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Description
THIS IS OUTDATED
I have updated the various Parasaurolophus skeletals and will be posting them as individual species.

Skeletal diagram showing select individuals of the three species of Parasaurolophus, a large lambeosaurine hadrosaurid from the middle-to-late Campanian of Laramidia. They are arranged in stratigraphic order, with the most recent species P. tubicen at the top. Parasaurolophus is known from several very complete skeletons (across the holotypes of P. walkeri and P. cyrtocristatus nearly the entire skeleton is known), as well as a number of large fragmentary skulls.

We also have a fairly solid ontogenetic series thanks to P. cyrtocristatus. Though several of the relevant specimens are undescribed, it appears based on the young juvenile RAM 14000 that Parasaurolophus crests developed much early in life than other lambeosaurines. The crest then grew to the distinctive curve seen in FMNH P27393 before straightening out as the animal reached full size. This raises several questions about the largest sizes reached by the other species: the largest fragmentary remains referred to P. walkeri are about 25-30% larger than the holotype (which is comparable to the difference between the largest P. cyrtocristatus and the holotype), but the holotype also has the straight crest that seems to indicate maturity. On the other hand, the two specimens of P. tubicen are both skulls and are nearly the same size; if P. tubicen had variability to the other species there could be 14-15m individuals waiting to be found, which is a bit terrifying to think of.

Parasaurolophus appears to be the largest hadrosaur running around Campanian Laramidia, but it is worth noting that there were other large hadrosaurs running around. In addition to Magnapaulia, there are >10m individuals of Gryposaurus and Probrachylophosaurus as well as >11m individuals of Prosaurolophus. Interestingly these animals are all much larger than the local theropods, even the largest of which seem to come in under 4 tonnes (with the possible exception of undescribed large tyrannosaurines from the Judith River Formation). It seems hard to think that these large animals were totally immune to predation, but it also seems hard to imagine that even a pack of tyrannosaurs would have been able to take down something that large.

References

Bertozzo, F., Manucci, F., Dempsey, M., Tanke, D. H., Evans, D. C., Ruffell, A., & Murphy, E. (2021). Description and etiology of paleopathological lesions in the type specimen of Parasaurolophus walkeri (Dinosauria: Hadrosauridae), with proposed reconstructions of the nuchal ligament. Journal of Anatomy, 238(5), 1055-1069.

Dalla Vecchia, F. M. (2020). The unusual tail of Tethyshadros insularis (Dinosauria, Hadrosauroidea) from the Adriatic Island of the European Archipelago. Rivista Italiana di Paleontologia e Stratigrafia, 126(3).

Evans, D. C., Bavington, R., & Campione, N. E. (2009). An unusual hadrosaurid braincase from the Dinosaur Park Formation and the biostratigraphy of Parasaurolophus (Ornithischia: Lambeosaurinae) from southern Alberta. Canadian Journal of Earth Sciences, 46(11), 791–800. doi:10.1139/e09-050

Farke, A. A., Chok, D. J., Herrero, A., Scolieri, B., & Werning, S. (2013). Ontogeny in the tube-crested dinosaur Parasaurolophus (Hadrosauridae) and heterochrony in hadrosaurids. PeerJ, 1, e182.

Gates, T. A., Lund, E. K., Boyd, C. A., DeBlieux, D. D., Titus, A. L., Evans, D. C., Getty, M. A., Kirkland, J. A. & Eaton, J. G. (2013). Ornithopod dinosaurs from the Grand Staircase-Escalante National Monument region, Utah, and their role in paleobiogeographic and macroevolutionary studies. At the Top of the Grand Staircase: The Late Cretaceous of Southern Utah, 463-481.

Gates, T. A., Evans, D. C., Birthisel, T., Bourke, J., Zanno, L. (2017) A new species of Parasaurolophus from the Upper Cretaceous Kaiparowits Formation of southern Utah based on a series of skulls. Meeting Program and Abstract Book of the 77th Annual Meeting of the Society of Vertebrate Paleontology, 117.

Gates, T. A., Evans, D. C., & Sertich, J. J. (2021). Description and rediagnosis of the crested hadrosaurid (Ornithopoda) dinosaur Parasaurolophus cyrtocristatus on the basis of new cranial remains. PeerJ, 9, e10669.

Ostrom, J. H. (1961). A new species of hadrosaurian dinosaur from the Cretaceous of New Mexico. Journal of Paleontology, 575-577.

Ostrom, J. H. (1963). Parasaurolophus cyrtocristatus, a crested hadrosaurian dinosaur from New Mexico. Chicago Nat. Hist. Mus..

Sullivan, R. M., & Williamson, T. E. (1999). A New Skull of Parasaurolophus (Dinosauria: Hadrosauridae) from the Kirtland Formation of New Mexico and a Revision of the Genus: Bulletin 15 (Vol. 15). New Mexico Museum of Natural History and Science.

Wagner, J. R., & Lehman, T. M. (2009). An enigmatic new lambeosaurine hadrosaur (Reptilia: Dinosauria) from the upper shale member of the Campanian Aguja Formation of Trans-Pecos Texas. Journal of Vertebrate Paleontology, 29(2), 605-611.

Wiman, C. (1931). "Parasaurolophus tubicen, n. sp. aus der Kreide in New Mexico". Nova Acta Regia Societatis Scientarum Upsaliensis. Series 4. 7 (5): 1–11.

Update Log
8/14/2021 - Had the bones in the forearm flipped, fixed it.
8/28.2021 - Added the other two species, which will probably whack my metrics a bit but I'm not copying and pasting this reference list three times.

Description
THIS IS OUTDATED
I have updated the various Parasaurolophus skeletals and will be posting them as individual species.

Skeletal diagram showing select individuals of the three species of Parasaurolophus, a large lambeosaurine hadrosaurid from the middle-to-late Campanian of Laramidia. They are arranged in stratigraphic order, with the most recent species P. tubicen at the top. Parasaurolophus is known from several very complete skeletons (across the holotypes of P. walkeri and P. cyrtocristatus nearly the entire skeleton is known), as well as a number of large fragmentary skulls.

We also have a fairly solid ontogenetic series thanks to P. cyrtocristatus. Though several of the relevant specimens are undescribed, it appears based on the young juvenile RAM 14000 that Parasaurolophus crests developed much early in life than other lambeosaurines. The crest then grew to the distinctive curve seen in FMNH P27393 before straightening out as the animal reached full size. This raises several questions about the largest sizes reached by the other species: the largest fragmentary remains referred to P. walkeri are about 25-30% larger than the holotype (which is comparable to the difference between the largest P. cyrtocristatus and the holotype), but the holotype also has the straight crest that seems to indicate maturity. On the other hand, the two specimens of P. tubicen are both skulls and are nearly the same size; if P. tubicen had variability to the other species there could be 14-15m individuals waiting to be found, which is a bit terrifying to think of.

Parasaurolophus appears to be the largest hadrosaur running around Campanian Laramidia, but it is worth noting that there were other large hadrosaurs running around. In addition to Magnapaulia, there are >10m individuals of Gryposaurus and Probrachylophosaurus as well as >11m individuals of Prosaurolophus. Interestingly these animals are all much larger than the local theropods, even the largest of which seem to come in under 4 tonnes (with the possible exception of undescribed large tyrannosaurines from the Judith River Formation). It seems hard to think that these large animals were totally immune to predation, but it also seems hard to imagine that even a pack of tyrannosaurs would have been able to take down something that large.

References

Bertozzo, F., Manucci, F., Dempsey, M., Tanke, D. H., Evans, D. C., Ruffell, A., & Murphy, E. (2021). Description and etiology of paleopathological lesions in the type specimen of Parasaurolophus walkeri (Dinosauria: Hadrosauridae), with proposed reconstructions of the nuchal ligament. Journal of Anatomy, 238(5), 1055-1069.

Dalla Vecchia, F. M. (2020). The unusual tail of Tethyshadros insularis (Dinosauria, Hadrosauroidea) from the Adriatic Island of the European Archipelago. Rivista Italiana di Paleontologia e Stratigrafia, 126(3).

Evans, D. C., Bavington, R., & Campione, N. E. (2009). An unusual hadrosaurid braincase from the Dinosaur Park Formation and the biostratigraphy of Parasaurolophus (Ornithischia: Lambeosaurinae) from southern Alberta. Canadian Journal of Earth Sciences, 46(11), 791–800. doi:10.1139/e09-050

Farke, A. A., Chok, D. J., Herrero, A., Scolieri, B., & Werning, S. (2013). Ontogeny in the tube-crested dinosaur Parasaurolophus (Hadrosauridae) and heterochrony in hadrosaurids. PeerJ, 1, e182.

Gates, T. A., Lund, E. K., Boyd, C. A., DeBlieux, D. D., Titus, A. L., Evans, D. C., Getty, M. A., Kirkland, J. A. & Eaton, J. G. (2013). Ornithopod dinosaurs from the Grand Staircase-Escalante National Monument region, Utah, and their role in paleobiogeographic and macroevolutionary studies. At the Top of the Grand Staircase: The Late Cretaceous of Southern Utah, 463-481.

Gates, T. A., Evans, D. C., Birthisel, T., Bourke, J., Zanno, L. (2017) A new species of Parasaurolophus from the Upper Cretaceous Kaiparowits Formation of southern Utah based on a series of skulls. Meeting Program and Abstract Book of the 77th Annual Meeting of the Society of Vertebrate Paleontology, 117.

Gates, T. A., Evans, D. C., & Sertich, J. J. (2021). Description and rediagnosis of the crested hadrosaurid (Ornithopoda) dinosaur Parasaurolophus cyrtocristatus on the basis of new cranial remains. PeerJ, 9, e10669.

Ostrom, J. H. (1961). A new species of hadrosaurian dinosaur from the Cretaceous of New Mexico. Journal of Paleontology, 575-577.

Ostrom, J. H. (1963). Parasaurolophus cyrtocristatus, a crested hadrosaurian dinosaur from New Mexico. Chicago Nat. Hist. Mus..

Sullivan, R. M., & Williamson, T. E. (1999). A New Skull of Parasaurolophus (Dinosauria: Hadrosauridae) from the Kirtland Formation of New Mexico and a Revision of the Genus: Bulletin 15 (Vol. 15). New Mexico Museum of Natural History and Science.

Wagner, J. R., & Lehman, T. M. (2009). An enigmatic new lambeosaurine hadrosaur (Reptilia: Dinosauria) from the upper shale member of the Campanian Aguja Formation of Trans-Pecos Texas. Journal of Vertebrate Paleontology, 29(2), 605-611.

Wiman, C. (1931). "Parasaurolophus tubicen, n. sp. aus der Kreide in New Mexico". Nova Acta Regia Societatis Scientarum Upsaliensis. Series 4. 7 (5): 1–11.

Update Log
8/14/2021 - Had the bones in the forearm flipped, fixed it.
8/28.2021 - Added the other two species, which will probably whack my metrics a bit but I'm not copying and pasting this reference list three times.