Echinoderms
Sea urchins, starfish, and blastoids — echinoderms with their five-fold symmetry have left a rich fossil record from the Ordovician to today.
Overview
Echinoderms — starfish, sea urchins, sea lilies and their extinct relatives — are marine animals built on a unique five-fold symmetry and a water-vascular system of hydraulic tube feet. Their calcite skeletons fossilise readily, giving the group a rich 480-million-year record.
Quick Facts
Key Characteristics
- •Pentaradial (five-fold) adult symmetry
- •Water vascular system powering tube feet for movement and feeding
- •Skeleton of interconnected calcite plates (stereom) with a distinctive porous texture
- •Range from stationary filter feeders (crinoids, blastoids) to grazers and predators
Fossil Record
Plated skeletons preserve well even when disarticulated — crinoid columnals litter many limestones ('Encrinite' limestones are almost entirely crinoid debris). Whole-starfish preservation needs quiet anoxic muds (e.g. Ordovician of Wales, Jurassic of England).
Global Distribution
Global in marine rocks — abundant in Palaeozoic limestones of North America, Europe and Asia and Cretaceous chalks worldwide.
Evolutionary & Scientific Importance
Echinoderms are important Palaeozoic index fossils (blastoids especially), record the evolution of a wholly unique body plan, and their ossicles are so abundant they chart entire seafloor ecosystems through time.