Study of Fossil: PENTREMITES (Blastoid Echinoderm)Fossil
Pentremites Fossil, Photo Credit: Mark Wilson
Systematic Position:
Kingdom:Animalia
Phylum:Echinodermata
Class:Blastoidea
Order:Spiraculata
Family:Pentremitidae
Genus:Pentremites
Origin:
Pentremites species lived in the early to middle Carboniferous, (from 359 million to 299 million years ago). Its fossils are known from North America.
Characters:
They are stalked echinoderms.
Averaged height of about 11 centimeters (4.3 in) but occasionally ranged up to about 3 times that size.
They were characterized by a regularity of structure.
Body region consisted of 13 plates of calcium carbonate, arranged in 3 circles about the body.
They, like other blastoids, superficially resemble their distant relatives, the crinoids , having a near identical, planktivorous lifestyle living on the sea floor attached by a stalk.
The theca of Pentremites has a rather nut-like shape,and fossil Pentremites are sometimes inaccurately called "fossil nuts" or "fossil hickory nuts".
They extended numerous feeding appendages (brachioles) from their ambulacra (the five “petals” on the upper surface and sides) for filter-feeding.
The theca is made of calcitic plates that are tightly fused together, thus ensuring they survive the vicissitudes of preservation.
Photo Credit: Mark Wilson
Evolutionary significance:
Blastoid, existed from the Middle Ordovician to the Late Permian periods. Their absence in the fossil layer indicates Permian mass extinction.
Blastoids lived from the Silurian to the Permian, that totals ~200 million years! That is an incredibly long amount of time and they were most successful echinoderm group in evolutionary history.
Unfortunately, the end Permian mass extinction was too extreme and they perished alongside many other marine organisms.
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