Lobopodia Fossils

The Enigmatic Lobopodians

Lobopodians are small, segmented animals of uncertain taxonomic placement that have apparent affinity to both arthropods and annelids, and that have a fossil record dating to the early Cambrian, but examples are also known from Lagerstatten from the Ordovician, Silurian and Carboniferous (e.g., Mazon Creek). The lobopods resemble Onychophorans, or velvet worms, that are terrestrial worms with legs, and indeed may be Onychophoran ancestors. A distinguishing characteristic of Lobopodians is dorsal-lateral plates or sclerites. Six genera, each with a single species, are described from the Chengjiang Biota, making the Chengjiang Maotianshan Shales the primary source of Lobopod fossils. Aysheaia from the Burgess Shale and the strange Hallucigenia have some resemblance, as does Xenusion from early Cambrian sandstones of eastern Europe that is known from only two specimens; these animals are now placed in the onychophorans (Superphyum Lophotrochozoa). Lobopodian morphologies in the Cambrian exhibit wide diversity, as if nature were experimenting (and maybe it was), spurring on classification debates for decades. The most recent cladistical work by Smith and Ortega-Hernández (Nature, 2014) concludes that Lobopodia should be placed in an unranked paraphyletic taxon, Panarthropoda, comprising three phyla Arthropoda, Tardigrada, Onychophora, as well as the genus Thelxiope (a stem group spiney arthropod occuring in the Burgess Shale, with no example with legs preserved).