When the English anatomist William H. Flower proposed that whales had evolved from terrestrial ungulates in 1883 he cast doubt upon the notion that the direct ancestors of early whales chiefly used their limbs for swimming. If they did, Flower reasoned, whales would not have evolved their distinctive method of aquatic locomotion, typified by vertical oscillations of their fluked tails. Instead Flower suggested that the stock that gave rise to whales would have had broad, flat tails that paved the way for cetacean locomotion as we know it today, and he closed his lecture with a vision of such creatures shuffling about the water's edge;
We may conclude by picturing to ourselves some primitive generalized, marsh-haunting animals with scanty covering of hair like the modern hippopotamus, but with broad, swimming tails and short limbs, omnivorous in their mode of feeding, probably combining water plants with mussels, worms, and freshwater crustaceans, gradually becoming more and more adapted to fill the void place ready for them on the aquatic side of the borderland on which they dwelt, and so by degree being modified into dolphin-like creatures inhabiting lakes and rivers, and ultimately finding their way into the ocean.
Flower's hypothesis was criticized by other naturalists and eventually forgotten, but it proved to be prescient in at least one respect. During Flower's time whales were thought to have evolved from terrestrial carnivorous mammals, perhaps going through a seal-like stage. Flower differed in that he favored ungulates, or hoofed mammals, and he made particular references to both pigs and hippopotamus (note that his hypothetical cetacean ancestor is an omnivore).
Both of these latter creatures are artiodactyls, mammals marked by an even number of hoofed toes and a distinctive ankle bone (the astragalus) with a "double pulley" shape to it. This is significant because studies undertaken during the past decade have confirmed that whales not only evolved from artiodactyls, but are derived artiodactyls adapted to life in the sea. Even though Flower did not have access to the majority of data we presently have his hypothesis held the hint of a relationship that would be confirmed over 100 years later.
Flower's hypothesis that the ancestors of whales used their tails to swim right from the start, however, has not stood up so well. In early whales there was a transition between using limbs, the limbs and undulations of the spine in combination, finally oscillations of the tail as locomotor methods. A new archaeocete, Maiacetus, is a creature "caught in the act" of this transition.
Just announced in the journal PLoS One, Maiacetus was a member of the Protocetidae, an extinct group of early whales that beautifully illustrate an important phase of whale evolution. Previously known members of the group include Rodhocetus and Protocetus from Pakistan and Georgiacetus from the southern United States, the latter animal illustrating that this group included the first whales able to cross oceans.
Unlike Basilosaurus, these whales still had hips that were attached to their vertebral column. Many members of this group probably swam by undulating their spine while paddling with their limbs, perhaps similar to the way an otter moves through the water. The fusion of the hips to the spine limited their range of movement, but it did allow them to support themselves on the shores of the estuaries and coastlines they inhabited.
These are generalities, of course, because not all members of the Protocetidae were the same. In particular they were marked by differences in limb proportions, and Maiacetus fits snugly into the continuum of anatomical types. Rodhocetus, for example, has very large hind limbs ended with flat, paddle-like feet. Protocetus, by contrast, had much smaller hind limbs that were probably not very important to locomotion; its tail was more important to its swimming style. Maiacetus is closer to Rodhocetus in form but its hind limbs are smaller and do not show the same adaptations for hind-foot propulsion. What does this mean?
There is more than one possible answer, especially since Rodhocetus and Maiacetus were contemporaries. Maiacetus could represent the form of the more-terrestrial stock from which Rodhocetus evolved, thus making the big feet of Rodhocetus an adaptation to an aquatic lifestyle. This is consistent with the fact that the range of undulatory motion in the spine of Maiacetus would have been limited as the sacral vertebrae of this animal, those that articulated with the hip, were still fused. (They are unfused and difficult to discern from neighboring vertebrae in whales that swim chiefly through tail oscillations.)
On the other hand, Maiacetus could represent the stage in protocetid evolution after Rodhocetus and thus represent a reduction in the hind limbs as tail propulsion became more important. In this scheme of transitional types a reduction in hind limb size would be seen from Rodhocetus to Maiacetus to Georgiacetus and Protocetus. No systematic analysis or phylogenetic tree was included in the paper, but it seems that in either scenario Maiacetus represents an important link between the form of Rodhocetus and other early whales.
What is clear is that Maiacetus, like Rodhocetus, had hips attached to its spine. Did this genus spend some time on dry land? It is certainly possible but there is a key complication needs to be addressed. Early whales had heavy, dense, hypermineralized bones that acted as a kind of "bone ballast" when they were in the water. (This adaptation would later be adapted-out when heavy bones became a liability to whales of the open ocean, like Dorudon.) This allowed them to spend more energy swimming and less on staying submerged, but it also made their skeletons more fragile on land. They would not have been able to run quickly along the shores and, like modern pinnipeds, probably stayed close to the water.
One of the Maiacetus skeletons contained an important clue that may support the idea that early protocetids hauled out onto the beach on occasion. The authors of the paper reported that a highly-developed Maiacetus fetus was found inside one of the skeletons. Its position (nearly inside the ribcage of its mother) illustrates that it may have shifted position between the time its mother died and when it became fossilized, but its orientation inside the mother might have been preserved in its natural state.
The fossil fetus faces towards the tail-end of the mother, and if this was its natural orientation (as the authors suggest) then it might be a clue that Maiacetus gave birth on land. Modern whales are born tail-first, an adaptation to life in the sea that prevents them from drowning. Terrestrial mammals, by contrast, are often born head first. The authors use this difference to hypothesize that Maiacetus came out onto land to give birth, meaning that these early whales were still tied to the coast.
This hypothesis cannot be accepted unequivocally, however. The orientation of the fetus is consistent with the author's hypothesis but if the baby's bones moved due to some taphonomic process then we have to be careful in considering what it might (or might not) mean. It should also be remembered that some protocetids were capable of crossing oceans, as shown by the presence of Georgiacetus in the United States. This is far from the hub of whale evolution in the region of present-day Pakistan, and it suggests that at least some protocetids were able to spend extended periods at sea. Given this information it is possible that Maiacetus had behavioral and physiological mechanisms that allowed it to give birth in the water.
Just as the skeletal anatomy of whales changed due to life in the water their physiology would have changed as well. There would have been physiological transitions just as there were skeletal ones, and it is possible (if not likely) that Maiacetus possessed a physiology different from both modern terrestrial artiodactyls and whales. Unfortunately it is difficult, if not impossible, to test this because there are no living Maiacetus to examine. Further research will be required, and it may take many years to find another protocetid skeleton with a preserved fetus inside it for comparison. For now, the hypothesis that Maiacetus gave birth on land is certainly open to question.
The fossil fetus was important for another reason, though. It showed that the individual that it was found inside was a female, and this provided a key to identifying the sexes of Maiacetus. It's all in the hips. The hips of female placental mammals are shaped differently than those of males and this is related directly to childbirth. As in humans, the place where the left and right hip bones of the male Maiacetus met on the ventral side created a narrow V shape. In female Maiacetus this area was probably wider and would have made a U shape, which is a consequence of the presence of a birth canal. The hips were missing from the female skeleton, but there is no reason to believe that Maiacetus would have differed from this pattern seen in terrestrial placental mammals.
The overall differences between the male and female skeletons were slight (the male was slightly longer and had slightly larger canine teeth), reflecting a moderate amount of sexual dimorphism. Males may have competed for mates but there was no evidence that these whales had an elephant seal-like harem arrangement where large, highly dimorphic males dominate a group of female and drive off competitors. The amount of dimorphism between the sexes, however, will have to be continually reviewed as new skeletons come to light. Variation between adults of both sexes will have to be accounted for in order to more precisely pin down the extent of sexual dimorphism in Maiacetus, although the authors are most likely correct that it was relatively minor.
There will be plenty to discuss about Maiacetus in the coming weeks, months, and years, but regardless of how hypotheses might change Maiacetus is a fantastic creature. it sat right at the nexus of the land-to-water transition in whale evolution and can tell us much about how that transition was affected. Although paleontologists were frustrated for decades by the dearth of early fossil whales there is now an abundance of material to analyze, with new discoveries being made every year. I wonder what William Flower would think of all this.
Philip D. Gingerich, Munir ul-Haq, Wighart von Koenigswald, William J. Sanders, B. Holly Smith, Iyad S. Zalmout (2009). New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism PLoS ONE, 4 (2) DOI: 10.1371/journal.pone.0004366
UPDATE: If you have visited the National Museum in Washington, D.C. sometime in the last few months you may have already seen Maiacetus. This past fall the Smithsonian museum revamped its ocean hall and according to the autumn 2008 issue of the magazine Inside Smithsonian Research Maiacetus has been on display there for months;
For some visitors, the most dramatic whale on display may not be the full-size right whale but a species some 40 to 50 million years old, provisionally labeled Maiacetus inuus, the earliest mammal to live a majority of its life in the ocean. Discovered in the deserts of Pakistan in 2002 by Philip Gingerich of the University of Michigan, this creature had well-developed limbs with feet and toes better adapted for swimming than for walking. Its lower backbone also was more flexible than the backbones of its hoofed-mammal ancestors, suggesting that it swam with assistance from its tail. A cast of this fossil in the Sant Ocean Hall is the first public display of M. inuus anywhere.
From what I understand the "premature" unveiling of the whale was simply the result of the long time it took to prepare the skeletons and their descriptions. The exhibit was ready first and the description lagged a little. Even so, I have a question for readers who are better versed in the complexities of taxonomic rules & regulations. Does the appearance of the name Maiacetus inuus in the pages of Inside Smithsonian Research have any significant implications for the taxonomic bookeeping of this new genus?
If you'd like to know more about whale evolution, see these posts;
W.H. Flower's Ungulate -> Cetacean Hypothesis
Ancient Toothed Whales Had Baleen
Shaking the Cetacean Evolutionary Bush
The Whereabouts of Buckley's Basilosaurus
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Brian, thanks for this marvellous and comprehensive post!
So, now we have Maiacetus,yet another piece in the whale evolution puzzle. It's amazing how we've gone from fragmentary remains to an embarrassment of riches regarding the whale's transition from land to sea. The "branching bush" of evolution certainly shows how diverse the group was,moving in different directions, and all of them certainly didn't succeed, or evolve into modern genera. I'll be interested in hearing more about this new find. P.S. Did you notice how fast the mesonychid hypothesis for whale ancestry became obsolete? Less than a decade and a half ago, it was the dominant view, and now has been undermined by both fossils and genetics. Some changes in science come quickly!
You beat me to this, Brian. I thought there was an embargo on the release, though...
I suppose the fetus is large enough that we can be confident it wouldn't have turned around before birth?
This was great reading Brian. And in fact, much thanks for all the previous posts on whale evolution - I used them as essential background reading when I was writing up my own post.
Great post, Brian! Thank you!
Brian,
Might I recommend linking this as a Trackback?
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004…
Interestingly Dawkins notes in 'The Ancestors Tale' that Ernst Haeckel also connected whales with Hippos in 1866
"the real stunner is where he puts the hippos...not in the artiodactyls, but as a tiny twig on the branch leading to Cetacea" p 209 (UK paper back edition)
I can't find a picture on-line, but it's plate 9 in the book.
Rosel; Thanks for the note about Haeckel. I did not know that, although I have to look into it to see how Haeckel justified this arrangement. Flower's hypothesis seems better thought-out to me, but I'll see what I can dig up about Haeckel's idea.
James; I tried to generate trackbacks both automatically and manually and it did not work. I have no idea why.
Carl Zimmer is encountering the same problem. I dropped Bora an email.
I am a HS physics teacher, and I was amazed by this reporting. Thank you for the good service you provide to me who loves knowledge.
Great stuff, Laelaps! I might have to go back to your previous whale posts to understand all the terms, though.
Thanks, Sci! I'm glad you liked it.
I tried to keep the jargon to a minimum, but if I did not explain something clearly, please let me know. I don't want to confuse anyone who is interested in this really neat discovery by throwing around technical terms.
Haeckel's book is online here:
http://tinyurl.com/avc5oz
The tree is on page 477. It seems he was right for the wrong reasons, as he thought whales evolved from sirenians (which he included in the Cetacea) and thought these were closest to hippos.
Sea turtles can cross oceans and still have to give haul up on beaches to lay eggs, so by analogy, I don't see that the early whales would necessarily have had adaptations to give birth in water.
How large was the Atlantic at this point? If I recall correctly there were still tenuous links between Europe and America, so migrating across oceans may not have been nearly as problematic as it became a few million years later.
very good sites
Dave; To my knowledge there hasn't been any evidence showing that the ancestors of Georgiacetus walked over some sort of land connection, and they probably could not. It is more likely that they swam, which would have been quite a distance for animals whose close relatives among the protocetids appear to have been adapted to a near-shore lifestyle. If some of the protocetids could have crossed oceans then I think the notion that they could have given birth in water deserved to be entertained.
I'm not sure sea turtles are a good analogy, either, particularly since they are reptiles and leave their eggs ashore to develop. Unfortunately we don't know (and probably can never know) the reproductive habits of Georgiacetus, including gestation time. The hypothesis that Maiacetus gave birth on land is interesting but the evidence provided for it is far from conclusive and I tried to bring in lines of evidence not mentioned in the paper to support my case for an alternate one. Like I said in the post, there's still a lot left to learn about these early whales.
If you tried to send a trackback - don't worry. TOPAZ upgrade saved them elsewhere and will automatically put them on the paper once the process is over.
(As I haven't said it, excellent examination of the paper.)
I wasn't meaning to suggest that the protocetes walked over a land connection, but that they could have spread along the coast. It might be a long way, but we've got several thousand years to play with ;) Unfortunately we'd need some European fossils that would indicate that this may have happened- and this is also lacking, so I feel that I'm just throwing out ill-informed guesses here.
On reflection I agree that turtles aren't a great analogy, but I was trying to think of an animal that spends most of its life in water but comes ashore to give birth/lay eggs. Seals didn't seem as good an example I automatically thought of Elephant Seals and their harems, and I don't know enough about the ecology of other seal species to know how different they are. If I recall correctly most breed on land (or ice caps). Turtles however mate at sea and the males don't come ashore after they've hatched, so have broken their ties to land as much as they possibly can.
Its a pity the report doesn't go into details about how Gingerich et al know that the fetus hasn't been disturbed. Hopefully this will come out in a future monograph.
Georgiacetus is a much more "advanced" whale than Maiacetus, and probably spent less time on shore: it might have been more "seaworthy". So, Atlantic crossing might have been a challenge for a Maiacetus-grade Protocetid, but more feasible for a Georgiacetus-grade one.
There's a picture of a skeletal reconstruction of Georgiacetus at
http://ceps.georgiasouthern.edu/museum/about/vogtle/
The hip bone is still more or less in contact with the sacrum in G., but not as firmly connected to it as in Maiacetus: I think I've seen the phrase "ligamentary connection" used to describe it. The people who did the Georgiasouthern.edu WWWebsite think the Georgiacetus sacroiliac wouldn't have been able to bear much weight, so G. might well have been able to haul itself out on the beach-- maybe it even still gave birth on land, as even the largest extant Pinnipeds do-- but it couldn't hike inland.
There's a paper in a recent ?? "Journal of Vertebrate Paleontology" ?? that proposes the name "Pelagicetae" for a clade of fully-marine Cetaceans: I'll have to check (and will post here if I find my memory has betrayed me), but I think the proposal was that Georgiacetus was JUST outside this clade (i.e. was sister taxon to it): was, so to speak, the most "advanced" Protocetid before you got to it.
(Scarequotes around "advanced": there was enough bushy-ness to the Protocetid family tree to make the idea of a linear development from something Pakicetus-like through Maiacetus to Georgiacetus to Basilosaurids to modern whales inaccurate, but for discussing the evolution of Cetacean mode of reproduction maybe it's not too much of an oversimplification.)
Allen; Thanks. Yes, Georgiacetus was right outside the "Pelagiceti" clade in that paper (by Uhen, if I remember right) and I recognized it as more "advanced" in the post. I wasn't suggesting that Maiacetus = Georgiacetus only that it was close and the ability of some protocetids to cross oceans might have some important implications for physiology, including reproduction. Mostly I didn't find the evidence for land birth in the paper to be as well-made as I had hoped from the title and was trying to think of alternate hypotheses.
Great post Brian. I share your skepticism about the birth interpretations, especially since some references (e.g. Ripple 1999 Manatees and Dugongs of the World) report that sirenians (which give birth in the water) can be born head or tail first. On the other hand, as Dave notes, all pinnipeds give birth on land (or ice) and are perfectly capable of trans-oceanic dispersal so I don't think the distribution of Georgiacetus really tells us anything one way or the other. On the other, other hand (hind limb?), Phil Gingerich is one of very few paleontologists I'm pretty happy to take at face value...especially when it comes to fossil whales.
As far as the ISR publication goes, article 8.1.1. of the ICZN states that publications naming a new taxon "must be issued for the purpose of providing a public and permanent scientific record." It seems to me that the ISR piece doesn't fit that criterion. Furthermore, article 8.2 states "A work that contains a statement to the effect that it is not issued for public and permanent scientific record, or for purposes of zoological nomenclature, is not published within the meaning of the Code" the fact that the ISR says "provisionally" might be interpreted as this kind of disclaimer. Also, the ICZN explicitly prohibits specimen labels (article 9.6.)
More references...
The paper I was remembering was (you were right, Brian) by Mark D. Uhen:
"New Protocetid whales from Alabama and Mississippi, and a new Cetacean clade, Pelagiceti," "Journal of Vertebrate Paleontology" vol. 28 (2008), pp. 589-593.
The "new whales" described are additional (incomplete) specimens of Georgiacetus. The new clade, Pelagiceti ("sea-going whales") is defined as the last common ancestor of the Basilosauridae and "Neoceti," where Neoceti seems to be the crown group, Odontoceti+Mysticeti. (Unlikely to catch on, since it seems likely that Basilosauridae is paraphyletic: that Neoceti arose within Basilosauridae, from something similar to Dorudon. Uhen's analysis didn't show this, which is why he didn't think his new name was redundant.) Georgiacetus, on his tree, was the immediate outgroup of Pelagiceti: the species from the paraphyletic Protocetidae CLOSEST to the, umm, "advanced" whales.
"Basicetology" (I just made that word up: study of BASAL Cetacea) is rife with paraphyletic classificatory groups: Protocetidae probably arose within Pakicetidae, Basilosauridae within Protocetidae (maybe from something not too different from Georgiacetus), etc. Toby White has an interesting discussion of this in the Cetartiodactyla section of "Palaeos.com": see under the heading "Making the Grade: a digression on Darwin and Hennig" at
http://palaeos.com/Vertebrates/Units/520Cetartiodactyla/520.120.html
He suggests that this may be a response to a real feature of the critters studied! Whales underwent a stunningly rapid process of adaptive morphological change (four-footed Maiacetus is about 48 million years old, whale-shaped Dorudon with vetigial hind limbs perhaps 39 million) in response to the intense selective pressure of a radically new environment (water). As a result, standard cladistic methods may be hard to apply, and a series of grade-groups more useful in organizing the subject matter!
So maybe, even if (as I think likely) Uhen's clade is redundant (being the same as the clade "Basilosauridae and all descendants of Basilosaurids"), we could use "Pelagiceti" as a grade: whales with flukes. (The form of the final caudal vertebrae-- assuming your fossil whale didn't lose them before you found it-- gives evidence as to whether a whale had flukes. Basilosaurids did. Evidence available to Uhen in 2006, when he submitted his article, didn't suggest that Georgicetus did.)
(Sorry to run on at such length. (Didn't intend, in my original post, to seem to be trying to correct you: just trying to clarify a point of possible confusion I thought might arise from the discussion.))
I agree with Neil - many modern pinnipeds (e.g. Callorhinus, Mirounga, Arctocephalus) have extensive ranges, and spend much of their lives in pelagic environments, crossing large expanses of oceans, meanwhile returning to land to breed and give birth.
Additionally, the fossil record and distribution of extant Trichechus spp. (Domning 2005) argues the Georgiacetus point null. The modern atlantic is far wider than it would have been during the Eocene, and manatees were able to cross it to west Africa sometime during the Pleistocene. While manatees do not give birth on land (or, are terrestrial at all for that matter), as a rule can only successfully inhabit and feed in areas close to river mouths where seagrasses live. There are absolutely no resources useful for a manatee in deep water, although that did not stop the dispersal of Trichechus to Africa. Sirenians are far more restricted than protocetids were, given the carnivorous diet of the latter.
Taphonomically speaking... given the articulation of the adult, the carcass did not spend much time at the sediment water interface, and was most likely buried before skeletonization. Due to this, I highly doubt that the fetus would have been able to flip around 180 degrees while confined by the mother's carcass and confining sediment outside the mother's carcass (especially given the size of the fetus). While it is true that the fetus has shifted, it has shifted anteriorly; additionally, keeping in mind the width of the ribcage here as preserved, it does not appear physically possible for the fetus to turn 180 degrees (unless, of course, the abdomen was in an advanced stage of decay, and the thorax not, and the fetus turning 180 degrees, and then shifting anteriorly). It just doesn't as taphonomically parsimonious.
Neil brings up a neat point about sirenians - although the pattern might differ within extant cetaceans.
In any event - as a whale person, this is a really really cool paper. And I should say - that thing had a gnarly looking skull!
D. P. Domning. 2005. Fossil Sirenia of the West Atlantic and Caribbean Region. VII. Pleistocene Trichechus manatus Linnaeus, 1758. Journal of Vertebrate Paleontology 25(3):685-701
That sentence at the end of the third paragraph should read "It just doesn't sound as taphonomically parsimonious."
Bobby
Neil brings up a neat point about sirenians - although the pattern might differ within extant cetaceans.
I'd love to see some better documentation on sirenian birth mechanics if anyone out there has it. All of this has me wondering about viviparity, metabolism and birth presentation in marine tetrapods. Anyone out there want to collaborate on a project drowning whale and manatee newborns? Just Kidding!
In any event - as a whale person, this is a really really cool paper. And I should say - that thing had a gnarly looking skull!
My first thought was: "that thing looks like a freaking mesonychid!"
Neil and Bobby; Good points, and thanks for the clarifications. As I said in the above comments, I wasn't trying to say that Georgiacetus = Maiacetus, only that the distribution of Georgiacetus suggests that at least some protocetids were very well adapted to life at sea and may have had some physiological mechanisms (including those related to reproduction) that we can't at present identify. I don't think that this point is "nullified" just as the hypothesis that Maiacetus gave birth on land is not proven. I was not particularly impressed with the analysis of the fetus in the paper and more work will need to be done (I hope we find another protocetid skeleton with a fossil fetus preserved in position!). Nor was I arguing that the orientation of the fetus had changed. With a fetus of that size it was not likely, but that its position changed inside the mother's skeleton seems likely to me (particularly since the back half of the skeleton is missing and the remains of the mother are pushed forward so they pile up around the skull). I didn't want to take away from how cool the paper is, only to suggest some points that did not get consideration in the paper itself.
The breathing while being born theory makes no sense to me. Please explain to me how an emerging fetus can take a breath while it is in the birth canal? If the head has emerged, the fetus is unable to breathe because its chest is still in the birth canal. Mammals breathe by expanding the volume of the pleural cavity through the actions of the diaphragm and intercostal muscles, creating negative pressure in the pleural cavity. This would be impossible while the fetuses chest is still in the birth canal, especially with the muscular contractions of labor pressing on it. Once the chest has been delivered and can expand, the rest of the fetus slips out rapidly (this even applies to quadrupeds born on land, and they have a pelvis that still needs to be delivered - for animals with a cetacean anatomy it would be even easier to deliver the posterior end of the animal once the head and chest are delivered), allowing the newborn to swim to the surface and breathe. It does not matter if the tail is presented first or the head is presented first, it is impossible for the newborn to breathe during the birth process, and it does not breathe until it breaks the surface of the water. To me the idea of the calf being in danger because it might breathe during labor is silly and unproven, and I don't know why it would be accepted as orthodoxy in scientific circles. It may be one explanation but certainly not the best!
OF COURSE, there must be some selective pressure on cetaceans to be born tail first, but this may be due to their specialized, non-quadrupedal anatomy and the mechanics of pushing out a fetus with the cetacean shape, NOT due to the fact that they are born in water. for example, it may be that it is easier to give birth to a fetus tail first if it has a large head relative to the rest of its body and a short stiff, relatively immobile neck and no pelvis. These features are not shared by seals and other marine mammals that give birth on land. Imagine if you had push a whale or dolphin against some resistant force, but could only do it by pushing its head or its much more narrow, flexible tail. Which would you pick? Maiacetus is a quadruped, just like seals, dogs and sea otters (and I am willing to bet that the quadripedal sea otters are born head first at sea - but I don't know this for sure). Maiacetus probably gave birth like a quadruped, maybe in the water or maybe on land. It might not need to give birth tail first because its fetus did not have that specialized cetacean anatomy. I think this is a much more convincing argument than can be made for the often repeated (but unproven and unlikely) popular idea that whales are born tail first so they won't breathe prematurely during birth. Maiacetus may have given birth head first because it was still a quadruped, regardless of whether it gave birth on land or at sea.
Brian,
I understand you weren't trying to equate Georgiacetus and Maiacetus. My point was that since 1) pelagic adapted pinnipeds have circum-ocean basin distributions, and that individuals often swim across ocean basins yet still return to land to breed/give birth, and 2)sirenians that are restricted to very shallow water environments because of their dietary/drinking needs yet still manage to disperse across ocean basins (e.g. Trichechus), that the distribution of protocetids doesn't necessarily have implications for aquatic adaptations. Going back to the pinniped argument, just like protocetids were, pinnipeds now inhabit the continental shelves and shorelines of every continent (no protocetids yet from Antarctica, if I remember correctly).
Additionally, it is also important to keep in mind that large marine vertebrates can float for long periods of time, and if caught in a current, long distances, and presumably outside one's normal distribution (e.g. baleen whales). Taphonomic factors such as this indicate that there is some 'geographic averaging' that occurs within marine environments.
Thanks Bobby. I wasn't trying to be combative, and I do appreciate your expertise on this subject (excellent blog, btw. I will have to add it to the blogroll.)
Indeed it is.
I don't understand that. How is Neoceti or Pelagiceti redundant? Also, the tree in the paper does show a paraphyletic "Basilosauridae", with Chrysocetus being the sister-group of Neoceti, Dorudon farther away, and Basilosaurus the sister-group to all the other pelagicetes together.
Well, now we have a single word that we can say instead of the eight-word phrase "the paraphyletic so-called 'Basilosauridae' plus all its descendants". If you call that redundance, all biological nomenclature is redundant. :-|
This is just nonsense. Palaeos.com is full of conclusions that are derived from misunderstandings/ignorance of cladistics.
Given the differences between Maiacetus, Rodhocetus, Protocetus and Georgiacetus, including the fact that the latter is more closely related to Neoceti than to the other three, I'd even say that the term "protocetid" is outright misleading.
Yep. Looks almost like an entelodont's.
Hey Brian, thanks for the comments - I wasn't trying to be either. My opinion of my blog might approximate yours once I actually make some more posts - its been slow thus far, but I've been pretty busy lately. It will improve, I will admit (or, potentially, lie). Excellent blog, by the way.
As far as the discussion about archaeocete phylogeny goes:
1) Archaeocete phylogeny has been getting fairly well resolved;
2) Pelagiceti (as David correctly points out) is basically Neoeceti + a few others (basilosauridae), and thus, is not redundant (unless you want to say a bunch of extra words every time you talk about said clade)
3) Archaeoceti and most families within it have been known/assumed to be paraphyletic for a couple decades (if not longer), and the names are only kept and still used as a matter of convienence (i.e. its easier to say "basilosaurid" in quotations than always saying 'stem pelagicete just outside neoceti'). And, as David correctly states, Uhen (2008) did show paraphyletic Basilosauridae.
P.S. Brian, I might add that the only negative thing about your blog: your articles are so informative and my schedule is so tight that its difficult to read most of it! In fact, the other night, I decided "I'll read all of his whale-relevant articles from the last couple years" (I'm on an archaeocete fact-finding kick), and needless to say it took me a while, but I had also been reading for several hours already, and it resulted in a splitting headache.
Not that I mind long articles or anything - you've really done your research on this stuff (especially on whales - as a rule I don't really read any whale stuff pre-Remington Kellogg, arguably the first 'modern' paleocetologist).
David Marjanovic-
Re your:
"I don't understand that. How is Neoceti or Pelagiceti redundant? Also, the tree in the paper does show a paraphyletic "Basilosauridae", with Chrysocetus being the sister-group of Neoceti, Dorudon farther away, and Basilosaurus the sister-group to all the other pelagicetes together.
So maybe, even if (as I think likely) Uhen's clade is redundant (being the same as the clade "Basilosauridae and all descendants of Basilosaurids")
Well, now we have a single word that we can say instead of the eight-word phrase "the paraphyletic so-called 'Basilosauridae' plus all its descendants". If you call that redundance, all biological nomenclature is redundant. "
I reply:
Redundant in that, if we want to use the term "Basilosauridae" for a clade rather than for a grade group, Pelagiceti would be synonymous with Basilosauridae. Suppose (for sake of illustrative example) we came up with evidence that fur evolved at about the beginning of Cynodontia: it would be like introducing a new name ("Trichosynapsida") for the clade containing Cynodontia and Mammaliamorpha.
What's up, I just wanted to say, you're wrong. Your blog doesn't make any sense.