FHalcyornithidae Pseudasturidae

Assignment of this taxon to stem group Psittaciformes is more controversial than that of the species discussed in Sect. 16.3.1, although its representatives are fairly abundant in the early and middle Eocene of Europe (Fur Formation, London Clay, Messel, Geisel Valley, and Egem in Belgium) and the early Eocene of the North American Green River Formation (Mayr 1998c, 2002a, h, 2007b; Dyke 2001e; Dyke and Cooper 2000; Kristoffersen 2002a; Waterhouse et al. 2008; see also Hoch 1988).

On the basis of a skeleton from the Green River Formation, the first species of this taxon was described as "Primobucco" olsoni by Feduccia and Martin (1976) and was assigned to the Primobucconidae, which were then considered to be piriform birds. The Primobucconidae are now assigned to the stem lineage of the Coraciidae/Brachypteraciidae, and the species of the type genus Primobucco are very different from "P." olsoni (Sect. 16.7.1). More light was shed on the affinities of "P." olsoni after recognition of several very similar species from the early and middle Eocene of Europe. In Messel, these birds are represented by complete and articulated skeletons that were assigned to Pseudasturides ("Pseudastur") macro-cephalus (Mayr, 1998), Serudaptus pohli Mayr, 2000, and at least two other unnamed species (Fig. 16.7; Mayr 1998c, 2000d, 2004f). Isolated bones from the London Clay locality Walton-on-the-Naze were described as Pulchrapollia gracilis by Dyke and Cooper (2000), who assigned this species to the Psittaciformes but explicitly, and erroneously, did not consider it related to the Pseudasturides-like birds from Messel (Fig. 16.8). Specimens of P. gracilis from Walton-on-the-Naze were also figured by Mayr and Daniels (1998), and the species closely resembles "Primobucco" olsoni, with which it has not yet been directly compared (Mayr 2002h). Other remains from the London Clay were described from the Isle of Sheppey by Dyke (2001e) and Mayr (2007b), and include a partial skeleton which was assigned to Pseudasturides cf. macrocephalus (Mayr 2007b).

I introduced the taxon "Pseudasturidae" for these birds (Mayr 1998c). New cranial material from Messel has shown, however, that this name is a junior synonym of the taxon Halcyornithidae. The latter was erected by Harrison and Walker (1972) for the earliest named fossil bird, Halcyornis toliapicus Koenig, 1825, a species known from a cranium from the London Clay of the Isle of Sheppey (Fig. 16.8; Harrison and Walker 1972; Mayr 2007b).

Pseudasturides and its allies are very different from extant parrots in many osteological features. The skull exhibits very large supraorbital processes and well-developed temporal fossae. The humerus is elongated and slender. The coracoid

Fig. 16.7 Pseudasturides macrocephalus (Mayr, 1998) (Halcyornithidae) from the middle Eocene of Messel (Staatliches Museum für Naturkunde Karlsruhe, Germany, SMNK-PAL.2373a). Specimen coated with ammonium chloride. (From Mayr 1998c; photo by Sven Tränkner)

Fig. 16.8 Halcyornithidae from the early Eocene of the London Clay. a Proximal left humerus of an undetermined species from Warden Point, Isle of Sheppey (Natural History Museum, London, UK, BMNH A 3553, paratype of Precursor parvus Harrison and Walker, 1977); b right ulna; c proximal right carpometacarpus; d proximal phalanx of left major wing digit; and e right tarsometatarsus of Pulchrapollia gracilis Dyke and Cooper, 2000 from Walton-on-the-Naze (holo-type, BMNH A 6207); f right and g left coracoid of an undetermined species from Walton-on-the-Naze (BMNH A 6218); h distal right humerus of an undetermined species from Warden Point, Sheppey, Kent, UK (BMNH A 6155); i distal left tarsometatarsus of ?Pseudasturides from Warden Point, Isle of Sheppey (BMNH A 6184); j cranium of Halcyornis toliapicus Koenig, 1825 from the Isle of Sheppey (holotype, BMNH A 130). All images to scale. (Photos by Sven Tränkner)

Fig. 16.8 Halcyornithidae from the early Eocene of the London Clay. a Proximal left humerus of an undetermined species from Warden Point, Isle of Sheppey (Natural History Museum, London, UK, BMNH A 3553, paratype of Precursor parvus Harrison and Walker, 1977); b right ulna; c proximal right carpometacarpus; d proximal phalanx of left major wing digit; and e right tarsometatarsus of Pulchrapollia gracilis Dyke and Cooper, 2000 from Walton-on-the-Naze (holo-type, BMNH A 6207); f right and g left coracoid of an undetermined species from Walton-on-the-Naze (BMNH A 6218); h distal right humerus of an undetermined species from Warden Point, Sheppey, Kent, UK (BMNH A 6155); i distal left tarsometatarsus of ?Pseudasturides from Warden Point, Isle of Sheppey (BMNH A 6184); j cranium of Halcyornis toliapicus Koenig, 1825 from the Isle of Sheppey (holotype, BMNH A 130). All images to scale. (Photos by Sven Tränkner)

is similar to that of extant Strigiformes in overall morphology; in contrast to the coracoid of crown group Psittaciformes, Psittacopes, and the Quercypsittidae, it exhibits a foramen for the supracoracoideus nerve.

Initially (Mayr 1998c), I considered the phylogenetic affinities of Pseudasturides and its allies uncertain, but subsequently suggested that they are stem group representatives of the Psittaciformes (Mayr 2002h). Apart from the presence of fully zygodactyl feet, this assumption was based on derived similarities in the tarsometa-tarsal trochlea for the fourth toe (the presence of a furrow for the tendon of the flexor perforatus muscle of the fourth toe), the tibiotarsus (the presence of a ridge on the medial surface of the proximal end), and the thoracic vertebrae. The absence of a furrow between the accessory trochlea and the trochlea for the fourth toe supports a position of halcyornithids outside a clade including Quercypsitta, Psittacopes, and crown group Psittaciformes (contra Dyke and Cooper 2000 who assumed that P. gracilis is the sister taxon of crown group Psittaciformes). Regarding the presence of a coracoidal foramen for the supracoracoideus nerve and supraorbital processes on the skull, halcyornithids closely match the group discussed in the following section.

0 0

Post a comment