|Deinosuchus rugosus swallows the remains of a large Cretaceous sea turtle. Other archosaurs notice, decide to interrupt.|
Perhaps because Deinosuchus is 'only' a giant crocodylian and not a member of a completely extinct, weirdo lineage, coverage of its palaeobiology is often limited to factoids on its immense size and probable habits of eating dinosaurs. Our short attention span for this animal is not new: one of the key players in its discovery, John Bell Hatcher, lost interest in describing the first significant Deinosuchus remains once its crocodylian identity (rather than dinosaurian, as originally supposed) became apparent in 1903 (Schwimmer 2002). It took further persuasion and a number of years for palaeontologists to actually publish, name and describe this animal after Hatcher died in 1904 (Holland 1909). As we'll discover in this article, the scant attention paid to this animal is rather criminal: over the last century a detailed and fascinating picture of Deinosuchus has developed.
|Deinosuchus is recognisable from its teeth alone. These specimens are from the posterior end of the jaws, and show the wrinkled enamel typical of the genus. Note the heavily worn and broken the tips. From Schwimmer (2010).|
The Deinosuchus fossil record is something of a mixed bag. There are hundreds of fossils of it, but most of them are isolated postcranial bones, broken bits of skull and, especially, those massive teeth and osteoderms. The state of many Deinosuchus fossils can be ascribed to its remains being reworked by storms after their initial burial. Some partial skeletons and more complete skulls escaped this treatment but are not yet described in detail. A silver lining to not having much in the way of complete material is that isolated Deinosuchus bones are distinctive enough to map its range across Campanian North America. Many of us might think of Deinosuchus as a Texan animal, but it actually enjoyed a wide distribution, and being most abundant in the southeastern United States. A clear palaeobiogeographical pattern can be gleaned from Deinosuchus fossils, a divide separating occurrences in Montana, Wyoming, Utah, Colorado, New Mexico, Texas, and Northern Mexico from remains on the eastern side of the United States - Mississippi, Alabama, Georgia, North Carolina, and New Jersey (Titus et al. 2008). This east-west distribution is no fluke of preservation but reflection of Deinosuchus populations being separated by the Western Interior Seaway, the continental sea which divided North America during the Cretaceous. Although apparently not a fully marine creature, it is thought Deinosuchus lived in the coastal waters and estuaries of this seaway as, to date, its fossils have not occurred in fully freshwater or terrestrial deposits. Further evidence of its preference for coastal waters is the recovery of more complete and associated remains from wholly marine deposits.
|A modern depiction of the Deinosuchus rugosus skull and mandible. From Schwimmer (2002).|
Less can be said about the body and limbs of Deinosuchus. Schwimmer (2002) reports that partial skeletons hint at a general form and proportion not unlike a modern alligator. However, some authors have noted discrepancies in scaling of Deinosuchus limb bones which might indicate reduced limbs in at least the largest specimens (Farlow et al. 2005, see below). One thing we can be sure of is that the body of Deinosuchus was covered in those aforementioned large, thickened osteoderms (below). The exact arrangement of these elements remains unknown, but we can predict that at least four rows of osteoderms extended along the body of Deinosuchus because of its affinities to modern crocodylians. These osteoderms become disproportionately massive and robust with growth, so that those of the largest individuals are distinctively chunky and have lost some definition of a keel found in smaller examples. Artists should take note of this: the dorsum of a big Deinosuchus would have looked more like a gnarly Dalek chassis than the back of any modern crocodylian. As is typical for crocodyliforms, these dermal bones might have reinforced the trunk skeleton as well as providing armour plating, forming a network of muscle, ligaments and bone which bound the torso together (Salisbury and Frey 2000). It is speculated that the presence of very large, robust osteoderms in the biggest Deinosuchus indicates the presence of a torso strong enough for terrestrial locomotion (Schwimmer 2002).
|The huge, deeply pitted and bulbous scutes which characterise Deinosuchus, as illustrated by Holland (1909). This image is a composite of two scutes from Holland's work, put together by FanCollector for Wikipedia. Both show cervical osteoderms, the left being a particularly big one|
Regardless of what the actual maximum size of Deinosuchus was, we have good reason to think that many individuals were not true giants. No specimens indicative of 10 m body length have been found among the many hundreds of Deinosuchus remains from the eastern side of the US, it being instead thought that eastern Deinosuchus didn't grow longer than 8 m. That's still pretty big of course, but not too far off crocodylians that we're familiar with today (the biggest saltwater and Orinoco crocodiles on record are a little over 6.5 m - Grigg and Krishner 2015). The true giants only occur in the west, and are much rarer fossils than their eastern counterparts. These fossils are also slightly younger than the eastern specimens, perhaps indicating changes across time and geography were responsible for Deinosuchus becoming exceptionally large. Research into the growth rates of Deinosuchus indicate that there might be nothing unusual about it's growth trajectory despite its size. It seems to have grown with a similar strategy to other crocodylians - relatively fast at first, and progressively slower over time - but simply stretched out the growth duration to many decades (Erickson and Brochu 1999). Growth rings in osteoderms indicate that the largest animals were about around 50 years old (below).
|Growth rates in living and extinct crocodylians (a) and growth rings in a Deinosuchus osteoderm (b). Note how the Deinosuchus growth trajectory is essentially a scaled up version of its smaller relatives. From Erickson and Brochu (1999).|
|Partial theropod hindlimb bone (tibia or metatarsal) post a one-on-one session with Deinosuchus jaws. This bone is meant to be subrounded in cross section. From Schwimmer (2010).|
|Deinosuchus bite marks in fragments of a turtle (Chedighaii barberi) plastron. The tooth marks are about 4-5 times larger than those made by 4 m long nile crocodiles. From Schwimmer (2010).|
The foraging habits of Deinosuchus brings us to new perspectives on where it fits into Mesozoic ecology. New evidence is eroding the uniqueness of Deinosuchus in Campanian North America, it no longer being the only very large or even giant crocodyliform species in some localities. These new finds include a currently poorly known, but obviously giant neosuchian from the Williams Fork Formation of Colorado (Foster and Hunt-Foster 2015) and a more completely known, 7 m long, undescribed neosuchian from Woodbine, Texas (Main 2012). The latter is currently being worked on, and early indications are that it might represent a late surviving goniopholidid - a much older branch of the crocodyliform lineage. Whatever they turn out to be, the Woodbine and Williams Fork animals suggest that very large crocodyliforms might not have been unusual in Campanian North America. Their presence in a timeframe deficient of large theropods has not gone unnoticed, it being speculated that these large crocodyliforms may have been doing work normally reserved for big predatory dinosaurs (e.g. Schwimmer 2002). Similar proposals have been made about other large bodied Late Cretaceous carnivores taking over typically theropodan roles (e.g. Witton and Naish 2015) - the notion of the Mesozoic as an all-dinosaur show is looking increasingly out of date.
As a closing thought, I find it interesting that we tend to portray Deinosuchus as something of a freak species, one of those rare forays of crocodylian evolution into gigantic size which never really seemed to last that long or lead anywhere. As might be apparent from this article, this view is somewhat misleading. Deinosuchus certainly represents an 'extreme' of crocodylian evolution, but it's at the end of a spectrum, not a weird outlier from the rest of the group. Much of what it did, how it did it, and what makes it a fascinating animal, is mirrored in its modern and fossil relatives. Contrary to some perspectives on this animal, the fact it represents an ancient member of a modern group does not make it tedious or dull. Quite the opposite is true: Deinosuchus reminds us that animals from Deep Time are part of a continuum with our own fauna, revealing the awesome things modern lineages have been capable of, the potential their anatomies have in the present, and what they might be up to in future. How anyone can find pondering an animal that gives such a raw perspective on evolution and adaptation boring or uninteresting is beyond me.
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- Blanco, R. E., Jones, W. W., & Villamil, J. (2015). The ‘death roll’of giant fossil crocodyliforms (Crocodylomorpha: Neosuchia): allometric and skull strength analysis. Historical Biology, 27(5), 514-524.
- Colbert, E. H., Bird, R. T., & Brown, B. (1954). A gigantic crocodile from the Upper Cretaceous beds of Texas. American Museum Novitates; no. 1688.
- Erickson, G. M., & Brochu, C. A. (1999). How the ‘terror crocodile’ grew so big. Nature, 398, 205-206.
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- Foster, J. R., & Hunt-Foster, R. K. (2015). First report of a giant neosuchian (Crocodyliformes) in the Williams Fork Formation (Upper Cretaceous: Campanian) of Colorado. Cretaceous Research, 55, 66-73.
- Grigg, G., & Kirshner, D. (2015). Biology and Evolution of Crocodylians. Csiro Publishing.
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- Holland, W. J. (1909) Deinosuchus hatcheri, a new genus and species of crocodile from the Judith River beds of Montana. Annals of the Carnegie Museum, 6, 281–294.
- Main, D. J. (2012). Crocodiles of the Texas Cretaceous; the Campanian of Big Bend to the Cenomanian of North Texas, a comparison of great size, feeding behaviour and paleoecology. Geological Society of America Abstracts with Programs, 44, 3.
- Schwimmer, D. R. (2002). King of the crocodylians: the paleobiology of Deinosuchus. Indiana University Press.
- Schwimmer, D. R. (2010). Bite marks of the giant crocodylian Deinosuchus on Late Cretaceous (Campanian) bones. New Mexico Museum of Natural History and Science Bulletin, 51, 183-190.
- Titus, A.L., Knell, M.J., Wiersma, J.P., Getty, M.A. (2008). First report of the hyper-giant Cretaceous crocodylian Deinosuchus from Utah. Geological Society of America Abstracts with Programs, 40, 58.
- Witton, M. P. and Naish, D. (2015) Azhdarchid pterosaurs: water-trawling pelican mimics or "terrestrial stalkers"? Acta Palaeontologica Polonica 60, 651-660.