On the Steinmanellidae (Bivalvia: Myophorelloidea); their palaeo-biogeography, evolution and classification

COOPER, MICHAEL R.; LEANZA, HÉCTOR A.

NEUES JAHRBUCH FUR GEOLOGIE UND PALAONTOLOGIE-ABHANDLUNGEN

E SCHWEIZERBARTSCHE VERLAGS

Año: 2017 vol. 285 p. 313 - 335

0077-7749

The trigoniid group"Pseudo-Quadratae" was introduced for Cretaceous descendents ofMyophorellidae with a convergent resemblance to Tethyan Quadratotrigoniinae (=Quadratae). Subsequently it was made the basis of the subfamily Steinmanellinaewhich herein is elevated to family rank. The earliest record of the group isfrom the Early-Middle Kimmeridgian of the Tethyan Realm (American Province),from where it spread into the Boreal and Gondwanic realms. Steinmanellids roseto dominance in the cool temperate waters of the Andean Province, and thelatter represents their centre of diversification. They are absent from the predominantlycold circum-polar waters of Southern and Eastern Gondwana, i.e. the Antarctic,Maorian and Australasian provinces. The evolution of the group is tracked andtwo lineages identified, comprising 50 nominal species assigned to 14 genera, 8of which are new: Stoyanowella, Philippiella,Garatella, Weaverella, Neuquenella, Popenoella, Louellaand Tashiroella. One lineage (Yaadiinae nov.) migrated northwards fromits Tethyan origin into the Cordilleran Province of the Boreal Realm andthence, in the Late Cretaceous, to the Oriental Province, surviving in bothbiochores into the Maastrichtian. The latter subfamily also occurs as a biogeographical(?convergent) anomaly in the Barremian of southeast Africa. The second lineage,the subfamily Steinmanellinae, appeared in the Early Tithonian of the AndeanProvince, where it radiated and survived until the Late Hauterivian. From thereit migrated eastwards into the Ethiopian Province, reaching as far as India,where it is recorded only from the Late Valanginian.