Fossil trilobite "death assemblage" slab - ROM2004_982_6

Trilobite sea-floor "death assemblage"

Fossil trilobite "death assemblage" slab

Place Collected
Africa, Morocco, Draa Valley, Ouled Slimane, SW of Agdz
Slab: 170 (L) x 140 (W) cm
Object number: ROMIP55070
Credit Line: Generously supported by the Louise Hawley Stone Charitable Trust
Not on view
DescriptionTrilobites are an extinct group of arthropods—joint-legged invertebrates (animals without a backbone). Trilobites had a sturdy, mineralized outer “shell” (exoskeleton) that covered the upper body. The exoskeleton featured a prominent middle lobe and two side lobes running down its length (hence the name tri-LOBE-ite). It was also divided cross-wise into three sections: a cephalon (head) usually with a pair of prominent, mineralized, compound eyes; a thorax (middle region) with between 2 and 40 narrow segments, hinged for flexibility; and a pygidium (tail). Individual bits of exoskeletons are often found as fossils, representing separate pieces shed during growth or parts of carcasses broken apart after death. Complete exoskeletons are much less common, and fossils preserving non-mineralized body-parts (legs, etc.) of trilobites are very rare. All trilobites were sea-dwellers—most crawled on or burrowed into the sea-floor, some swam or floated. The oldest trilobite fossils come from rocks about 540 million years old, and the last trilobites died out about 250 million years ago. This magnificent slab is a sea-floor “death assemblage”. It records the mass mortality and burial of about 30 large trilobites, of three different species, probably as a result of storm turbulence that buried them in mud. The assemblage was excavated in many pieces, carefully prepared to reveal the fossils, and then reassembled. The trilobite near the centre of the slab was moved from an outlying area to its new position.
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