lpetrich
Contributor
Mary’s Monday Metazoan: Lobopods forever! -- Pharyngula
The world's weirdest creature finds descendants in cuddly velvet worms -- The Conversation
Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians -- Proceedings of the Royal Society B: Biological Sciences
When it was discovered, Hallucigenia sparsa was reconstructed as walking on some long spines and having tubes on its back. But more recently, that reconstruction has been reversed to a more plausible one in which those tubes are legs and those spines defensive structures.
It was about 0.5 - 3.5 cm long, and it lived in the Middle Cambrian, about 500 million years ago.
Jean-Bernard Caron, Martin R. Smith and Thomas H. P. Harvey, the author of that PRS B paper, took a close look at some Hallucigenia spins, showing that they were multilayered, each layer likely being added as a result of a molt. Present-day onychophorans (velvet worms) have similar layered jaws and claws, in addition to overall anatomical similarity to Hallucigenia. They look a lot like caterpillars, at least if one does not look very closely. They also looked at various difficult-to-classify fossils from the Cambrian, and they decided that they were also hallucigeniid spines.
They conclude that hallucigeniids emerged in the early Cambrian, about when there was a lot of evolution of biomineralization and defense mechanisms. They were then abundant and widespread into the middle Cambrian, the time of the Burgess Shale, and they went into decline in the late Cambrian. The researchers carefully considered the possibility of artifacts of preservation, and found it unlikely.
Hallucigenia is one of several lobopods known from the Cambrian, named from their stubby legs. Lobopods are the closest relatives to arthropods, and some lobopods survive to the present, notably tardigrades (water bears) and onychophorans.
The world's weirdest creature finds descendants in cuddly velvet worms -- The Conversation
Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians -- Proceedings of the Royal Society B: Biological Sciences
When it was discovered, Hallucigenia sparsa was reconstructed as walking on some long spines and having tubes on its back. But more recently, that reconstruction has been reversed to a more plausible one in which those tubes are legs and those spines defensive structures.
It was about 0.5 - 3.5 cm long, and it lived in the Middle Cambrian, about 500 million years ago.
Jean-Bernard Caron, Martin R. Smith and Thomas H. P. Harvey, the author of that PRS B paper, took a close look at some Hallucigenia spins, showing that they were multilayered, each layer likely being added as a result of a molt. Present-day onychophorans (velvet worms) have similar layered jaws and claws, in addition to overall anatomical similarity to Hallucigenia. They look a lot like caterpillars, at least if one does not look very closely. They also looked at various difficult-to-classify fossils from the Cambrian, and they decided that they were also hallucigeniid spines.
They conclude that hallucigeniids emerged in the early Cambrian, about when there was a lot of evolution of biomineralization and defense mechanisms. They were then abundant and widespread into the middle Cambrian, the time of the Burgess Shale, and they went into decline in the late Cambrian. The researchers carefully considered the possibility of artifacts of preservation, and found it unlikely.
Hallucigenia is one of several lobopods known from the Cambrian, named from their stubby legs. Lobopods are the closest relatives to arthropods, and some lobopods survive to the present, notably tardigrades (water bears) and onychophorans.