. Bulletin of the British Ornithologists' Club. 71 [Bull. 1976: 96(2)] The skull (Fig. 1) is of particular interest, and differs extensively from the skulls of Ama^ona spp.—the genus with which Deroptyus has been associ- ated in recent lists. Table 1 compares skull and vertebra proportions in Deroptyus with a single specimen of Amayona aestiva. A much more extensive programme of measurements should obviously form part of any future investigation. Nevertheless inspection of a wide range of genera seems to indicate that the main points emerging from this limited comparison would hold good
. Bulletin of the British Ornithologists' Club. 71 [Bull. 1976: 96(2)] The skull (Fig. 1) is of particular interest, and differs extensively from the skulls of Ama^ona spp.—the genus with which Deroptyus has been associ- ated in recent lists. Table 1 compares skull and vertebra proportions in Deroptyus with a single specimen of Amayona aestiva. A much more extensive programme of measurements should obviously form part of any future investigation. Nevertheless inspection of a wide range of genera seems to indicate that the main points emerging from this limited comparison would hold good not only for other Ama^ona species, but probably for most other parrots except very large forms. The principal differences can be summarised as follows:— 1. The cranium is slightly shorter in Deroptyus\ but with much enlarged exoccipital (="opisthotic") processes which protrude beyond the posterior of the cranium and with a proportionately more expanded occipital region. 2. Palatine, quadrate and orbits are larger relative to both cranium length and body size in Deroptyus. 3. The lower jaw is considerably deeper in Deroptyus', and shows a prominent mandibular foramen (absent or very small in Ama^ond) and little emargination of the anterior edge. It is worth noting, in passing, that the orbital ring is complete in both specimens, although Garrod (1876) described it as incomplete; possibly his specimen was a young Fig. 1: Lateral views of skulls of (a) Deroptyus accipitrinus (b) Ama^pna aestiva. The most notable modifications are those of the occipital region, the large relative size and posterior protrusion of the exoccipital processes being equalled only be a few genera of very large parrots {Nestor, Strigops, Probos- ciger, Anodorhynchus, Ara). The modifications increase the area available for the insertion of the muscles concerned with turning and raising the head, which are particularly important for sideways wrenching movements used in. Please note tha
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