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The Echinoderms and Permian-Triassic Time
The Permian-Triassic boundary is not of special significance in the development of most of the echinoderms. Although the Paleozoic echinoids are very unlike those of the Mesozoic, the transition between the two groups is gradual, covering a long period of time, and not confined to the Permian-Triassic. The period of greatest change in the echinoids is during the Late Triassic and Early Jurassic period. Over half of all the known orders of echinoids were introduced during this time, including the introduction of the “irregular” echinoids, development of compound ambulacral plates, introduction of gills, and the keeled tooth.
Although five orders and suborders of crinoids became extinct after the Guadalupian, this change, as related to the Permian-Triassic boundary, is not as catastrophic as it might seem at first glance. The decline in these taxa must have started earlier because all the Guadalupian species except one are restricted to Timor. Many genera became extinct at the end of the Permian but a large number also became extinct at the end of earlier and later periods. The Triassic and the Permian crinoid faunas are very distinct but much of this distinction may be due to the small number of crinoids known from the Triassic, and the lack of any Lower Triassic species. Although there is more evidence of significant change over the Permian-Triassic boundary in the crinoids than among any other echinoderms, this change is probably more apparent than real. However, the absence of Triassic crinoids must indicate significant differences between the marine shallow-water environments of the Permian and Triassic.
Although the blastoids became extinct at the end of the Permian, their extinction probably bears little relationship to any events during the Late Permian, for their decline had begun far earlier. Only four genera are known from the Pennsylvanian of the world, and no Permian blastoids are known from the United States or Western Europe. The asteroids underwent no significant change during this period, with no new families originated during the Permian or Triassic. No new orders were introduced among the Ophiuroidea and no families became extinct during the Pennsylvanian, Permian, or Triassic. All the other classes of echinoderms became extinct before the Permian, and, therefore, are not dealt with here.
In general, an evolutionary spurt did not occur in the echinoderms during the very late Permian or Early Triassic, but the absence of many echinoderms in the Early Triassic is evidence that the marine shallow-water environment was much different during this time than earlier or later. A great spurt in echinoderm evolution occurred at the end of the Triassic and during the Early Jurassic. This great radiation may have been caused by the breakup of the continents which would have produced many new niches.
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