Whales are beautifully ridiculous. They are majestic divers, in some cases plunging nearly two miles underwater. And yet sooner or later they must rise back to the surface to breathe air. They breathe through a rather ridiculous-looking hole on top of their head. Unlike fish, which often reproduce by spraying millions of eggs and swimming away, whales give birth to one calf at a time, which they proceed to nurse for months. Some whales are like underwater bats, shrieking through their blowholes and listening to the echoes. And perhaps most ridiculous of all are whales that turn themselves into giant filters, thanks to a ridiculous tissue called baleen.
Baleen is a giant frond-like growth that sprouts from the jaws of 11 species of whales. Baleen whales open up their toothless mouths, sucking clouds of krill and other animals. They then ram the water out with their massive tongues, trapping food in their overlapping plates of baleen. Licking off the food, they open their mouths for another gulp.
Whales are ridiculous thanks to their history.They evolved from mammals on land. Their swimming, reproduction, breathing, and other adaptations to life in water are all the result of tinkering with a terrestrial animal's body. Fossil discoveries have documented how coyote-like mammals moved into the water about 45 million years ago and became more and more adapted to the marine life. The evolution of whales was not a single leap, however, but a long series of transitions. Even after whales had abandoned life on land, they were still not yet like whales today. None of them, for example, had baleen.
Among living whales, baleen is an all-or-nothing affair. If you're a whale you either have baleen or you have none. All other whales are profoundly different, with teeth instead of baleen. And while toothed whales can all echolocate, baleen whales cannot. Studies on whale DNA only reinforce the sharp divide between baleen whales and other whales. All baleen whales share genetic markers not found in toothed whales. In other words, the evolutionary tree of living whales is split into two branches. Paleontologists have found many extinct members of those two branches from the past 30 million years, bearing the hallmarks of either baleen whales or toothed whales.
In a sense, then, the origin of baleen whales is as remarkable as the origin of all whales. Yet that fact does not represent a real challenge to evolution. After all, there was a time when scientists had not yet found walking whales, and now they've found plenty. Other scientists have meanwhile been searching for the fossils of the earliest baleen whales. And, as I'll describe below the fold, they've now found a particularly interesting one: a baleen whale without the baleen.
The whale in question is called Janjucetus hunderi, named after the Australian town of Jan Juc where it was found, and a Mr. S. Hunder who found its fossils. Among its 25-million year old remains are a nearly complete skull, some vertebrae, ribs, and a bone from its flipper. As you can see from the skull, which I've reproduced here, this was an animal with big eyes and plenty of sharp teeth. To understand where it fits in the history of life, Erich Fitzgerald, a graduate student at Monash University in Australia made a careful study of its bones. He then compared over 200 fine anatomical details in Janjucetus to 23 other whale species. Some of these whales are living, and some are extinct, including a few that have yet to be fully described by scientists. Fitzgerald also compared these whales to pigs and hippos, which are among the closest terrestrial relatives to whales. The results of his study appear in the Proceedings of the Royal Society of London. Here I've reproduced the evolutionary tree that sums up his work.
The new results support previous studies, showing that living whales only represent the crown of branches on a very deep tree. The common ancestor of toothed and baleen whales lived about 35 million years ago, about 10 million years after early whales began moving into the water. As I decribed in my book, At the Water's Edge, whales lost their hind legs almost completely during those ten million years, except for a few vestigial bones in their body wall. Their nostrils moved partway up their snout. Their ears adapted for hearing underwater. The lineage that gave rise to the toothed and baleen whales is the only one that survives today, while all the other whales became extinct.
Janjucetus is a whale with teeth. And yet Fitzgerald found that they belong to the baleen lineage, not the lineage of living toothed whales. (Nor do they belong to an earlier branch of the whale tree.) Its teeth may bear no resemblance at all to the frond-filled mouths of living baleen whales, but Janjucetus shares with them some key traits not found in other whales, such as very wide lower jaw bones that were joined at the front not by a bony chin but by a mesh of cartilage.
Fitzgerald points out that Janjucetus's sharp teeth, powerful biting muscles, and big eye sockets make it resemble a leopard seal. He argues that it got food in the same way, hunting after individual fish and tearing their bodies apart. On its hunts, Janjucetus may have also relied on a sharp sense of hearing. It had a large hollow space in its lower jaws, which may have been stored with fat that could have conducted sound to its ears. But it shows no trace of the equipment toothed whales use for echolocation.
In other words, baleen whales evolved baleen long after splitting off from other whales. Their baleen-free ancestors apparently thrived as leopard-seal-like hunters for millions of years. Over time, their descendants evolved some of the traits that are found in all baleen whales today. Their jaws grew flatter and pointier. They still had teeth, which they may have been able use to filter food. Their teeth had changed shape, so that they were no longer good for shearing. Instead, they locked together. Crab-eating seals have similar teeth, which they use for filtering prey. As these whales shifted away from leopard-seal lifestyle, their eyes got smaller as well.
Some of these transitional whale fossils not only have teeth but also have marks suggesting they also held baleen. (Baleen plates are not giant teeth. They are made of keratin, the stuff in our hair and fingernails, rather than enamel.) As Fitzgerald's tree shows, the mixed-mouth whales gave rise to new species that kept the baleen and lost the teeth. They had become fully adapted to a new style of filter-feeding, and the results were dramatic: baleen whales proceeded to evolve to much bigger sizes. With the emergence of the blue whale, they became the biggest animals to ever exist on Earth.
Yet even the first "true" baleen whales were not like today's baleen whales. Some fine-tuning still remained, such as pushing the blow hole all the way to the top of the head, for example. But as Darwin himself noted, today's true baleen whales still preserve signs of their distant toothy past. Their embryos develop tooth buds, which are absorbed into the jaw as plates of baleen grow over them.
This study on Janjucetus is hardly the last word on baleen whale evolution. Paleontologists have found a number of other early baleen whale fossils that have yet to be carefully studied--a process that can take years. The branch marked ChMTM represents some whale fossils at the Charleston Museum of Natural History that have yet to be named, for example. Fitzgerald's analysis suggests that these fossils are even more primitive than Janjucetus. You can expect more work on baleen whale DNA and even on the evolution of their development--which embryonic signals changed to produce baleen and to kill off teeth? And paleoecologists will be offering insights into the changing environment in which baleen whales emerged--a cooling ocean in which krill and other plankton began to produce in bigger concentrations. Whale evolution is a very big picture, and one that's still coming into focus.
But Janjucetus already points to some important rules about major evolutionary transformations. As species adapt to new ecological niches, they become mosaics of primitive and advanced traits. It's much the same story for baleen whales as for land vertebrates, as demonstrated by the fish with legs, Tiktaalik, that made news earlier this year. Lurking in the Earth are strange beasts that straddle the divides of life as we know it today.
Source: Erich M. G. Fitzgerald, A bizarre new toothed mysticete (Cetacea) from Australia and the early evolution of baleen whales. Proc. R. Soc. B doi:10.1098/rspb.2006.3664 1
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That was fascinating! Can you send me a pdf of Fitzgeralds' article?
That was fantastic! At the risk of being labeled a suck-up, I'd also like to note that I recently finished the "Smithsonian Intimate Guide to Human Origins" and enjoyed it thoroughly. Thanks for the fascinating reading!
Great research (as always). Have a couple of your books here, Evolution (including video series)... which really drew my deep interest in Whale Evolution when it aired on PBS (at the same time National Geographic was releasing its own "Evolution of Whales" co-written by J.G.M. Thewissen). Great book, At The Water's Edge... reading the blog at Corante last night on "The Parasite Files", (*surprised to see your blog's moved here*) curious about Parasite Rex. Gotta fan!
Found this of great interest.. "...embryos develop tooth buds, which are absorbed into the jaw as plates of baleen grow over them..."
At the risk of imposing, recently Professor Thewissen shared some lab photos of Dolphin embryo limb buds, which too are reasorbed during development.
What will science discover next about the whales/mammals?
Jon:1:17: Now the Lord had prepared a great fish... Jonah was in the belly of the fish three days and three nights.
Jon:2:1: Jonah prayed ... out of the fish's belly,
Jon:2:10: the Lord spake unto the fish...
Mt:12:40: Jonas was three days and three nights in the whale's belly...
Besides that "Whales" are not "Fish".
Keep up the great work!
One other interesting thing about the baleen whales (to me, at least) is the high correlation between baleen and large size. Almost all baleen whales are bigger than almost all toothed whales. The only baleen whale in the normal toothed-whale size range is the Pygmy Right Whale; the only toothed whale that reaches baleen-whale-like sizes is the Sperm Whale.
Fascinating. How are modern seals releated to these guys if at all? Do seals represent a whole different mammal migration into the ocean? Are they younger or older than whales in this respect?
Carl Zimmer's book, At the Water's Edge, goes into the difference between the lineages of whales, seals, and manatees. Yes, seals are a very different mammal migration. As I recall, an important difference between whales and seals is that whales have huge tails and nonexistent (or occasionally vestigal) rear legs, whereas seals have large, paddle-shaped rear flippers and nonexistent (or very small) tails. There's a chapter in the book that ties this difference to heat loss and retention (biothermal regulation).
Again, as I recall from the book, the ancestors of seals evolved from mammals that lived in colder climates that lost their tails so as to preserve heat. The ancestors of whales evolved from mammals that lived in warmer climates, so the tail was kept, and gradually developed larger so as to aid propulsion. Manatees are a very different lineage altogether, but they too seem to have followed the same general body pattern development (large tail, no rear legs) that whales did - and note that manatees/dugongs all live in areas with very warm water.
There's more to it than my brief summary, of course. I strongly recommend the book; it's very well written, and not too technical, I think.
Beautifully told, Carl Zimmer! The time line graph informed me that the whale and hippo linages began at the Paleocene-Eocene Thermal Optimum, when everywhere was quite hot. No wonder all these creatures took up living at the beach and in the water...
This is great. Is there a link between the size of balleen whales and their feeding mechanism? Is there a difference in the efficiency between filter feeding and hunting?
Intriguing post, thanks!
owlmirror; chris
whales evolved from artiodactyls; seals from carnivores (perhaps more than once?); manatees/dugongs are most closely related to elephants.
also, the current warm-water distribution of dugongs/manatees is skewed by history. steller's sea cow, now extinct at human hands, lived in the seas around aleutians.
two features strike me about the skull: the huge nasal opening with its elaborate bony architecture; and the bony flange at the back. the nose must have been huge. perhaps it had something like a snorkel, which might require powerful muscles and a place (the flange) to anchor them.
any thoughts on this, anyone?
Any thoughts about the origins of (water-lovin') elephants? There was a story about one elephant who spent two years swimming from island to island in the Indian Ocean, and another elephant who spent 11 hours at a stretch in a swimming hole, refusing to come out.
djlactin:
While the water here is a lot colder than "warm water", keep in mind that the North Pacific side of the Aleutian Chain is warmed by the Japanese Current - especially at the western end where (IIRC) he catalogued the Sea Cow. It's not nearly as cold as the Bering Sea. In general, temperatures here - both sea and land - are moderate, relatively speaking.
I only point this out because people have a tendency to associate any part of Alaska/Siberia with the Arctic Circle.
I find it fascinating that the baleen whales develope tooth buds and these regress as the baleen plates form. Teeth and the keratinous epidermal appendages such as hair, nails, tounge papillae, scales and feathers, have a large # of similarities in their developmental processes and share a common set of evolutionarily conserved pathways (Shh, Eda, Wnts, etc). The timing and mechanism of the replacement of the tooth buds with baleen implies that there is a different mechanism for the development of the baleen plates. It would be interesting to see some expression data during the tooth resorbtion/baleen development phase. Although certainly not interesting enough to justify the "so-called scientific" slaughter of these wonderful animals...
Lesley: Any thoughts about the origins of (water-lovin') elephants? There was a story about one elephant who spent two years swimming from island to island...
A few curious notes on Elephants and Manatee...
"The first manateelike animla, dating from about 15 million years ago, was Protosiren, yet it lacked the replacement teeth that enable modern manatees to eat abrasive plant material. Recently, Domning and Gingerich (1994) suggested that Protorastamus and Protosiren were quadrupedal amphibious creatures that lived along the seashores. What did they look like? Domning (1991) wrote, "The Seven Rivers [Jamaica] prorastomids, which are slightly more derived than Prorasatomus itself, were pig-sized quadrupeds with long trunks, and a substantial though not powerfully-muscled tail." Certain anatomical characteristics "indicate that they were more aquatic than modern hippopotami; they probably fed as well as rested in the water, but at least the earlier of them could probably support their weight onland. In a 1916 paper, "Sea Cows, Past and Present," Frederic Lucas wrote: "It would of course be one link in the chain, one step towards a four-footed animal, if we could find a four-paddled porpoise, but none has yet come to light, and here is where the sea cow comes forward with an important bit of evidence. When paleontologists were hunting in the Fayum, Egypt, for ancestors of existing elephants, they came upon the remains of a manatee, not unlike those of today, save that it possessed four well-developed paddles; and because it was so evidently the predecessor of the modern sea cows, it was named Eosiren," from Eos, the Greek goddess of dawn. In fact, says Domning, "Eosiren libyca (late Eocene) had vestigial hind limb bones, but the hind limbs probably did not show on the outside of the body. In no case have we actually found a complete hind foot for any of these, paddlelike or otherwise. Lucas's statement is a broadly valid inference based on the pelvic bones, which were the only relevant elements available in his time" (personal communication, 2000).
[...]
"The news about the aquatic descent of elephants was startling enough to make many newspapers and television news programs when the paper was published in May 1999, but Elaine Morgan was way ahead of Gaeth, et al. In her 1985 revision of 'The Descent of Woman', she wrote:
Elephants are good swimmers now, so there is every reason to assume that they were good swimmers in the past, and for swimmers, she wrote "a snorkel makes sense."
--Richard Ellis, AquaGenesis
"If you have collected fossils to any great extent in marine Tertiary deposits of tropical or once-tropical latitudes, you have probably come across cylindrical pieces of thick, dense, vertebrae bone several centimeters in diameter that someone told you were the ribs of sirenians, or seacows. You may even have learned to apply the term "pachyostotic" to such bones. Inquiring further, you probably learned that seacows (manatees and dugongs) are the legendary mermaids, that they are the nearest living relatives of elephants, and that they all replace their teeth horizontally, back to front, just like elephants do. Such is education: a random mixture of truth and error, hopefully favoring the former."
--Daryl Domning, 1999
One more interesting note on Elephant and Sea Cows, which raise an interesting question on evolution [I cannot answer, seems like too broad and a complex subject]...
[Sharon: Curious myself, if salt vs. fresh water is an evolutionary step in itself? Many fish species have presumably branched from salt water to fresh water (as most all life did), and some have moved from dependency on fresh water, to salt water.]
The point being, Cetaceans are dependent (for most part) on salt water, and the fresh-water elephant relative (sirenian) are not... at least not completely, yet. In a few more million years, who knows? I could find little on Google regarding Elephants and their sentiment toward sea water. *smile*
jon; djlactin; chris:
I was probably making a false inference by pointing out that modern manatees and dugongs prefer warm water. It isn't the current habitat that I should have been emphasizing, but the habitat of the original ancestor. After all, modern whales have a range that extends to the polar regions, because while their ancient ancestor evolved in warm waters (and thus with tails), the Earth has cooled since then, and the various descendent lineages have now evolved blubber as insulation. It is quite possible that Steller's Sea Cows evolved a similar biological mechanism to cope with the cooler waters of the Aleutians -- which even if they are temperate, they are still cooler than the near-tropical waters that manatees & dugongs prefer.
Anyway, a little research indicates that the earliest manatee ancestor Pezosiren (with legs, even) was found on the island of Jamaica, and like the whale ancestor Pakicetus, developed during the Eocene warm period.
The question is are baleen whales and toothed whales the same 'kind'.
Carl, apologies for cluttering the Baleen Whale comments, with Manatee and Sea Cow questions. Really, I think these amazing creatures, the Sirenians, are under-rated in their importance. I have a great interest in cetaceans -whale evolution, but Sea Cows... it really is like a "modern peek" back into whale evolution some millions of years ago. With your knowledge, you might have points to disagree, but for instance, some of them have even lost their toe nails, and developed smooth paddles like Cetaceans).
I have been seeking info on manatee for a few years now, and the available information is sparse, like womens' sports... people just don't seem to have as much interest.
Daryl Domning (Expert on Early Sea Cows) writes: "Unfortunately, no one has put much effort into drawing accurate pictures of most of the extinct sirenians, mainly because all the ones from about the end of the Eocene onward looked outwardly not much different from the modern ones, especially as regards hind limbs. Protosiren (Middle Eocene) still had substantial though weak hindlimbs; ones like Eosiren (Late Eocene) probably had vestigial external hindlimbs; but after that there was probably nothing else visible on the outside -- only bony vestiges inside the body outline." :o/
I was turned on to these amazing creatures, somewhere about the same time (2002) as Evolution: Triumph of an Idea (Zimmer), and National Geographic: Evolution of Whales (Thewissen) came out. Reading Rainbow broadcasted the most insightful little episode "Sam the Sea Cow", visiting Homosassa Springs, where LeVar Burton gets upclose and personal with injured Manatee. They showed the major traits in common with elephants. After tracking down one of the producers - I finally obtained permission to re-use some clips from their video. In my opinion, the manatee are very important in the evolution creation debate. In their own way, perhaps more than whales, because they have so many obvious intermediate traits, and appear to be still moving toward the direction whales did many millions of years ago. Beautiful elephant toe nails. Recently completed flash/wmv clip w/ LeVar Burton and doctors, here and photos explaining the relation with elephants.
Please, if you should ever cover sirenians, I really want to know... I think people really need to understand more, besides that these creatures are endangered. (www.savethemanatee.org)
This blog is always astounding.
I have a question about the diagram of baleen whales' evolutionary tree. There are numbers at the base of each branch, like 57(2). From what I could tell from the study these are "branch support values" representing the probability that the computer program has drawn the tree correctly. So with a "1" next to the Janjucetus and Mammalodon figures, does that mean it's not sure where to put them, or what?
Carl, this is one of your best columns ever.
For a great video about Manatee's - and lots of other animals besides*, check out Chris and Martin Kratt's "Be the Creature" an excellent nature show geared towards kids from the National Geographic channel.
In the Manatee episode they spent some time swimming with manatees, in the winter manatees must stay by hot springs, venturing into the colder waters only long enough to feed.
They also discuss the evolution and relationship to elephants.
*Other animals include wild dogs, mongooses, bats, baboons, seals and some others
Speaking of books . . . I just skipped over to Carl Zimmer's site, and browsed some of the articles he's written over recent years. The one in National Geographic. "How Old Is It?" National Geographic, September 2001 (Cover story), cool... if I recall, it explains dating methods, but was a little surprised by .. none other than, *ouch*, from which I quoted above,
I found AquaGenesis quite interesting for some insight into certain species of prehistoric creatures (interesting footnotes, quotes, very nice illustrations are in the book), interesting info on early snakes... penguins, though I had read elsewhere (amazon.com being one), some negative reviews.
Accuracy is admittedly important. All in all, I still prize my copy of AquaGenesis though, and At The Water's Edge... basically anything I can get my mits on about land to sea transitions, mammal evolution. *smile*
If anyone is curious about the source of the baleen whales baleen, I suggest looking at the mustache vibrissae in walruses, and consider that while the nose arose, the mustache may have inverted slowly towards the gums. Note that baleen is only found on the upper jaw, like the mustache. The early baleen whales probably had a bristly mustache like walruses which assist in suction feeding, and baleen whales use forms of suction feeding as well. The face of the right whale gives a clue as well