Additions to the subfamily Acanthohoplitinae from the British Isles, including the first verifiable record of Acanthohoplites (Lower Cretaceous, upper Aptian)

Abstract

Acanthohoplites aschiltaensis, a late Aptian ammonite originally described from the Caucasus of Dagestan, is recognised from the British Isles for the first time. A study of the full ontogenetic development of this species is enabled owing to the preservation of a mature body-chamber, not previously known. Stratigraphically, it confirms the correlation of the Fullers' Earth deposits within the Parahoplites nutfieldiensis Zone at Baulking, Oxfordshire, with strata of the Parahoplites melchioris Zone at the type locality and elsewhere. Palaeobiogeographically, it underlines the strong relationship between the Boreal fauna of western Europe and that of the Mediterranean-Caucasian Subrealm of the Tethyan realm. Additionally, a small Hypacanthoplites spp. fauna is described from the H. rubricosus Subzone of the Hypcanthoplites jacobi Zone at the Aptian/Albian boundary interval exposed in the Shanklin area, Isle of Wight. From this locality, otherwise almost devoid of ammonite remains, we present fairly well-preserved specimens of ‘Hypacanthoplites’ elegans, H. plesiotypicus, H. pricei, H. tenuiformis, H. rubricosus, H. sigmoidalis and H. sp. 1 indet., only known thanks to some decades of intensive collecting. In addition to the other members of this genus previously described from the British Isles, the occurrence of ‘H.’ elegans and H. plesiotypicus further supports the existence of narrow sea connections eastwards onto the European continent.