Hadrosauridae

'' teeth Ferdinand Vandeveer Hayden, during expeditions near the Judith River in 1854 through 1856, discovered the very first dinosaur fossils recognized from North America. These specimens were obtained by Joseph Leidy, who described and named them in 1856; two of the several species named were Trachodon mirabilis of the Judith River Formation and Thespesius occidentalis of the "Great Lignite Formation". The former was based on a collection of teeth whilst the latter on two and a . Although most of the Trachodon teeth turned out to belong to ceratopsids, the holotype and remains of T. occidentalis would come to be recognized as the first recognized hadrosaur specimens. Around the same time in Philadelphia, on the other side of the continent, geologist William Parker Foulke was informed of numerous large bones accidentally uncovered by farmer John E. Hopkins some twenty years earlier. Foulke obtained permission to investigate the now scattered fossils in 1858, and these specimens as well were given to Leidy. They were described in the same year as Hadrosaurus foulkii, giving a slightly better picture of the form of a hadrosaur. Leidy provided additional description in a 1865 paper. Among his 1858 work Leidy briefly suggested that the animal was likely amphibious in nature; this school of thought about hadrosaurs would come to be dominant for over a century to come. Further discoveries such as "Hadrosaurus minor" and "Ornithotarsus immanis" would come from the East, and Edward Drinker Cope led an expedition to the Judith River Formation where Trachodon was found. Upon the fragments discovered he named seven new species in two genera, as well as assigning material to Hadrosaurus. Hadrosaur research experienced a surge in the decade of the 2000s, similar to the research of other dinosaurs. In response to this, the Royal Ontario Museum and the Royal Tyrrell Museum collaborated to arrange the International Hadrosaur Symposium, a professional meeting about ongoing hadrosaur research that was held at the latter institution on September 22 and 23 in 2011. Over fifty presentations were made at the event, thirty-six of which were later incorporated into a book, titled Hadrosaurs, published in 2015. The volume was brought together primarily by palaeontologists David A. Eberth and David C. Evans, and featured an afterword from John R. Horner, all of whom also contributed to one or more of the studies published therein. The first chapter of the volume was a study by David B. Weishampel about the rate of ornithopod research over history, and the interest in different aspects of it over that history, using the 2004 volume The Dinosauria as the source of data on the amount of works published in each decade. Various periods of high and low activity were found, but the twenty-first century was found to overwhelmingly be the most prolific time, with over two-hundred papers published. The advent of the internet was cited as a likely catalyst for this boom. Hadrosaur research experienced high levels of diversity within the decade, with previously uncommon subjects such as growth, phylogeny, and biogeography experiencing more attention, though the functional morphology of hadrosaurids was found to have declined in study since the dinosaur renaissance. == Distribution ==

Hadrosaurids likely originated in North America, before shortly dispersing into Asia. During the late Campanian-Maastrichtian, a saurolophine hadrosaurid migrated into South America from North America, giving rise to the clade Austrokritosauria, which is closely related to the tribe Kritosaurini. During the late early Maastrichtian, several lineages of Lambeosaurinae from Asia migrated into the European Ibero-Armorican Island (what is now France and Spain), including Arenysaurini and Tsintaosaurini. One of these lineages later dispersed from Europe into North Africa, as evidenced by Ajnabia, a member of Arenysaurini. ==Classification==

The family Hadrosauridae was first used by Edward Drinker Cope in 1869, then containing only Hadrosaurus. Since its creation, a major division has been recognized in the group between the hollow-crested subfamily Lambeosaurinae and the subfamily Saurolophinae, historically known as Hadrosaurinae. Both of these have been robustly supported in all recent literature. Phylogenetic analysis has increased the resolution of hadrosaurid relationships considerably, leading to the widespread usage of tribes (a taxonomic unit below subfamily) to describe the finer relationships within each group of hadrosaurids. Lambeosaurines have also been traditionally split into Parasaurolophini and Lambeosaurini. These terms entered the formal literature in Evans and Reisz's 2007 redescription of Lambeosaurus magnicristatus. Lambeosaurini is defined as all taxa more closely related Lambeosaurus lambei than to Parasaurolophus walkeri, and Parasaurolophini as all those taxa closer to P. walkeri than to L. lambei. In recent years Tsintaosaurini and Aralosaurini have also emerged. The use of the term Hadrosaurinae was questioned in a comprehensive study of hadrosaurid relationships by Albert Prieto-Márquez in 2010. Prieto-Márquez noted that, though the name Hadrosaurinae had been used for the clade of mostly crestless hadrosaurids by nearly all previous studies, its type species, Hadrosaurus foulkii, has almost always been excluded from the clade that bears its name, in violation of the rules for naming animals set out by the ICZN. Prieto-Márquez defined Hadrosaurinae as just the lineage containing H. foulkii, and used the name Saurolophinae instead for the traditional grouping. The two main subfamilies of Lambeosaurinae and Saurolophinae belong to the clade Euhadrosauria (sometimes called Saurolophidae), defined as "the smallest clade containing Lambeosaurus lambei and Saurolophus osborni, provided it does not include Hadrosaurus foulkii". '', the type taxon of Lambeosaurinae '', the type taxon of Saurolophinae }} The following cladogram is from Ramírez-Velasco (2022), including most recently named taxa. }} ==Anatomy==

'' skull, Oxford University Museum of Natural History The most recognizable aspect of hadrosaur anatomy is the flattened and laterally stretched rostral bones, which gives the distinct duck-bill look. Some members of the hadrosaurs also had massive crests on their heads, probably for display and/or to make noises. From these impressions, the hadrosaurs were determined to be scaled, and not feathered like some dinosaurs of other groups. Hadrosaurs, much like sauropods, are noted for having their manus united in a fleshy, often nail-less pad. The two major divisions of hadrosaurids are differentiated by their cranial ornamentation. While members of the Lambeosaurinae subfamily have hollow crests that differ depending on species, members of the Saurolophinae (Hadrosaurinae) subfamily have solid crests or none at all. Lambeosaurine crests had air chambers that may have produced a distinct sound and meant that their crests could have been used for both an audio and visual display. ==Paleobiology==

Diet of hadrosaurs as semi-aquatic animals that could only chew soft water plants, a popular idea at the time. While studying the chewing methods of hadrosaurids in 2009, the paleontologists Vincent Williams, Paul Barrett, and Mark Purnell found that hadrosaurs likely grazed on horsetails and vegetation close to the ground, rather than browsing higher-growing leaves and twigs. This conclusion was based on the evenness of scratches on hadrosaur teeth, which suggested the hadrosaur used the same series of jaw motions over and over again. As a result, the study determined that the hadrosaur diet was probably made of leaves and lacked the bulkier items, such as twigs or stems, that might have required a different chewing method and created different wear patterns. However, Purnell said these conclusions were less secure than the more conclusive evidence regarding the motion of teeth while chewing. The hypothesis that hadrosaurs were likely grazers rather than browsers appears to contradict previous findings from preserved stomach contents found in the fossilized guts in previous hadrosaur studies. As a result of that finding, Tweet concluded in September 2008 that the animal was likely a browser, not a grazer. dentary with teeth, typical of hadrosauridae Mallon et al. (2013) examined herbivore coexistence on the island continent of Laramidia, during the Late Cretaceous. It was concluded that hadrosaurids could reach low-growing trees and shrubs that were out of the reach of ceratopsids, ankylosaurs, and other small herbivores. Hadrosaurids were capable of feeding up to a height of when standing quadrupedally, and up to a height of bipedally. Coprolites (fossilized droppings) of some Late Cretaceous hadrosaurs show that the animals sometimes deliberately ate rotting wood. Wood itself is not nutritious, but decomposing wood would have contained fungi, decomposed wood material and detritus-eating invertebrates, all of which would have been nutritious. Neurology Hadrosaurs have been noted as having the most complex brains among ornithopods, and indeed among ornithischian dinosaurs as a whole. John Ostrom would give a more informed analysis and review in 1961, pulling on data from Edmontosaurus regalis, E. annectens, and Gryposaurus notabilis (then considered a synonym of Kritosaurus). Though still obviously small, Ostrom recognized that the brains may be more significantly developed than expected, but supported the view that dinosaur brains would have only filled some of the endocranial cavity, limiting possibility of analysis. In 1977 James Hopson introduced the use of estimated encephalization quotients to the topic of dinosaur intelligence, finding Edmontosaurus to have an EQ of 1.5, above that of other ornithischians including earlier relatives like Camptosaurus and Iguanodon and similar to that of carnosaurian theropods and modern crocodilians but below that of coelurosaurian theropods. Reasonings suggested for their comparably high intelligence were the need for acute senses in the lack of defensive weapons, and more complex intraspecific behaviours as indicated by their acoustic and visual display structures. The advent of CT scanning for use in palaeontology has allowed for more widespread application of this without the need for specimen destruction. Modern research using these methods has focused largely on hadrosaurs. In a 2009 study by palaeontologist David C. Evans and colleagues, the brains of lambeosaurine hadrosaur genera Hypacrosaurus (adult specimen ROM 702), Corythosaurus (juvenile specimen ROM 759 and subadult specimen CMN 34825), and Lambeosaurus (juvenile specimen ROM 758) were scanned and compared to each other (on a phylogenetic and ontogenetic level), related taxa, and previous predictions, the first such large-scale look into the neurology of the subfamily. Contra the early works, Evans' studies indicate that only some regions of the hadrosaur brain (the dorsal portion and much of the hindbrain) were loosely correlated to the brain wall, like modern reptiles, with the ventral and lateral regions correlating fairly closely. Also unlike modern reptiles, the brains of the juveniles did not seem to correlate any closer to the brain wall than those of adults. It was cautioned, however, that very young individuals were not included in the study. Amurosaurus, a close relative of the taxa from the 2009 study, was the subject of a 2013 paper once again looking into a cranial endocast. A nearly identical EQ range of 2.3 to 3.8 was found, and it was again noted this was higher than that of living reptiles, sauropods and other ornithischians, but different EQ estimates for theropods were cited, placing the hadrosaur numbers significantly below even more basal theropods like Ceratosaurus (with an EQ range of 3.31 to 5.07) and Allosaurus (with a range of 2.4 to 5.24, compared to only 1.6 in the 2009 study); Reproduction Neonate sized hadrosaur fossils have been documented in the scientific literature. Tiny hadrosaur footprints have been discovered in the Blackhawk Formation of Utah. In contrast, Edmontosaurus nestlings appear to have been capable of fully quadrupedal locomotion, and do not show much change in limb proportions through growth. Quadrupedal tracks of a small, presumably juvenile hadrosaur are known from the Cantwell Formation in Alaska. Pathology Spondyloarthropathy has been documented in the spine of a 78-million year old hadrosaurid. Other examples of pathologies in hadrosaurs include healed wounds from predators, such as those found in Edmontosaurus annectens, and tumors such as Langerhans cell histiocytosis, hemangiomas, desmoplastic fibroma, metastatic cancer, and osteoblastomas, found in genera such as Brachylophosaurus and Edmontosaurus. Osteochondrosis is also commonly found in hadrosaurs. ==References==