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Alioramini

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Alioramini is a clade of long-snouted tyrannosaurine tyrannosaurids from the Late Cretaceous epoch. It includes the tyrannosaurid genera Alioramus and Qianzhousaurus. Although tyrannosaurids are known from a variety of places around the globe, alioramins are currently restricted to Asia in mostly Maastrichtian strata.[1] Many of the fossils attributed to Alioramini are not from fully developed individuals.[2]

Alioramins
Temporal range: Late Cretaceous,
~70–66 Ma
↓
Holotype skull of Alioramus altai
Qianzhousaurus holotype skull
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Tyrannosauridae
Subfamily: †Tyrannosaurinae
Clade: †Alioramini
Olshevsky, 1995
Type species
Alioramus remotus
Kurzanov 1976
Genera

Description

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Size comparison of three alioramin species with a human

Alioramins are medium-sized tyrannosaurids, reaching around 5–7 m (16–23 ft) in length. They have a more gracile body plan as compared to most other tyrannosaurines.[3][4] Alioramins have rather shallow snouts, a trait that is rather rare among tyrannosaurs but can be found in the early tyrannosauroid, Xiongguanlong.[5] Alioramins are unique when compared to contemporary tyrannosaurs from the same time, such as Tarbosaurus and Tyrannosaurus, because most of the longer snouted tyrannosauroids, such as Xiongguanlong, were found in deposits dating to earlier times during the Cretaceous. Members of the alioramins also have an elongated maxillary fenestra. Besides their elongated snouts, perhaps another major trait that makes alioramins stand out is their nasal ridges. While most other tyrannosaurids have nasal ridges, the nasal ridges in alioramins are pronounced and discrete. They form well developed bumps on the surface of the nasal bones, forming their nasal crest. Within the dentary bone, alioramins have 18 or more teeth. [6][1]

Classification

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The name Alioramini was first coined in 1995 by George Olshevsky only to contain the at-the-time uncertain Alioramus. Olshevsky classified Alioramini within the base of Tyrannosaurinae and considered it to be a tribe or a "paratribe" (a name for a paraphyletic tribe, emphasizing Olshevsky's view that the hypothetical common ancestor of tyrannosaurids could be classified as an alioramin).[7] Alioramini were first described as a clade by Junchang Lü and colleagues in 2014, who defined it as a branch-based clade containing all tyrannosaurids more related to Alioramus than to Albertosaurus, Proceratosaurus, and Tyrannosaurus. Hence, the clade Alioramini consists of three species, namely Alioramus altai, Alioramus remotus, and Qianzhousaurus sinensis.[1]

Some researchers have tried to synonymize Qianzhousaurus with Alioramus,[8] but many others maintain that they are separate genera. Alioramini is usually considered to be a part of the Tyrannosaurinae subfamily within the Tyrannosauridae family; however, some phylogenetic studies find them to be outside the Tyrannosauridae. Alioramini is a part of Tyrannosaurinae, based on several features. These features include a maxillary process of the premaxilla that points upwards; the deep joint surface in the maxilla conceals certain features related to tooth roots; the particular shape of the lacrimal, mostly hidden from view; and an ectopterygoid with a pneumatic recess that possesses a distinctive round or triangular shape.[9] Dryptosaurus, usually placed as a basal eutyrannosaur is found to be a member of Alioramini under a Bayesian analysis in 2016 Carr and Brusatte paper, but this is the only time in the 2016 paper an analysis yields such a result with the rest of the paper placing Dryptosaurus in its usual position.[10]

Below is a cladogram showing the placement of Alioramini within the Tyrannosaurinae, according to Brusatte & Carr (2016).[10]

Tyrannosauridae

Another cladogram showing the relationships of Alioramini by Loewen et al. (2013) places Alioramini outside of the Tyrannosauridae.[11]

Tyrannosauroidea

Paleobiology

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Life restoration of Alioramus in the paleoenvironments of the Nemegt Formation

Alioramins, due to their relatively gracile build and long snouts, were likely specialized in hunting small-sized prey with quick turns. Such feeding strategies may have avoided direct competition with other tyrannosaurids. In contrast to robust tyrannosaurids, whose juveniles underwent drastic changes in their skull, the characteristic elongated snout morphology of alioramins was likely maintained throughout their ontogeny (growth).[12][13]

Studies on the morphology of tyrannosauroid skulls published in August, 2024 suggest that alioramins experienced lower amounts of stress in their skulls when biting and feeding. The same study indicates that these theropods likely did not utilize puncture-and-pull feeding like larger tyrannosaur genera such as Tyrannosaurus and Daspletosaurus.[14]

See also

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References

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  1. ^ a b c Lü, J.; Yi, L.; Brusatte, S. L.; Yang, L.; Li, H.; Chen, L. (2014). "A new clade of Asian Late Cretaceous long-snouted tyrannosaurids" (PDF). Nature Communications. 5 (3788): 3788. Bibcode:2014NatCo...5.3788L. doi:10.1038/ncomms4788. PMID 24807588.
  2. ^ Holtz, Thomas R. (2004). "Tyrannosauroidea". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.). The Dinosauria (Second ed.). Berkeley: University of California Press. pp. 111–136. ISBN 978-0-520-24209-8.
  3. ^ Molina-Pérez, R.; Larramendi, A. (2016). "List of Theropods". Dinosaur Facts and Figures: The Theropods and Other Dinosauriformes. Princeton: Princeton University Press. p. 266. doi:10.1515/9780691190594. ISBN 9788416641154. JSTOR j.cdb2hnszb. S2CID 198839986.
  4. ^ Xing, L.; Niu, K.; Lockley, M. G.; Klein, H.; Romilo, A.; Scott Persons IV, W.; Brusatte, S. L. (2022). "A probable tyrannosaurid track from the Upper Cretaceous of southern China". Science Bulletin. 64 (16): 1136−1139. Bibcode:2019SciBu..64.1136X. doi:10.1016/j.scib.2019.06.013. hdl:20.500.11820/05d88bb3-8039-426c-88bf-cfb6f08608e7. PMID 36659682. S2CID 197083656.
  5. ^ Li, Daqing; Norell, Mark A.; Gao, Ke-Qin; Smith, Nathan D.; Makovicky, Peter J. (2009). "A longirostrine tyrannosauroid from the Early Cretaceous of China". Proceedings of the Royal Society B: Biological Sciences. 277 (1679): 183–190. doi:10.1098/rspb.2009.0249. PMC 2842666. PMID 19386654.
  6. ^ Brusatte, S. L.; Carr, T. D.; Norell, M. A. (2012). "The osteology of Alioramus, a gracile and long-snouted tyrannosaurid (Dinosauria, Theropoda) from the late Cretaceous of Mongolia". American Museum Novitates (366): 1−197. doi:10.1206/770.1. hdl:2246/6162. S2CID 84550111.
  7. ^ Olshevsky, G. (1995). "The origin and evolution of the tyrannosaurids, Part 2". Kyoryugaku Saizensen. 10: 75–99.
  8. ^ Paul, Gregory S. (2016). The Princeton field guide to dinosaurs. Princeton field guides (2nd ed.). Princeton: Princeton university press. ISBN 978-0-691-16766-4.
  9. ^ Brusatte, Stephen L.; Norell, Mark A.; Carr, Thomas D.; Erickson, Gregory M.; Hutchinson, John R.; Balanoff, Amy M.; Bever, Gabe S.; Choiniere, Jonah N.; Makovicky, Peter J.; Xu, Xing (2010-09-17). "Tyrannosaur Paleobiology: New Research on Ancient Exemplar Organisms". Science. 329 (5998): 1481–1485. Bibcode:2010Sci...329.1481B. doi:10.1126/science.1193304. ISSN 0036-8075. PMID 20847260.
  10. ^ a b Brusatte, Stephen L.; Carr, Thomas D. (2016-02-02). "The phylogeny and evolutionary history of tyrannosauroid dinosaurs". Scientific Reports. 6 (1): 20252. Bibcode:2016NatSR...620252B. doi:10.1038/srep20252. ISSN 2045-2322. PMC 4735739. PMID 26830019.
  11. ^ Loewen, Mark A.; Irmis, Randall B.; Sertich, Joseph J. W.; Currie, Philip J.; Sampson, Scott D. (2013-11-06). "Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans". PLOS ONE. 8 (11): e79420. Bibcode:2013PLoSO...879420L. doi:10.1371/journal.pone.0079420. ISSN 1932-6203. PMC 3819173. PMID 24223179.
  12. ^ Brusatte, S. L.; Carr, T. D.; Erickson, G. M.; Bever, G. S.; Norell, M. A. (2009). "A long-snouted, multihorned tyrannosaurid from the Late Cretaceous of Mongolia". Proceedings of the National Academy of Sciences. 106 (41): 17261–17266. doi:10.1073/pnas.0906911106. PMC 2765207. PMID 19805035.
  13. ^ Foster, W.; Brusatte, S. L.; Carr, T. D.; Williamson, T. E.; Yi, L.; Lü, J. (2022). "The cranial anatomy of the long-snouted tyrannosaurid dinosaur Qianzhousaurus sinensis from the Upper Cretaceous of China". Journal of Vertebrate Paleontology. 41 (4): e1999251. doi:10.1080/02724634.2021.1999251. hdl:20.500.11820/85571b5c-0e63-4caa-963a-f16a42514319. S2CID 246799243.
  14. ^ Rowe, Andre J.; Rayfield, Emily J. (September 2024). "Morphological evolution and functional consequences of giantism in tyrannosauroid dinosaurs". iScience. 27 (9): 110679. doi:10.1016/j.isci.2024.110679. ISSN 2589-0042. PMC 11387897.
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