Bactrosaurus

*Bactrosaurus johnsoni*

Bactrosaurus, meaning "Club lizard," is a genus of herbivorous dinosaur that lived in east China during the late Cretaceous, about 70 mya. The position *Bactrosaurus* occupies in the Cretaceous makes it one of the earliest known hadrosaurs, and although it is not known from a full skeleton, *Bactrosaurus* is one of the best known of these early hadrosaurs, making its discovery a significant finding.

*Bactrosaurus* was originally described as lacking a crest, which would be typical for an iguanodont, but anomalously primitive for a lambeosaurine like Velafrons. However subsequent study of *Bactrosaurus* remains uncovered pieces of what appear to be the base of an incompletely preserved crest.

## Discovery

The first *Bactrosaurus* remains recovered from the Iren Dabasu Formation in the Gobi Desert of China were composed of partial skeletons of six individual *B. johnsoni*. The specimens collected appear to come from a variety of age groups, from individuals that may be hatchlings to full-sized adults. The fossils were described in 1933 by Charles W. Gilmore, who named the new animal *Bactrosaurus*, or "club lizard", in reference to the large club-shaped neural spines projecting from some of the vertebrae. The Iren Dabasu Formation has been dated to the Cenomanian stage, around 95.8 ± 6.2 million years ago.

No complete remains have yet to be uncovered, but *Bactrosaurus* is still better known than most of the early hadrosaurs. Known parts of the anatomy of *Bactrosaurus* include the limbs, pelvis, and most of the skull (although the crest is notably absent).

"Bakesaurus" is an informal name based on a maxilla from the Majiacun Formation of China assigned to *Bactrosaurus* in 2001. The *nomen nudum* was created and pictured in a Chinese-language book by Zhou (2005) and first surfaced on the Internet during February 2006 when it was mentioned on the *Dinosaur Mailing List* by Jerry D. Harris.

## Description

A typical *Bactrosaurus* would have been 6 meters (20 ft) long and 2 metres (6.6 ft) high when standing on all fours, and weighed 1.1 to 1.5 tonnes (2,400 to 3,300 lb), with an 80 centimeters (2.6 ft) femur.

It was an early relative of *Lambeosaurus* and shows a number of iguanodont-like features, including three stacked teeth for each visible tooth, small maxillary teeth, and an unusually powerful build for a hadrosaur. It shows features intermediate between those of the two main hadrosaurid groups. Its femur measured 80 centimetres (2.6 ft) long, and may represent an ancestral form that evolved from an earlier iguanodontid dinosaur.

*Bactrosaurus* was originally thought to be a lambeosaurine hadrosaurid, supposedly the oldest and most primitive known, and its crestless head was seen as an anomaly. A 1990 popular book suggested that it had an incompletely preserved crest, but recent studies place *Bactrosaurus* as a more basal hadrosauromorph. Basal members do not preserve hollow crests, so *Bactrosaurus* itself is likely to be crestless.

## Paleobiology

In 2003, evidence of tumors, including hemangiomas, desmoplastic fibroma, metastatic cancer, and osteoblastoma was discovered in fossilized *Bactrosaurus* skeletons. Rothschild *et al.* tested dinosaur vertebrae for tumors using computerized tomography and fluoroscope screening. Several other hadrosaurids, including *Brachylophosaurus*, *Gilmoreosaurus*, and *Edmontosaurus*, also tested positive. Although more than 10,000 fossils were examined in this manner, the tumors were limited to *Bactrosaurus* and closely related genera. The tumors may have been caused by environmental factors or genetic propensity.

## JPInstitute.com Description

Bactrosaurus was a smaller duckbill dinosaur that lived in what is now Asia and Russia.

This was a very early ancestor of Lambeosaurus, another duckbill. Like its relatives, Bacrtrosaurus was a plant-eater that had many hundreds of teeth, long back legs and short front legs, and a beak on the front of its mouth for cutting and tearing tough plants.

Bactrosaurus was more powerfully built than most other hadrosaurs and was very heavy for its size. It almost appears to be a transitional animal linking iguanodonts with hadrosaurs, and researchers have noted that it almost looks more like an iguanodont than a hadrosaur.

## Links

https://web.archive.org/web/20031008030303fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_bactr.html

https://web.archive.org/web/20080502014813/http://kids.yahoo.com/dinosaurs/344--Bactrosaurus

## References

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