a carnivorous tyrannosauroid theropod dinosaur from the Late Cretaceous of Mongolia.
Pronunciation: ah-LEK-tro-SOR-us
Meaning: Mateless lizard
Author/s: Gilmore (
1933)
Synonyms: None known
First Discovery: Inner Mongolia, China
Acta Ordinal: #172
Alectrosaurus olseni
When Charles Whitney Gilmore clapped eyes on the remains that would become Alectrosaurus in 1933, he was struck by the unusually long upper arm and the enormously large claws — features so unlike any known Upper Cretaceous "deinodont" that they "at once set the animal off as a new type of theropod dinosaur". As luck would have it, he was half right. "Deinodontidae" had already been sunk as a synonym of Tyrannosauridae more than a decade before that, and the impressive clawed forelimb on which he based his claim actually belongs to an as-yet unidentified member of Therizinosauroidea. But Alectrosaurus itself was indeed a new type of theropod dinosaur, of the smooth-snouted tyrannosauroid variety, though one teetering on the brink of Tyrannosauridae proper.
(Olsen's Mateless lizard)Etymology
Alectrosaurus is derived from the Greek "alektros" (mateless, unmarried, or alone) and "sauros" (lizard). Confusion often stems from the similar Greek "alektor" (rooster) but
Alectrosaurus was definately no "rooster lizard!"
The
species epithet,
olseni, is a nod to discoverer George Olsen.
ZooBank registry:
urn:lsid:zoobank.org:act:1D8F7D04-1197-4346-B071-040969B5BAE4.
Discovery
The first fossils of
Alectrosaurus were recovered from the Iren Dabasu Formation (also known as Iren Nor, which roughly translates as "colorful salt lake") of Nei Mongol Zizhiqu (Inner Mongolia), China, by George Olsen during the third AMNH Central Asiatic Expedition, led by Walter Granger, on April 25th, 1923. The lectotype (AMNH 6554) consists of three left metatarsals, a right hindlimb—proportionately odd for a "tyrant lizard", as the thigh, shin, and foot were all roughly the same length—and, tentatively, a couple of hand claws.
Olsen found a second specimen (AMNH 6368: a partial arm) approximately 30 meters away from the first, on May 4th, 1923, that he assigned as co-type, but it belongs to something else entirely. Likewise, remains from Baishin Tsav, Mongolia (MPC-D 100/50 and MPC-D 100/51), described by Perle in 1977; Dhzarakuduk, Uzbekistan, described by Nessov in 1995; and Tsagaan Teg, Mongolia (MPC-D 102/4), described by Tsuihiji
et al. in 2012—which have all been assigned, or at least linked, to
Alectrosaurus—likely belong elsewhere.
A partial skull (AMNH 6266) from close to the holotype site, collected in 1922 by Granger and catalogued as "
Deinodon? sp." but never documented in the literature until 100 years later, may belong to
Alectrosaurus, but it lacks any elements that can be directly compared to confirmed
Alectrosaurus fossils.
In 2026, Voris
et al. named MPC-D 100/50 as the holotype of
Khankhuuluu mongoliensis, and referred MPC-D 100/51 and MPC-D 102/4 to it.
• Matthew WD and Brown B (1922) "The family Deinodontidae, with notice of a new genus from the Cretaceous of Alberta".
Bulletin of the American Museum of Natural History, 46(6): 367-385.
• Gilmore CW (1933) "
On the dinosaurian fauna of the Iren Dabasu Formation".
Bulletin of the American Museum of Natural History, 68(2-3): 23-78.
• Perle A (1977) "O pervoy nakhodke Alektrozavra (Tyrannosauridae, Theropoda) iz pozdnego Mela Mongolii" [On the first discovery of
Alectrosaurus (Tyrannosauridae, Theropoda) in the Late Cretaceous of Mongolia].
Problemi geologii mongolii [Problems of Mongolian Geology] / Shinzhlekh Ukhaany Akademi Geologiin Khureelen, 3(3):104-113 3(3): 104–113.
• Mader BJ and Bradley RL (1989) "A redescription and revised diagnosis of the syntypes of the Mongolian tyrannosaur
Alectrosaurus olseni".
Journal of Vertebrate Paleontology, 9(1): 41-55. DOI: 10.1080/02724634.1989.10011737.
• Nessov LA (1995) "
Dinosaurs of the Northern Eurasia: new data about assemblages, ecology and paleobiogeography".
St. Petersburg State University, Institute of the Earth Crust, St.Petersburg: 1-156. DOI: 10.30906/1026-2296-1996-3-2-206-208. [English translation by Tatayana Platonov and Hans-Dieter Sues.]
• Holtz TR jr. (2001) "The phylogeny and taxonomy of the Tyrannosauridae". In Tanke and Carpenter "
Mesozoic Vertebrate Life".
• Currie PJ (2003) "Theropods from the Cretaceous of Mongolia". Page 434-455 in Benton, Shishkin, Unwin and Kurochkin "
The Age of Dinosaurs in Russia and Mongolia".
• Brochu C (2003) "Osteology of Tyrannosaurus rex: Insights from a Nearly Complete Skeleton and High-Resolution Computed Tomographic Analysis of the Skull".
Journal of Vertebrate Paleontology, 22(sup4): 1-138.
DOI: 10.1080/02724634.2003.10010947.
• Holtz jr TR (2004) "Tyrannosauroidea". In "
The Dinosauria: Second Edition".
• Tsuihiji T, Watabe M, Tsogtbaatar K, Barsbold R and Suzuki S (2012) "A tyrannosauroid frontal from the Upper Cretaceous (Cenomanian-Santonian) of the Gobi Desert, Mongolia".
Vertebrata PalAsiatica, 50(2): 102–110.
• Carr TD (2023) "A reappraisal of tyrannosauroid fossils from the Iren Dabasu Formation (Coniacian–Campanian), Inner Mongolia, People’s Republic of China".
Journal of Vertebrate Paleontology: e2199817.
DOI: 10.1080/02724634.2023.2199817.
• Voris JT, Zelenitsky DK, Kobayashi Y, Modesto SP, Therrien F, Tsutsumi H, Chinzorig T and Khishigjav Tsogtbaatar K (2025)
"A new Mongolian tyrannosauroid and the evolution of Eutyrannosauria".
Nature, 642: 973–979.
DOI: 10.1038/s41586-025-08964-6.
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To cite this page:
Atkinson, L.
"
ALECTROSAURUS :: from DinoChecker's dinosaur archive".
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