Over on AAB I have been debating the relative sizes of the giant theropods Tyrannosaurus and Giganotosaurus with sauropod expert Mike Taylor. Those regular readers of this blog will know I have a longstanding interest in dinosaur body sizes and mass estimates and they are a question that comes up again and again when then the public or media get to grill palaeontologists, if only as framed as “which was the biggest?”.
These are however a very interesting pair of taxa and illustrate a few concepts quite well (namely different concepts of being the ‘biggest’) and are often foremost in people’s minds when they think of giant dinosaurian predators. Tyrannosaurus is famous for its size and is probably one of the most recognisable dinosaurs going, and there is little doubt it was huge – around 12 m in length and something like 8t in mass. For a very long time it was regarded as the largest terrestrial predator and the absence of any detailed information about Spinosaurus (rapidly followed by the absence of any material following World War II) meant that until recently, Tyrannosaurus was pretty much unchallenged. Then a flurry of discoveries in South America threatened the crown of the king severely, most notably through Giganotosaurus, a real giant and almost certainly taking the crown for the longest theropod known at a round 14 m, though Tyrannosaurus was quite probably heavier.
This gives me the opportunity to wheel out this image that I produced for a grant application I made of giant predators that gives you an idea of just how big some of these got. At the front you have a Siberian tiger (white – the largest living terrestrial predator) and Andrewsarchus (grey – the largest known mammalian predator, though its status as a carnivore has been questioned) and then across the back Spinosaurus (white – actually drawn too large, it has recently been scaled back a bit from this and the biggest carnosaur), Giganotosaurus (black – the biggest allosauroid), Tyrannosaurus (grey – the biggest tyrannosaur) and Carnotaurus (white – the biggest known abelisaur). As you can see Tyrannosaurus is massive by any measure, but what interests me is the actual build of the animals and most notably the respective skulls of our featured animals.
This post was inspired by the fact that I ended up discussing (i.e. arguing) about them with Mike the day after I spotted this image online via my colleague Canadian palaeontologist and Tyrannosaurus specialist Eric Snively who kindly passed it on. It is made from CT scans of sculpture reconstructions, of Sue (the famously complete and very large Tyrannosaurus, by Brian Cooley) and the type of Giganotosaurus (by Maria Gravino). It’s taking a team from five countries to turn these into finite element models for bite force comparison research I am I very grateful for being allowed to use it.
The scale may not be exactly right, but it is good enough and it really demonstrates the point I want to make. Tyrannosaurs might not be the longest, or even the heaviest theropod, and certainly it *is* the most over exposed and overstudied, BUT it is also has an absolutely huge skull for its size. Not only is the skull pretty much the same in overall dimensions as that coming from an animal supposedly much larger than itself, but that cranium is far far more massively built. The skull is incredibly robust and well built in comparion to that of Giganotosaurus. It really gives you a feel of just how different and specialised Tyrannosaurs seems to be, since Giganotosaurus really does have a pretty ‘typical’ theropod skull, if a very big one.