Old Earth Ministries Online Dinosaur Curriculum
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Lesson 64 - Parasaurolophus
Parasaurolophus (meaning "near crested lizard" in reference to Saurolophus) is a genus of ornithopod dinosaur from the Late Cretaceous Period of what is now North America, about 76.5-73 million years ago. It was a herbivore that walked both as a biped and a quadruped. Three species are recognized: P. walkeri (the type species), P. tubicen, and the short-crested P. cyrtocristatus. Remains are known from Alberta (Canada), and New Mexico and Utah (USA). It was first described in 1922 by William Parks from a skull and partial skeleton in Alberta.
Parasaurolophus is a hadrosaurid, part of a diverse family of Cretaceous dinosaurs known for their range of bizarre head adornments. This genus is known for its large, elaborate cranial crest, which at its largest forms a long curved tube projecting upwards and back from the skull. Charonosaurus from China, which may have been its closest relative, had a similar skull and potentially a similar crest. The crest has been much discussed by scientists; the consensus is that major functions included visual recognition of both species and sex, acoustic resonance, and thermoregulation. It is one of the rarer duckbills, known from only a handful of good specimens.
Length: 31+ feet
Weight: 5,400+ lbs
Date Range: 76 - 73 Ma, Campanian Age, Late Cretaceous Period
|Parasaurolophus cyrtocristatus, Field Museum of Natural History (Picture Source)|
As is the case with most dinosaurs, the skeleton of Parasaurolophus is incompletely known. The length of the type specimen of P. walkeri is estimated at 9.5 meters (31 ft).
Like other hadrosaurids, it was able to walk on either two legs or four. It probably preferred to forage for food on four legs, but ran on two. The neural spines of the vertebrae were tall, as was common in lambeosaurines; tallest over the hips, they increased the height of the back. Skin impressions are known for P. walkeri, showing uniform tubercle-like scales but no larger structures.
The most noticeable feature was the cranial crest, which protruded from the rear of the
As its name implies, Parasaurolophus was initially thought to be closely related to Saurolophus because of its superficially similar crest. However, it was soon reassessed as a member of the lambeosaurine subfamily of hadrosaurids—Saurolophus is an hadrosaurine. It is usually interpreted as a separate offshoot of the lambeosaurines, distinct from the helmet-crested Corythosaurus, Hypacrosaurus, and Lambeosaurus. Its closest known relative appears to be Charonosaurus, a lambeosaurine with a similar skull (but no complete crest yet) from the Amur region of northeastern China, and the two may form a clade Parasaurolophini. P. cyrtocristatus, with its short, rounder crest, may be the most basal of the three known Parasaurolophus species, or it may represent subadult or female specimens of P. tubicen.
The type species P. walkeri, from Alberta, is known from a single definitive specimen from the Dinosaur Park Formation, though others from the Dinosaur Park probably belong to it. It differs from P. tubicen by having simpler tubes in its crest, and from P. cyrtocristatus by having a long, unrounded crest and a longer upper arm than forearm. It lived between 76.5 and 75.3 million years ago.
P. tubicen, from New Mexico, is known from the remains of at least three individuals. It is the largest species, with more complex air passages in its crest than P. walkeri, and a longer, straighter crest than P. cyrtocristatus. P. tubicen is known only from the De-na-zin Member of the Kirtland Formation, and lived about 73.4-73 million years ago, making it the most recent species.
P. cyrtocristatus, from the Kaiparowits and Fruitland Formations of New Mexico and Utah, is known from three possible specimens. It lived 75.5-74.5 million years ago, and is the smallest species, with a short rounded crest. Its small size and the form of its crest have led several scientists to suggest that it represents juveniles or females of P. tubicen, though P. tubicen lived at least one million years later. As noted by Thomas Williamson, the type material of P. cyrtocristatus is about 72% the size of P. tubicen, close to the size at which other lambeosaurines are interpreted to begin showing definitive sexual dimorphism in their crests (~70% of adult size). However, this position has been rejected in recent reviews of lambeosaurines.
Parasaurolophus walkeri, from the Dinosaur Park Formation, was a member of a diverse and well-documented fauna of prehistoric animals, including well-known dinosaurs such as the horned Centrosaurus and Chasmosaurus; fellow duckbills Gryposaurus and Corythosaurus; tyrannosaurid Gorgosaurus; and armored Edmontonia, Euoplocephalus and Dyoplosaurus. It was a rare constituent of this fauna. The Dinosaur Park Formation is interpreted as a low-relief setting of rivers and floodplains that became more swampy and influenced by marine conditions over time as the Western Interior Seaway transgressed westward.
In New Mexico and Utah, the species P. cyrtocristatus shared its environment with the horned ceratopsians Utahceratops, Kosmoceratops, and Pentaceratops, and the coelurosaur Ornithomimus, and the tyrannosaur Teratophoneus.
The last and largest of the Parsaurolophus species, P. tubicen, lived in New Mexico alongside the large sauropod Alamosaurus, duckbill Kritosaurus, horned Pentaceratops, armored Nodocephalosaurus, Saurornitholestes, and the tyrannosaurid Bistahieversor. The Kirtland Formation is interpreted as river floodplains appearing after a retreat of the Western Interior Seaway. Conifers were the dominant plants, and chasmosaurine horned dinosaurs were apparently more common than hadrosaurids.
As a hadrosaurid, Parasaurolophus was a large bipedal/quadrupedal herbivore, eating plants with a sophisticated skull that permitted a grinding motion analogous to chewing. Its teeth were continually replacing and packed into dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. It used its beak to crop plant material, which was held in the jaws by a cheek-like organ. Feeding would have been from the ground up to around 4 meters (13 ft) above. As noted by Bob Bakker, lambeosaurines have narrower beaks than hadrosaurines, implying that Parasaurolophus and its relatives could feed more selectively than their broad-beaked, crestless counterparts.
Many hypotheses have been advanced as to what functions the cranial crest of
Differences between species and growth stages
As for other lambeosaurines, it is believed that the cranial crest of Parasaurolophus changed with age and was a sexually dimorphic characteristic in adults. Recent restudy of a juvenile braincase previously assigned to Lambeosaurus, now assigned to Parasaurolophus, provides evidence that a small tubular crest was present in juveniles.
Instead, social and physiological functions have become more supported as function(s) of the crest, focusing on visual and auditory identification and communication. As a large object, the crest has clear value as a visual signal, and sets this animal apart from its contemporaries. The large size of hadrosaurid eye sockets and the presence of sclerotic rings in the eyes imply acute vision and diurnal habits, evidence that sight was important to these animals. If, as is commonly illustrated, a skin frill extended from the crest to the neck or back, the proposed visual display would have been even showier. As is suggested by other lambeosaurine skulls, the crest of Parasaurolophus likely permitted both species identification (such as separating it from Corythosaurus or Lambeosaurus) and sexual identification by shape and size.
However, the external appearance of the crest does not correspond to the complex internal anatomy of the nasal passages, which suggests another function accounted for usage of the internal space. Carl Wiman was the first to propose, in 1931, that the passages served an auditory signaling function, like a crumhorn; Hopson and David B. Weishampel revisited this idea in the 1970s and 1980s. Hopson found that there is anatomical evidence that hadrosaurids had strong hearing. There is at least one example, in the related Corythosaurus, of a slender stapes (reptilian ear bone) in place, which combined with a large space for an eardrum implies a sensitive middle ear. Furthermore, the hadrosaurid lagena is elongate like a crocodilian's, indicating that the auditory portion of the inner ear was well-developed. Weishampel suggested that P. walkeri was able to produce frequencies of 48 to 240 Hz, and P. cyrtocristatus (interpreted as a juvenile crest form) 75 to 375 Hz. Based on similarity of hadrosaurid inner ears to those of crocodiles, he also proposed that adult hadrosaurids were sensitive to high frequencies, such as their offspring might produce. According to Weishampel, this is consistent with parents and offspring communicating.
Computer modeling of a well-preserved specimen of P. tubicen, with more complex air passages than those of P. walkeri, has allowed the reconstruction of the possible sound its crest produced. The main path resonates at around 30 Hz, but the complicated sinus anatomy causes peaks and valleys in the sound.
The large surface area and vascularization of the crest also suggests a thermoregulatory function. P.E. Wheeler first suggested this use in 1978 as a way to keep the brain cool. Teresa Maryańska and Osmólska also proposed thermoregulation at about the same time, and Sullivan and Williamson took further interest. David Evans' 2006 discussion of lambeosaurine crest functions was favorable to the idea, at least as an initial factor for the evolution of crest expansion.
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