Review of the British Haramiyidae (? Mammalia, Allotheria), their molar occlusion and relationships

Abstract

Haramiyid teeth from the Rhaeto-Lias of Holwell Quarry, England, which had been previously described, were re-examined in the light of the large sample from Saint-Nicolas-de-Port. Haramiya and Thomasia are interpreted as upper and lower teeth, respectively. Differences within each ‘genus’ are ascribed largely to position within the dentition (anterior ‘molars’, posterior ‘molars’, ‘premolars’). There is much individual variation within each of these tooth groups, but at Holwell, as well as Saint-Nicolas-de-Port, it is possible to distinguish a larger ( Thomasia moorei ) and a smaller species ( T. antiqua , including T. anglica, H. butleri , and probably H. fissurae ). Upper molars, but not lower molars, appear to be more advanced at Holwell than at Saint-Nicolas-de-Port. It is inferred from tooth wear that the upper and lower molars were reversed buccolingually and anteroposteriorly, and the effective chewing stroke was longitudinal and backwards (palinal), but with an orthal component at the beginning of the stroke, giving a crushing-grinding action. The chewing movement resembled in principle that of the traversodontid Scalaenodon . Opposition between the teeth has probably evolved by the development of a second row of cusps from the lingual cingulum in both jaws. However, the transformation of a triconodont into a haramiyid would involve a major change from unilateral, transverse chewing to presumably bilateral, longitudinal chewing. Possible relationships of haramiyids to multituberculates and to broad-toothed cynodonts are discussed, with their implications for early mammalian phylogeny. Support is given for ordinal separation from the Multituberculata, as Haramiyida. A new interpretation is proposed of the cusp pattern of Theroteinidae, as haramiyid relatives.