Tag: marine mammal

Antaecetus

Antaecetus aithai was an early whale that lived during the late Eocene (~40 million years ago) in what is now Morocco, at a time when northern Africa was covered by a warm shallow sea.

It was part of the “basilosaurids“, some of the first fully aquatic cetaceans – traditionally considered to be a single defined group, but more recently found to be more of an “evolutionary grade” of multiple early whale lineages – and much like Basilosaurus it had elongated back vertebrae that would have given it a very long slender body shape.

Antaecetus also had a proportionally smaller head and smaller teeth than other basilosaurids, along with much denser bones and a stiffer spine that would have made it a rather slow swimmer with reduced maneuverability. It was also fairly small overall compared to most of its relatives, probably around 6m long (~20′).

It was probably a slow-moving coastal water animal somewhat like modern sirenians – except unlike manatees and dugongs it was carnivorous. Its relatively delicate teeth suggest it was feeding on soft-bodied prey like cephalodpods, and with its lack of speed it must have been some sort of ambush predator, waiting around for potential prey to come within striking range.

It Came From The Wastebasket #11: A Cetothere Change

Cetotheres were a group of small baleen whales, one of three major lineages of these cetaceans alongside the rorquals and the right whales. They first appeared in the fossil record in the mid-Miocene, about 14 million years ago (but are estimated to have actually originated 10-15 million years earlier), and disappeared during the Pleistocene about 2 million years ago.

First recognized in the mid-19th century, for a long time the cetotheres were used as a wastebasket for all fossil baleen whales that didn’t clearly fit into any modern whale families. By the start of the 21st century nearly 30 different genera representing numerous different species were all lumped into the group – and the genus Cetotherium was another wastebasket in itself with at least 12 assigned species, many of which were based on fragmentary or dubious remains.

An illustration of Ciuciulea, an extinct cetothere baleen whale. It looks similar to modern rorquals, with a streamlined and relatively slender body, but lacking the typical throat grooves of that type of whale. Its jaws are long and narrow, with a paired blowhole at the top of its head and small eyes set near the corners of its mouth. It also has fairly small flippers, a dorsal fin set about two-thirds of the way down its back, and a horizontal tail fluke. It's coloration is countershaded, mostly grey on top and white underneath.
Ciuciulea davidi

This was finally cleaned up in the 2000s, when a revision of the cetotheres cut the group down to just 6 genera. Since then a handful of additional new genera and species have been named, and while a few polyphyletic Cetotherium species may still need tidying up the cetotheres have overall gone from being a total taxonomic mess to actually being one of the best studied groups of fossil baleen whales.

Their exact evolutionary relationships with each other are still in flux, but the most surprising discovery from the improved understanding of these ancient whales is that they might not be extinct after all.

A set of three screenshots from the animated movie "Ice Age: Dawn of the Dinosaurs". The first image shows the two opossum characters Crash and Eddie asking, "Were you killed?!" The second image shows the weasel buck looking away and replying, "Sadly, yes…" The third image shows Buck leaning closer and adding "but I lived!" Buck's face has been photoshopped into that of a Cetotherium whale in both shots.

A study in the early 2010s suggested that the pygmy right whale may actually be a living cetothere. This classification was initially controversial, but further discoveries of fossil relatives of this enigmatic modern whale and comparisons of their distinctive inner ear anatomy have provided stronger evidence for an evolutionary link.

At this point it seems fairly likely that the pygmy right whale really is either the last surviving representative of the cetothere lineage, or at least is a very close evolutionary “cousin” (a “cetotherioid”) closer related to them than to any other modern baleen whales.

Casatia

Modern beluga whales and narwhals are the only living representatives of the monodontid lineage, found only in cold Arctic and sub-Arctic waters. But this whale family actually first evolved in much warmer climates – and some of them were downright tropical.

Casatia thermophila lived about 5 million years ago during the early Pliocene, in the Mediterranean Sea around Tuscany, Italy. Although known only from a couple of partial skulls and a few vertebrae it was probably similar in size to its modern relatives, around 5m long (16’4″).

It seems to have had a larger number of functional teeth than modern monodontids, and probably didn’t suction feed like its modern close relatives. Instead it may have fed more like most porpoises and dolphins, relying more on speed and snapping jaws to capture prey.

It inhabited the Mediterranean at a time not long after the sea there had mostly dried up and then been rapidly refilled. The presence of warm-water marine species such as bull sharks, tiger sharks, and dugongs in the same fossil beds as Casatia indicates the local climate at the time was hotter than it is today, with tropical temperatures – and suggests that this whale’s ancestors must have originally moved into the replenishing Mediterranean from lower latitudes alongside these other warmth-adapted animals.

This tropical monodontid was also much closer related to modern belugas than modern narwhals are, which raises the possibility that the two living monodontid species actually specialized for colder conditions completely independently of each other rather than descending from a cold-adapted common ancestor. Instead modern belugas and narwhals may have originated from separate warm-water monodontid ancestors who evolved similar cold-tolerant adaptations in parallel as the climate cooled during the onset of the Quaternary ice age, while the rest of their relatives all went extinct.

Kogiopsis

Kogiopsis floridana was a physeteroid whale that lived near the coast of the southeastern United States from the mid-Miocene to the early Pliocene, about 14-4 million years ago.

Known just from fossilized lower jaws and teeth, with some teeth up to nearly 13cm long (~5″), its full life appearance and size are uncertain – but it may have been slightly larger than a modern bottlenose dolphin at around 4.5m long (~14’9″). It’s traditionally been considered to be part of the kogiid family, closely related to modern pygmy and dwarf sperm whales, but some studies disagree with that classification and instead place it in the true sperm whale lineage.

It was probably a predator in a similar ecological role to modern orcas, adapted for hunting prey like squid, fish, and smaller marine mammals. But unlike orcas it wouldn’t have been the apex predator of its ecosystem, subject to predation pressure by even larger carnivores like macroraptorial sperm whales and everyone’s favorite ridiculously huge shark – and as a result it probably had a “live fast and die young” lifestyle similar to modern kogiids and other small-to-medium-sized Miocene physeteroids, rapidly maturing and only living to around 20 years old.

I’ve reconstructed Kogiopsis here as a kogiid-like animal, with a similar sort of shark-like head shape and “false gill” markings. In the background a second individual is depicted displaying “inking” behavior, releasing a defensive cloud of reddish-brown fluid from a specialized sac in its colon.

Phiomicetus

Named after the canine-headed Ancient Egyptian god, Phiomicetus anubis is the first fossil cetacean to discovered, described, and named entirely by a team of Arab paleontologists.

Living during the mid-Eocene, about 43 million years ago, in a shallow sea-covered region that is now part of Egypt‘s Western Desert, Phiomicetus was an early protocetid – an amphibious foot-powered swimmer, at a transitional point in the evolution of whales from deer-like terrestrial animals to fully aquatic screaming torpedoes.

About 3m long (~10′), it had large jaw muscles and sharp teeth with wear patterns that suggest it was a raptorial hunter grabbing and snapping at prey with powerful bites. It would have probably tackled fairly big prey compared to other protocetids, hunting things like large fish, turtles, and even smaller whales in an ecological role similar to that of modern orcas.

Along with the distantly-related long-snouted Rayanistes it’s one of the earliest known whales from Africa, giving us further glimpses at a time period when early cetaceans were first dispersing out from the South Asian subcontinent via the ancient Tethys Sea.

Allodesmus

Desmatophocids were a group of seal-like pinnipeds that appeared very early in the group’s evolution, around 23 million years ago. They were found across the northern Pacific from the west coast of North America to Japan, and were the first pinnipeds to get big, with some species reaching sizes comparable to modern northern elephant seals.

They had a mixture of anatomical features similar to true seals, sea lions, and walruses, but weren’t actually the ancestors of any of those modern groups. Instead they seem to have just been their own separate thing, a very early diverging “cousin” lineage of pinnipeds that convergently developed close resemblances to their later relatives.

Allodesmus demerei here was one of the last known desmatophocids, living in the late Miocene (~9 million years ago) in what is now southwest Washington, USA. 

It would have been a sea lion-like animal, able to walk on all fours when hauled out on land, and showed distinct sexual dimorphism, with males growing to sizes of around 4m long (13′) and females being somewhat smaller. It powered its swimming using its front flippers, and may have mostly foraged in deep dark waters, using both keen vision and sensitive whiskers to locate prey.

The nasal region of its skull also shows some similarities to modern elephant seals, and some reconstructions depict males with the same sort of large proboscis. 

Borealodon

Modern mysticete whales all have baleen plates in their mouths, but before the evolution of these specialized filter-feeding structures the early members of their lineage still had toothy jaws.

Borealodon osedax here was one of those “toothed mysticetes”, living about 30-28 million years ago during the mid-Oligocene off the coast of Washington state, USA.

Unlike modern baleen whales it was small, about the size of a modern porpoise at around 2m long (6’6″), and the wear on its multi-cusped teeth suggest it was a predator taking slicing bites of fish – possibly using suction-assisted feeding like its close relatives the aetiocetids.

Its fossilized remains are also a rare example of an ancient whale fall, with characteristic bore holes in its bones from Osedax worms.

Eons Roundup 9

New year, new PBS Eons commission roundup day!

  • An illustration of an extinct early walrus. Unlike modern walruses it has no tusks, more resembling a sea lion in appearance.
    Neotherium mirum
  • An illustration of an extinct species of walrus. It has shorter thicker tusks than modern walruses, and it's depicted grubbing around on a muddy seafloor for buried shellfish.
    Valenictus sp.

The ancient walruses Neotherium and Valenictus, from “How the Walrus Got Its Tusks”
https://www.youtube.com/watch?v=BKDGYGV2LK8

  • An illustration of an extinct nodosaur, a type of quadrupedal herbivorous dinosaur. Its body is covered in densely-packed knobbly spiky armor.
    Borealopelta markmitchelli (life restoration)
  • An illustration of the carcass of an extinct nodosaur, a type of quadrupedal herbivorous dinosaur. Its body is covered in knobbly spiky armor, and its belly is massively bloated up from trapped gasses, forcing it to have turned upside down.
    Borealopelta markmitchelli (“bloat-and-float” carcass)

The nodosaurid ankylosaur Borealopelta, in both alive and “bloat-and-float” carcass states, from “The Dinosaur Who Was Buried at Sea”
https://www.youtube.com/watch?v=a-UZXBF63z4

  • An illustration of an extinct ankylosaur, a type of quadrupedal herbivorous dinosaur. Its body is covered in knobbly spiky armor, but unlike most other ankylosaurids it has no bony club at the tip of its tail.
    Gobisaurus domoculus
  • An illustration of an extinct ankylosaur, a type of quadrupedal herbivorous dinosaur. Its body is covered in knobbly spiky armor, and it has a small bony club at the tip of its tail.
    Dyoplosaurus acutosquameus

The ankylosaurid ankylosaurs Gobisaurus and Dyoplosaurus, from “How Ankylosaurs Got Their Clubs”
https://www.youtube.com/watch?v=lRt-4SdzWrk

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.

Eons Roundup 8

Once again it’s a PBS Eons commission roundup day!

  • An illustration of an extinct baleen whale. It's looks very similar to modern rorquals, with pleated throat grooves.
    Cerro Ballena rorqual
  • An illustration of an extinct seal. it has an unusually long neck.
    Acrophoca longirostris

An unnamed Cerro Ballena rorqual whale and the long-necked seal Acrophoca, from “How the Andes Mountains Might Have Killed a Bunch of Whales”
https://www.youtube.com/watch?v=iNk6r5WljGc

  • An illustration of an extinct pseudosuchian, a relative of modern crocodiles. It resembles a dinosaur much more than a croc, standing bipedally, with a long neck, tiny arms, and a long counter-balancing tail.
    Shuvosaurus inexpectatus
  • A skeletal diagram of an extinct pseudosuchian, a relative of modern crocodiles. It resembles a dinosaur much more than a croc, standing bipedally, with a long neck, tiny arms, and a long counter-balancing tail.
    Effigia okeeffeae skeletal diagram

The poposauroid pseudosuchians Shuvosaurus (life restoration) and Effigia (skeletal) from “When Dinosaur Look-Alikes Ruled the Earth”
https://www.youtube.com/watch?v=QsmV34Co32c