Tag Archives: baleen

Llanocetus denticrenatus

Early baleen whales were fearsome predators with wicked teeth, but lost them entirely

Baleen whales (parvorder Mysticetes) haven’t always been ‘baleen’, new research shows — and this unique adaptation hasn’t evolved from teeth, as previously suspected.

Llanocetus denticrenatus

A reconstruction of Llanocetus denticrenatus.
Image credit Carl Buell.

Today’s baleen whales are truly distinctive. Their most distinctive feature, the baleen — the comb-like filter-feeder system such whales use to capture krill — is so unique, we’ve used it to name the whole group. According to new research, however, the group didn’t always sport this specialized feeding apparatus. Just 34 million years ago, they were using good ol’ fashion teeth to do some good ol’ fashioned chomping with, one fossil reveals.

Teethy giants

“Llanocetus denticrenatus is an ancient relative of our modern gentle giants, like humpback and blue whales,” says lead author Felix Marx of the Royal Belgian Institute of Natural Sciences. “Unlike them, however, it had teeth, and probably was a formidable predator.”

Although you wouldn’t tell by their girth, whales actually originate from land mammals. Because of this, researchers knew the whales had to pick up filter-feeding after retreating back to the oceans (since you can’t really filter-feed on land). Up until now, common wisdom held baleen whales first started filter-feeding back in the days they still had teeth, but this may not have been the case.

Skull.

Skull of Llanocetus denticrenatus. (A) Dorsal view. (B) Ventral view.
Image credits R. Ewan Fordyce, Felix G. Marx, (2018) / Current Biology.

Just like modern whales today, Llanocetus denticrenatus sported a series of distinctive grooves on the roof of its mouth (palate), the team reports. These grooves create the space necessary for blood vessels that supply the baleen in present-day Mysticetes. In Llanocetus, however, the grooves are clustered around teeth sockets — which suggests that they were feeding gums and teeth, not baleen. Baleen is fragile and would have been too exposed in such areas, liable to be crushed. Instead, the Marx suspects that the beast “simply had large gums and, judging from the way its teeth are worn, mainly fed by biting.”

Given that Llanocetus could grow to about 8 meters (26.2 feet), it likely had to do a lot of biting to keep reasonably fed. Thankfully for it, it came equipped for the job, the team finding a row of sharp, widely-spaced teeth with marked wear embedded in its rostrum.

I asked Ewan Fordyce, Professor at the Department of Geology at the University of Otago, New Zealand and paper co-author about what Llanocetus‘ meals likely consisted of. He admits that the team is “not sure” yet what this toothy whale hunted, but that its anatomy can yield some clues:

“It was probably not a top predator, Because these small teeth could only deal with medium-sized prey,” he told ZME Science in an e-mail. “It ate prey that was processed in part at least by teeth that could shear and pierce. Perhaps took small to medium-sized fish, not too bony, and maybe squid.”

Feeding apparatus

Feeding Apparatus of Llanocetus denticrenatus.
Image credits R. Ewan Fordyce, Felix G. Marx, (2018) / Current Biology.

The team’s findings suggest that baleen actually evolved from the gums, not the teeth themselves. The soft tissue gradually became more complex over evolutionary time and developed into the baleen, the team writes. This transition likely happened after the whales had already lost their teeth, and switched from biting larger victims to slurping in small pray. Marx and Fordyce believe that baleen evolved as a way to more effectively keep such prey inside the animals’ mouth — meaning they had to already be doing it for evolution to favor the baleen.

One factor that could be behind this change of menu is simple economics:

“Felix and colleagues have made the point that by feeding on small food, baleen whales move down the food chain,” Fordyce added for ZME Science, “[where] they have more resources than if they were at the top of the food chain.”

The results show that the evolution of baleen whales was more convoluted than previously thought, the team says. Next, they’ll try to get a better understanding of the baleen whales’ evolutionary path.

The paper “Gigantism precedes filter feeding in baleen whale evolution” has been published in the journal Current Biology.

Why whales are so big

The gentle giants of the oceans have fascinated people since time immemorial. Now, in a new study, researchers have found why whales grew to such impressive sizes — and why they don’t get even bigger.

As far as we know, the blue whale is the largest creature in history — which is a bit strange if you think about it. Even during the warm, lush times of the Cretaceous, when giant dinosaurs reigned supreme both on land and in the sea, nothing even came close to the blue whale.

It’s not just the blue whale as an outlier: several species of marine mammals grow to dramatic sizes. According to recent research, they have no other choice — their marine environment forces them to grow and grow.

“Many people have viewed going into the water as more freeing for mammals, but what we’re seeing is that it’s actually more constraining,” said co-author Jonathan Payne, a professor of geological sciences at Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth). “It’s not that water allows you to be a big mammal, it’s that you have to be a big mammal in water – you don’t have any other options.”

Marine mammals as a whole are a pretty strange bunch. Contrary to popular belief, marine mammals have nothing in common with fish or other non-mammal sea creatures. Marine mammals started evolving some 50 million years ago, from land-dwelling creatures. To this day, they maintain many physical features from their terrestrial ancestors, despite their aquatic lifestyle. The most common theory is that they took to the sea in order to evade an overly competitive land environment and exploit an unfilled ecological niche in the sea. To paint an even weirder family picture, groups of marine mammals aren’t even related to each other — whales and dolphins are related to hippos and other hoofed land mammals, manatees share ancestry with elephants, while seals and sea lions are rather related to dogs.

In order to make sense of this unusual group, researchers compiled body masses for 3,859 living and 2,999 fossil mammal species from existing data sets (70% of living creatures, and 25% from extinct species). They found that as animals adapted to a more aquatic lifestyle, they quickly grew in size, converging at about 450 kg (1000 pounds). Using computer models to map and interpret the data, they drew a comprehensive picture of marine mammals and their mass.

“The key is having a phylogenetic tree to understand how these species are related to one another and the amount of time that has taken place between different evolutionary branching events,” said lead author Will Gearty, a graduate student at Stanford Earth. “The tree of ancestral relationships allows us to build models based on data from modern species to predict what the ancestors’ body sizes would have been and see what evolutionary trajectories best fit with what we see in the modern day.”

The reason why these animals grew so much and so fast, researchers say, is heat. Being bigger is simply more efficient in terms of conserving your own body heat.

“When you’re very small, you lose heat back into the water so fast, there’s no way to eat enough food to keep up,” Payne said.

So animals had an incentive to get bigger, but they also couldn’t get too big, otherwise they just couldn’t eat enough food to support themselves.

“Basically, animals are machines that require energy to operate. This need for energy places hard limits on what animals can do and how big they can be,” said Craig McClain of the Louisiana Universities Marine Consortium, who was a co-author on the study.

Interestingly, the sea seems to be a much more unforgiving place than land, as it allows for less variation. This lies in contrast with previous studies which claimed that evolutionary pressure is more relaxed in water as animals don’t need to support their body on legs.

“The range of viable sizes for mammals in the ocean is actually smaller than the range of viable sizes on land,” Payne said. “To demonstrate that statistically and provide a theory behind it is something new.”

Of course, there are also exceptions to this rule. At the lower end, we have creatures like otters. Otters took to the water much later than other creatures, and they still spend a significant part of their lives on land — these are probably the main reasons why they don’t follow the trend. At the other end, we have the true giants: baleen whales.

Baleen whales, which range in size from the 20 ft (6 m) and 6,600 lb (3,000 kg) pygmy right whale to the 112 ft (34 m) and 190 t (210 short tons) blue whale, broke the trend by completely changing how they eat. They don’t have teeth, instead filtering the oceans for zooplankton and krill. It’s this adaptation that allowed them to get so immensely big; without it, they would taper off in size and mass much faster.

“The sperm whale seems to be the largest you can get without a new adaptation,” Gearty said. “The only way to get as big as a baleen whale is to completely change how you’re eating.”

The study has been published in the Proceedings of the National Academy of Sciences.

North Atlantic Right Whale.

Right whales face extinction if humans don’t intervene fast, NOAA researchers warn

Federal government officials aren’t mincing words on this one: North Atlantic right whales (Eubalaena glacialis) are in the fast lane to extinction unless we intervene.

North Atlantic Right Whale model.

Image credits Ryan Somma / Flickr.

North Atlantic right whales are some of the rarest marine mammals in the world. These gentle giants can grow up to 15m (50 ft) in length and weigh up to roughly 72 tons (158,000 lbs). They’re black colored, sometimes with white patches on their bellies, and have a stocky build, no dorsal fin, and a large head spanning about one-quarter of their body length.

They’re also well underway to becoming the rarest animal anywhere, and then going extinct. The right whales have had a very rough 2017, according to NOAA scientists, who report that the 450-or-so-strong species has lost 17 members this year.

Prospects are so bleak for the whales’ survival that the researchers urge U.S. and Canadian officials to intervene. Without action, and action taken soon, this dwindling species is likely never to recover, said John Bullard, the Northeast Regional Administrator for NOAA Fisheries.

Wrong decade for the right whales

NOAA Endangered Species Act consultant Mark Murray-Brown says that right whales have been in decline since 2010, constantly losing numbers. Females, he adds, seem to be taking the brunt of it, shrinking as a percentage in the overall population. They tend to be larger than males, although it’s not known if this contributes to their predicament.

Compounding the whales’ hardships is the fact that this year of high mortality is also a very poor one for whale-romance. There are fewer than 100 breeding female North Atlantic right whales left according to NOAA’s estimates, under a quarter of the total population — which doesn’t bode well for repopulation efforts. Factor in that gestation in the right whales lasts one whole year, with an average of about three to six years between individual pregnancies, and prospects are looking even bleaker.

“You do have to use the extinction word, because that’s where the trend lines say they are,” says Bullard. “That’s something we can’t let happen.”

“The current status of the right whales is a critical situation, and using our available resources to recover right whales is of high importance and high urgency,” Murray-Brown added.

North Atlantic Right Whale.

Image credits Lauren Packard / Flickr.

NOAA officials discussed the whales’ plight during a meeting of the regulatory New England Fishery Management Council, held last Tuesday. They warned that both the U.S. and Canada have to work together and safeguard the whales. Impacts with vessels and entanglement in fishing nets are the two most pressing concerns for the scientists, as these cause the majority of whale deaths. These are especially pressing issues as right whale nursery areas are in shallow, coastal waters.

All of this year’s deaths, the researchers added, were off the coast of New England and Canada. The whales come here over spring and summer to feed, before returning to the temperate waters off Georgia and northern Florida to give birth. Calving occurs from December through March.

Why are the whales dying?

The World Wildlife Fund (WWF) estimates that there are even fewer right whales, between 300 and 350, still alive and kicking. They blame a long history of human exploitation for leaving them “one of the most endangered of all large whales” even to this day, despite protection from whaling since the 1930s.

But if they’re not being hunted, why aren’t they recovering?

Previous research has shown that the whales tend to move around more than expected. This would put them at risk of colliding with fishing boats, if and when they move outside of protected areas in search of food. There are two areas designated as critical habitats for the species, one in the Northeast U.S., and one in the Southeast U.S.

Even if they manage to avoid a direct hit, fishermen spell more bad news for the whales. Fecal samples recovered from whales bound up in nets over longer periods revealed high concentrations of stress hormones in their system. These would have a dramatic impact on the mammals’ ability and willingness to reproduce for a long time after the traumatic event.

NOAA published a five-year assessment of the right whales in October, arguing that officials should keep the species listed as endangered. The document also includes recommendations on how best to protect the whales. Suggestions include the development of a plan to monitor population trends and habitat use over the long term, as well as more research into the impact of commercial fishing on right whales.

Mystacodon selenensis

Ancient 36-million-year-old fossil helps track down how baleen whales lost their teeth

Baleen whales, also known as mysticetes, are the largest animals in the world. There are 12 baleen whale species divided into 4 families, among them the famous humpback and blue whales. Some of the defining features of mysticetes, beyond their husky size, are the paired blowholes and the long plates of baleen which hang in a row (like the teeth of a comb) from their upper jaws. It’s through these baleen plates that the whales filter water to capture tons of krill, other zooplankton, crustaceans, and small fish. At one point, however, mysticetes had teeth and a newly discovered 36-million-year-old fossil skeleton is helping scientists unravel the timeline of this transformation.

 Mystacodon selenensis

A mysterious jaw

The new mysticete ancestor was discovered in the Pisco Basin, right on the southern coast of Peru, by paleobiologists from Europe and Peru. The new find is called  Mystacodon selenensis, which means “toothed mysticete” owing to the fact that this is the oldest member of the group found thus far. All early mysticetes had teeth, unlike their modern versions which all employ a hallmark adaptation: baleen, a series of horny filtering combs that line the upper jaw. We can still to this day see the legacy of the toothed mysticetes in animals like orcas, dolphins, and other toothed whales.

Gray whale baleen plates.

Gray whale baleen plates at the Beaty Biodiversity Museum in Vancouver, British Columbia.

At what point and what mechanism this transition employed are some of the questions scientists been asking themselves for a while. Mystacodon was gracious enough to answer some. For instance, judging from its age, we know for sure mysticetes still had teeth some 36 million years ago. We’ve also come to understand that the striking transition from sharp teeth to baleen didn’t happen overnight.

According to  Olivier Lambert, a paleontologist at the Royal Belgian Institute of Natural Sciences in Brussels and co-author of the new study, Mystacodon was likely only 4 meters long or about the size of a pilot whale.

Mystacodon also holds on to some primitive whale features like a protruding hip bone, a remnant from the time when the whale’s ancestors were 4-legged, terrestrial creatures. For its timeline, some scientists had through this hind limb would be more or less gone but the findings clearly show the transition took longer than previously believed. The process also happened independently in toothed whales, not one time in the common ancestor of both toothed and baleen whales.

 The skull of Mystacodon has as a flattened snout and a mouth full of teeth, which baleen whales later lost.

The skull of Mystacodon has a flattened snout and a mouth full of teeth, which baleen whales later lost.

That’s not to say that Mystacodon lacks modern features. Its snout was flattened just like any other modern mysticetes. Additionally, Mystacodon couldn’t move the joints in the front flippers, a feature shared by modern mysticetes. Earlier whales could still flex these front flipper joints, likely a relic of the time when the flippers were actually legs. As such, Mystacodon can be considered a nice example of the final step of the transition of the forelimbs into flippers, as reported in Current Biology.

The fossil teeth were also more abraded and the eye sockets were found to be higher up on the skull. All of these are signs that these ancient animals used to hunt at the bottom of the ocean as it’s the sand of the sea floor that often wears teeth to such a degree and the higher-set eyes can help the animal look forward above its snout.

Clever innovation — fishing with a net instead of a hook

The fact that Mystacodon used to be so small compared to, say, a blue whale that can grow to 29.9 meters (98 ft) in length and 173 tonnes in weight, can be easily attributed to the baleen innovation. This is a rather clever strategy that allows the modern mysticetes to cut out predatory middlemen and feast directly on the abundance at the bottom of the food chain. The transition from a toothed to a baleen jaw, however, has always proved problematic. How could hard, slicing teeth and comparatively soft baleen occupy the same space in the jaw, and yet not get in each other’s way?

Wear on Mystacodon’s teeth tells us that this was a suction feeder who vacuumed up its prey instead of chomping it with its sharp teeth. Suction feeding is common among living marine mammals, including seals, dolphins and toothed whales, who use it either to capture prey or to prevent it from floating away while they swallow. Some scientists believe that suction feeding is a step toward the filter-feeding strategy we see today in baleen whales, considering early mysticetes show similar signs of wear. The connection between the two feeding mechanisms, however, is not clearly established.

To get to the bottom of things, scientists will have to dig more and deeper. A good place to start is in the same Peruvian desert where Mystacodon was unearthed where there’s a huge potential for excavations.