Ceratosaurus Part 1: The history of a predatory horned dinosaur.

Disclaimer: I promised you all a post about the teeth of Ceratosaurus. This is not that post. In reviewing the history of Ceratosaurus I found the post growing with background knowledge but no discussion of teeth. It make sense; there is backstory here dating back to Marsh in the 1880s! So I have decided to break this into two posts. The first post, this one, covers the history of Ceratosaurus research. The next post, out soon, will cover just the dental aspects of this charismatic animal.

Ceratosaurus, the "horned lizard," was cool beast, no doubt about it! Here we have a theropod with huge fangs that was over 20 feet long, and had bone studded armor along its back! And that is to say nothing about those flamboyant crests on its face; one sits above its nose and another one above each of its eye. It was initially described by Marsh back in 1884 and is relatively well known thanks to a number of specimens from across the American West, mainly in Colorado and east-central Utah. There are large animals, presumed to be adults, and smaller individuals (presumably juveniles) in our sample as well, so we should theoretically have a good grasp on what this animal was like. Let's take a look at the history of Ceratosaurus, starting after Marsh's initial publication.

Gilmore in 1920 redescribed Marsh's animal (thankfully!) and revised the diagnosis for Ceratosaurus. I have quoted him in full below.

Generic characters: Premaxillaries with three teeth; maxillaries with 15 teeth; dentary with 15 teeth; 9 cervical vertebrae plano-concave; dorsal vertebrae biconcave; 5 sacrals; distal caudals without special lengthening of prezygapophyses; pelvis coossified; pubis with closed obturator foramen; 4 digits in manus, first and fourth reduced; probably 3 digits in pes; dermal ossifications; abdominal ribs present.

Plate 17, Figure 1 from Gilmore (1920), showing the right side of the holotype of Ceratosaurus

Plate 17, Figure 2 from Gilmore (1920), showing the left side of the holotype of Ceratosaurus

This is a workable definition for the time but we know that some of these are not autapomorphies (things found only in one type of organism). In fact, some of these characters are ancestral for theropods, or even archosaurs. Still, we can't fault Gilmore. He was working with what comparative material he had at the time and did an excellent job. Perhaps most outstanding, even compared to papers being published in the 21st century, are his excellent illustrations of the material he is describing.

That same year (1920), Werner von Janensch published on several theropods recovered by German expeditions to the Tendaguru beds. The most famous of these is probably Elaphrosaurus bambergi, a medium sized ceratosaur subject to much speculation in the decades since. In this same publication Janensch commented on the presence of Allosaurus, which he later named Allosaurus tendagurensis (Janensch, 1925), though this has been suggested to be a carcharodontosaurid. Additionally, and relevant to the post here, he identified Ceratosaurus (?) sp., Megalosaurus (?) ingens, and Labrosaurus stechowi from the same beds.

The butt of Elaphrosaurus on display in Berlin during the 2014 SVP meeting.

Tibia, teeth, and dorsal vertebra of "Allosaurus tendagurensis", also on display in Berlin. Whatever it was, it was big.

 Janensch didn't illustrate his Ceratosaurus sp., which was based on three dorsal vertebrae, but he did illustrate his "Megalosaurus" ingens and "Labrosaurus" stechowi. These will be relevant to our discussion on the teeth of Ceratosaurus.

Figure 6 from Janensch (1920) with the tooth of  Megalosaurus (=?Ceratosaurus) ingens

Figures 7 & 8 from Janensch (1920) with a ?labial and basal view of the tooth of  Labrosaurus stechowi (=?Ceratosaurus sp.)

Work continued sporadically on the genus. In 1963 Jim Madsen and William Stokes presented at the Geological Society of America meeting in Provo about new material from the Cleveland-Lloyd Quarry in central Utah. It was obvious that there was more to this animal than had been previously described. The last (so far) phase in new Ceratosaurus species came in 2000 when Madsen and Sam Welles named two new species: C. magnicornis and C. dentisulcatus. C. magnicornis was so-named from its large nasal horn, while C. dentisulcatus derives its specific name from grooves Madsen and Welles saw on the premaxillary and anterior dentary teeth; this taxon included the remains initially described in that 1963 abstract, while C. magnicornis was named from remains found in western Colorado.

Your faithful author with part of the holotype of Ceratosaurus magnicornis at Dinosaur Journey in Fruita, Colorado

In addition to coining two new species, Madsen and Welles looked over the material that had previously been assigned to the genus by other workers, including the material from Tendaguru. This was the most comprehensive review of all the material assigned to Ceratosaurus to date. Here's a summary of their findings.

• Ceratosaurus roechlingi (Janensch 1925) may be a very large Ceratosaurus but isn't diagnostic past Ceratosaurus sp.
• Labrosaurus stechowi is likely a junior synonym of C. roechlingi
• The Ceratosaurus vertebrae that Janensch (1920) identified as Ceratosaurus sp. are correctly IDed
• Labrosaurus meriani (Janensch 1920), based on an isolated fluted tooth from the Bern Jura, in Switzerland is referred to Ceratosaurus sp.
• Bones previously referred to Ceratosaurus from Oklahoma (Stovall, 1938) are indeterminate theropod bones at best
• Ceratosaurus sp. teeth from western Colorado are in fact correctly IDed
• Material collected by BYU at Dry Mesa, Colorado and Agate Basin, Wyoming, will be described soon and represent the largest known specimen of Ceratosaurus. As of 1999 the preparation of this specimen was complete.
• Megalosaurus ingens, sometimes referred to as Ceratosaurus ingens (Rowe and Gauthier, 1990), is too big to be Ceratosaurus
• Labrosaurus sulcatus, based on an isolated fluted tooth from the Morrison Formation of Colorado, is referred to Ceratosaurus sp.

Now some of these conclusions have held up while others have not been mentioned since 2000. Later workers, for example, don't discuss any non-North American Ceratosaurus sp. remains. There is probably a good reason for this; I will go into more detail about that on my next post. Other claims are somewhat odd (a junior synonym of a newer taxon that isn't diagnostic?). Even today, however, Madsen and Welles (2000) is the best review of all material historically assigned to Ceratosaurus.

2000 was a busy year for Ceratosaurus research. That year Brooks Britt and colleagues presented about new specimens of Ceratosaurus from Colorado, Utah, and Wyoming at the Society of Vertebrate Paleontologists annual meeting; this likely includes the material that Madsen and Welles referenced in their publication as being held at BYU. While some of this information has made its way into later publications, for the most part these specimens remain undescribed to my knowledge.

As paleontology is an evolving science, new analytical tools are always being developed. The same year that Madsen and Welles revised our view of Ceratosaurus and Britt et al. clued us in to new specimens from Wyoming, Oliver Rauhut used modern phylogenetic techniques to define Ceratosaurus as part of his Ph.D. thesis. His found the following autapomorphies (taken from Rauhut (2000) by way of Wikipedia, since I don't have access to the original thesis).

• a narrow rounded horn core centrally placed on the fused nasals
• a median oval groove on nasals behind horn core
• a premaxilla with three teeth
• premaxillary teeth with reduced extent of mesial serrations
• chevrons that are extremely long
• a pubis with a large, rounded notch underneath the obturator foramen
• small epaxial osteoderms

Some of these characters still look good 16 years later, but some of them are a bit subjective, such as, "chevrons that are extremely long." This may be due to someone simplifying what Rauhut said for Wikipedia or it may reflect the long-term trend away from relative character states. Without having Rauhut's thesis I can't really say either way.

Breaking up this wall of text with a Ceratosaurus illustration. Image by DiBgd at English Wikipedia, CC BY 2.5

Rauhut (2000) wasn't the last word on the question of, "What is Ceratosaurus?" In 2008, Matt Carrano and Scott Sampson published a revised phylogentic analysis of the ceratosaurs. Since Ceratosaurus is kind of essential to understand if you're talking about a group of animals sharing its name, they came up with another revised diagnosis.

Ceratosaur with: (1) mediolaterally narrow, rounded midline horn core on the fused nasals, (2) medial oval groove on nasals behind horn core, (3) pubis with large, rounded notch underneath the obturator foramen, (4) small median dorsal osteoderms

As time passes you can see that the subjective characters have disappeared, such as the extremely long chevrons. Others characters are now better defined. We've arrived at what is essentially the definition we are using today in 2016 when we want to refer material to Ceratosaurus. Of course you may notice that this list is pretty small, meaning that most of the skeleton can't be used to identify individual bones. Carrano and Sampson (2008) do a couple of other interesting things in regards to the history of Ceratosaurus; they restrict the use of Ceratosaurus to North America (though without discussing the African material), and explain how the Madsen and Welles (2000) taxa are junior synonyms with no unambiguous autapomorphies. So from this point onward it is generally accepted that only one species of Ceratosaurus is valid, C. nasicornis, and that the genus Ceratosaurus is found only in the Morrison Formation of western North America, a point that Carrano et al. (2012) reiterate.

Juvenile Ceratosaurus partial skeleton on display at the North American Museum of Ancient Life. Photo by Zach Tirrell, CC BY-SA 2.0

Last, and most late-breaking, is a paper out today in JVP! In this paper Carrano and Choiniere discuss the arm of the holotype of Ceratosaurus from the US National Museum. The paper stays true to its subject and redescribes the arm, something the entire skeleton is in need of, as it has undergone de-mounting and additional preparation work. They found that, as many have suspected, the hand and arm of Ceratosaurus is most similar to those of early theropod dinosaurs like Dilophosaurus, and not as closely aligned with later theropods. Even from its fellow derived ceratosaurs, the Abelisauroidea, the hand and arm appear primitive - which would make sense considering its placement relative to abelisauroids in the theropod family tree. Carrano and Choiniere (2016) also show that Ceratosaurus didn't have a useless hand either. Although small and oddly shaped compared to contemporaneous Allosaurus, the hand of Ceratosaurus was still adapted to grasp items (though not to the same extent as other theropods). The lack of any preserved claws from across the Morrison associated with Ceratosaurus skeletons makes things even more difficult; was Ceratosaurus tiny-clawed, grabbing small prey items? Or did it have huge grappling-hook slashers, ready to grab on to passing sauropods? We just don't know.

Cast of the hand of the holotype of Ceratosaurus nasicornis. Note the lack of any preserved fingers. Photo by Smokeybjb, CC BY-SA 3.0

In conclusion, how can we sum up what we know of Ceratosaurus? Well there appears to be one wide-spread but relatively uncommon (compared to Allosaurus) species of Ceratosaurus that existed in western North America during the Late Jurassic. Variation that has led to different species in the Morrison Formation being named, such as Ceratosaurus magnicornis and Ceratosaurus dentisulcatus are best explained by individual variation and changes associated with the animal's growth. Other examples of Ceratosaurus may exist outside of North America but those specimens have not been rigorously examined since 2000. Numerous teeth from across western North America, Europe, and Africa have been referred to this animal, but most workers view the non-North American specimens as not part of the Ceratosaurus hypodigm. Are these referrals sound? For that, you'll have to wait until my next post!

Works Cited

Britt, Brooks, Chure, D. J., Holtz, T. R., Jr., Miles, C. A. & Stadtman, K. L. 2000. A reanalysis of the phylogenetic affinities of Ceratosaurus (Theropoda, Dinosauria) based on new specimens from Utah, Colorado, and Wyoming. Journal of Vertebrate Paleontology 20: 32A

Carrano, Matthew T., Roger BJ Benson, and Scott D. Sampson. 2012. "The phylogeny of Tetanurae (Dinosauria: Theropoda)." Journal of Systematic Palaeontology 10.2: 211-300

Carrano, Matthew T.  & Jonah Choiniere 2016. New information on the forearm and manus of Ceratosaurus nasicornis Marsh, 1884 (Dinosauria, Theropoda), with implications for theropod forelimb evolution. Journal of Vertebrate Paleontology

Carrano, Matthew T., and Scott D. Sampson. 2008. "The phylogeny of Ceratosauria (Dinosauria: Theropoda)." Journal of Systematic Palaeontology 6.02: 183-236.

Gilmore, Charles W. 1920. Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. Bulletin of the United States National Museum 110: 1–154.

Janensch, Werner. "Über Elaphrosaurus bambergi und die megalosaurier aus den Tendaguru-Schichten Deutsch-Ostafrikas." Sitzungsberichte der Gesellschaft naturforschender Freunde zu Berlin 8 (1920): 226-235.

Janensch, Werner. 1925. "Die Coelurosaurier und Theropoden der Tendaguru-Schichten Deutsch-Ostafrikas". Palaeontographica, Supplement 7 1: 1–99.

Madsen, Jim H. Jr., and Stokes, William L., 1963, New information on the Jurassic dinosaur Ceratosaurus: Geological Society of America, Special Paper 73, p. 90 (abs.)

Madsen, Jim H.; Welles, Samuel P. 2000. Ceratosaurus (Dinosauria, Theropoda): A Revised Osteology. Utah Geological Survey. pp. 1–80.

Marsh, O.C. 1884. "Principal characters of American Jurassic dinosaurs, part VIII: The order Theropoda" American Journal of Science 27(160): 329–340
Rauhut, Oliver. 2000. The interrelationships and evolution of basal theropods (Dinosauria, Saurischia). Ph.D. dissertation, Univ. Bristol [U.K.]. 440 pp

Rauhut, Oliver W. M. 2011. "Theropod dinosaurs from the Late Jurassic of Tendaguru (Tanzania)". Special Papers in Palaeontology 86: 195–239.

Rowe, T., and Jacques Gauthier. 1990. "Ceratosauria." in The Dinosauria, Weishampel, Dodson, and Osmólska, eds. University of California Press. pp. 151-168.
Stovall, J. Willis. 1938. "The Morrison of Oklahoma and its dinosaurs." The Journal of Geology: 583-600.