Alioramus

This is a good article. Click here for more information.
Source: Wikipedia, the free encyclopedia.

Alioramus
Temporal range:
Ma
↓
Skeleton mount at Texas A&M University-Commerce
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Tyrannosauridae
Tribe: †Alioramini
Genus: †Alioramus
Kurzanov, 1976
Type species
†Alioramus remotus
Kurzanov 1976
Other species
  • †A. altai Brusatte et al., 2009
Synonyms
  • Lü et al., 2014[1]

Alioramus (

Tarbosaurus bataar. However, the discovery of Qianzhousaurus indicates that it belongs to a distinct branch of tyrannosaurs, namely the tribe Alioramini
.

Alioramus were

Tyrannosaurus rex
, but their adult size is difficult to estimate since both Alioramus species are known only from juvenile or sub-adult remains. The genus Alioramus is characterized by a row of five bony crests along the top of the snout, a greater number of teeth than any other genus of tyrannosaurid, and a lower skull than most other tyrannosaurids.

History of discovery

A. altai skeletal diagram, known portions in yellow

The

pelvic girdle and hindlimbs. The name for this species, altai, is in reference to the Altai Mountains.[3]

Description

Size of A. remotus compared with a Human

Alioramus remotus was estimated at 5 to 6 m (16 to 20 ft) in length when originally described by Sergei Kurzanov in 1976.[2] In 1988 Paul gave a similar length of 6 m (20 ft) and a weight of 700 kg (1,500 lb).[4] In 2016 Molina-Pérez and Larramendi estimated A. remotus at 5.5 m (18 ft) and 500 kg (1,100 lb), and A. altai at 5 m (16 ft) and 385 kg (849 lb).[5] Kurzanov, however, did not correct for lengthening of the skull by deformation during fossilization, which may indicate a shorter overall body length for this individual. If this specimen is a juvenile, then adult Alioramus would have reached greater lengths, but no confirmed adult specimens are known.[6]

Skull

(A) maxilla, (B) lacrimal, (C) dentary, and (D) jugal bones of A. altai
Braincase complex of A. altai

The skull of A. remotus was approximately 45 cm (1.48 ft) long.

sutured together. These crests all measure more than 1 cm (0.39 in) tall.[2][8]

At the back of the skull there is a protrusion, called the nuchal crest, arising from the fused

avialan conditions.[11][8]

Postcranial skeleton

Femur head of A. altai
(A) cervical vertebra, (B) right ilium, (C) right ischium, and (D) right tibio-astragalar complex bones of A. altai

The rest of the skeleton of Alioramus remotus is completely unknown except for three

metatarsals (bones of the upper foot), but the discovery of A. altai, which is known from substantially more complete remains, has shed light on the anatomy of the genus.[3][8]

Classification

Life restoration of A. remotus

cladistic analysis published in 2003 found Alioramus could be further classified into the family Tyrannosauridae and the subfamily Tyrannosaurinae, alongside Tyrannosaurus, Tarbosaurus and Daspletosaurus.[12] A 2004 study supported this result but suggested it was equally probable that Alioramus belonged outside the family Tyrannosauridae entirely, with its supposed juvenile characters actually reflecting a more basal position within Tyrannosauroidea.[6] Another study omitted Alioramus altogether due to the only specimen's fragmentary nature.[13] The description of A. altai in 2009 confirmed the placement of the genus within the Tyrannosaurinae.[3]

Tarbosaurus and Alioramus shared several skull features, including a locking mechanism in the lower jaw between the dentary and angular bones, and both lacked the prong of the nasal bones which connected to the lacrimal bones in all other tyrannosaurids except adult Daspletosaurus. The two genera may be closely related, representing an Asian branch of the Tyrannosauridae.[9][12] Some specimens of Tarbosaurus have a row of bumps on the nasal bones like those of Alioramus, although much lower. The long and low shape of the only known Alioramus remotus skull indicated that it was immature when it died and might even have been a juvenile Tarbosaurus, which lived in the same time and place. The more prominent nasal crests and much higher tooth count of Alioramus, however, suggested it was a separate taxon, even if it is known only from juvenile remains,[10] confirmed by the discovery of A. altai.[3] Specimens identified as immature Tarbosaurus have the same tooth count as adults.[14][15]

The description of Qianzhousaurus in 2014 erected a new branch of the tyrannosaur family named Alioramini; consisting of the long-snouted Q. sinensis and the two known species of Alioramus. This clade had an uncertain placement relative to other members of the tyrannosaur branch in the initial analysis that discovered it. The primary phylogenetic analysis found Alioramini to be closer to Tyrannosaurus than to Albertosaurus, and therefore a member of the group Tyrannosaurinae. However, a second analysis in the same paper found it to be located outside of the clade including Albertosaurinae and Tyrannosaurinae, and therefore the sister group of Tyrannosauridae. Below is the first analysis found by the authors:[16]

Restoration of A. altai
Tyrannosauridae

Paleobiology

Feeding

A. remotus Skull diagram, known portions in white

Brusatte and colleagues in 2009 indicated that Alioramus lacks many of the robust and brute skull traits (such as a deep maxilla, robust lower jaws, or peg-like teeth) that are necessary to employ a "puncture-pull" feeding characteristic of large tyrannosaurids. They suggested that Alioramus may have exploited a different feeding style, such as focusing small-sized prey. This would also suggest that both Alioramus and Tarbosaurus—whose remains have also been collected at the Tsagan Khushu locality, making them

different feeding strategies, avoiding competition.[3]

Foster with team in 2022 hypothesized that due to their slim and gracile build, Alioramin genera may have been hunters of small, particularly fast and nimble prey, which would have allowed alioramins to avoid competition with larger tyrannosaurs that specialized in killing larger animals. The long and delicate snouts of alioramins like Alioramus and Qianzhousaurus may have also prevented them from killing the same prey species that juvenile and adult tyrannosaurids of tyrannosaurids like Tarbosaurus hunted, though these larger tyrannosaurs themselves may have hunted alioramins as prey on occasion. Alioramins may also have had a different feeding strategy than other tyrannosaurids, as their jaws seem to have been weaker than those of the larger genera, and even juveniles of larger species have proportionately higher bite forces than alioramins of equivalent size. Furthermore, Alioramins seemingly remained confined to Asia, suggesting some factor prevented them from colonizing the better-sampled fossil deposits from North America. Why this may be remains a mystery until more evidence is discovered.[17]

Ontogeny

Size comparison of three alioramin species (Alioramus in yellow)

ontogenic (growth) series of other dinosaurs evidence that ornamentation increases throughout growth. The latter may suggest that adult Alioramus possessed a rather elaborate cranial ornamentation.[3]

Examinations of Qianzhousaurus and its comparisons with both species of Alioramus published in 2022 suggests that both Alioramus species are known from juvenile specimens in different growth stages, and that Qianzhousaurus represents an adult example of the alioramini. The examinations also suggest that the variation seen between the various species is consistent with the growth trends seen in other tyrannosaurid genera, though specimens that could constitute a full growth series from infant to adult for each species have not been recovered for any of these tyrannosaurs. One part of the growth series across all specimens in this study was discovered to remain unique to alioramin tyrannosaurs; the rugose process of the jugal starts small and conical in early life, but becomes massive and indistinct as the animals grow. This same study also suggests Alioramins did not undergo a secondary metamorphosis from slender juveniles to robust adults like other tyrannosaurs such as Tarbosaurus and Tyrannosaurus did, but maintained a unique physiology better suited to pursuit of fast, small prey.[17]

Paleoenvironment

Cretaceous-aged Dinosaur fossil localities of Mongolia; Alioramus has been collected in area A (left)

The Beds of Nogon-Tsav are considered to be the same age as the

stage, at the end of the Late Cretaceous.[18]

Life restoration of Alioramus in the paleoenvironments of the Nemegt Formation

The Maastrichtian stage in Mongolia, as preserved in the Nemegt Formation and at Nogon-Tsav, was characterized by a wetter and more humid climate compared with the semi-arid environment preserved in the earlier, underlying

sauropods were also potential prey for predators in the Nemegt.[9]

See also

References

  1. PMID 28358353
    .
  2. ^ a b c d e Kurzanov, Sergei M. (1976). "A new carnosaur from the Late Cretaceous of Nogon-Tsav, Mongolia" (PDF). The Joint Soviet-Mongolian Paleontological Expedition Transactions (in Russian). 3: 93–104.
  3. ^
    PMID 19805035
    .
  4. ^ Paul, Gregory S. (1988). Predatory Dinosaurs of the World. New York: New York Academy of Sciences. p. 327.
  5. ^ Molina-Pérez & Larramendi (2016). Récords y curiosidades de los dinosaurios Terópodos y otros dinosauromorfos. Spain: Larousse. p. 266.
  6. ^
    ISBN 978-0-520-24209-8
    .
  7. ISBN 978-0-521-54582-2
    .
  8. ^
    S2CID 84550111
    .
  9. ^ a b c Hurum, Jørn H.; Sabath, Karol (2003). "Giant theropod dinosaurs from Asia and North America: Skulls of Tarbosaurus bataar and Tyrannosaurus rex compared". Acta Palaeontologica Polonica. 48 (2): 161–190.
  10. ^
    Currie, Philip J.
    (2003). "Cranial anatomy of tyrannosaurids from the Late Cretaceous of Alberta". Acta Palaeontologica Polonica. 48 (2): 191–226.
  11. PMID 21853125
    .
  12. ^
    Currie, Philip J.
    ; Hurum, Jørn H; Sabath, Karol (2003). "Skull structure and evolution in tyrannosaurid phylogeny". Acta Palaeontologica Polonica. 48 (2): 227–234.
  13. S2CID 86243316
    .
  14. Doklady Akademii Nauk SSSR
    (in Russian). 104 (5): 779–783.
  15. doi:10.1139/e02-083
    .
  16. PMID 24807588
    .
  17. ^
    S2CID 246799243
    .
  18. ^
    doi:10.1016/0195-6671(91)90015-5
    .
  19. ISBN 978-0-12-226810-6
    .

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Alioramus&oldid=1205885517"