Maiasaura

*Maiasaura peeblesorum*

* Jurassic Park Institute Artwork
* Timothy Bradley Artwork
* Robert F Walters Artwork

***Maiasaura*** (from the Greek "μαία + σαύρα", meaning "caring mother lizard") is a large duck-billed dinosaur genus that lived in the area currently covered by the state of Montana in the Cretaceous Period, about 77-74 million years ago in what is now The Two Medicine Formation.

The Dinosaur get's it's name from the term good mother lizard. This comes from some various evidence that seems to indicate that they cared for their hatchlings.

## Description

*Maiasaura* was large, growing up to 9 metres (30 ft) long and had the typical hadrosaurid flat beak and a thick nose. It had a small, spiky crest in front of its eyes. The crest may have been used in headbutting contests between males during the breeding season.

This dinosaur was an herbivore. It walked both on two or four legs and seemed to have no defense from predators, though its heavy muscular tail and its herd behaviour both could have been one. These herds were quite large and could have been made up of as much as 10,000 individuals. *Maisaura* lived in an inland habitat.

## History

*Maiasaura* was discovered by Laurie Trexler and described by dinosaur paleontologist Jack Horner (paleontologic advisor for the *Jurassic Park* movies) and Robert Makela. He named the dinosaur after Marion Brandvold's discovery of a nest with remains of eggshells and babies too large to be hatchlings. These discoveries led to others, and the area became known as "Egg Mountain", in rocks of the Two Medicine Formation near Choteau in western Montana. This was the first proof of giant dinosaurs raising and feeding their young. Over 200 specimens, in all age ranges, have been found. The announcement of *Maiasaura's* discovery attracted renewed scientific interest to the Two Medicine Formation and many other new kinds of dinosaurs were discovered as a result of the increased attention. Choteau *Maiasaura* remains are found in higher strata than their Two Medicine River counterparts.

## Classification

The closest phylogenetic relation of the genus Maiasaura seems to fall with Brachylophosaurus . To reflect on this, both are in the same tribe, and are thus differentiated from the other components of this subfamily: Aralosaurus, Hadrosaurus and Gryposaurus .

Recently, along with Brachylophosaurus and Acristavus, Maiasaura was located in a new clade called Brachylophosaurini .

## Paleobiology

### Reproduction

*Maiasaura* lived in herds and it raised its young in nesting colonies. The nests in the colonies were packed close together, like those of modern seabirds, with the gap between the nests being around 23 ft; less than the length of the adult animal. The nests were made of earth and had 30 to 40 eggs laid in a round or coiled pattern. The eggs were about the size of ostrich eggs.The eggs were incubated by the heat caused by rotting vegetation placed into the nest by the parents, rather than a parent sitting on the nest. Fossils of baby *Maiasaura* show that, when they hatched, their legs were not fully developed and thus they could not leave the nest. Fossils also show that their teeth were partly worn, which means that the adults brought food to the nest.The hatchlings grew from a size of 16 to 58 inches long in the span of their first year. At this point, or perhaps after another year, the animal left the nest. This high rate of growth may mean they were warm blooded. The hatchlings had different facial proportions from the adults, with larger eyes and a shorter snout. These traits are associated with cuteness and are common in animals that depend on their parents when they are young.

### Contemporaries

In the Two Medicine Formation, *Maiasaura* lived alongside the tyrannosaur *Daspletosaurus*, the oviraptorosaur *Chirostenotes*, a troodontid (possibly *Stenonychosaurus*), the dromaeosaurs *Bambiraptor* and *Saurornitholestes*, the enantiornithe bird *Avisaurus*, the nodosaur *Edmontonia*, the ankylosaur *Euoplocephalus*, the ceratopsids *Achelousaurus*, *Brachyceratops*, *Einiosaurus*, and *Styracosaurus ovatus*, the hypsilophodont *Orodromeus*, and the hadrosaurids *Hypacrosaurus stebingeri* and *Prosaurolophus*. *Hypacrosaurus* coexisted with *Maiasaura* for some time, as *Hypacrosaurus* remains have been found lower in the Two Medicine Formation than was earlier known. The discovery of *Gryposaurus latidens* in *Maiasaura's* range has shown that the border between theorized distinct faunas in the upper and middle is less distinct than once thought. There seems to be a major variation in ornithischian taxa after the appearance of *Maiasaura* within the Two Medicine Formation. The close examination of strata found along the Two Medicine River (which exposes the entire upper half of the Two Medicine Formation) indicates that the apparent variation was a real event rather than from preservational biases.

## JPInstitute.com Description

Maiasaura is one of the most famous of the duck-billed dinosaurs because it proved to many scientists that dinosaurs had nests, nesting grounds and took care of their young. It was a medium-sized member of the duck-billed hadrosaur family, which included Parasaurolophus and Lambeosaurus. More than 200 specimens of this dinosaur have been discovered, making it one of the best known. What is especially interesting is that many babies and young adults have been found.

Jack Horner's discovery of Maiasaura set the world of paleontology on fire and also rekindled public interest in dinosaurs. Until its discovery, most scientists thought that dinosaurs laid their eggs, left them on their own to hatch and then let the babies fend for themselves. The nests Horner discovered seem to clearly show evidence of babies that remained in the nest for some time and would have been cared for by adults.

Apart from the spectacular nature of its discovery, and the number of specimens, Maiasaura was a fairly typical, mid-sized hadrosaur. It had no real crest, but it did have a small spike-like crest in front of its eyes.

## Links

http://web.archive.org/web/20040419173620fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_maias.html

## References

1. ↑ "Maiasaura," Dodson, et al.(1994); pages 116-117.
2. ↑ "Judithian Climax," Lehman (2001); page 315.
3. ↑ "Maiasaura," Dodson, et al.(1994); pages 116-117.
4. ↑ Horner and Gorman (1988).
5. ↑ "Introduction," Trexler (2001); pages 299-300.
6. ↑ "Faunal Turnover, Migration, and Evolution," Trexler (2001); page 304.
7. ↑ Gates, T.A.; Horner, J.R.; Hanna, R.R.; and Nelson, C.R. (2011). «New unadorned hadrosaurine hadrosaurid (Dinosauria, Ornithopoda) from the Campanian of North America». *Journal of Vertebrate Paleontology* **31** (4): pp. 798-811. doi:10.1080/02724634.2011.577854.
8. ↑ Palmer (1999); page 148.
9. ↑ "Maiasaura," Dodson, et al.(1994); pages 116-117.
10. ↑ Weishampel, et al. (2004); pages 517–606.
11. ↑ Faunal Turnover, Migration, and Evolution," Trexler (2001); page 306