Aegicetus

The protocetids were some of the first oceanic cetaceans, occupying a transitional position in the evolution of whales, with four paddle-like limbs and nostrils only partway up their snouts.

Early members of this group swam like otters, using a combination of undulating their bodies and paddling with large hind limbs, but somewhere in the Late Eocene they switched over to propelling themselves entirely with their tails and gave rise to even more whale-like forms like the basilosaurids.

And Aegicetus gehennae was right in the middle of that switch.

Discovered in the Wadi Al-Hitan (“Valley of the Whales”) fossil site in Egypt, Aegicetus lived around 37-35 million years ago. It was similarly-sized to earlier protocetids like Georgiacetus, measuring about 3.5m long (11’6″), but its hind limbs were proportionally smaller. Its hips were also completely disconnected from its vertebrae, giving it much more flexibility to undulate its body and tail – and preventing it from supporting its weight on land, suggesting that it spent its entire life in the water.

It wasn’t a direct ancestor to more “advanced” cetaceans, since it lived alongside several species of basilosaurids. Instead it seems to represent a late-surviving example of what the earlier protocetid-basilosaurid transitional forms would have looked like.

Ensidelphis

Last week’s weird-snouted Furcacetus wasn’t the only recently-discovered ancient platanistoid dolphin that deserves some attention.

Ensidelphis riveroi was described in the same paper, and also lived in the coastal waters around Peru during the early Miocene, about 19 million years ago. It was a little less closely related to its modern river-dwelling cousins than Furcacetus, and was slightly larger, estimated to have measured about 3m long (9’10”).

But what made it weird was its incredibly long snout, lined with around 256 tiny sharp teeth, which also curved markedly to the right side along its 55cm (1’10”) length.

Expectation vs reality

With only one known skull of Ensidelphis it’s impossible to tell if this was a natural condition for the species or if it was some sort of anomalous individual. It doesn’t seem to be a deformation of the fossil, at least.

Similar unusual right-side bending has been seen in the skulls of a few individuals of modern South Asian river dolphins, franciscanas, and Amazon river dolphins, possibly caused by injuries at a young age being exaggerated as the animals grew. However, many other platanistoid dolphins (especially squalodelphinids) are known to have naturally had similar bends in their snouts – but always to the opposite side, curving to the left instead of the right.

But naturally bent or not, what might Ensidelphis have been doing with that incredibly lengthy snoot?

Its long slender jaws would have had a fairly weak bite, so it probably wasn’t able to catch large prey, and it had a very flexible neck. Possibly it swam along near the seafloor using its snout to probe and sweep around in the sediment for buried small prey.

Modern South Asian river dolphins swim along on their sides while doing this – almost always on their right sides, interestingly enough – and if Ensidelphis did the same sort of thing then a snout bent in that direction might have been an advantage.

Furcacetus

The two living subspecies of the South Asian river dolphin are the last surviving members of a lineage known as the Platanistoidea, an early evolutionary branch of the toothed whales. This group was once much more diverse and widespread than their modern representatives, found in oceanic habitats around the world from the Oligocene to the mid-Miocene.

Many of them had forward-pointing protruding teeth at the tips of their snouts, resembling those of some plesiosaurs or pterosaurs, suggesting they were a convergent adaptation used for snagging hold of slippery soft-bodied aquatic prey.

Furcacetus flexirostrum is one the newest additions to this group, named and described in late March 2020. It lived in Pacific coastal waters around Peru during the early Miocene, about 19-18 million years ago, and was about the same size as modern South Asian river dolphins at around 2.3m long (7’7″).

And it had a uniquely-shaped snout for a cetacean, curving upwards for most of its length but then turning downwards right at the tip, which along with large forward-pointing teeth gave its jaws a vaguely crocodilian appearance.

A closeup view of the jaws of Furcacetus.

Much like slender-snouted crocodilians and spinosaurids, this arrangement would have allowed Furcacetus to make quick bites at small-fast-moving prey like fish and crustaceans.

Weird Heads Month #19: Sword-Snouted Whales

Cetaceans are just weird animals in general. Fully aquatic mammals best described as “fat screaming torpedoes“, with bizarre head anatomy and their nostrils pulled up to the top of their heads behind their eyes. Some of them are among the largest animals to ever exist, some of them can live to over 200 years old, and some can dive to incredible depths below the ocean surface.

And they’re all descended from tiny deer-like creatures, with their closest living relatives being hippos and other even-toed ungulates.

Some ancient cetaceans were particularly odd-looking, evolving walrus-like tusks or elongated chins – or in the case of Eurhinodelphis longirostris here, an incredibly long swordfish-like snout.

Living during the mid to late Miocene, about 14-7 million years ago, Eurhinodelphis ranged across the Mediterranean and the North Atlantic, with fossil remains known from Western Europe, Turkey, and the East Coast of the United States. It was a fairly small dolphin-like cetacean about 2m long (6’6″), and was part of a lineage of early toothed whales called eurhinodelphinids.

Its upper jaw was around five times longer than the rest of its skull, and toothless past the point where the lower jaw ended. Much like the modern billfish it resembled, it probably used its snout to slash at fast-moving fish, stunning them and making them easier to catch.

Maiabalaena

The earliest baleen whales didn’t actually have any baleen plates in their mouths, and the evolutionary origin of these unique filter-feeding structures is still poorly understood.

It was thought to have been a fairly simple linear process from toothed ancestors to a mix of teeth and baleen and then to fully toothless with just baleen, but more recent discoveries have begun to cast doubt on that idea. The teeth of ancestral baleen whales weren’t suited to filter-feeding at all, instead still being adapted for predatory piercing and chewing – actions which would have been constantly interfering with and damaging any proto-baleen forming alongside them, and making it seem much more unlikely that there would have ever been a transitional form that had both teeth and baleen at the same time.

But then how did baleen whales get their baleen?

Maiabalaena nesbittae here provides a possible solution. Discovered in Oregon, USA, this early baleen whale dates to the early Oligocene, around 33 million years ago, and compared to most of its modern relatives it was comparatively tiny, only about 4.6m long (15′).

And it had no teeth at all, but possibly also no baleen.

Baleen rarely fossilizes, so it’s unclear whether Maiabalaena actually had any or not, but the shape of its skull suggests it probably didn’t – it lacked the broad thickened upper jaw associated with supporting racks of baleen plates. It instead seems to have been adapted for suction feeding similar to modern belugas and beaked whales, using muscular cheeks and tongue to manipulate water pressure and pull small prey like fish and squid straight into its mouth.

Since it lived at a time when the Antarctic Circumpolar Current was forming and cooling the oceans, changing ecosystems and prey availability, it may represent a previously unknown stage in baleen whale evolution – a point when they’d moved towards specializing for suction feeding and lost their teeth entirely, before transitioning again over to filter-feeding with baleen in a completely separate evolutionary development a few million years later.

Livyatan

The modern sperm whale is already an impressive animal, being by far the largest of the living toothed whales and famous for its ability to dive over 2km down (1.2 miles) to feed on deep-sea animals like giant squid.

But some of its ancient relatives were terrifying.

Livyatan melvillei here has an appropriately monstrous name, inspired by both the Hebrew name for the Leviathan and Herman Melville, the author of Moby-Dick. Known from the Pacific coast of South America during the late Miocene, around 10-9 million years ago, it’s estimated to have measured somewhere between 13.5m and 17.5m long (~44′-57′) – comparable in size to an adult male sperm whale.

Unlike the relatively slender mouth of its modern cousin, however, it instead had thick strong jaws full of enormous teeth.

Livyatan melvillei skull by Ghedoghedo | CC BY-SA 4.0
(for an idea of the sheer size of this reconstructed skull – some of those teeth are almost the length of your forearm)

It was part of a loose grouping of what are known as “macroraptorial sperm whales“, which all had similarly toothy jaws and occupied the same sort of ecological niche as modern orcas, specializing in hunting prey like large fish, squid, seals, and other whales.

Livyatan‘s main food source was probably smaller baleen whales about half its own size, and its only real competition for this prey was the equally huge megalodon shark that shared the same waters.

A huge fossil tooth found in Australia suggests that Livyatan or a very close relative of it survived at least into the early Pliocene, about 5 million years ago. Around this time a cooling climate and dwindling numbers of its preferred prey would have eventually made a population of such enormous apex predators unsustainable, and driven this “killer sperm whale” into extinction – probably around the same time megalodon disappeared, about 3.6 million years ago.

Island Weirdness #60 — Hippopotamus minor

Cyprus is one of the most isolated islands in the Mediterranean, having had no close connections to the mainland for the last 5.3 million years and being uplifted to close to its modern size during the Pleistocene. As a result it had very few land mammals, all of which arrived by swimming or rafting: rodents, shrews, a genet, dwarf elephants, and a dwarf hippopotamus.

Hippopotamus minor (sometimes called Phanourios minor) seems to have been descended from the common hippo, which probably swam across to Cyprus from the Levant region sometime in the mid-to-late Pleistocene, around 400,000 years ago. Isolated with no predators and limited space it rapidly became dwarfed compared to its ancestors, reaching at most 75cm tall at the shoulder (2’6″) — making it the tiniest known island hippo, and slightly smaller than the modern pygmy hippo.

It became much more terrestrial, with more digitgrade feet adapted for walking and climbing over rugged rocky terrain. Its teeth suggest a diet of pig-like browsing on forest vegetation — and much like pigs (and other hippos) they may have been opportunistic omnivores occasionally also eating small animals and carrion.

Despite being so small for a hippo, it was still one of the largest animals living on Cyprus, weighing about the same as the dwarf elephants it lived alongside. It also seems to have been the most common of the mammals on the island, with remains of thousands of individuals having been found.

While larger dwarf hippos are known from several other Mediterranean islands, the Cypriot species is the only one that seems to have survived into the early Holocene.

The earliest known evidence of humans in Cyprus comes from a rock shelter on the southern coast, dating to about 12,000 years ago, consisting of stone tools and a massive concentration of burned animal bones — with over 200,000 of them coming just from Hippopotamus minor. It’s possible that in addition to being so abundant on the island, the dwarf hippos’ evolution in the absence of predators meant they had no fear of humans and were much less aggressive than their larger relatives, making them particularly easy to hunt and kill.

…Or they were just especially tasty.

Later deposits from about 2000 years later show no sign of the hippos at all, with their role in the Cypriot ecosystem completely replaced by introduced species like deer, sheep, and goats.

Inticetus

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.

An close-up view of Inticetus' jaws, showing the differences in tooth shape from front to back.
Closeup of Inticetus‘ jaws

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.

Island Weirdness #21 – The Malagasy Mini-Hippos

Much like elephants, hippos have frequently made their way onto islands and developed dwarfed forms. These mini-hippos are mostly known from the Mediterranean, but further south they also occurred on Madagascar.

Hippopotamus madagascariensis (also sometimes called Hexaprotodon madagascariensis or Choeropsis madagascariensis; its exact classification is uncertain) was similar in size and appearance to the modern West African pygmy hippo – which it might have been closely related to, or may have just ended up resembling through parallel evolution.

Standing under 1m tall at the shoulder (3′3″) and measuring about 1.8m long (5′11″) it lived in the forested highlands and was much more terrestrial than its larger cousins. Its eyes were further down on the sides of its head, and it was better adapted for walking and running around on land, with proportionally longer legs and a more digitigrade posture.

It also had an unusually small brain for its size – about 30% smaller than expected – which may have been an energy-saving adaptation.

Two other species of dwarf hippo have been identified on Madagascar – the similarly-sized but more aquatic Hippopotamus lemerlei in the west of the island, and the larger and poorly-known Hippopotamus laloumena in the east. It’s not clear when exactly the ancestors of these various hippos first arrived on the island, and they may even represent three independent colonization events.

The last known subfossils date to about 1000 years ago, but surprisingly accurate accounts of similar creatures in Malagasy folklore raise the possibility that small isolated populations of these hippos may have survived into more recent times. One of the most intriguing examples is the kilopilopitsofy, described as having large floppy ears and supposedly being sighted as recently as the 1970s.

Rayanistes

Remingtonocetids were an early branch of the whale evolutionary family tree, known from about 49-41 million years ago and splitting off somewhere between the famous “walking whale” Ambulocetus and the more oceanic protocetids. With otter-like bodies, tiny eyes, and long gharial-like snouts, they lived in near-shore shallow marine habitats and probably swam using a combination of their hind feet and tails.

They were initially found only in Pakistan and India, but then Rayanistes afer here was discovered all the way over in Egypt – suggesting that these early whales were much more widespread than previously thought, dispersing through the Tethys Sea at about the same time as their protocetid cousins.

Dating to the Middle Eocene (~45-41 mya), Rayanistes was probably about 2.5m long (8′2”). It had powerful hindlimb musculature that would have given it a very strong kicking swimming stroke, but it probably couldn’t actually support its own weight on land since its femur wasn’t very well anchored into its pelvis.