Alalcomenaeus, Unusual Opabinid Arthropod Fossil Chengjiang

Alalcomenaeus sp

Geological Time: Early Cambrian (~525 million years ago)

Size: 10 mm

Fossil Site: Chengjiang Maotianshan Shales, Quiongzhusi Section, Yu’anshan Member, Heilinpu Formation, Maotianshan, Yuxi, Chengjiang County, Yunnan Province, China

Alalcomenaeus ChengjiangDescription: This unusual arthropod is known as Alalcomenaeus. The taxon is known from a number of examples, with this one from the most famous location of all, Maotianshan (Mao Tian Hill), site of the discovery of the Chengjiang Biota by Hou Xian-guang in 1984. The diversity of soft-tissue fossils is astonishing: algae, medusiforms, sponges, priapulids, annelid-like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day.

The specimen is a member of the “great appendage arthropods” known as the opabinids after Opabinia from the Burgess Shale Fauna. Other members from Chengjiang are Jianfengia and Leanchoilia (see my other offerings for examples). The exceptional detail of the appendages are readily apparent in this fine specimen. The taxon is unknown outside the Chengjiang Biota. This is a truly exceptional specimen, one that is sure to become a cornerstone of any collection of material from the Cambrian Explosion.

Also see: Chengjiang Biota List Chengjiang Fossils

click fossil pictures to enlarge

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