G.J. DYKE 



Fig. 4 Distal end of left tarsometatarsus (BMNH A 6184) in plantar view. 

 The pointer indicates the laterally retroverted portion of trochlea 

 metatarsi IV (the senhenhalter of Steinbacher, 1935). 



BMNH A 5193 since they all refer to the distal portions of the 

 tarsometatarsus. Further, Mayr (1998) commented on the status of 

 ' Primobitcco" olsoni and noted that it is likely that the type specimen 

 of this taxon may also be referable to the Pseudasturidae. 



CONCLUSIONS 



( 1 ) The referral of a number of new specimens from the London 

 Clay Formation to the extinct landbird clade Pseudasturidae 

 Mayr confirms the fully zygodactyl foot morphology of these 

 birds. 



(2) The recognition of specimens referable to the Pseudasturidae 

 within the fossil bird collections of the London Clay Formation 

 further serves to highlight the compositional similarity seen 

 between this deposit and the roughly contemporaneous deposit 

 of Grube Messel, Germany (see Mayr, 1998). At least in terms 

 of the clades of landbirds, the two deposits are remarkably 

 uniform in their composition (Dyke, 1998) and serve to illus- 

 trate the 'settling' of a number of the landbird clades by the 

 time of the earliest Eocene. 



Acknowledgements. For access to specimens (fossil and recent), I 

 thank the staff of The Natural History Museum (London and Tring). Gerald 

 Mayr (Frankfurt) kindly provided me with much access to the specimens in 

 his care (including material on loan from the Wyoming Dinosaur Centre) and 

 made many comments on previous versions of this manuscript. All the 

 photographs used here were taken by Phil Crabb (NHM Photographic Serv- 

 ices); this work was funded by a NERC studentship (GT049728ES). 



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