Alectrosaurus

*Alectrosaurus olseni*

*Alectrosaurus* (Greek, "alone lizard") was a tyrannosauroid from Late Cretaceous China and Mongolia, around 83 to 74 mya. It was a small tyrannosauroid; which was 16.4 feet (5 meters) long, 8 feet (2.5 meters) in height and weighed 420 kilograms. It is only known from a partial skeleton, and is likely a primitive fast-running tyrannosauroid. Its fossil was found in the Gobi Desert in Mongolia. It had sharp teeth, and was a bipedal carnivore. It was named after a mythical deity, Alectra, by C. W. Gilmore in 1933. The genus' only and type species is *Alectrosaurus olseni*.

## Etymology

The generic name *Alectrosaurus* can be translated as "alone lizard," and is derived from the Greek words alektros and sauros ("lizard"). The meaning of the generic name is troublesome because the Greek work "alektros" (αλεκτρος) has also been alternatively translated as "unmarried" and even "rooster". At the time of its discovery, it was unlike any other Asian carnivore known, which may suggest that Gilmore selected a Greek word that reflected the meaning of alone. There is one named species (*A. olseni*), which is named in honor of George Olsen, who discovered the first specimens. Both genus and species were described and named by American paleontologist Charles Gilmore in 1933.

## Discovery and naming

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 25th, assistant paleontologist George Olsen recovered the holotype (AMNH 6554), or name-bearing specimen, of *Alectrosaurus*, a nearly complete right hindlimb. This included the distal end of the right femur, the tibia, the fibula, the astragalus, the calcaneum, an incomplete right pes, three metatarsals of the left hind foot, two manual unguals, a manus, and the distal end of the pubis known as the pubic foot. On May 4th, Olsen discovered AMNH 6368 approximately 30 meters away from his first find. This specimen included a right humerus, two incomplete manual digits, four fragmentary caudal vertebrae, and other poorly preserved material. These discoveries were made at the Iren Dabasu Formation in what is now the Inner Mongolia Autonomous Region (Nei Mongol Zizhiqu) of the People's Republic of China. The age of this geologic formation is not clear, but is commonly cited as the Campanian stage of the Late Cretaceous Period, about 83 to 72 million years ago.

### Referred specimens

More material, including comparable hind limb material as well as skull and shoulder elements, has been referred to *Alectrosaurus*. These fossils were found in the Bayan Shireh Formation of Outer Mongolia, a formation which is also of uncertain age. It may possibly extend into the early Campanian, but recent estimates suggest it was deposited from Cenomanian through Santonian times. Iren Dabasu and Bayan Shireh dinosaur faunas are similar, but van Itterbeecka et al. claimed that the Iren Dabasu is probably Campanian-Maastrichtian in age and possibly correlated with the Nemegt Formation, so it is not surprising that a species of *Alectrosaurus* would be found there. Furthermore, several more partial skeletons may have been found in both Inner and Outer Mongolia.

## Description

*Alectrosaurus* was a species of medium-sized, moderately built theropod. The length of its tibia (lower leg bone) and femur (thighbone) are very close, in contrast to the majority of other tyrannosauroids, where the tibia is longer. The hind foot (and ankle) are also closer in size to the tibia than in most other tyrannosauroids, where the hind foot is usually longer.

## Classification

In 1933, Charles Gilmore examined the available material and concluded that AMNH 6554 and AMNH 6368 were syntypes belonging to the same genus. He based this on his observation that the manual unguals from both specimens were morphologically similar. Observing similarities with the hindlimbs of specimen AMNH 5664 *Gorgosaurus sternbergi*, he classified this new genus as a "Deinodont", a term that is now considered equivalent to tyrannosaurid. Due to its fragmentary nature, there is presently very little confidence in restoring its relationships with other tyrannosauroids and many recent cladistic analyses have omitted it altogether. One study recovered *Alectrosaurus* at no less than eight equally parsimonious positions in a tyrannosauroid cladogram.

*Alectrosaurus* was originally characterized as a long-armed theropod Dinosaur, but Mader and Bradley in 1989 observed that the forelimbs (AMNH 6368) did not belong to this individual and assigned them to the Segnosauridae. The remaining material, AMNH 6554 represents the hind limb of a true tyrannosauroid, and were assigned as the lectotype for *Alectrosaurus* olseni. Mader and Bradley also described and assigned caudal vertebrae AMNH 21784 to this genus. These researchers concluded that *Alectrosaurus* was closely related to *Maleevosaurus novojilov* based on hind limb proportions.

## Paleobiology

The hindlimb of the specimen AMNH 6554 is notable for the particular elongated digits and metatarsals, differing from other tyrannosauroids. These traits are found in terrestrial runner birds, suggesting that Alectrosaurus was suited as a fast-running tyrannosauroid dinosaur with well developed hindlimbs; probably a pursuit predator. This interpretation is consistent with the results obtained in the limb proportion analysis performed by Scott Persons IV and Currie in 2016. By comparing the limbs of numerous theropods they noted that most tyrannosauroids were highly cursorial and leggy animals, with the exception of giant and stocky-legged forms such as Tarbosaurus or Tyrannosaurus. Alectrosaurus was recovered with a relatively high CLP (Cursorial-limb-proportion) score at 16.5, higher than most carnosaurs. In 2001, a study conducted by Bruce Rothschild and colleagues, examined 23 foot bones referred to Alectrosaurus for signs of stress fractures, but none were found.

## JPInstitute.com Description

Alectorsaurus is another Asian ancestor of Tyrannosaurus.

Alectrosaurus was only about half the size of T. rex and it was more lightly built - closer to Albertosaurus. It was about 20 feet long and had a mouth full of large, razor-sharp teeth that would have made this a pretty ferocious animal.

Alectrosaurus was discovered in 1923 during one of the American Museum of Natural History expeditions to China led by Roy Chapman Andrews. It was described in 1933 and re-described in 1989. It is considered to be a typical tyrannosaur family member and may in fact be a direct ancestor of Tyrannosaurus bataar.

Not much of this dinosaur has been found, and some of the fossils that were originally thought to belong to Alectrosaurus were later determined to belong to another dinosaur.

## Links

http://web.archive.org/web/20040214170203fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_alect.html