Coelophysis

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Saurischia

Family: Coelophysidae

Genus:Coelophysis

Species:Coelophysis bauri

Introduction

Coelophysis was a medium-sized predator that lived in the Late Triassic period in the forests and scrub of North America. An early dinosaur, Coelophysis represents a lineage of terrestrial predators that would dominate the environment throughout the Mesozoic and would eventually lead to the evolution of the largest land predators in history.

In the Triassic period, the continents of the earth were joined in a single supercontinent called Pangaea. The territory that is now Europe was partially separated from Africa by a body of water called the Tethys Seaway. In the Jurassic and Cretaceous, Pangaea split into two supercontinents, Gondwana in the south and Laurasia in the north. Relatives of Coelophysis spread across Pangaea during the Triassic period, giving rise to ancestors in both supercontinents after the break-up of Pangaea.

Coelophysis was relatively common throughout much of its range and shared its environment with some of the largest prehistoric reptiles that evolved in the previous period. The basic structure of Coelophysis was one of the most successful predatory designs in history and became the template for many terrestrial predators for more than 200 million years.

Classification

Scientists use two primary methods to organize animals into different groups. Linnaean taxonomy, also called “systematics,” groups organisms in a hierarchical fashion according to overall physical similarity, while an alternate system called “cladistics” attempts to create groups that better reflect the evolutionary relationships between species. The more shared features they have, the more likely it is that they also shared a common ancestor, placing them in the same clade.

According to systematic analysis, Coelophysis belongs to the order Saurischia because of the lizard-like structure of its pelvis (though, by the end of the second decade of the twenty-first century, the traditional division into the orders Saurischia and Ornithischia was challenged by some scientists). From there, the species is placed in the suborder Theropoda, a broad group of bipedal dinosaurs that were primarily predatory (though a few were omnivorous). The family Coelophysidae contains small and mid-sized predatory dinosaurs that were among the first theropods to evolve.

Cladistic analysis places Coelophysis in the theropod clade, which is distinguished partially by elongated necks, air sacks in the vertebrae, bipedal stance, and the presence of a furcula or “wishbone” on the chest. The clade Coelophysoidea divides from the ancestor species at the base of the theropod clade and contains features considered primitive in relation to later theropod groups.

Anatomy

Coelophysis was a medium-sized predator, reaching lengths of between 2.8 and 3 meters (9.2–9.8 ft) and standing roughly 1 meter (3.2 ft) at the hip. The animal was lightly built, weighing approximately 40–50 kilograms (88–110 lbs) as an adult. Compared to the non-dinosaurian predators of the day, Coelophysis was very different in construction, built for speed and agility rather than power.

Coelophysis was bipedal with long, muscular rear legs terminating in three-toed, clawed feet. Its arms were shorter and thinner, though still muscular, with sharp claws on each of its three functional fingers. The animal had a long neck and a narrow muzzle, with large, forward-facing eyes. The tail was long and narrow, with bony struts reinforcing the vertebrae, keeping the tail straight while the animal was in motion.

The teeth of Coelophysis were sharp and curved, with fine serrations along the outer and inner surfaces. The skull had pronounced fenestrae (small anatomical openings), strengthened by bony ridges and struts. The animal's snout was pointed, and it had long nasal cavities. It is likely that Coelophysis had fine, mosaic scales, as found in skin impressions of other dinosaur species.

Intelligence

Theropods had higher EQ values than other dinosaurs, and it was the theropod group that paleontologists believe gave rise to the birds in the Jurassic. While some later theropods would have EQ ratings as high as 5.8, Coelophysis was a relatively early member of the group and probably had a significantly lower EQ value. Dinosaurs in general are believed to have been more intelligent than the prehistoric reptiles that preceded them, and it is likely that Coelophysis was one of the most intelligent animals during its time.

Reproduction and Population

Coelophysis fossils are relatively common in North American fossil sites from the Late Cretaceous, indicating that the species may have been widespread. Upon the initial discovery of Coelophysis specimens, paleontologists believed that they discovered a small, juvenile Coelophysis skeleton within the abdominal cavity of an adult specimen. This was taken as evidence that Coelophysis may have been cannibalistic or, alternatively, may have given birth to live young. However, subsequent analysis indicated that the “juvenile specimen” belonged to a crocodile-like reptile, not a baby Coelophysis, so it did not indicate cannibalism. Paleontologists now believe that Coelophysis reproduced by laying eggs. Adult skeletons of Coelophysis show considerable size distribution, ranging from large, heavy individuals to slender, more delicate fossils. This has led some paleontologists to suspect that the animal may have displayed some degree of sexual dimorphism, with either females or males being larger. As of 2020, paleontologists had no evidence to suggest whether Coelophysis was a solitary breeder or whether the animal gathered in groups to lay eggs or engage in cooperative parental behavior.

Diet

Coelophysis was a carnivore and most likely relied on speed and agility. Some Coelophysis specimens appear to have the remains of small reptiles in their abdominal cavities, suggesting that these formed part of the species’ diet. It is also likely that Coelophysis hunted fish and amphibians in the lakes, rivers, and floodplains of western Pangea.

Some paleontologists have suggested that Coelophysis gathered in groups, which may have permitted the species to prey on larger herbivores by hunting cooperatively. Alternatively, Coelophysis may have gathered into chaotic groupings around potential food sources, similar to the behavior of modern crocodiles and vultures on the African savannahs.

Behavior

The theory that male and female Coelophysis differed in size brings into question whether the species displayed any competitive mating behavior. In some modern birds, mammals, and reptiles, individuals gather during mating seasons and compete for mates, a behavior that may also have been common among some dinosaurs.

Though Coelophysis is more closely related to theropods of the Jurassic and Cretaceous than to modern birds, some paleontologists believe that, given the animal's structure, it may already have adopted some “bird-like” behaviors, especially in comparison to the large prehistoric reptiles that were still common in its environment. Paleontologists have compared Coelophysis to living species of storks that hunt a variety of small animals in Africa, relying on speed and agility to catch prey and to avoid predators.

Habitat and Other Life Forms

Late Triassic North America was significantly warmer than in the modern period. The southern portion of the continent was dotted by lakes, rivers, and flood plains, while the central portion was largely arid. Gymnosperms like conifers and cycads were the dominant type of vegetation in arid zones and dry forests, while ferns and tree ferns thrived in areas with more available freshwater.

In addition to dinosaurs, Late Triassic North America had a variety of wildlife including many small reptiles and amphibians. Pterosaurs, the first flying vertebrates, evolved during the Triassic and dominated the skies until the Cretaceous. In addition to Coelophysis, there were large predatory reptiles, such as Postosuchus, living in North America. Herbivorous reptiles like the aetosaur Typothorax were present in large numbers.

While dinosaurs were beginning to spread, the large prehistoric reptiles were still common in the Triassic. Some of the largest predators were crocodylomorphs, ancestors of modern crocodiles and reptiles that evolved into a variety of terrestrial and semi-aquatic hunters. The dicynodonts, large prehistoric reptiles that had existed for millions of years before the Triassic, were in a state of decline, but at least one species was still present in North America in the Late Triassic.

Research

Coelophysis was named by pioneer paleontologist Edward Drinker Cope in 1889 from a specimen found by an amateur hired fossil collector in 1881. The name means "hollow form" and is in reference to the hollow limb bones. Paleontologist Edwin Colbert was among the most important contributors to the study of Coelophysis when he described specimens unearthed from the Ghost Ranch fossil site in New Mexico in 1947. A substantial number of full and partial specimens were retrieved from Ghost Ranch, and later specimens were found in other beds across the Southwest. This site was called a “graveyard” because of quantity of specimens, and scientists speculated that the mass burial was caused by a flash flood. In 1981, an early species of Coelophysis was honored as the New Mexico State Fossil by the State Legislature.

Since its discovery, Coelophysis has been important in the effort to reconstruct the evolution of the theropods and also in determining the evolutionary relationships between dinosaurs and birds. Paleontologists remained interested in the fossils recovered from the Ghost Ranch site, particularly those of Coelophysis found in the Whitaker Dinosaur Quarry, and debates as well as research continued into determining why so many Coelophysis skeletons were found there. By 2020, it had been revealed that fossilized footprints had been discovered in layers of rock in South Africa's Karoo Basin; upon initial study, some scientists proposed that the larger tracks believed to have been left by a theropod may have been those of a Coelophysis or a similar species.

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