Stories tagged whale evolution


Happy as a whale in: ... in whatever.
Happy as a whale in: ... in whatever.Courtesy Ineuw
We love whale poop around here. Love it love it love it. Can’t get enough. It’s fortunate for us that whales poop so much—if you were to get the planet’s daily supply of whale poop in one place, and if you were also in that place, you would suffocate. It’d be awful.

The reason we love whale poop so much is because of its role in what Elton John and I like to call “the circle of life.”

We’ve already discussed how sperm whales have a net negative contribution to atmospheric CO2, because of all the iron in their poop. (The iron rich waste feeds tiny sea creatures, which, in turn, suck up CO2.)

It turns out that whales and their poop are also vital for the nitrogen cycle. Nitrogen is a vital nutrient for ocean life. While some parts of the ocean have too much nitrogen—extra nitrogen from fertilizers washes out through rivers, causing algae to grow out of control and create a dead zone—other areas contain a very small amount nitrogen, and local ecosystem productivity is limited by nitrogen availability.

So what brings more nitrogen to these nitrogen-poor areas? Microorganisms and fish bring it from other parts of the ocean, and release it by dying or going to the bathroom. But, also… whales bring it. Whales bring it by the crapload.

Whales, it turns out, probably play a very heavy role in the nitrogen cycle. And because the nitrogen feeds tiny ocean creatures, and those tiny ocean creatures feed larger ocean creatures, and on and on until we get to fish, more whales (and whale poop) means more fish. And we (humans) love fish.

Commercial whaling over the last several hundred years reduced global whale population to a small fraction of what it once was, but even at their current numbers whales contribute significantly to nitrogen levels in some areas. More whales, the authors of a recent whale poop study say, could help offset the damage humans have done to the oceans and ocean fisheries, while relaxing restrictions on whaling could have much further reaching ramifications than we might expect.

See? Whale poop is the best! (Whales too, I guess.)


A sperm whale: You will never get my precious iron feces! Never!
A sperm whale: You will never get my precious iron feces! Never!Courtesy Pacman
It would be a very special day indeed if a better story than this one popped up. But I wouldn’t ask for that. How could you want any more than this: whale poop fights global warming*.

Sperm whales are the particular focus of this study. The population of sperm whales in the Southern Ocean (the waters around Antarctica) is thought to be about 12,000. (There are more sperm whales in the world, but the study looked at Southern Ocean sperm whales.) Those 12,000 whales are thought to put about 200,000 metric tons of the greenhouse gas carbon dioxide into the atmosphere each year. That’s about the same amount that 40,000 passenger cars contribute each year. Destroy those polluting whales, right?

Wrong! See, it turns out that these sperm whales are also responsible for the removal of 400,000 metric tons of CO2 each year, making up for the amount they produce two times over. Their secret is this: they poop iron.

They don’t only poop iron, but sperm whales poop a lot of iron—each whale is thought to defecate about 50 metric tons of iron each year. That’s over 300 pounds a day! Obviously the whales aren’t pooping out solid iron ingots, though. It’s mixed in with their liquid feces. And that’s important.

The whales themselves don’t remove those 400,000 tons of CO2. They’re removed by phytoplankton. Phytoplankton are microscopic organisms that, like plants, use sunlight and CO2 to build their bodies. And they feed on iron.

The whales have lots of iron in their diets, because of the large amounts of fish and squid they eat. So the iron-rich whale poop is an ideal nutrient for phytoplankton. When the phytoplankton dies, the carbon they contain falls to the bottom of the ocean instead of being released back into the atmosphere. Where more carbon is trapped than is released back into the atmosphere, it’s called a “carbon sink,” and that’s what whale poop and phytoplankton create in the Southern Ocean.

Other parts of the ocean may naturally contain more iron for phytoplankton, but the Southern Ocean is poor in the nutrient, and the microorganisms rely on an iron cycle that the whales apparently play a large part in. More whales, greater carbon sink. Fewer whales, less whale poop, more atmospheric carbon.

Coincidentally, the International Whaling Commission will be meeting next week, to discuss regulations on how many whales can be harvested from the oceans each year. It’s a complicated world, isn’t it?

*I thought about making the headline “Whale poop is ‘green’” but… yuck.


The Ambulocetus: Not looking very fearsome at the moment, but it's thinking horrible, horrible thoughts.
The Ambulocetus: Not looking very fearsome at the moment, but it's thinking horrible, horrible thoughts.Courtesy ArthurWeasley
It’s Friday, y’all, and you know what that means!

No, not falling asleep at a booth in Applebee’s (should have gone to TGIF, right?)!

No, not a methadone suppository (not from me, anyway)!

And, no, not matching butterfly tattoos (that’s a Saturday thing)!

What’s left? Why a Science Buzz creature feature, of course! Sure, Friday has never been Creature Spotlight day before, sure, and, yes, it’s unlikely that I’ll remember to do it next Friday… But, hey, we’re Buzzketeers, right? We live in the now.

And so, with a small current science introduction, the creature of the week:

The crocowhale* (also known as ambulocetus, or “walking whale”).

If you’re keeping up on your cetacean evolution paleontology, you might have noticed this story recently. The ancestors of whales, paleontologists are quite certain, were land animals. Finding the evolutionary steps of their return to the water has been a challenge, however.

The distant ancestors of whales were carnivorous ungulates (ungulates are hoofed animals), that probably looked a little like dogs (with hooves). At some point these creatures began adapting to live and hunt in and around the water, eventually evolving into fully aquatic species.

Living vertebrates that swim employ a variety of propulsion methods. Several swimming styles seem to develop in sequence as a group of animals becomes more fully adapted to living in the water: swimming with four legs, paddling with just the back legs, undulation of the hips, undulation of the tale, and finally oscillation of the tail. The sequence of whale ancestor fossils seemed to follow this pattern (with modern whales having lost their hind legs to propel themselves with just their tails), except that for a long time it appeared that the step of swimming by hip undulation.

Recent fossil discoveries, however, show a whale ancestor that appeared to have a long fluke-less tail (it didn’t have big tail fins, like a modern whale), along with long hind legs and large, webbed feet. The skeleton seems to indicate that this creature would have propelled itself by undulating its hips, using its webbed hind feet as hydrofoils. And so, la de da, we have an important step in whale evolution in the bag. But, for the creature spotlight, we’re going back a couple branches in the cetacean family tree.

Before the group had evolved to the point of the hip wiggler above (called georgiacetus, by the way), there was the ambulocetus. Ambulocetus was a creature that probably still spent some of its time on land. It was about 10 feet long, and moved around on short, powerful legs. With its eyes and nostrils located on top of its long head, it probably looked something like a furry crocodile. Indeed, paleontologists think that ambulocetus probably acted very much like a crocodile, and filled a similar ecological niche.

Ambulocetus could have waited for large prey almost entirely submerged in shallow water, with only its eyes and nostrils breaking the surface. When something worthwhile came down to the water’s edge, it could have launched its body out of the water with its particularly powerful hind legs, ambushing its prey. The ambulocetus would have then dragged its struggling meal back into the water, and waited for it to drown. Yes! Crocowhale!

Here’s a cool illustration of ambulocetus in action.

* “Crocowhale” is a brand new term, and while I’m all for you using it in everyday life, don’t put it in any biology papers or anything. Yet.


Solving the mystery of whales' missing legs: Credit: Carole Harwood/NEOUCOM  Solving the mystery of whales' missing legs
Solving the mystery of whales' missing legs: Credit: Carole Harwood/NEOUCOM Solving the mystery of whales' missing legs

Every week, as I stand under the Science Museum of Minnesota's whale skeleton, I wonder if there is any remnant of its back legs and pelvis? I learned in a recent exhibit that whales once lived on land - they actually share a common ancestor with hippos, camels and deer.
A recent paper by J.G.M. 'Hans' Thewissen in the Proceedings of the National Academy of Sciences helped me to understand what might have happened.
One way to figure out evolution is to watch embrionic development. By studying hindlimb development in dolphin embryos, Thewissen theorised that "The presence of the initiation of hindlimb development suggests that dolphins had terrestrial ancestors with four limbs." Several of these ancestors have been found as fossils.

In most mammals, explains Thewissen, "a series of genes is at work at different times, delicately interacting to form a limb with muscles, bones, and skin. The genes are similar to the runners in a complex relay race, where a new runner cannot start without receiving a sign from a previous runner."

In dolphins, however, at least one of the genes drops out early in the race, disrupting the genes that were about to follow it. That causes the entire relay to collapse, ultimately leading to the regression of the animals' hind limbs. By analyzing dolphin embryos, Thewissen showed that the dropout is a gene called "Sonic Hedgehog," which is important at several stages of limb formation.

In whales, however, the story is more complex. Between 41 million and 50 million years ago, whales' hind limbs did shrink greatly as the former land animals began a return to the sea. But their legs showed no change in the basic arrangement and number of bones, which proved that Sonic Hedgehog was still functioning. Its loss must have come later. In short, "the dramatic loss of Sonic Hedgehog expression was not the genetic change that drove hind limb loss in whales".

Instead, Thewissen and his colleagues conclude, whales' hind limbs regressed over millions of years via "Darwinian microevolution": a step-by-step process occurring through small changes in a number of genes relatively late in development.

Abstract from PNAS: Developmental basis for hind-limb loss in dolphins and origin of the cetacean bodyplan

Among mammals, modern cetaceans (whales, dolphins, and porpoises) are unusual in the absence of hind limbs. However, cetacean embryos do initiate hind-limb bud development. In dolphins, the bud arrests and degenerates around the fifth gestational week. Initial limb outgrowth in amniotes is maintained by two signaling centers, the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA). Our data indicate that the cetacean hind-limb bud forms an AER and that this structure expresses Fgf8 initially, but that neither the AER nor Fgf8 expression is maintained. Moreover, Sonic hedgehog (Shh), which mediates the signaling activity of the ZPA, is absent from the dolphin hind-limb bud. We find that failure to establish a ZPA is associated with the absence of Hand2, an upstream regulator of Shh. Interpreting our results in the context of both the cetacean fossil record and the known functions of Shh suggests that reduction of Shh expression may have occurred {approx}41 million years ago and led to the loss of distal limb elements. The total loss of Shh expression may account for the further loss of hind-limb elements that occurred near the origin of the modern suborders of cetaceans {approx}34 million years ago. Integration of paleontological and developmental data suggests that hind-limb size was reduced by gradually operating microevolutionary changes. Long after locomotor function was totally lost, modulation of developmental control genes eliminated most of the hind-limb skeleton. Hence, macroevolutionary changes in gene expression did not drive the initial reduction in hind-limb size.

photos and comments on whale limb rudiments
NSF press release