Learning about Nanotyrannus

Last night I spent five hours watching National Geographic shows about dinosaurs, reading about dinosaurs online, and watching TED talks given by experts in the field.  I've always been fascinated by dinosaurs and try to continuously learn more about them.  Last night's foray was inspired by the mystery of the Nanotyrannus.  The Nanotyrannus is a proposed species of predatory dinosaur.  I say proposed because there is much debate among paleontologists as to whether Nanotyrannus actually existed.  In theory it is a smaller version of T. Rex which had longer arms and hunted in packs.

One of the shows I watched centered around a unique fossil showing a battle between a Triceratops and a tyrannosaur of some sort.  Both creatures suffered mortal wounds during the battle.  The fossil of the tyrannosaur is what caused the most confusion, though.  It was too small to take down the Triceratops on its own and had characteristics that made it unique from a T. Rex.  The finding of this fossil led scientists to look at other fossils that were assumed to be juvenile T. Rexes.  Upon closer look, these scientists believe that these fossils are in fact a different species, the Nanotyrannus.  Watching the show, their reasons made sense.
- The brain cavities in the smaller specimens were a different shape and make up than the full grown creatures.
- The smaller skulls had more teeth than the larger skulls.
- The teeth found in the smaller specimens were different than the larger ones.
- The arms on the smaller creatures were larger and attached differently

All these signs pointed to the existence of Nanotyrannus.  It all made perfect sense to me.  So I went online and started reading, and that's where I discovered how heated the debate was.  There seems to be clear factions that either believe or don't believe in Nanotyrannus.

Then I remembered a TED talk I saw a while back.  This talk was all about why we don't see baby dinosaurs in museums.  It was given by Jack Horner, who is a very well respected name in the field.  He claims that when scientists find a specimen that is even slightly different from other specimens, despite having some similarities, scientists want to consider it a completely different species.  But they fail to look at growth patterns and bone density.  He says the easiest way to determine if a skeleton is from a juvenile or adult is to cut into the bone.  Juvenile bone is spongier while adult bone is more solid.  He looked at a series of different different species and by looking at the bones was able to hypothesize that dinosaurs previously assumed to be separate species were actually juveniles of other species.  One of these species was the Nanotyrannus.  He says that those bones claiming to belong to Nanotyrannus were actually juveniles, lending credence to the fact that they were actually younger T. Rexes.  This also sounded incredibly believable, so I don't really know what to think.

I want to believe that Nanotyrannus existed because it sounds cool, but I really don't know.  I lean towards whatever Jack Horner says, since I recognize his name as the technical advisor for Jurassic Park.  Clearly he must have done something to earn that right.  And since we have no way of truly knowing how long dinosaurs lived, we really don't know what full grown means.  Obviously we can hypothesize based on the fossils we have found, but no one can say with 100% certainty.  Until then, the debate over Nanotyrannus will continue.