Titanis: Beast of the Week

Titanis walleri was a large, flightless bird that lived in what is now southern North America between the late Pliocene and early Pliestocene epochs, between 5 and 2 million years ago.  The largest found Titanis towered at over eight feet tall, but there were many smaller individuals found, as well, suggesting sexual size dimorphism.  It's beak, which was hooked at the tip and sharp on the edges, suggests it was a meat-eater.  When Titanis would have coexisted with many famous prehistoric mammals, like saber-toothed cats, giant sloths, Glyptodon, mammoths, and even early humans.  The name, Titanis, translates to "titan" which means "giant", and is also the name of the first Greek gods (the generation before Zeus)  It is an appropriate name because this bird was HUGE.

Titanis walleri about to swallow a young capybara.  Painting by Christopher DiPiazza. 

Titanis was a member of the extinct group of large, predatory, flightless birds, called phorusrachidae, but their nickname, "terror birds", is cooler sounding.  There were a few kinds of known terror birds that have been discovered and described, but Titanis was the largest, and it was also the only known member of this family to have lived in North America.  All of the others were found in South America, which is where Titanis' lineage likely migrated from for reasons that are still a mystery to paleontologists. 

Titanis skeletal mount on display at the Florida Museum of Natural History.

Phorusrachids do have one very close relative that is alive today, called the Seriema.  Seriemas belong to the order of birds, called cariaformes, which includes the terror birds.  The modern seriema, although much smaller than its ancient cousins, gives us many clues as to how birds like Titanis may have lived.  For one thing, seriemas are also predators, specializing in killing smaller prey, like lizards and snakes by grabbing them in their beaks and beating the poor little creatures to death against the ground.  They also will use their feet to stun or immobilize prey.  In fact, the second toe on each of their feet houses an enlarged "killer claw" just like their even older, more distant cousins, the dromaeosaurids, like Velociraptor and Deinonychus!  Both seriemas and Titanis also have similar wrists and hands (wings), which could flex to a certain degree, but from what we see in seriemas, have no specific purpose that we know of.

Red-legged Seriema with an enlarged picture of the foot, showing the enlarged talon.

Titanis also had sharp, curved claws on its toes, which no doubt could have helped it pin down prey, but its major weapon was probably its head, which was armed with a massive, hooked beak.   There are a few schools of thought as to how Titanis used its beak.  The most popular idea is that the great bird would have swung its head at its prey, like a pickaxe, nailing it with the hooked end to kill it or immobilize it. It then may have pinned the unfortunate creature down with its strong claws as it used the hooked tip of the beak, paired with the sharp edges to rip off pieces of the likely still living prey to eat like a fork and knife. (Check out the video below of the Eurasian Hawk I work with using this method on a dead mouse I gave her.)  If the prey was small enough, Titanis likely would have swallowed it whole, which is something living predatory birds also do.  Another interesting possibility is that Titanis could have used its beak to hold smaller prey and beat them against the ground like its modern relative, the seriema does.

Titanis is an amazing example of convergent evolution, recycling a successful design more than once in the same major lineage of animals.  Titanis, as you know, was a bird, and therefore a kind of theropod dinosaur.  Unlike other large, flightless theropods, like Tyrannosaurus, however, Titanis did not live during the Mesozoic, but much later after the meteorite that wiped out most of its ancient kin hit the earth.  Furthermore, Titanis did not evolve directly from these large predatory dinosaurs, but rather from smaller birds that were probably capable of flight.  Dinosaur evolution is complicated!

That is all for this week!  As always feel free to comment below or on our facebook page!

References

Alvarenga, H. M. F.; Höfling, E. (2003). "Systematic revision of the Phorusrhacidae (Aves: Ralliformes)". Papéis Avulsos de Zoologia 43 (4): 55–91.

Baskin, J. A. (1995). "The giant flightless bird Titanis walleri (Aves: Phorusrhacidae) from the Pleistocene coastal plain of South Texas". Journal of Vertebrate Paleontology 15 (4): 842–844.

MacFadden, Bruce J.; Labs-Hochstein, Joann; Hulbert, Richard C.; Baskin, Jon A. (2007). "Revised age of the late Neogene terror bird (Titanis) in North America during the Great American Interchange" (PDF). Geology 35 (2): 123–126.