angulare; os dent., os dentale; os max., os maxillare; os nas., os nasale; os pal., os palatinum; os qd.jug., os quadratojugalis; os parasphen., os parasphenoideum; os prae-art., os prae-articulare; os praemax., os praemaxillare; os pter., os pterygoideum; os spl., os spleniale; os sq., os squamosum; os supra-ang., os supra-angulare; proc.dors.dent., processus dorsalis dentalis; proc.front.praemax., processus frontalis praemaxillae; proc.jug.max., processus jugalis maxillae; proc.max.praemax., processus maxillaris praemaxillae; proc.maxpal., processus maxillopalatinus; proc.pal.praemax., processus palatinus praemaxillae; proc.praemax.max., processus praemaxillaris maxillae; proc.praemax.pal., processus praemaxillaris palatini; proc.qd.pter., processus quadraticus pterigoidei; proc.ventr.dent., processus ventralis dentalis; r.parasph., rostrum parasphenoideum; symph.mand., symphysis mandibulae.