Article: A new lacazellin thecideoid brachiopod from the Middle Jurassic of the Cotswolds, England
Peter G. Baker
Restudy of the thecideoid fauna from organo-detrital residues of Aalenian age from two Cotswold localities revealed the presence of a rare form assignable to the Lacazellinae. Its morphology and shell microstructure enabled it to be identified as the earliest clear representative of the subfamily and the possession of ramuli, jugal pillar, reniform brachial lobes and partially suppressed fibrous secondary shell layer indicate proximity to the rootstock of the Lacazella Munier-Chalmers line of descent in a position possibly ancestral to Praelacazella Smirnova. In the absence of near stratigraphical or geographical relatives the Aalenian specimens are assigned to Protolacazella scripta gen. et sp. nov. The suppression of fibrous secondary shell in P. scripta mirrors the phylogenetic suppression of the secretion of fibrous secondary shell in the Lacazellinae as a whole and may provide an insight into the mechanism by which it was achieved.