| Lambeosaurus | |
|---|---|
 | |
| MountedLambeosaurus skeleton, Pacific Museum of Earth,UBC | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Family: | †Hadrosauridae |
| Subfamily: | †Lambeosaurinae |
| Tribe: | †Lambeosaurini |
| Genus: | †Lambeosaurus Parks,1923[1] |
| Type species | |
| †Lambeosaurus lambei Parks, 1923 | |
| Other species | |
| Synonyms | |
Species synonymy
| |
Lambeosaurus (/ˌlæmbiəˈsɔːrəs/LAM-bee-ə-SOR-əs[7]) is agenus ofhadrosauriddinosaur that lived during theLate Cretaceousperiod of western North America. The first skull ofLambeosaurus found was used bypalaeontologistLawrence M. Lambe to justify the creation of the new genusStephanosaurus, though it was not part of the originalStephanosaurus material. The incomplete nature of the originalStephanosaurus material ledWilliam A. Parks to nameLambeosaurus lambei for this skull in1923 to honour Lambe. Multiple further species ofLambeosaurus have been named since, includingL. clavinitialis andL. magnicristatus in 1935, andL. laticaudus in 1981 which was later moved to its own genusMagnapaulia. It has also been identified that some species earlier identified as belonging toTetragonosaurus andCorythosaurus are now considered juveniles ofLambeosaurus.Lambeosaurus is the eponymous member of its subfamilyLambeosaurinae and tribeLambeosaurini. Lambeosaurins, which also includesCorythosaurus andHypacrosaurus from western North America, are understood to be some of the most specializedornithopods.
AdultLambeosaurus would have grown to around 7–7.7 m (23–25 ft) long and weighed 2.6–3.4 t (2.6–3.3 long tons; 2.9–3.7 short tons). It was able to move on two or four legs, with a deep tail, long limbs, and a highly distinct and hollow cranial crest. This crest, which can be used to separate the three recognized species ofLambeosaurus, projects well above the eye and slightly over the snout, and adults of some species possess a backwards spur. The function of the crest, which is also found in other lambeosaurines, is debated historically, but modern studies show that it could have been used as aresonating device for vocalisation, with a secondary function ofsexual orspecies identification. The crest also allows for the identification of juveniles ofLambeosaurus, which are otherwise nearly indistinguishable from juveniles ofCorythosaurus. It is through this identification of juveniles that the growth ofLambeosaurus is well-known, with the crest developing late but expanding in height by an order of magnitude by the time individuals reached adulthood. Skin impressions are known fromLambeosaurus and show that it had unornamented scales across the entire body.
The species ofLambeosaurus are only known from the middleCampanian of theDinosaur Park Formation ofAlberta.L. clavinitialis is known from a restricted range as the oldest species, overlapping withL. lambei which lived for around 0.3 million years, beforeL. magnicristatus evolved later in the Campanian. This temporal separation suggests thatL. clavinitialis, which was for a time believed to be a female of eitherL. lambei orL. magnicristatus, is a separate species or at least earlier population.Lambeosaurus would have lived alongside the lambeosaurinesCorythosaurus andParasaurolophus, and also the hadrosaurineProsaurolophus. Dental wear suggests thatLambeosaurus would have avoided competition withProsaurolophus by occupying different feedingniches, preferring more closed habitats and browsing lower to the ground with a more generalist diet. The habitatLambeosaurus lived in was a coastal plain where meandering river separated regions of dense vegetation, covered in a diversity ofconifers,ferns and other shrubs, and occupied by plentifulinvertebrates,fishes,mammals andreptiles, especially othermegaherbivorous dinosaurs.
In the 1880s and 1890s, expeditions of theGeological Survey of Canada intoAlberta discovered that the rocks along theRed Deer River bore dinosaur fossils of scientific importance. These deposits were identified as belonging to either theEdmonton orBelly River Series, of the middle to endCretaceous. Canadian palaeontologistLawrence M. Lambe undertook three expeditions in1897,1898 and1901 to an extensive series ofbadlands between Berry Creek[a] and Deadlodge canyon[b]. The fossils discovered were fragile and therefore difficult to excavate, but belonged to many species, including three new species of the hadrosaurTrachodon that Lambe namedTrachodon selwyni,Trachodon marginatus, andTrachodon altidens in1902.T. marginatus was named for a partial skeleton as well as isolated jaw and limb bones, andT. altidens was named for a partialmaxilla with many teeth.[8] In the same publication, American palaeontologistHenry Fairfield Osborn summarized thefauna of the mid-Cretaceous across North America, and provided the possible new subgenus nameDidanodon forT. altidens.[9]
A1913 expedition of the Geological Survey to the same location resulted in the discovery of multiple hadrosaur skeletons by American palaeontologistCharles Hazelius Sternberg. Among these specimens was a skull, skeletons, and skin impressions, which Lambe regarded as additional material ofT. marginatus in1914.[10] One of these specimens (CMN 351), found by Sternberg 5.6 km (3.5 mi) southeast of the mouth of Berry Creek,[11] was described by Lambe more thoroughly later in 1914. Based on this specimen, Lambe concluded thatT. marginatus belonged in a new genus, which he namedStephanosaurus. ToStephanosaurus he assigned the original material ofT. marginatus, as well as CMN 351 and another specimen found by Sternberg in 1913.[12] Lambe also attempted to replace theholotype ofS. marginatus (CMN 419), the partial skeleton he described in 1902, with the isolated jaw bones (CMN 361 and 362) he described in the same year, which is not permitted by the rules ofzoological nomenclature.[10][12][11] However, American palaeontologistBarnum Brown argued later that year that the skull and jaws cannot be confidently assigned toStephanosaurus because the type specimen does not include any skull material to compare with, and noted similarities with the skull of his new genusCorythosaurus.[13] In1920, Lambe assigned another, even more complete skull (CMN 2869) toStephanosaurus that showed differences toCorythosaurus.[14] This skull was found byCharles Mortram Sternberg (son of C.H. Sternberg) in 1917 from around 6.4 km (4 mi) southeast of the mouth of Little Sandhill Creek.[c][11] However, Canadian palaeontologistWilliam A. Parks noted that Brown's logic still applied, and designated the new genus and speciesLambeosaurus lambei for the complete skulls CMN 351 and CMN 2869 in 1923, as they could not justifiably be assigned toStephanosaurus. Parks chose the nameLambeosaurus lambei to give Lambe, who had died in 1919, as much credit as possible for the initial identification of new hadrosaur.[1][15]
In1924, American palaeontologistCharles W. Gilmore described the type material ofLambeosaurus in more detail. He found that the type material ofStephanosaurus was likely not the same taxon as the skulls and may have belonged toKritosaurus, and that the two jaw specimens Lambe tried to designate as types were also possiblyKritosaurus.[11] Gilmore selected the better preserved skull that Lambe described in 1920 (CMN 2869) as the type specimen ofLambeosaurus lambei, as no type specimen had been designated by Parks.[2] Additional specimens that Gilmore assigned toLambeosaurus include CMN 351 and CMN 8503, the latter of which includes 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.[11] Other early material ofLambeosaurus includes one of the specimens collected by C.H. Sternberg in 1913 that is now at theUniversity of British Columbia, where it was put on display in 1950;[16][17] a skull (FMNH UC 1479) collected in 1926 byLevi Sternberg (son of C.H. Sternberg); and a skeleton missing the skull (FMNH PR 380) collected in 1922 by an expedition of theField Museum of Natural History, which was originally identified asProsaurolophus before being prepared and mounted as aLambeosaurus being scavenged byDaspletosaurus. It was earlier believed that the skull and skeleton could have belonged to the same individual, but it is now known that they were found 9.7 km (6 mi) apart.[18]
TheAmerican Museum of Natural History also excavated in the Red Deer River region, primarily through the work of Brown from 1909 to 1914. One particularly small individual discovered by Brown, was assigned to as "Procheneosaurus" by American palaeontologistWilliam Diller Matthew in 1920, and then again in 1923 by Matthew and Brown where the specimen in question was identified as AMNH 5340.[3][19] Matthew himself did not believe that the description was adequate to name a new taxon, writing to C.M. Sternberg in 1921 that "Procheneosaurus" should be considered anomen nudum, an informal name not to be used in taxonomy.[20] In1931, Parks described more small, crested hadrosaurs found by expeditions of theUniversity of Toronto into the Red Deer badlands. The first (ROM 3577) was found around 3.2 km (2 mi) southeast of Little Sandhill Creek by L. Sternberg. Parks described this specimen, which includes a skull and part of thevertebral column, as the new taxonTetragonosaurus praeceps. The second specimen, ROM 3578, was found in1927 by L. Sternberg around 2.4 km (1.5 mi) downriver of Little Sandhill Creek. This specimen, which comprises only the skull, was namedTetragonosaurus erectofrons by Parks. Together, both species were considered to be close toCheneosaurus and had similar low-domed crests.[4]
In1935, Charles M. Sternberg reassessed the taxonomy of crested hadrosaurs after completing the preparation of the 18 skulls and skeletons at the Canadian Museum of Nature. This work resulted in the naming of two new species ofLambeosaurus,L. clavinitialis andL. magnicristatum, and one new species ofTetragonosaurus,T. cranibrevis. The latter was based on a partial skull (CMN 8633) that Sternberg found in1928 ca. 3.62 km (2.25 mi) south of the mouth of Berry Creek.L. clavinitialis was named for a skull and skeleton (CMN 8703) that Sternberg found nearby, also in 1928, ca. 4.0 km (2.5 mi) south of the mouth of Berry Creek.L. magnicristatum[d] was named for a mostly complete skull and skeleton (CMN 8705) Sternberg found in 1919, about 4.8 km (3 mi) southwest of the mouth of Little Sandhill Creek. Sternberg also reassigned the specimen CMN 8503 toCorythosaurus; this specimen was previously assigned toL. lambei by Gilmore.[2] Also in 1935, Parks named the new speciesCorythosaurus frontalis for a specimen from the same area (ROM 869).[6]
In,1942, American palaeontologistsRichard Swann Lull and Nelda E. Wright assessed the extensive number of hadrosaur genera and species in areview article. Lull and Wright consideredL. lambei,L. clavinitialis, andL. magnicristatus as valid species ofLambeosaurus, each known from multiple specimens. ToL. lambei they assigned 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, and the latter collected in the 1919 expedition on the south side of Red Deer River.L. clavinitialis included the specimens CMN 8703, CMN 351, andYPM 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. Several other specimens (CMN 8502, AMNH 5353, AMNH 5373, AMNH 5666, andUSNM 10309) were assigned toLambeosaurus but not to a particular species.[5]
Lull and Wright considered the description ofProcheneosaurus to be sufficient for the name to be valid rather than anomen nudum, and that it could not be distinguished fromTetragonosaurus on a generic level, whereProcheneosaurus would have priority by 11 years. They also stated that Parks namedTetragonosaurus under the belief thatProcheneosaurus was invalid.[e] BecauseTetragonosaurus was a synonym ofProcheneosaurus, and becauseProcheneosaurus was named without a species, they establishedProcheneosaurus praeceps as the type species. Consequently, Lull and Wright also created thenew combinationsProcheneosaurus erectofrons andProcheneosaurus cranibrevis for the other former species ofTetragonosaurus.Trachodon altidens was also assigned toProcheneosaurus, asP. altidens.[5] This treatment was upheld by a petition by Lull to theInternational Commission on Zoological Nomenclature, which ruled in favour ofProcheneosaurus in 1947 as a valid name with seniority overTetragonosaurus, and thatP. praeceps would be the type species that also includes AMNH 5340, the originalProcheneosaurus specimen. The commission also considered thatTetragonosaurus was not anavailable name due to lacking a clearly designated type species.[22] In addition to their type specimens (ROM 3577 forP. praeceps, ROM 3578 forP. erectofrons, CMN 8633 forP. cranibrevis and CMN 1092 forP. altidens), Lull and Wright also assigned AMNH 5461 and AMNH 5469 toP. erectofrons, which were collected by Brown inMontana in 1916 and included a skull and much of a skeleton, as well as a partial skeleton, respectively.[5]
The hadrosaur taxonomy of Lull and Wright was followed by American palaeontologistJohn Ostrom in the early 1960s, who described the skulls of the differentLambeosaurus andProcheneosaurus species,[23][24] and assigned the fragmentary speciesHadrosaurus paucidens toLambeosaurus, asLambeosaurus paucidens.[25] The use ofProcheneosaurus was furthered by Russian palaeontologistAnatoly K. Rozhdestvensky in1968, who described the new speciesProcheneosaurus convincens for an almost complete skeleton and skull from Kazakhstan (PIN 2230), demonstrating links between the Asian and North American faunas. This specimen had been found in 1961 north ofTashkent, as the most complete dinosaur discovered in Kazakhstan, and came from theSantonian agedDabrazinskaya Svita.[26] However, C.M. Sternberg had opposed in 1953 the use ofProcheneosaurus overTetragonosaurus as advocated by Lull and Wright, instead retaining all the species in the latter genus and believing "Procheneosaurus" to be anomen nudum as suggested by Matthew.[20]
In1975, American palaeontologistPeter Dodson assessed how crest shape changed during growth (ontogeny) inlambeosaurines based on comparisons with modern reptiles and by assuming that smaller individuals were younger. Dodson reassessed the 12 named species ofLambeosaurus,Procheneosaurus andCorythosaurus believed to have lived together in theOldman Formation (historic Belly River series), analysing the crests of a total of 36 individuals. He also commented on the status ofHypacrosaurus and coexistingCheneosaurus from theHorseshoe Canyon Formation. These specimens showed extreme variation in their crests which led Dodson to conclude that the crest itself is a poor indicator of identity if age and sex are not taken into account. He found that the smallerProcheneosaurus specimens were juveniles of the largerLambeosaurus andCorythosaurus specimens, withProcheneosaurus praeceps being a juvenile form ofLambeosaurus lambei andProcheneosaurus erectofrons andP. cranibrevis being juvenile forms ofCorythosaurus.Lambeosaurus magnicristatus remained distinct. Dodson also proposed that variation among individuals of the same size was due tosexual dimorphism, resulting in the identifications of ROM 869, CMN 351, YPM 3222 and CMN 8503[f] as females ofL. lambei, and CMN 2869, ROM 1218, ROM 5131, AMNH 5353 and AMNH 5373[g] as males ofL. lambei.L. magnicristatus was represented by one male and one female individual, the type CMN 8705 andRoyal Tyrrell Museum specimen 1966.04.1, respectively.[27]
Dodson's interpretation of the low-crested "cheneosaurs" (Cheneosaurus andProcheneosaurus) as juveniles ofLambeosaurus,Corythosaurus, andHypacrosaurus was followed by subsequent studies, with some slight adjustments.[28][29][30][31] American palaeontologistJames A. Hopson suggested thatL. clavinitialis could represent female individuals ofL. magnicristatus rather thanL. lambei.[28] Polish palaeontologistsTeresa Maryańska andHalszka Osmólska concluded thatP. convincens is likely a separate species and identified it as "Procheneosaurus"convincens in 1981.[32] American palaeontologist William J. Morris even argued that there is very little that separatesLambeosaurus,Corythosaurus, andHypacrosaurus beyond the anatomy of the skull, preventing a confident identification of any material that lacks the skull.[33] In1981, Morris described specimens excavated from theEl Gallo Formation ofBaja California between 1968 and 1974 as a new species that he tentatively assigned toLambeosaurus as ?Lambeosaurus laticaudus, the type specimen of which isLACM 17715. The assignment of this species toLambeosaurus was tentative given the similarity betweenLambeosaurus and its close relatives.[34] In 1979, American palaeontologistJohn R. Horner assigned partial jaw bones from theBearpaw Formation of Montana toL. magnicristatus, representing the first lambeosaur specimen frommarine sediments.[35]
In a1990 review of theHadrosauridae by American palaeontologistsDavid B. Weishampel and Horner,Lambeosaurus was considered to includeL. lambei,L. magnicristatus, and ?L. laticaudus as diagnostic species', whileTetragonosaurus praeceps,L. clavinitialis, andCorythosaurus frontalis were synonyms ofL. lambei. They also consideredDidanodon andProcheneosaurus as synonyms ofLambeosaurus, while the other species described by Lambe (T. selwyni,T. altidens andT. marginatus) and the speciesHadrosaurus paucidens wereundiagnostic hadrosaurids that could not be synonymized withLambeosaurus.Procheneosaurus convincens was listed as a juvenile ofJaxartosaurus aralensis, andT. erectofrons andT. cranibrevis were listed as juveniles ofCorythosaurus.[36] British and American palaeontologistsDavid B. Norman andHans-Dieter Sues, on the other hand, argued thatJaxartosaurus was too separate in time and space fromProcheneosaurus convincens, and that although its validity was questionable, it could not be assigned to any known genera.[37]
The taxonomy of Weishampel and Horner was reiterated in the2004 review of Hadrosauridae by Horner and colleagues.[38] In2005, Canadian paleontologistDavid C. Evans revisited the taxonomy of the species ofTetragonosaurus with a more detailed description ofT. erectofrons. Dodson had not included the type specimen ofT. erectofrons in his analysis of lambeosaurs due to its incomplete skull. Evans and colleagues identified features that separatedCorythosaurus fromLambeosaurus regardless of age, facilitating the assessments of the juveniles. They were able to identify diagnostic traits ofCorythosaurus inT. erectofrons and a specimen assigned toT. cranibrevis. However, the type ofT. cranibrevis showed the anatomy ofLambeosaurus, making the species a synonym ofLambeosaurus rather thanCorythosaurus.[39]
WhileL. lambei was well documented by the descriptions of skulls and skeletons of differentontogenetic stages,L. magnicristatus remained the only lambeosaurine from Alberta without a description of its skeleton. Evans and Canadian palaeontologistRobert R. Reisz redescribedL. magnicristatus in2007. The type, CMN 8705, was originally a largely complete skeleton and skull when excavated, but was significantly damaged by water while it was stored and before it could be prepared, and much of the limbs and girdles had to be discarded.[21] Evans and Reisz therefore based their redescription mostly on TMP 1966.04.1, which was originally discovered by C.M. Sternberg in 1937, around 11 km (7 mi) southeast ofManyberries, Alberta. This specimen was originally excavated for the Canadian Museum of Nature, but was given to theProvincial 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 withplaster and then jacketed it into five separate blocks that were shipped in straw-packed wooden crates toOttawa. 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.[40] The 2007 redescription showed thatL. magnicristatus can be separated fromL. lambei based on its anatomy as well as on its geologically younger age. It also raised the question of whetherL. clavinitialis were individuals ofL. lambei or belonged to a separate species, though this required further study.[21] Including all specimens, the skeletons ofL. lambei andL. clavinitialis are completely known, and the known skeleton ofL. magnicristatus is 81% complete.[41]
The question whetherL. clavinitialis represents a separate species was also considered by Evans in other studies, with newstratigraphic data suggesting that there is a temporal separation betweenL. lambei andL. clavinitialis. Though they could still representchronospecies (a single evolutionary lineage that gradually changes through time), it is unlikely that they represent different sexes of the same species.[42][43] As a result,L. clavinitialis has been recognised as a separate species in subsequent studies, known from five specimens in the middle Campanian,[h] whileL. lambei is known from 11 specimens from the middle and late Campanian,[i] and some specimens cannot be identified to the species level.[44][45][46][47] A2022 phylogenetic analysis by Hai Xing and colleagues foundL. clavinitialis to bebasal toL. lambei andL. magnicristatus, which aresister taxa,[48] and Canadian palaeontologist Kristin S. Brink and colleagues found in 2014 that the crest morphometrics ofL. clavinitialis differ significantly fromL. lambei andL. magnicristatus.[46]
In2012, Spanish palaeontologist Albert Prieto-Márquez and colleagues redescribed the material of ?L. laticaudus, which was found to be closest toVelafrons, the only other lambeosaurine known fromMexico at the time. It was more distant from the species ofLambeosaurus, and showed enough anatomical differences that they gave it the new genus nameMagnapaulia.[45] Similarly, the skull ofProcheneosaurus convincens was redescribed by Brink and Canadian palaeontologists Phil R. Bell in 2013, who found that it could be differentiated from other lambeosaurines of similar age includingJaxartosaurus, giving if the new genus nameKazaklambia.[49] It has been found to be an early member ofLambeosaurini and only distantly related toLambeosaurus.[50]
Lambeosaurus is primarily distinguished from other hadrosaurids by its skull and crest, otherwise being very close in anatomy to its close relativesCorythosaurus andHypacrosaurus.[33][51][52] It was a large hadrosaurid, with highly developed jaws full of grinding teeth, a long tail stiffened byossified tendons that prevented it from drooping, and more elongate limbs suggesting they were semi-quadrupedal (could move on both two legs and all fours), as also shown by footprints of related animals. The hands had four fingers, lacking thethumb, and while the second, third, and fourth fingers were bunched together, thelittle finger was free and could have been used to manipulate objects. Each foot had only the three central toes.[38]L. lambei,L. magnicristatus , andL. 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. This is comparable to all species ofCorythosaurus andHypacrosaurus 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 forMagnapaulia.[52]Lambeosaurus is also one of many hadrosaurs to preserve the impressions of skin, which has been found across the neck, pelvis, legs, and tail.[53]
The skull ofLambeosaurus 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. Almost all of the crest is formed by thepremaxillae of the snout, which have elongated and expanded over the skull in a way that has rearranged the other bones of theskull roof. A rear "spur" is seen inL. lambei andL. clavinitialis, but absent inL. magnicristatus, which is formed by thenasals.[11][5][27] The crest is particularly pronounced inL. magnicristatus, where it is expanded into a large, rounded profile and overhangs the snout.[21] The crest inL. lambei andL. clavinitialis is less pronounced, with a hatchet shape that is at its greatest height above the eye, and a posterior spike that is more pronounced inL. lambei thanL. clavinitialis. The composition of the crest is similar betweenLambeosaurus andCorythosaurus, but in the latter, the premaxillae extend between two branches of the nasal, which allows for separating individuals of the two genera at even the youngest ages before their crests develop different forms.[51] Inside the crests there are S-shaped looping passages that connect theexternal nares (nostrils) with theinternal nares, which expand the crest on either side.[24][54] On the sides of the crest above the nostril, where the branches of the premaxilla and nasal meet, there is anunossified region (fontanelle) that reduces in size during growth; once fully ossified, the crest might not have been able to change shape further.[29]
Beyond the crest, the snout consisted entirely of the premaxillae, which surround the entire external naris (bony nostril). Beneath, it is braced by themaxilla, which is large and contained 39 to 40 uniform teeth in a closely-packeddental battery.[11][2][21] To the rear, the maxilla articulated with thejugal andlacrimal of the face, as well as the bones of the palate. The lacrimal is very small and subrectangular as in other lambeosaurines, and only contributes to a part of the front margin of theorbit.[11][21] The jugal is large and flat, forming the entire bottom margin of the orbit as well as theinfratemporal fenestra. The jugal andpostorbital together separate the orbit and infratemporal fenestra, and at the rear of the skull the jugal forms an overlapping joint with both thequadratojugal andquadrate.[21] Above the orbit is the nasal, which forms parts of the crest's sides and has an extensive articulation with the premaxilla, and also articulates with the prefrontal and frontal. Theprefrontal forms the upper margin of the orbit between the lacrimal and the postorbital, completely excluding thefrontal from the margin.[11] 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 theparietal to the rear. The parietals andsquamosals surround thesupratemporal 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. Thebraincase is made up by many fused bones with consistent anatomy betweenLambeosaurus,Corythosaurus, andHypacrosaurus, though inLambeosaurus theophthalmic nerve is enclosed by bone to form a tunnel while in the other genera it is exposed as a groove. Theoccipital condyle for articulation between the head and neck is reniform in shape, and the pairedparoccipital processes are flared away from the midline of the skull.[21]
The lower jaw inLambeosaurus is made up of thedentary,surangular, andangular on the outer surface, thesplenial,prearticular, andarticular on the inner surface, and capped at the front by an unpairedpredentary.[5] The predentary is crescentric, forming the joint between the two dentaries, and with an irregular, sharp, cutting edge to support the horn of a beak.[11] The dentary is large, with an elongate and downturned region at the front that lacked teeth similar toCorythosaurus andHypacrosaurus, followed by an extensive tooth battery as in the maxilla that contains 40 or 41 vertical columns of up to three functional teeth each.[11][21] At the rear of the dentary is a very elevatedcoronoid process that slots on the inside of the jugal when the jaws closed. 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.[21] 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. Only one side of the tooth crowns is ornamented and bearsenamel for use in chewing (outer side in the maxilla, inner side in the dentary), with the other side embedded in the jaw bones to form columns of functional teeth that compose the dental battery.[11]
Lambeosaurus is known from several completely but briefly described skeletons, and while no features of the skeleton can distinguish it as a genus fromCorythosaurus andHypacrosaurus, thepubic bone differs between the species: while inL. lambei,Corythosaurus andHypacrosaurus it is bulbous with a large expansion in front of the hip joint, inL. magnicristatus this expansion is much smaller.[21] The neck ofLambeosaurus bears 14 or 15cervical vertebrae, which is fewer than inOlorotitan but more than inParasaurolophus. 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 tallerneural spine above the vertebral body. The spines of the following cervicals are nearly absent, though the articulations between vertebrae are strong andopisthocoelous (concave-convex) as in other hadrosaurids.[4][21] The cervical vertebrae are very consistent in length, only varying between 75 and 82 mm (3.0 and 3.2 in) inL. magnicristatus specimen TMP 1966.04.1.[21] There were 15 to 16dorsal vertebrae present in the torso, with the spines much taller than in the cervicals and rectangular.[4][21] The vertebrae of the tail have hexagonal articular faces, as in other hadrosaurids.[21]
Thescapula in the shoulder girdle is an elongate, flat bone, 781 mm (30.7 in) long in TMP 1966.04.1 and gently curved as inCorythosaurus. 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. Thesternum is hatchet-shaped as in other hadrosaurids.[21] Thehumerus is relatively shorter than inCorythosaurus, but is still the most massive bone of the arm.[2][21] It bears a large crest for the deltopectoral muscles (theDeltopectoral crest) that extends for half the length of the bone, before sharply merging into the shaft of the bone.[21] Theradius andulna are longer than the humerus as in other lambeosaurines, but are morerobust than inCorythosaurus.[2] While the ulna is one third longer than the humerus, it has very little expansion at the elbow or wrist.[21] The hand is also more robust than inCorythosaurus, with longer digits relative to themetacarpals, making it similar toParasaurolophus. 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 ofLambeosaurus has been suggested to be different from other hadrosaurs, but the variation withinHypacrosaurus andMaiasaura shows that these differences are probably individual and not related to species. Theilium is elongate, with a humped upper margin that bears a prominent shelf overhanging the hip joint.[2][21] Multiple scars from muscle attachments can be seen on the surface, and thepostacetabular (rear) process of the ilium is very similar betweenL. lambei,L. magnicristatus andCorythosaurus.[21] Theischium is subequal in length to thefemur, with a slightly sigmoid outline and more massive proportions than those ofCorythosaurus. 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 smaller inLambeosaurus species than inParasaurolophus andHypacrosaurus.[2][21]
The femur is massive and columnar, and as in other hadrosaurids it is slightly longer than thetibia of the lower leg. It is broad, with deep ridges for muscle attachments including a strongly developed and semicircularfourth trochanter. Thecondyles for the knee articulation are expanded enough to fully enclose a tunnel for extensor ligaments, resulting in a long articular surface. The tibia is massive and does not differ from that of other hadrosaurids, with the upper third of its length taken up by thecnemial crest that forms an arc to brace thefibula from the front. The fibula is slender and the same length as the tibia, though its robustness is more similar toHypacrosaurus thanCorythosaurus.[2][21] The femur is 1.02 m (3.3 ft) long inL. 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.[38]
Impressions of scales are known from three specimens ofLambeosaurus, theL. lambei specimen ROM 1218, theL. clavinitialis specimen CMN 8703, and theL. magnicristatus specimen TMP 1966.04.1. The location of theL. lambei impression on the body is unknown, but the scales are relatively large at 7–9 mm (0.28–0.35 in) in diameter. Unusually, this specimen also preserves a subcircular 12 mm (0.47 in) arrangement of feature scales (larger scales within a matrix of smaller scales) formed by eight wedge-shaped scales converging to one central point.[53] The skin impressions ofL. clavinitialis 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 patches onL. magnicristatus were left in original position along the neck, forelimb, and leg, and are unusual in that they consist primarily of connected raised ridges, and thus may represent the natural casts of the original impressions. 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.[21] InCorythosaurus, enlarged dome-like scales are present on the leg, but these feature scales are absent inLambeosaurus.[53]
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Lambe assigned the initial Canadian hadrosaur discoveries to the familyTrachodontidae, and, after better skull material was discovered, found that they most closely resembleSaurolophus.[8][12] Upon describingCorythosaurus in 1914, Brown separated the crested genera andSaurolophus fromTrachodon within the new subfamilySaurolophinae, which are united by a cranial crest.[13] Lambe disagreed with the inclusion ofSaurolophus as the crest in the genus was not made by the premaxillae, and named the new subfamilyStephanosaurinae in 1920 to accommodateStephanosaurus (including the crested skulls),Corythosaurus,Hypacrosaurus, as well asCheneosaurus.Saurolophus andProsaurolophus were united within Brown's Saurolophinae, while all other members of Hadrosauridae (the preferred name for Trachodontidae) were withinHadrosaurinae. Upon recognizing that a new name was needed for the crested skulls of Lambe, Parks namedLambeosaurus and replaced Stephanosaurinae withLambeosaurinae as no crested skull was now known forStephanosaurus. Parks limited Lambeosaurinae toLambeosaurus,Corythosaurus, andCheneosaurus, but noted thatParasaurolophus showed some similarities as well.[1] Gilmore revised the classifications of Hadrosauridae in 1924, where he noted that the limited material ofTrachodon 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 includedLambeosaurus,Corythosaurus,Parasaurolophus,Hypacrosaurus andCheneosaurus.[11] This classification was followed by Gilmore in 1933 who added the Mongolian genusBactrosaurus to Lambeosaurinae, and byAnatoly Riabinin in 1939 who added the genusJaxartosaurus from Kazakhstan.[55][56]
The review of North American Hadrosauridae by Lull and Wright in 1942 supported the three subfamilies separated by Gilmore, withLambeosaurus,Corythosaurus,Hypacrosaurus, andParasaurolophus forming Lambeosaurinae, but also chose to name a fourth subfamily,Cheneosaurinae, forCheneosaurus andProcheneosaurus on behalf of their small size and limited crests.[5] German palaeontologistFriedrich von Huene supported similar relationships in his classifications of hadrosaurs, but elevated the subfamilies to family rank creatingLambeosauridae in 1948 andCheneosauridae in 1956.[57][58] However, in1953, C.M. Sternberg recognized that the divisions of previous studies were not useful as they were based on arbitrary decisions of feature significance, a problem that especially affected the separation of Cheneosaurinae from Lambeosaurinae. 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 includedLambeosaurus,Corythosaurus,Hypacrosaurus,Parasaurolophus,Cheneosaurus,Tetragonosaurus, andTrachodon; a classification he reiterated in 1954.[20][59] Following the recognition of cheneosaurs as juveniles ofLambeosaurus,Corythosaurus, andHypacrosaurus, American palaeontologistMichael K. Brett-Surman published a phylogeny of all accepted genera of Hadrosauridae in 1979, and expanded Lambeosaurinae to also includeTsintaosaurus, withJaxartosaurus andBactrosaurus as early members, andLambeosaurus,Corythosaurus andHypacrosaurus as one another's closest relatives.[30] The 1990 review of hadrosaurs by Weishampel and Horner was unable to conclude ifTsintaosaurus was a lambeosaurine or hadrosaurine, but added the Asian generaBarsboldia andNipponosaurus to Lambeosaurinae.[36]
The content of Lambeosaurinae expanded over the next decades before the second review by Horner in 2004. During this period, the Asian generaAmurosaurus,Charonosaurus, andOlorotitan were named and added to Lambeosaurinae, and the status ofTsintaosaurus as a lambeosaurine was solidified.[38]Phylogenetics began to be used to understand the relationships of genera within Lambeosaurinae, with two distinct groups being identified.Aralosaurus was previously thought to be a hadrosaurine, and only later was identified as the earliest lambeosaurine.Tsintaosaurus,Jaxartosaurus andAmurosaurus showed a gradual acquisition of features basal to a clade that included two groups. The first of these groups was related toParasaurolophus, and the other was related toCorythosaurus.[21][60] TheParasaurolophus-group, containingParasaurolophus andCharonosaurus, was thus namedParasaurolophini by Evans and Reisz in 2007, while theCorythosaurus-group, includingLambeosaurus,Corythosaurus,Hypacrosaurus,Nipponosaurus andOlorotitan, was namedCorythosaurini by Evans and Reisz. The latter group, which includedLambeosaurus, was defined as all taxa closer toCorythosaurus than toParasaurolophus.[21] However, in 2011, American palaeontologistRobert M. Sullivan and colleagues recognized that asLambeosaurus, the type genus of Lambeosaurinae, was included within Corythosaurini, the group should be more properly called Lambeosaurini.[61] The groupCorythosauria was then named by Polish palaeontologist Daniel Madzia and colleagues in 2021 to unite the groups Parasaurolophini and Lambeosaurini.[62] Lambeosaurines are united by the presence of only one process at the front of the maxilla, adorsal process of the maxilla that is taller than wide, and an ovoid supratemporal fenestra.[63]
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Many phylogenetic analysis on Lambeosaurinae have been conducted since Evans and Reisz, beginning with the revision work of Prieto-Márquez in 2010.Lambeosaurus is sometimes found to be the closest relative ofCorythosaurus while being more distantly related toHypacrosaurus and other genera.[63] Other results since have foundLambeosaurus as the mostbasal genus of lambeosaurin,[64][65][66] closest toCorythosaurus and deeply nested within Lambeosaurini,[50][67] or intermediate within Lambeosaurini.[68][69][70] The revision of the anatomy ofAmurosaurus in 2022 by Xing Hai and colleagues recognized that the reevaluated anatomy ofAmurosaurus had many similarities withLambeosaurus 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.[48]
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Hadrosaurids were the most specialized and diverse group ofornithopods and are often treated together in discussions about their palaeobiology, even though they appear to have been quite variable in the way they lived, ate, and moved.[38][63] Early studies suggested that hadrosaurs were amphibious, but they are now understood to have been facultativebipeds that walked quadrupedally when moving slowly or standing still, but adopted a bipedal stance to run.[38]
Characterized as large herbivores, hadrosaurs have historically been compared with modernungulates in diet and feeding habits, but this comparison does not take into account the profound differences between modern and Cretaceous forests.[71]Lambeosaurus and other hadrosaurs had a unique feeding apparatus of extensive dental batteries, only found elsewhere inceratopsids, that has been the focus of much research. While some early studies suggested this tooth arrangement was an adaptation for front-to-back (propalinal) chewing, others suggested a more complex chewing motion involving flexing of bone-to-bone joints in the jaws (pleurokinesis). The microscopicwear on teeth from chewing shows that it was not purely due to propalinity or kinesis, and instead a combination of both mechanisms contributed to the two-direction chewing motion of hadrosaurs: an oblique up-down power stroke, supplemented by front-back grinding.[72] Among hadrosaurids, the age-related variation of the beak and limbs suggests a dietary shift during growth in hadrosaurines, while lambeosaurines retained a consistent diet. The jaws and snout of lambeosaurines are broader and more downturned, and the upper limbs are longer but maintain consistent proportions through growth.[73][74][75][47] As a result,Lambeosaurus is believed to have been a less selective feeder than hadrosaurines, and instead may have prioritized efficient movement to consume greater amounts of food of lower nutritional value. The broad and slightly separate feeding envelopes of both hadrosaur subfamilies therefore may have prevented direct competition for food.[75][47] Thisniche separation between lambeosaurines and hadrosaurines can be seen directly inLambeosaurus andProsaurolophus, which coexisted but show differences in dentalmicrowear resulting from their different diets.[47]
Reported hadrosaur gut contents and possible hadrosaurcoprolites contain abundant material fromconifers including decayed wood, as well as seeds, fruits, and leaf material ofangiosperms, which agree with interpretations of generalistbrowsing.[47] Hadrosaur teeth show more pit marks than ceratopsids, which are known to have had high-fibre diets and also have dental batteries, providing evidence for the consumption of fruits and seeds inLambeosaurus. A generalist diet of fruits and seeds, as well as leaves and stems, is more similar toankylosaurids and suggests the dental batteries of hadrosaurids and ceratopsids functioned differently. Teeth ofLambeosaurus have fewer and smaller microwear scratches than those ofProsaurolophus, which suggests the former had a diet of coarser plants, or fed higher up in the canopy away from the ground.[72] Less scratches may suggest thatLambeosaurus browsed in more closed (forested) habitats than hadrosaurines that fed in open plains, and the additional lack of lambeosaurinebonebeds supports the idea thatLambeosaurus was a closed-habitat browser of herbaceous vegetation that lived solitarily and perhaps with territorial tendencies.[71][72]
The function of the elaborate crest ofLambeosaurus, as well as those of other hadrosaurs, has been a topic of scientific debate for decades. The anatomy of the crests is a primary distinguishing feature between several species.[27] Brown believed that the crest ofCorythosaurus was a display structure comparable to that of thecassowary. However, the internal anatomy of the crests of lambeosaurines differ considerably from that of cassowaries. Lambeosaurine crests have an extensive system of internal sinuses, which the crests of cassowaries lack completely.[13][27]
Alternative suggestions have included ideas that the crest served to assist with underwater feeding, an improved sense of smell (olfaction),thermoregulation,sodium regulation, communication, or sexual identification.[54] In 1962, Ostrom proposed that theolfactory bulb of the brain, responsible for smell, was redirected upwards into the crest in lambeosaurines to increase the acuity of their sense of smell.[24] Dodson instead suggested in 1975 that the extent of the crest could be used to separateLambeosaurus into male and female individuals as a form of sexual dimorphism.[27] Hopson, later the same year, proposed that the crests instead served as a display organ for both visual and acoustic communication, with the hollow lambeosaur crests acting asresonating device for vocalization. He believed that the crests, which varied between species and were sexually dimorphic, worked as elongatedpipe organs that varied in the exact sounds they could produce. Hopson also found that the anatomy of the ear inCorythosaurus was well-developed, which suggests their sense ofhearing was well-developed.[28]
Weishampel proposed in 1981 that it could be possible to assess the functionality of the crest as a resonating chamber by creating three-dimensional models of the crests and assessing their resonance and harmonics. He usedParasaurolophus as a representative taxon for Lambeosaurinae as its internal nasal passages are simpler and easier to investigate than those ofLambeosaurus andCorythosaurus. From the internal crest length ofParasaurolophus, Weishampel supported the idea of the crests' use as sound-amplifying structures. Under this hypothesis, juveniles with smaller crests would have produced higher-frequency vocalizations, while adults would make lower sounds that would be able to travel across greater distances to assist in socialization.Lambeosaurus, with its different crest anatomy, would presumably produce a distinct vocalization frequency fromParasaurolophus, but still be able to use its crest in much the same way.[54]
In 2006, David Evans conducted the first detailed study of the available braincase material of lambeosaurines. He found that there was no evidence the olfactory nerves entered the nasal loops, and therefore the passages were non-olfactory and the nerves did not branch up into the crest. Evans was thus able to reject Ostrom's idea that the crest aided in a sense of smell, and instead suggested acoustic resonance as the primary driver for its evolution, with visual display as an important secondary function.[76] Studies of the brain anatomy of lambeosaurines by Evans and colleagues in 2009 also suggested that the crest served as a signaling structure in social behavior.[77]
Studies on the effects of growth inLambeosaurus began when Peter Dodson identifiedProcheneosaurus as juvenile specimens ofLambeosaurus.[27] The ontogeny of the lambeosaurinesHypacrosaurus andParasaurolophus has been examined, but no direct studies of the absolute ages ofLambeosaurus specimens have ever been performed. All inferences about the ages ofLambeosaurus specimens are based on the relative size of the specimens.[43][78] Based on the study of other hadrosaurs, it has been identified that the development of the crest began late in growth in all lambeosaurines exceptParasaurolophus.[78] Throughout their maturation, the skulls ofLambeosaurus and other lambeosaurines increased in length by an order of magnitude or greater, up to the largest individuals ofLambeosaurus being 93% the size ofHypacrosaurus. The crest itself grew faster than the rest of the body, with the greatest increase in size occurring inL. magnicristatus andCorythosaurus, whileL. lambei,L. clavinitialis, andHypacrosaurus all reached similar crest sizes.[43] The growth pattern of the spur on the crest ofLambeosaurus is difficult to establish due to its breakage during fossilisation of some specimens and the difficulty in assigning juveniles toL. lambei orL. clavinitialis.[27] The fontanelle between the nasal and premaxilla described by Maryañska and Osmólska does not show a clear decrease in size during growth despite initial suggestions, so its function with relation to crest development remains uncertain. Patterns of crest growth are most similar betweenCorythosaurus andHypacrosaurus, likely reflecting their closer phylogenetic relationship than toLambeosaurus.[43]
Excluding the crest, the skull ofLambeosaurus grew more slowly than the rest of the skeleton. The skull changed in proportions during growth, with the snout becoming slightly longer while the maxilla and height of the skull excluding the crest, as well as the general size of the brain, decreased proportionally. The facial skeleton ofCorythosaurus andLambeosaurus maintained their similarities during growth, while theparietal ofHypacrosaurus decreased in size proportionally allowing it to be distinguished.[43] General changes during growth also occurred throughout the rest of the skull and body of hadrosaurids, including an increase in the total number of teeth, a decrease in the proportional size of the orbit, and the development of textured regions for increased muscle attachment.[79]
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The Belly River series, as it was known when the first fossils ofLambeosaurus were found, is now known as the Belly River Group, spanning theCampanianForemost, Oldman, and Dinosaur Park formations. Along the Red Deer River, only the Oldman and Dinosaur Park formations are exposed, reaching athickness of around 90 m (300 ft).[80]Lambeosaurus is only known from the Dinosaur Park Formation, which has been constrained in age between 76.47 and 74.44million years ago byradiocarbon dating, and divided into three faunal zones. The oldest faunal zone is identified by the coexistence ofCorythosaurus and the ceratopsidCentrosaurus apertus, and transitioned at 75.77 million years ago into a fauna characterized byProsaurolophus maximus and the ceratopsidStyracosaurus albertensis. The youngest faunal zone coincides with the presence ofbituminous coal at 75.098 mya, and the replacement of the commonmegaherbivores from older beds with the much rarerL. magnicristatus, and ceratopsids includingChasmosaurus irvinensis and a ceratopsid similar toAchelousaurus.[81]L. clavinitialis is the oldest species ofLambeosaurus, found only within the middle Campanian coexisting withCorythosaurus andCentrosaurus.L. lambei is younger, coexisting with bothCorythosaurus andCentrosaurus, as well asStyracosaurus andProsaurolophus from the middle to late Campanian with some possible overlap with bothL. clavinitialis andL. magnicristatus.[47]
With the exception of the mud-dominated coal zone, the sediments of the Dinosaur Park Formation are indicative of analluvial environment with channels andoverbanks of river channels of both low and highsinuosity. Some channel widths may even have exceeded 200 m (660 ft), flowing east towards theBearpaw Sea across the coastal plain.[80] While some studies suggest that theDinosaur Provincial Park region of the Dinosaur Park Formation was under both river andoceanic influence, there are no signs oftidal influence, placing the deposits further inland above the potential for anybackwater from tidal change. The Dinosaur Park Formation was deposited on a low slope during the start of the last majormarine transgression of the shallowWestern Interior Seaway that spanned central North America, where it expanded westward to cover the region in the marine deposits of the Bearpaw Formation. The environment of the coal zone directly before the submersion is less studied, but it shows mixed freshwater-brackish-marine assemblages and coastal erosion.[82]
Thecordillera to the west of Alberta was tectonically active, with volcanic eruptions spreading ash into the formation, and warmer climates than modern with little to nofrost. There may have been seasonality of wetter and drier parts of the year, allowing for a diversity in plants and animals. The rivers of the coastal plain were lined with narrow zones of dense vegetation, and as the seaway approached, some areas would see periodic flooding or even standingswamps ormires that accumulated into the coal deposits. The ground would have been wet everywhere, with conifers dominating thecanopy whileferns,tree ferns, and floweringherbs andshrubs formed theunderstory. The ground would have been covered withmosses,lichens, andfungi, and a layer of decaying plant matter. Standing water would be vegetated by water plants andalgae.Insects were plentiful, with the streams and surrounding environment inhabited byclams,snails,fish,turtles, andcrocodiles, as well aspterosaurs, dinosaurs, and smallmammals.[83]
A rich and diverse vertebrate assemblage is known from the Dinosaur Park Formation, with the lower region, excluding theLethbridge Coal Zone, being formed by terrestrial and coastal deposits.[84] The constant presence of water in the formation led many forms of freshwater or marine animals to enter the otherwise predominantly terrestrial ecosystem.[85] In the lower Dinosaur Park Formation, assemblages of crevasse sites show that the freshwaterclamSphaerium was the most commonmollusk, and it occurred with abundantgastropods of the generaGoniobasis andLioplacodes.[84] A variety of forms of fish are present in thefluvial beds of the formation, includingchondrichthyans,teleosts and otherray-finned fishes. The rayMyledaphus is characteristic of the formation and lived alongside the less common sharkHybodus montanensis, andpaddlefish,sturgeons,bowfins, theaspidorhynchidBelonostomus, thegarLepisosteus, and small teleosts includingParatarpon andCretophareodus.[86] At least nine forms ofamphibians were present in the formation, including thesalamander-likeAlbanerpeton,frogs, and salamanders from the generaScapherpeton,Lisserpeton,Opisthotriton,Habrosaurus.[87] Turtles are common and represented by thebaenidsPlesiobaena,Boremys andNeurankylus, themacrobaenidJudithemys, an unnamed but new form ofsnapping turtle, the primitivetrionychoidsAdocus andBasilemys, and thesoftshelled turtlesApalone andAspideretoides.[88] Six smalllizards are known but nosnakes, with theteiidsSocognathus andGlyptogenys, thexenosauridExostinus, thehelodermatidLabrodioctes, thenecrosauridParasaniwa, and thevaranidPalaeosaniwa.[89]Choristoderes, an extinct group of semi-aquatic animals withcrocodilian features, are represented byCteniogenys and many well-preserved skulls and skeletons of its relativeChampsosaurus.[90] The major types of Cretaceous mammals have been found in the formation: themultituberculatesCimexomys,Cimolodon,Cimolomys,Meniscoessus, andMesodma, themarsupialsAlphadon,Eodelphis,Pediomys, andTurgidodon, and theplacentalsCimolestes,Gypsonictops, andParanyctoides.[91]
Microfossil sites are common, but ataphonomic bias is present in the formation towards the better preservation of large-bodied animals likeLambeosaurus.[41]Mosasaurs andplesiosaurs are both known from the formation, though apart from the relatively completeelasmosauridFluvionectes, both are poorly known.[85][89][92] Two or three true crocodilians are known, including the generaLeidyosuchus andAlbertochampsa, and twopterosaurs have been found, theazhdarchidCryodrakon and an unnamedpterodactyloid.[93][94][95] While no other dinosaurs were recovered at the same sites as anyLambeosaurus specimens, correlation and comparisons of localities throughout the formation show it coexisted with a large variety of animals.[96] The herbivorous fauna of the formation can be divided into two Megafaunal Assemblage Zones, defined as the lowest 28 m (92 ft) directly above the Oldman Formation, and the deposits above those, where the commonceratopsidCentrosaurus andhadrosauridParasaurolophus are absent.Lambeosaurus, which has been found from around 17 to 52 m (56 to 171 ft) above the contact, is from the upper portion of the older MAZ-1 to the upper portion of the younger MAZ-2, and would have coexisted with the ankylosauridEuoplocephalus, nodosauridPanoplosaurus, ceratopsidsCentrosaurus,Styracosaurus andChasmosaurus belli, and hadrosauridsCorythosaurus intermedius,Parasaurolophus, andProsaurolophus.[44] As well as herbivorous megafauna, unnamedornithopods, the primitiveceratopsianUnescoceratops and thepachycephalosauriansStegoceras validum,Stegoceras sternbergi andStegoceras brevis are known from the formation, though their stratigraphic correlations are uncertain.[51][97] Amongtheropods, thedromaeosauridsDromaeosaurus andSaurornitholestes are known, the former from a single specimen of uncertain provenance, and the latter from many specimens such as teeth throughout the entire formation, andtroodontids from the MAZ-1 are limited toStenonychosaurus whileLatenivenatrix is known from MAZ-2.[98][99] Three genera ofoviraptorosaurs are known, all of which likely coexisted in the formation:Caenagnathus,Chirostenotes andCitipes.[100] It is possible that atherizinosaur was present based on a singlefrontal bone, and threeornithomimosaurs are preserved in the MAZ-1,Rativates,Ornithomimus, andStruthiomimus.[98][101] The only large theropods to coexist withLambeosaurus were thetyrannosauridsGorgosaurus and an unnamed species ofDaspletosaurus.[102]
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