Claim 1. T. rex was a scavenger.
This all started with Jack Horner giving a talk around 1993 where he discussed the idea that T. rex was a very strange build for a predatory dinosaur with its tiny arms. Through the years it keeps re-appearing as a common question, and Jack Horner himself happily will raise it as a debate starter although there is no evidence he truly believes it. *There was an extensive chapter in a book in 2008 by Thomas Holtz that critically appraised this field (and covers many of the same points I do here, although I must admit I hadn't read it at the time of first publishing this article).* Brian Switek has written a great blog post on the whole debate back in 2013, shortly after a paper in PNAS described fossils of two fused hadrosaur vertebrae with a T. rex tooth crown embedded in them. The vertebra in question had regrowth around the damage showing the hadrosaur had survived its hunting and lived for at least a while longer, although the regrowth and trauma may well have led to its ultimate demise.
hunt more of their food than scavenge. The link is to a BBC article I accept, but the scientist interviewed has published many papers on the matter (e.g, Holekamp et al., 1997). As for the lion fact there is far less data out there, however it is widely accepted that lions can, and do, scavenge large percentages of their food. The reason for this is blatantly obvious: lions are the largest carnivores in their environment, if they stumble across a kill from another smaller predator (single hyena, leopard, cheetah etc.) they can easily scare it away and eat the food with no energy expenditure of the hunt (and their hunting success rate is low: 10-20%), so why wouldn't they? So why do we think that dinosaurs would be any different? T. rex was the largest carnivore in its environment so it will almost certainly have done both to varying extents depending on prey and carrion availability.
Claims 2-many. Spinosaurus.
Where to start with this one. I've worked on spinosaurs as part of my MSci project and have published on their snouts and convergences so am potentially biased from that work, but I hope I can walk through my reasoning on many of the issues with publications in the last few years. Just a quick background (if you don't know), spinosaurs are a crazy group of theropod dinosaurs that evolve incredibly elongate snouts. The group has gained its name from the first species found, Spinosaurus aegpytiacus which was discovered in Africa, and remains the largest known of the spinosaurs (and length-wise one of the biggest theropods ever) and possessing the biggest sail on its back. It only really came to global fame with Jurassic Park 3 as the big dinosaur that chased around the actors and killed a T. rex.
Spinosaurs being big and weird, with a global following garner a lot of interest in publications. This is further helped by the fact the original Spinosaurus specimen were destroyed during WW2 in a bombing raid of Munich so new fossils help inform us on this enigmatic group.
|The original Spinosaurus specimen found by Stromer in 1912, now lost.|
|Dal Sasso et al., 2005. The largest known Spinosaurus snout showing the highly elongate snout.|
|Gharial skull showing the elongate narrow snout, with terminal rosette expansion (photo from Glasgow Museum Collections)|
However, everyone fails to take into account size.
Whilst the biggest gharials are 970kgs, the biggest spinosaurs are amongst the largest theropods to have ever lived with mass estimates between 7-20 tonnes. This is where my research came in. Spinosaurs do have incredibly rubbish snout morphology for relative strength as they are effectively solid cylinders. Alligators flatten their snouts so have big, flat, wide ones which are much stronger than similar sized cylinders. However, when size is taken into account, all crocodiles snouts were less strong than the Spinosaurus and Baryonyx snouts. Again I know people may argue that it means they are just able to take bigger fish, and there were indeed 6ft long saw-fish in the regions where Spinosaurus lived. However, that argument comes under the Tyrannosaurus only scavenging. Why would a super-massive predatory dinosaur with a strong skull (due to size over shape) only eat fish in an environment that would have had loads of other prey items, whether to hunt or scavenge? Many crocodiles are known to change diets as they get bigger shifting from mainly fish and amphibians to increasing amounts of terrestrial vertebrates. In the case of alligators, they shift from invertebrates and amphibians, to fish, then turtles and ultimately large terrestrial prey as they grow up. Whilst impossible to prove for Spinosaurus at present, a tooth from a South American spinosaur was found embedded in a pterosaur vertebra and an Iguanodon bone was found in proximity to the Baryonyx remains which may have also been consumed.
|Ibrahim et al., 2014 reconstruction of Spinosaurus.|
Does the evidence back this up? Well, not yet. The problem with reconstruction is they are based on lots of different specimens, so the reconstruction is a chimera. If any part of these comes from a different species the reconstruction will be wrong. Since the new Spinosaurus reconstruction in 2014, Evers et al., 2015, and Hendrickx et al., 2016 suggest there are at least 2 spinosaur species found in the same deposits, and some of the second - Sigilmassasaurus was used in the reconstruction of Spinosaurus. Even worse, we don't even know the specimens in the museum and the newly collected fossils from the field are from the same individual despite the word of the professional fossil collector in Morocco. There is no collection map that would be typical for any fossil collection to show how the specimens were found. The biggest oddity remains the legs. They are so short compared to any other known theropod. An older, African spinosaur for which a single specimen exists showing a lot of the skeleton (Suchomimus, Sereno et al., 1998) shows relatively normal leg sizes.
|Sereno et al., 1998 reconstruction of Suchomimus showing the discovered specimen.|
The extraordinary claim really is going to have to wait for a more complete publication of all of the original authors' finds. Unfortunately Science only publishes short papers, so the full monograph description has yet to happen. Whether it will, or gets caught up in never ending peer review due to some of the issues that are now being raised in other publications we shall have to wait and see. Ultimately, we really need an exceptionally complete individual fossil to back it up (like the Suchomimus fossil). Undoubtedly there is one out there, quite possibly in the Kem Kem of Morocco, but it needs a proper excavation and not a piecemeal extraction and selling by a commercial dealer who may have ulterior motives.
In science, the extraordinary claims make the big headlines, lead to publications in the highest impact journals, and this in turn often helps make researchers' careers. The problem in palaeontology, like all sciences, is this leads to overstatements or overreaches for the data that we have (particularly for small sample sizes). I have been lucky to work in labs that have been very good at helping me tone down my language to accept that there are uncertainties in our work, and really extraordinary claims do require extraordinary evidence. I hope anyone reading considers this when writing their next manuscripts.
*Update. It has been pointed out to me that I missed an important reference in the T. rex scavenging debate which I have now included. My apologies. Please continue to add further reading/comments with regards to the topic.
Amoit R, et al., 2010. Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods
Charig AJ, Milner AC, 1997. Baryonyx walkeri, a fish-eating dinosaur from the Wealdon of Surrey. Bulletin of the Natural History Museum of London 53, 11-70.
Cuff AR, Rayfield EJ, 2013. Feeding mechanics in spinosaurid theropods and extant crocodilians. PLoS One 8, e65295.
DePalma et al., 2013. Physical evidence of predatory behaviour in Tyrannosaurus rex. Proceedings of the National Academy of Sciences USA 110, 12560-12564.
Evers S et al., 2015. A reappraisal of the morphology and systematic position of the theropod dinosaur Sigilmassasaurus from the “middle” Cretaceous of Morocco. PeerJ e1323.
Holtz Jr, T.R., 2008. A critical reappraisal of the obligate scavenging hypothesis for Tyrannosaurus rex and other tyrant dinosaurs. Tyrannosaurus rex the Tyrant King, 371, p.396.
Ibrahim N, et al., 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345, 1613-1616.
Rayfield EJ, et al., 2007. Functional morphology of spinosaur 'crocodile-mimic' dinosaurs. Journal of Vertebrate Paleontology 27, 892-901.