Lambeosaurus Temporal range: Late Cretaceous (Campanian), 76–75 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Mounted Lambeosaurus skeleton, Pacific Museum of Earth
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Neornithischia
Clade:	†Ornithopoda
Family:	†Hadrosauridae
Subfamily:	†Lambeosaurinae
Clade:	†Corythosauria
Tribe:	†Lambeosaurini
Genus:	†Lambeosaurus Parks, 1923[1]
Type species
†Lambeosaurus lambei Parks, 1923
Other species
†L. magnicristatus Sternberg, 1935[2] †L. clavinitialis? Sternberg, 1935
Synonyms
Genus synonymy Procheneosaurus Matthew, 1920 (conserved name)[3] Tetragonosaurus Parks, 1931[4] Species synonymy Tetragonosaurus praeceps Parks, 1931 Procheneosaurus praeceps (Parks, 1931) Lull & Wright, 1942[5] Tetragonosaurus cranibrevis Sternberg, 1935 Procheneosaurus cranibrevis (Sternberg, 1935) Lull & Wright, 1942 Corythosaurus frontalis Parks, 1935[6]

Lambeosaurus (/ˌlæmbiəˈsɔːrəs/ LAM-bee-ə-SOR-əs,^[7] meaning "Lambe's lizard") is a genus of hadrosaurid dinosaur that lived about 75 million years ago, in the Late Cretaceous period (Campanian stage) of North America. This bipedal/quadrupedal, herbivorous dinosaur is known for its distinctive hollow cranial crest, which in the best-known species resembled a mitten. Several possible species have been named, from Canada, the United States, and Mexico, but only the two Canadian species are currently recognized as valid.

Material relevant to the genus was first named by Lawrence Lambe in 1902. Over twenty years later, the modern name was coined in 1923 by William Parks, in honour of Lambe, based on better preserved specimens. The genus has a complicated taxonomic history, in part because small-bodied crested hadrosaurids now recognized as juveniles were once thought to belong to their own genera and species. Currently, the various skulls assigned to the type species L. lambei are interpreted as showing age differences and sexual dimorphism. Lambeosaurus was closely related to the better known Corythosaurus, which is found in slightly older rocks, as well as the less well-known genera Hypacrosaurus and Olorotitan. All had unusual crests, which are now generally assumed to have served social functions like noisemaking and recognition.

L. lambei specimen CMN 8503 being excavated in Alberta

In the 1880s and 1890s, expeditions of the Geological Survey of Canada into Alberta identified that the rocks along the Red Deer River bore dinosaurs of scientific importance. These deposits were identified as either the Edmonton or Belly River Series, of the middle to end Cretaceous. Canadian palaeontologist Lawrence M. Lambe participated in three expeditions in 1897, 1898 and 1901, narrowing down a locality along an extensive series of badlands between Berry Creek and Dear Lodge canyon as the locality for excavations. The greatest difficulty with the dinosaur bones discovered was that they had been scattered before burial and very fragile, but from these expeditions Lambe acquired material of Deinodon, Ornithomimus, Palaeoscincus, Monoclonius, the new armoured dinosaurs Stereocephalus and Stegoceras, and three new species of Trachodon of the subgenus Pteropelyx that he named Trachodon selwyni, Trachodon marginatus, and Trachodon altidens in 1902. T. selwyni, named for former Geological Survey director Alfred Selwyn, was established for a jaw with many teeth, and a provisionally-referred femur, T. marginatus was named for the partial skeleton of one individual, as well as isolated jaw and limb bones, and T. altidens was named for a partial maxilla with many teeth.^[8] American palaeontologist Henry Fairfield Osborn, summarizing the fauna of the mid-Cretaceous across all of North America in the preceding article of the same publication, briefly discussed Lambe's species, and even provided the possible new subgenus name Didanodon for T. altidens.^[9]

A later Geological Survey expedition in 1913 resulted in American paleontologist Charles Hazelius Sternberg discovering a specimen of hadrosaur with skin impressions from along the same stretch of river, which Lambe described in 1914 and referred to Trachodon marginatus. Sternberg also found a second specimen in the same expedition, and the two specimens combined showed that the skin and pelvis of T. marginatus could distinguish it from other hadrosaurs, including a specimen that had been provisionally referred from the younger Edmonton series.^[10] Lambe described the specimens more thoroughly later in 1914, and determined from the nearly complete skull of one individual that T. marginatus belonged in a new genus, for which he named Stephanosaurus. To Stephanosaurus he referred the original jaws, skeleton, and isolated elements he described in 1902, as well as the two specimens found in 1913 by Sternberg.^[11] However, American palaeontologist Barnum Brown highlighted later that year that the referred specimens of Stephanosaurus may not belong to the same taxon as the type skeleton, which preserves the partial articulated forelimb, but not any material of the skull. As a result, Brown considered the identity of the skulls as uncertain, highlighting similarities with his new genus Corythosaurus.^[12] Lambe, in 1920, referred another even more perfect skull to Stephanosaurus, showing separation from Corythosaurus.^[13] However, Canadian palaeontologist William A. Parks noted that the logic of Brown still applied, and designated the new genus and species Lambeosaurus lambei for the complete skulls that could not be justifiably referred to Stephanosaurus, to give Lambe (who was deceased) as much credit as possible for the new hadrosaur.^[1]

American palaeontologist Charles W. Gilmore more completely described the type material of Lambeosaurus and provided discussion of Stephanosaurus in 1924. He found that the type material of Stephanosaurus, Canadian Museum of Nature specimen 419, could not be the same taxon as the skulls. The better-preserved skull that Lambe described in 1920, CMN 2869, was identified as the type specimen, having been found by Charles Mortram Sternberg in 1917 from around 6.4 km (4 mi) southeast of mouth of Little Sandhill Creek, 30 m (100 ft) below the top of the Belly River beds. Additional referred specimens include CMN 351, a half skull with limb bones that is one of the specimens found by C.H. Sternberg in 1913 5.6 km (3.5 mi) southeast of the mouth of Berry Creek, and CMN 8503, a partial skull and articulated skeleton also found by C.M. Sternberg in 1917 5.6 km (3.5 mi) west of the mouth of Little Sandhill Creek.^[14]

The American Museum of Natural History also excavated in the region of the Red Deer River, primarily through the work of Brown from 1909 to 1914. One individual discovered, prepared into a panel mount for display at the AMNH, was referred to by the name Procheneosaurus by American paleontologist William Diller Matthew in 1920, as a particularly small hadrosaur.^[3] In 1931, Parks described more small crested hadrosaurs found by expeditions of the University of Toronto into the Red Deer badlands. The first was named for the Royal Ontario Museum specimen 3577, which was found on 24 June 1930 91 m (300 ft) above the river level and 3.2 km (2 mi) southeast of Sand Creek, being excavated and mounted by American paleontologist Levi Sternberg. Parks named this specimen, which included a skull and some of the vertebral column, as the new taxon Tetragonosaurus praeceps. The second specimen, ROM 3578, was found in 1927 by Levi Sternberg from 23 m (75 ft) above the river level and 2.4 km (1.5 mi) downriver of Sand Creek. This specimen, including only the skull, was named Tetragonosaurus erectofrons by Parks. Together, both species were considered close to Cheneosaurus, and showed similar low, domed crests.^[4]

Charles M. Sternberg identified that the crested hadrosaurs were in need of reassessment, and began his 1935 study of them by finishing the preparation of the numerous skulls and skeletons present at the Canadian Museum of Nature. Among these 18 specimens, Sternberg found that CMN 8703, a nearly complete skeleton with skin, could be referred to Lambeosaurus, while CMN 8503, previously referred, was instead a specimen of Corythosaurus. A second undescribed species of Lambeosaurus was identified from a skull and skeleton, as well as a new species of Tetragonosaurus. This new species of Tetragonosaurus was named T. cranibrevis, based on the partial skull CMN 8633 found by C.M. Sternberg in 1928 at a level of 43 m (140 ft) above the river and 3.62 km (2.25 mi) south of the mouth of Berry Creek. The new species of Lambeosaurus was named L. clavinitialis for the skull and skeleton CMN 8703 found by C.M. Sternberg in 1928 at a level of 43 m (140 ft) above the river and 4.0 km (2.5 mi) south of the mouth of Berry Creek. Finally, Sternberg named the new species Lambeosaurus magnicristatum for the mostly complete skull and skeleton CMN 8705 found by C.M. Sternberg in 1919 4.8 km (3 mi) southwest of the mouth of Little Sandhill Creek and near the top of the beds.^[2] Parks also named the new species Corythosaurus frontalis for ROM 869 from the same area.^[6]

The extensive species and genera of hadrosaurs was reviewed in 1942 by American paleontologists Richard Swann Lull and Nelda E. Wright. Lull and Wright considered L. lambei, L. clavinitialis, and L. magnicristatus as valid and distinguishable species of Lambeosaurus, each known from multiple specimens. To L. lambei they referred CMN 2869, ROM 5131, and ROM 1218, the second collected in 1920 by Levi Sternberg 2.4 km (1.5 mi) northeast of Happy Jack Ferry, while the latter was collected in the 1919 expedition on the south side of Red Deer River. L. clavinitialis included the specimens CMN 8703, CMN 351, YPM 3222, the latter found in 1919 by C.M. Sternberg 4.8 km (3 mi) south of the mouth of Little Sandhill Creek. L. magnicristatus was limited to the type CMN 8705, but numerous specimens could be referred to Lambeosaurus but not a species within (CMN 8502, AMNH 5353, AMNH 5373, AMNH 5666, and USNM 10309).^[5]

Lull and Wright interpreted the description of Procheneosaurus as sufficient to identify that Matthew was referring to AMNH 5340, a nearly complete skull and skeleton, that could not be distinguished from the Tetragonosaurus species on a generic level. They interpreted that Parks naming Tetragonosaurus was under the belief that Procheneosaurus was invalidly described, and as Procheneosaurus and Tetragonosaurus were synonymous with the former lacking a species, they established Procheneosaurus praeceps as the type species. As a result, Lull and Wright also created the combinations Procheneosaurus erectofrons and Procheneosaurus cranibrevis, for the other former species of Tetragonosaurus. Trachodon altidens was also referred to Procheneosaurus, as P. altidens.^[5] This treatment was upheld by a petition by Lull to the International Commission on Zoological Nomenclature, that ruled in 1947 in favour of Procheneosaurus as a valid name with seniority over Tetragonosaurus and that P. praeceps would be the type species by including AMNH 5340. The commission also considered that Tetragonosaurus was not an available name due to lacking a clearly designated type species.^[15] In addition to their type specimens (ROM 3577 for P. praeceps, ROM 3578 for P. erectofrons, CMN 8633 for P. cranibrevis and CMN 1092 for P. altidens), Lull and Wright referred AMNH 5340 to P. praeceps, AMNH 5461 and AMNH 5469 to P. erectofrons, with the latter two specimens collected by Brown from Montana in 1916 and including a skull and much of a skeleton, and a partial skeleton, respectively.^[5]

The hadrosaur taxonomy of Lull and Wright was followed by American palaeontologist John Ostrom who described the skulls of the different Lambeosaurus and Procheneosaurus species,^[16][17] as well as reassessed the fragmentary species Hadrosaurus paucidens, considering it particularly similar to Lambeosaurus lambei and reassigning it as Lambeosaurus paucidens.^[18] The use of Procheneosaurus was furthered by Russian palaeontologist Anatoly K. Rozhdestvensky, who described in 1968 some new hadrosaurs that linked between the Asian and North American faunas. One of these new hadrosaurs was the species he named Procheneosaurus convincens, for an almost complete skeleton and skull accessioned at the Paleontologital Institute as PIN 2230. This skeleton had been found in 1961 at the Shakh-Shakh locality 45 km (28 mi) north of Tashkent, as the most complete dinosaur discovered in Kazakhstan, and came from the Santonian aged Dabrazin Formation.^[19]

In 1975, American palaeontologist Peter Dodson published a study assessing the impacts of growth on the anatomy of lambeosaurine hadrosaurs. Based on the changes shown by living reptiles during growth, Dodson reassessed the three genera and 12 species of lambeosaur believed to have lived in the Oldman Formation (historic Belly River series), which showed extreme cranial variation in their crests alone. He measured and plotted morphometrics of the crests of 36 individuals, including the types of all three Lambeosaurus species and all three North American Procheneosaurus species, and compared them with the sizes of the individuals, assuming that smaller individuals would be younger. From this, it could be seem that the smaller Procheneosaurus specimens appeared to form a gradual increase in size and crest form into the larger Lambeosaurus and Corythosaurus specimens, and were best considered juveniles. Dodson concluded that Procheneosaurus praeceps were juveniles of Lambeosaurus lambei, and Procheneosaurus erectofrons and P. cranibrevis were juveniles of Corythosaurus. Lambeosaurus magnicristatus remained distinct. Dodson also proposed that variation among individuals of the same size was due to sexual dimorphism, resulting in the identifications of CMN 8503 (referred to C. intermedius), ROM 869 (type of C. frontalis), CMN 351 and YPM 3222 (referred to L. clavinitialis), and CMN 8703 (type of L. clavinitialis) as females of L. lambei, and CMN 2869, ROM 1218, ROM 5131, AMNH 5353 and AMNH 5373 (all previously referred to L. lambei) as males of L. lambei. L. magnicristatus was represented by one male and one female individual, the type CMN 8705 and Royal Tyrrell Museum specimen 1966.04.1 respectively.^[20]

The interpretation of Dodson of the low-crested cheneosaurs as juveniles of Lambeosaurus, Corythosaurus, and Hypacrosaurus was followed by subsequent studies, with some slight adjustments.^{[21][22][23][24]} American paleontologist James A. Hopson suggested that in addition to Dodson's identification of the species of Procheneosaurus, L. clavinitialis could represent female individuals of L. magnicristatus rather than L. lambei.^[21] Polish palaeontologists Teresa Maryańska and Halszka Osmólska also identified that P. convincens is likely a separate species from the others and identified it as "Procheneosaurus" convincens.^[22] American paleontologist William J. Morris even noted that there is very little that separates Lambeosaurus, Corythosaurus, and Hypacrosaurus beyond the skull anatomy, and that a specimen from Baja California cannot be identified as either Hypacrosaurus or Lambeosaurus.^[25] These Baja California specimens were excavated from 1968 to 1974 in the El Gallo formation, and were more completely described from additional material by Morris in 1981, where he found that they were a new species he named ?Lambeosaurus laticaudus with the type specimen of Natural History Museum of Los Angeles County number 17715, only tentatively referring the species to Lambeosaurus.^[26] As well as material from Baja California assigned to the new species,^[26] material was described from the Bearpaw Formation of Montana that was tentatively referred to L. magnicristatus. This would represent the first lambeosaur specimen from marine sediments, though it only included partial jaw bones.^[27]

In the 1990 review of the Hadrosauridae by American palaeontologists David B. Weishampel and John R. Horner, Lambeosaurus was considered to include L. lambei, L. magnicristatus, and ?L. laticaudus, with Tetragonosaurus praeceps, L. clavinitialis, and Corythosaurus frontalis as synonyms of L. lambei. They also considered Didanodon and Procheneosaurus as synonymic genera with Lambeosaurus, while the other species described by Lambe: T. selwyni, T. altidens and T. marginatus, and the species Hadrosaurus paucidens, were dubious hadrosaurids that could not be classified. Procheneosaurus convincens was a juvenile and synonym of Jaxartosaurus aralensis from a similar locality, and T. erectofrons and T. cranibrevis were juveniles of Corythosaurus.^[28] American paleontologists David B. Norman and Hans-Dieter Sues conversely argued that Jaxartosaurus was too separate in time and space from Procheneosaurus convincens, and that though its validity was questionable, it could not be referred to any known genera.^[29]

The taxonomy of Weishampel and Horner was reiterated in the 2004 review of Hadrosauridae by Horner and colleagues,^[30] though the taxonomy of the species of Tetragonosaurus would be revisited with a more detailed description of T. erectofrons in 2005 by Canadian paleontologist David C. Evans and colleagues. Dodson had not included the type specimen of T. erectofrons in his analysis of lambeosaurs, due to its partially incomplete skull. However, Evans and colleagues were able to identify features that separated Corythosaurus from Lambeosaurus regardless of age, therefore providing more completely justified assessments of the juveniles. They were able to identify diagnostic traits of Corythosaurus in T. erectofrons and a referred specimen of T. cranibrevis, but the type of T. cranibrevis showed the anatomy of Lambeosaurus making the species a synonym of it rather than Corythosaurus.^[31]

Following the descriptions of skulls and skeletons of various ontogenetic stages of L. lambei, L. magnicristatus remained the only lambeosaurine from the Cretaceous of Alberta to lack a description of its skeleton. Evans and Canadian paleontologist Robert R. Reisz redescribed L. magnicristatus in 2007, based primarily on TMP 1966.04.1. The type, CMN 8705, was originally a largely complete skeleton and skull when excavated, but prior to being named it was significantly damaged by water, destroying much of the limbs and girdles which were discarded, before it was named by Sternberg.^[32] TMP 1966.04.1 was originally discovered by C.M. Sternberg in 1937, around 11 km (7 mi) southeast of Manyberries, Alberta, and around 7.6 m (25 ft) below the top of the formation. It was originally excavated for the Canadian Museum of Nature, but was given to the Provincial Museum and Archives of Alberta in 1966, which later became the Royal Tyrrell Museum. When first discovered, the left side was exposed and had been badly weathered, probably over hundreds of years. To preserve it, Sternberg reinforced the skeleton with plaster and then jacketed it into five separate blocks that were shipped in straw-packed wooden crates to Ottawa. After being acquired by the PMAA, it was prepared for exhibition, with the better-preserved right side being exposed and bolted into a large wooden frame with styrofoam blocks cut out to hold it in place. It has been displayed since mid-1969.^[33] The redescription by Evans and Reisz showed that L. magnicristatus could be separated from L. lambei by anatomy as well as being a younger species. It also raised the question of whether L. clavinitialis were only individuals of L. lambei, or possibly belonged to a similar but separate species, though this required further study.^[32]

The suggestion of L. clavinitialis as a separate species from L. lambei was also considered by Evans in other studies, with new stratigraphic data suggesting that there is an age separation between the different "morphs", with temporal separation between L. lambei and L. clavinitialis, though they could still represent chronospecies or evolutionary lineages.^[34][35] As a result, L. clavinitialis has been identified as separate in following studies, occurring alongside L. lambei in the older deposits of the Dinosaur Park Formation, while L. magnicristatus is younger, but more restricted than L. lambei only being found within the lower formation. AMNH 5382, ROM 869, CMN 8703, YPM 3222 and TMP 1981.37.1 have all been referred to L. clavinitialis, while AMNH 5353, AMNH 5373, CMN 351, CMN 2869, CMN 8503, ROM 794, ROM 1218, FMNH 380, FMNH 1479, TMP 1982.38.1, and TMP 1997.012.0128 have been referred to L. lambei, and some specimens cannot be identified to the species level.^[36][37][38] It was included in the phylogenetic analysis of Hai Xing and colleagues in 2022 as a separate species for the first time and found to be more distant, with L. lambei and L. magnicristatus as sister taxa,^[39] and its crest morphometrics also differ significantly from L. lambei and L. magnicristatus.^[38]

In 2012, Spanish palaeontologist Albert Prieto-Márquez and colleagues redescribed the material of ?L. laticaudus, which was found to be closest to Velafrons, the only other lambeosaurine known from Mexico at the time. It was more distant from the species of Lambeosaurus, and showed enough anatomical differences that they gave it the new genus name Magnapaulia after Paul G. Haaga Jr. for his support of the Natural History Museum of Los Angeles County.^[37] Similarly, the skull of Procheneosaurus convincens was redescribed by Canadian palaeontologists Phil R. Bell and Kirstin S. Brink, who found that it could be differentiated from other lambeosaurines of similar age, and the taxa Jaxartosaurus and Aralosaurus found nearby, giving if the new genus name Kazaklambia in honour of the country it was found in.^[40] It has been found to be an early member of Lambeosaurini and relatively far from Lambeosaurus.^[41]

Lambeosaurus, Corythosaurus and Hypacrosaurus are considered very close relatives of each other, and differ very little in anatomy beyond the skull and crest.^[25][42][43] They were large hadrosaurids, with highly developed jaws full of grinding teeth, a long tail stiffened by ossified tendons that prevented it from drooping, and more elongate limbs suggesting they were semi-quadrupedal and could move on both two legs and all fours as shown by footprints of related animals. The hands had four fingers, lacking the thumb of the generalized five-fingered tetrapod hand, and while the second, third, and fourth fingers were bunched together, the little finger was free and could be used to manipulate objects. Each foot had only the three central toes.^[30] L. lambei, L. magnicristatus , and L. clavinitialis would have reached around 7–7.7 m (23–25 ft) in length, and 2.6–3.4 t (2.6–3.3 long tons; 2.9–3.7 short tons) in weight, respectively. This is comparable to all species of Corythosaurus and Hypacrosaurus which were around 8 m (26 ft) in length and 3 t (3.0 long tons; 3.3 short tons), and makes them the largest lambeosaurines except for Magnapaulia.^[43] Lambeosaurus is also one of many hadrosaurs to preserve the impressions of skin, which has been found across the neck, pelvis, legs, and tail.^[44]

The skull of Lambeosaurus is particularly distinct, bearing an elaborate, narrow and tall crest. The form of the crest is variable between individuals, sexes, and ages, but is consistently perpendicular to the snout and with a rear "spur". Almost all of the crest is formed by the premaxillae of the snout, which have elongated and expanded over the skull in a way that has rearranged the other bones of the skull roof.^[14][5][20] The crest is particularly pronounced in L. magnicristatus, where it is expanded to significantly overhang the snout and has a large, rounded profile.^[32] The crest in L. lambei and L. clavinitialis is less extreme, with a hatchet shape that is at its greatest height above the eye, and a posterior spike that is more pronounced in L. lambei than L. clavinitialis. The composition of the crest is similar in Lambeosaurus and Corythosaurus, but premaxilla bifurcating the nasal in Corythosaurus allows for separating individuals of the two genera at even the youngest ages before their crests develop different forms.^[42] Inside the crests, which are slightly broad, there are S-shaped looping passages that connect the external nostril with the internal naris, which is debated in function.^[17][45] On the sides of the crest above the nostril, where the branches of the premaxilla and nasal that make the crest meet, there is an unossified region (fontanelle) that changes in size during growth, with the suggestion that once fully closed, the crest would not be able to change shape any further.^[22]

Beyond the crest, the premaxilla contributed entirely to the snout of Lambeosaurus, extending forwards and surrounding the entire bony nostril. Beneath, it is braced by the maxilla, which is large and contains 39 to 40 uniform teeth in closely-packed dental battery.^[14][2][32] To the rear, the maxilla articulated with the jugal and lacrimal of the face, as well as the bones of the palate. The lacrimal is very small and subrectangular, being reduced as in lambeosaurines and only contributing to part of the front margin of the orbit.^[14][32] The jugal is large and flat, forming the entire bottom margin of the orbit as well as the infratemporal fenestra. The jugal and postorbital together separate the orbit and infratemporal fenestra, and at the rear of the skull the jugal forms an overlapping joint with both the quadratojugal and quadrate.^[32] Above the orbit is the nasal, forming some of the side of the crest and articulating with the premaxilla extensively, and the prefrontal and frontal as well. The prefrontal forms the upper margin of the orbit between the lacrimal and the postorbital, completely excluding the frontal from the margin.^[14] The frontal is slightly domed as in other lambeosaurines, and forms a platform that supports the rear of the crest. It articulates with the nasal and prefrontal in front, the postorbital to the side, and the parietal to the rear. The parietals and squamosals surround the supratemporal fenestra with the postorbitals, and also support the quadrates behind the infratemporal fenestra. The quadrate forms the rear margin of the skull as a tall bone that ends in the jaw joint. The braincase is made up by many fused bones with consistent anatomy between Lambeosaurus, Corythosaurus, and Hypacrosaurus.^[32]

The lower jaw in Lambeosaurus is made up of the dentary, surangular, and angular on the outer surface, the splenial, prearticular, and articular on the inner surface, and capped at the front by an unpaired predentary.^[5] The predentary is crescentric, forming the beak between the joint of the two dentaries, and with an irregular, sharp, cutting edge to support the horn of the beak.^[14] The dentary is large, with an elongate and downturned region in the snout that lacks teeth similar to Corythosaurus and Hypacrosaurus, followed by an extensive tooth battery as in the maxilla that contains 40 or 41 vertical columns of up to three functional teeth.^[14][32] At the rear of the dentary is a very elevated coronoid process that slots on the inside of the jugal when the jaws close. The surangular is the larger of the bones behind the dentary, with a robust central region supporting the jaw joint and a shallow but distinct triangular depression for muscle attachment. The angular is long and splint-like, forming the bottom margin of the jaw below the surangular and behind the dentary.^[32] The prearticular is a thin bone bracing the surangular and angular from the inside of the jaw, as well as the articular, which forms the remainder of the jaw joint between the surangular and prearticular. The teeth of both jaws are typical for lambeosaurines, being very tall relative to their width, having very faint crenellations along their edges, and showing a single strong keel along the center of the side possessing enamel.^[14]

Lambeosaurus is known from several completely but briefly described skeletons, with no features of the skeleton distinguishing it from relatives, though L. lambei and L. magnicristatus can be separated by the skull and one feature of the pelvis.^[32] The neck of Lambeosaurus bears 14 or 15 cervical vertebrae, which fewer than Olorotitan but more than Parasaurolophus. They are generally consistent in form along the neck, with the exception of the first two cervicals which are specialized for supporting the skull with a taller neural spine above the vertebral body. The spines of the following cervicals are nearly absent, though the articulations between vertebrae are strong and opisthocoelous (concave-convex) as in other hadrosaurids.^[4][32] The cervical vertebrae are very consistent in length, only varying between 75 and 82 mm (3.0 and 3.2 in) in L. magnicristatus specimen TMP 1966.04.1.^[32] There were 15 to 16 dorsal vertebrae present in the torso, with the spines much taller than in the cervicals and rectangular.^[4][32] The vertebrae of the tail have hexagonal articular faces, as in other hadrosaurs.^[32]

The scapula in the shoulder girdle is an elongate, flat bone, 781 mm (30.7 in) long in TMP 1966.04.1 and gently curved as in Corythosaurus. The surface of the bone is relatively smooth, except for a large crest near the shoulder joint that serves to anchor muscles in the region. The sternum is in the shape of a hatchet as in other hadrosaurids.^[32] The humerus is relatively shorter than in Corythosaurus, but is still the most massive bone of the arm.^[2][32] It bears a large crest for the deltopectoral muscles that extends for half the length of the bone, before sharply merging into the shaft of the bone.^[32] The radius and ulna are longer than the humerus as in other lambeosaurines, but are more robust than in Corythosaurus.^[2] While the ulna is one third longer than the humerus, it has very little expansion at the elbow or wrist.^[32] The hand is also more robust than in Corythosaurus, with longer digits relative to the metacarpals, making it similar to Parasaurolophus. The second digit is the longest of the hand, despite the third and fourth metacarpals being longer, and the second and third digits bore hooves, which would have faced slightly inwards when walking.^[2]

Pelvic material of Lambeosaurus has been suggested to be different from other hadrosaurs, but the variation within Hypacrosaurus and Maiasaura show that these differences are probably individual and not related to species. The ilium is elongate, with a humped upper margin that bears a prominent shelf overhanging the hip joint.^[2][32] Multiple scars from muscle attachments can be seen on the surface, and the postacetabular (rear) process of the ilium is very similar between L. lambei, L. magnicristatus and Corythosaurus. The pubic bone however, differs between the taxa: while in L. lambei and Corythosaurus it is bulbous with a large expansion in front of the hip joint, in L. magnicristatus this expansion is much smaller, and the entire projection is relatively shorter.^[32] The ischium is subequal in length to the femur, with a slightly sigmoid outline and more massive proportions than Corythosaurus. The shaft of the bone is straight, but there are expansions at either end. Near the hip joint, the ischium broadens to articulate with the pubis and ilium, and at the underside of this region of the pelvis the ischium is notched. The opposite end of the ischium is sharply expanded into a pendant foot, which, though large and unique to lambeosaurines, is similar between Lambeosaurus species as being smaller than Parasaurolophus and Hypacrosaurus.^[2][32]

The femur is massive and columnar, and as in other hadrosaurs it is slightly longer than the tibia of the lower leg. It is broad, with deep ridges for muscle attachments including a strongly developed and semicircular fourth trochanter. The condyles for the knee articulation are expanded enough to fully enclose a tunnel for extensor ligaments, giving a long articular surface. The tibia is massive and does not differ from other hadrosaurids, with the upper third of its length taken up by the cnemial crest that forms an arc to brace the fibula from the front. The fibula is slender and the same length as the tibia, though its robustness is more similar to Hypacrosaurus than Corythosaurus.^[2][32] The femur is 1.02 m (3.3 ft) long in L. clavinitialis, while the humerus is 52.0 cm (20.5 in) and the ilium is 1.035 m (3.40 ft).^[2] The foot in hadrosaurids is reduced to only three digits, which each bear spade-shaped hooves.^[30]

Impressions of scales are known from three specimens of Lambeosaurus, the L. lambei specimen ROM 1218, the L. clavinitialis specimen CMN 8703, and L. magnicristatus specimen TMP 1966.04.1. The location of the ROM 1218 impression on the body is unknown, but they are relatively large at 7–9 mm (0.28–0.35 in) in diameter. Unusually, ROM 1218 also preserves a subcircular 12 mm (0.47 in) arrangement of feature scales formed by eight wedge-shaped scales converging to one central point.^[44] The skin impressions of CMN 8703 are extensive and remain in original position, covering the ribs and leg in front of the femur, the area over the hip, and the first 1.2 m (4 ft) of the tail. The scales are relatively small and undifferentiated in size or pattern, though the scales of the tail are slightly larger. The skin of the tail shows some slight folding, and the continuity of the skin from the torso to the side of the leg shows that the upper leg was enclosed within the body wall.^[2] Skin on L. magnicristatus is known from regions left in place along the neck, forelimb, and leg, and are unusual in that they consist primarily of connected raised ridges, showing they may have been a negative impression in regions. The pattern across all patches is consistent, with small polygonal scales around 5 mm (0.20 in) in diameter with no overlap or pattern to their arrangement.^[32] In Corythosaurus, enlarged dome-like scales are present on the leg, but these feature scales are absent in Lambeosaurus.^[44]

The initial Canadian discoveries of hadrosaurs by Lambe had them referred to the family Trachodontidae as species of Trachodon, with the discovery of better skull material allowing comparisons where the greatest similarities were identified with Saurolophus.^[8][11] Upon describing Corythosaurus in 1914, Brown separated the crested skulls of Lambe and Saurolophus from Trachodon within the new subfamily Saurolophinae, united by a cranial crest also seen in Hypacrosaurus.^[12] Lambe disagreed with the inclusion of Saurolophus as the crest in the genus was not made by the premaxillae, and named the new subfamily Stephanosaurinae in 1920 to accommodate Stephanosaurus (including the crested skulls), Corythosaurus, Hypacrosaurus, as well as Cheneosaurus. Saurolophus and Prosaurolophus were united within Brown's Saurolophinae, while all other members of Hadrosauridae (the preferred name for Trachodontidae) were within Hadrosaurinae. Upon recognizing that a new name was needed for the crested skulls of Lambe, Parks named Lambeosaurus, as well as renamed Stephanosaurinae to Lambeosaurinae since Stephanosaurinae couldn't be used for the group of crested hadrosaurs. Parks limited Lambeosaurinae to Lambeosaurus, Corythosaurus, and Cheneosaurus, but noted that Parasaurolophus showed some similarities as well.^[1] Gilmore revised the classifications of Hadrosauridae in 1924, where he noted that the material of Trachodon prevented identifying it as either a crested or non-crested hadrosaur and advocated for abandoning the family named after it, with Hadrosauridae composed of Hadrosaurinae, Saurolophinae, and a Lambeosaurinae that included Lambeosaurus, Corythosaurus, Parasaurolophus, Hypacrosaurus and Cheneosaurus.^[14] This classification was followed by Gilmore in 1933 with the addition of Bactrosaurus to Lambeosaurinae, and by Anatoly Riabinin in 1939 with the addition of Jaxartosaurus, both from Asia.^[46][47]

The review of North American Hadrosauridae by Lull and Wright supported the three subfamilies separated by Gilmore, with Lambeosaurus, Corythosaurus, Hypacrosaurus, and Parasaurolophus forming Lambeosaurinae, but also chose to name the new subfamily Cheneosaurinae for Cheneosaurus and Procheneosaurus on behalf of their small size and limited crests.^[5] German palaeontologist Friedrich von Huene supported similar relationships in his classifications of hadrosaurs, but elevated the subfamilies to family rank creating Lambeosauridae in 1948 and Cheneosauridae in 1956.^[48][49] However, Sternberg in 1953 recognized that the subfamilial divisions of earlier studies did not distinguish genera well, with differences between Cheneosaurus and Corythosaurus between subfamilies being less significant than differences between Corythosaurus and Parasaurolophus, which were believed to be the same subfamily. As a result, he condensed Hadrosauridae into only two subfamilies, Hadrosaurinae and Lambeosaurinae, with saurolophines being members of Hadrosaurinae, and cheneosaurines being members of Lambeosaurinae. Within Lambeosaurinae he included Lambeosaurus, Corythosaurus, Hypacrosaurus, Parasaurolophus, Cheneosaurus, Tetragonosaurus, and Trachodon, which is a classification he reiterated in 1954.^[50][51] Following the recognition of cheneosaurs as juveniles of Lambeosaurus, Corythosaurus, and Hypacrosaurus, American palaeontologist Michael K. Brett-Surman published a phylogeny of all accepted genera of Hadrosauridae in 1979, and expanded Lambeosaurinae to also include Tsintaosaurus, with Jaxartosaurus and Bactrosaurus as early members, and Lambeosaurus, Corythosaurus and Hypacrosaurus as closest relatived.^[23] The 1990 review of hadrosaurs by Weishampel and Horner was unable to conclude if Tsintaosaurus was a lambeosaurine or hadrosaurine, but added the Asian genera Barsboldia and Nipponosaurus to Lambeosaurinae.^[28]

The content of Lambeosaurinae expanded over the next decades before the second review by Horner in 2004, with the Asian genera Amurosaurus, Charonosaurus, and Olorotitan being named and added to Lambeosaurinae, and the status of Tsintaosaurus as a lambeosaurine solidified.^[30] Phylogenetics began to be used to understand the relationships of genera within Lambeosaurinae, with two distinct groups being identified. Aralosaurus, previously thought to be a hadrosaurine, was now the earliest lambeosaurine, and Tsintaosaurus, Jaxartosaurus and Amurosaurus showed a gradual acquisition of features that united one group related to Parasaurolophus with another related to Corythosaurus.^[32][52] The Parasaurolophus-group, containing Parasaurolophus and Charonosaurus, was thus named Parasaurolophini by Evans and Reisz in 2007, while the Corythosaurus-group, including Nipponosaurus outside a group of Lambeosaurus, Corythosaurus, Hypacrosaurus and Olorotitan was named Corythosaurini by Evans and Reisz, defined as all taxa closer to Corythosaurus and Parasaurolophus.^[32] It was recognized in 2011 however, that as Lambeosaurus, the type of Lambeosaurinae, was included within Corythosaurini, the group should be more properly called Lambeosaurini.^[53] The group Corythosauria was then named by Polish palaeontologist Daniel Madzia and colleagues in 2021 to unite the groups Parasaurolophini and Lambeosaurini.^[54]

Many phylogenetic analysis on Lambeosaurinae have been conducted since Evans and Reisz, beginning with the revision work of Prieto-Márquez in 2010, where Lambeosaurus was closest to Corythosaurus and more distantly related to Hypacrosaurus and various other lambeosaurines.^[55] Other results since have found Lambeosaurus as the earliest genus of lambeosaurin,^[56][57][58] closest to Corythosaurus and deeply nested within Lambeosaurini,^[41][59] or intermediate within Lambeosaurini.^[60][61][62] The revision of the anatomy of Amurosaurus and recognition of it as the senior synonym of Sahaliyania in 2022 by Xing Hai and colleagues recognized that the updated anatomy of Amurosaurus showed many features shared with Lambeosaurus that had not been previously recognized in the facial skull, crest, teeth, and pelvis, which should help stabilize similar results in the future. Their results are visible below.^[39]

As a hadrosaurid, Lambeosaurus was a large bipedal/quadrupedal herbivore, eating plants with a sophisticated skull that permitted a grinding motion analogous to mammalian chewing. Its teeth were continually replaced and were packed into dental batteries that each 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 feet) above.^[30] As noted by Bob Bakker, lambeosaurines have narrower beaks than hadrosaurines, implying that Lambeosaurus and its relatives could feed more selectively than their broad-beaked, crestless counterparts.^[63]

Like other lambeosaurines such as Parasaurolophus and Corythosaurus, Lambeosaurus had a distinctive crest on the top of its head. Respiratory tracts, ending in a nasal cavity, ran back through this crest, making it mostly hollow. Many suggestions have been made for the function or functions of the crest, including housing salt glands, improving the sense of smell, use as a snorkel or air trap, acting as a resonating chamber for making sounds, or being a method for different species or different sexes of the same species to recognize each other.^[21][64] Social functions such as noisemaking and recognition have become the most widely accepted of the various hypotheses.^[30]

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. The hadrosaurid sense of hearing also appears to be strong. 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, and the hadrosaurid lagena is elongate like a crocodilian's. This indicates that the auditory portion of the inner ear was well-developed.^[21] If used as a noisemaker, the crest could also have provided recognizable differences for different species or sexes, because the differing layouts of the nasal passages corresponding to the different crest shapes would have produced intrinsically different sounds.^[45]

Lambeosaurus lambei and L. magnicristatus, from the Dinosaur Park Formation, were members of a diverse and well-documented fauna of prehistoric animals that included such well-known dinosaurs as the horned Centrosaurus, Styracosaurus, and Chasmosaurus, fellow duckbills Prosaurolophus, Gryposaurus, Corythosaurus, and Parasaurolophus, tyrannosaurid Gorgosaurus, and armored Edmontonia and Euoplocephalus.^[65] 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.^[66] The climate was warmer than present-day Alberta, without frost, but with wetter and drier seasons. Conifers were apparently the dominant canopy plants, with an understory of ferns, tree ferns, and angiosperms.^[67] The anatomically similar L. lambei, L. magnicristatus, and Corythosaurus were separated by time within the formation, based on stratigraphy. Corythosaurus fossils are known from the lower two-thirds of the Formation, L. lambei fossils are present in the upper third, and L. magnicristatus remains are rare and present only at the very top, where the marine influence was greater.^[42]

• Dinosaurs portal
• Canada portal
• Timeline of hadrosaur research

• Currie, Phillip J.; Koppelhus, Eva, eds. (2005). Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Bloomington: Indiana University Press. ISBN 978-0-253-34595-0.

• Lambeosaurus Paleobiology Database (technical)
• Lambeosaurus Natural History Museum