Maiasaura

Maiasaura
Temporal range: Late Cretaceous (Santonian – Campanian),
Mounted cast, Brussels Natural History Museum
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Ornithopoda
Family: †Hadrosauridae
Subfamily: †Saurolophinae
Tribe: †Brachylophosaurini
Genus: †Maiasaura
Horner & Makela, 1979
Type species
†Maiasaura peeblesorum
Horner & Makela, 1979

Maiasaura (from Greek: μαῖα,[a] lit. 'good mother' and Greek: σαύρα, the feminine form of saurus, lit. 'reptile') is a large herbivorous saurolophine hadrosaurid ("duck-billed") dinosaur genus that lived in the area currently covered by the state of Montana and the Canadian province of Alberta,[1] in the Upper Cretaceous (mid to late Campanian), from 86.3 to 70.6 million years ago.[2]

The species description of Maiasaura first came in 1979 from paleontologists Jack Horner and Bob Makela following the discovery of a site located South of Choteau, Montana. They named the new genus and species Maiasaura peeblesorum in which the given genus name Maiasaura, commonly translated as 'good mother lizard', refers to the conclusion of Makela and Horner, still accepted today, that at least this species of dinosaur took care of their offspring keeping temporarily the hatchlings at the same nests where they had hatched. A discovery of capital importance in the history of paleontology and dinosaur research, the first instance of parental and social behavior in dinosaurs. Collected data at the site allowed for interpretations such as that Maiasaura fed its young while they were in the nest. This was completely new in the late 1970s and in complete contradiction with the at-the-time common idea of dinosaurs being cold-blooded animals laying eggs and abandoning them immediately after. The Makela-Horner discovery occurred during the years of the so-called dinosaur renaissance, which had started in the mid-1960s. Further work in the area led to the discovery of more dinosaur eggs, leading to the area being named "Egg Mountain".

Maiasaura, whose bones have been found by hundreds in the state of Montana, has been chosen as Montana's state fossil.

Description

Skull cast, Royal Ontario Museum
Size comparison with human

Maiasaura peeblesorum were large, attaining a maximum known length of about 9 metres (30 ft) and a body mass is measured approximately up to 4 metric tons (4.4 short tons).[3] They had a large "duck-billed" mouth structure and rows of hundreds of teeth, typical of hadrosaurids. Since hadrosaurids have very similar post-cranial body plans,[4] the distinguishing characteristic of Maiasaura peeblesorum is a prominent short, solid crest-like structure situated between their eyes. This crest may have been used in headbutting contests between males during the breeding season.

Maiasaura were herbivorous. They were capable of walking both on two (bipedal) or four (quadrupedal) legs. Studies of the stress patterns of healed bones show that young juveniles under four years old walked mainly bipedal, switching to a mainly quadrupedal style of walking when they grew larger.[5] Maiasaura, like most other hadrosaurs, possessed little in the way of obvious weaponry, though likely could defend themselves with kicks, stomps, or their muscular tails. It is likely that they primarily resorted to fleeing in the face of danger, using the vast sizes of their herds to be less likely to be targeted. Mass bone beds discovered in the Two Medicine Formation show that herds could be extremely large and comprise as many as 10,000 individuals.[6] Hundreds of specimens have been found throughout all stages of life, allowing for M. peeblesorum to be used for understanding how hadrosaurids grew.[7] Maiasaura peeblesorum lived in a terrestrial habitat.

Discovery

Map of Brachylophosaurus specimen discovieres in Alberta and Montana. The first remains of Maiasaura have been found south of Choteau, visible on the map.

For years until the 1960s and 1970s, anyone who has traveled through the area south of Choteau, Montana might have come across Maiasaura remains, whether such remains have been or have not been attributed to a dinosaurian origin.

The first people who are confirmed as having found Maiasaura remains laying on the "Egg Mountain" area (as it is called today), are two homestead families of Bynum, Montana: the Brandvolds and the Trexlers. Marion Kathryn Brandvold (1912-2014, née Nehring), had inherited the "rock shop", Trex Agate Shop, that had been founded in 1937 by her first husband, Clifford "Trex" Trexler (1908-1962). In the years that preceded 1978, she and her second husband, John Brandvold, had been finding small bones and they had been trying to put them together.[8] But in 1978 paleontologists Bob Makela and Jack Horner arrived at the shop in Bynum. Not having found interesting fossils to them, they were about to leave, then Marion Brandvold told them that she had something else. Still at the shop, she showed them two tiny bones that Horner identified as baby hadrosaur bones. They followed her to the Brandvolds' house, where she'd been keeping the remains of at least four individuals in a coffee can. This made Makela and Horner go to the site where these remains were apparently abundant (South of Choteau, Montana), and they discovered nests and eggs of a till-then unknown species of hadrosaur which the next year in 1979 they described and named with the type species being Maiasaura peeblesorum. With time the site earned the name "Egg Mountain", because of the abundance of hadrosaur eggs and eggshell pieces found in it. David Trexler, the second son of Clifford Trexler and Marion, grew up in such a context that he ended up by becoming a paleontologist himself. In 1995 he founded in Bynum The Montana Dinosaur Center.

A skull of Maiasaura, specimen PU 22405 (now in the collections of the Yale Peabody Museum of Natural History as YPM PU 22405 following the transfer of the Princeton University vertebrate paleontology collections), was discovered by Laurie Trexler, spouse of David Trexler, in 1979. It is the specimen that paleontologists Jack Horner and Robert Makela had used the same year as the holotype of the new species. The specific name honours the families of John and James Peebles, on whose land the finds were made.[9][10]

Over 200 specimens, in all age ranges, have been found.[11] The announcement of the discovery of Maiasaura 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.[12] Choteau Maiasaura remains are found in higher strata than their Two Medicine River counterparts.[13]

Classification

Cast of a juvenile skeleton
Life restorations of an adult and juvenile

Maiasaura peeblesorum is in the tribe Brachylophosaurini along with these related taxa:

  • Acristavus gagslarsoni[14]
  • Brachylophosaurus canadensis[15]
  • Ornatops incantatus[16]
  • Probrachylophosaurus bergei[17]

The following cladogram of hadrosaurid relationships was published in 2013 by Albert Prieto-Márquez et al.:[18]

Saurolophinae

Paleobiology

Reconstructed cast by Jack Horner of a Maiasaura emerging from its egg

Maiasaura lived in herds and it raised its young in nesting colonies. The nests in the colonies were packed closely together, like those of modern seabirds, with the gap between the nests being around 7 metres (23 ft); less than the length of the adult animal.[19] The nests were made of earth and contained 30 to 40 eggs laid in a circular or spiral pattern. The eggs were about the size of ostrich eggs and are oval shaped with one slightly more pointed end.[20] Fossilized M. peeblesorum eggs are black in color and have high, prominent ridges on the outer surface.[20]

The eggs were incubated by the heat resulting from rotting vegetation placed into the nest by the parents, rather than a parent sitting on the nest. Upon hatching, fossils of baby Maiasaura show that their legs were not fully developed and thus they were incapable of walking. Fossils also show that their teeth were partly worn, which means that the adults brought food to the nest.[21]

Reconstruction of a nest with eggs

The hatchlings grew from a size of 41 to 147 centimetres (16 to 58 in) 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 be evidence of warm bloodedness. The hatchlings had different facial proportions from the adults, with larger eyes and a shorter snout.[21] These features are associated with cuteness, and commonly elicit care from parents in animals dependent on their parents for survival during the early stages of life. Based on metabolic growth rates and age estimations of juvenile specimens both in and outside the nests, it is suggested that infant Maiasaura were altricial and left the confines of their nests after 40-75 days (or roughly a little over 1-2 months old). These studies also were compared to the related lambeosaurine hadrosaur Hypacrosaurus, for which neonates are also known. These analyses suggest Hypacrosaurus was more precocial than Maiasaura, based on its ecological traits.[22]

Studies led by Holly Woodward, Jack Horner, Freedman Fowler et al. have given insight into the life history of Maiasaura, resulting in what is perhaps the most detailed life history of any dinosaur known, and to which all others can be compared. From a sample of fifty individual Maiasaura tibiae, it was found that Maiasaurs had a mortality rate of about 89.9% in their first year of life. If the animals survived their second year, their mortality rate would drop to 12.7%. The animals would spend their next six years maturing and growing. Sexual maturity was found to occur in their third year, while skeletal maturity was attained at eight years of age. In their eighth year and beyond, the mortality rate for Maiasaura would spike back to around 44.4%. The studies that followed also found that Maiasaurs were primarily bipedal as juveniles, and switched to a more quadrupedal stance as they aged. It was also found that Maiasaura also included rotting wood in its diet, as well that its environment had a long, dry season prone to drought. The results of the study were published in the journal Palaeobiology on September 3, 2015.[23][24]

Diet

A paper from 2007 showed that Maiasaura had a diet consisting of fibrous plants, wood, rotting wood, tree bark, leaves, branches, ferns, angiosperms and possibly grasses. This would imply that Maiasaura was both a browser and a grazer.[25][26][27] Analysis of its dental wear patterns show that juvenile M. peeblesorum exhibited more crush wear than adults, which displayed more shear wear than juveniles. This suggests that adults fed more on tough, fibrous vegetation while juveniles fed more on hard, brittle objects like nuts, seeds, or berries.[28]

Sexual dimorphism

Studies of Maiasaura by Saitta et al., suggest that one sex was roughly 45% larger than the other according to the mathematical analysis known as size statistics. However, it cannot be ascertained at this time whether the larger sex was male or female.[29][30]

Palaeoecology

Illustration of a herd of Maiasaura walking along a creekbed, as found in the semi-arid Two Medicine Formation fossil bed. This region was characterized by volcanic ash layers and conifer, fern and horsetail vegetation.

Maiasaura is a characteristic fossil of the middle portion (lithofacies 4) of the Two Medicine Formation, dated from about 86.3 to 70.6 million years ago.[2] Maiasaura lived alongside the troodontids Stenonychosaurus and Troodon and the basal ornithopod Orodromeus, as well as the dromaeosaurid Bambiraptor and the tyrannosaur Daspletosaurus.[2] Another species of hadrosaurids, referable to the genus Hypacrosaurus, coexisted with Maiasaura for some time, as Hypacrosaurus remains have been found lower in the Two Medicine Formation than was earlier known.[31] The discovery of an additional hadrosaurid, Gryposaurus latidens, in the same range as Maiasaura has shown that the border between hypothesized distinct faunas in the upper and middle is less distinct than once thought.[31] There seems to be a major diversification in ornithischian taxa after the appearance of Maiasaura within the Two Medicine Formation.[31] The thorough examination of strata found along the Two Medicine River (which exposes the entire upper half of the Two Medicine Formation) indicates that the apparent diversification was a real event rather than a result of preservational biases.[31] While Maiasaura has historically been associated with the Two Medicine formation ceratopsid Einiosaurus in a single fauna, this is inaccurate, as Maiasaura is known exclusively from older strata.[32]

In the Oldman Formation of Alberta, Maiasaura lived alongside the ceratopsians Albertaceratops, Anchiceratops, Chasmosaurus, Coronosaurus, and Wendiceratops, as well as the dromaeosaurids Dromaeosaurus, Saurornitholestes, and Hesperonychus, the tyrannosaurid Daspletosaurus, the orodromine thescelosaurid Albertadromeus, the pachycephalosaurs Foraminacephale and Hanssuesia, the ornithomimid Struthiomimus, the other hadrosaurids Brachylophosaurus, Corythosaurus, and Parasaurolophus, and the ankylosaurid Scolosaurus.[1]

Maiasaura and the popularisation of the "dinosaur renaissance"

Within the first years of the discovery of Maiasaura, the importance of such a remarkable find had a durable impact on the public and media contributed to that:

As of 1983, dinosaur renaissance artist Doug Henderson started painting anatomically modern-view life restorations of Maiasaura for a children's book authored by Jack Horner, James Gorman and Jeri D. Walton. Finally published in 1985 the book was titled Maia: A Dinosaur Grows Up and, via its illustrations, showed to the public Maiasaura and other of its contemporary dinosaurs on horizontal-backbone posture, contrary to the till-then traditional, popular and incorrect posture seen in dinosaurs (bipedal or not) that permanently were dragging their tails on the ground.[33]

In 1985 as well, the CBS television documentary Dinosaur! showed Jack Horner talking to the camera about the "Egg Mountain" site and its related discoveries. Dinosaur! was seminal too showing to the CBS audiences the CT scan image of a Maiasaura embryo found inside an egg that had been previously collected at "Egg Mountain".

In 1991 two short documentaries produced by Earthtalk Studios: A Giant Leap for Dinosaurs and Dinosaur Hunters, both directed by Daniel J. Smith, showed Jack Horner at Camp Makela (the scientists' camp that is on site at "Egg Mountain") talking with children and adolescents about the cutting edge of dinosaur research.[34]

See also

Notes

  1. ^ Μαῖα term also related to Maia, one of the seven sisters (Pleiades) and the mother of Hermes by Zeus in Greek mythology.

References

  1. ^ a b McFeeters, Bradley D.; Evans, David C.; Ryan, Michael J.; Maddin, Hillary C. (2021-03-01). "First occurrence of Maiasaura (Dinosauria, Hadrosauridae) from the Upper Cretaceous Oldman Formation of southern Alberta, Canada". Canadian Journal of Earth Sciences. 58 (3): 286–296. Bibcode:2021CaJES..58..286M. doi:10.1139/cjes-2019-0207. ISSN 0008-4077. S2CID 233851376.
  2. ^ a b c Horner, J. R., Schmitt, J. G., Jackson, F., & Hanna, R. (2001). Bones and rocks of the Upper Cretaceous Two Medicine-Judith River clastic wedge complex, Montana. In Field trip guidebook, Society of Vertebrate Paleontology 61st Annual Meeting: Mesozoic and Cenozoic Paleontology in the Western Plains and Rocky Mountains. Museum of the Rockies Occasional Paper (Vol. 3, pp. 3-14).
  3. ^ Wosik, M.; Chiba, K.; Therrien, F.; Evans, D.C. (2020). "Testing Size–frequency Distributions As a Method of Ontogenetic Aging: A Life-history Assessment of Hadrosaurid Dinosaurs from the Dinosaur Park Formation of Alberta, Canada, with Implications for Hadrosaurid Paleoecology". Paleobiology. 46 (3): 379–404. Bibcode:2020Pbio...46..379W. doi:10.1017/pab.2020.2. S2CID 221666530.
  4. ^ Brett-Surman, M. K. (February 1979). "Phylogeny and palaeobiogeography of hadrosaurian dinosaurs". Nature. 277 (5697): 560–562. Bibcode:1979Natur.277..560B. doi:10.1038/277560a0. ISSN 0028-0836. S2CID 4332144.
  5. ^ Cubo, Jorge; Woodward, Holly; Wolff, Ewan; Horner, John R. (2015). "First Reported Cases of Biomechanically Adaptive Bone Modeling in Non-Avian Dinosaurs". PLOS ONE. 10 (7) e0131131. Bibcode:2015PLoSO..1031131C. doi:10.1371/journal.pone.0131131. PMC 4495995. PMID 26153689.
  6. ^ Varricchio, David J.; Horner, John R. (1993-05-01). "Hadrosaurid and lambeosaurid bone beds from the Upper Cretaceous Two Medicine Formation of Montana: taphonomic and biologic implications". Canadian Journal of Earth Sciences. 30 (5): 997–1006. Bibcode:1993CaJES..30..997V. doi:10.1139/e93-083. ISSN 0008-4077.
  7. ^ McFeeters, Bradley; Evans, David; Maddin, Hillary (2021). "Ontogeny and variation in the skull roof and braincase of Maiasaura peeblesorum from the Two Medicine Formation of Montana, U.S.A." Acta Palaeontologica Polonica. 66. doi:10.4202/app.00698.2019. ISSN 0567-7920. S2CID 239729209.
  8. ^ John R. Horner, ProQuest, "Dinosaur Behavior", ProQuest (Phi Kappa Phi Journal); Summer 1998
  9. ^ Browne, Malcolm W. (1980-02-12). "Baby Fossils Lead To New Theories About Dinosaurs; Fossils Lead to New Theories on Dinosaurs Warmblooded Thesis Is Attacked". The New York Times. ISSN 0362-4331. Retrieved 2026-03-23.
  10. ^ Horner, J.R.; Makela, R. (1979). "Nest of juveniles provides evidence of family structure among dinosaurs". Nature. 282 (5736): 296–298. Bibcode:1979Natur.282..296H. doi:10.1038/282296a0. S2CID 4370793.
  11. ^ Horner and Gorman (1988).
  12. ^ "Introduction," Trexler (2001); pages 299-300.
  13. ^ "Faunal Turnover, Migration, and Evolution," Trexler (2001); page 304.
  14. ^ Gates, Terry A.; Horner, John R.; Hanna, Rebecca R.; Nelson, C. Riley (July 2011). "New unadorned hadrosaurine hadrosaurid (Dinosauria, Ornithopoda) from the Campanian of North America". Journal of Vertebrate Paleontology. 31 (4): 798–811. Bibcode:2011JVPal..31..798G. doi:10.1080/02724634.2011.577854. ISSN 0272-4634. S2CID 8878474.
  15. ^ Prieto-Marquez, Albert (2005-03-11). "New information on the cranium ofBrachylophosaurus canadensis(Dinosauria, Hadrosauridae), with a revision of its phylogenetic position". Journal of Vertebrate Paleontology. 25 (1): 144–156. doi:10.1671/0272-4634(2005)025[0144:niotco]2.0.co;2. ISSN 0272-4634. S2CID 85767827.
  16. ^ McDonald, Andrew T.; Wolfe, Douglas G.; Freedman Fowler, Elizabeth A.; Gates, Terry A. (2021-04-02). "A new brachylophosaurin (Dinosauria: Hadrosauridae) from the Upper Cretaceous Menefee Formation of New Mexico". PeerJ. 9 e11084. doi:10.7717/peerj.11084. ISSN 2167-8359. PMC 8020878. PMID 33859873.
  17. ^ Freedman Fowler, Elizabeth A.; Horner, John R. (2015-11-11). "A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana". PLOS ONE. 10 (11) e0141304. Bibcode:2015PLoSO..1041304F. doi:10.1371/journal.pone.0141304. ISSN 1932-6203. PMC 4641681. PMID 26560175.
  18. ^ Prieto-Márquez, A.; Wagner, J.R. (2013). "A new species of saurolophine hadrosaurid dinosaur from the Late Cretaceous of the Pacific coast of North America". Acta Palaeontologica Polonica. 58 (2): 255–268. doi:10.4202/app.2011.0049.
  19. ^ Palmer (1999); page 148.
  20. ^ a b Hirsch, Karl F.; Quinn, Betty (1990-12-20). "Eggs and eggshell fragments from the Upper Cretaceous Two Medicine Formation of Montana". Journal of Vertebrate Paleontology. 10 (4): 491–511. Bibcode:1990JVPal..10..491H. doi:10.1080/02724634.1990.10011832. ISSN 0272-4634.
  21. ^ a b "Maiasaura," Dodson, et al. (1994); pages 116-117.
  22. ^ Bert, Hugo; Woodward, Holly; Rinder, Nicolas; Amiot, Romain; Horner, John R.; Lécuyer, Christophe; Sena, Mariana; Cubo, Jorge (2025-07-10). "Neonatal state and degree of necessity for parental care in Maiasaura based on inferred neonatal metabolic rates". Scientific Reports. 15 (1): 24827. doi:10.1038/s41598-025-06282-5. ISSN 2045-2322. PMC 12246098.
  23. ^ "Largest dinosaur population growth study ever shows how Maiasaura lived and died: Decades of research on Montana's state fossil -- the 'good mother lizard' Maiasaura peeblesorum -- has resulted in the most detailed life history of any dinosaur known".
  24. ^ Woodward, Holly N.; Freedman Fowler, Elizabeth A.; Farlow, James O.; Horner, John R. (2015). "Maiasaura, a model organism for extinct vertebrate population biology: A large sample statistical assessment of growth dynamics and survivorship". Paleobiology. 41 (4): 503–527. Bibcode:2015Pbio...41..503W. doi:10.1017/pab.2015.19. S2CID 85902880.
  25. ^ Chin, Karen (1 September 2007). "The Paleobiological Implications of Herbivorous Dinosaur Coprolites from the Upper Cretaceous Two Medicine Formation of Montana: Why Eat Wood?". PALAIOS. 22 (5): 554–566. Bibcode:2007Palai..22..554C. doi:10.2110/palo.2006.p06-087r. JSTOR 27670451. S2CID 86197149. Retrieved 29 August 2020.
  26. ^ ""The Best of all Mothers" Maiasaura peeblesorum". bioweb.uwlax.edu/. University of Wisconsin-La Crosse. Archived from the original on 16 June 2022. Retrieved 22 March 2021.
  27. ^ Chin, Karen; Gill, Bruce D. (1996). "Dinosaurs, Dung Beetles, and Conifers: Participants in a Cretaceous Food Web". PALAIOS. 11 (3): 280–285. Bibcode:1996Palai..11..280C. doi:10.2307/3515235. ISSN 0883-1351. JSTOR 3515235. Retrieved 25 April 2026. {{cite journal}}: Unknown parameter |va= ignored (help)
  28. ^ Hunter, John P.; Janis, Christine M. (15 May 2026). "Tooth wear in juvenile and adult hadrosaurs: implications for parental care in Maiasaura". Palaeogeography, Palaeoclimatology, Palaeoecology. 690: 113707. doi:10.1016/j.palaeo.2026.113707. Retrieved 25 April 2026 – via Elsevier Science Direct.{{cite journal}}: CS1 maint: article number as page number (link)
  29. ^ "Using math to examine the sex differences in dinosaurs".
  30. ^ "Statistical analysis reveals differences between dinosaur sexes".
  31. ^ a b c d "Faunal Turnover, Migration, and Evolution," Trexler (2001); page 306.
  32. ^ Sullivan, R. M.; Lucas, S. G. (2006). "The Kirtlandian land-vertebrate "age"–faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America". New Mexico Museum of Natural History and Science Bulletin. 35: 7–29.
  33. ^ Jack Horner, James Gorman and Jeri D. Walton, Maia: A Dinosaur Grows Up, published by Museum of the Rockies, all illustrations by Doug Henderson (1985).
  34. ^ thisisyellowstone.com, "Yellowstone Geology", list of geology documentaries by Earthtalk Studios.

Bibliography

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  • Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 116-117. ISBN 0-7853-0443-6.
  • Horner, Jack and Gorman, James. (1988). Digging Dinosaurs: The Search that Unraveled the Mystery of Baby Dinosaurs, Workman Publishing Co.
  • Lehman, T. M., 2001, Late Cretaceous dinosaur provinciality: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 310–328.
  • Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 148. ISBN 1-84028-152-9.
  • Trexler, D., 2001, Two Medicine Formation, Montana: geology and fauna: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 298–309.
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