Not all Cretaceous Period animals were dinosaurs! On this page is a list of interesting Cretaceous animals that weren’t dinosaurs.
- You can see examples of Cretaceous dinosaurs here: Cretaceous Dinosaurs List with Pictures & Facts
- Become a Cretaceous Period expert: The Ultimate Guide to the Cretaceous Period
Page Index
- Introduction
- Animals of the Cretaceous Period that Weren’t Dinosaurs
- Cretaceous Period Mammals
- Insects and other Invertebrates of the Cretaceous Period
- Non-Dinosaur Land Reptiles of the Cretaceous Period
- Cretaceous Period Pterosaurs
- Pseudosuchians In The Cretaceous Period
- Cretaceous Period Snakes & Lizards
- Birds of the Cretaceous Period
- Ocean Animals of the Cretaceous Period
- Cretaceous Fish
- Marine Reptiles Of The Cretaceous Period
- Cretaceous Turtles
- Cretaceous Plesiosaurs
- Cretaceous Ichthyosaurs
- Cretaceous Mosasaurs
- Cretaceous Period Marine Invertebrates
- Cretaceous Period Animals That Weren’t Dinosaurs: Conclusion
- Cretaceous Period Animals: Discover More at Active Wild
Cretaceous Period Animals: Introduction
Although the best-known Cretaceous animals were the dinosaurs, they weren’t the only animals around at the time.
Scurrying between the feet of fearsome meat eaters such as Tyrannosaurus and Spinosaurus were many types of early mammal – some of which (as you’ll find out below) were even big enough to eat small dinosaurs.
The pterosaurs continued to diversify, with both the biggest and the smallest-known species appearing during the course of the Cretaceous Period.
During this time the pterosaurs’ rule of the skies was being challenged by birds, which were becoming ever more like the species of today. (Although, strictly speaking, birds are dinosaurs, we’ve included some example species on this page.)
In the Cretaceous oceans the ichthyosaurs and plesiosaurs were joined by another branch of marine reptile – the mosasaurs: fearsome predators that had evolved from lizards. Fish, sharks, and numerous invertebrates also thrived in the marine environment.
With the appearance of flowering plants, and insects such as bees and moths, Earth was becoming ever more familiar.
Little did the animals of the Cretaceous Period know that approaching from the dark depths of space was an asteroid that would spell the end not just of the dinosaurs, but of 75% of all species.
The Cretaceous – Paleogene Extinction Event occurred 66 million years ago. It brought the Cretaceous Period to a close, and led to a new chapter for life on Earth.
Animals of the Cretaceous Period that Weren’t Dinosaurs
Cretaceous Period Mammals
The mammals of the Cretaceous Period were mostly small and nocturnal – a lifestyle forced upon them by the existence of dinosaurs. They probably led rodent-like lifestyles, but they were not rodents; the modern mammalian orders of today (rodents, bats, primates, etc.) would not appear until after the Cretaceous – Paleogene Extinction Event.
By the end of the Cretaceous Period the three main mammalian branches – monotremes (egg laying mammals), metatheria (marsupials), and eutherians (placental mammals) – had appeared.
Repenomamus – Dinosaur-Eating Cretaceous Mammals
Repenomamus giganticus was one of the largest-known mammals of the Cretaceous period. It weighed about 13kg (28 pounds) and was around 1m (3 feet) in length. Fossil evidence suggests that it was carnivorous.
A fossilized specimen of the closely-related Repenomamus robustus was found with the remains of a dinosaur in its stomach. This short-legged, stocky mammal lived in China in the Early Cretaceous.
Steropodon – The First Monotreme
Volaticotherium – Carnivorous Gliding Mammal
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Although most Cretaceous mammals were ground-dwelling, there were exceptions; several groups are thought to have been arboreal (tree-dwelling). Volaticotherium is one of a small number of Cretaceous mammals that not only lived in trees, but also developed the ability to glide.
Stretched between Volaticotherium’s limbs were skin membranes which would have supported the animal in gliding flight.
This 20 cm (8 in.) mammal lived in China. The structure of its teeth suggest that it was an insectivore (insect-eater).
Insects and other Invertebrates of the Cretaceous Period
The arrival of flowering plants in the Cretaceous Period led to several new insect groups.
Bees first appeared in the Early Cretaceous, having evolved from wasps. (Wasps appeared during the Jurassic Period.)
Also evolved from wasps were ants, who, like the bees, made their first appearance in the Early Cretaceous.
Although the first termite fossils are from the Cretaceous, it is likely that they appeared earlier in the Mesozoic Era.
The wasp family Cynipidae, also known as the gall wasps, first appeared in the Cretaceous. These insects lay their eggs in trees. Chemicals from either the larvae or the parent induce a growth to appear in the tree. The larva develops inside the growth, which provides it with both protection and food.
Fleas too appeared in the Early Cretaceous, forming a parasitic relationship with both mammals and birds.
Insect groups that had appeared before the Cretaceous, such as Coleoptera (beetles), Lepidoptera, (butterflies and moths) and Odonata (dragonflies and damselflies) continued to evolve and diversify throughout the period.
Non-Dinosaur Land Reptiles of the Cretaceous Period
Although dinosaurs were the dominant animals on land, several other reptile groups were present on land (and in the air) during the Cretaceous Period.
Cretaceous Period Pterosaurs
Pterosaurs – the first flying vertebrates – had first appeared in the Triassic Period. They were abundant during the early and mid-cretaceous, but declined somewhat during the late cretaceous. This may have been due to the success of the birds.
Nemicolopterus
Pteranodon
Pteranodon, a genus of pterosaur with two known species, Pteranodon longiceps and Pteranodon sternbergi, appeared in the Late Cretaceous.
More Pteranodon specimens have been discovered than any other type of pterosaur. Pteranodon were among the largest pterosaurs. They lived in North America.
Quetzalcoatlus
Pseudosuchians In The Cretaceous Period
The archosaurs were a group of reptiles that first appeared in the Triassic Period (or perhaps even earlier). They quickly split into two groups: Pseudosuchia (crocodile-type reptiles), and Avemetatarsalia (the dinosaurs and pterosaurs).
By the Cretaceous Period the only surviving pseudosuchians were the Crocodyliformes – a group of animals that included the ancestors of the crocodilians of today (i.e. the crocodiles, alligators and gharial).
Sarcosuchus
Sarcosuchus imperator lived in Africa in the Early Cretaceous. It is one of the largest crocodile-type animals ever to have lived, reaching a length of 11.65 m (38.2 ft.) and a potential weight of 8 tonnes. (By comparison, the saltwater crocodile – the largest living crocodilian – reaches lengths of around 6 m (20 ft).)
Cretaceous Period Snakes & Lizards
The squamates (the reptile group that includes lizards and snakes) had first appeared way back in the Triassic Period. In the Jurassic Period, lizard groups such as geckos and skinks appeared.
The Cretaceous Period saw the appearance of the earliest snakes. They had evolved either from monitor lizards or a similar lizard group.
Pachyrhachis
Pachyrhachis lived in what is now the Middle East during the Late Cretaceous Period.
Birds of the Cretaceous Period
The first birds appeared in the Jurassic Period, having evolved from theropod dinosaurs.
In the Cretaceous Period the early birds became more like the birds of today, with some groups losing their ancestral tails and teeth.
By the end of the Cretaceous Period bird groups such as the Palaeognathae (ostriches and other flightless birds), Anseriformes (waterfowl), Galliformes (landfowl) and Neoaves (all other modern bird types) had appeared. They were to be the only birds to make it through the Cretaceous – Paleogene Extinction Event.
Confuciusornis
This pigeon-sized bird still retained features from its dinosaur ancestors, including clawed hands. Its short tail and toothless beak, however, meant that it would have looked much more like a modern bird than a dinosaur.
Ichthyornis
Ichthyornis lived in what is now the United States during the Late Cretaceous.
Ocean Animals of the Cretaceous Period
Cretaceous Fish
Fish that inhabited the oceans of the Cretaceous Period included bony fish such as the teleosts (a group of fish that accounts for 96% of all of today’s fish) and sturgeons. Cartilaginous fishes such as sharks and rays were also common.
Xiphactinus
Reaching an estimated length of up to 6 m (20 ft.), Xiphactinus was one of the largest fish ever to have lived. It had a large forked tail and was likely to have been a powerful swimmer.
Xiphactinus specimens have been found with the remains of other species, including other Xiphactinus, inside their stomachs. A Xiphactinus specimen found in 2010 had a mosasaur flipper in its mouth.
Cretoxyrhina
Marine Reptiles Of The Cretaceous Period
Cretaceous Turtles
Turtles first appeared in the Triassic Period, and both freshwater and marine turtles lived during the Cretaceous Period.
Archelon
Cretaceous Plesiosaurs
Two types of plesiosaur roamed the oceans of the Cretaceous Period: the long-necked, small-headed plesiosauroids and the short-necked pliosauroids (also known as pliosaurs). Both types propelled themselves through the water with four powerful flippers.
The pliosauroids may have hunted in deeper water, and for larger prey, than the plesiosauroids.
Elasmosaurus
Kronosaurus
Cretaceous Ichthyosaurs
The ichthyosaurs lost their place as top marine predators to the plesiosaurs in the Jurassic Period. They were still present throughout much of the Cretaceous, but became extinct around 95 Mya, before the end of the Late Cretaceous.
Platypterygius
Mosasaurs
Mosasaurs were a group of marine reptiles that appeared in the Early Cretaceous, having evolved from aquatic lizards. At the very end of the Cretaceous Period, mosasaurs became the dominant marine predators after both the ichthyosaurs and the pliosaurs became extinct.
Mosasaurus
Growing to an estimated length of 17 m (56 ft.), Mosasaurus was one of the largest-known mosasaurs. It lived right at the end of the Cretaceous Period, and became extinct along with the non-avian dinosaurs in the Cretaceous-Paleogene extinction event.
Mosasaurus swam using undulations of its body, aided by its powerful tail. This fearsome marine predator hunted fish, ammonites, turtles and other marine animals near the surface of the ocean.
Cretaceous Period Marine Invertebrates
Crustaceans had appeared millions of years prior to the start Mesozoic Era. Prawns had appeared in the Triassic, and they were joined by crabs and shrimps in the Jurassic. The Cretaceous saw the appearance of the first true lobsters, and also of many new species of crab.
Avitelmessus
Avitelmessus was a crab that lived in what is now the southeastern United States during the Late Cretaceous. Its shell was around 6 cm (2.25 in) long. This extinct animal would have looked much like the crabs of today.
Mollusks
Mollusks were well-established before the Mesozoic Era. Animals such as ammonites, octopuses and nautiluses all swam in the oceans of the Cretaceous Period. The Cretaceous saw the appearance of the first squid.
Scaphites
Scaphites was an ammonite that swam in the oceans of the late Cretaceous Period. It was extremely widespread, with specimens having been found all over the world. Rather than growing in a complete spiral, part of scaphites’ shell is straight, giving the animal a hook-like appearance.
Cretaceous Period Animals That Weren’t Dinosaurs: Conclusion
Although dinosaurs were the dominant land animals during the Cretaceous Period, many other animal groups thrived at the time. The dinosaurs never adapted to life in the sea, and in the Cretaceous oceans the ichthyosaurs and plesiosaurs were joined by the mosasaurs.
The world was becoming ever-more familiar during the Cretaceous Period, with the continents assuming their current positions and flowering plants making their appearance.
Who knows what Earth would look like today if it hadn’t been struck by the extinction-causing asteroid 66 million years ago?
