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In this restoration by Emiliano Troco, a Sauroniops feeds on a juvenile Spinosaurus. (And yes, all the dinosaurs in this image are fluffy.) Image courtesy Andrea Cau.

Earlier this year, paleontologists Andrea Cau, Fabio Dalla Vecchia and Matteo Fabbri described a strange, 95-million-year-old skull scrap from an unknown dinosaur. Acquired by a commercial collector from Morocco’s Kem Kem beds and later donated to Italy’s Museo Paleontologico di Montevarchi, the bone showed signs that it belonged to a carcharodontosaurid–massive cousins of the familiar Allosaurus. There was something odd about the fossil. The bone was a frontal–situated at the top of the skull just above and in front of the dinosaur’s eye opening–but, unlike the same bone in related species like Carcharodontosaurus, a small dome protruded from the middle of the specimen. No caracharodontosaurid has been found with a dome before.

The skull fragment of Sauroniops, showing where it would have fit on a carcharodontosaur skull (human skull for scale). Image courtesy Andrea Cau.

While a single piece of skull isn’t much to go on, Cau and colleagues nevertheless were able draw on the dome and other subtle features to determine that the frontal didn’t belong to any previously known dinosaur. Still, at the conclusion of their brief Acta Palaeontologica Polonica report, the scientists cautioned against naming a new species from an isolated skull bone. “Although the combination of features present in [the frontal] is unique and should support the institution of a new species,” Cau and coauthors concluded, “pending more complete specimens we feel it would be inappropriate to erect a new taxon.”

Cau, Dalla Vecchia and Fabbri quickly changed their minds. While the rest of the dinosaur remains unknown, after reanalyzing the frontal the paleontologists decided that it was truly unique enough to merit establishing a new name. The subtly-domed dinosaur is now known as Sauroniops pachytholus–the genus name a tribute to the demonic Sauron of the Lord of the Rings series, and the species name for the thick dome on the dinosaur’s head.

I emailed Cau to ask why he changed his mind about the dinosaur so quickly. During the year between the time the two papers were submitted, Cau replied, several papers were published showing that carcharodontosaurids–such as the high-spined Acrocanthosaurus from North America–had frontal bones that were so distinct that they could be use to tell one theropod genus from another. That inspired Cau to take another look at the domed specimen from Morocco.

Ultimately, Cau wrote, “the collected data showed that the unique morphology of our specimen was as diagnostic as those available from the type specimens of other African carcharodontosaurids (e.g., the holotypes of Eocarcharia [a single postorbital bone], Carcharodontosaurus iguidensis [a single maxilla], Veterupristisaurus [a single caudal vertebra]).” If all these dinosaurs were based on isolated bones, Cau explained, “then there are no real objections for erecting Sauroniops even from a single frontal.”

Frustratingly, though, the limited material means that we only have the barest outline of what Sauroniops was like in life. The size of the frontal, compared to the bone in other carcharodontosaurs, indicates that the dinosaur probably exceeded thirty feet in length. The carnivore was probably just as big as the better-known Carcharodontosaurus, which it lived alongside, but such estimates always await the test of more fossils.

And then there’s the dome. Why did such a large theropod have a prominent bump on its head? In other theropod lineages, such as the abelisaurids, bumps, knobs and horns are common forms of ornamentation. Perhaps the same was true for Sauroniops–thanks to Acrocanthosaurus and the sail-backed Concavenator, we know that carcharodontosaurs showed off with visual signals. Then again, Cau and coauthors speculate that the dome might have been a sexual signal or might have even been used in head-butting behavior. I think the last hypothesis is unlikely, especially since we don’t know what the microstructure of the dome looks like and there’s no evidence of pathology, but it’s still a distant possibility.

So Sauroniops has a name and a family. Like its cousins Kelmayisaurus and Shaochilong, though, we don’t know very much about this dinosaur’s appearance or biology. The lone frontal is a tantalizing glimpse at a dinosaur that paleontologists will have to hunt down in the deserts of Morocco. With some luck, and a lot of persistence, we may eventually become better acquainted with the dome-skulled dinosaur.

For more on this discovery, see Cau’s blog post at Theropoda.

References:

Cau, A., Dalla Vecchia, F., Fabbri, M. 2012. Evidence of a new carcharodontosaurid from the Upper Cretaceous of Morocco. Acta Palaeontologica Polonica 57, 3. 661-665

Cau, A., Dalla Vecchia, F., Fabbri, M. 2012. A thick-skulled theropod (Dinosauria, Saurischia) from the Upper Cretaceous of Morocco with implications for carcharodontosaurid cranial evolution. Cretaceous Research, in press. DOI: 10.1016/j.cretres.2012.09.002

A reconstruction of Deinosuchus at the Natural History Museum of Utah. Photo by the author.

From the time of their origin around 230 million years ago, to the extinction of the non-avian forms 66 million years ago, dinosaurs ruled the Earth. That’s how we like to characterize the Mesozoic menagerie, anyway. We take the long success of the dinosaurs as a sign of their long-lived and terrifying domination, but, despite our belief that they were the most vicious creatures of all time, there were creatures that even the dinosaurs had reason to fear. Chief among them was Deinosuchus – North America’s “terrible crocodile.”

Between 80 and 73 million years ago, when North America was divided in two by the shallow Western Interior Seaway, the marshes and swamps along the coasts were ruled by Deinosuchus. Fossils of this Cretaceous cousin of modern alligators have been found from Mexico to Montana and in east coast states such as North Carolina and Georgia, tracing the margins of the western subcontinent Laramidia and its eastern counterpart, Appalachia. For the most part, paleontologists have found the bony armor, vertebrae, and teeth of Deinosuchus, but pieces of jaw and partial skeletons found in places such as Texas and Utah indicate that this alligatoroid was a giant, growing over thirty feet in length and approaching forty feet among the biggest individuals.

During the heyday of Deinosuchus, adults of the aquatic ambush predator were among the largest carnivores in their ecosystems. The enormous Tyrannosaurus rex was over five million years off, and the tyrannosaurs of the time were not quite so long or bulky. (Teratophoneus, found in southern Utah among strata that also yield Deinosuchus, was about twenty feet long, and Daspletosaurus from Montana grew to be about thirty feet long.) A fully mature Deinosuchus would have outstretched and outweighed the dinosaur competition, and would have undoubtedly been a deadly apex predator in the water habitats it haunted.

The skull of Deinosuchus testifies to its destructive potential. The alligatoroid’s skull was large, broad, and equipped with an array of teeth deployed to pierce and crush. Indeed, even though there were other giant crocodylomorphs of near-equal size during the Mesozoic (such as the narrow-snouted Sarcosuchus), Deinosuchus appears to be unique in having the anatomical necessities to take down hadrosaurs and other unwary dinosaurs at the water’s edge. And, thanks to tooth-damaged fossils, we know that Deinosuchus truly did dine on dinosaurs. Two years ago, Héctor Rivera-Sylva and colleagues described hadrosaur bones bearing tell-tale Deinosuchus toothmarks from Mexico, and similar finds have been reported from Texas. There may be other candidates in museum drawers elsewhere.

Of course, we don’t know whether the bitten bones record hunting or scavenging. Unless the injuries show signs of healing, toothmarks on bones record feeding rather than hunting behavior. The evidence only takes us so far. Adult Deinosuchus were apparently capable of taking down dinosaurs, but, as yet, there’s no direct evidence of such an incident. Indeed, while images of Deinosuchus chomping on dinosaurs fires our imagination, we actually know relatively little about how this alligatoroid fed and what it ate. Probably, like modern alligators, large Deinosuchus were generalists that snagged fish, turtles, and whatever carrion it happened upon. We don’t know for sure. Nevertheless, dinosaurs in the habitat of this monstrous croc would have been wise to carefully approach the water’s edge, looking for teeth and scutes hiding just beneath the surface.

Part of a multi-step sequence by which Tyrannosaurus could have beheaded Triceratops, based on research by Fowler et al. Art by Nate Carroll.

For a dinosaur so terrifyingly powerful as Tyrannosaurus, there was no greater rival than Triceratops. Each was the acme of their respective lineage–one a hypercarnivorous bone-crusher, the other an immense three-horned herbivore. No wonder that artists, paleontologists, filmmakers and children on playgrounds have been pitting these dinosaurs against each other for over a century. Yet, despite how much we love to revel in the Cretaceous gore of such scenarios, we don’t really know whether Tyrannosaurus and Triceratops ever fought each other.

Earlier this week, Nature News reported on a delightfully gruesome Cretaceous vignette presented at the 72nd Society of Vertebrate Paleontology conference. After examining tooth marks on Triceratops frills, paleontologist Denver Fowler of the Museum of the Rockies in Bozeman, Montana, reconstructed how Tyrannosaurus could have torn the head off the great three-horned dinosaur to gain access to the herbivore’s succulent neck meat. There wouldn’t have been much flesh on the frill of Triceratops, Fowler pointed out, so it’s more likely that hungry tyrannosaurs used the bony collars for leverage to wrench the skull of the ceratopsid away from its body. Fowler also notes that he’s still studying these trace fossils and that a paper spilling the full details is in progress.

But the preliminary research only shows how Tyrannosaurus dined on Triceratops. Despite sensational ledes about the study that play up the “immortal battle” between the dinosaurs, the work doesn’t tell us anything about whether the enormous tyrant was capable of killing old three-horned face. Bitten bones and even fossil feces can help us fill out what was on the Maastrichtian menu for Tyrannosaurus, but they can’t tell us how our favorite Cretaceous carnivore acquired that meat.

Consider a damaged Triceratops pelvis described by Gregory Erickson and Kenneth Olson in 1996. The fossil was dotted with at least 58 punctures that were mostly likely created by an adult Tyrannosaurus. These were not injuries caused during predation, but they record the feeding behavior of a tyrannosaur as it ripped the hips off the Triceratops and  defleshed that mass of meat and bone as best it could. That’s as far as the evidence goes. Tracing those punctures back to the Cretaceous scene, the Tyrannosaurus is already standing over the felled Triceratops. What killed the Triceratops in the first place is a mystery.

So far, no one has found direct evidence of a Tyrannosaurus versus Triceratops battle. A healed bite wound on a Triceratops skeleton or an injured Tyrannosaurus bone corresponding to damage that could have only been made by a horn would provide paleontologists with a sign that these dinosaurs actually fought. After all, paleontologist Andrew Farke and colleagues recently found that tussling Triceratops  wounded each other, so there’s at least a possibility that Triceratops horns might have left tell-tale signs in the bones of an attacking Tyrannosaurus. For now, though, we are left with more indirect clues that will undoubtedly disappoint some dinosaur fans.

Tyrannosaurus was undoubtedly both a hunter and a scavenger. There is no longer any reasonable debate on that point. But, despite the dinosaur’s fearsome reputation, there’s no reason to think that Tyrannosaurus ate whatever it wanted. Tackling an adult Triceratops would have been a dangerous proposition, because of both the ceratopsid’s horns and bulk, so Tyrannosaurus might have avoided such risky encounters. Instead, as David Hone and Oliver Rauhut have pointed out, Tyrannosaurus and other large, carnivorous theropods may have preferentially hunted younger, less-imposing individuals, as well as the old and infirm. And there’s no reason to think that Tyrannosaurus would have passed up Triceratops carrion when the opportunity arose.

The ornaments of Triceratops don’t do much to help the predator-prey scenario, either. Although this dinosaur’s horns and frill have been characterized as weapons, the only direct evidence known of combat is for fights between adult Triceratops. Likewise, even though ceratopsids lived alongside tyrannosaurs for tens of millions of years, predator defense doesn’t seem to have anything to do with horn evolution. If horned dinosaurs developed horns to ward off attacks by big theropods, we would expect there to be an optimal form for defense, or at least severe constraints on the shapes of horns and frills so that they would still be effective. Instead, paleontologists have recorded a confounding array of different horn arrangements among ceratopsids, and the adornments appear to have more to do with communication within their species than defense against others. This is just as true for Triceratops as other horned dinosaurs. While some horns are better than none when confronted by a tyrannosaur, there’s no indication that the ornaments evolved as a predator defense strategy.

We need to reimagine what a confrontation between Tyrannosaurus and Triceratops would have looked like. Instead of two equally matched dinosaurs squaring off against each other, adult Tyrannosaurus probably ambushed young, unwary Triceratops or picked off sick individuals too weak to put up much of a fight. Tyrannosaurus had no sense of honor to uphold–the tyrant was an apex predator that had to maximize its chances of acquiring flesh, and the only safe adult Triceratops was a dead one. Perhaps, someday, a lucky researcher will stumble across evidence of our favorite Hell Creek scene at a field site or in a museum drawer. For now, though, we need to consider the magnificent Tyrannosaurus and Triceratops as real animals and not slavering monsters made to gore each other for our delight.

References:

Erickson, G., Olson, K. 1996. Bite marks attributable to Tyrannosaurus rex: Preliminary description and implications, Journal of Vertebrate Paleontology, 16:1, 175-178 DOI: 10.1080/02724634.1996.10011297

Farke, A., Wolff, E., Tanke, D. 2009. Evidence of Combat in Triceratops. PLOS ONE 4(1): e4252. doi:10.1371/journal.pone.0004252

Fowler, D., Scannella, J., Goodwin, M., Horner, J. 2012. How to eat a Triceratops: Large sample of toothmarks provides new insight into the feeding behavior of Tyrannosaurus. Society of Vertebrate Paleontology 72 poster.

Holtz, T. 2008. A Critical Reappraisal of the Obligate Scavenging Hypothesis for Tyrannosaurus rex and Other Tyrant Dinosaurs, pp. 370-396 in Larson, P. and Carpenter, K. (eds) Tyrannosaurus rex: The Tyrant King. Bloomington: Indiana University Press.