Challenges fundamentals of echinoderm evolution. From ScienceDaily:
Echinoderms are among the marine invertebrates that suffered the most severe losses at the end-Permian extinction.
At least that was the consensus until a team of European paleontologists — Ben Thuy, Hans Hagdorn, and Andy S. Gale — cast a critical eye on some poorly studied Triassic echinoderm fossils. The fossils turned out to belong to groups that supposedly went extinct by the end of the Paleozoic.
Some ancient echinoids, ophiuroids, and asteroids had slipped the bottleneck and coexisted with the ancestors of modern-day sea urchins, brittle stars, sand dollars, and relatives, for many millions of years. These echinoderm hangovers occurred almost worldwide and had spread into a wide range of paleo-environments by the late Triassic.
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Some ancient echinoids, ophiuroids, and asteroids had slipped the bottleneck and coexisted with the ancestors of modern-day sea urchins, brittle stars, sand dollars, and relatives, for many millions of years. These echinoderm hangovers occurred almost worldwide and had spread into a wide range of paleo-environments by the late Triassic.
This discovery challenges the fundamentals of echinoderm evolution with respect to end-Permian survival and sheds new light on the early evolution of the modern clades, in particular on Triassic ghost lineages of the crown-group look-alikes of the Paleozoic hangovers. Paper. (paywall) – Andy S. Gale et al. Paleozoic echinoderm hangovers: Waking up in the Triassic. Geology, March 2017 DOI: 10.1130/G38909.1 More.
One problem is that our knowledge of the past is so fragmentary that it must be hard in many cases to determine when – or even if – a life form is extinct at a given period. We only have “last seen” records, not death certificates. In the present ay. Lazarus species (species presumed extinct in the present day) turn up again frequently. Their greatly exaggerated demise may be an artifact of the fact that we have so much information about life forms today that we can regularly be mistaken—but then find out about it. Things can be way worse.
See also: Slow but sure, the extinct snail turned up again
and
Lazarus species: animals listed as extinct that turned up again.
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