Hypacrosaurus

Hypacrosaurus

Hypacrosaurus was agenusofduckbilldinosaursimilar in appearance to Corythosaurus . Like Corythosaurus , it had a tall, hollow rounded crest, although not as large and straight. It is known from the remains of two species that spanned 75 to 67 million years ago,in theLate Cretaceous of Alberta, Canada, andMontana, United States, and is the latest hollow-crested duckbill known from good remains inNorth America. It was an obscure genus until the discovery in the 1990s ofnests,eggs, and hatchlingsbelonging to H. stebingeri .

Hypacrosaurus is most easily distinguished from other hollow-crested duckbills (lambeosaurines) by its tallneural spinesand the form of its crest. The neural spines, which project from the top of thevertebrae, are 5 to 7 times the height of the body of their respective vertebrae in the back,which would have given it a tall back in profile. The skulls hollow crest is like that of Corythosaurus , but is more pointed along its top, not as tall, wider side to side, and has a small bony point at the rear.Unlike other lambeosaurines, the passages for the airways do not form an S-curve in the crest (at least not in H. altispinus ).The animal is estimated to have been around 9.1 meters (30 feet) long,and to have weighed up to 4.0tonnes(4.4tons).As with most duckbills, its skeleton is otherwise not particularly remarkable, although somepelvicdetails are distinctive.Like other duckbills, it was a bipedal/quadrupedalherbivore. The two known species, H. altispinus and H. stebingeri , are not differentiated in the typical method, ofunique characteristics, as H. stebingeri was described as transitional between the earlier Lambeosaurus and later Hypacrosaurus .Photographs of an adult H. stebingeri skull show an animal that looks very similar to H. altispinus .

Thetype remainsof Hypacrosaurus remains were collected in 1910 byBarnum Brownfor theAmerican Museum of Natural History.The remains, a partialpostcranialskeleton consisting of several vertebrae and a partial pelvis (AMNH 5204), came from along theRed Deer Rivernear Tolman Ferry,Alberta, Canada, from rocks of what is now known as theHorseshoe Canyon Formation(early Maastrichtian,Upper Cretaceous). Brown described these remains, in combination with other postcranial bones, in 1913 as a new genus that he considered to be like Saurolophus .No skull was known at this time, but two skulls were soon discovered and described.

Hypacrosaurus was a lambeosaurinehadrosaurid, and has been recognized as such since the description of its skull.Within the Lambeosaurinae, it is closest to Lambeosaurus and Corythosaurus ,withJack HornerandPhil Currie(1994) suggesting that H. stebingeri is transitional between Lambeosaurus and H. altispinus ,and Michael K. Brett-Surman (1989) suggesting that Hypacrosaurus and Corythosaurus are the same genus.These genera, particularly Corythosaurus and Hypacrosaurus , are regarded as the helmeted or hooded branch of the lambeosaurines, and thecladethey form is sometimes informally designated Lambeosaurini. Although Suzuki et al. s 2004 redescription of Nipponosaurus found a close relationship between Nipponosaurus and Hypacrosaurus stebingeri , indicating that Hypacrosaurus may beparaphyletic,this was rejected in a later, more comprehensive reanalysis of lambeosaurines, which found the two species of Hypacrosaurus to form acladewithout Nipponosaurus , with Corythosaurus and Olorotitan being the closest relatives.

As ahadrosaurid, Hypacrosaurus would have been a bipedal/quadrupedal herbivore, eating a variety ofplants. Its skull permitted a grinding motion analogous tochewing, and itsteethwere continually replacing and packed intodental batteriesthat contained hundreds of teeth, only a relative handful of which were in use at any time. Plant material would have been cropped by its broad beak, and held in the jaws by acheek-like organ. Its feeding range would have extended from the ground to about 4m (13ft) above.

Crest functions

The hollow crest of Hypacrosaurus most likely had social functions, such as a visual signal allowing individuals to identify sex or species, and providing a resonating chamber for making noises. The crest and its associated nasal passages have also figured in the debate aboutdinosaur endothermy, specifically in discussions aboutnasal turbinates.

Turbinates are thin bones orcartilagesthat come in two types, with two functions. Nasalolfactoryturbinates are found in all livingtetrapodsand function in smell. Respiratory turbinates function to prevent water loss through evaporation and are found only inbirdsandmammals, modernendotherms(warm-blooded animals) who could lose a great deal of water while breathing because they breathe more often than comparably sizedectotherms(cold-blooded animals) to support their higher metabolism. Ruben and others in 1996 concluded that respiratory turbinates were probably not present in Nanotyrannus , Ornithomimus or Hypacrosaurus based onCT scanning, thus there was no evidence that those animals were warm-blooded.

The discovery of tooth marks in the fibula of a Hypacrosaurus specimen inflicted by a bite from the teeth of a tyrannosaurid indicated that this, and other hadrosaurids were either preyed upon or scavenged by large theropod dinosaurs during the Late Cretaceous period.

Examining the oxygen-isotope ratio from the bones from different parts of an extinct animals body should indicate which thermoregulation mode an animal used during its lifetime. An endothermic (warm-blooded) animal should maintain a very similar body temperature throughout its entire body (which is called homeothermy) and therefore there should be little variation in the oxygen-isotope ratio when measured in different bones. Alternatively, the oxygen-isotope ratio differs considerably when measured throughout the body of an organism with an ectothermic (cold-blooded) physiology.Oxygen-isotope ratios calculated for Hypacrosaurus suggesting that the ratios varied little, indicating that Hypacrosaurus was a homeotherm, and likely was endothermic.This is in contrast to the Ruben et al. (1996) finding that Hypacrosaurus was not warm-blooded, which was based on the absence of nasal turbinates (see Crest functions subsection, above).

Source: https://en.wikipedia.org/

Also read: Minmi and Ouranosaurus