Triceratops: Beast of the Week

Here at Prehistoric Beast of the Week, I do my best to cover a different prehistoric animal each week (or as close as I can get to each week).  I make a point to shine a spotlight on some of the lesser-celebrated creatures that don't get as much attention as they deserve, or newly described ones that are hot in the news.  Many times I cover special requests of readers like you.

We're not doing any of that this week.  Today we will shamelessly revisit my favorite animal (let alone dinosaur) the mighty Triceratops!

Triceratops horridus in watercolors by Christopher DiPiazza.

Triceratops was a plant-eating dinosaur that lived in what is now North America during the late Cretaceous period between 68 and 66 million years ago and adults measured about thirty feet long from beak to tail.  There are currently two species of Triceratops recognized.  Triceratops horridus lived a few million years earlier and had a longer, more narrow snout, and Triceratops prorsus lived later and had a deeper snout with a much longer nose horn.  The genus was one of the largest and most well studied members of the ceratopsian family with many good specimens on the fossil record.  When alive, Triceratops would have coexisted with other well known dinosaurs like Ankylosaurus, Edmontosaurus/Anatotitan, Pachycephalosaurus, Dracorex and of course, Tyrannosaurus rex.  

Quick sketch comparing the two recognized species of Triceratops.  The slightly younger T. prorsus on the left and T. horridus on the right.  I feel it is important to note the exact shape and tilt of the brow horns seem to still be subject to individual variation even within each species.

The name, Triceratops, translates to "Three Horn Face" which makes sense considering this animal indeed had three horns...on its face; one short one between the nostrils and a long one above each eye.  Triceratops also had a round frill that was made of solid bone.  This is unique to this genus since all other ceratopsians known have holes, or what are known as fenestrae, in their frills to make them lighter.  The exact reason why Triceratops had a solid frill is the subject of some debate.  One such explanation could be for stronger defense against predators.  While the horns and frills of ceratopsians were probably for display purposes, I'm sure they were effective weapons against predators if need be as well.  That being said consider the fact that Triceratops lived alongside Tyrannosaurus.  This may be a result of an evolutionary arms race where the predator and prey keep evolving more advanced weapons and defenses to deal with one another.  Another very likely idea that is supported by evidence in the form of healed wounds on Triceratops frills, is that they played a larger role in intraspecies combat for dominance, and needed to take hits from the horns of other Triceratops regularly.

Triceratops horridus skeletal mount at the National Museum in Washington D.C.

In addition to the horns and frill, Triceratops is also known for its curved beak, which it could have used for clipping vegetation.  Beyond the beak, farther into the mouth were batteries of many small teeth perfect for slicing the tough plant material. The jaws themselves would have been backed up by extremely powerful muscles which would have allowed the dinosaur to bite through the tough vegetation it was eating.  I also wouldn't be surprised if Triceratops, and other ceratopsians regularly used biting as a form of defense.

Baby(left) and juvenile (right) Triceratops skulls on display at the National Museum of Natural History.  Note the upturned horns of the juvenile.

Like I stated above, Triceratops is a well-studied animal thanks to a huge amount of fossils that have been found from it over the years.  Among these fossils we have massive adults, possessing some of the largest skulls of any land animal all the way down to tiny babies with horns no larger than my thumb.  We also have what are believed to be juveniles, older than babies but not yet sexually mature adults, with upturned brow horns which would grow more forward later in life.

Some scientists believe that the animal we call Triceratops was actually only a sub-adult form of a more mature form, which is currently considered a different genus, Torosaurus.  Torosaurus had a longer frill that is much thinner than that of Triceratops and possessed two finestrae (holes).  Despite the fact that this hypothesis has been getting a lot of press lately (because Triceratops is such a popular animal) a lot of paleontologists still don't agree with it.  One major problem with this idea is the fact that many definite Torosaurus skulls are smaller than some Triceratops skulls.  Even though this doesn't completely disprove the hypothesis (individual size variation is possible) a lot more solid evidence and data is needed to prove it.  As of now, Triceratops and Torosaurus are still widely accepted as different genera.

Torosaurus skull on display at the Academy of Natural Sciences in Philladelphia.  Note the two large finestra in the frill.

Within the past few years there was even some preserved scaly skin discovered from a Triceratops.  The scales, believed to be from the animal's back, are all either heptagon, hexagon or pentagon shaped and arranged much like mosaic tiles.  They vary in size with larger ones surrounded by smaller ones forming almost rosette-type patterns.  The larger scales also come up to a shallow point like a Hershey kiss...or a nipple. The scales from the ventral(belly) side of the animal are supposedly rectangular shaped like the belly scales from a crocodile.

Chunk of fossilized Triceratops skin.  Check out those nipple scales.

The texture of Triceratops' skull implies that there was a layer of keratin, the same material that horns and beaks are made of, over almost the entire face and head!  This facial covering could have made Triceratops look like it was wearing a helmet, or the keratin also may have grown in scale-like formations, or even scute-like patterns like the shell of a turtle.  Regardless, the newest discoveries on Triceratops are implying it would have been a seriously awesome-looking beast!

I suppose we shall stop here.  Hope you enjoyed my birthday as much as I have!  As always you are welcome to comment below!  Farewell until next time.

References


Dodson, P.; Forster, C.A.; and Sampson, S.D. (2004) Ceratopsidae. In: Weishampel, D. B.; Dodson, P.; and Osmólska, H. (eds.), The Dinosauria (second edition). University of California Press, Berkeley, pp. 494–513. ISBN 0-520-24209-2.

Farke, A. A. (2004). Horn use in Triceratops (Dinosauria: Ceratopsidae): testing behavioral hypotheses using scale models. Palaeontologia Electronica, 7(1), 1-10.

Horner, J. R., & Marshall. C. (2002). Keratinous covered dinosaur skulls. Journal of Vertebrate Paleontology 22(3, Supplement):67A.

Lehman T.M. (1987). "Late Maastrichtian paleoenvironments and dinosaur biogeography in the Western Interior of North America". Palaeogeography, Palaeoclimatology and Palaeoecology 60 (3): 290. doi:10.1016/0031-0182(87)90032-0.

Longrich NR, Field DJ (2012) Torosaurus Is Not Triceratops: Ontogeny in Chasmosaurine Ceratopsids as a Case Study in Dinosaur Taxonomy. PLoS ONE 7(2): e32623. doi:10.1371/journal.pone.0032623
Rega, E.; Holmes, R.; and Tirabasso, A. (2010). "Habitual locomotor behavior inferred from manual pathology in two Late Cretaceous chasmosaurine ceratopsid dinosaurs, Chasmosaurus irvinensis (CMN 41357) and Chasmosaurus belli (ROM 843)". In Ryan, Michael J.; Chinnery-Allgeier, Brenda J.; and Eberth, David A. (editors.). New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium. Bloomington and Indianapolis: Indiana University Press. pp. 340–354. ISBN 978-0-253-35358-0.
Scannella, J.; and Horner, J.R. (2010). "Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny". Journal of Vertebrate Paleontology 30 (4): 1157–1168. doi:10.1080/02724634.2010.483632.


Ostrom, J. H. (1966). "Functional morphology and evolution of the ceratopsian dinosaurs". Evolution 20 (3): 290–308. doi:10.2307/2406631. JSTOR 2406631.