BEAR DOG

Amphicyonidae is an extinct family of large terrestrial carnivores belonging to the suborder Caniformia (meaning "dog-like") and which inhabited North America, Europe, Asia, and Africa from the Middle Eocene subepoch to the Pleistocene epoch 46.2—1.8 Mya, existing for approximately  million years.Amphicyonids, often referred to as "bear 

dogs", crossed from Europe to North America during the Miocene epoch and are considered an Old World taxon. The earliest to appear is the (rather large)Ysengrinia (30—20 Mya), followed by Cynelos (24—7 Mya) and Amphicyon (23—5 Mya). These animals would have followed ungulates and other mammals to the New World for a period of approximately 7 million years. The New World amphicyonids of the subfamilies Daphoeninae (42-16 Mya) and Temnocyoninae (33-20 Mya) coexisted with the Old World counterparts. Note that the (often similar looking) members of the family Hemicyonidae are often called "bear-dogs" as well (although they are increasingly referred to as "dog-bears" to avoid confusion).While amphicyonids have traditionally been viewed as closely related to ursids (bears), some evidence suggests that they may instead be basal caniforms. (Hunt, 2004b). They were about as tall as the American black bear and were most likely ambushers because their legs were made for short, sudden bursts of speed. Bear-dog also nested their young in underground burrows.During the early Miocene, a number of large amphicyonids migrated from Eurasia into North America. These taxa belong to the Old World amphicyonid sub-family Amphicyoninae. The earliest to appear is the large bear dog Ysengrinia Ginsburg, followed by Cynelos Jourdan, and then by Amphicyon. This influx of amphicyonines, accompanied by other Old World ungulates and small mammals, indicates a prolonged interval (from 23 to 16.5 Ma) of faunal exchange between Asia and North America in the early Miocene, using the trans-Beringianroute.New World daphoenines (Daphoenodon, Borocyon) and temnocyonines coexisted with Old World amphicyonines
 (Ysengrinia, Amphicyon, Cynelos) 23.7-17.5 million years ago. These are the largest terrestrial carnivorans 50 kilograms (110 lb) to 200 kilograms (440 lb) that evolved on the North American continent up to this time. The immigrant 

amphicyoninesYsengrinia, Cynelos and Amphicyon appear at 23, 19.2, and 18.8 Ma, respectively, and herald the beginning of a Eurasian amphicyonine migration into North America that continued into the mid-iocene.Amphicyonids were as small as 5 kilograms (11 lb) and as large as 100 to 600 kilograms (220 to 1,300 lb) and evolved from wolf-like to bear-like.The diet of the amphicyonids was fully carnivorous as opposed to hypercarnivorous to mesocarnivorous in Canidae.

PTERANODON: THE HOODED MONSTER

Pteranodon from the Late Cretaceous geological period of North America in present day Kansas, Alabama, Nebraska, Wyoming, and South Dakota, was one of the largest pterosaur genera and had a maximum wingspan of over 6 metres (20 ft). Pteranodon is known from more fossil specimens than any other pterosaur, with about 1,200 specimens known to science, many of them well preserved, with complete skulls and articulated skeletons. It was an important genus of the animal community present in the Western Interior Seaway.Adult Pteranodon specimens from both major species can be divided into two distinct size classes. The smaller class of specimens have small, rounded head crests and very wide pelvic canals, even wider than those of the much larger size class. The size of the pelvic canal was probably to allow the laying of eggs, indicating that these smaller adults are females. The larger size class, representing male individuals, have narrow hips and very large crests, which were probably for display.Pteranodon was a reptile, but not a dinosaur. By definition, all dinosaurs belong to the groups Saurischia and Ornithischia, which excludes pterosaurs. Nevertheless, Pteranodon is frequently featured in dinosaur books and is strongly associated with dinosaurs by the general public.Specimens assigned to Pteranodon have been found in both the Smoky Hill Chalk deposits of the Niobrara Formation, and the slightly younger Sharon Springs deposits of the Pierre Shale Formation. WhenPteranodon was alive, this area was covered by a large inland sea, known as the Western Interior Seaway. Famous for fossils collected since 1870, these formations extend from as far south as Kansas in theUnited States to Manitoba in Canada. However, Pteranodon specimens (or any pterosaur specimens) have only been found in the southern half of the formation, in Kansas, Wyoming, and South Dakota. Despite the fact that numerous fossils have been found in the contemporary parts of the formation in Canada, no pterosaur specimens have ever been found there. This strongly suggests that the natural geographic range of Pteranodon covered only the southern part of the Niobrara, and that it's habitat did not extend farther north than South Dakota.

Some very fragmentary fossils belonging to pteranodontian pterosaurs, and possibly Pteranodon itself, have also been found on the Gulf Coast and East Coast of the United States. For example, some bone fragments from the Mooreville Formation of Alabama and the Merchantville Formation of Delaware may have come from Pteranodon, though they are too incomplete to make a definite identification.Some remains from Japan have also been tentatively attributed to Pteranodon, but their distance from its known Western Interior Seaway habitat makes this identification unlikelyAdult male Pteranodon were among the largest pterosaurs, and were the largest flying reptiles known until the late 20th Century, when the giant azhdarchid pterosaurs were discovered. The wingspan of an average adult male Pteranodon was 5.6 metres (18 ft). Adult females were much smaller, averaging 3.8 metres (12 ft) in wingspan. The largest specimen of Pteranodon longiceps from the Niobrara Formation measured 6.25 metres (20.5 ft) from wingtip to wingtip. An even larger specimen is known from the Pierre Shale Formation, with a wingspan of 7.25 metres (23.8 ft), though this specimen may belong to the distinct genus and species Geosternbergia maysei.While most specimens are found crushed, enough fossils exist to put together a detailed description of the animal.Pteranodon longiceps would have shared the sky with the giant-crested pterosaur Nyctosaurus. Compared to P. longiceps, which was a very common species,Nyctosaurus was rare, making up only 3% of pterosaur fossils from the formation. Also less common was the early toothed bird, Ichthyornis.

Methods used to estimate the weight of large male Pteranodon specimens (those with wingspans of about 7 meters) have been notoriously unreliable, producing a wide range of estimates from as low as 20 kilograms (44 lb) and as high as 93 kilograms (210 lb). In a review of pterosaur size estimates published in 2010, researchers Mark Witton and Mike Habib demonstrated that the latter, largest estimates are almost certainly incorrect given the total volume of a Pteranodon body, and could only be correct if the animal "was principally comprised of aluminium." Witton and Habib considered the methods used by researchers who obtained smaller weight estimates equally flawed. Most have been produced by scaling modern animals such as bats and birds up to Pteranodon size, despite the fact that pterosaurs have vastly different body proportions and soft tissue anatomy than any living animal.It is likely that, as in other polygynous animals (in which males compet for association with harems of females), Pteranodon lived primarily on offshore rookeries, where they could nest away from land-based predators and feed far from shore; most Pteranodon fossils are found in locations which at the time, were hundreds of kilometres from the coastline.Below the surface, the sea was populated primarily by invertebrates such as ammonites and squid. Vertebrate life, apart from basal fish, included sea turtles such asToxochelys, the plesiosaur Styxosaurus, and the flightless diving bird Parahesperornis. Mosasaurs were the most common marine reptiles, with genera including Clidastes and Tylosaurus. At least some of these marine reptiles are known to have fed on Pteranodon. Barnum Brown, in 1904, reported plesiosaur stomach contents containing "pterodactyl" bones, most likely from Pteranodon.The diet of Pteranodon is known to have included fish; fossilized fish bones have been found in the stomach area of one Pteranodon, and a fossilized fish bolus has been found between the jaws of another Pteranodon, specimen AMNH 5098. Numerous other specimens also preserve fragments of fish scales and vertebrae near the torso, indicating that fish made up a majority of the diet of Pteranodon (though they may also have taken invertebrates).Fossils from terrestrial dinosaurs also have been found in the Niobrara Chalk, suggesting that animals who died on shore must have been washed out to sea (one specimen of a hadrosaur appears to have been scavenged by a shark).Traditionally, most researchers have suggested that Pteranodon would have taken fish by dipping their beaks into the water while in low, soaring flight. However, this was probably based on the assumption that the animals could not take off from the water surface.It is more likely that Pteranodon could take off from the water, and would have dipped for fish while swimming rather than while flying. Even a small, female Pteranodon could have reached a depth of at least 80 centimetres (31 in) with its long bill and neck while floating on the surface, and they may have reached even greater depths by plunge-diving into the water from the air like some modern long-winged seabirds. In 1994, Bennett noted that the head, neck, and shoulders of Pteranodon were as heavily built as diving birds, and suggested that they could dive by folding back their wings like the modern Gannet.