Monster Sized Images

©Luis Rey

The general feeling, though I have seen that Coria and Currie did not, by some sources, want the idea of pack hunting to be explicitly thought of with Mapusaurus (Coria and Currie believed the mass grave they excavated was actually an animal trap like La Brea and others), is that, though an enormous dinosaur itself, Mapusaurus would have needed to employ paired or pack hunting characteristics in order to hunt the largest herbivores of Argentina. Considering that even the mighty Allosaurus was thought to hunt in packs to bring down massive sauropods this makes sense. The major difference, however, is that Allosaurus was significantly smaller than Mapusaurus, which actually may have a slight edge on Tyrannosaurus in the size department. Thinking of a theropod larger and perhaps even meaner than Tyrannosaurus is quite a task given the ferocity in which Tyrannosaurus is typically portrayed. In Luis Rey's illustration two Mapusaurus are working to take out a young, maybe an early juvenile, Argentinosaurus. We can imagine the numbers needed to take down one of the large ones in the background if it takes two to get a juvenile to become dinner.

©Nobu Tamura

Let us take out all the clouds of dust and other animals and scenery a moment and just look at Mapusaurus. Its closest cousins, the Giganotasaurs, look a lot like Mapusaurus, but there are many differences that can be pointed out. Coria and Currie pointed out a lot of key differences between Giganotosaurus and Mapusaurus. In their paper they summarized those differences as follows (Coria R. A. & Currie P. J. (2006). A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. Geodiversitas 28(1):71-118.):

thick, rugose unfused nasals that are narrower anterior to the nasal/maxilla/lacrimal junction; larger extension of the antorbital fossa onto maxilla; smaller maxillary fenestra; wider bar (interfenestral strut) between antorbital and maxillary fenestrae; lower, flatter lacrimal horn; transversely wider prefrontal in relation to lacrimal width; ventrolaterally curving lateral margin of the palpebral; shallow interdental plates; higher position of Meckelian canal; more posteriorly sloping anteroventral margin of dentary. Mapusaurus roseae is unique in that the upper quadratojugal process of jugal splits into two prongs; small anterior mylohyoid foramen positioned above dentary contact with splenial; second and third metacarpals fused; humerus with broad distal end and little separation between condyles; brevis fossa of ilium extends deeply into excavation dorsal to ischial peduncle. It also differs from Giganotosaurus in having conical, slightly curving cervical epipophyses that taper distally; axial posterior zygapohyses joined on midline; smaller and less elaborate prespinal lamina on midline of cervicals; remarkably sharp dorsal margin of cervical neural spines; tall, wider neural spines; curved ischiatic shaft; more slender fibula.

©Sergey Krasovskiy

Admittedly those few long sentences are a lot to try to understand. Basically what it boils down to is that the skull of Mapusaurus is thicker at the front of the nose but narrows as we move back to the eyes. Also, the fenestrae, holes in the skull that allow for muscle and organs while also lightening the skull somewhat, are of different sizes than those found in Giganotosaurus. Other differences within the bones and how they situated and fused in the skull also exist but that is not the only place in which Mapusaurus and Giganotosaurus are different. The arms are slightly more robust in Mapusaurus and the ilium is deeper and the legs are a bit slender in comparison, possibly making the slightly larger carnivore slightly more agile. The vertebrae are built completely different as well, making the backbone of Mapusaurus completely different from that of Giganotosaurus. The general appearance in all illustrations are pretty much the same, though they all accentuate the jaws of Mapusaurus somewhat differently and, given that it is one of its most identifying characteristics, that is fairly important. Rey's Mapusaurus has a thin, side to side, skull that does not appear long enough, which is one of those diagnostic features of Mapusaurus. Does a longer skull indicate stronger or weaker jaws? We will see how research has addressed this question in the near future and what the answer means for Mapusaurus.