FPsittacopes and Allies

Unambiguous remains of early and middle Eocene stem group representatives of the Psittaciformes were reported from the London Clay and Messel (Mayr and Daniels 1998). The Messel species was named Psittacopes lepidus Mayr and Daniels, 1998, and is known from two skeletons. The London Clay remains belong to at least three different species, which are represented by three-dimensionally preserved skulls and bones of most major limb elements (Fig. 16.6; Mayr and Daniels 1998). All are very similar to the sparrow-sized P. lepidus, and closely resemble crown group Psittaciformes in their postcranial features. The slender tarsometatarsus exhibits an accessory trochlea for the retroverted fourth toe. As in the Quercypsittidae (Sect. 16.3.2) and extant Psittaciformes, but unlike in other zygodactyl birds except the Piciformes, this accessory trochlea is separated from the main trochlea by a distinct furrow (Mayr and Daniels 1998). The humerus of Psittacopes and its allies is less stout than that of crown group Psittaciformes and has a less protruding deltopectoral crest. The derived humerus morphology of extant parrots is functionally correlated to the large crop and weak furcula of these birds, and their ability for hovering flight over a short period of time (Stegmann 1964).

Molecular Clock Birds Fossil

Fig. 16.6 Undescribed psittaciform bird from the early Eocene London Clay of Walton-on-the-Naze (collection of Paul Bergdahl, Kirby-le-Soken, UK, BC 8917A). a, b Skull (with matrix); c mandible; d right quadrate; e atlas; f cervical vertebra; g right scapula; h right coracoid; i omal extremity of left scapula; j proximal right humerus; k distal left humerus; l left ulna; m distal radius; n proximal left carpometacarpus (with matrix); o proximal tibiotarsus; p ungual phalanges. All images to scale. (From Mayr and Daniels 1998, modified)

Fig. 16.6 Undescribed psittaciform bird from the early Eocene London Clay of Walton-on-the-Naze (collection of Paul Bergdahl, Kirby-le-Soken, UK, BC 8917A). a, b Skull (with matrix); c mandible; d right quadrate; e atlas; f cervical vertebra; g right scapula; h right coracoid; i omal extremity of left scapula; j proximal right humerus; k distal left humerus; l left ulna; m distal radius; n proximal left carpometacarpus (with matrix); o proximal tibiotarsus; p ungual phalanges. All images to scale. (From Mayr and Daniels 1998, modified)

These features seem to have been absent or at least much less developed in the Eocene stem group representatives.

The most significant differences between Psittacopes, the unnamed London Clay species, and extant Psittaciformes, however, concern the morphology of the beak. Although the upper beak is short and quite robust, expectedly for a stem group representative of the Psittaciformes, it is much less downcurved than in extant parrots, has much larger narial openings, and the mandible is not as deep and short (Fig. 16.6). The tarsometatarsus of Psittacopes and its London Clay relatives also exhibits a less derived morphology than that of extant parrots in that the accessory trochlea of the fourth toe is less elongated and the trochlea for the second toe is smaller. I have argued elsewhere (Mayr 2002h) that the highly specialized morphology of the beak and feet of crown group Psittaciformes are an example of synorganization, i.e., the concerted evolution of different parts of the body, which together form a functional unit. Extant parrots regularly use their feet to assist their husking food, and it is likely that their tarsometatarsal specializations constitute adaptations to increase the grasping capabilities of the foot. Because of the absence of the derived tarsometatarsus and skull features in the fossil species, Psittacopes and its London Clay relatives certainly had a feeding technique different from that of extant parrots, being rather generalized, possibly granivorous feeders.

16.3.2 fQuercypsittidae

Another taxon of early Paleogene stem group Psittaciformes are the Quercypsittidae, which occur in the late Eocene (MP 17) locality La Bouffie of the Quercy fissure fillings (Mourer-Chauvire 1992c) and the early Eocene London Clay (Mayr and Daniels 1998). Two species, Quercypsitta ivani Mourer-Chauvire, 1992 and Q. sudrei Mourer-Chauvire, 1992, were named from La Bouffie, and the described skeletal elements include an incomplete carpometacarpus, coracoids, distal tibio-tarsi, tarsometatarsi, and pedal phalanges. Likewise, a distal tarsometatarsus from the middle Eocene (MP 11-13; Mlikovsky 2002) of England, which was referred to the nonpsittaciform Palaeopsittacus georgei (Sect. 12.1) in the original description, closely resembles that of Quercypsitta (Mayr and Daniels 1998).

After the recent discovery of abundant new fossils, including several tarsometa-tarsi, it became obvious that Vastanavis eocaena Mayr et al., 2007 from the early Eocene of the Vastan Lignite Mine in India is also a Quercypsitta-like psittaciform bird (personal observation). The original description of this species was based on coracoids and scapulae, and the former were erroneously likened to the Otididae (bustards; Mayr et al. 2007).

The short and stout tarsometatarsus of the Quercypsittidae is reminiscent of the corresponding bone of some extant parrots in its proportions. The accessory trochlea for the retroverted fourth toe is, however, less well developed than that of crown group Psittaciformes. The coracoid also strongly differs from that of modern parrots and exhibits a plesiomorphic, cup-like scapular articulation facet

(Mourer-Chauviré 1992c), which indicates a position of quercypsittids outside a clade including Psittacopes and crown group Psittaciformes. Ungual pedal phalanges preserved in a London Clay quercypsittid resemble those of strigiform birds (Mayr and Daniels 1998).

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