Lobopodia is a group of poorly understood animals, which mostly fall as a stem group of arthropods. Their fossil range dates back to the Early Cambrian. Lobopods are segmented and typically bear legs with hooked claws on their ends.
The oldest near-complete fossil lobopods date to the Lower Cambrian; some are also known from a Silurian Lagerstätte. They resemble the modern onychophorans (velvet worms) in their worm-like body shape and numerous stub-legs. They differ in their possession of numerous dorsal armour plates, "sclerita", which often cover the entire body and head. Since they taper off into long, pointed spikes, these probably served a role in defence against predators. Individual sclerita are found among the so-called "small shelly fauna" (SSF) from the early Cambrian period. The "lobopodia" group is considered to include these Cambrian forms in addition to the extant onychophorans.
The better-known genera include, for example, Aysheaia, which was discovered among the Canadian Burgess Shale and which is the most similar of the Lobopoda in appearance to the modern velvet worms; a pair of appendages on the head have been considered precursors of today's antennae. Xenusion was apparently able to roll itself up, spines outward, giving insight into the defensive strategies of the Lobopoda. However, by far the most famous of the lobopod genera is Hallucigenia, named on account of its bizarre appearance. It was originally reconstructed by with long, stilt-like legs and mysterious fleshy dorsal protuberances, and was long considered a prime example of the way in which nature experimented with the most diverse and bizarre body designs during the Cambrian. However, further discoveries showed that this reconstruction had placed the animal upside-down: interpreting the "stilts" as dorsal spines made it clear that the fleshy "dorsal" protuberances were actually legs. This second reconstruction also exchanged the front and rear ends of the creature, which further investigation showed to be erroneous.
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