Shelley, Shelley & Floyd, 2014

Shelley, Rowland M. & Floyd, Samuel D., 2014, Expanded concept of the milliped family Spirobolidae Diplopoda: Spirobolida: Spirobolidea): Proposals of Aztecolini n. tribe and Floridobolinae / ini and Tylobolini n. stats.; (re) descriptions of Floridobolus and F. penneri, both Causey, 1957, and F. orini n. sp.; hypotheses on origins and affinities, Insecta Mundi 2014 (357), pp. 1-50 : 22

Tribe Tylobolini Keeton, 1960a , new status

Tylobolinae Keeton, 1960a:96–97. Buckett, 1964:23. Hoffman, 1980a:77; 1999:41. Kevan, 1983:2962. Shelley et al., 2000:23. Shelley, 2002a:98 .

Type-genus. Tylobolus Cook, 1904 .

Diagnosis. Rounded/cylindrical ( Fig. 33 ), glabrous/glossy Spirobolidae , body tapering only at caudal end. Gnathochilarial mentum without convexity. 7 th pleurotergites of males lengthened and/or expanded, noticeably distorting body to accommodate gonopods. Epiproct apically narrow, slightly produced but never completely obscuring paraprocts dorsally; latter with or without marginal rims, slightly re-entrant or not. Legs at most extending only slightly beyond lateral pleuroteral margins, partly visible in dorsal view. Males with pregonopodal lobes on 3 rd, 4 th, and 5 th coxae. Anterior gonopod sternum widening mediad but without distinct lobes, only slightly separating coxal endites. Latter broad, margins curvilinear, medial corners usually noticeably extended or narrowed; telopodites apically uncinate or not. Posterior gonopod coxal apodeme usually prolonged. Telopodite varying from subupright to leaning mediad or curving strongly dorsad and imparting uncinate appearance to structure. Prefemoral process varying from a small lobe to slightly elongate. Anterior acropodital surface variably thickened and without processes, expanding into either two highly variable lobes or one lobe prolonged apically and strongly decurved. Caudal acropodital surface not extended.

Components. Two extant genera – Tylobolus Cook, 1904 , and Hiltonius Chamberlin, 1918 – to which we add the Mongolian Cretaceous fossil genus, Gobiulus Dzik, 1975 .

Distribution ( Fig. 12 ). Extant forms occupy the four subfamilial regions in the western US, Mexico, and Guatemala, a latitudinal distance of approximately 4,272 km (2,670 mi) that extends from north of the Columbia River in Washington state, USA, to the western periphery of Guatemala. Apparent tylobolinine fossils have been discovered in southern Mongolia, Asia, where living representatives have never been encountered.

Origin. The differences between Tylobolini and Floridobolini , losses of the posterior gonopod sternal remnant and the extension of the caudal acropodital surface, are minor in comparison to those between Tylobolini and Spirobolinae and likely evolved rapidly. Tylobolini is thus the second clade to evolve/ disperse, and we arbitrarily date its origin at <301 mya.

Remarks. Keeton (1960a) believed that Tylobolini (then Tylobolinae) probably arose from early spiroboline stock and considered Hiltonius the more “primitive” genus and the direct ancestor of Tylobolus . From the knowledge available then, these are remarkably prescient insights; we concur with both, although Tylobolini actually derived from floridoboline stock.

Gonopodally similar to Floridobolini , as evidenced by the acropodital lobe resemblances between H. carpinus and Floridobolus spp. , Tylobolini have autapomorphically lost the extension of the caudal acropodital surface. In several respects, Tylobolini are intermediate, and bridge anatomical gaps, between Floridobolini and Spirobolinae . On the anterior gonopods, Floridobolini lack the medial sternal lobe and exhibit non-uncinate telopodites whereas all spirobolines possess both the lobe and uncinate telopodites; tylobolinines display both conditions in both structures. Tylobolinines display both long and short posterior gonopod apodemes, intermediate between the long ones of Floridobolini and the exclusively short ones of Spirobolinae . Tylobolinine prefemoral processes are intermediate in size between the nubbin-like ones in Floridobolini and the large structures in Spirobolinae . Additionally, the paraprocts in Floridobolini are slightly re-entrant whereas those in Spirobolinae possess distinct rims and lips; again, tylobolinines exhibit both conditions. Thus Tylobolini link these somatically and gonopodally dissimilar taxa, thereby substantiating confamilial status for Floridobolini / Floridobolus . The latter are clearly related to Tylobolini , unequivocal spirobolids, so Floridobolini / Floridobolus must also belong to this taxon and not a separate, monotypic family.

Figures

Figure 12. Distribution of Floridobolinae plotted against Cretaceous land patterns; submerged, marine Florida terrane and approximate maximal dimensions of the Western Interior Seaway in light blue. Ap, Appalachia. F, Floridobolus/Floridobolini. L, Laramidia. SA, Presumptive Source Area in the “northern Mexican Highlands.” Black lines and dot (delineated by the arrow), Hiltonius/Tylobolini. Red line, Tylobolus/Tylobolini. Green line and dot (in Florida), Floridobolus/Floridobolini. The area where Tylobolini/Hiltonius and Aztecolus overlap constitutes the presumptive source area.

Figure 33. Ring profiles in Spirobolidae. Left two rings, transversely ovoid profile shown by Floridobolinae/ Floridobolini. Right two rings, rounded profile demonstrated by Floridobolinae/Tylobolini and Spirobolinae. Photo courtesy of O. McMonigle.