Alioramus
From Latin 'alio' meaning 'different' and 'ramus' meaning 'branch', meaning 'different branch', referring to its divergent position within the tyrannosaurid family tree.
Alioramus is a genus of tyrannosaurid theropod dinosaurs from the Late Cretaceous period of Asia. It currently contains two species. The type species, A. remotus is known from a partial skull and three foot bones recovered from the Mongolian Nemegt Formation, which was deposited in a humid floodplain. These remains were named and described by Soviet paleontologist Sergei Kurzanov in 1976. A second species, A. altai, known from a much more complete skeleton also from the Nemegt Formation, was named and described by Stephen L. Brusatte and colleagues in 2009. Its relationships to other tyrannosaurid genera were at first unclear, with some evidence supporting a hypothesis that Alioramus was closely related to the contemporary species Tarbosaurus bataar. However, the discovery of Qianzhousaurus indicates that it belongs to a distinct branch of tyrannosaurs, namely the tribe Alioramini.
Diagnosis
- Skull very low and elongated, with a skull length-to-height ratio of about 3.6 (vs. 2.1-2.5 in other tyrannosaurids)
- Nasals bearing well-developed separate crests about 1-1.5 cm high
- Second antorbital fenestra displaced anteriorly, reaching the level of the anterior end of the 5th tooth
- High tooth count: 16 maxillary teeth and 18 dentary teeth
- Labial foramina arranged in two rows on the jaws
- Teeth narrow and oval in transverse section, slightly compressed at mid-length
Species (2)
Alioramus remotus Kurzanov, 1976
Type species
From Latin 'remotus' meaning 'removed', reflecting Soviet paleontologist Sergei Kurzanov's belief that this dinosaur was far removed from other members of the tyrannosaurid family.
- Holotype
- PIN 3141/1 , Paleontological Institute, Russian Academy of Sciences
- Material
- Incomplete skull, four middle dorsal vertebrae, proximal parts of several ribs, incomplete tibia and fibula, and left pes
- Horizon
- lower Nemegt Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
- Locality
- Nogoon Tsav, Bayankhongor, Mongolia
Alioramus altai Brusatte et al., 2009
Altai, in reference to the Altai mountain range, a prominent topographic feature of southern Mongolia
- Holotype
- IGM 100/1844 , Paleontological Center, Mongolian Academy of Sciences
- Material
- Disarticulated skull; cervical series; some dorsal, sacral, and caudal vertebrae; ribs; chevrons; right ilium; both ischia; both femora; right crus, tarsus, and metatarsus; some pedal elements
- Horizon
- Nemegt Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
- Locality
- Tsagaan Khushuu, Ömnögovi, Mongolia
- Diagnosis
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- Accessory pneumatic fenestra posterodorsal to the promaxillary fenestra
- Maxillary fenestra strongly elongate (length:depth ratio 1.9)
- Conical, dorsally projecting cornual process (horn) on the lacrimal
- Laterally projecting horn (hornlet) on the jugal
- 20 dentary alveoli (18 in A. remotus)
- Posterior margin of the iliac postacetabular process projects posterodorsally
References
- Kurzanov, S. M. (1976). Noviy pozdnemelovoy karnozavr is Nogon-Tsava, Mongoliya [A new Late Cretaceous carnosaur from Nogon-Tsav, Mongolia]. Paleontology and Biostratigraphy of Mongolia. The Joint Soviet-Mongolian Paleontological Expedition, Transactions 3: 93-104. kurzanov1976b
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Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.
Source of the appearance features.
paul2024a - 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. Proceedings of the National Academy of Sciences. doi:10.1073/pnas.0906911106 brusatte2009b
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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. Bulletin of the American Museum of Natural History 366: 1-197. American Museum of Natural History. doi:10.1206/770.1
Monographic redescription of the A. altai holotype (IGM 100/1844) whose diagnosis supersedes the original 2009 description; source of the diagnostic features and material inventory.
brusatte2012b