484
Journal of Paleontology 92(3):478–487
Figure 4. ?Diplopod, LPI-63009, consisting of 21 segments (Fig. 4.1–4.4). (1) Entire incomplete specimen; (2–4) enlarged details. Specimen consists of a series of similar segments, most ~ 1mm long, with a slightly longer segment at one end.
is within the range of extant callipodids (which have 36 to 89 segments including the telson) and is somewhat greater than that of chordeumatids (which have ~26–32 segments including the telson). Tapering of the anterior and, especially, posterior is like that of chordeumatids. In the presence of spines on the swellings (as interpreted here), Sinosoma luopingense n. gen. n. sp. is more like a chordeumatid (see for example Shear, 1977, fig. 1). The relatively large head, especially compared to the collum, is also like a chordeumatid. The new species differs from chordeuma- tids, however, in its lack of a prominent midline. Segment number of the new millipede is very close to that
of palaeosomatid archipolypods, which have up to 38 segments (Hannibal and Krzemin´ ski, 2005, p. 208). The pleurotergites of palaeosomatids have ozopores born on lateral bosses, however.
Class ?Diplopoda
Order, family, genus, and species incertae sedis Figure 4
Description.—Segmented organism with 21 segments pre- served (Specimen LPI-63009). Segments ~1mm long. Margin (s) rimmed. Larger segment at one end.
Remarks.—This specimen can conceivably be a fossil millipede because it consists of a series of similar segments. Details of its segments are difficult to interpret, however, and it lacks suffi- cient features to be sure of an assignment to the Diplopoda. These segments are in the same size range, but are simpler, than those of Sinosoma n. gen.
Mesozoic millipedes
Mesozoic millipedes have been described, noted, and/or illu- strated in a number of publications, beginning in the mid 1850s. These reported occurrences are reviewed below to put the occurrence of Sinosoma n. gen. into context. This brief review updates the reviews of Mesozoic millipedes in Shear et al. (2009), Shear and Edgecombe (2010), and Edgecombe (2015). A number of Triassic millipedes have been previously
noted, although only two have been named and described in detail. These are Tomiulus angulatus Martynov, 1936, and Hannibaliulus wilsonae Shear et al., 2009. Tomiulus angulatus, found in Siberia, is a julimorph-like millipede. It was diagnosed by Sharov (1962), based on Martynov (1936), and subsequently redescribed by Dzik (1981), who assigned it to the family Xyloiulidae Cook, 1895. This specimen is preserved in lateral view, with only the pleurotergites preserved. Reexamination of the holotype at the Paleontological Institute Moscow shows that its pleurotergites are terminated ventrally by a distinct, rounded rim (JTH, personal observation, 1998), a feature indicated in Sharov’s (1962, p. 23) diagnosis (see translation by Dzik, 1981, p. 397). This implies that the sternites were not fused to the pleurotergites. Ozopores appear to be lacking. The lack of preserved sternites in the holotype of Tomiulus also indicates that the sternites and pleurotergites were unfused. Furthermore, it is likely that the sternites were narrow. The Xyloiulidea, as diag- nosed by Wilson (2006, p. 639), include elongate, cylindrical millipedes with ozopores, short legs, and ornamentation com- posed of longitudinal striations ranging from parallel to slightly sinusoidal in orientation. As Shear et al. (2009) have pointed out, only the lattermost character is present in Tomiulus, so its identity
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