Page 371 - Introduction to Paleobiology and The Fossil Record

358 INTRODUCTION TO PALEOBIOLOGY AND THE FOSSIL RECORD

develop a particular search image when confuse predators like the song thrush by pre-
seeking their favored prey. Living terrestrial senting a wide range of images. If a predator
snails show a wide range of color patterns and targets as prey one particular variant in the
the purpose of this variability may be to population, then other variants would be free

Box 13.9 Mesozoic marine revolution

The post-Paleozoic seas and oceans were probably different in many ways from those before. One
key difference is the more intense predator–prey relationships, signaled by the Mesozoic marine
revolution (MMR). During this interval, shell predation by, for example, crushing and drilling,
became commoner. A Mesozoic arms race, with predators evolving more highly developed weapons
of attack, was balanced by prey evolving better defensive mechanisms and structures. Thus whereas

crustaceans developed the efficiency of their claws, jaws and pincers, mollusks grew thicker, more
highly-ornamented shells and perhaps burrowed deeper and faster into the sediment. This form of
escalation is somewhat different from the mechanism of coevolution; organisms adapt to each other
rather than merely change together. In this system, predators will always be one step ahead of their
prey. Liz Harper (2006) has reviewed the evidence for post-Paleozoic escalation, plotting the ranges
of durophagous body and trace fossils that may have been predatory together with evidence for
crushing and drilling of shells (Fig. 13.27). The MMR may have been a complex series of events:

(i) a Triassic radiation of decapods, sharks and bony fishes; (ii) Jurassic-Cretaceous radiations of
malacostracans and marine reptiles; (iii) a Paleogene explosion of neogastropods, teleosts and sharks;
and (iv) the Neogene appearance of mammals and birds.

Body fossil record Trace fossil record
drill holes repaired crushes
My
Tertiary 20
40
60
80
Cretaceous 100
120
140
∗ ∗Sporadic evidence
160 of crushing
Jurassic ∗
180 Taphonomic ∗ marine reptiles?
200 void?
∗∗St Cassian ∗ ∗St Cassian
220
Triassic
240

Nautiloids Ammonoids Brachyuran crabs Stomatopods Sharks Rays Bssal actinopterygii Teleosts Placodonts Marine reptile Sea mammal Shore birds Naticid gastropods Muricid gastropods Octopods

Crushers Drillers
Figure 13.27 Stratigraphic relationships between predators and prey during the Mesozoic marine
revolution. The St. Cassian Formation, Italy has excellent preservation of aragonitic gastropods.
Double asterisks show the level of the St. Cassian Formation, while single asterisks indicate
sporadic evidence of crushing. (From Harper 2006.)