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Fossil pseudasturid birds (Aves, 

 Pseudasturidae) from the London Clay 



-7 JUN 2001 



■IL'J3PAR Y 



GARETH J. DYKE 



Department of Ornithology, American Museum of Natural History, Central Park W at 79''' Street, New York NY 

 10024, USA. 



Synopsis. Fossil remains from the Lower Eocene ( Ypresian) London Clay Formation of England are referred to the extinct 

 higher-order group of birds, the Pseudasturidae Mayr. This material includes the specimen BMNH A 5 193, referred by Harrison 

 (1982) to the taxon ' Primobucco' olsoni Feduccia & Martin, previously the oldest published record of a piciform bird (barbets and 

 relatives) known from the fossil record. The description of three-dimensionally preserved tarsometatarsi from the London Clay 

 confirms the fully zygodactyl nature of the pseudasturid foot (fourth toe directed backwards). 



INTRODUCTION 



The extinct avian family Pseudasturidae was erected by Mayr ( 1 998) 

 for the reception of a number of small, zygodactyl, landbirds that are 

 known from the Lower-Middle Eocene of Europe and North America. 

 Mayr (1998) diagnosed this higher-taxon on the basis of a number of 

 putatively derived (apomorphic) characters of the skull, vertebrae 

 and limbs and included within the group two species from the 

 Middle Eocene deposit of Grube Messel, Hessen, Germany 

 {Pseudastur macrocephalus [Fig. 1 ] and an unnamed taxon), as well 

 as the enigmatic taxon 'Primobucco' olsoni (Feduccia & Martin, 

 1976) known from the Eocene of North America, and from the 

 London Clay (see Mayr, 1998). 



In this paper, I present the descriptions of a number of fossil 

 specimens from the London Clay Formation of England that are 

 referable to the Pseudasturidae, as defined by Mayr (1998). Amongst 

 this material is a proximal portion of tarsometatarsus (BMNH A 

 5193) that was classified by Harrison (1982) within the order 

 Piciformes (barbets and relatives), previously the oldest published 

 record for this group of modem birds. The three-dimensional preser- 

 vation of the London Clay specimens serves to confirm the 

 supposition of Mayr (1998) that the pseudasturid birds had a fully 

 developed zygodactyl foot (fourth toe turned backwards to facilitate 

 perching and climbing) with a prominent sehnenhalter or medial or 

 plantar projection of the fourth trochlea (Steinbacher, 1935). 



The fossil specimens discussed here are housed in the collections of 

 The Natural History Museum, London, UK, (Palaeontology Depart- 

 ment; BMNH A), the Forschungsinstitut Senckenberg, Frankfurt am 

 Main, Germany (SMF), the Wyoming DinosaurCenter.Thermopolis, 

 USA (collection POHL, examined in Frankfurt), and the Staatliches 

 Museum fiir Naturkunde, Karlsruhe, Germany (SMNK). Recent 

 osteological specimens examined during the course of this work are 

 held in the ornithological collections of The Natural History Museum, 

 Tring, Hertfordshire, UK (BMNH S ). Anatomical nomenclature used 

 follows Howard (1929) and Baumel & Witmer (1993). 



SYSTEMATIC PALEONTOLOGY 



Class AVES Linnaeus, 1758 

 Order INCERTAE SEDIS 

 Family PSEUDASTURIDAE Mayr, H 



Genus and Species INDET. 



Referred London Clay specimens 



Material. BMNH A 6218 (Fig 2A), associated bones consisting 

 of: a partially complete right scapula ( lacking extreme lateral portion 

 of extremitas caudalis); a partially complete right coracoid (lacking 

 the processus procoracoideus, lateral extremity of processus 

 acrocoracoideus and lateral portion of facies articularis sternalis): a 

 proximal end of a left coracoid and portion of shaft; a proximal end 

 of a right humerus and portion of shaft; a nearly complete left femur 

 (lacking portions of condylus medialis, sulcus intercondylaris, 

 condylus lateralis and crista trochanteris). BMNH A 6184 (Fig. 2F), 

 a distal end of a left tarsometatarsus and portion of shaft. 



Geological age and localities. BMNH A 62 1 8 was collected 

 from an unknown horizon within the London Clay Formation at 

 Walton-on-the-Naze, Essex, England by Mr. W. George in 1977 (his 

 original collectors number is unknown). BMNH A 6184 was col- 

 lected from within division D-E of the London Clay Formation at 

 Warden Point, Isle of Sheppey. Kent, England by AUeyn School 

 (donated via Mr. Salmon) in 1 983. The age of the Walton and Warden 

 beds of the London Clay Formation (Bed A2; King. 1981) are 

 approximately 54.4 Mya (after Harland etai, 1990; Berggren etal., 

 1995). 



BMNH A 6218 



Scapula (Fig. 2B). The blade of the scapula is broad and gently 

 curved although the extremitas caudalis is lacking. The facies 

 articularis humeralis is flat and ovate in form and is not excavated. 

 The tuberculum coracoideum is small and obsolete, the acromion is 

 rounded and blunt. 



Coracoid (Fig. 2A). The processus acrocoracoideus is very abrupt 

 and blunt with almost no point. The brachial tuberosity is very 

 markedly folded over towards the processus procoracoideus; this 

 tuberosity only extends laterally to level with the edge of the cotyla 

 scapularis. The margin between the glenoid and scapular facets is 

 raised and pronounced, the scapular facet is shallow but has a raised 

 distal margin (much higher than the shaft). On both of the preserved 

 coracoids, the extremity of the procoracoid process is broken but this 

 does appear to have been flat laterally. There is a small foramen nervi 

 supracoracoidei in the middle of the shaft distal to the sternal facet. 

 Overall, the coracoid shaft is straight, but there is a slight kink 

 immediately distal to the foramen nervi supracoracoidei. The sterno- 

 coracoid impression is rectangular and shallowly excavated centrally; 

 the distal borders of this impression are raised and the angulus 



© The Natural History Museum, 2001 



