Microdictyon sinicum , A Lobopodian from Chengjiang
Cambrian Explosion Lobopodian - Velvet Worm

Microdictyon sinicum

Phylum Lobopodia

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

Size: Microdictyon fossil is 23 mm long

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

Microdictyon sinicumThe Lobopodians are small marine and terrestrial animals termed colloquially “velvet worms” or “worms with legs”. While all Recent forms are terrestrial, most fossil Lobopodians are marine, and are known primarily from the Cambrian. Six named genera, each with a single species, are known from the Chengjiang Biota, making it the richest source of fossils of the type on Earth. This is one of the most striking, and quite rare; as of Microdictyon sinicum2004, only some 80 examples were known. The maximum length is 77 mm. It possesses 9 pairs of trunk sclerites which have been likened to the compound eyes of arthropods. While there are some 10 species found in the Cambrian of North and Central America, Europe, Asia, and Australia, only M. sinicum is found in the Chengjiang, and it is the only one based upon more than just sclerites. Microdictyon probably used its clawed feet to attach itself to other creatures, particularly the medusoid Eldonia. It is thought to be most closely related to Hallucigenia, another Lobopodia from the Chengjiang Maotianshan Shales.

The discovery of the Chengjiang Biota by Hou Xian-guang in 1984 resulted in a clear window on what is known as the Cambrian Explosion. 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.

Also see: Chengjiang Biota Chengjiang Fossils Cambrian Explosion

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