This week I’ll be covering some of the weirder animals of prehistory, most of which are relatively unknown (sorry, no T-rex’s here!) but just as awesome.
**Prehistory will be a three-part series covering lesser known terrestrial, aerial and aquatic prehistoric creatures.
Upon reading/seeing/hearing the word ‘prehistory’, most people will think of dinosaurs and cavemen. But there is a staggering amount of biodiversity that lived on our planet before our hominid ancestors came into the picture, and many that sadly perished at their hands.
One thing that many known prehistoric creatures have in common though, and the thing that most people find scary about them is that a lot of them were huge. Everyone knows about the gigantism of T-rex, Diplodocus, and Megalodon. But there were also ground sloths the size of modern-day elephants, dragonflies the size of hawks, and cockroaches the size of domestic cats (eek!).
How did prehistoric creatures grow to be so large? No one knows for sure, but there are a few theories out there. Before I go into them though, I’d just like to clarify a common misconception. Not all prehistoric creatures were large, despite larger fossil remains being more commonly found. The earliest known ancestor of the modern-day horse, for example, grew to a maximum size of the modern-day fox. Naww…
The other thing is that most gigantic prehistoric animals did not occur at the same time. The largest known dinosaurs – the herbivorous sauropods and the predatory theropods – did not coexist. In fact, they lived within different geological periods altogether.
What I’m getting at here is that gigantic animals took a whole lot of time to evolve – a lot longer than we humans have been on Earth. There hasn’t really been enough time since the last major extinction event for new massive animals to evolve, meaning that it is very much possible that new gigantic species will develop in the future.
I, for one, would love to see a gigantic kitten.
So, how ’bout that gigantism?
Theory 1: Cope’s rule
Edward Drinker Cope was an American paleontologist who postulated that species tend to increase in body size over evolutionary time. Seems pretty plausible, right? Cope didn’t really go into specifics about what caused the increase in body size, but other scientists have put their foot forward and provided some insights.
- The evolutionary advantages of being big
So, the premise here is that being a larger animal makes you less vulnerable to predation and makes you better equipped to take on competitors for valuable resources. The growth of herbivorous creatures meant that their predators also had to grow to even have a chance of taking them on. Just imagine trying to keep up with Dreadnoughtus – the largest known terrestrial creature ever.
It is thought that species got large in response to environmental factors. For example, in mammals and other warm-blooded creatures, being larger would help you retain heat more efficiently in colder climates. For cold-blooded creatures like dinosaurs and fish, being larger would help insulate the animal more efficiently in warmer climates.
Another postulated reason is that dense, woody foliage might have contributed to the super-sizing of herbivorous dinosaurs, as a large body frame would have been able to accommodate a longer digestive tract, giving their gut bacteria more time to extract nutrients.
Theory 2: availability of oxygen
This one applies more to the super-sized insects of prehistory. It is thought that they were able to grow so large due to elevated oxygen levels in the Permian, which was the point in evolutionary history where insect diversity exploded. Air was 31% oxygen back then, today it is little over 20%.
This is important for insects because of the way they breathe. Insects don’t have lungs. They breathe through trachea, tubes that carry air from the outside towards the internal muscles. With a higher level of oxygen in the air, there would have been more respiratory efficiency, allowing the insect to grow larger.
Next time! Prehistoric creatures that just look…weird.
Featured image depicts ‘A more Ancient Dorset’: a watercolour painting of 1830 by the geologist Henry De la Beche, based on fossils found by Mary Anning. Sourced from http://en.wikipedia.org/wiki/History_of_paleontology#/media/File:Duria_Antiquior.jpg.