Old Earth Ministries Online Dinosaur Curriculum
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Lesson 59 - Edmontosaurus
Edmontosaurus is a genus of crestless duck-billed dinosaur. The fossils of this animal have been found in rocks of western North America that date from the late Campanian stage to the end of the Maastrichtian stage of the Cretaceous Period, between 73 and 65.5 million years ago. It was one of the last non-avian dinosaurs, and lived alongside Triceratops and Tyrannosaurus shortly before the Cretaceous–Tertiary extinction event.
Edmontosaurus was one of the largest hadrosaurids, measuring up to 13 meters (43 ft) long and weighing around 4.0 metric tons (4.4 short tons). It is known from several well-preserved specimens that include not only bones, but in some cases extensive skin impressions and possible gut contents.
Edmontosaurus was widely distributed across western North America. The distribution of Edmontosaurus fossils suggests that it preferred coasts and coastal plains. It was a herbivore that could move on both two legs and four. Because it is known from several bone beds, Edmontosaurus is thought to have lived in groups, and may have been migratory as well. The wealth of fossils has allowed researchers to study its paleobiology in detail, including its brain, how it may have fed, and its injuries and pathologies, such as evidence for a tyrannosaur attack on one edmontosaur specimen.
Length: 43 feet
Weight: 8,800 lbs
Date Range: 73 - 65.5 Ma, Campanian - Maastrichtian Age, Cretaceous Period
|Edmontosaurus in the Oxford University Museum of Natural History (Picture Source)|
Edmontosaurus has been described in detail from several specimens. Like other hadrosaurids, it was a bulky animal with a long, laterally flattened tail and a head with an
The skull of a fully grown Edmontosaurus was around a meter (or yard) long. The skull
Teeth were present only in the maxillae (upper cheeks) and dentaries (main bone of the lower jaw). The teeth were continually replaced, taking about half a year to form. They grew in columns, with an observed maximum of six in each, and the number of columns varied based on the animal's size. Known column counts for the various species are: 51 to 53 columns per maxilla and 48 to 49 per dentary (teeth of the upper jaw being slightly narrower than those in the lower jaw) for E. regalis; 43 columns per maxilla and 36 per dentary for E. annectens; and 52 and 44 for E. saskatchewanensis.
Multiple specimens of Edmontosaurus have been found with preserved skin impressions.
AMNH 5060, the "Trachodon mummy" (so-called because it appears to be a fossil of a natural mummy), is now recognized as a specimen of E. annectens. It was found to have skin impressions over the snout, much of the neck and torso, and parts of the arms and legs. The tail and part of the legs eroded before collection, so these areas are unknown for the specimen. Additionally, some areas with skin impressions, such as sections associated with the neck ridge (see below) and hands, were accidentally removed during preparation of the specimen. The specimen is thought to have desiccated in a dry stream bed, probably on or near a point bar. The circumstances of the location and preservation of the body suggest that the animal died during a prolonged drought, perhaps from starvation. The desiccated carcass was eventually buried in a sudden flood, surrounded by sediment that had enough fine particles to make a cast of the epidermal structures.
The epidermis was thin, and the scalation composed of small nonoverlapping scales, as seen in the Gila monster. Two general types of scales were present over most of the body: small pointed or convex tubercles, 1 to 3 millimeters (0.039 to 0.12 in) in diameter with no definite arrangement (ground tubercles); and larger, flat polygonal tubercles (pavement tubercles) typically less than 5 millimeters (0.20 in) in diameter, but up to 10 millimeters (0.39 in) over the forearm. The pavement tubercles were grouped into clusters separated by ground tubercles, with transitional scales between the two types. Over most of the body, the pavement tubercles were arranged in circular or oval clusters, while near the shoulder on the upper arm, they formed strips roughly parallel to each other and the shoulder blade. Generally, clusters were larger on the upper surfaces of the body and smaller on the underside. Clusters up to 50 centimeters (20 in) in length were present above the hips.
Brain and nervous system
The brain of Edmontosaurus has been described in several papers and abstracts through
As a hadrosaurid, Edmontosaurus was a large terrestrial herbivore. Its teeth were continually replaced and packed into dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. It used its broad beak to cut loose food, perhaps by cropping, or by closing the jaws in a clamshell-like manner over twigs and branches and then stripping off the more nutritious leaves and shoots. Because the tooth rows are deeply indented from the outside of the jaws, and because of other anatomical details, it is inferred that Edmontosaurus and most other ornithischians had cheek-like structures, muscular or non-muscular. The function of the cheeks was to retain food in the mouth. The animal's feeding range would have been from ground level to around 4 meters (13 ft) above.
The diet and physiology of Edmontosaurus have been probed by using stable isotopes of carbon and oxygen as recorded in tooth enamel. When feeding, drinking, and breathing, animals take in carbon and oxygen, which become incorporated into bone. The isotopes of these two elements are determined by various internal and external factors, such as the type of plants being eaten, the physiology of the animal, salinity, and climate. If isotope ratios in fossils are not altered by fossilization and later changes, they can be studied for information about the original factors; warmblooded animals will have certain isotopic compositions compared to their surroundings, animals that eat certain types of plants or use certain digestive processes will have distinct isotopic compositions, and so on. Enamel is typically used because the structure of the mineral that forms enamel makes it the most resistant material to chemical change in the skeleton.
A 2004 study by Kathryn Thomas and Sandra Carlson used teeth from the upper jaw of three individuals interpreted as a juvenile, a subadult, and an adult, recovered from a bone bed in the Hell Creek Formation of Corson County, South Dakota. In this study, successive teeth in columns in the edmontosaurs' dental batteries were sampled from multiple locations along each tooth using a microdrilling system. This sampling method takes advantage of the organization of hadrosaurid dental batteries to find variation in tooth isotopes over a period of time. From their work, it appears that edmontosaur teeth took less than about 0.65 years to form, slightly faster in younger edmontosaurs. The teeth of all three individuals appeared to show variation in oxygen isotope ratios that could correspond to warm/dry and cool/wet periods; Thomas and Carlson considered the possibility that the animals were migrating instead, but favored local seasonal variations because migration would have more likely led to ratio homogenization, as many animals migrate to stay within specific temperature ranges or near particular food sources.
Pathologies and health
In 2003, evidence of tumors was described in Edmontosaurus bones. Researchers tested dinosaur vertebrae for tumors using computerized tomography and fluoroscope screening. Several other hadrosaurids, including Brachylophosaurus, Gilmoreosaurus, and Bactrosaurus, also tested positive. Although more than 10,000 fossils were examined in this manner, the tumors were limited to Edmontosaurus and closely related genera. The tumors may have been caused by environmental factors or genetic propensity.
Osteochondrosis, or surficial pits in bone at places where bones articulate, is also known in Edmontosaurus. This condition, resulting from cartilage failing to be replaced by bone during growth, was found to be present in 2.2% of 224 edmontosaur toe bones. The underlying cause of the condition is unknown. Genetic predisposition, trauma, feeding intensity, alterations in blood supply, excess thyroid hormones, and deficiencies in various growth factors have been suggested. Among dinosaurs, osteochondrosis (like tumors) is most commonly found in hadrosaurids.
Like other hadrosaurids, Edmontosaurus is thought to have been a facultative biped, meaning that it mostly moved on four legs, but could adopt a bipedal stance when needed. It probably went on all fours when standing still or moving slowly, and switched to using the hind legs alone when moving more rapidly. Research conducted by computer modeling in 2007 suggests that Edmontosaurus could run at high speeds, perhaps up to 45 kilometers per hour (28 mph). Further simulations using a subadult specimen estimated as weighing 715 kilograms (1,580 lb) when alive produced a model that could run or hop bipedally, use a trot, pace, or single foot symmetric quadrupedal gait, or move at a gallop.
Interactions with theropods
The time span and geographic range of Edmontosaurus overlapped with Tyrannosaurus,
Another specimen of E. annectens, pertaining to a 7.6 meters (25 ft) long individual from South Dakota, shows evidence of tooth marks from small theropods on its lower jaws. Some of the marks are partially healed. Michael Triebold, informally reporting on the specimen, suggested a scenario where small theropods attacked the throat of the edmontosaur; the animal survived the initial attack but succumbed to its injuries shortly thereafter. Some edmontosaur bone beds were sites of scavenging. Albertosaurus and Saurornitholestes tooth marks are common at one Alberta bone bed, and Daspletosaurus fed on Edmontosaurus and fellow hadrosaurid Saurolophus at another Alberta site.
Extensive bone beds are known for Edmontosaurus, and such groupings of hadrosaurids are used to suggest that they were gregarious, living in groups. Four quarries containing edmontosaur remains are identified in a 2007 database of fossil bone beds, from Alaska (Prince Creek Formation), Alberta (Horseshoe Canyon Formation), South Dakota (Hell Creek Formation), and Wyoming (Lance Formation). One edmontosaur bone bed, from claystone and mudstone of the Lance Formation in eastern Wyoming, covers more than a square kilometer, although Edmontosaurus bones are most concentrated in a 40 hectares (0.15 sq mi) subsection of this site. It is estimated that disassociated remains pertaining to 10,000 to 25,000 edmontosaurs are present here.
Because of its wide distribution, which covers a distance from Alaska to Colorado and includes polar settings that would have had little light during a significant part of the year, Edmontosaurus has been considered possibly migratory. A 2008 review of dinosaur migration studies by Phil R. Bell and Eric Snively proposed that E. regalis was capable of an annual 2,600 kilometers (1,600 mi) round-trip journey, provided it had the requisite metabolism and fat deposition rates. Such a trip would have required speeds of about 2 to 10 kilometers per hour (1 to 6 mph), and could have brought it from Alaska to Alberta. The possible migratory nature of Edmontosaurus contrasts with many other dinosaurs, such as theropods, sauropods, and ankylosaurians, which Bell and Snively found were more likely to have overwinter.
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