LIFE × EVOLUTION

Durophagy: the Shell Crushers

~235 to 66 million years ago

Phanerozoic · Mesozoic · Triassic

Crabs, rays and bony fishes able to crush shells spread through the seas from 235 million years ago to the end of the Mesozoic era, and their prey evolved thicker shell walls, spines and the habit of burrowing.

Durophagy is the habit of feeding on hard-shelled prey. Crabs, rays and bony fishes capable of crushing a shell spread through the seas of the Mesozoic, the geological era that ended 66 million years ago. Their prey evolved thicker shell walls, more tightly coiled shells, spines and the habit of burrowing. Palaeontologists call the combined change the Mesozoic marine revolution. After it, an animal could no longer survive by remaining stationary and exposed on the seafloor.

Why it matters

Fossil shells preserve both sides of the relation between predator and prey, which is rare. The shell shows the protection of the prey, and its drill holes and crush marks show the attacks. Researchers can thus follow how predation shaped bodies over durations no experiment can reach. Benthic animals are animals that live on the seafloor. Since the Middle Devonian at least, a time long before the Mesozoic, their morphology, the shape of their body, and the persistence of their lineage have depended in part on the predators that can break them.

Dating & uncertainty

Escalation is the parallel increase of shell-crushing predators and of defences in their prey. Researchers read it from fossil shells: thicker walls, tighter coiling, spines, and drill holes left by predators. Its start date, its rate and its cause are disputed. When predators and armoured prey develop simultaneously, the fossils show a correlation, not yet an arms race, in which each side evolves in response to the other. Signor and Brett (1984) described a well-documented precedent in the middle of the Palaeozoic, the era before the Mesozoic. Oji, Ogaya and Sato (2003) counted broken shells, and their counts indicate that much of the increase in shell crushing is Cenozoic, from the era after the Mesozoic. The Mesozoic would then be an intermediate phase, not the whole phenomenon.

Earth history as one day

22:45:271 h 15 min before midnight

if Earth’s 4.54 billion years were compressed into a single day