Cetiosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Cetiosauridae

Genus: Cetiosaurus

Species: Cetiosaurus oxoniensis

Introduction

Cetiosaurus was an early form of sauropod dinosaur. Sauropods were giant, herbivorous (plant-eating) dinosaurs with long necks, long tails, small heads, round bodies and four pillar-like legs. Some of the best known sauropod genera include Apatosaurus, Brachiosaurus, and Diplodocus. Cetiosaurus has the honor of being the first sauropod ever discovered, and at a time when paleontology was still an emerging field of science. Cetiosaurus's hulking form was such a mystery to scientists in the 1840s that the animal was believed to be a giant marine reptile—hence the name bestowed on it, “whale lizard.” Scientists have since reclassified Cetiosaurus as a member of Sauropoda, a group that contains the largest animals ever known to walk the earth.

Classification

Scientists classify dinosaurs in different ways. The Linnaean system is a hierarchical classification system that narrows organisms into order, genera, and species. In the late twentieth and early twenty-first centuries, paleontologists moved towards cladistic or phylogenetic classification systems to classify dinosaurs according to their common ancestry and shared physical characteristics. In the Linnaean system, Cetiosaurus is a member of the larger Sauropodomorpha suborder of dinosaurs, and the infraorder Sauropoda. Apatosaurus and Brachiosaurus are among some of the best known sauropods. They reached over 20 meters (60 feet) in length and weighed up to 50 tons (110,000 pounds). Sauropods share a number of common physical characteristics, including small heads suspended on long necks, long tails, large round bodies, large pillar-like legs, peg-like teeth and nares (nostril channels) positioned high on the skull.

Cladistic analysis is based on more specific physical characteristics that contribute to an understanding of an organism's ancestral connections. Cetiosaurus is a member of the Cetiosauridae clade, or “group,” which consists of a number of primitive sauropod genera from different regions of the world. This group is characterized by broad teeth, solid vertebrae of the spine, and chevrons (a series of bones in the underside of the tail). The cetiosaurids include Cetiosaurus from the United Kingdom, Patagosaurus from Argentina, and Barapasaurus from India. The cetiosaurids also fall in the Eusauropoda clade, a group of Middle Jurassic dinosaurs that are bigger than their ancestors, but smaller than their descendants. Note that cladistic analyses can change over time as new specimens are discovered and as the science advances.

Anatomy

Cetiosaurus was a giant, lumbering animal that carried its 25-ton (55,000-pound) frame on four sturdy legs. Its appearance was similar to Apatosaurus and Diplodocus, except for a comparatively shorter tail. An evolutionary connection between Diplodocus and Cetiosaurus is suggested by the presence of chevrons in both genera. Cetiosaurus is distinguished from later sauropods by the unique structure of its forelegs and vertebrae. While more advanced sauropods had hollow spaces in their vertebrae to assist with weight reduction, Cetiosaurus had solid vertebrae that added significant weight to the animal. These hulking giants would have been slow movers, probably walking at an average speed of approximately 5 kilometers (3 miles) an hour.

When first identified in 1841 by Sir Richard Owen, Cetiosaurus was believed to be a huge marine reptile. The original description of Cetiosaurus reconstructed it with a sprawled, crocodilian gait. Owen proposed that the animal used its long neck and high nostril channels to breathe at the water's surface while its body was submerged. As more sauropod remains were discovered in subsequent years, the marine reptile theory was refuted. It is agreed today that Cetiosaurus, as with all sauropods, was a terrestrial animal.

Intelligence

With extremely small heads compared with their massive bodies, creatures in the Sauropodomorpha suborder have the lowest EQ of all dinosaurs. Their EQ score is less than 0.5 (Hopson), compared with 1.0 for a crocodile, up to 2.0 for theropods, and 5.8 for dromaeosaurids. Cetiosaurus's low EQ further implies that these animals were docile, lumbering giants.

Reproduction and Population

Scientists extrapolate that sauropod dinosaurs each had similar reproductive behaviors. From the discovery of a fossilized sauropod nesting ground in Argentina in 1987, scientists have been able to confirm that sauropod dinosaurs were oviparous (egg-laying). While scientists cannot definitively say if sauropod dinosaurs cared for their eggs, the close proximity of egg clusters, combined with the large size of these dinosaurs, suggests that parental care of the eggs, or brooding, would have been difficult. Alternatively, it is possible that adults protected the nesting ground from a distance. It is not known if dinosaurs cared for their young after hatching, but herding behavior demonstrated in fossilized track sites implies that the young were adopted into groups. Scientific investigation of sauropod bones indicates that these animals may have grown quickly after hatching, possibly reaching sexual maturity in less than 20 years.

The Cetiosaurus population is unknown, but scientists do know that the animal died out due to a non-mass extinction cause. They speculate that Cetiosaurus's extinction may have been due to over-competition for environmental resources or habitat depletion caused by climate or geological change.

Diet

Cetiosaurus's peg-like teeth were designed for eating a diet that consisted of plant matter. The animal ingested its food by stripping leaves from branches and swallowing them whole without chewing. Digestion was probably aided by the presence of gastroliths (stomach stones) in the animal's stomach. These small stones, which were swallowed by the animal, helped to grind up food as it passed through the digestive system.

Since Cetiosaurus weighed around 25 tons (55,000 pounds), its energy requirements meant that it spent the majority of each day browsing. High food demand also suggests that these dinosaurs roamed over a wide geographic area. Cetiosaurus's diet likely consisted of mid-level and tree-sized plants, such as gymnosperms (non-flowering seed-bearing plants), which included ferns and cycads. The dinosaur may have reared on its hind legs to reach higher foliage, although some scientists believe that balancing would have been too difficult for these giant beasts to perform. Although researchers agree that sauropods were terrestrial animals (lived on land), they may have also used their long necks for feeding along river banks and in shallow water.

Behavior

Fossilized trackways (footprints preserved in mud) suggest that sauropods were docile animals that moved slowly in herds. The diversity of prints found in trackways implies that these large animals sometimes moved in mixed groups. It is not known if Cetiosaurus had a simple or complex social structure or whether the species preferred a social or solitary existence. Scientists do know that their large size prevented them from walking quickly. Traveling in numbers, therefore, may have provided protection from predators, especially for the young.

As an herbivorous animal with a large calorie requirement, Cetiosaurus needed to move from place to place in search of food. These big animals would have been capable of destroying large areas of vegetation quickly as they foraged. It is estimated, therefore, that they ranged 20 to 40 kilometers (12 to 25 miles) a day in search of food.

Habitat and Other Life Forms

The climate of the Middle Jurassic period was warm and humid, contributing to lush forests and fertile plains. Angiosperms (flowering plants) were yet to evolve, but there was an abundance of gymnosperms (non-flowering, seed-bearing plants). These plants included tree ferns, conifers, cycads, and Gingkoes.

Cetiosaurus lived in the geographic area we know today as the United Kingdom in Europe and possibly Morocco in Africa. Sauropods are believed to have originated in Asia, supporting the theory that the continents of the southern and northern hemispheres were once joined in a supercontinent called Pangaea. The area looked much different in the Middle Jurassic period than it does today. The geography consisted of subtropical low-lying floodplains and open woodland. Cetiosaurus very likely ranged the plains and marshy shores in exclusive or mixed herds.

Cetiosaurus shared its environment with other herbivorous sauropods, as well as a host of carnivorous (meat-eating) dinosaur species, such as Megalosaurus, Eustreptospondylus, Magnosaurus, Metriacanthosaurus, and Proceratosaurus. There was also Lexovisaurus, a 1,000-kilogram (2,200-pound) stegosaur, and the iguanodontian Callovosaurus.

Research

In 1842, one year after Sir Richard Owen identified Cetiosaurus, he coined the term “Dinosauria.” The word means “fearfully great lizard” and was apt to describe what Owen believed to be a taxon of giant reptiles. Given that Cetiosaurus's discovery occurred when paleontology was only an emerging field of science, there has been a tendency to misidentify the animal. For example, the first species identified, C. brevis, was found to be contaminated with Iguanodon bones, causing the description to be inaccurate. C. medius was chosen as the type (standard) species, but it presented paleontologists with serious difficulties because its identification is based on very incomplete specimens; C. oxoniensis eventually became the new Cetiosaurus standard species because its identification is based on a nearly complete skeleton. Over time, fourteen species were assigned to the genus, of which thirteen came from England and one from Morocco. However, in their 2003 reassessment, Paul Upchurch and John Martin contended only C. oxoniensis truly belonged to the genus. As new sauropod specimens were discovered thereafter, their characters were frequently compared to those of Cetiosaurus in attempts to classify the fossil properly.

The United Kingdom has proved to be extremely rewarding for paleontology. The first British dinosaur remains were categorized in 1824, and explorations have since resulted in the identification of more than one hundred species, including Cetiosaurus. The so-called Rutland Dinosaur found in 1968 represents the most complete Cetiosaurus skeleton. The high concentration of dinosaur species in the United Kingdom is attributed to the arrangement of the continents during the Mesozoic period. During the Early to Middle Jurassic, it is believed that the United Kingdom formed a land bridge connecting other regions. The Dorset and East Devon Coast in the southeast of England provide a sequence of rock formation that spans approximately 185 million years; the area is of such paleontological significance that it was designated a World Heritage Site in 2001. Yorkshire yielded a 176 million-year-old eusauropod bone from the Middle Jurassic, which was described in 2015 and displaced Cetiosaurus as the oldest sauropod fossil found in England by about 4 million years.

Sauropod trackways discovered in the 2015 on Scotland's Isle of Skye dated to 170 million years ago. Scientists thought the footprints might be attributable to Cetiosaurus, indicating sauropod presence in coastal habitats, such as lagoons. The find reaffirmed the idea of a connection between the terrestrial creatures and the water that had been largely abandoned once sauropods like Cetiosaurus were determined to be land animals, and furthered scientific understanding of the little-known Middle Jurassic.

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