The Phanerozoic aftermath of the Cambrian information revolution: sensory and cognitive complexity in marine faunas

The Cambrian information revolution describes how biotically-driven
increases in signals, sensory abilities, behavioral interactions, and
landscape spatial complexity drove a rapid increase in animal cognition
concurrent with the Cambrian radiation. Here, we compare cognitive
complexity in Cambrian and post-Cambrian marine ecosystems, documenting
changes in animal cognition after the initial Cambrian increase. In a
comparison of Cambrian and post-Cambrian Lagerstätten, we find no strong
trend in the proportion of genera possessing two types of macroscopic
sense organs (eyes and chemoreceptive organs such as antennae, feelers or
nostrils). There is also no trend in general nervous system complexity.
These results suggest that sophisticated information processing was
already common in early Phanerozoic ecosystems, comparable with behavioral
evidence from the trace fossil record. Most taxa capable of complex
information processing in Cambrian ecosystems were panarthropods, whereas
mollusks and chordates made up larger proportions afterward. In both the
Cambrian and present day, ecological occupation of diverse habitat tiers
and feeding modes are possible with even simple nervous systems, but
ecological lifestyles requiring rapid, regular movement are almost
exclusively associated with brain-bearing taxa, suggesting a connection
with fast information processing abilities and bodily responses. The
overall rise in cognitive sophistication in the Cambrian was likely a
unique event in the history of life, although some lineages subsequently
developed more elaborate sensory systems and/or larger brains.