Cretaceous Period Animals That Weren’t Dinosaurs

Not all Cretaceous Period animals were dinosaurs! On this page is a list of interesting Cretaceous animals that weren’t dinosaurs.

Page Index

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.)

Cretaceous Period Landscape
Midway through the Cretaceous Period there was a period of high temperature - possibly caused by volcanic activity - that resulted in a mass extinction. This was before the Cretaceous - Paleogene Extinction Event that spelled the end of the large dinosaurs.

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. Image by Nobu Tamura ( [CC BY 3.0]
Repenomamus was a genus of Cretaceous mammals. Two species have so far been identified: Repenomamus giganticus and Repenomamus robustus.

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

Steropodon. Image by Nobu Tamura [CC BY 3.0]
One of the earliest-known monotremes (and one of the earliest known of all Australian mammals) is Steropodon galmani. Growing to around 50 cm (20 in), it may have resembled the platypus of today. Steropodon galmani lived around 105 Mya (million years ago) in the Early Cretaceous.

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 fossil. Photo by Tim Evanson [CC BY-SA 2.0]
The smallest-known pterosaur, Nemicolopterus crypticus, lived in the Early Cretaceous. It had a wingspan of just under 25 centimeters (10 in). It lived in China around 120 million years ago.



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. Image by Johnson Mortimer (cropped / resized by ActiveWild) [CC BY 3.0]
The largest pterosaur was Quetzalcoatlus. It is one of the largest flying animals of all time, with a wingspan that may have reached 15.9 m (52 ft.). Quetzalcoatlus was discovered in Texas.

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. Image by Rhunevild [CC BY-SA 4.0]
Although the dinosaurs ruled, they didn’t have it all their own way; early crocodiles such as those in the genus Sarcosuchus were fearsome predators that preyed on dinosaurs and a variety of other Cretaceous animals.

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. Photo: Ghedoghedo [CC BY-SA 4.0]
Pachyrhachis is one of the earliest-known snakes. Although its body was long and thin like that of a modern snake, it had a small pair of hind legs. This was a remnant of the snake’s lizard ancestry.

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. Art by Velizar Simeonovski. Published by Quanguo Li​, Julia A. Clarke, Ke-Qin Gao, Jennifer A. Peteya, Matthew D. Shawkey [CC BY 4.0]
Several hundred Confuciusornis specimens have been found in Early Cretaceous rock formations in China, making it one of the best-known Cretaceous birds.

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. Image by Nobu Tamura ( [CC BY 3.0]
Ichthyornis was well-adapted for flying, having a similar breastbone and wings to those of modern birds. Having been discovered shortly after the publication of Darwin’s groundbreaking On The Evolution Of Species, this toothed flying dinosaur was used to support Darwin’s controversial theory.

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. Image by ДиБгд.

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.


Artist's impression of Cretoxyrhina attacking Pteranodon. Image by Mark Witton [CC BY 4.0]
Cretoxyrhina mantelli was a large shark of the Late Cretaceous. It grew to 7 meters (23 ft.) in length and preyed on fish and marine reptiles including mosasaurs and plesiosaurs. Most Cretaceous sharks were smaller than the sharks of today.

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. Image: Nobu Tamura ( [CC BY-SA 3.0]
Archelon ischyros was the largest turtle ever to have lived. This Late Cretaceous marine species was found in the shallow sea that covered much of Central North America. It reached lengths of up to 4.6 m (15 ft.).

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. Image: DiBgd [CC BY-SA 4.0 (]
Elasmosaurus, a plesiosaur of the Late Cretaceous, is one of the longest-necked animals ever to have lived. Its neck – thought to reach around 7 m (23 ft.) – was so long that paleontologists initially thought that it was the animal’s tail.


Kronosaurus. Image by Saúl Velasco Martel [CC BY-SA 3.0]
Kronosaurus, a pliosaur genus of the Early Cretaceous, grew to lengths of around 10.5 meters (34 ft.). It was one of the largest pliosaurs. Two species are known: Kronosaurus queenslandicus, specimens of which were found in Australia; and Kronosaurus boyacensis, which was discovered in Columbia.

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.


Platypterigius. Creator: Dmitry Bogdanov [CC BY 3.0]
Platypterygius was a 7 m (23 ft.) long, fish-like ichthyosaur. Its fossilized remains show that it ate turtles and birds, and it is likely to have been an apex predator. Platypterygius specimens have been found all over the world.


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 hoffmanni.
Mosasaurus hoffmanni. Image by Dmitry Bogdanov.

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 - Cretaceous Period Crab
Avitelmessus. Photo: Eduard Solà [CC BY-SA 3.0]
Although crabs first appeared in the Jurassic Period, they began to become more widespread and abundant during the Cretaceous Period.

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 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 Cretaceous Period Fossil

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?

Cretaceous Period Animals: Discover More at Active Wild

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