page_title: Alectrosaurus
section_title: Discovery and naming
hierarchical_section_title: Alectrosaurus / Discovery and naming
caption_attribution_description: English: Excavating the hind limb of Alectrosaurus olseni, field No. 136, about 200 yards south of the camp at Iren Dabasu Telegraph Station in Mongolia, 1923.
context_page_description: Alectrosaurus is a genus of tyrannosauroid theropod dinosaur that lived in Asia during the Late Cretaceous period, about some 96 million years ago in what is now the Iren Dabasu Formation. It was a medium-sized, moderately-built, ground-dwelling, bipedal carnivore, estimated at 5 to 6 m with a body shape similar to its much larger advanced relative, Tyrannosaurus. Alectrosaurus was a very fast running tyrannosauroid as indicated by the elongated hindlimbs that likely filled the niche of a pursuit predator, a trait that seems to be lost by the advanced and robust tyrannosaurids.
context_section_description: In 1923, the Third Asiatic Expedition of the American Museum of Natural History, led by chief paleontologist Walter W. Granger was hunting for dinosaur fossils in Mongolia. On April 25, assistant paleontologist George Olsen excavated and recovered the holotype AMNH 6554, a nearly complete right hindlimb. This included a virtually complete right hindlimb with some elements from the left pes and two manual unguals. On May 4, Olsen discovered another specimen approximately 30 m (98.4 ft) away from his first find, catalogued as AMNH 6368. This specimen included a right humerus, two incomplete manual digits, four fragmentary caudal vertebrae, and other two or three unspecified elements that were discarded due to badly preservation. These discoveries were made at the Iren Dabasu Formation in what is now the Inner Mongolia Autonomous Region (Nei Mongol Zizhiqu) of China.
  Both genus and species were formally described and named by the American paleontologist Charles Gilmore in 1933. The generic name, Alectrosaurus, can be translated as "alone lizard" or "mateless lizard", derived from the Greek words ἄλεκτρος (meaning alone or unmarried) and σαῦρος (meaning lizard). The specific name, olseni, is in honor of George Olsen, who discovered the first specimens.
  Since then, more material has been referred to Alectrosaurus. Possible findings of two additional specimens at the Bayan Shireh Formation were reported and described by the Mongolian paleontologist Altangerel Perle in 1977. The specimen IGM 100/50 consists of a partial maxilla, scapulocoracoid and manual ungual, and specimen IGM 100/51 compromises a fragmentary skull with lower jaws and other elements, incomplete ilium, and metatarsals of the right foot. These fossils were found in Outer Mongolia. Iren Dabasu and Bayan Shireh dinosaur faunas are very similar, so it is not surprising that a species of Alectrosaurus would be found there. Furthermore, several partial skeletons found in both Inner and Outer Mongolia might belong to Alectrosaurus. Alexander Averianov and Hans-Dieter Sues 2012 have estimated that the Iren Dabasu Formation is Santonian in age, correlating the Upper Bayan Shireh Formation. Van Itterbeeck et al. 2005 suggested that the Iren Dabasu Formation is probably Campanian-Maastrichtian in age and possibly correlated with the Nemegt Formation.
  Near the holotype, the specimen AMNH 6556 was found in the same strata but at different points also in 1923. It consists of premaxillary and lateral teeth, incomplete left lacrimal, maxillary process of the left jugal, partial right quadratojugal, jugal process of the right ectopterygoid and the quadrate ramus to the right pterygoid. Although the specimen seems to represent a smaller individual. Its affinity to Alectrosaurus is somewhat unresolved since the specimen lacks hindlimb material, making direct comparisons with Alectrosaurus quite complicated.
caption: Excavation of the right hindlimb of A. olseni specimen AMNH 6554, in 1923. George Olsen on the right
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