A NEW GUILLEMOT, CEPPHUS SPECIES, FROM THE LOWER PLEISTOCENE C . J . O . HARRISON F O S S I L evidence of auks of the genus Cepphus IS rare. Apart from a few archaeological sites Brodkorb (1971) lists only Upper Pleistocene records from Chudleigh, Devon, England and from Vardo, Norway, both of the Black Guillemot Cepphus grylle. The Prestwich Collection in the Department of Palaeontology, British Museum (Natural History) contains an alcid carpometacarpus. This is from the Lower Pleistocene Red Crag of Suffolk. The bone is large, similar in size to that of a razorbill Alca torda but in the finer details of its structure it resembles carpometacarpi of the genus Cepphus. Prominences on the bone are worn and most of the metacarpal I I I bridge and metacarpal I flange are missing.
The genus Cepphus contains three species, all Recent. The Black Guillemot C. grylle of the North Atlantic and Arctic seas, and the Pigeon Guillemot C. columba of the North Pacific are very similar. A third species, the Sooty Guillemot C. carbo of the sea of Japan and sea of Okhotsk, is a little larger. From their similarity and zoogeographical distribution it is likely that speciation within this genus occurred in the Pleistocene, the last species probably evolving as an isolate in the restricted region in which it now occurs (Storer 1952). The present specimen is similar to the carpometacarpi of C. grylle and C. columba in most respects but about a quarter larger; and is slightly shorter than that of C. carbo with the proximal carpal trochlea portion proportionally slightly larger. The projecting flange of metacarpal I is stouter at the base than in these species and metacarpal III is narrower at the proximal end. In view of its early origin and location it is likely that the Suffolk specimen represents either another large isolate of the genus, now extinct, or was part of the parental stock from which some or all of the Recent Cepphus species are derived. The specimen cannot be referred to existing forms and I am therefore describing it as a new species. Family ALCIDAE genus Cepphus species Cepphus storeri sp. nov. Etymology. T h e species is named after Professor Robert W. Storer in recognition of his work on the Alcidae. Material. Holotype only, an imperfect left carpometacarpus B.M.N.H. no. A4986. From the Prestwich Collection, purchased May, 1894.
A NEW GUILLEMOT
Occurrence.
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Red Crag, Lower Pleistocene: Suffolk, England.
Diagnosis. Carpometacarpus larger than those of C. grylle and C. columba and smaller than that of C. carbo. Flange of metacarpal I stouter at base. Anterior carpal fossa larger. Description. The holotype is a left carpometacarpus, with prominent surfaces worn, especially at the distal end, and the greater part of metacarpal III and the anconal end of metacarpal I missing. In general proportions and details it resembles the corresponding bone of Cepphus species, the prominent flange of metacarpal I being short and not compressed on the internal side at the proximal end as in other alcid genera; but compared with Recent Cepphus species metacarpal I is stouter, lacking the concavity of the internal and external surfaces near its base. The anterior carpal fossa is deeper and more rounded, and the fossa at the palmar end of the carpal trochlea appears less deep than on Recent species. The carpal trochlea is proportionally slightly longer. Measurements. Greatest length to groove of trochlea (flanges are worn) 18.9 mm.; width of metacarpal II 3.8, palmar/anconal thickness 3.1 mm.; basal length of metacarpal I flange 6.5 mm., basal thickness at middle 2.6 mm. References Brodkorb, P. (1971). Catalogue of fossil birds; Part 3. Bull. Fla. St. Mus., Biol. Sei. 2, 99-220. Storer, R. W. (1952). A comparison of Variation, behaviour and evolution in the sea bird genera Uria and Ceppus. Univ. Calif. Publ. Zool. 52, 121-222.
C. J. O. Harrison, British Museum (Natural History).