Hypacrosaurus

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Hypacrosaurus
Temporal range:
Ma
H. altispinus fossil at the
Royal Tyrrell Museum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Ornithopoda
Family: †Hadrosauridae
Subfamily: †Lambeosaurinae
Tribe: †Lambeosaurini
Genus: †Hypacrosaurus
Brown, 1913
Type species
†Hypacrosaurus altispinus
Brown, 1913
Other species
  • †H. stebingeri
    Currie
    , 1994
Synonyms

Hypacrosaurus (meaning "near the highest lizard" [Greek υπο-, hypo- = less + ακρος, akros, high], because it was almost but not quite as large as

eggs, and hatchlings
belonging to H. stebingeri.

Discovery and history

Skeletal mount of H. altispinus at Canadian Museum of Nature

The

Upper Cretaceous). Brown described these remains, in combination with other postcranial bones, in 1913 as a new genus that he considered to be like Saurolophus.[1] No skull was known at this time, but two skulls were soon discovered and described.[5]

During this period, the remains of small hollow-crested duckbills were described as their own genera and species. The first of these that figure into the history of Hypacrosaurus was Cheneosaurus tolmanensis, based on a skull and assorted limb bones, vertebrae, and pelvic bones from the Horseshoe Canyon Formation.

Procheneosaurus.[7] These and other taxa were accepted as valid genera until the 1970s, when Peter Dodson showed that it was more likely that the "cheneosaurs" were the juveniles of other established lambeosaurines. Although he was mostly concerned with the earlier, Dinosaur Park Formation genera Corythosaurus and Lambeosaurus, he suggested that Cheneosaurus would turn out to be composed of juvenile individuals of the contemporaneous Hypacrosaurus altispinus.[8] This idea has become accepted,[9] although not formally tested. The Two Medicine Procheneosaurus, meanwhile, was not quite like the other Procheneosaurus specimens studied by Dodson, and for good reason: it was much more like a species that would not be named until 1994, H. stebingeri.[10]

Species

H. stebingeri holotype skull

H. altispinus, the type species, is known from 5 to 10 articulated skulls with some associated skeletal remains, from juvenile to adult individuals found in the Horseshoe Canyon Formation. H. stebingeri is known from an unknown but substantial number of individuals, with an age range of embryos to adults.[9] The hypothesis that H. altispinus and H. stebingeri form a natural group excluding other known hadrosaur species may be incorrect, as noted in Suzuki et al.'s 2004 redescription of Nipponosaurus; their phylogenetic analysis found that Nipponosaurus was more closely related to H. altispinus than H. stebingeri was to H. altispinus.[11] This was rejected by Evans and Reisz (2007), though.[12]

The new species Hypacrosaurus stebingeri was named for a variety of remains, including hatchlings with associated eggs and nests, found near the top of the

Upper Cretaceous) Two Medicine Formation in Glacier County, Montana, and across the border in Alberta. These represent "the largest collection of baby skeletal material of any single species of hadrosaur known".[10]

Description

Size comparison between the two species and a human

Hypacrosaurus is most easily distinguished from other hollow-crested duckbills (

quadrupedal herbivore. The two known species, H. altispinus and H. stebingeri, are not differentiated in the typical method, of unique characteristics, as H. stebingeri was described as transitional between the earlier Lambeosaurus and later Hypacrosaurus.[10]

Classification

Life restoration of H. altispinus
Hindfoot of H. altispinus
Hypacrosaurus mount at the Philip J. Currie Dinosaur Museum

Hypacrosaurus was a lambeosaurine

Phil Currie (1994) suggesting that H. stebingeri is transitional between Lambeosaurus and H. altispinus,[10] and Michael K. Brett-Surman (1989) suggesting that Hypacrosaurus and Corythosaurus are the same genus.[16] These genera, particularly Corythosaurus and Hypacrosaurus, are regarded as the "helmeted" or "hooded" branch of the lambeosaurines, and the clade they form is sometimes informally designated Lambeosaurini. Although Suzuki et al.'s 2004 redescription of Nipponosaurus found a close relationship between Nipponosaurus and Hypacrosaurus stebingeri, indicating that Hypacrosaurus may be paraphyletic,[11] this was rejected in a later, more comprehensive reanalysis of lambeosaurines, which found the two species of Hypacrosaurus to form a clade without Nipponosaurus, with Corythosaurus and Olorotitan being the closest relatives.[12]

The following cladogram illustrating the relationships of Lambeosaurus and its close relatives was recovered in a 2022 phylogenetic analysis by Xing Hai and colleagues. Unlike other modern analyses, they found the genus Magnapaulia to be within Hypacrosaurus, indicating it could be a potential third species.[17]

Xuwulong

Bactrosaurus

Telmatosaurus

Lambeosaurinae
Aralosaurini
Tsintaosaurini

Jaxartosaurus

Arenysaurini
Corythosauria
Parasaurolophus

Parasaurolophus cyrtocristatus

"Charonosaurus" jiayinensis

Parasaurolophus tubicen

Parasaurolophus walkeri

Lambeosaurini

Olorotitan

Velafrons

Amurosaurus

Lambeosaurus

Lambeosaurus clavinitialis

Lambeosaurus magnicristatus

Lambeosaurus lambei

Corythosaurus

Corythosaurus intermedius

Corythosaurus casuarius

Hypacrosaurus

Hypacrosaurus altispinus

"Magnapaulia" laticaudus

Hypacrosaurus stebingeri

Paleobiology

As a

dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. Plant material would have been cropped by its broad beak, and held in the jaws by a cheek-like organ. Its feeding range would have extended from the ground to about 4 m (13 ft) above.[9]

Crest functions

AMNH

The hollow crest of Hypacrosaurus most likely had social functions, such as a visual signal allowing individuals to identify sex or species, and providing a resonating chamber for making noises.

nasal turbinates.[citation needed
]

Turbinates are thin bones or

CT scanning, thus there was no evidence that those animals were warm-blooded.[19]

Thermoregulation

Examining the oxygen-isotope ratio from the bones from different parts of an extinct animal's body should indicate which thermoregulation mode an animal used during its lifetime. An endothermic (warm-blooded) animal should maintain a very similar body temperature throughout its entire body (which is called homeothermy) and therefore there should be little variation in the oxygen-isotope ratio when measured in different bones. Alternatively, the oxygen-isotope ratio differs considerably when measured throughout the body of an organism with an ectothermic (cold-blooded) physiology.[20] Oxygen-isotope ratios calculated for Hypacrosaurus suggesting that the ratios varied little, indicating that Hypacrosaurus was a homeotherm, and likely was endothermic.[21] This is in contrast to the Ruben et al. (1996) finding that Hypacrosaurus was not warm-blooded, which was based on the absence of nasal turbinates (see Crest functions subsection, above).[citation needed]

Nests and growth

H. stebingeri nest

Hypacrosaurus stebingeri laid roughly spherical

Secondary cartilage has been found in the skull of a hatchling specimen of H. stebingeri.[25]

Cells

Hypacrosaurus MOR 548 supraoccipital with microscopic magnification showing the preserved chondrocyte-like structures, in comparison to those of an emu

In 2020,

supraoccipital bone, and upon microscopic magnification, chondrocyte-like structures were found. Several of these structures were preserved in the final stages of mitosis, with some preserving putative traces of celular nuclei. Bailleul and colleagues isolated some of these cells in order to be tested with DNA staining: stains DAPI and PI. They also exposed emu chondrocytes, and these tied up to DNA fragments. H. stebingeri cells tested positive to possible chemical markers of DNA, in a similar way to the emu cells, suggesting the potential preservation of this molecule. The team concluded that the find was not a product of fossil contamination, and DNA may last much longer than previously assumed.[26]

Paleopathology

The discovery of tooth marks in the fibula of a Hypacrosaurus specimen inflicted by a bite from the teeth of a tyrannosaurid indicated that this, and other hadrosaurids were either preyed upon or scavenged by large theropod dinosaurs during the Late Cretaceous period.[citation needed]

Paleoecology

Taphonomy

The large, monospecific assemblage of Hypacrosaurus stebingeri in Montana was interpreted as a group of dinosaurs that was killed by a volcanic ashfall.[20] This assemblage is considered autochthonous, meaning that the remains are thought to have been buried on or near the same spot where the individuals died. The variety of ages in this group supports that this was a biocoenosis—an actual life assemblage of animals.[27] The cause of death in a volcanic ashfall is suffocation by the ash and by the gases released from volcanic eruptions. The preservation of this diverse group of dinosaurs provides researchers with a growth series, which is a sequence of growth stages from juvenile to adult.[citation needed]

Environment

Restoration of H. altispinus in environment

H. altispinus shared the Horseshoe Canyon Formation with fellow hadrosaurids

shallow sea that covered the midsection of North America through much of the Cretaceous.[29] H. altispinus may have preferred to stay more landward.[9]

The slightly older Two Medicine Formation, home to H. stebingeri, was also populated by another well-known nesting hadrosaur,

Rubeosaurus were also present.[28] This formation was more distant from the Western Interior Seaway, higher and drier, with a more terrestrial influence.[30]

See also

References

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  5. ^ a b Gilmore, Charles Whitney (1924). "On the genus Stephanosaurus, with a description of the type specimen of Lambeosaurus lambei, Parks". Canada Department of Mines Geological Survey Bulletin (Geological Series). 38 (43): 29–48.
  6. ^ Lambe, Lawrence M. (1917). "On Cheneosaurus tolmanensis, a new genus and species of trachodont dinosaur from the Edmonton Cretaceous of Alberta". The Ottawa Naturalist. 30 (10): 117–123.
  7. ^ Matthew, William Diller (1920). "Canadian dinosaurs". Natural History. 20 (5): 1–162.
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  13. ^ a b c Lull, Richard Swann; Wright, Nelda E. (1942). Hadrosaurian Dinosaurs of North America. Geological Society of America Special Paper 40. Geological Society of America. pp. 206–208.
  14. ^ Weishampel, David B. (1981). "The nasal cavity of lambeosaurine hadrosaurids (Reptilia:Ornithischia): comparative anatomy and homologies". Journal of Paleontology. 55 (5): 1046–1057.
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  16. ^ Brett-Surman, Michael K. (1989). A revision of the Hadrosauridae (Reptilia:Ornithischia) and their evolution during the Campanian and Maastrichtian. Ph.D. dissertation. Washington, D.C.: Graduate School of Arts and Sciences of The George Washington University. pp. 1–272.
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  18. ^ Chinsamy, Anusuya; and Hillenius, Willem J. (2004). "Physiology of nonavian dinosaurs". The Dinosauria, 2nd. 643-659.
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  21. ^ Barrick, R. E., Showers, W. J. and Fischer, A. G. 1996. Comparison of thermoregulation of four ornithischian dinosaurs and a varanid lizard from the Cretaceous Two Medicine Formation: Evidence from oxygen isotopes. Palaios 11: 295–305.
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  27. ^ Behrensmeyer, A. K. 1991. Terrestrial vertebrate accumulations. In Allison P. A. and Briggs D. E. G. (Eds), Taphonomy: Releasing the Data Locked in the Fossil Record. New York: Plenum Press.
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External links

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