''Maiasaura'' (from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''μαῖα'', meaning "good mother" and ''σαύρα'', the feminine form of ''saurus'', meaning "reptile") is a large herbivorous

saurolophine Saurolophinae is a subfamily (biology), subfamily of hadrosaurid dinosaurs. It has since the mid-20th century generally been called the Hadrosaurinae, a group of largely non-crested hadrosaurs related to the crested sub-family Lambeosaurinae. How ...

hadrosaurid Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which inclu ...

("duck-billed")

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

that lived in the area currently covered by the state of

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

and the province of

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

in the Upper

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

(mid to late

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

), about 76.7 million years ago.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). The first remains of ''Maiasaura'' were discovered in 1978 by Bynum, Montana resident Laurie Trexler. The genus was named in 1979. The name refers to the find of nests with eggs, embryos and young animals, in a nesting colony. These showed that ''Maiasaura'' fed its young while they were in the nest, the first time such evidence was obtained for a dinosaur. Hundreds of bones of ''Maiasaura'' have been dug up. ''Maiasaura'' was about long. Young animals walked on their hind legs, adults on all fours. ''Maiasaura'' was probably closely related to ''

Brachylophosaurus ''Brachylophosaurus'' ( or ; meaning "short-crested lizard", Greek ''brachys'' = short + ''lophos'' = crest + ''sauros'' = lizard, referring to its small crest) was a mid-sized member of the hadrosaurid family of dinosaurs. It is known from sev ...

''.

Description

''Maiasaura'' were large, attaining a maximum known length of about . They had a flat beak typical of

s, and thick noses. They had a small, spiky crest in front of the eyes. This crest may have been used in headbutting contests between males during the breeding season. Its body mass is measured approximately up to . ''Maiasaura'' were

herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

. They were capable of walking both on two (

bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

) or four (

quadrupedal Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor ...

) 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. ''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

herd A herd is a social group of certain animals of the same species, either wild or domestic. The form of collective animal behavior associated with this is called ''herding''. These animals are known as gregarious animals. The term ''herd'' is ...

s to be less likely to be targeted. Herds were extremely large and could have comprised as many as 10,000 individuals. ''Maiasaura'' lived in an inland habitat.

Discovery

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 in 1979 and described by dinosaur

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

s Jack Horner and Robert Makela as the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

of a new species. They named the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

''Maiasaura peeblesorum''. The generic name refers to the Greek goddess

Maia Maia (; Ancient Greek: Μαῖα; also spelled Maie, ; la, Maia), in ancient Greek religion and mythology, is one of the Pleiades and the mother of Hermes, one of the major Greek gods, by Zeus, the king of Olympus. Family Maia is the daugh ...

, the "Good Mother"; to emphasise this, they used the feminine form of ''saurus'': ''saura''. The specific name honours the families of John and James Peebles, on whose land the finds were made. The generic name refers to Marion Brandvold's discovery in 1978 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 The Two Medicine Formation is a geological formation, or rock body, in northwestern Montana and southern Alberta that was deposited between and (million years ago), during Campanian (Late Cretaceous) time. It crops out to the east of the Rocky M ...

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 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. Choteau ''Maiasaura'' remains are found in higher strata than their

Two Medicine River The Two Medicine River is a tributary of the Marias River, approximately 60 mi (97 km) long, in northwestern Montana in the United States. It rises in the Rocky Mountain Front in Glacier National Park at the continental divide and f ...

counterparts.

Classification

The following cladogram of hadrosaurid relationships was published in 2013 by Alberto Prieto-Márquez et al.:

Palaeobiology

''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 ; less than the length of the adult animal. 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 Ostriches are large flightless birds of the genus ''Struthio'' in the order Struthioniformes, part of the infra-class Palaeognathae, a diverse group of flightless birds also known as ratites that includes the emus, rheas, and kiwis. There are ...

eggs. The eggs were incubated by the heat resulting from rotting vegetation placed into the nest by the parents, rather than a parent

sitting Sitting is a List of human positions, basic action and resting position in which the body weight is supported primarily by the bony ischial tuberosities with the buttocks in contact with the ground or a horizontal surface such as a chair seat, in ...

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. Maiasaura Nest Model

The hatchlings grew from a size of 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 Evidence for a proposition is what supports this proposition. It is usually understood as an indication that the supported proposition is true. What role evidence plays and how it is conceived varies from field to field. In epistemology, evidenc ...

of warm bloodedness. The hatchlings had different facial proportions from the adults, with larger eyes and a shorter snout. These features are associated with

cuteness Cuteness is a subjective term describing a type of attractiveness commonly associated with youth and appearance, as well as a scientific concept and analytical model in ethology, first introduced by Konrad Lorenz. Lorenz proposed the concept ...

, and commonly elicit care from parents in animals dependent on their parents for survival during the early stages of life. 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.

Diet

A paper from 2007 showed that ''Maiasaura'' had a diet consisting of fibrous plants,

wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...

, rotting wood,

tree bark Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside the vascular cambium and is a nontechnical term. It overlays the wood and cons ...

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

branches A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term ''twig'' usually r ...

ferns A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except th ...

angiosperms Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

and possibly grasses. This would imply that ''Maiasaura'' was both a browser and a

grazer Grazer may refer to: *grazer, an animal that grazes *Grazer, a native or inhabitant of Graz *GRAZER, the shoegaze band GRAZER Astronomy * Earth Grazer, Earth-grazing fireball that enters the Earth's atmosphere and leaves again * Mercury grazer, ...

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 gender was male or female.

Palaeoecology

''Maiasaura'' is a characteristic fossil of the middle portion (lithofacies 4) of the Two Medicine Formation, dated to about 76.4 million years ago. ''Maiasaura'' lived alongside the

troodontid Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil disco ...

Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a wastebasket taxon and a dubious genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Late Cretaceous period (about 77 mya). It includes at leas ...

'' and the basal

ornithopod Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous wo ...

Orodromeus ''Orodromeus'' (meaning "Mountain Runner") is a genus of herbivorous orodromine thescelosaurid dinosaur from the Late Cretaceous of North America. Only one species is known, the type species ''Orodromeus makelai''. Discovery and naming The rem ...

'', as well as the

dromaeosaurid Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...

'' Bambiraptor'' and the

tyrannosaur Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent ...

Daspletosaurus ''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 79.5 and 74 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three species ...

''. Another species of hadrosaurids, referable to the genus ''

Hypacrosaurus ''Hypacrosaurus'' (meaning "near the highest lizard" reek υπο-, ''hypo-'' = less + ακρος, ''akros'', high because it was almost but not quite as large as ''Tyrannosaurus'') was a genus of duckbill dinosaur similar in appearance to ''Co ...

'', 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 an additional hadrosaurid, ''

Gryposaurus latidens ''Gryposaurus'' (meaning "hooked-nosed (Greek ''grypos'') lizard"; sometimes incorrectly translated as "griffin (Latin ''gryphus'') lizard") was a genus of duckbilled dinosaur that lived about 80 to 75 million years ago, in the Late Cretaceo ...

'', 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. There seems to be a major diversification in

ornithischian Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...

taxa after the appearance of ''Maiasaura'' within the Two Medicine Formation. 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. While ''Maiasaura'' has historically been associated with the Two Medicine formation ceratopsid ''

Einiosaurus ''Einiosaurus'' is a genus of herbivorous centrosaurine ceratopsian dinosaur from the Upper Cretaceous (Campanian stage) of northwestern Montana. The name means 'buffalo lizard', in a combination of Blackfeet Indian ''eini'' and Latinized Ancie ...

'' in a single fauna, this is inaccurate, as ''Maiasaura'' is known exclusively from older strata. In the

Oldman Formation The Oldman Formation is a stratigraphic unit of Late Cretaceous (Campanian stage) age that underlies much of southern Alberta, Canada. It consists primarily of sandstones that were deposited in fluvial channel and floodplain environments. It was ...

of Alberta, ''Maiasaura'' lived alongside the

ceratopsia Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. ...

ns ''

Albertaceratops ''Albertaceratops'' (meaning "Alberta horned face") was a genus of centrosaurine horned dinosaur from the middle Campanian-age Upper Cretaceous Oldman Formation of Alberta, Canada. Description ''Albertaceratops'' is unusual in combining long ...

'', ''

Anchiceratops ''Anchiceratops'' ( ) is an extinct genus of chasmosaurine ceratopsid dinosaur that lived approximately 72 to 71 million years ago during the latter part of the Cretaceous Period in what is now Alberta, Canada. ''Anchiceratops'' was a medium-si ...

'', ''

Chasmosaurus ''Chasmosaurus'' ( ) is a genus of ceratopsid dinosaur from the Upper Cretaceous Period of North America. Its name means 'opening lizard', referring to the large openings ( fenestrae) in its frill (Greek ''chasma'' meaning 'opening' or 'hollow' ...

'', ''

Coronosaurus ''Coronosaurus'' is a genus of centrosaurine ceratopsian dinosaurs which lived in the Late Cretaceous, in the middle Campanian stage. Its remains, two bone beds, were discovered by Phillip J. Currie in the Oldman Formation of Alberta, Canada, a ...

'', and ''

Wendiceratops ''Wendiceratops'' is a genus of herbivorous centrosaurine ceratopsian dinosaur from the Late Cretaceous of Canada. Discovery In 2010, Canadian fossil hunter Wendy Sloboda found a centrosaurine bonebed in the Pinhorn Provincial Grazing Reser ...

'', as well as the

s ''

Dromaeosaurus ''Dromaeosaurus'' (, "running lizard") is a genus of dromaeosaurid theropod dinosaur which lived during the Late Cretaceous period (middle late Campanian and Maastrichtian), sometime between 80 and 69 million years ago, in Alberta, Canada and the ...

'', ''

Saurornitholestes ''Saurornitholestes'' ("lizard-bird thief") is a genus of carnivorous dromaeosaurid theropod dinosaur from the late Cretaceous of Canada (Alberta) and the United States (Montana, New Mexico, Alabama, North Carolina, and South Carolina). Two spec ...

'', and ''

Hesperonychus ''Hesperonychus'' (meaning "western claw") was a small, carnivorous dinosaur. It was a member of the family Dromaeosauridae, along with its larger relatives ''Deinonychus'' and ''Velociraptor''. There is one described species, ''Hesperonychus el ...

'', the

tyrannosaurid Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...

'', the

orodromine Orodrominae is a subfamily of thescelosaurid dinosaurs known from the Cretaceous of North America and Asia. Distribution Orodromines were a mostly North American based group with fossils from Canada and United States only. ''Albertadromeus'', a ...

thescelosaurid Thescelosauridae is a clade of neornithischians from the Cretaceous of Asia, North America and possibly South America. The group was originally used as a name by Charles M. Sternberg in 1937, but was not formally defined until 2013, where it was ...

Albertadromeus ''Albertadromeus'' is an extinct genus of orodromine thescelosaurid dinosaur known from the upper part of the Late Cretaceous Oldman Formation (middle Campanian stage) of Alberta, Canada. It contains a single species, ''Albertadromeus syntars ...

'', the

pachycephalosaurs Pachycephalosauria (; from Greek παχυκεφαλόσαυρος for 'thick headed lizards') is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephal ...

Foraminacephale ''Foraminacephale'' (meaning "foramina head") is a genus of pachycephalosaurid dinosaur from Late Cretaceous (Campanian stage) deposits of Canada. Description ''Foraminacephale'', as a pachycephalosaurid, was a small, bipedal herbivore with a ...

'' and ''

Hanssuesia ''Hanssuesia'' is a genus of pachycephalosaurid dinosaurs from the late Cretaceous period. It lived in what is now Alberta and Montana, and contains the single species ''Hanssuesia sternbergi''. ''Hanssuesia'' is based on a skull dome originally ...

'', the

ornithomimid Ornithomimidae (meaning "bird-mimics") is a family of theropod dinosaurs which bore a superficial resemblance to modern ostriches. Ornithomimids were fast, omnivorous or herbivorous dinosaurs known mainly from the Late Cretaceous Period of Laura ...

Struthiomimus ''Struthiomimus'' (meaning "ostrich mimic", from the Ancient Greek, Greek στρούθειος/''stroutheios'' meaning "of the ostrich" and μῖμος/''mimos'' meaning "mimic" or "imitator") is a genus of Ornithomimidae, ornithomimid dinosaurs ...

'', the other hadrosaurids ''

'', ''

Corythosaurus ''Corythosaurus'' (; ) is a genus of hadrosaurid "duck-billed" dinosaur from the Upper Cretaceous Period, about 77–75.7 million years ago. It lived in what is now North America. Its name means "helmet lizard", derived from Greek κόρυ� ...

'', and ''

Parasaurolophus ''Parasaurolophus'' (; meaning "near crested lizard" in reference to '' Saurolophus)'' is a genus of herbivorous hadrosaurid ornithopod dinosaur that lived in what is now North America and possibly Asia during the Late Cretaceous Period, abou ...

'', and the

ankylosaurid Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known Ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...

Scolosaurus ''Scolosaurus'' is an extinct genus of ankylosaurid dinosaurs within the subfamily Ankylosaurinae. It is known from the lower levels of the Dinosaur Park Formation and upper levels of the Oldman Formation in the Late Cretaceous (latest middle Cam ...

''.

Footnotes

References

* 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. . * 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. * * 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. {{Taxonbar, from=Q132414 Fossils of Canada Oldman fauna Paleontology in Alberta Late Cretaceous dinosaurs of North America Monotypic dinosaur genera Paleontology in Montana Saurolophines Fossil taxa described in 1979 Taxa named by Jack Horner Campanian life Campanian genus first appearances Campanian genus extinctions Ornithischian genera

Description

Discovery

Classification

Palaeobiology

Diet

Sexual dimorphism

Palaeoecology

See also

Footnotes

References