It’s no question that there’s a huge range of diversity among the animals of the Earth. In fact, no one really knows just how varied this diversity gets: around 10,000 new species are discovered every year, and some estimates put the total number of animal species somewhere between 2 million and a whopping 50 million. According to what is currently believed to the most accurate estimate, there are likely about 8.7 million species in total. However, only around 1.9 million of those animals have been named and described. That means there are still many millions of creatures that nobody even knows about!
All this diversity had to come from somewhere. For all the millions of species on our planet, there are millions more that have gone extinct. Paleontologists study the fossil record and make connections between these extinct species and their modern day descendants. Comparing today’s animals with their prehistoric relatives can lead to some interesting discoveries.
As we have discussed in previous blogs, birds aren’t just descended from dinosaurs, they ARE dinosaurs. So when you’re looking at a mockingbird, it’s really not too far removed from a Velociraptor. But what about other reptiles? Aside from birds, the closest living dinosaur relatives are the crocodilians – alligators and crocodiles. Where did they come from? Well, all crocodilians living today are members of the order Crocodilia, the first examples of which appeared in the Late Cretaceous period, around 84 million years ago. However, Crocodilia is a relatively small group within a much larger superorder known as Crocodylomorpha, which includes crocodilians and all their extinct relatives. These include Kaprosuchus, a tusked crocodylomorph from 95 million years ago that likely lived most of its life on land, unlike today’s crocodiles which live mostly in and around water. On the opposite end of Kaprosuchus is Plesiosuchus, a crocodile relative from 150 million years ago that lived entirely in the water. Its feet had evolved into flippers and its tail was specially shaped to help it swim through the sea.
Speaking of ancient aquatic animals, have you ever wondered how long sharks have been around? The answer might shock you: almost 450 million years! The first sharks were quite different from what we recognize as a shark today, but even what we consider to be modern sharks have been around for 100 million years. The great white shark, probably the most well-known shark of all, has only been around for 16 million years or so. These sharks can grow quite large, up to 20 feet, but their extinct relative the Megalodon was even larger. This shark lived from 23 million to around 2.6 million years ago, and is believed to be the largest shark of all time – even bigger than the whale shark. While whale sharks are harmless filter feeders, the Megalodon was a huge predatory fish that preyed on prehistoric whales. Since shark skeletons are made of cartilage, they don’t preserve well, which means Megalodons are known mostly from their huge fossilized teeth. This makes estimating their size difficult, but it’s believed by most paleontologists that they could reach between 50 and 80 feet in length.
Many prehistoric creatures were much larger than their present day relatives. The Megatherium, for example, was a giant ground sloth that first appeared around 5 million years ago and became extinct just 10,000 years ago. It was one of the largest land animals ever known, and could grow to about the size of a modern elephant! By contrast, the two-toed sloth of today only grows to about two feet long and lives almost entirely in trees.
Another mammal grouping that has shrunken in size over the years is the armadillo order. Glyptodonts like Doedicurus went extinct 11,000 years ago, and could grow to 13 feet long. They had huge armored shells and a spiked club at the end of their tail. Their shells were so big that ancient humans used them as shelters. Today’s armadillos, like the nine-banded armadillo, don’t grow much longer than two or three feet in length and are much less fearsome.
The large prehistoric ancestors of today’s animals are called “megafauna”. While these creatures have gone extinct from a variety of factors from climate change to human overhunting, there are still some animals alive today that are considered megafauna. These include the elephants, some of the largest land animals in existence today. In fact, today’s elephants represent a rare example of prehistoric animals not being significantly larger than their modern day counterparts. The woolly mammoth is a hairy relative of today’s elephants that went extinct around 5,000 years ago. The largest mammoth species reached about 13 feet at the shoulder, which is similar in size to the largest African elephants ever recorded. It should be noted, however, that the Asian elephant is more closely related to the mammoth, and is the smaller of the two living elephant species.
It can be quite awe-inspiring to think of how many species there are today, and even more overwhelming to think of how many there have been throughout the history of the world. But today, this strong biodiversity faces a serious threat: scientists estimate that between 150 and 200 species of plants and animals go extinct every single day! This extremely high rate of extinction is largely influenced by human activity, including climate change, habitat destruction and overhunting. Only through intensive conservation efforts can we put a stop to this catastrophic loss.
Bernie’s Bonus Matching Game: Using figures from our Wild Safari Prehistoric World, Wildlife and Sea Life collection, you can take a trip through time with a matching game that can help children learn about how prehistoric animals developed into those we know today. See if your children can match the modern day animal figure with its Prehistoric World relative based on similar features, such as the trunks of the mammoth and elephant, the hooked claws of the giant ground sloth and two-toed sloth, or the sharp teeth of the Megalodon and great white shark.