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Dinosaur with an identify crisis - Majungasaurus

Majungasaurus

Majungasaurus Fossil Crates

 

Majungasaurus, "Mahajunga lizard", lived in Madagascar at the end of the reign of the dinosaurs, from ~70 mya right up to the very end 66 mya.  
Like most early-named dinosaurs, its naming history is, uh, complicated.  Though not as bad as others, this animal, based on 2 teeth, two backbones (sacral, caudal), and a hand claw [photo 2] were originally dubbed Megalosaurus crenatissimus "mega lizard notched most" thanks to having serrations on the front and back of its teeth, in 1896 by Depéret.  

 

In 1925, Depéret decided to move it to Dryptosaurus (=Laelaps) because the serrations on the teeth occupy the entire crown, not just the top 2/3rd like Megalosaurus, which you can see if you look closely at tooth 5.  
Majungasaurus Fossil Crates
Deperet 1896 - Megalosaurus crenatissimus

 

In 1955 Lavocat changed the name to Majungasaurus as a jaw with similar teeth was found but this jaw looked very different than other theropods, being strongly curved (the jaw drawing, shown from above).   
Majungasaurus Fossil Crates
Lavocat 1955 - Majungasaurus crenatissimus 
 
In 1979, in Nature no less, Sues and Taquet revealed to the world the first pachycephalosaur material from south of the Equator, Majungatholus "Majunga dome", which they provided stereo-photographs of in the paper (very cutting edge!).
Majungasaurus Majungatholus Fossil Crates
Taquet and Sues 1979 - Majungatholus atopus the pachycephalosaurid

 

In 1996 Sampson et al. published on a premaxilla with teeth they had excavated in Madagascar that looked like the originally found Majungasaurus teeth but were attached to a premaxilla which looked nearly identical to #Indosuchus which, in turn, looked like Abelisaurus.  We now knew for sure Majungasaurus was an abelisaurid.  I happened to arrive at Stony Brook in 1996 while all of the Madagascar excitement was building.  
In 1998, making the cover of Science, Sampson et al. published on an extraordinary skull which just so happened to have the identical dome to that of Majungatholus.  Bye-bye pachy, hello awesome theropod!  They decided Majungasaurus was a nomen dubium based on lack of diagnostic characters.  

 

In 2007, however, after much more study, they brought back the name Majungasaurus, as the original dentary found did look like their awesome skull, plus it has "...weakly developed interdenticular sulci...." which Indosuchus does not.
Whew!  So it was as complex as all pre-1900 dinosaur names after all :-)

 

Majungasaurus Fossil Crates

 

Everyone jokes about Tyrannosaurus having small arms, however, abelisaurs take it to an entirely new level.  All while maintaining 4 fingers!  You can see that in the bottom right inset.  The complete hand has been found and, yep, ridiculously tiny.  Look at the super-tiny radius and ulna!  There are no ossified carpals (if you are wondering what is missing). The humerus isn't even the length of the coracoid (part of the shoulder bone).  What in the world were they doing with such tiny arms?  I'm open to suggestions.  They were muscular so it was likely they were doing *something* with them, but what?  It is possible they lacked claws and the fingers may have been like mittens!  What? Yet they were highly flexible.  I have this vision of it swirling each tiny nub around in circles while it charged at animals with its missile-head loaded with teeth.  One suggestion is the hands were used for mating displays, or even during mating like some boas, who use their vestigial legs to stroke their mate.  

 

The only large herbivores that it lived amongst were #titanosaurs.  It has been suggested this animal was a sauropod specialist, using its stout, robust, broad skull with a powerful bite to take down a sauropod.  It would bite, use its massively strong neck to rip backward and take out a huge chunk of flesh.  Notice its legs aren't long, this animal was likely an ambush predator.  A burst of speed from the treeline, bam, it is on a smaller sauropod, rending huge quantities of flesh.

 

Or, did it use such powerful bites to strip the flesh off of dead, dry animals?  Spending most of its time as a scavenger?  This blends into the proposed cannibalism as 2 specimens (FMNH PR2100, UA 8678) were found with bite marks on ribs and vertebrae that clearly came from other Majungasaurus.  I love the line in the paper Majungasaurus "...regularly defleshed dinosaur carcasses."  

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