Smilodon Vs. Thylacosmilus: The Saber-Toothed Marsupial

Two million years ago, a saber-toothed predator stalked the landscape of South America.  Possessed with long, dagger-like teeth, Thylacosmilus was undoubtedly a terrifying predator of the plains of Patagonia.  This saber-toothed predator would have given even the saber-toothed cats pause, despite the fact that (to paraphrase Obi-Wan Kenobi), "He's more kangaroo now than cat."  Despite superficial similarities, Thylacosmilus was not a saber-toothed cat.  Instead, it was a six foot long, 500 pound saber-toothed marsupial.

A reconstruction of Thylacosmilus by the talented young artist Sam Lippincott.  Interestingly, the super-sized canines of Thylacosmilus grew continually throughout its life, unlike those of Smilodon or Xenosmilus (see below), two of the actual saber-toothed cats.  Photo Credit: Sam Lippincott

The immense canines possessed by Thylacosmilus had previously evolved in both the cat-like Nimravids and the various saber-toothed cats (amongst others), and is a classic example of convergent evolution, a topic, in my opinion, that is one of the most interesting happenstances in nature.  We will hopefully talk about convergent evolution sometime next week.

A mounted skeleton of Xenosmilus, a type of saber-toothed feline, at the Mace Brown Museum of Natural History at the College of Charleston in South Carolina.  I got to visit here in July of 2014, and it was a very nice little museum.  Compare the skull of Xenosmilus with that of Thylacosmilus (below).

Anyways, Thylacosmilus lived during the Miocene and the Pliocene Epochs, from 10-2 MYA.  Up until 2 MYA, South America had been its own, separate land mass, not connected to any other continents since some time during the Cretaceous.  2 MYA, however, something extraordinary happened: the Isthmus of Panama was formed, connecting the two continents.  With this connection, came something scientists have dubbed the "Great American Interchange."  Animals from both continents could move, and spread out into the other continents.  For some creatures, like the saber-toothed cats, this was a good thing; they moved down into South America from North America and dominated the landscape.  For other predators, like the terror-bird Titanis(again, a topic for another time), it was good, for a while; after moving into the southern part of North America, however, Titanis was outcompeted by other predators.  For Thylacosmilus, it was down-right disastrous.  Shortly after the Great American Interchange, fossil evidence of Thylacosmilus entirely disappears, similar to the competition between the dingo and the thylacine that drove the thylacine to extinction on mainland Australia.

The skull of Thylacosmilus on display at the American Museum of Natural History in New York.  Got to see this sucker in person in August 2014, when I visited with my good buddy Zach Evens! 

This is a partial post for the "Convergent Evolution" series.  That means that this post is partially included, but was not made specifically to be a part of that series.  HERE is a link to the Homebase for this series.  

The Biggest Carnivorous Dinosaur Part 2: Carcharodontosaurus Vs. Spinosaurus

As I promised yesterday, today we are going to take a closer look at Carcharodontosaurus (kar-kar-o-DON-to-SAUR-us).  Carcharodontosaurus was a relative of Colorado's own Allosaurus.  However, Carcharodontosaurus was four times larger, and found in Egypt, Morocco, Algeria, Libya, and Niger.  At around 46 feet long, Carcharodontosaurus was similar in size to yesterday's Giganotosaurus (pronounced jig-a-NOTE-o-saur-us), and longer than Tyrannosaurus, though Tyrannosaurus was undoubtedly much bulkier.  Regardless, Carcharodontosaurus was a monster-sized killer, and almost certainly had a monster-sized appetite to match.  It is almost a certainty that such an animal would have a fairly large territory, and would have needed to eat a great deal to maintain its fast metabolism, similar to your average teenage dude.

Clearly, such a large predator had little competition from other carnivorous dinosaurs.  Or did it?  As a matter of fact, 95 MYA, North Africa was home to not one, but two monster-sized killers, Carcharodontosaurus, and the even longer, 50 foot (15 meter) Spinosaurus.  (Some not so conservative estimates even place the maximum size for Spinosaurus as 60 feet (18 meters) in length, but this does seem extreme.)

Now, in the modern day, predators can inhabit the same area.  Take the plains of Africa, for example; in many places, lions, leopards, cheetahs, wild dogs and hyenas all inhabit the same area.  There is a clear hierarchy amongst the animals, and each seems to get enough to eat.  However, this is partly because each animal exploits a slightly different set of resources, so contact amongst them is less frequent than if all five of the large carnivores all hunted the same animal, say, the Thomson's Gazelle.  This is a phenomenon known as resource partitioning, and it occurs all over the place in nature, arguably one of the most important factors involving ecology and evolution. Scientists believe that a similar sort of partitioning took place between the two mega-carnivores of Mid-Cretaceous North Africa, with Carcharodontosaurus being a terrestrial carnivore, while Spinosaurus took to the water.  We will conclude "The Biggest Carnivorous Dinosaur" trilogy tomorrow with a look at the environment Spinosaurus was able to so successfully exploit.

A fantastic visual representation of resource partitioning amongst large herbivorous mammals in Africa.  The giraffe, the zebra, and the wildebeest will all inhabit the same area and eat plants, but the types of plants can differ.  Photo Credit: Ted and Gail Neher