Middle Cambrian of Avalonian Massachusetts: Stratigraphy and correlation of the Braintree trilobites

Although Middle Cambrian trilobites of the Braintree Member in eastern Massachusetts were among the first published on in North America, re-examination of this fauna has led to wholesale taxonomic and biostratigraphic re-evaluation. This low diversity fauna now includes at least seven species, with the first report of agnostoids (three poorly preserved taxa) and the ellipsocephalidKingaspis avalonensisnew species.Paradoxides(Acadoparadoxides)harlaniGreen emend., a senior synonym ofP. (A.) haywardiRaymond, allows correlation into the lowest Middle Cambrian elsewhere in Avalon. However, all the polymeroid species are endemic, and this precludes a highly resolved correlation into other Cambrian paleocontinents. A breakdown of provincial barriers in the late Early Cambrian as western Gondwana passed from equatorial to the higher south latitudes of Avalon led to faunal exchanges between these continents.Paradoxides(Acadoparadoxides) andKingaspisof the Braintree fauna are shared with western Gondwana, while Braintreella and “Agraulos”quadrangularisare closest to genera known from the Spanish, Moroccan, and Perunican (Bohemian) margins of Gondwana.