. Bulletin of the British Museum (Natural History), Geology. ENGLISH EOCENE H YRACOTHERIUM 109 in hypoconulid length (M15130) is nevertheless typical in its overall length/width proportions and appears to have achieved this by relative elongation of the talonid. Other variable characters such as cingular development and outline shape of upper molars as well as different wear stages (specimens figured chosen as far as possible to show similar wear) make the specimens shown in Figs 1-4 appear more different from one another than their specific diagnoses indicate. HI I I A
. Bulletin of the British Museum (Natural History), Geology. ENGLISH EOCENE H YRACOTHERIUM 109 in hypoconulid length (M15130) is nevertheless typical in its overall length/width proportions and appears to have achieved this by relative elongation of the talonid. Other variable characters such as cingular development and outline shape of upper molars as well as different wear stages (specimens figured chosen as far as possible to show similar wear) make the specimens shown in Figs 1-4 appear more different from one another than their specific diagnoses indicate. HI I I A 85 75 85 95 100a ~tr a Mr (o) 9- 8- I. - TO J A ? D OT (O) M1"2 Oj ' ' 8 9 10 11 12 9- 0 fr A D D To o 7 T o M3 r 8 9 10 Fig. 5 (a) Histogram of perpendicular distance from hypolophid to hypoconulid (a), as a percentage of hypolophid length (b), in M3 of Hyracotherium cuniculus, H. vulpiceps and H. aff. vulpiceps; (b-e) Scatter diagrams of maximum length (I) and width (w), in mm, of M3, P3, M1-2 and M3 respectively. Symbols: H. cuniculus (o), H. aff. vulpiceps (n), H. vulpiceps (o) and H. leporinum (a). Symbols in brackets indicate estimates; T indicates a plot of the primary type of a species; in Fig. 5d pre- ultimate molars identified as M1 or M2 are indicated by solid left or right half symbol, respectively. C. F. Cooper (1932& : 442-443), unaware that H. leporinum occurred above H. vulpiceps, considered the latter to be more advanced because its P3 resembled that of North American late Wasatchian forms such as H. venticolum (Cope), which were molarizing their premolars in the direction of Orohippus. In England, and probably the rest of Europe, the initial trend of molar- ization of P3 by the North American equid method ( by enlargement of the protoconule and distal shift of the protocone) changed to the European palaeothere method ( by addition of a hypocone behind the protocone, as occurred in the molarization of P4 in both North American and Europe
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