Hey guys, you remember all that hubbub with Spinosaurus a few years back? Well, time to teach the controversy! Erm... Or not. Anyways, Spinosaurus has always fascinated me, even before the new findings were published in 2014. The fact that there were possibly semiaquatic dinosaurs is amazing! But how should we depict it? Like the four legged superaquatic form that Ibrahim and colleagues propose? Or some other way? Note: I am no expert. If I get something wrong, let me know. Also, I know I have not used my own artwork yet, but don't worry. I will very soon. It's just been difficult to find something for me to draw...
What Ibrahim and Colleagues Proposed
The bones that Ibrahim et al. studied came from a fossil dealer, and so the exact location of the fossils are unknown. This can be a bit of a problem, because if the bones didn't come from the same location, then you can be dealing with a chimaera. Anyways, the bones seemed to have come from a subadult
Spinosaurus, including some spines, toe bones, claws, hips, and tail. These seemed to show that it had proportionally a very small hip, as well as very small feet for it's size. Ibrahim et al. therefore proposed that it couldn't support it's whole weight on just two legs, and must've walked on its knuckles as well (I'll get to that in a moment). They also show that the toe claws were flat and dull, unlike other theropods. This is indicative of possible webbing between the toes, like a duck. They also seemed to show that the sail had a sort of dip in the middle, not continuing to the tail, and that the sail was tightly packed in skin. An interesting finding was that the bones lacked medullary bone, and were very dense, unlike other theropods. Together with the webbed feet, small legs, and freshwater deposits they were found in, Ibrahim et al. came to the conclusion that
Spinosaurus was semiaquatic, more comfortable in the water than on land, having to walk on it's four limbs to do the latter.
The Response
Obviously, this paper got many responses and criticism. Many people pointed out that the bones came from a fossil dealer, and their location of origin is unknown, and that it seemed to have drastically shortened the leg size as problems. Jaime Headden (come back!) also had a problem with the sail, saying that there is evidence that it extended onto the tail. Others even said that the supposed
Spinosaurus tail is actually from an ornithischian. Headden also pointed out that it would be nearly impossible for
Spinosaurus to knuckle walk, let alone walk on four limbs.
The authors did publish a response about the size of the hind limbs. It seems that they measured it differently than they way they are usually measured, and so this caused some confusion. Tiny legged
Spinosaurus for the win! As for the dense bones, I think that is something you really can't argue. Dense bones, PLUS the isotopic studies on
Spinosaurus teeth, seems to firmly argue that
Spinosaurus was more aquatic than previously believed. And then there was that paper published last year that indicated that
Sigilmassasaurus is indeed it's own genus, and so casted even further doubt that the remains actually belonged to
Spinosaurus.
What Do I Think?
Given the placement of the nostrils, the dense bones, the foot claws and toes, the small size of the legs, and the isotopic ratios, I think that
Spinosaurus probably was as aquatic as Ibrahim et al suggests. Do I think it was quadrupedal? I don't think so. There are other ways for it to still support it's weight on two legs. Andrea Cau suggested that it had neck muscles pulling it's head back, forcing it to stand up. I personally believe that either some areas of the body were less dense to balance it out, or that it had a particularly long, or heavy, tail. I think it walked like a pangolin or a penguin when on land. It should be noted that theropod legs tend to get smaller as they reach adulthood, and unless
Spinosaurus didn't do this, the adults may have had slightly smaller legs. I know some people probably think it couldn't walk and belly crawled. I think it could belly crawl, but it could also definitely walk on it's hindlimbs. I also agree that the spines were tightly packed in skin and not used to warm the animal up, but instead for display. I find it very hard to believe that the tall spines could support a hump like structure, and it seems a bit much. You can store fat in many other areas, such as the torso or tail. I also have doubts about the sail shape. Paul Sereno (one of the authors in the Ibrahim et al. paper) suggested that sail shape may have varied between individuals. I find that to be a cool idea. I have looked at the spines, and some of do extend onto the tail. I think I'll go with the idea that the sail shape may have varied between individuals, and that maybe it changes as it grows. So in short, while I think Ibrahim et al. made a lot of headway and gave loads of new and compelling ideas about
Spinosaurus, they do not have the whole picture. Obviously, we will need to wait and see what else North Africa churns out in the coming years, and hopefully we'll get a more detailed look at this incredible animal.
Next up, more
Spinosaurus! This is gonna be the first part in a series of posts about spinosaurs. And the next installment features babies...
References
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