Plesiosauria includes the large, carnivorous, marine reptiles the Plesiosaurs and Pliosaurs. They used their flippers to propel themselves through the water, rather like a turtle except that they used both the front and rear flippers. Scientists were intrigued to find that using all four flippers didn't make them faster. In fact, the opposite was true, as turbulence from the front flippers interfered with the efficiency of the rear flippers. However, four flippers did make it easier to get going and brake. So while Plesiosaurs and Pliosaurs may not have been ultra-speedy, they would have been agile and quick to react to passing prey.
Neanderthals looked much like modern humans only shorter, more heavily built and much stronger, particularly in the arms and hands. Their skulls show that they had no chin and their foreheads sloped backwards. The brain case was lower but longer housing a slightly larger brain than that of modern humans. As almost exclusively carnivorous, both male and female Neanderthals hunted. Evidence of a huge number of injuries - like those sometimes seen in today's rodeo riders - suggests that hunting involved dangerously close contact with large prey animals.
Tundra
Tundra is the cold, treeless region around the poles that has permafrost as one of its defining features. Even at the height of summer, the soil a few centimetres under the surface remains frozen. The tundra therefore lacks animals that dig deep burrows and plants that require deep root systems. The permafrost, plus the short summer and seasonal waterlogging, also explains why trees don't grow here.
Very little is known about dinosaur courtship, rivalry, pairing and mating.
EGGS
Dinosaurs hatched from eggs laid by females after sexual reproduction. The eggs were round or elongated and had hard, brittle shells. Internally, these eggs were similar to those of reptiles, birds and primitive mammals; they contained a membrane (called the amnion) that kept the embryo moist. Some dinosaurs cared for their eggs, others simply laid them and then abandoned them.
The first fossilized dinosaur eggs found (and the biggest yet to be found) were football-shaped Hypselosaurus eggs found in France in 1869. These eggs were 1 foot (30 cm) long, 10 inches (25 cm) wide, had a volume of about half a gallon (2 liters), and may have weighed up to 15.5 pounds (7 kg). The smallest dinosaur eggs are about 1 inch across; they are from Mussaurus.
Many fossilized dinosaur eggs have been found, at over 200 sites in the USA, France, Spain, Mongolia, China, Argentina, and India. Very rarely, the eggs have preserved parts of embryos in them, which can help to match an egg with a species of dinosaur. Without an embryo, it it difficult to match an egg to a dinosaur species. The embryo in an egg sheds light on dinosaur development.
FOSSIL OR ORIGINAL SHELL?
According to Dr. Kenneth Carpenter of the Denver Museum, most dinosaur eggshells still have the original shell, not a fossilized replica, "The slightest change in the calcite making up the shell destroys the very fine detail that can be seen with the scanning electron microscope. Amino acids have also been recovered that are very similar to those found in modern bird eggshell."
RECENT FINDS
About 10 large dinosaur eggs (plus 3 egg impressions) were found 1999 in southwestern France (near Albas, in the foothills of the Pyrenee Mountains). No bone fossils were found. The eggs had been buried in two layers in the sand. No one knows what type of dinosaur the eggs were.
Much larger egg sites have been found nearby, in northeastern Spain near Tremp, where hundreds of thousands of eggs (of both sauropods and theropods) have been found. Other huge dinosaur eggs sites have been found in Argentina and China.
NESTS
Fossils of dinosaurs' burrows and nests can reveal a lot about their behavior. Nests vary from simple pits dug into the earth or sand to more complicated nests constructed with mud rims. They may appear in large groups or all alone. The nests and the clutches of eggs reveal information about the dinosaur's nurturing behavior.
Woolly mammoth
A great deal has been found out about woolly mammoths from analysis of carcasses frozen in the Siberian permafrost and from depictions in ancient art. They were built like elephants, but with adaptations to prevent heat loss - tiny ears, short tails and a thick coat of dark brown hair. On the underbelly, the hair grew up to a metre long and was probably shed in the summer. Their trunks ended with two 'fingers' that helped pluck grass. Humps of hair and fat behind the head made the shoulders seem higher than the pelvis. However, the front and back legs were actually about the same length.
Scientific name: Mammuthus primigenius
Rank: Species
Common names: Tundra mammoth
The Cretaceous ended with the most famous mass extinction in history - the one that killed the dinosaurs. Prior to that, it was a warm period with no ice caps at the poles. Much of what we now know as dry land - such as southern England and the midwest of the USA - was underwater, since sea levels reached their highest ever during this time. The Atlantic Ocean grew much wider as North and South America drew apart from Europe and Africa. The Indian Ocean was formed at this time, and the island that was India began its journey north towards Asia.
Duck-billed dinosaurs were successful and common herbivores from the upper Cretaceous period. The secret of their success perhaps lay with the duck-shaped bill that clipped vegetation and the many small teeth that ground it down. There were two types: some with a bony crest on their head for resonating sound and some without. Fossilised nest sites have shown that some species may have travelled to communal nesting grounds to lay eggs, as many bird species do today. Fossils from the many species are found all over modern-day Europe, Asia and North America, and show that some grew to around 12 metres.
A relative of Iguanodon, Muttaburrasaurus had the same spiked thumb and ability to walk either on all fours or on its hind legs. However, it differed in that it may have eaten meat as well as plants. Its name comes from the Australian town where it was first discovered. Muttaburrasaurus had an unusual rounded muzzle with a hollow chamber inside it the purpose of which is unknown. Perhaps it was to improve the sense of smell or to resonate sound and enable Muttaburrasaurus to make loud cries.
Plant-eating Iguanodons were large dinosaurs capable of walking on two legs or on all four. Their outstanding feature was a highly specialised, five-fingered hand made up of an erect and spiked thumb used for defence or perhaps foraging, three middle fingers and a grasping fifth finger. Iguanodons were one of the first dinosaurs ever described and artistic impressions have changed much with each new discovery. Currently, it's thought they held the head low to the ground and their long, heavy tail in the air for balance rather than vice versa. Herds of Iguanodon - the different species varying in size - flourished in Europe and North America during the lower Cretaceous period.
The tail of the small, plant-eating Leaellynasaura dinosaur was three times as long as its body. Described in 1989 after skull fragments and bones were found in Australia's Dinosaur Cove - one of the few dinosaurs ever found in Australia - they were named after the discoverer's daughter (Leallyn). Large eye sockets and optic nerve casings may have given leaellynasaura enhanced vision to cope with the long, dark winter months. Odd to think of Australia having such winters, but during the early Cretaceous some 110 million years ago, this part of the world fell within the Antarctic circle
With some of the most advanced chewing apparatus ever developed by a reptile, ornithopod dinosaurs became a most successful group of herbivorous dinosaurs. They rapidly became a prominent feature on North America's Cretaceous landscape, until they were wiped out by the famous Cretaceous-Tertiary, or K-T, extinction event. Early ornithopods were only about a metre long and could probably run very fast on their hind legs. They evolved to become as large as some of the mighty sauropods, walking and grazing on all four legs, but still using the hind legs for running and reaching up into trees. Notable ornithopods include the duck-billed hadrosaurs and, of course, iguanodon.
Ceropod dinosaurs were all plant-eaters and include the horned and duck-billed dinosaurs. The secret of their success was in their teeth. These were much more efficient at grinding up plant food than your typical dinosaur's dentition, so cerapods were able to extract more nutritional value from their food and tackle plants that others found too tough to digest. It wasn't until big herbivorous mammals evolved that such efficient chewing teeth were seen again on Earth.
Ankylosaurs
Looking like reptilian armadillos, or prehistoric tanks, Ankylosaurs were heavily armoured dinosaurs with protective plates over their head and shoulders. Some species took their protection to extremes and even had armoured eyelids. Spikes and protrusions were common in a bid to deter predators from taking a bite. Some ankylosaurs had a large, heavy club at the end of the tail for wielding as a weapon or, as has also been suggested, for sexual selection. To carry the weight of all this heavy armour, these plant-eating dinosaurs had very short, stout legs.
Impact events, proposed as causes of mass extinction, are when the planet is struck by a comet or meteor large enough to create a huge shockwave felt around the globe. Widespread dust and debris rain down, disrupting the climate and causing extinction on a global, rather than local, scale. The demise of the dinosaurs at the end of the Cretaceous has been linked to an impact that left a crater in the seabed off the Yucatan peninsula of Mexico. Impacts have also been blamed for other mass extinctions, but the timing and links between cause and effect for these is still debated by scientists.
The Cretaceous-Tertiary mass extinction - also known as the K/T extinction - is famed for the death of the dinosaurs. However, many other organisms perished at the end of the Cretaceous including the ammonites, many flowering plants and the last of the pterosaurs. Some groups had been in decline for several million years before the final event that destroyed them all. It's suggested that the decline was due to flood basalt eruptions affecting the world's climate, combined with drastic falls in sea level. Then a huge asteroid or comet struck the seabed near the Yucatan Peninsula in Mexico and was the straw that broke the camel's back.
The Permian mass extinction has been nicknamed The Great Dying, since a staggering 96% of species died out. All life on Earth today is descended from the 4% of species that survived. The event turns out to have been complex, as there were at least two separate phases of extinction spread over millions of years. Marine creatures were particularly badly affected and insects suffered the only mass extinction of their history. Many causes have been proposed for the event: asteroid impact, flood basalt eruptions, catastrophic methane release, a drop in oxygen levels, sea level fluctuations or some combination of these.
Ichthyosaurs were predatory marine reptiles that swam the world's oceans while dinosaurs walked the land. They appeared in the Triassic period, dying out around 25 million years before the extinction event that wiped out the dinosaurs. Ichthyosaurs (literally 'fish-lizards') evolved from an as yet unidentified land reptile that moved back into the water. These huge animals rapidly diversIchthyosaurs were predatory marine reptiles that swam the world's oceans while dinosaurs walked the land. They appeared in the Triassic period, dying out around 25 million years before the extinction event that wiped out the dinosaurs. Ichthyosaurs (literally 'fish-lizards') evolved from an as yet unidentified land reptile that moved back into the water. These huge animals rapidly diversified from being lizards with fins to developing a much more streamlined, fish-like form built for speed. One species has been calculated to have a cruising speed of 3.6 km/h. These enormous predators remained at the top of the food chain until they were replaced by the plesiosaurs.ified from being lizards with fins to developing a much more streamlined, fish-like form built for speed. One species has been calculated to have a cruising speed of 3.6 km/h. These enormous predators remained at the top of the food chain until they were replaced by the plesiosaurs.
