Huang et al.—New Triassic millipede from Yunnan, China
as a xyloiulid cannot be confirmed, although it is certainly likely that this form was also elongate, cylindrical, and juliform-like in general configuration. Additional millipedes have, however, been noted and illu-
strated, but not formally described or named, from Triassic rocks. These include juliform millipedes from the Lower Triassic of Bethulie and Bergville, South Africa, noted several decades ago by Kitching (1977, p. 9) and Lawrence (1984, p. 134). Lawrence described them as gregarious juvenile juli- form millipedes. Reisz and Laurin (1991, fig. 1) identified similar forms found in association with the skeletons of the procolophonid Owenetta as millipede-like arthropods, and interpreted these arthropods as scavengers. Subsequently, Groenewald and Kitching (1995, p. 37) listed millipedes comparable to extant Gymnostreptus Brölemann, 1902 (a spir- ostreptid in the superorder Juliformia) as occurring in the Lystrosaurus Assemblage Zone of the Beaufort beds (earliest Triassic) of South Africa. More recent mentions include those of Reisz and Scott (2002, fig. 1), who again illustrated what appear to be juliform millipedes. These same millipedes were subsequently illustrated in color by MacRae (1999, p. 195). Retallack et al. (2003, p. 1142) noted that the specimens pre- viously reported from Bethulie were comparable to extant Gymnostreptus, a spirostreptid. More recently, Abdala et al. (2006, p. 507, fig. 3D) noted and illustrated what they identified as a probable juliform millipede preserved with tetrapods in a carbonate concretion (collected by B.J. Kitching) from the Bethulie area. They did not observe any limbs on the millipede, which they interpreted as sharing a burrow with Owenetta (Abdala et al., 2006, p. 511). Based on the published comments and the published illustrations of these forms, it is probably safe to state that these are juliform-like millipedes. A supposed millipede body-fossil impression has been descri-
bed from the Triassic of Utah (Mickelson et al., 2006), but Lerner et al. (2007) have disputed its identity as a millipede body fossil. This leaves two groups of Triassic millipedes: juliform-like
millipedes and millipedes that are at least similar to nematophorans. The Jurassic record consists of the enigmatic form Dec-
orotergum warrenae Jell, 1983. This form, which is rounded in cross-section with clear prozonites and metazonites, has been accepted by recent authors as a chilognath millipede, although without support of an original assignment as an oniscomorph or a polydesmid (Shear et al., 2009; Edgecombe, 2015). Even its identity as a millipede is in need of confirmation; some of the ventral terminations of the pleurotergites appear to be arched dorsally. There are a number of examples of misidentification of millipedes as other taxa, and vice versa (see Hannibal, 2001). Cretaceous forms, however, have a decidedly modern look
to them. These include polyxenids (Duy-Jacquemin and Azar, 2004; Rasnitsyn and Golovatch, 2004), colobognaths (Wilson, 2006, fig. 4; Carlson, 2007), spirobolids (Dzik, 1975), sipho- niulids (Liu et al., 2017), and a polydesmid (Wilson, 2006, fig. 4). Of these, only the polyxenids, spirobolids, and siphoniulids have been well studied. The polyxenids (three genera) have been referred to families that include extant forms. The colobognaths, one noted as a polyzoniid with siphonophorid characters, have not been described in detail. Gobiulus Dzik, 1975, is a spirobolid that Shelley and Floyd (2014, p. 24–25; but see also Shear et al., 2009, p. 10–11) assigned to an extant subfamily. Polydesmids
485
were first noted as occurring in the Cretaceous by Wilson (2006), and subsequently illustrated without descriptions from Myanmar (Xia et al., 2015, p. 151). The siphoniulids, including two new species of genus Siphoniulus from Myanmar (Liu et al., 2017), have morphology similar to that of recent species in Central America, and this discovery satisfies the viewpoint of the Siphoniulida as a “declining” order (Golovatch, 2015) or living relic (Shelley and Golovatch, 2011). Recently, however, a new Cretaceous millipede fauna has been noted by Poyato-Ariza and Buscalioni (2016), and Selden and Shear (2016) assigned the millipedes from this fauna tentatively to the superfamily Xyloiuloidea, which does not include extant taxa. Fritsch (1910, p. 6–7, pl. 4, figs. 9–13) also described
Cretaceous myriapods from Bohemia, including specimens he identified as a (?)glomerid and a julid. He did not name these taxa, and these specimens are poorly preserved and difficult to interpret. Of these, the specimen of the supposed glomerid is the most millipede-like. These Cretaceous specimens are more poorly preserved than the specimens he described from the Gaskohle of Bohemia, and Fritsch’s illustrations of the Czech Cretaceous material are not as accurate as are those of the material of the Gaskohle, which, in turn, are not very accurate (JTH, personal observation, 1984, 1993). Based on the original description and illustrations, the species ?Xylobius mexicanus Mullerried, 1942 from the Upper Cretaceous of Mexico, may be an authentic millipede. The specimen is missing however, so its identity cannot be confirmed. Excluded from consideration here is Julopsois cretacea Heer, 1874, a Cretaceous form interpreted as a julid by Scudder (1886, p. 18), which Hoffman (1969, p. R605) excluded from the Diplopoda. Also excluded is Calci- philus, a Cenozoic millipede that a number of authors, including Hoffman (1969, p. R604) correctly included in the Diplopoda, but erroneously listed as being Cretaceous (see McKee [1946] for a description of the deposit). Based on the sparse fossil record of the Mesozoic, it
appears that is was only in the Cretaceous that the Diplopoda took on a modern aspect.
Paleoecological implications
Millipedes, along with conifers, are clear terrestrial components of the predominantly marine Luoping biota. Based on the preservation of conifer remains, Hu et al. (2011, p. 2278) hypothesized that conifers were transported ~10km into the Luoping Basin. Comparisons can be made with other biotas that have mixed marine and terrestrial components. Fossil millipedes are a small component, for instance, of the Essex fauna of Mazon Creek (Baird and Anderson, 1997; Hannibal, 1997, p. 173; Hannibal, 2000, p. 30), which has been interpreted as being marginal marine, consisting of predominantly marine organisms capable of tolerating changes in salinity (Baird et al., 1985; Baird, 1997). And the Triassic Hannibaliulus wilsonae is from a brackish-water facies that has yielded marine or marginal mar- ine organisms including lingulid brachiopods and limulids (Shear et al., 2009, p. 2), two groups that are also found in the Luoping biota. The Luoping biota has a stronger marine influ- ence than have these other facies, however. The assumed transportation distances to the basin are not extreme for milli- pedes. Distribution of extant millipedes shows that millipedes
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