Early Cretaceous Animals

The Cretaceous was the third and final period of the Mesozoic Era, spanning from 145 to 66 million years ago. Earth's two great Northern and Southern landmasses; Laurasia and Gondwana continued to break up into smaller but still mostly connected continents. By the end of the Cretaceous most of the continents we see today would be somewhat recognizable. North America and Asia were still connected and Europe was still mostly covered in shallow seas, creating a vast archipelago of islands. Madagascar had separated from India and Africa to become its own landmass, and South America, Antarctica and Australia were still connected as well. North America was for up until the very end of the Cretaceous split in half by a shallow sea known as the Western Interior Seaway. The Atlantic Ocean between Africa and North America was about half as wide as it is today. The global climate was generally warm and humid throughout the Cretaceous, but there were a few episodes, especially towards the end, where the climate turned temperate. The poles had no glaciation, but temperatures dropped low enough for snow to fall at least.

Life continued to flourish as it did during the Jurassic, with plants and animals taking on more and more forms. The first flowering plants evolved in the early Cretaceous, including oaks, magnolias, figs, sycamores, and maples, which by the end of the period had started to largely replace more ancient types of plants such as ferns, cycads, and conifers, although these were still very common. The earliest grasses are also believed to have appeared in the late Cretaceous, though it would be millions of years after this time period before they would dominate the Earth's flora as they do now. Many new types of insects appeared as well such as ants, bees, wasps and butterflies. The first of these pollinating insects co-evolved with the first flowering plants; the mutual symbiosis between them helped each-other spread throughout the world. The largest and most ecologically important terrestrial vertebrates of this time were still the dinosaurs, and during the Cretaceous they became even more diverse and widespread. Groups are found on every part of the globe in almost every terrestrial habitat. Sauropods grew even larger than in the Jurassic, culminating in the enormous titanosaurs; the biggest land animals of all time with some species weighing nearly 100 tons. By the late Cretaceous, however, sauropods rarely grew so huge with most species weighing less than 10 tons, and inhabiting mostly the southern continents. In the north several new families of giant herbivores evolved to replace the sauropods, including the heavily armored ankylosaurs; cousins of the stegosaurs(who died out early in the period), the horned and frilled ceratopsians like Triceratops, and the duckbilled hadrosaurs many of which held bizarre crests on their heads. Smaller two legged ornithopods were still common along with the strange pachycephalosaurs, herbivores with thick bony domes at the top of their skulls. The biggest carnivores varied throughout the Cretaceous; in the early-mid Cretaceous giant carnosaurs like Carcharodontosaurus ruled most of the world, but by the end of the Cretaceous two groups ruled different parts of the planet. In the south there were the deep-skulled and short-armed abelisaurs like Carnotaurus, and in the north the similarly short-armed but more famous tyrannosaurs like Tyrannosaurus. Smaller more bird-like theropod dinosaurs exploded in diversity from the fearsome dromaeosaurs armed with lethal claws on their feet to giant long-necked therizinosaurs with massive claws on their hands for reaching into trees, to the ostrich-like ornithomimisaurs. Some small bird-like dinosaurs lived mostly in the trees, some forms even becoming able to glide, and at least one species of spinosaurid theropod adapted to living mostly in water. True birds became very diverse by the late Cretaceous, though most species still retained primitive characteristics such as teeth and clawed wings. Pterosaurs grew larger and larger until some species had wingspans as long as an airplane, although only a handful existed by the end of the period. Other kinds of reptile thrived as well, from crocodiles which grew large enough to feed on giant dinosaurs, to the earliest limbless snakes to several families of marine reptiles. Ichthyosaurs died out in the mid-Cretaceous but were replaced by the giant mosasaurs; marine lizards in the same family as monitor lizards. Long and short-necked plesiosaurs were still common alongside giant turtles, fish, sharks and ammonites. On land mammals were still mostly confined to the shadows, but they still came in a wide range of shapes from small burrowers and tree-climbers up to cat-sized terrestrial hunters. The first marsupials and placentals appeared before the period ended, although none of them resembled their modern descendants.

About 66 million years ago at the end of the Cretaceous, an extinction even occurred that wiped out roughly 75% of all species on Earth at the time, most famously all of the non-avian dinosaurs. This extinction event is one of the most well-studied with the overall consensus being that it was caused by an asteroid about the size of Mt. Everest colliding with Earth near what is today Mexico's Yucatan Peninsula. The impact triggered earthquakes, tsunamis, and volcanic eruptions across the globe along a rain of super-heated debris which ignited globe wildfires. On top of all of this was a massive cloud of ash and dust soon covered the planet, blocking out the sun for perhaps as long as several years. The end result was something akin to a nuclear winter. Dropping temperatures, toxic fallout and lack of sunlight caused the global food web to collapse with plants dying off first, then plant eating animals followed by predators that fed on them. The dinosaurs with their great size and high metabolisms could not stand against this sudden and catastrophic change. But many other groups also either completely vanished such as the pterosaurs, plesiosaurs, mosasaurs, and ammonites, or suffered tremendous losses as did fish, mammals and birds. Aside from turtles and crocodiles, no tetrapod larger than 55 pounds survived.

†Hyphalosaurus lingyuanensis: this small reptiles from the family known as Choristodera, was one of the most common freshwater animals of Chian 122 mya. With smooth, flat scales, a tall, flattened tail, webbed feet and long neck it was a well adapted swimmer which may have feed on small fish and other aquatic prey. Well preserved fossils show that Hyphalosaurus gave birth to live young.

†Repenomamus robustus: Repenomamus was an unusually large mammals from early Cretaceous China. At up to 13 pounds it was as big as an opossum, and the largest mammal known from the age of dinosaurs. It was a stocky, ground-dwelling carnivore that hunted small prey, which, based on fossilized stomach contents, included newly hatched dinosaurs.

†Utahraptor ostrommaysorum: the largest of the dromaeosaurs, or raptors, Utharaptor grew up to 23 feet long and weighed as much as a polar bear, making ti one of the top predators of early Cretaceous North America. Armed with powerful jaws full of sharp teeth, long claws on both its hands and feet, Utahraptor may have hunted in packs or alone.

†Sinocalliopteryx gigas: this feathered carnivore was a cousin of the famous Compsognathus, though it was much bigger at 8 feet long. Fossils show bones of smaller feathered dinosaurs, including early birds, in its stomach.

†Caudipteryx zoui: one of the first feathered dinosaurs known to science, Caudipteryx resembled a turkey with a short skull and small teeth in its beak. It was likely an omnivore feeding on leaves, seeds, fruits and insects. Feather impressions in the fossils show a long fan of feathers on the short tail as well as long wing-like feathers on the forearms. This animal could not fly but likely used these feathers for display.

†Iguanodon bernisartensis: this large ornithopod was one of the first two dinosaurs to be scientifically described in the early 19th century and was also one of the most common kinds of herbivore 125 mya. Growing 30 feet long and weighing 3 tons, it was one of the first types of dinosaur that were able to chew plant matter with powerful cheek teeth. Iguanodon had a long claw on its thumb used for defense and for fighting one another.

†Tupandactylus imperator: this large pterosaur from Brazil had a massive crest made of skin supported by bony spines on its head. This crest was likely brightly colored an used for display or perhaps as a sort of sail to help when flying. Like other large pterosaurs it probably fed on fish, although some believe it used its large beak for crushing heavy fruits.

†Suchomimus tenerensis: a smaller cousin of the famous giant Spinosaurus, Suchomimus was still huge at over 30 feet long. It was equipped with powerful forearms with huge hooked claws and a long, narrow crocodile like snout, all used for hunting fish and other aquatic prey.

†Sauropelta edwardsorum: this 17 feet long ankylosaur from North America had massive spikes covering its neck and shoulders while its back, tail and head were covered in bony scutes. Heavily armored ankylosaurs like this replaced their cousins the stegosaurs by the mid-Cretaceous.

†Eoconfuciusornis zhengi: this magpie-sized bird from China was one of the first birds to develop a horny beak instead of a toothy-snout. It also lost the bony-tail but still had claws on its wings. A pair of long, strange feathers stuck out for the end of its short tail, the purpose of which is uncertain.

†Psittacosaurus mongoliensis: this sheep-sized herbivore was one of the first ceratopsians, a group that included the dozens of giant horned and frilled dinosaurs like Triceratops. Psittacosaurus itself had no frill or horns but did have a pair of spikes jutting out of its cheeks as well as a strong parrot-like beak from which it gets its name. Long quill-like structures grew from the lower back and tail. Recent studies suggest that this dinosaurs coloration was darker on the face and top of the body and lighter on the underside, a technique known as countershanding and a useful form of camouflage in a forested environment.