Lambeosaurus
Lambeosaurus | |
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Mounted L. lambei skeleton, Royal Ontario Museum | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | †Ornithischia |
Clade: | †Ornithopoda |
Family: | †Hadrosauridae |
Subfamily: | †Lambeosaurinae |
Clade: | † Corythosauria
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Tribe: | †Lambeosaurini |
Genus: | †Lambeosaurus Parks, 1923 |
Type species | |
†Lambeosaurus lambei Parks, 1923
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Other species | |
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Synonyms | |
Genus synonymy
Species synonymy
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Lambeosaurus (
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.
History and species
Early discoveries and names
Lambeosaurus has a complicated taxonomic history, beginning in 1902 with Lawrence Lambe's naming of hadrosaurid limb material and other bones (originally GSC 419) from Alberta as Trachodon marginatus.[2] In the same publication Trachodon altidens, a left upper jaw (GSC 1092) from the Dinosaur Park Formation was also described by Lambe.[3] In the same volume, Henry Fairfield Osborn suggested T. altidens could belong to a new genus, which he labelled "Didanodon" without further discussion.[2]
Paleontologists began finding better remains of hadrosaurids from the same rocks in the 1910s, in what is now known as the
Procheneosaurus and Tetragonosaurus
Although the early workers in Alberta did not recognize it at the time, they were finding the remains of juvenile Lambeosaurus as well. These fossils of small-bodied crested duckbills were interpreted as adults of a distinct lineage of hadrosaurids, the subfamily Cheneosaurinae.[6] In 1920, William Diller Matthew used the name Procheneosaurus (no species name) in a brief mention of a skeleton at the American Museum of Natural History, from the Dinosaur Park Formation (AMNH 5340).[7] Parks believed that the procedure and description were inadequate for the name to be considered valid, and to address the situation, he coined the genus Tetragonosaurus. Into this genus he placed the type species T. praeceps (based on ROM 3577) and a second species T. erectofrons (based on ROM 3578) for small skulls from the Dinosaur Park Formation, and assigned Matthew's Procheneosaurus skeleton to T. praeceps.[8] Charles M. Sternberg followed in 1935 by adding the slightly larger T. cranibrevis, based on GSC (now NMC) 8633.[9]
The use of Tetragonosaurus was rejected by Richard Swann Lull in favor of Procheneosaurus. Lull requested that the name Tetragonosaurus be suppressed in favor of Procheneosaurus, which was granted, and Procheneosaurus received official approval from the ICZN as a conserved name.[10] In 1942 he and Wright transferred the Tetragonosaurus species and, tentatively, Trachodon altidens, to Procheneosaurus, with P. praeceps serving as the type species.[11] This usage was generally followed until 1975, when Peter Dodson proposed all three species were actually juveniles of Lambeosaurus.[12]
"Procheneosaurus" convincens, from the Late Cretaceous of Kazakhstan, is known from a nearly complete skeleton missing only the snout and end of the tail. It was named by A. K. Rozhdestvensky in 1968.[13] It has at times been considered synonymous with Jaxartosaurus aralensis,[14] or deserving of its own genus.[15] Bell and Brink (2013) made "P." convincens the type species of the new genus Kazaklambia.[16]
Other discoveries
The "cheneosaurines" weren't the only crested duckbills being studied and named in the early 1900s. It was then the accepted practice to name genera and species for what is now seen as more likely individual variation, variation due to age or sex, or distortion from fossilization. Three more species were named during this period that relate to Lambeosaurus, all in 1935. Sternberg, in the same paper as T. cranibrevis, named a skull and partial skeleton (GSC-8705, now NMC—8705) L. magnicristatum (corrected in 1937 to magnicristatus), and a smaller skull (GSC—8705, now NMC—8703) L. clavinitialis, with a less prominent crest and reduced spine pointing from the back.[9] Parks contributed Corythosaurus frontalis, based on skull GSC 5853 (now ROM 869), which differed from the well-known tall, straight, rounded crest of other specimens of Corythosaurus by having a low crest cocked forward.[17]
New specimens were not described for many years following the activity of the early 1900s. In 1964
Dodson's two species model to present
In 1975, Peter Dodson, examining why there should be so many species and genera of lambeosaurine duckbills within such a short geological time frame and small area, published the results of a morphometric study in which he measured dozens of skulls. He found that many of the species had been based on remains that were better interpreted as juveniles or different sexes, something touched on but largely ignored in older literature. For Lambeosaurus, he found that L. clavinitialis was probably the female of L. lambei, and Corythosaurus frontalis and Procheneosaurus praeceps were probably its juveniles. L. magnicristatus was different enough to warrant its own species. He interpreted Procheneosaurus cranibrevis and P. erectofrons as juvenile corythosaurs.[12] However, restudy of the Procheneosaurus/Tetragonosaurus remains indicates that within species, assignments had become confused, and the type specimen of P. cranibrevis was a Lambeosaurus juvenile, whereas others were Corythosaurus, based on the distinctive form of the contact of the nasal bone with the premaxilla.[19]
Dodson's model would become widely accepted, and two species of Lambeosaurus are regularly recognized today, with a third sometimes accepted. L. lambei (Parks, 1923) is known from at least 17 individuals, with seven skulls and partial skeletons and around ten isolated skulls. L. clavinitialis (C.M. Sternberg, 1935), Corythosaurus frontalis (Parks, 1935), and Procheneosaurus praeceps (Parks, 1931) are all still regarded as synonyms of L. lambei in recent reviews.[14] Some palaeontologists suggest that L. clavinitialis skulls without the backward spine may represent L. magnicristatus individuals instead,;[20] this was rejected in the 2007 redescription of L. magnicristatus.[21]
The second species, L. magnicristatus (C.M. Sternberg, 1935) is only definitely known from two specimens, both with skulls. Unfortunately, the majority of the articulated skeleton of the type specimen has been lost. Many of the bones were extensively damaged by water while in storage and were discarded before description; other portions of this skeleton have also been lost. Its remains come from slightly younger rocks than L. lambei.
Other less accepted species have been discussed in the 21st century. Lambeosaurus paucidens (named by Marsh 1889 and referred to Lambeosaurus in 1964) is generally regarded as a dubious name and was listed as Hadrosaurus paucidens in a 2004 review,[14] although at least one author, Donald F. Glut, has accepted it as a species of Lambeosaurus.[24] In this case, the specific epithet is derived from the Latin pauci- "few" and dens "tooth".[22] The irregularities of Procheneosaurus cranibrevis, and the identity of the type as a juvenile lambeosaur, were recognized in 2005.[19] Finally, "Didanodon altidens" has been assigned without comment to Lambeosaurus in two 21st Century reviews.[25][14]
During the late 1970s,
Description
Lambeosaurus, best known through L. lambei,[28] was quite similar to Corythosaurus in everything but the form of the head adornment. Compared to Corythosaurus, the crest of Lambeosaurus, largely formed by the premaxillae, was shifted forward, and the hollow nasal passages within were at the front of the crest and stacked vertically.[12] It also can be differentiated from Corythosaurus by its lack of forking nasal processes making up part of the sides of the crest, which is the only way to tell juveniles of the two genera apart, as the crests took on their distinctive forms as the animals aged.[19] Lambeosaurus was like other hadrosaurids, and could move on both two legs and all fours, as shown by footprints of related animals. It had a long tail stiffened by
The most distinctive feature, the crest, was different in the two well-known species. In L. lambei, it had a hatchet-like shape when the dinosaur was full-grown, and was somewhat shorter and more rounded in specimens interpreted as females.[12] The "hatchet blade" projected in front of the eyes, and the "handle" was a solid bony rod that jutted out over the back of the skull. The "hatchet blade" had two sections: the uppermost portion was a thin bony "coxcomb" that grew out relatively late in life, when an individual neared adulthood; and the lower portion held hollow spaces that were continuations of the nasal passages.[12] In L. magnicristatus, the "handle" was greatly reduced, and the "blade" expanded,[29] forming a tall, exaggerated pompadour-like crest. This crest is damaged in the best overall specimen, and only the front half remains.[21]
Large adult specimens of Lambeosaurus have been estimated to be around 7–7.7 m (23–25 ft) in length and 2.5–3.3 metric tons (2.8–3.6 short tons) in body mass.[30] Impressions of the scales are known for several specimens; a specimen now assigned to L. lambei had a thin skin with uniform, polygonal scutes distributed in no particular order on the neck, torso, and tail.[31] Similar scalation is known from the neck, forelimb, and foot of a specimen of L. magnicristatus.[21]
Classification
Lambeosaurus is the
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Paleobiology
Feeding
As a hadrosaurid, Lambeosaurus was a large bipedal/quadrupedal herbivore, eating
Cranial crest
Like other
The large size of hadrosaurid