Echinochiton dufoei

Overview

Echinochiton dufoei is an Ordovician chiton whose eight dorsal plates and hollow lateral spines catch the eye. Follow its single row of armor to examine the order in which the small plates fitted together.^[1]

Key facts

Researchers considered the large hollow spines projecting from the known plates particularly unusual. Fossils revealed spiny armor that would have been difficult to anticipate from other chitons.^[1]

Time and place

A 2003 study introduced it as an Ordovician fossil from near Beloit in present-day Wisconsin, USA. The material came from the Forreston Member of the Grand Detour Formation.^[1]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The dorsal plates are bilaterally symmetrical, with eight arranged in a single row. The outlines of the intermediate plates range from nearly triangular to rectangular, and some lateral spines are also preserved.^[1]

The six surviving dorsal plates of the type specimen of Echinochiton dufoei measure 3cm in length. Adding an estimate for the two missing plates, the researchers in 2003 estimated the full plate series at about 4cm.^[4]

Habitat and reproduction

From the arrangement of small associated shells, researchers interpreted the assemblage as fossils transported from elsewhere and redeposited. The plates remaining articulated despite evidence of transport provide an intriguing clue.^[1]

Fossil discovery

The new-species study was based on four fully or partly articulated specimens. BMNH1998.011.01 and .02 in Fig.1 are matching faces of one specimen, showing eight plates and some spines.^[1]

References

1. Pojeta et al. (2003) — Armour of a spiny Ordovician chiton
2. Pojeta et al. (2003) — Armour of a spiny Ordovician chiton
3. Harvard Museum of Comparative Zoology — Spines and articulated exoskeleton of Ceraurus
4. Pojeta et al. (2003) — Spiny Echinochiton

Research questions

The study explains that chiton fossils are often found as isolated plates or fragments. Articulated armor offers an opportunity to examine an original arrangement that would be difficult to infer from detached plates alone.^[1]

Observation

Count the eight dorsal plates running from front to back in the illustration. Moving your gaze from their junctions to the spines extending sideways reveals the armor’s distinctive construction.^[1]