FOSSIL PSEUDASTURID BIRDS 



Tentatively referred London Clay specimens 



Material. BMNH A 6224 (Fig. 2G), a proximal end of a right 

 tarsometatarsus and portion of siiaft (lacking the crista intermediae 

 hypotarsi). BMNH A 5193 (Fig. 3), a proximal end of a right 

 tarsometarsus (referred to 'Primobucco' olsoni Feduccia & Martin 

 [Aves, Piciformes] by Harrison, 1982). A complete description of 

 this element was provided by Harrison (1982). 



Geological age and localities . Both the specimens BMNH A 

 6224 and A 5 1 93 were collected from divisions D-E of the London 

 Clay Formation at Warden Point, Isle of Sheppey, Kent, England (A 

 6224 collected and presented by Mr. D. Ward in 1982; A 5193 

 collected and presented by Mr. S. Silverstein in 1980). The age of 

 these beds of the London Clay Formation is approximately 54.4 My a 

 (after Harland et ai, 1990; Berggren et al. 1995). 



BMNH A 6224 



Tarsometatarsus (Fig. 2G). The proximal tarsometatarsus of 

 BMNH A 6224 has a smoothly flattened medial shaft and a flat 

 hypotarsus; the rims of the medial and lateral cotyles (cotylae 

 mediale and laterale) extend distally to about the same level, the area 

 intercotylaris is not raised significantly above the surface of the 

 cotyles. On the proximal surface, both the cotyles are rounded in 

 outline and have raised lateral rims. There are two preserved cristae 

 intermediae hypotarsi. Two oblong proximal foramina are seen on 

 the surface of the shaft; the outer one is somewhat larger but they are 

 both at the same level on the proximal shaft. 



Measurements 



Bmnh a 6224: proximal right tarsometatarsus, total preserved 

 length - 5.2mm, medio-lateral width of hypotarsus - 2.2mm. 



Bmnh A 5193: proximal right tarsometatarsus, total preserved 

 length - 7.8mm, width of distal end - 2. 1mm, width at tibialis articus 

 scar- 1.3mm (Harrison, 1982). 



COMPARISONS AND REMARKS 



Although the tarsometatarsi are clearly visible in dorsal view on the 

 Messel pseudasturid specimens, detailed comparisons of this ele- 

 ment are only possible between BMNH A 6 1 84 and the well preserved 

 tarsometatarsi of Pseudastur macrocephalus (WDC-C-MG-94; 

 Mayr, 1998: text-fig. \). P. macrocephalus 2.ndBMNHk6\%A2ie an 

 almost exact match in terms of size and shape; in both specimens, 

 trochlea metatarsi III is very broad (compared to the trochlea for 

 metatarsals II and IV) and is extended far distally (especially with 

 respect to trochlea metatarsi IV, which is small and located proxi- 

 mally on the shaft). Again, in both specimens there is a prominent 

 medial furrow on the distal trochlea metatarsi III and trochlea 

 metatarsi IV is turned somewhat plantarly to form a small phlange. 

 Based on the characters outlined by Mayr (1998), the specimen 

 BMNH A 6 1 84 can be referred with confidence to the Pseudasturidae, 

 especially because of the presence of the two characters: large 

 foramen vasculare distale and trochlea metatarsi IV bearing a 

 sehnenhalter (characters 10 and 11 of Mayr, 1998). 



However, although BMNH A 6184 and the tarsometatarsus of 

 Pseudastur macrocephalus are very much alike (and are certainly 

 from very similar birds), there are a number of subtle differences: in 

 P. macrocephalus the distal margin of the shaft is raised (the shaft of 

 BMNH A 6184 is somewhat flatter and wider distal to the foramen 

 vasculare distale; the foramen vasculare distale is more elongate and 



Fig. 3 Proximal end of right tarsometatarsus (BMNH A 5 1 93) referred by 

 Harrison (1982) to the Piciformes ( 'Primobucco' olsoni Feduccia & 

 Martin; Primobucconidae). A, posterior; B, lateral; C, medial; D. 

 anterior views. Unstippled areas are not preserved. Total length of 

 specimen = 7.82 mm; scale bar = 2 mm. Redrawn after Harrison ( 1982). 



teardrop shaped in P. macrocephalus (more circular in BMNH A 

 6 1 84); and the trochlea metatarsi IV of BMNH A 6 1 84 is wider and 

 more robust. Lateral to the foramen vasculare distale (on the surface 

 of the trochlea) there is a flat and shelf-like angled surface. 



On the basis of the Messel material, Mayr (1998) was unable to 

 conclusively demonstrate the fully or faculatively zygodactyl nature 

 of members of the Pseudasturidae (cf. Pseudastur macrocephalus): 

 "whether Pseudastur macrocephalus was fully or faculatively 

 zygodactyl is difficult to assess on the basis of the skeletons from 

 Messel known so far'. This is because in all the known Messel 

 specimens, the anterior portion of the trochlea metatarsi IV is 

 obscured as a result of compaction during preservation (Mayr, 

 1998). On the basis of BMNH A 6184, an entirely uncrushed 

 specimen, it is possible to confirm the observation of Mayr (1998) 

 that members of this extinct clade had developed a fully zygodactyl 

 foot morphology (Fig. 4). 



BMNH A 6224 and A 5193 can be tentatively referred to the 

 Pseudasturidae on the basis of comparisons with Pseudastur macro- 

 cephalus (WDC-C-MG-94). Both of the London Clay specimens are 

 of a similar size and correspond with the proximal tarsometatarsi of 

 WDC-C-MG-94 (although they are slightly larger; see measure- 

 ments). As in WDC-C-MG-94, the foramina vascularia proximalia 

 are at the same level on the shaft, the inner one bemg somewhat 

 larger. The hypotarsal areas in the three specimens are identical 

 (although only the crista medialis hypotarsi is seen clearly in WDC- 

 C-MG-94); this protrudes over the fossa infracotylaris dorsalis and 

 the impressio ligamentis collateralis is pronounced in all three 

 specimens. 



Harrison (1982) referred BMNH A 5193 (Fig. 3) to the taxon 

 'Primobucco' olsoni (quotation marks added after Mayr, 1998) 

 within the extinct family Primobucconidae erected by Feduccia & 

 Martin ( 1 976) within the order Piciformes. He noted that 'within that 

 family, it [BMNH A 5193] appears to match in characters and size 

 the corresponding bone of Primobucco olsoni Feduccia & Martin, as 

 described and figured by them". Harrison (1982) provided no further 

 indication of what these characters might be. Referral of this speci- 

 men to within the order Piciformes cannot be confirmed with any 

 degree of confidence: although monophyly of the order has been 

 ';upported on the basis of a number of characters (i.e. zygodactyl 

 foot, type IV flexor tendons, and m. flexor hallucis longus three- 

 headed; Simpson & Cracraft, 1981; Swierczewski & Raikow, 1981; 

 Raikow & Cracraft, 1983), none of these can be confirmed for 



