A New Whale with Crazy Teeth

This week, a [paper] came out that described a new fossil whale from South Carolina (USA). The fossil is from the Oligocene (~ 30 million years ago) and it has a basically complete skull, some vertebrae, and a few ribs.

A reconstruction of Coronodon by A. Gennari.

The authors named the fossil Coronodon havensteini, meaning ‘crown tooth.’ It was found by Mark Havenstein, so the specific epithet (the second part of the name) is in his honor. The teeth of this fossil are particularly interesting.

Figure 2 from the paper showing the teeth of Coronodon.

Instead of simple, conical teeth (like in dolphins), or baleen (like in the blue whale), Coronodon has teeth with many bumps, giving each tooth the appearance of a little crown. Food and other particles left little scrape marks on the teeth, which indicate the direction of water flow through the mouth, and how the teeth were used during feeding. When the mouth was closed, the upper teeth sat on the outside of the lower teeth, providing just enough space for water to escape through the teeth, leaving delicious food bits inside the mouth.

Figure 2f from the paper showing how water would have flowed between the teeth.

Coronodon was using its crazy teeth to filter feed! Why is this important? Because understanding how filter feeding began in whales is an ongoing question. Coronodon is one of the earliest relatives of the mysticetes (baleen whales), but it has no baleen itself. It used its teeth the same way mysticetes use their baleen. Later on in mysticete evolution, baleen began to develop and finally took over as the dominant feeding structure. Coronodon represents the first step in that process. Another idea is that whales went through a toothless, suction-feeding phase before filter-feeding with baleen came about, but Coronodon shows that suction-feeding wasn’t part of the evolution of filter-feeding.

We can learn a lot about how extinct animals ate their food through looking at the shape and tiny scrape marks on the teeth (called microwear), and Coronodon is new amazing example of that!

Oceans, Whales, and Time

I don’t always talk about whales on this blog, but when I do, I prefer to talk about their size or echolocation. This time it’s about size. We all know many whales are really, really big. What we hadn’t quite understood yet is when they got big, or why.

A photo of several baleen whales surfacing as they engulf tiny krill. Source unknown.

Thankfully, a new [article] ran an analysis to figure out these two missing pieces. The authors used a dataset of 13 living and 63 extinct whales, including DNA (for the living ones) to create an evolutionary tree with time estimates for each branching point (called branch lengths). Using this tree and a dataset of body sizes, the authors used a model-testing approach to assess how the timing of whale evolution took place.

What’s a model testing approach? A model-testing approach is when we use computers to test the fit of different models to the data we give it. In this case, the authors gave the computer the tree and the body size data. The authors picked several different models for the computer to test. One of the models was based on random events driving evolution. One of them was based on evolution with a trend towards one trait. Some of the models were combinations of the others, where the model changes at a certain point during evolution. Once the computer is done testing each model, it produces a few statistical values that tell us how well each model fit the data.

A representation of the authors hard at work.

For this study, the authors wanted to know which model of evolution best fit the evolution of giant sizes in whales. The computer’s analysis showed that body size evolved randomly until around 3 million years ago when there was a shift to evolution with a trend of becoming very large. Even though filter feeding using baleen had been present in whales since 25 million years ago, it wasn’t until recently that they became very large. Around 3 million years ago, during the Plio-Pleistocene, wind-driven upwelling (where wind patterns on the surface bring up nutrients from the ocean floor) started getting stronger. This concentration of small food items is probably what lead to whales getting gigantic.

How upwelling works. Higher winds on the surface push the warmer surface water away from the coast. Colder, nutrient-filled water from the bottom gets pulled up. From NOAA.

A New Fossil Whale

Today’s whale come in two basic varieties: those with baleen, and those with teeth. These two varieties reflect a difference in how the whales eat. The ones with baleen (Mysticetes) filter out the tiny plankton they eat by bringing in large mouthfuls of water and then pushing the water through the baleen.

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© Walt Disney

The toothed whales (Odontocetes) use echolocation to hunt down larger fish, squid, and other foods.

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Bailey echolocating. © Walt Disney

But now there is a third variety of whale thanks to a new [fossil] that was reported this week. This new whale is identified only from its specimen number and its nickname, Alfred, until a larger description is published. Alfred has parts of its skull, mandible, teeth, and some other bones preserved and was found in the Pysht Formation of Washington, USA. These rocks date back to the Late Oligocene (28 to 23 million years ago). Features of its head tell us that it was Aetiocetid whale, however we do not yet understand how these whales are related to the whales of today.

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A reconstruction of Alfred by C. Buell/Museums Victoria.

Alfred’s teeth preserve microscopic grooves that can tell us about how it ate. Teeth are made up of soft dentine on the inside, and hard enamel on the outside. If an animal is continuously eating rough food, then the enamel will wear away. If the animal is chewing or eating in the same way day after day, then the wear pattern we see on the enamel can show us how that animal ate. By analyzing Alfred’s wear pattern, the authors discovered that it was probably using its tongue to create a suction force to bring in prey. Alfred would then expel the water through its teeth. As sand and other hard bits bumped into its teeth on the way out, they created grooves on Alfred’s teeth.

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How suction feeding would work in Alfred. By Museums Victoria.

This fossil shows that baleen may have evolved later than we thought, as this whale has no evidence of having had baleen. It also tells us that this suction feeding may have been an intermediate step between toothed whales and filter feeding whales.

A Whale of a Tale

This week, an [article] was published in which the authors try to answer the question: “How many times did whales become big?” In biology, there are a couple of ‘rules’ about how large body size is evolved. Cope’s Rule says that over evolutionary time, lineages of animals tend to get larger. Now, biological rules are not scientific laws (laws are backed by lots of scientific experiments and are considered to be true, like the law of gravity). Biological rules can, and do, have many exceptions, but can sometimes be useful in addressing evolutionary questions.

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An example of Cope’s Rule using horses. When horses first evolved, they were small, and got larger as their lineage continued to evolve.

Now, does the evolution of large body size in whales follow Cope’s Rule? To answer this, the authors compiled a list of all known stem baleen whales (that’s all the baleen whales that are not within the living baleen whale group), their body sizes, geographic locations, and geologic ages. Because the relationships of baleen whales are not well-known, they used three different phylogenies (diagrams of evolutionary trees) to test out how body size changed in this group over time.

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A living blue whale with a human for scale. They’re tremendous animals.

By using the body sizes of the known fossils, paleontologists can use a method called Ancestral State Reconstruction to make an educated guess about what size the ancestral form was. They found that having a small body size was more likely for the ancestral form, and that large size was independently evolved multiple times in baleen whales. However, some recently extinct forms also evolved small forms. So Cope’s Rule is not enough to explain body size evolution in whales.

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A drawing of the early whale Herpetocetus morrowi, with a human for scale. From Adli et al. 2014.

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A larger early whale, Llanocetus, with a human for scale.

How to Speak Whale

Whales are an amazing group of animals. They evolved from hoofed animals, like hippos, deer, giraffes, and cows. The fossil record shows us how whales went from being hoofed animals to the aquatic giants we see today. They gradually shortened their arms and legs, lengthened their bodies, and changed their skull shape to be better suited for the water.

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Evolution of whales (evolution.Berkeley.edu)

Today, whales come in a variety of shapes, sizes, and colors. The smallest is the Hector’s dolphin at 5 feet long, and the largest is the blue whale at 100 feet long.

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Whales can be divided into two main groups, based on how they eat. The mysticetes (= baleen whales) have baleen odontocetes (= ‘toothed whales’) have teeth. The mysticetes will gulp and/or lunge feed by taking in a big gulp of water filled with microorganisms (mmmmmm krill).


(from BBC’s Blue Planet)

The odontocetes, like dolphins and killer whales, tend to be better at fast hunting and chasing prey. Because mammals have poor vision, especially underwater, odontocetes developed echolocation to help them understand their surroundings and find prey. To use echolocation, odontocetes produce high frequency sounds near their blowhole that are amplified and directed with a big organ called the melon. The melon is what gives these animals that bump on the front of their heads:

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Dolphin Anatomy (from Texas Marine Mammal Stranding Network)

The high frequency sounds travel out into the water, bounce off of any object, and return to the whale. The sound waves enter the whale’s lower jaw, where they are transferred to the middle ear – the hearing organ. These whales can use hearing to ‘see’ their environment!

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Whale echolocation (from Wikipedia)

In April (2016) a [paper] was published that described the hearing organ of the earliest odontocete whale from the Oligocene (33-23 million years ago). The shape of the middle ear shows is very similar to that of modern echolocating whales, and it shows that even the earliest odontocetes were using echolocation. Apart from helping them find prey, echolocation allows these whales to communicate with each other, which makes pack hunting and living in big groups easier.

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Orcas making a big wave to hunt.

 

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Dolphin’s hunting using mud walls (From BBC The Wonder of Animals episode 9)

Echolocation may be what helped these whales become so diverse and successful today!