BY DR. JOSE PALU-AY DACUDAO
(Part 3)
THE GREATEST mass extinction in the planet’s history occurred around 252 million years ago, at the junction of the Permian Period (299 million to 252 million years ago) and the Triassic Period (251 million to 200 million years ago).
The synapsid therapsids, from which mammals derive from and to which clade mammals belong to, were the dominant land creatures during the Permian. But shortly after the mass extinction event, sauropsid archosaurs (from which dinosaurs and crocodilians are derived from) took over (the so-called Triassic takeover).
Perhaps, it was because of the advantages offered by the archosaurs’ urinary and respiratory systems mentioned earlier, but the case is unclear.
In the latter part of the Triassic true dinosaurs began to dominate. Thus, dinosaurs and their immediate ancestors dominated the medium to large animal niches of the Earth for most of the Mesozoic Era (251 to 66 million years ago).
For that extended period of time, mammals (which like dinosaurs also appeared in the latter part of the Triassic, derived from therapsid cynodonts) mostly remained the size of shrews and mice.
Then non-avian dinosaurs became extinct 65 million years ago at the end of the Cretaceous Period (145 million to about 65 million years ago). (The two most popular theories are a bolide strike from outer space in Mexico or prolonged volcanism that formed the Deccan Traps flood basalts of India or both.) This despite the dinosaur’s’ more efficient respiratory and excretory systems compared to mammals.
The mammals rapidly took over the niches occupied by dinosaurs. A popular theory is that the small burrowing mammals could resist catastrophic environmental changes better than large exposed dinosaurs that needed more food.
In my opinion the intelligence and adaptability that bigger brains with more numerous neurons confer to their owners was the more decisively important factor.
If dinosaurs had a cerebral cortex, they might be ruling the world until now. But it is us mammals that have it, and so we are ruling the word now.
Among mammals the brain to body mass ratio generally increases as more complex behavior becomes necessary to obtain food. Thus, herbivores usually have the smallest brains, while omnivores and carnivores have bigger brains. That figures – a herbivore such as a carabao does not need much brains in order to chomp on vegetation found all over the place.
Omnivores and carnivores often need more complex hunting abilities in order to catch prey or collect food. Cooperative group behavior may also be associated with larger brains. In general, the bigger brain to body ratio, the more intelligent a creature.
The other generally accepted factor is that the more convoluted the brain is, the more intelligent its possessor. This happens because the mammalian brain is confined in a rigid skull that limits its growth; and so in ontogeny, the more neurons are added to the cerebral cortex, the more its tissues have to twist, just to fit in the skull. (To be continued)/PN
