Living between about 2.5 million and 13,000 years ago, it would have stood around 80cm tall (2′7″), with a wingspan of almost 2m (6′6″) and a fairly hefty body weight of 3kg (6.6lbs). Its feet had less grasping ability than other eagles but it also had particularly strong leg muscles, suggesting it was much better adapted for walking around on the ground.
With its large size, long legs, and terrestrial habits it seems to have convergently evolved to fill the same ecological niche as the modern secretarybird – a grassland-dwelling walking predator that hunted on foot, kicking and stomping small prey animals like snakes, lizards, and rodents.
While this might look like a sci-fi alien design, it was actually a very real Earth animal!
This strange-looking creature was Clausocaris lithographica, a member of a group of unique marine arthropods known as thylacocephalans. Only about 3.5cm long (1.4″), it lived in a shallow tropical lagoon environment during the Late Jurassic of Germany, about 150-145 million years ago.
Like most other thylacocephalans it had a narrow flattened shield-like carapace, three pairs of large grasping limbs, and a battery of swimming appendages further back – along with absolutely enormous bulbous eyes. Based on this anatomy it would have been a highly visual hunter, using its huge eyes to locate prey items and then snagging them with its long spiny limbs.
And we’re not even entirely sure what type of arthropods thylacocephalans actually were. They’re generally thought to be some sort of crustacean, but their highly modified anatomy makes linking up their exact evolutionary affinities very difficult. Whatever they were, they must have been incredibly successful as a group because they first appeared in the early Cambrian (~518 mya) and survived all the way into the Late Cretaceous (~94 mya).
While most modern toothed whales have jaws full of teeth that are all the same simple pointed shape – an adaptation for better holding onto slippery prey – their ancient ancestors had teeth much more like other mammals, with differentiated incisors, canines, and molars.
In-between them were whales like Inticetus vertizi, which lived off the coast of southwestern Peru during the Early Miocene, about 18 million years ago.
At over 3.5m long (11′6″) it was one of the larger known toothed whales around at the time, but it wasn’t the direct ancestor of any living whales. Instead it was more of an evolutionary “cousin” to them, part of an older offshoot lineage that lived alongside the early members of modern toothed whale groups.
Inticetus had a long and unusually wide-based snout, somewhat croc-like in appearance, with sharp pointed teeth at the front and multi-lobed cheek teeth further back. A lack of obvious wear on its back teeth suggests it wasn’t using them to chew up its food, and it may have had a fairly specialized diet – possibly using those back teeth to sieve small prey out of the water in a similar manner to modern lobodontine seals.
Inticetus-like teeth have also been found in Miocene-aged deposits in the eastern USA, the Atlantic coast of France, and southeast Italy, indicating that this ancient whale lineage was quite widespread.