Scalpelloid and brachylepadomorph barnacles (Cirripedia, Thoracica) from the Upper Cretaceous Mt. Laurel Sand, Delaware

Abstract

A diverse cirriped fauna, including the scalpelloids Cretiscalpellum homseyi n. sp., Arcoscalpellum withersi Collins, Arcoscalpellum bakeri Collins, Virgiscalpellum gabbi heintzi n. subsp., Virgiscalpellum sp., V. cf. V. gabbi apertus Collins, and the brachylepadomorph Brachylepas solida n. sp., occurs in the Upper Cretaceous Mt. Laurel Sand at the Biggs Farm locality on the Chesapeake and Delaware Canal, New Castle County, Delaware. This fauna represents the Maastrichtian Virgiscalpellum Zone originally identified in the Ripley and Prairie Bluff formations of the eastern Gulf Coast.

Origin of the balanomorph barnacles (Crustacea, Cirripedia, Thoracica): new evidence from the Late Cretaceous (Campanian) of Sweden

“…The same situation probably obtains in Epibrachylepas and Parabrachylepas described below, although articulated material of these is not known. In most brachylepadids the lower peduncular scales have a highly specialized articulation of interpenetrant knobs and grooves (Withers 1935;Zullo et al 1987).…”

“…Withers (1935) showed how the morphology of scuta of successive species of Pycnolepas and Brachylepas approached the condition present in balanomorphs, with progressive movement of the apicobasal ridge towards the tergal margin, and concomitant reduction in the tergal surface of the scutum, until the condition in B. guascoi is reached, where the tergal surface is reduced to a small vertical region ("tergal slip") and the apicobasal ridge forms the tergal margin. Zullo et al (1987) briefly discussed Wither's ideas from a functional viewpoint, but the lion's share of attention in balanomorph origins has been devoted to homologies of wall plates (see above).…”

“…Indeed, the standard illustration of tergal and scutal 13 terminology, used by Withers (1935Withers ( , 1953, Newman et al (1969) and Southward (2006) has not changed for over 160 years. This is a particularly acute problem in the case of the articulation between the scutum and tergum, which shows significant morphological change in the transition between the scalpellomorphs and balanomorphs (Withers 1935;Zullo et al 1987) and, indeed, within balanomorphs. The structural modifications and homologies of scutal and tergal stuctures are more complex than has hitherto been realised.…”

“…Pycnolepas ranges from the Late Jurassic to the Miocene (Jagt et al 2007), whereas Brachylepas is Late Cretaceous in age (Zullo et al 1987). A living brachylepadid, Neobrachylepas, was described from vent faunas in the Pacific (Newman & Yamaguchi 1995).…”

“…Brachylepas, however, remains poorly known, with only a single articulated specimen, and four species known from only a small number of isolated plates. A fourth species, B. americana, is known from abundant isolated plates (Zullo et al 1987).…”