Eudromia elegans, I. Geoffroy Saint-Hilaire, 1832

Maxwell, Erin E., 2009, Comparative ossification and development of the skull in palaeognathous birds (Aves: Palaeognathae), Zoological Journal of the Linnean Society 156 (1), pp. 184-200 : 193

EUDROMIA ELEGANS

Day 9: There is no cranial ossification. The two rami of Meckel’s cartilage have a broad contact, as in ratites.

Day 10: The prenasal process is curved ventrally, as is the area of the lower jaw where the rami of Meckel’s cartilage are in contact. Dorsal outgrowth of the trabecula communis in the area of the nasal capsule initiates the formation of the parietotectal cartilage and the preoptic root of the orbital cartilage. The jugal and frontal processes of the premaxilla are ossified, as is the quadratojugal.

Day 11 ( Fig. 1D): The prenasal process is straighter than in younger embryos, and only a slight terminal hook remains. The squamosal, premaxillary process of the nasal, maxilla, palatine, vomer, and jugal are ossifying, as are the dentary, supra-angular, angular, and splenial. This is followed by the ossification of the parasphenoid rostrum and lamina, the basisphenoid, parietal, frontal, lacrimal, pterygoid, quadrate, prearticular, and ceratobranchials. The ossification of the quadrate is variable, as it does not always ossify before day 12 (YPM 112522). The premaxilla completely covers the prenasal process. The maxillary process of the nasal does not contact the nasal process of the maxilla. The beak forms a rigid ossified framework, but the calvarium is not well ossified.

Day 12: The basioccipital is ossifying.

Day 14: The exoccipital, laterosphenoid, prootic, opisthotic, epiotic, and mesethmoid are ossifying ( Figs 1E, 2F ). The supraoccipital is ossifying from a single centre. The mesethmoid lacks a broad dorsal exposure.

Figures

Figure 2. Palatal view of selected palaeognath embryos. A, B, Struthio camelus (modified from Parker, 1866). C, Rhea americana, stage 37 (day 17 of incubation, RM 7219). D, Rhea americana (modified from Müller, 1963). E, Dromaius novaehollandiae, stage 37 (day 28 of incubation, RM 8026). F, Eudromia elegans, day 14 of incubation (YPM 112524). Scale bars = 5 mm. Abbreviations: bo, basioccipital; exo, exoccipital; mx, maxilla; pal, palatine; pmx, premaxilla; psl, parasphenoid lamina; psr, parasphenoid rostrum; pt, pterygoid; q, quadrate; v, vomer.