Pteranodon

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Pterosauria

Family: Pteranodontidae

Genus:Pteranodon

Species:Pteranodon longiceps

Introduction

Pteranodon is a genus of large, toothless pterosaurs, winged reptiles of the Mesozoic Era. Pteranodon and other pterosaurs are not dinosaurs, though they share a distant but common ancestor with the dinosaurs. However, they are heavily associated with dinosaurs in popular media and culture, and as one of the most recognizable pterosaur species, "Pteranodon" is sometimes incorrectly used to refer to the larger group. Similarly, they are often incorrectly called a "pterodactyl," a general name derived from another pterosaur genus, Pterodactylus.

The two species of Pteranodon, P. longiceps (the type species) and P. sternbergi, were almost identical, with wingspans up to 8 meters (26 ft) or more, small torsos, short rear limbs, and long, toothless upper and lower jaws that tapered to a point. The only difference between the two species was the shape of the head crest; P. longiceps males had long, pointy crests that jutted backwards, while P. sternbergi males had shorter, squatter crests that projected upwards.

Fossils provide paleontologists with a wealth of information about extinct organisms. Pteranodon fossils are hard to interpret, however, because they often consist of broken bones and many times pieces are missing. Particularly with flying creatures, such as pterosaurs, which featured hollow and thin-walled bones adapted for flight (reducing body weight), the fragile bones were usually crushed after death. Rarely did they survive fossilization intact. Fossilized Pteranodon remains have only been found in the United States, in Kansas, Wyoming, and South Dakota.

Classification

Pteranodon, like all pterosaurs, was a diapsid, a reptile with two openings on either side of the skull by the eye. Scientists debate where pterosaurs should be placed on the diapsid family tree, because when pterosaurs evolved the ability to fly, their anatomy became so specialized that they no longer looked like other diapsids. Some believe that pterosaurs should be put near the bottom of the tree with the basal archosauromorphs (diapsid reptiles) due to common characteristics in the neck. Other scientists put pterosaurs higher up with the dinosauromorphs, as diapsids are more closely related to dinosaurs than archosauromorphs, owing to their hind limb structure.

The Linnaean system of classification groups organisms together with similar physical characteristics. It places them in a hierarchy that descends from a level with the least amount of similarities to one with the most. In the Linnaean system, Pteranodon is in the same kingdom, phylum, class, and order as all other pterosaurs, but diverges at the family level, where there is considerable disagreement between various researchers. Traditionally it has been placed in the Pteranodontidae family, but the membership and even the validity of this family has been disputed.

The phylogenetic system of classification also groups organisms together with similar physical characteristics, but it takes into account their evolutionary histories. Each grouping, or clade, shares similar physical characteristics, and therefore at some point in their evolution, a common ancestor. Pteranodon belongs to the Ornithocheiroidea clade, which also includes pterosaurs such as Istiodactylus, Ornithocheirus, and Nyctosaurus, though exact classification is often subject to dispute. Many members of the Ornithocheiroidea clade had wingspans much longer than 1 meter (3 ft), weak hind limbs compared to forelimbs, and wings that were positioned higher on their bodies than other pterosaurs.

Anatomy

One of the largest pterosaurs, Pteranodons with wingspans of 8 meters (26 ft) have been collected. Both species—Pteranodon longiceps and P. sternbergi—had large heads with elongated, toothless jaws tapering to a point. But while P. longiceps males had cranial crests that jutted backwards and mirrored the length and v-shape of their jaws, P. sternbergi males had cranial crests that were shorter and wider and projected upwards. (Females of both species had much smaller crests. Though some researchers have suggested the crests may have acted as a rudder during flight or helped with temperature regulation, most scientists believe they were more likely displays for mating or other purposes.

From the neck down, Pteranodon longiceps and P. sternbergi were virtually identical—both had small torsos, short hind limbs, and small tails. Their featherless, membranous wings were narrow and curved in a boomerang-like shape, and were attached to long forelimbs and the extremely elongated fourth finger of their hands. Pteranodon was covered with thick “proto” hairs, insulation that suggested it might have been warm-blooded.

The Pteranodon skeleton was engineered for flight. Pteranodon bones were hollow and had walls only 2 to 3 millimeters thick so that an individual with an 8 meter (26 ft) wingspan most likely weighed around 11 kilograms (24 lbs). Hollow, thin-walled bones reduced weight, thereby reducing energy used during flight. But Pteranodon was not so fragile. Its bones were strengthened by tiny struts, its chest and abdomen were almost completely encircled by ribs, and many of its spinal vertebrae were fused together into a notarium, which stabilized the spine and allowed it to support the muscles of the shoulders and wings. Holes in the vertebrae assisted during respiration by filling with air.

Intelligence

Digital endocasts of the brains of two pterosaurs, Rhamphorhynchus and Anhanguera, show that pterosaur brains were similar to those of birds. Like birds, pterosaurs had large cerebral hemispheres—the parts of the brain concerned with cognition—as well as large optic lobes which controlled vision, large semicircular canals in the inner ear which regulated balance, and extremely large floccular lobes, which may have interpreted sensory information from their wings. It can be inferred from these endocasts that pterosaur brains, Pteranodon included, were well-adapted for flight.

Scientists estimated the intelligence of Rhamphorhynchus and Anhanguera by calculating their encephalization quotient (EQ), a measurement of an organism's intelligence based on brain and body size. The EQ of Rhamphorhynchus has been calculated to be 0.39, and 0.34 for Anhanguera. This puts pterosaurs between reptiles and birds in terms of intellect—they were more intelligent than reptiles, but less so than birds. (Humans have the highest EQ, measuring up to 7.44 in some assessments.)

Reproduction and Population

Fossilized pterosaur eggs containing embryos have recently been found, proving that pterosaurs laid eggs. The skeletal structure necessary for flight was present in the embryos, leading to the speculation that pterosaur hatchlings were flight-ready. In the case of Pteranodon, more than one thousand specimens were found in the middle of what was once the Western Interior Sea, leading paleontologists to believe that hatchlings and juveniles may have required parental care. Only adults and nearly grown sub-adults were found out to sea, so very young Pteranodons may not have been strong fliers and therefore unable to fend for themselves.

Pteranodon was sexually dimorphic, meaning that there were differences in physical appearance between males and females. Males were much larger than females and had significantly bigger cranial crests. (It has been theorized that the large crests served as displays to attract females.) Males also had narrower pelvic channels than females, presumably because they did not lay eggs.

Diet

The Western Interior Sea that spanned the middle of North America during the Late Cretaceous period sustained a variety of marine life. From a Pteranodon specimen collected with digested bones in its pelvis, and another with fish vertebrae and a crustacean joint in its throat, it has been established that Pteranodon ate the marine animals that inhabited the Western Interior Sea.

How Pteranodon fed is a question that has puzzled paleontologists for some time. One theory is that Pteranodon caught fish and other small marine animals by skimming the water with its beak mid-flight. This theory is based on the jaw similarities between pterosaurs and a living skim-feeding bird named rynchops. Opponents of this theory propose that Pteranodon lacked the jaw anatomy and wing power needed to catch fish mid-flight. Some studies have suggested that Pteranodon was physically incapable of skim-feeding because the action would have required too much energy. Later research indicates Pteranodon likely caught fish while floating on the surface of the water, or even could dive much like some seabirds of today.

Behavior

Almost nothing is known about how Pteranodon interacted with its own kind or its environment. Pteranodon probably used flight to escape predators, which may have included plesiosaurs, large, flippered marine reptiles, a specimen of which was discovered with Pteranodon remains in its stomach. It is uncertain, however, whether the plesiosaur was a true predator of Pteranodon or if it just scavenged a carcass that had fallen into the sea.

It has been determined that Pteranodon was a strong flier due to its anatomy and the fact that more than one thousand Pteranodon longiceps and P. sternbergi individuals were collected from what was once the floor of the Western Interior Sea, hundreds of miles from shore. To have flown that far over open water, Pteranodon must have been able to stay aloft for long periods of time. A generally accepted theory is that it was a glider rather than an active wing-flapper, but flapped its wings when taking off and landing. Reconstructions of pterosaur skeletons suggest that on the ground Pteranodon walked on all fours in a flat-footed manner, folding its wings towards its body and out of the way.

Habitat and Other Life Forms

Pteranodon lived roughly 90 to 80 million years ago during the Late Cretaceous period, the last of three geologic periods that comprise the Mesozoic Era. Its home was the land surrounding the Western Interior Sea, where Kansas, Wyoming, and South Dakota in the United States are today. During the Late Cretaceous period, the Western Interior Sea, a shallow ocean that covered the middle of what would become North America from the Gulf of Mexico to the Arctic Circle, was in the process of receding. Plate tectonics that formed the Rocky Mountains were forcing the sea floor upwards. The climate, meanwhile, was warm, reflecting a global rise in temperature.

Many different animals co-existed with Pteranodon in and around the Western Interior Sea in Kansas. These included primitive birds, nodosaurs (relatively small, armor plated, quadrupedal dinosaurs), and a smaller species of pterosaur called Nyctosaurus gracilis. Marine animals that inhabited the sea itself include plesiosaurs, mosasaurs (large marine lizards), sharks, giant clams, turtles, bony fish, squid, and shelled ammonites.

Research

The first Pteranodon specimen was collected in 1870 in the Smoky Hill Chalk in Kansas by paleontologist Othniel Charles Marsh. Marsh was involved in the “Great Bone Wars” with rival paleontologist Edward Drinker Cope, which resulted in a significant increase in dinosaur remains, increased research, and expanding collections for museums. His discovery of Pteranodon was the first pterosaur to be discovered in North America, which was significant. (The Smoky Hill Chalk, the ancient floor of the Western Interior Sea, eventually yielded the remains of over 1,000 Pteranodons.)

For the rest of the nineteenth century and much of the twentieth, paleontologists were concerned primarily with classifying Pteranodon remains. Numerous species were named. However, eventually most researchers agreed that there are only two clear species of Pteranodon: P. longiceps and P. sternbergi. The much less common P. sternbergi existed for millions of years before P. longiceps and is believed to have died out when P. longiceps appeared roughly 84 million years ago. Classification of pterosaurs continues to evolve as new evidence emerges.

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