10 Giant Ancestors of Modern Animals

When it comes to sheer size, the sauropod dinosaurs were easily the most impressive animals that ever roamed the land. However, entirely different classes of animals, such as mammals, reptiles and even insects and millipedes, have produced some extraordinarily large variants over the course of natural history. In this week’s listicle, we’ll be exploring some of the most extreme ancestors of modern animals. These creatures continue their lineage to this day, albeit in diminutive forms.

#1. Paraceratherium

Paraceratherium was a type of hornless rhinoceros that lived between 34 and 23 million years ago across Eurasia. It was one of the largest land mammals in the world during its existence, boasting a weight of up to 20 tonnes and a height almost three times greater than a modern rhinoceros. Far larger than any elephant, the herbivorous beast was likely a herd animal and roamed the dunes and forests of what is now Central Asia and Siberia. Paraceratherium was a type of hyracodont, a now extinct perissodactyl, the family that includes horses, rhinos and tapirs.

#2. Castoroides

CastoroidesCharles R. Knight

An extinct family of giant beavers, castoroides grew to more than six feet long and weighed at least as much as an adult human. These giant beavers may have even coexisted with humans in what is now North America to where they were native. They only disappear from the fossil record about 11,000 years ago. Castoroides was the largest known rodent that ever existed. While superficially similar in appearance to modern beavers, it had a smaller brain-to-body ratio and a different dental arrangement that likely made them less able to build beaver dams.

#3. Megatherium

Megatherium means ‘giant beast’, which is quite a suitable name given that they were among the largest terrestrial mammals of all time. These elephant-sized creatures were the ancestors of modern ground sloths. They lived until as recently as 10,000 years ago when climate change following the end of the last ice age, combined with human encroachment, likely played a central role in their extinction. Megatherium were almost certainly herbivorous like modern sloths. They lived throughout South America and were likely hunted by humans.

#4. Deinosuchus

Living between 80 and 73 million years ago, deinosuchus was a contemporary of the Late Cretaceous dinosaurs. A member of the highly successful crocodilian order, which survived the extinction of the dinosaurs, deinosuchus was very similar in appearance to its closest modern relative, the American alligator. However, with a body length of 35 feet (10.6 metres), deinosuchus was even more terrifying than its modern relative. Deinosuchus, aptly meaning ‘terrible crocodile,’ had one of the strongest bite forces of any animal, and may have even preyed on large dinosaurs.

#5. Carbonemys


An ancestor of modern turtles, carbonemys was the largest turtle to ever exist. It lived approximately 60 million years ago during the early Palaeocene epoch in South America. Carbonemys evolved around five million years after the extinction of the dinosaurs. The species was discovered relatively recently in 2005 when an enormous shell measuring 5”8’ (172 cm) was found in a coal mine in Columbia. That specimen remains the only one ever found to date, indicating that carbonemys lived in a rather small geographic and temporal range.

#6. Titanoboa

A contemporary of the carbonemys, the titanoboa was the largest snake ever known. This terrifying creature was longer and heavier than any other snake, and it lived for around 10 million years after the extinction of the dinosaurs. A member of the boidae family of non-venomous snakes, the titanoboa likely fed almost exclusively on fish, thriving in the lush tropical climate of South America. More than 28 fossils of the 40-foot-long (12 metres) snake have been discovered, giving palaeontologists extensive insights into the climate and geography of the time.

#7. Gigantopithecus


Primates have a long history dating back to the demise of the dinosaurs 66 million years ago. Nonetheless, early ones were usually tiny and barely resembled anything like a modern ape. However, gigantopithecus was undoubtedly an exception. The aptly named ‘giant ape’ lived in what is now southeast Asia, and it grew to a height of up to 10 feet (3 metres) and weighed over 1,000 pounds (454 kg). The species exhibited enormous sexual dimorphism too, with females being around half the size. Gigantopithecus lived from around nine-million years to 100,000 years ago.

#8. Megalodon

Move along Jaws. Megalodon was a prehistoric shark that made even notorious apex predators like the modern great white shark look like small fish. Megalodon dominated the oceans between 23 and 2.6 million years ago, and it reached lengths of 60 feet (18.3 metres), making it almost three times larger than the biggest of today’s sharks. Dwarfing even the great white shark, the megalodon closely resembled it in terms of appearance, but it would have preyed on much larger animals. After all, it’s teeth are significantly larger than human hands.

#9. Meganeura

It wasn’t only the ancestors of reptiles, mammals and fish that grew to enormous sizes. Meganeura was the largest insect ever known to exist. With a wingspan of 25 inches (64 cm), this ancient predecessor to the dragonfly had a body the size of a domestic cat and lived 300 million years ago during the Carboniferous period. The enormous size of meganeura, among other large insects at the time, has baffled the science world ever since its discovery in 1880. However, it is now believed that much higher oxygen levels of the time allowed for the gigantification of insects.

#10. Phorusrhacid

Also known as terror birds, phorusrhacids were a group of extremely large and fast flightless birds. These ferocious apex predators were armed with sharp beaks and claws that allowed them to literally rip their prey apart, making them much more terrifying than the angriest ostrich ever. Adult birds also grew to 10 feet (3 metres) in height. They lived throughout the Palaeocene and Pleistocene eras until around 1.8 million years ago across the Americas. The only relatives they leave behind are the South American seriemas, a group of small and utterly inoffensive birds.

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