Falconidae Falcons

The phylogenetic interrelationships of the modern species indicate that the Falconidae, which today have a worldwide distribution, originated in South America (Griffiths 1999). For this reason and because some molecular analyses provide support for a clade including the Cariamidae, Falconidae, Psittaciformes, and Passeriformes (Ericson et al. 2006; Hackett et al. 2008), it is tempting to speculate about possible affinities to the raptorial Phorusrhacidae, which are stem group representatives of the Cariamidae (Sect. 13.1; see also p. 108 in Olson 1985).

Unfortunately, the Paleogene fossil record of falcons is very poor, and includes no unambiguously identified specimens. Harrison (1982c) described a tiny distal tarsometatarsus with a few associated pedal phalanges from the London Clay of Walton-on-the-Naze as Parvulivenator watteli, and tentatively assigned the species to the Falconidae. The distal width of the tarsometatarsus is only about 3 mm, and its morphology does not suggest a closer relationship to falcons or any other diurnal bird of prey. I hypothesized that it may represent a coliiform bird (Mayr 2005a), but now rather think that its affinities are indeterminable without more material. A photo of the holotype is reproduced here for the first time (Fig. 14.1). As noted previously (Mayr 2005a), there is a second distal tarsometatarsus of this species,

Horusornithidae

Fig. 14.1 a Right tarsometatarsus of Parvulivenator watteli Harrison, 1982 from the early Eocene London Clay of Walton-on-the-Naze (holotype, Natural History Museum, London, UK, BMNH A 5172); b right tarsometatarsus of Stintonornis mitchelli Harrison, 1984 from the London Clay of the Isle of Sheppey (holotype, BMNH A 5284); c-g selected skeletal elements of Horusornis vianeyliaudae Mourer-Chauviré, 1991 (Horusornithidae) from the late Eocene locality La Bouffie of the Quercy fissure fillings in France. c, d Left tarsometatarsus (holotype, Université des Sciences et Techniques du Languedoc, Montpellier, France, BFI 1974); e distal left tibiotarsus (BFI 1962); f distal left tarsometatarsus (BFI 1978); g distal right humerus (craniodistal view, BFI 1960). Same scale bar for all images except b. (Photos of Horusornis courtesy of Cécile Mourer-Chauviré, others by Sven Tränkner)

Fig. 14.1 a Right tarsometatarsus of Parvulivenator watteli Harrison, 1982 from the early Eocene London Clay of Walton-on-the-Naze (holotype, Natural History Museum, London, UK, BMNH A 5172); b right tarsometatarsus of Stintonornis mitchelli Harrison, 1984 from the London Clay of the Isle of Sheppey (holotype, BMNH A 5284); c-g selected skeletal elements of Horusornis vianeyliaudae Mourer-Chauviré, 1991 (Horusornithidae) from the late Eocene locality La Bouffie of the Quercy fissure fillings in France. c, d Left tarsometatarsus (holotype, Université des Sciences et Techniques du Languedoc, Montpellier, France, BFI 1974); e distal left tibiotarsus (BFI 1962); f distal left tarsometatarsus (BFI 1978); g distal right humerus (craniodistal view, BFI 1960). Same scale bar for all images except b. (Photos of Horusornis courtesy of Cécile Mourer-Chauviré, others by Sven Tränkner)

also from the London Clay, in the collection of the Natural History Museum. Another putative falconid from the London Clay of the Isle of Sheppey, Stintonornis mitchelli Harrison, 1984, is also based on the distal end of a tarsometatarsus

(Fig. 14.1). This specimen is more similar to extant Falconidae, but is also too fragmentary for a reliable identification. Mourer-Chauvire (2006) mentioned the presence of still undescribed Falconidae in the late Eocene and early Oligocene of the Quercy fissure fillings.

A distal tarsometatarsus from the middle Eocene of the La Meseta Formation of Seymour Island (Antarctica) was assigned to the Falconidae by Tambussi et al. (1995) and Tambussi and Acosta Hospitaleche (2007). This fossil comes from a species that was the size of the extant Crested Caracara (Caracara plan-cus), to which it was also considered morphologically similar. At least judging from the published figure (Tambussi and Acosta Hospitaleche 2007), however, the trochlea for the second toe does not reach as far distally as in extant Falconidae, and additional skeletal elements are needed to confirm identification of the specimen.

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