Cretaceous Research (1996) 17, 135 –150 Early Cretaceous cementing pectinid bivalves *E. M. Harper, †J. D. Radley and ‡T.J. Palmer * Department of Earth Sciences , University of Cambridge , Downing St. , Cambridge CB2 3EQ , UK † Department of Geology , University of Portsmouth, Burnaby Building , Burnaby Rd , Portsmouth PO1 3QL , UK ‡ Institute of Earth Studies , University of Wales , Aberystwyth SY23 3DB, UK Revised manuscript accepted 25 October 1995 Large thick-shelled cementing pectinids, variously described as Prohinnites , are conspicuous, if not abundant, epifaunal bivalves in shallow marine facies deposited in a range of Tethyan and Southern Temperate locations during the Early Cretaceous. The relationships between these bivalves and Jurassic members of the genus Eopecten, some individuals of which were able to cement to hard substrata, have previously been unclear. The recent discovery of well preserved specimens of Prohinnites in the Aptian Perna Beds Member of the Isle of Wight has allowed a re-examination of Early Cretaceous cementing pectinids and description of their morphology and shell microstructure. Comparisons with Middle and Upper Jurassic cementing Eopecten have shown that the Cretaceous Prohinnites are closely but not directly related. It is probable that these taxa represent multiple evolution of the cemented habit from a well pre-adapted Eopecten-group of byssally attached pectinids. ÷ 1996 Academic Press Limited KEY WORDS: Bivalvia; Pectinidae; cementation; Eopecten; Prohinnites . 1. Introduction Primitive members of the bivalve family Pectinidae were byssally attached, resting on their right valves. Although all living species pass through a byssate stage early in their ontogeny, and many retain this lifestyle for their entire lives, several taxa have abandoned this habit in their mature state to either lie free upon the substrate surface (e.g., Pecten) or become cemented in the manner of oysters. It has long been recognized that the ability to cement to a hard substratum is polyphyletic within the Pectinidae, i.e., that the habit has evolved independently at dif ferent times and within dif ferent genera (Dall, 1898; Bernard, 1986; Harper & Palmer, 1993; Waller, 1993), but it is uncertain how many times. Bernard (1986) recognized a number of cementing clades from Tertiary and Recent times and also the Lower Cretaceous genus Prohinnites Gillet. More recently, Harper & Palmer (1993) described cementing members of the genus Eopecten Douville ´ from rocks of Middle Jurassic (Bajocian to Callovian) age from France and southern England. They also noted that the specimens of Upper Jurassic (Kimmeridgian) E. obliquus from Portugal illustrated by Fu ¨ rsich & Werner (1989) appeared also to have cemented, though this was not confirmed. As not all large Eopecten specimens show signs of an attachment scar, instead maintaining a persistent byssal notch into maturity, Harper & Palmer concluded that the ability to cement was either restricted to certain species or that the habit was facultative within either the genus or some species. The genus Eopecten has a stratigraphic range from the Lower Jurassic (Hettangian) to the Lower Cretac- eous (Albian) (Hertlein, in Moore, 1969). Given that this range overlaps with that of Prohinnites , Harper & Palmer (1993) speculated that the two genera 0195– 6671 / 96 / 010135 + 16 $12.00 / 0 ÷ 1996 Academic Press Limited