Tynommatidae, n. stat., a family of western North American millipeds: Hypotheses on origins and affinities; tribal elevations; rediagnoses of \u3ci\u3eDiactis\u3c/i\u3e Loomis, 1937, and \u3ci\u3eFlorea\u3c/i\u3e and \u3ci\u3eCaliactis\u3c/i\u3e, both Shelley, 1996; and description of \u3ci\u3eD. hedini\u3c/i\u3e, n. sp. (Callipodida: Schizopetalidea)

Abstract

Tynommatidae, n. stat., elevated from Tynommatinae, is established as a schizopetalidean family encompassing the western North American callipodidans previously assigned to the Mediterranean Schizopetalidae. It is considered a valid taxon despite somewhat anatomically dissimilar subfamilies, and Colactidinae, Texophoninae, Diactidinae, and Aspidiophoninae constitute tribal elevations and additional new statuses. With a subbasal telopodal prefemoral process, Diactis hedini, n. sp., requires rediagnoses of all three diactidine genera, Diactis Loomis, 1937, and Florea and Caliactis, both by Shelley, 1996, and suggests that telopodal branches ‘B’ in congeners and Florea represent distal relocations of the process along the stem. Similarities in the sizes and shapes of the pleurotergal carinae suggest a sister-group relationship with the other, and partly sympatric, New World family, Abacionidae, which is supported by gonopodal similarities between Colactidinae and Abacion Rafinesque, 1820. The Western Interior Seaway of the Cretaceous Period, Mesozoic Era, ~141–66 million years ago, appears to have fueled divergence by isolating “proto-abacionid stock” in “Appalachia,” the Eastern North American land mass, which has subsequently spread well into previously inundated areas. The allopatric position of Texophoninae, on the Gulf Coast of south Texas around 1,136 km (710 mi) east of the most proximate familial records, is attributed to this waterway, which eradicated faunal linkages with “proto-Tynommatidae” in “Laramidia,” the Western North American land mass. Texophoninae probably survived the Cretaceous on insular refugia; however, it is rarely encountered anymore and seems destined for imminent extinction. Representatives of the east-Asian families, Caspiopetalidae, Paracortinidae, and Sinocallipodidae, also possess demarcated pleurotergal crests and, implausible though it seems, may share ancestry with the North American taxa vis-à-vis the “Asiamerica” and or “Boreotropic” concepts