Page 417 - Introduction to Paleobiology and The Fossil Record

404 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

Lower Jurassic Lower Tertiary

Hettangian Sinemurian Toarcian Paleocene
anus sea urchins

anus
heart urchins sand dollars
anus water
sediment

flattening of test
elongation of test
decrease in size of tubercles and spines
increase in number of tubercles and spines
shifting of anus posteriorly
shifting of peristome anteriorly
decrease in size of peristome

(a)

regular debris-covered irregular, flat, shallow,
echinoids regular echinoids rapidly burrowing echinoids

lagoon high-energy bar offshore

10–30 m

deep-burrowing
irregular echinoids

shallow-burrowing
irregular echinoids
(b)
Figure 15.12 Echinoid life modes: (a) transition from the sea urchins through the heart urchins to the
sand dollars; (b) habits and modes of life of echinoids. (a, based on Kier, P. 1982. Palaeontology 25;
b, based on Kier, P. 1982. Smithson. Contr. Paleobiol. 13.)

the echinoids change through the section, but
this seems to be related to the grain size of the Evolution
sediment, where high, narrow forms favor fi ne The first echinoids had appeared by the Mid

sediment. The case history is available at http:// Ordovician but it is only in Lower Carbonif-
www.blackwellpublishing.com/paleobiology/. erous rocks that echinoids become relatively