Parasaurolophus: Beast of the Week

This week we will be taking a look at a very popular duck-billed dinosaur.  Say hello to Parasaurolophus!  Parasaurolophus was a plant-eating, duck-billed dinosaur that lived in what is now North America during the Late Cretaceous, about 77 to 73 million years ago.  Parasaurolophus measured about thirty one feet long from beak to tail, but certain incomplete specimens show evidence of having been a bit larger.  Parasaurolophus is most well-known for its long, curved crest that grew from the back of its head, giving it one of the most iconic profiles of any dinosaur.  The name Parasaurolophus translates to "Near Crested Lizard/Reptile" and is in reference to it being compared to another duck-billed dinosaur with a smaller crest, called Saurolophus (just "crested lizard/reptile"), which was discovered earlier.  Turns out that Parasaurolophus and Saurolophus, although both hadrosaurids (duck-billed dinosaurs), weren't really that closely related.  Parasaurolophus belongs to what is called the lambeosaurine branch of hadrosaurs which had hollow crests and narrow beaks, which Saurolophus did not have.  Parasaurolophus was much more closely related to Corythosaurus, Velafrons, and Tsintaosaurus, to name a few examples.

Parasaurolophus walkeri pair by Christopher DiPiazza.  The short-crested female is based on speculation.

There are actually a few different named species of Parasaurolophus.  The most well-recognized is called Parasaurolophus walkeri, and it lived in what is now Alberta, Canada, and would have coexisted with other well-known dinosaurs like Styracosaurus, Chasmosaurus, Struthiomimus, Corythosaurus, and Eouplocephalus.  From the southwestern United States, however, there was also Parasaurolophus tubicen, which is incompletely known, but was probably the largest species, and Parasaurolophus cyrtocristatus, which had a much shorter, more curved crest, and would have coexisted with (and ran away from) Teratophoneus.  

Parasaurolophus walkeri skull on display at the American Museum of Natural History in New York City.

At one time, some paleontologists made a hypothesis that Parasaurolophus cyrtocristatus was actually a female of one of the other two species, due to its smaller crest, but further research concluded this was probably not true since they did not live during the exact same time period.  This being said, it is not unreasonable to guess that the Parasaurolophus females could have had shorter crests anyway, since we can observe similar trends of sexual dimorphism (males and females look different) in other lambeosaurine hadrosaurids that are known from a bigger pool of specimens, like Corythosaurus.

Parasaurolophus cyrtocristatus skeleton on display at the Field Museum of Natural History, in Chicago.

Recently, in 2013, a specimen of a baby Parasaurolophus was published by scientists at the Raymond M. Alf Museum of Paleontology in California, shedding more light on the growth and development of this interesting dinosaur.  The specimen, which was just under six feet long from beak to tail (small when you consider the animal we are talking about!), is estimated to have only been one year old when it died.  Paleontologists could tell this by looking at the cross-section of a the dinosaur's bone and counting the ring-like patterns on the inside, similar to a tree. This specimen hadn't developed any rings yet at the time of its death.  Despite this, the tiny dinosaur's crest had already started to grow from the front of  its skull, almost between its eyes.  At the age that it dies, that specimen would have likely still been under it's mother's care, according to the information and evidence on the fossil record about other hadrosaurid mothers.

Fossil remains of the baby Parasaurolophus published in 2013.  Photograph is from Dr. Andrew Farke's paper, cited below.

So what was the crest for, anyway?  At first some people thought that hadrosaurids, like Parasaurolophus, were amphibious, and spent a lot of their time in the water because the skin that preserved around the toes of one specimen (an Edmontosaurus) that looks like webbing at first glance (it turned out to have been more like padding for walking) and the fact that they had flat bills like ducks (which weren't really that similar to a duck's bill!)  To go with this incorrect idea, some proposed the crest of Parasaurolophus was a snorkeling adaptation, since it was hollow on the inside and would have connected to the animal's airways.  A more likely reason for this crest, however, is to help the animal to produce a distinctive sound.  the dinosaur would inhale through it's nose, the air would pass through the tubes inside the crest and become amplified, then released through the mouth as a loud bellow.  The mechanics would have been very similar to playing a trombone, actually.  With the help of some more modern technology, scientists were able to scan the inside of a Parasaurolophus crest and reproduce what they might have sounded like based on their findings.  According to what they came up with, the sounds of Parasaurolophus would have been pretty eerie!  Check out the audio below!

The fact that Parasaurolophus probably used its crest to make sounds, combined with the fact that we know the young had short crests, leads us to the undeniable fact that the young and adults must have sounded different.  (young would have been more higher pitched)  This makes sense for communication reasons.  A mom would have an easier time finding her babies by their calls if they ever became separated.  You can actually observe very similar baby to parent vocalizations in modern dinosaurs, the birds, and also crocodilians.  The sounds were also probably a good way for adults to attract mates and establish dominance, which can also be seen in a myriad of modern animals.

There was more to Parasaurolophus than just the crest, remember.  In the front of its mouth, it had a flat, and relatively narrow beak, which would have been good for selectively foraging its favorite plants to eat.  This is different from the widened, bills of other hadrosaurids, like Anatotitan's, which were probably more adapted for a generalist plant diet.  Like all hadrosaurids, Parasaurolophus had hundreds of tiny teeth in the back of its mouth, which were tightly packed together to form what we call a dental battery.  these structures were perfect for chewing tough plants much like the molars that plant-eating mammals use to chew with today.

Parasaurolophus had relatively long arms and could have walked on four or two limbs depending on how fast it wanted to move.  Its vertebrae had tall neural arches, especially on its back, which would have given it a hump-like profile in life.  Like all hadrosaurids, Parasaurolophus' tail was especially thick, and also pretty rigid.  The tail would have probably been its weapon of choice if it needed to defend itself or its young.

That is all for this week!  As always feel free to comment below or on our facebook page!

References

Barden, Holly. "Sexual dimorphism in dinosaurs: a review of the evidence and approaches" (PDF). APS 402 Dissertation. University of Sheffield.

Currie, Phillip J.; Koppelhus, Eva, eds. (2005). Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Bloomington: Indiana University Press. pp. 312–348. ISBN 0-253-34595-2.

Evans, David C. "Nasal Cavity Homologies and Cranial Crest Function in Lambeosaurine Dinosaurs." Paleobiology 32.1 (2006): 109-25. Web.

Farke, Andrew A., Derek J. Chok, Annisa Herrero, Brandon Scolieri, and Sarah Werning. "Ontogeny in the Tube-crested Dinosaur(Hadrosauridae) and Heterochrony in Hadrosaurids." PeerJ 1 (2013): E182.

Sullivan, R.M.; Lucas, S.G. (2006). "The Kirtlandian Land-Vertebrate "Age"-Faunal Composition, Temporal Position, and Biostratigraphic Correlation in the Nonmarine Upper Cretaceous of Western North America". In Lucas, S.G.; Sullivan, R.M. Late Cretaceous vertebrates from the Western Interior (PDF). New Mexico Museum of Natural History and Science Bulletin 35. pp. 7–23.

Weishampel, D.B. "Acoustic Analysis of Vocalization of Lambeosaurine Dinosaurs." Paleobiology 7.2 (1981): 252-61. 

Wilfarth, Martin (1947). "Russeltragende Dinosaurier". Orion (Munich) (in German) 2: 525–532.