10 Little-Known Prehistoric Animals that Lived before the Dinosaurs

When it comes to prehistoric animals, dinosaurs are usually the first creatures that come to mind. Nonetheless, while this highly successful group has roamed the Earth for over 230-million years (if you include birds, which continue their lineage to this day), some of the lesser-known animals from even further back are more mysterious still. After all, the world has changed immeasurably over the 750-million years that animals have been around, and it has given rise to some peculiar creatures. In today’s list, we’ll take a look at some of the most unusual of these animals that lived before the dinosaurs.

#1. Dickinsonia

Nobu Tamura

The most iconic of all Precambrian fossils is one that belongs to an especially bizarre creature called Dickinsonia, which lived during the Ediacaran, the period immediately before the Cambrian. The fossils, which are up to 600-million years old, are presumed to belong jellyfish-like creatures ranging in length from a few millimeters to up to a meter. However, about the only thing that is consistent about these organisms is that they are bilateral, meaning that they feature symmetrical bodies. Other than that, it’s not entirely certain that they even were animals, and may instead have been primitive plants, fungi or even a lost kingdom of life.

#2. Haikouichthys

Nobu Tamura

The Ediacaran seas were teaming with life, but it is an ecosystem still shrouded in mystery, not least because there appears to have been a major extinction event before the Cambrian began. Nonetheless, many of the phyla of modern species did evolve in these far-off times, including fish. The most ancient fish known is haikouichthys, a primitive jawless fish that grew one inch (2.5 cm) long and explored the oceans between 520- and 535-million years ago. Unlike almost any other fossil animals dating from the time, haikouichthys is most notable for having a distinct head and tail to such an extent that it would have vaguely resembled modern fish.

#3. Astraspis

Nobu Tamura

Jawless fish started evolving rapidly from the beginning of the Cambrian explosion, diverging into various classes in the process. One of the oddest among them was astraspis, a fish characterized by its huge head and armor-plated body. It lived around 450-million years ago during the Ordovician when animal life was still entirely confined to the vast tropical oceans that covered much of the world. Astraspis was probably distantly related to haikouichthys, but it was much larger, typically being 8 inches (20 cm) in length. It likely developed its armor plating to defend itself against nautiloids like orthoceras, which were the apex predators of the time.

#4. Pneumodesmus Newmani

Matteo De Stefano/MUSE

428-million years ago, near the end of the Silurian period, a small millipede named pneumodesmus newmani became the first ever creature known to take a breath of air and live on the land. This brave little creature is known only from a single 1-cm-long fossil fragment discovered in Scotland in 2004, but it is one of the most significant paleontological discoveries of recent years. At a time when the Earth’s continents were dead and barren, save for some primitive mosses and other tiny plants sticking close to sea shores, this creature became the first among our ancestors to colonize the land some 50-million years earlier than previously thought.

#5. Akmonistion

Nobu Tamura

Sharks are some of the most ancient creatures still on the planet, having evolved at least 420-million years ago. However, the most ancient sharks looked quite different to what we are familiar with today. Akmonistion, which lived during the Early Carboniferous, looked particularly bizarre. Males had an anvil-like crest in place of a dorsal fin, making it look more like a sort of mobile blacksmith than an actual fish. That was not the only bizarre feature of this three-foot-long (1m) shark, however. It also had a triangular patch of spines on the top of its head. Exactly what these bizarre features were for remains a complete mystery.

#6. Scutosaurus

Nobu Tamura

During the Permian period, between 252- and 299-million years ago, terrestrial reptiles and amphibians were well-developed. Peculiar creatures like the hulking scutosaurus roamed the Earth, still millions of years before the dinosaurs would take their place as the dominant terrestrial animals. Scutosaurus was a truly enormous reptile for its time, a creature that grew up to 10 feet (3m) in length and had a skull 20 inches (50cm) wide. Its name means ‘shield lizard’, owing to its armor-plated body and the various spikes that adorned its skull. However, despite its formidable appearance, scutosaurus was a slow, lumbering tank-like herbivore.

#7. Dimetrodon Angelensis

Dmitry Bogdanov

People often mistake dimetrodons as dinosaurs, but they are not in any way related. In fact, these Permian animals were more closely related to mammals than reptiles or birds. Of the several species that have been defined, the largest was dimetrodon angelensis, one of the most enormous apex predators of its time when it lived some 295-million years ago. Growing 15 feet (4.6m) long, it had a huge sail on its back, as is characteristic of all dimetrodons. The animal lived in swampy regions, likely feeding on the gigantic insects of the time as well as other prey. The dimetrodons were among the most successful (and largest) of all the animals that lived before the dinosaurs.

#8. Jaekelopterus

Dmitry Bogdanov

During the Devonian period, some 390-million years ago, giant sea scorpions were the apex predators of their environmental niches. The horrifyingly large jaekelopterus was not only the biggest of the lot, growing up to 8.5 feet (2.5m) long; it is also the biggest known arthropod to have ever existed. However, evidence suggests that the creature dwelled in riverbeds and other freshwater regions rather than the open ocean. Either way, it would have been right at the top of its food chain, hunting around lakes and estuaries with its 18-inch (46cm) claw-like mouth parts (chelicera) latching onto almost anything in its path.

#9. Titanichthys

Dmitry Bogdanov

The appropriately named titanichthys (titan fish) was one of the biggest of all the armored prehistoric fishes belonging to the class of placoderms. These armored fish were already pretty bizarre and, disappearing some 360-million years ago, they were unlike anything alive today. Although the more famous dunkleosteus gets most of the attention in this category, the titanichthys was possibly even more formidable, reaching lengths of at least 26 feet (8m) and probably as long as 33 feet (10m). Titanichthys also had a bigger mouth, despite having blunter teeth than its famous cousin. As such, it may also have been one of the earliest filter feeding fishes.

#10. Aegirocassis

Nobu Tamura

You could be forgiven for thinking that the aegirocassis is from another planet, but it is actually distantly related to the relatively famous Cambrian maritime super predator anomalocaris canadensis. However, this arthropod, reaching lengths of 7 feet (2.1m), was most likely the largest animal in the world when it lived during the Early Ordovician some 480-million years ago. Superficially, aegirocassis would have looked vaguely like a horribly large prawn with two pairs of swimming flaps and frontal spines dangling down from its mouth. Unlike its earlier ancestors, however, aegirocassis was likely a filter feeder, owing to its size.