Pleurocystites
foriolus
Deuterostomata,
Class Homalozoa, Order Rhombifera, Family Pleurocystitidae
Geological
Time: Upper Ordovician, Ashgillian Stage
Size
(25.4 mm = 1 inch): Theca: 32 mm by 41 mm tall (including appendages)
and 12 mm articulated stem Matrix: 100 mm by 110 mm
Fossil Site:
Lady Burn Starfish Beds, Girvan District, Ayrshire, Scotland
Code: UKF164
Price: Sold
Description:
I have recently been able to acquire a number of specimens coming
from the famous Upper Ordovician Lady Burn Starfish Beds of the
Girvan District of Scotland. While it is the most important starfish
locality in the British Isles, it also contains a diverse representation
of trilobite crinoids, carpoids and others. Specimens from the
locality are not often made available, so this divers grouping
is most uncommon. This plate contains an excellent example of
the carpoid Pleurocystites foriolus. The carpoids are one of
the most contentious groups of fossil organisms known. While
they have been studied for over 150 years, their unique character
combinations have caused a number of disputes over both their
paleobiology and relationships. While some place them in the
Echinodermata, their lack of pentaradial symmetry calls that
placement into question. Additionally many carpoids are thought
to have possessed gill slits (this one has been so interpreted),
a feature characteristic of chordates and hemichaordates. Many
possess one or two “appendages” which have been interpreted
variously as feeding tubes, tails with notocords and muscular
feet. The carpoid body was supported by a skeleton of calcitic
plates like those found in modern Echinoderms. Some believe that
a carpoid may have been the common ancestor between Echinoderms
and Vertebrates. It is important to note the carpoids differ
from ALL other animals, living and extinct, in that many are
completely asymmetrical. With so much debate over assignment
of the appendages to specific functions, how can one come to
a conclusion about their assignment in the Tree of Life? This
one is a very large example of the type.
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