These pre-dinosaur animals evolved in a very different world to the one we know. This was a world without grass, without flowers; a world that was, for a time, dominated by a single supercontinent surrounded by a vast ocean. From car-sized millipedes to fish that walked on four fleshy fins, here are ten of the wackiest, weirdest and most wonderful animals that lived during this period of Earth’s history.

10 prehistoric animals that ruled before the dinosaurs

Anomalocaris

 

An apex predator with alarming appendages

More than half a billion years ago, the world’s oceans were stalked by a soft-bodied predator that looked unlike anything alive today. This bizarre-looking animal was Anomalocaris, or ‘unusual shrimp’, and is widely regarded as the world’s first apex predator – the killer whale of its day.

Anomalocaris was the largest hunter of the Cambrian period, measuring up to a metre in length from its grasping, frontal appendages to the tips of its tail fans. The appendages are thought to have been used to catch and crush prey. 

For a long time, hard-shelled marine arthropods known as trilobites were assumed to have been Anomalocaris’s favourite snack, but new research has suggested that this predator was more of a weakling, incapable of cracking tough trilobite armour. It’s now believed Anomalocaris was a hunter that relied on speed, agility and superior sight rather than strength. It probably targeted other fast, soft-bodied animals that lived in open water.

Arthropleura

The largest invertebrate to ever walk the Earth

Before vertebrates established their dynasty on land, the arthropods – a huge group that includes insects, spiders and crustaceans – ruled unchallenged. Largest among them was Arthropleura, a 2.6m-long, mulch-eating millipede that roamed the beaches and forests of ancient England.

 

This giant creepy-crawly lived during the Carboniferous period, a time when sprawling rainforests acted as the Earth’s ‘lungs’, drawing in carbon dioxide and breathing out masses of oxygen. It’s thought there was 5-10 per cent more oxygen in the air during this time, which is one reason why Arthropleura grew so large. Another was lack of competition. It took another 40 million years and a worldwide rainforest collapse before distant ancestors of Tiktaalik began to outcompete arthropod.

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Inostrancevia

 

 A sabre-toothed ancestor of modern mammals

Cross a polar bear with a sabre-tooth cat, and you’d get something resembling Inostrancevia. It was a protomammal, an ancient ancestor of today’s modern mammals, like Dimetrodon, but looked very different – less like a reptile and more like a big cat. It also had longer legs than Dimetrodon, which suggests it was a runner – and a fast one at that.

Inostrancevia had sabre-shaped canines that could land killer blows on the necks of megaherbivores such as Scutosaurus. As a protomammal, its jaws were packed with other kinds of teeth, too, but these weren’t used for chewing. Instead, Inostrancevia used a ‘puncture-pull’ strategy, tearing away huge chunks of meat.

It’s unknown whether Inostrancevia was covered in scale-like skin, like its ancestors, or fur, like its mammalian descendants. That said, researchers have found some clues in coprolites (fossilised faeces) that may have been left by them or some close relatives. It’s thought that hair-like structures contained within the coprolites came from smaller members of the same clade, therapsids, that Inostrancevia likely preyed upon. If smaller therapsids had ‘hair’, then Inostrancevia probably did too.

Scutosaurus

The giant lizard that was built like a bulldog

There weren’t many animals bigger than Scutosaurus during the Late Permian, particularly in the ‘cold deserts’ of ancient Russia. These forklift-sized reptiles weren’t just long, at around 3m from head to tail, but heavy too, breaking the scales at a whopping 1,100kg – equivalent to a black rhino. 

A lot of Scutosaurus’s weight was from a thick layer of rough plates, or osteoderms, that covered almost its entire body. It wasn’t particularly fast or agile, so this bony armour was its main defence against its arch-rival Inostrancevia. To maintain its huge size, Scutosaurus had to eat constantly.

Scutosaurus and other large members of the pareiasaur family were among the first megaherbivores to walk the Earth. They were pioneers in a niche that would later be dominated bydinosaurs such as Stegosaurus, Triceratops and Ankylosaurus. 

Scutosaurus looked a lot like these dinosaurs, but was as distantly related from them as we are from whales and dolphins. Interestingly, Scutosaurus’s closest living relative is another armoured reptile with a similar reputation as a slowcoach: the tortoise.

Tiktaalik

The fish that led a revolution on land

Fish aren’t typically known for their ability to walk on land, but Tiktaalik wasn’t your typical fish. It was, by definition, a fish, but sporting primitive, air-breathing lungs (as well as gills) and four fleshy appendages that resembled limbs, it was well on its way to becoming a fully fledged, terrestrial tetrapod.

From fossils found in Arctic Canada, it’s estimated that Tiktaalik grew to lengths of 3m. This huge size, combined with large jaws full of needle-like teeth, a mobile neck and eyes on the top of its head, suggests it was a predator specially adapted for hunting fish in the shallows. Some think it may have even preyed on other, smaller ‘fishapods’ that lived on the margins between land and water.

In pursuit of prey, Tiktaalik relied not only on what it had up top, but underneath too. Unlike most other fish, Tiktaalik had robust fins that could support its weight outside of the water, attached to highly mobile joints. It’s this combination that allowed Tiktaalik and others of its kin to experiment with a life on land.

Where Tiktaalik falls on the vertebrate family tree is debated, but there’s no denying that it lived during an important time in the evolution of four-limbed animals. From Tiktaalik and its close cousins a new dynasty spawned – one that would give rise to reptiles, dinosaurs, birds, mammals and, eventually, humans.

Dimetrodon

A dinosaur lookalike with a hole in the head

Just one look at Dimetrodon and your eyes are immediately drawn to the huge sail on its back – a feature shared by the iconic dinosaur Spinosaurus. This scaly, tiger-sized beast wasn’t a dinosaur though. In fact it’s more closely related to us than Spinosaurus.

Dimetrodon was a protomammal and had a few features that set it apart from dinosaurs, most of which were found in its skull. Behind its eyes it had a a temporal fenestra, a small hole where lower jaw muscles attach to the skull. Dimetrodon and other protomammals had just one of these; dinosaurs and their ancestors had two. It also had different teeth for different functions, which is where its name Dimetrodon, or ‘two-measure tooth’, comes from. In contrast, dinosaurs and their ancestors were equipped with rows of identical teeth.

Its most iconic feature, though, was that sail. For a long time, researchers thought its function was to regulate body temperature across a range of habitats. It’s now thought the sail was used as a giant billboard to display sexual readiness and scare off rivals.

Coelacanth

The ‘extinct’ fish that was rediscovered in the 1930s

This elusive fish still inhabits some deep parts of the Indian Ocean, but up until the mid-20th century it was thought to be long-extinct. Then, in 1938, a strange-looking, 1.5m-long fish was caught off the coast of South Africa. After intense deliberation, expert ichthyologist JLB Smith declared it to be a Coelacanth. 

Coelacanth is a not-too-distant cousin of Tiktaalik. It also has four fleshy fins that resemble limbs, but never made the transition to life on land. Instead, it’s thought Coelacanth adapted to life in the deep, sheltering in caves during the day and only venturing out at night to hunt.It’s probably this adaptation that saved Coelacanth from annihilation during four of Earth’s ‘Big Five’ mass extinctions.