This video is called Fish of the Silurian Period.
By Jennifer Viegas:
Did Super-Sized Animals Live Long Before Dinosaurs?
June 12, 2014 11:00 AM ET
It’s generally believed that Earth’s earliest animals were not very big, but discovery of a huge new fish that lived around 423 million years ago has scientists rethinking what life was like close to 200 million years before the first dinosaurs emerged.
The fish, named Big Mouth Blunt Tooth (Megamastax amblyodus), is described in the latest issue of Scientific Reports. For its time, the toothy and lobe-finned fish was in the number one spot on the food chain.
“At 1 meter (3.3 feet) in length or greater, it was vastly larger than any other animal,” lead author Brian Choo told Discovery News, adding that Big Mouth was “likely the earliest vertebrate (backboned) apex predator in the fossil record.”
Choo, a paleontologist at the Chinese Academy of Sciences and Flinders University, and his colleagues analyzed Big Mouth’s remains, which were unearthed at the Kuanti Formation in Yunnan, southwestern China. During the fish’s lifetime, a period known as the Silurian, this region was part of the South China Sea. It is where the marine ancestors of all jawed animals, including humans, first evolved.
Equipped with both piercing and crushing teeth, Big Mouth likely preyed upon hard-shelled moving species, such as mollusks and armored fishes. The second largest animal at the time, Guiyu onerios — aka Ghost Fish, was a mere one-third of Big Mouth’s size.
Why then was Big Mouth so big?
One reason, according to the researchers, is that competition among fish appears to have been fierce.
Co-author Min Zhu explained, “During the Silurian period, the South China Sea, then at the equator, was the cradle of early jawed vertebrates, thus the ecological competition among these creatures was very intense.”
Another reason is that Big Mouth probably had plenty of oxygen. Modern fish are generally worse off in low oxygen conditions, and big fish require more oxygen than small ones, Choo said. Big Mouth therefore could not have existed unless sufficient oxygen was present.
See also here.