A Juliform Millipede From The Upper Pennsylvanian (Virgilian) Bursum Formation, Carrizo Arroyo, Central New Mexico

Abstract

Fossil millipedes are rare elements the Paleozoic assemblages of western North America and when found are often so poorly preserved that distinguishing diagnostic features proves impossible. The presence of a millipede at Carrizo Arroyo (NMMNH locality 3433), a Virgilian locality in the Red Tanks Member of the Bursum Formation with an extensive invertebrate fauna, was initially described as a singular occurrence. However, a recent reexamination of the collected material from Carrizo Arroyo has led to the discovery of five additional millipede specimens. These specimens range in completeness from a dozen midbody segments to a specimen that preserves the first 48 segments of an individual, in part and counterpart, including the individual’s head. All millipede specimens share consistent segment morphology and thus pertain to a single taxon. In contrast to modern millipedes, which are diagnosed at the species-level based on genital structure, fossil millipedes are distinguished based on segment ornamentation. The Carrizo millipede possesses the following diagnostic characters: a mid-segment ridge running dorsoventrally the height of the segment that serves to separate the prozonite and the metazonite; and no additional ornamentation of the segments. The Carrizo millipede is only one of three examples of Paleozoic millipedes known from western North America; others include material from the Upper Pennsylvanian to Lower Permian limestones of Hamilton County, Kansas and the Upper Pennsylvanian Kinney Brick quarry of central New Mexico. Thus, these new millipede specimens add significantly to our understanding of Paleozoic millipedes and help to fill gaps in the sparse fossil record of this group.