Coloradisaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Plateosauridae

Genus: Coloradisaurus

Species: Coloradisaurus brevis

Introduction

Once referred to as Coloradia, Coloradisaurus was discovered in the late twentieth century. In October 1971, paleontologists from the Fundación Miguel Lillo (Miguel Lillo Foundation) found this creature's remains in the Upper Los Colorados Formation, located near La Rioja, Argentina. The bones were in the upper third of the formation, an area of red sands and limestone, lower than other specimens that had been recovered from the area. Some scientists have theorized that Coloradisaurus is really an adult version of Mussaurus, of which scientists have only uncovered juveniles, hatchlings, and eggs. Because the name Coloradia had already been assigned to a moth, paleontologist David Lambert renamed the dinosaur.

Coloradisaurus lived during the Norian age, the middle of three divisions during the Late Triassic period, when all land was a single mass located near the equator. Known as Pangaea, it included two smaller continents, Laurasia in the north and Gondwana in the south. Pangaea, which covered about one-fourth of the earth's surface, experienced little variation in the warm climate; however, near the end of the period, it grew drier and hotter. Despite the similarities in climate, researchers have observed differences in plant life between the northern and southern part of Pangaea.

Dinosaurs first appeared during the Triassic period. Because they were able to roam freely around this single supercontinent, other species, including some amphibians and mammal-like reptiles, may have been threatened and declined.

Classification

Paleontologists use two major systems to classify their discoveries, and because the nature of this field is fluid and constantly advancing, scientists do not always agree on classification. New discoveries often lead to adjustments or complete rethinking of previously held beliefs, resulting in changes in classification.

Carl Linnaeus, a Swedish botanist, developed the most common classification system in the eighteenth century, called the Linnaean system. This system is hierarchical and separates animals and plants into divisions such as order, class, and phylum. According to this system, Coloradisaurus is a member of the group called Sauropodomorpha. These dinosaurs usually have lightweight but strong vertebrae and long necks and tail. They are also noted for having five “toes” on both the front and back feet.

Sauropodomorphs have been classified as members of the order Saurischia (lizard-hipped dinosaurs), which has included theropods as well; some paleontologists have proposed that theropods were actually more closely related to the bird-hipped dinosaurs than to sauropodomorphs, however. Theropods included all the carnivorous, or meat-eating, dinosaurs, as well as some herbivores, or plant-eating dinosaurs. All sauropodomorphs were herbivorous. Paleontologist Jose Bonaparte assigned Coloradisaurus to the family Plateosauridae. Dinosaurs in this family had fingers that could spread out from short hands.

Paleontologists increasingly prefer to use a cladistic, or phylogenetic, system to classify dinosaur species. This method, developed during the 1950s, looks at shared physical characteristics and evolutionary history to group creatures, including dinosaurs, into clades. Family groups are placed in cladograms that show the relationships between species.

In cladistics, Coloradisaurus falls into the saurischian clade. In particular, Coloradisaurus is closely related to the prosauropod Mussaurus in cladistic analysis. Prosauropods are early herbivorous dinosaurs characterized by small heads, long necks, and short forelimbs. It is also grouped with other prosauropods, namely Lufengosaurus (found in modern-day Asia) and Massospondylus (from what is now Africa), both dating to the Early Jurassic. They shared similar jaw construction, among other skull and teeth structures.

The phylogenetic classification of prosauropods is in transition, as scientists try to understand the relationship of sauropods and prosauropods; specifically, scientists want to know if prosauropods were the ancestors of sauropods, or if they existed and evolved simultaneously in sister clades. Later research has leaned towards the latter—that prosauropods and sauropods were distant cousins and that their development was parallel.

Anatomy

The Coloradisaurus fossil was incomplete when discovered; the majority of the information available is on the skull. Coloradisaurus's skull was wide and tall, but comparatively short, with 23 or 24 teeth. All sauropodomorphs have tall tooth crowns.

Coloradisaurus belongs to the suborder Sauropodomorpha. Dinosaurs of this suborder possess large bodies and small heads. Compared to the other members of this suborder, Coloradisaurus had a shorter snout. The skull indicates large eye sockets on either side of the head, resulting in monocular vision. Consequently, the dinosaur could not judge distances but had a good wide-angle perspective.

Sauropods had extra vertebrae in the neck, with weaker back vertebrae. Sauropods had at least 12 cervical vertebrae. Scientists are divided as to whether Coloradisaurus walked on two legs or four. Some believe the dinosaur may have been both bipedal and quadrupedal. The first toe of the front foot had a claw attached.

Intelligence

Sauropods are at the bottom of the table of dinosaur intelligence that James A. Hopson devised. An alligator of the present day has an EQ of 1.0; one of the most intelligent dinosaurs, Troodon, had an EQ of 5.8. Scientists assume that Coloradisaurus had enough intelligence to find food, escape predators, and mate. Hopson placed prosauropods low on the scale, with an EQ of 0.05.

Reproduction and Population

In 1979, paleontologists Bonaparte and Martin Vince discovered a nest of seven juvenile dinosaurs and two eggs. The skulls of the juveniles were small enough to be held in the palm of a hand, and it was postulated that the juveniles were several weeks old, as they could not have fit into the eggs found at the same site. They were classified as Mussasaurus patagonicus, the same species thought to be a juvenile of Coloradisaurus.

The eggs found at the site were wedge-like in structure and the clutch (number of eggs) was fairly small. Given the size of the hatchlings, scientists propose that these prosauropods grew quickly.

Diet

Coloradisaurus was a large, herbivorous creature. Seed-bearing plants were widely available during the Late Triassic period.

The plants of the Late Triassic period generally had outer coverings that were thorny or tough, which lessened the nutritional value of the plants. As a result, Coloradisaurus and other sauropods would have needed to consume large quantities of plants. In addition, because such plants were more difficult to digest, the dinosaurs had elongated guts and some relied on gastroliths, or small stones in the digestive system, to facilitate digestion. Conifers reached higher than any previous land plants. Paleontologists theorize that the long neck and ability to stand on two legs was an adaptation of some prosauropod dinosaurs to allow feeding on the conifers.

Behavior

Little is known about the lifestyle of Coloradisaurus. Scientists believe that prosauropods were facultatively bipedal, meaning that they were able to walk on all fours but could walk bipedally, using their forelimbs for walking, climbing and grasping, when necessary. Prosauropods have been characterized as non-aggressive and may have travelled in mixed species herds, as their consumption of large amounts of plant matter necessitated their continued migration.

Habitat and Other Life Forms

Coloradisaurus was discovered near La Rioja, in present-day northwest Argentina, an area that was probably a plain that had been flooded and consequently marshy. During the Late Triassic period, the climate became less dry; scientists think monsoons may have provided moisture for the development of plants such as mosses, ferns, and horsetails. Algae also developed during this time. The abundant vegetation would have provided plenty of food for Coloradisaurus.

The red sands suggest that the environment provided excess oxygen, known as an oxidizing environment. In an oxidizing environment, the iron in rocks and soil changes chemically and produces a deep rust color. This is the case at La Rioja. Contemporaries of Coloradisaurus included Riojasaurus, an Argentinean prosauropod, as well as Pisanosaurus and Guaibasaurus. Carnivores in the Late Triassic included Eoraptor and Staurikosaurus. Argentina has been a rich source of fossil finds.

Research

Some scientists believe Coloradisaurus may be the adult form of Mussaurus. Researchers have found only juvenile specimens of this smaller dinosaur. This idea of both being the same species, however, has yet to be proved.

The Coloradisaurus also resembles a dinosaur from southern China, Lufengosaurus, which was a larger animal that lived slightly later (in the Early Jurassic) than Coloradisaurus. The two species have similar builds, supporting the idea of a single continent with widely ranging animals.

In the 2000s and 2010s, based on comparisons of body features, a number of scientists proposed that Coloradisaurus be reclassified as massospondylids, in the same clade as Massospondylus rather than Plateosaurus; however, the skull features of Coloradisaurus bear striking resemblance to plateosaurids. Thus, debate remains over the nearness of relation between Coloradisaurus and Massospondylus versus Coloradisaurus and Plateosaurus. Other sauropodomorphs since discovered in China and Africa, such as Leyesaurus, Xingxiulong, and Ledumahadi, were compared to Coloradisaurus in attempts not only to identify those dinosaurs but also to clarify the phylogenetic relationships among the sauropodomorphs generally.

Paleontologists disagree as to whether dinosaurs were warm-blooded or cold-blooded. One theory suggests that both metabolic options were possible or that some dinosaurs had a system somewhere in between the two extremes.

Bibliography

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