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Seals, the early years

The views expressed are those of the author and are not necessarily those of Scientific American.


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It’s the moment you’ve all been waiting for… stem-pinnipeds at Tet Zoo. Or, probable stem-pinnipeds anyway. This minimum-effort post is brought to you on the back of work showing that pinnipeds (seals, sea lions and walruses) are monophyletic, not diphyletic, and that the taxa shown here – Potamotherium, Puijila and so on – really are early members of the pinniped lineage, not convergently pinniped-like carnivorans of some sort. If there are any questions or areas of debate — hey, that’s what the comment section is for. Without further ado…

The illustrations of Semantor are from Orlov (1933). The images of Puijila, and the cladogram shown at the bottom, are from Rybczynski et al. (2009) (the cladogram is arguably odd in showing the name Pinnipedia as being attached to the entire clade rather than just to the crown-group… which isn’t shown on the tree). The skeletal reconstruction of Potamotherium is from Savage & Long (1986) and the life restoration of it is by Graham Allen. For previous Tet Zoo articles on pinniped-branch carnivorans, see…

Refs – -

Orlov, Y. A. 1933. Semantor macrurus (ordo Pinnipedia, Fam. Semantoridae Fam. nova) aus den Neogen-Ablagerungen Westsibiriens. Trudy Paleontologicheskii Institut Akademiia Nauk SSSR 2, 249-253.

Rybczynski, N., Dawson, M. R., & Tedford, R. H. 2009. A semi-aquatic Arctic mammalian carnivore from the Miocene epoch and origin of Pinnipedia. Nature 458, 1021–1024.

Savage, R. J. G. & Long, M. R. 1986. Mammal Evolution: An Illustrated Guide. Facts on File Publications, New York & Oxford.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com!

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The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Sebastian Marquez 12:08 am 06/12/2014

    Short tails due to cooler climate? Short enough to limit future tail powered propulsion I take it?

    Tet Zoo articles about stem-anything make me happy :)

    Link to this
  2. 2. Jenny Islander 1:31 am 06/12/2014

    My money’s on Puijila, because of the oosik.

    Link to this
  3. 3. DavidMarjanovic 6:12 am 06/12/2014

    Neogen Ablagerungen Wèstsibiriens

    The accent is a typo (doesn’t exist in German), and Neogen-Ablagerungen needs a hyphen which it almost certainly has in the original.

    Short tails due to cooler climate?

    That of Puijila isn’t actually all that short.

    Link to this
  4. 4. DavidMarjanovic 6:14 am 06/12/2014

    It’s probably thin, though, perhaps unlike that of Potamotherium.

    How old is Potamotherium?

    Link to this
  5. 5. Andreas Johansson 6:45 am 06/12/2014

    Speaking of tails, Semantor‘s specific epithet macrurus means “long-tailed”, so the name-giver presumably thought its tail not short by some standard.

    Link to this
  6. 6. irenedelse 7:24 am 06/12/2014

    The fact that Pinniped ancestors seem to have first evolved in freshwater environments reminds me of a recent discussion at TetZoo about sea turtles and the mechanical challenges of the sea/land interface, with the crashing waves, etc.

    @Jenny Islander:
    Have there been no bacula (baculums?) found for Potamotherium?

    Link to this
  7. 7. Boesse 7:39 am 06/12/2014

    Here’s some shameless self promotion (at Darren’s request). Myself- and other pinniped researchers – are not fully convinced that Puijila is a pinniped. One of the only postcranial features linking Puijila to pinnipeds is a posteriorly expanded scapula, although it’s not really that much more developed than in extant lutrines. It’s got a large infraorbital foramen – but that’s present in a number of aquatic and fossorial musteloids (e.g. Lutrinae, Taxidea) – which doesn’t really distinguish it from musteloids. Two dental features – an M2 that is positioned medial to P4/M1, and a protocone shelf on the P4 – are also developed in the “oyster bear” Kolponomos from the Oligo-Miocene of the Pacific Northwest. Kolponomos also shares an additional feature with Puijila and pinnipeds – a posteriorly expanded palate. A number of other basicranial features unite Kolponomos with pinnipeds. For whatever reason, Kolponomos was not included in the cladistic analysis of Rybczynski et al. 2009 – despite Tedford et al. (1994: Proceedings of the San Diego Society of Natural History:29:11-32) identifying it as a probable sister taxon to Pinnipedimorpha. The point is, if Puijila has any relation to pinnipeds instead of being an early lutrine relative, then Kolponomos probably factors in as well, since it shares all of these features. The interesting point is that these three taxa, if a monophyletic group – lutrine-convergent semiaquatic pseudo-otters like Potamotherium/Semantor/Puijila, the “oyster bear” Kolponomos, and true pinnipeds – reflect a mid-Cenozoic diversification of aquatic arctoids into fairly different niches and environments.

    To be totally clear: I do not reject the hypothesis that Puijila is a pinniped, and do not embrace the alternative hypothesis that it is an early lutrine (if I recall correctly it predates true lutrines by quite a bit of time). I’m just skeptical, and I think more evidence is necessary for me to be convinced one way or another.

    Anyway, there’s more on this here (regrettably, in my haste to leave the US and begin my Ph.D. down under I never completed part two of this series, which was to focus on Kolponomos and its relationship with pinnipeds):

    http://coastalpaleo.blogspot.co.nz/2012/01/is-puijila-pinniped.html

    Also, there has been a very dubious publication of an Eocene pinniped. I wrote a critical review of the paper here:

    http://coastalpaleo.blogspot.co.nz/2012/04/an-eocene-pinniped-critique-of-diedrich.html

    And, somewhat tangentially related is a very recent post about the phylogenetic relationships of Allodesmus:

    http://coastalpaleo.blogspot.co.nz/2014/06/the-best-known-fossil-pinniped-part.html

    Link to this
  8. 8. irenedelse 7:50 am 06/12/2014

    @ Darren:

    Typo alert: it’s Puijila, not Pujila. (First paragraph, then the one after the pictures.)

    Link to this
  9. 9. naishd 8:32 am 06/12/2014

    Thanks to all for comments. Thanks indeed, Bobby (comment # 7), for sharing the scepticism about Puijila here – I was obviously hinting at this by referring to these animals as ‘probable’ stem-pinnipeds. Thanks, irene, for typo-spotting (now corrected).

    As goes the tails of these animals: you need to consider this within the context of other arctoids. Yes, the tail of Puijila (and Potamotherium) looks long-ish (and that of Semantor is certainly long for a pinniped relative: photo), but it’s proportionally shorter than the inferred ancestral condition, and seemingly thinner and more lightweight overall. Or so it’s been claimed away…

    If these animals are pinniped-branch carnivorans, the implication is that they were reducing their tails as a consequence of evolution in cool climates, a trend that might encourage limb-propelled locomotion and the near loss of the tail in later members of the group (in contrast, sirenians and cetaceans originated in tropical or subtropical places, and look what happened to them).

    Link to this
  10. 10. ekocak 8:55 am 06/12/2014

    Where was this article when I was looking for short articles to cartoonify?! We need like a Tet Zoo wiki…

    Link to this
  11. 11. Gigantala 10:54 am 06/12/2014

    Pinnipedia are the palindromic palisades of an empire of pus.

    Anyways, I’m pretty certain colder climates aren’t necessary to explain limb based propulsion over tail based propulsion. Unless sauropterygians evolved in the poles as well.

    Link to this
  12. 12. naishd 11:04 am 06/12/2014

    Gigantala — no no no, the idea is that cold climates encourage the evolution of short(er) tails, thus that swimming mammals that evolved in cold climates are less likely to become tail-propelled swimmers. There are, of course, other evolutionary pressures that might encourage swimmers to become limb-propelled ones rather than tail-propelled ones (like presence of an already stiffened body), plus I don’t know that the mammal-focused idea mooted here is applicable to reptiles. This hypothesis is also discussed in Carl Zimmer’s At The Water’s Edge, I think.

    Link to this
  13. 13. irenedelse 11:48 am 06/12/2014

    If stem pinnipeds are descended from fossorial animals that already didn’t use their tail much (compared to tree dwelling species where the tail is used for balance), wouldn’t that be another possible factor in tail reduction? Current fossorial mustelids tend to have relatively short and/or thin tails if I’m not mistaken.

    Link to this
  14. 14. Heteromeles 1:46 pm 06/12/2014

    (in contrast, sirenians and cetaceans originated in tropical or subtropical places, and look what happened to them)..

    I take it hippos evolved in the Arctic then?

    Also, I believe the Hawaiian Monk Seal is considered the most primitive living seal, and it’s certainly not pining for the fjords.

    And how cold were said fjords when the pinnipeds were evolving, again? The Miocene was a wee bit warmer than it is today.

    I’d speculate that you’re focusing on the wrong sort of “tail” in speculating about climate. The critical difference between cetaceans, sirenians, and pinnipeds is that pinnipeds can’t give birth in the water. That inconvenient little fact probably has warped their anatomy more than anything else. I don’t know how sirenians and cetaceans “figured out” how to turn the embryo around so that it’s born tail first, but that may be the critical innovation that let them repurpose their lower vertebral column into a swimming machine, rather than leaving it as an amphibious machine as in the pinnipeds. That may be a better explanation than the length of the tail in winter.

    Besides, I’ve seen otters goofing around on very frozen lakes. Long tails are not a handicap in the snow.

    Link to this
  15. 15. naishd 5:16 pm 06/12/2014

    Thanks to all for further comments. Some responses to Heteromeles (comment # 14)…

    I take it hippos evolved in the Arctic then?

    Obviously, there are other reasons behind tail reduction in other animals. Hippos belong to a group of artiodactyls that have proportionally short tails whether amphibious or not. In short, this is a non sequitur.

    Also, I believe the Hawaiian Monk Seal is considered the most primitive living seal, and it’s certainly not pining for the fjords.

    The Hawaiian monk seal is deeply nested within Phocidae, and thus deeply nested within (crown)Pinnipedia, thus there is no indication that its anatomy or physiology or lifestyle is relevant as goes discussions about the earliest stages of evolution within the clade in question. If the Hawaiian monk seal were truly outside the clade that contains all other pinnipeds, you’d have a point.. but, no, this is another non sequitur.

    And how cold were said fjords when the pinnipeds were evolving, again? The Miocene was a wee bit warmer than it is today.

    Part of what I said comes from the Puijila paper (Rybczynski et al. 2009). They state that “Puijila lived in a cool temperate environment where the freshwater lakes would have frozen over in the winter” (p. 1023).

    I’d speculate that you’re focusing on the wrong sort of “tail” in speculating about climate. The critical difference between cetaceans, sirenians, and pinnipeds is that pinnipeds can’t give birth in the water. That inconvenient little fact probably has warped their anatomy more than anything else.

    I certainly agree that pinnipeds appear strongly tied to terrestriality (though sea ice or lake ice can represent the ‘land’ in some species), but I’ve always thought that it’s their moult cycle that might be the constraint. And given that the juveniles of some seals (Hooded seals) are weaned within four days of birth and can swim from their day of birth onwards, I’m not wholly sure that there is some constraint stopping pinnipeds from giving birth in the water – there are, of course, a few records of some seals (Grey seals) doing exactly this. Anyway, I’m with you on the idea that pinnipeds still need an emergent substrate for birthing. I don’t see what this would have to do with tail length, however.

    I don’t know how sirenians and cetaceans “figured out” how to turn the embryo around so that it’s born tail first, but that may be the critical innovation that let them repurpose their lower vertebral column into a swimming machine, rather than leaving it as an amphibious machine as in the pinnipeds. That may be a better explanation than the length of the tail in winter.

    Hmm, I just don’t see what any of this might have to do with tail length. And are you sure that sirenians give birth tail first? There isn’t much to go on, but it seems that there’s no definite head-first or tail-first tendency (Ripple’s Manatees and Dugongs of the World and other sources). Furthermore, one fossil indicates that stem-cetaceans with enormously hefty tails (I’m referring to Maiacetus) were still giving birth head-first, in which case it isn’t wholly obvious that tail-first birth is, as you infer, linked with tail re-tooling.

    Besides, I’ve seen otters goofing around on very frozen lakes. Long tails are not a handicap in the snow.

    Nobody said they were. The idea is that long tails are disadvantageous when you live, for generations, in cool or cold climates. Conversely, there is no such pressure for tail reduction if you evolve in the tropics. Phylogenies and fossils indicate that otters are predominantly tropical and subtropical, with Lutrini and the Enhydra lineage representing separate invasions into cool and cold environments. And, guess what? Lutrines have proportionally shorter tails than tropical otters, and enhydrins have proportionally shorter tails than lutrines.

    I used a bunch of references in compiling these arguments. Am in a rush so haven’t cited them but let me know if you want to see them.

    Link to this
  16. 16. Gigantala 5:46 pm 06/12/2014

    I also doubt it that headfirst birth is correlated to sirenian/cetacean repurposing of the lower spinal cord; ichthyosaurs and polycotylids did not alter the lower spinal cord in a similar fashion (and the latter didn’t swim using their tail at all) and yet pulled off the same trick.

    Link to this
  17. 17. Heteromeles 6:20 pm 06/12/2014

    @15: Um, you missed the turn, Darren. The nearest living relative of whales, is of course, the hippo. Which is amphibious. That’s not a non-sequitur, it’s pointing out that two members of a clade found radically different methods for entering the water. Water temperature is not destiny.

    It’s good to have the references for seals, since I didn’t know about that gray seals had given birth successfully in the water.

    As for otters, the ones I’m thinking of were in northern Wisconsin, where they’d lived for who knows how long (I’m guessing around 10,000 years), without apparently freezing their tails off (and it was around 0oF when I saw them). Nor, for that matter, do beavers freeze their tails off when they wander around in the winter snows. Conversely, sea otters “freeze their tails off” in the water off the California coast, which gets as low as the low 50s, yet they have shorter tails. I don’t think there’s as good a correlation between temperature and tail length as people have posited. Perhaps there’s a difference in swimming style?

    I should point out, since I didn’t know it until just now, the sea otters give birth in the water, apparently tail first, while manatees are born either head-first or tail-first, according to what I could find.

    I should also point out that we should be careful when analyzing fossils that died in the act of giving birth in assuming that they are giving birth in the normal direction for the species. For example, if a woman died giving birth to a child feet first (a breach birth) and was fossilized in the act, future paleontologists would assume that was normal rather than lethal.

    @16: spinal cord? I’m talking about taking the vertebral column and associated muscles from the diaphragm on down and using it to power the tail flukes in an up and down direction (effectively it’s a modified gallop). Sea otters do something similar. Seals swim effectively with a modified walk (flippers alternate side to side), while sea lions “fly” underwater with their forefins. The basic point of all this is that, apparently, if evolution alters your body so that you swim with a highly modified gallop, you become extremely ungainly on land, whether or not you lose your hind limbs. I’m proposing here that being able to give birth in water makes this type of swimming possible, while not being able to give birth in water (and I stand corrected here with regards to the gray seal) means that an animal is “stuck” with some other mode of motion that also allows them to haul out onshore to give birth.

    Darren rightly questions it, and it’s possible that the spinal modifications and reduction of hind limbs are not enabled by shifts in reproductive mode, but have to something to do with tail length as correlated with water temperature over evolutionary timespans. I think the evidence for this is weak at best, but whatever. Rational people can disagree.

    Link to this
  18. 18. irenedelse 7:17 pm 06/12/2014

    Maybe it’s because I don’t know enough about evolutionary theory and anatomy, but the notion that tail reduction by itself could drive stem Pinnipeds to rely on their limbs only for propulsion in the water seems to me… unsatisfying.

    Reduction in tail length external associated to life in a cool climate makes sense, and as Darren pointed out at #15, today’s Lutrine otters do have a shorter tail than species adapted for warmer climates. (Isn’t the correlation of temperature with the size of tails and ears one of the named ‘laws’ or ‘rules’ of zoology? Anyway.)

    But these otters still have a chunky, muscular tail, useful in locomotion. Pinnipeds might well have taken this path of evolution, couldn’t they? The stem Pinnipeds discussed in the article were apparently short legged, long bodied, semi-aquatic animals with shortish, more or less muscular tail, and could theoretically have gone on to swim like otters, with undulations of the body and tail. Retaining a substantial tail, they might even have later given rise to a group of Cetacean-like animals using tail propulsion?

    Ok, I’ll stop the speculation here. But it’s still intriguing. Were seals fated to be the way they are, or did randomness play a part in steering their ancestors toward the particular evolutionary pathway they took to become marine mammals?

    Link to this
  19. 19. Cameron McCormick 8:08 pm 06/12/2014

    Also, I believe the Hawaiian Monk Seal is considered the most primitive living seal

    This odd claim can be found in Wikipedia (of course), but it’s present in some fairly recent literature:

    Williams, T. et al. (2011) Metabolic Demands of a Tropical Marine Carnivore, the Hawaiian Monk Seal (Monachus schauinslandi): Implications for Fisheries Competition. Aquatic Mammals 37(3) 372-376.

    Unlike Wikipedia, Williams et al. actually cite their source — Repenning & Ray (1977). The ear morphology, lack of proximal tibia-fibula fusion, posterior vena cava and innominate bone were all interpreted as “primitive” by these and some earlier authors.

    Repenning, C. & Ray, C. (1977) The origin of the Hawaiian monk seal. Proceedings of the Biological Society of Washington 89(58) 667-688

    Link to this
  20. 20. Boesse 8:25 pm 06/12/2014

    Monachus in general is relatively plesiomorphic amongst phocids, and has been recognized as such by most pinniped workers, and the early diverging position of Monachus has been borne out by molecular and morphological cladistics. There’s a recent paper (Scheel et al. 2014) which took the Caribbean and Hawaiian monk seals and erected a new genus for them, Neomonachus; these two species are sister taxa, with the Mediterranean Monk seal (which they left as Monachus monachus) sister to them. Ultimately, the three still form a monophyletic clade, and it escapes me why it was even necessary to erect a new genus – it comes across as needless splitting in favor of conservation politics.

    Scheel, D.-M., et al. 2014. Biogeography and taxonomy of extinct and endangered monk seals illuminated by ancient DNA and skull morphology. Zookeys 409:1-33.

    Link to this
  21. 21. irenedelse 8:30 pm 06/12/2014

    @Cameron McCormick:

    Actually, Repenning, C. & Ray, C. (1977) is the first reference cited in the section of the Wikipedia article about the Hawaiian monk seal. Another cite is the more recent Berta, Annalisa; Sumich, James L (1999). “Marine Mammals”. Evolutionary Biology (Academic Press).

    Link to this
  22. 22. Heteromeles 8:31 pm 06/12/2014

    Interesting thing here is that seals and sea lions (and especially walruses) seem to swim more like baby otters than like adult otters (giant otter here). I’m not sure modern otters are the best model.

    Link to this
  23. 23. Cameron McCormick 9:49 pm 06/12/2014

    Boesse — my favorite summary of Scheel et al. (2014) is “scientists have discovered a new genus of monk seal… the first in the modern seal family in more than 140 years”. I wonder how many casual readers — and cryptozoologists — are under the impression that a big novel seal was recently discovered, instead of just given a debatable new moniker.

    irenedelse — my apologies to Wikipedia!

    Link to this
  24. 24. Heteromeles 12:18 am 06/13/2014

    I should note that I didn’t check Wikipedia when I made the assertion about Hawaiian monk seals. I’ve heard and read it in so many different places that I didn’t think it was controversial. Don’t blame Wikipedia for this one.

    Link to this
  25. 25. naishd 4:07 am 06/13/2014

    Thanks to all for continuing comments (the comments section at Tet Zoo remains the most active place on the whole SciAm network, so far as I can see…).

    There is indeed a ‘rule’ relating to the size of tails and other appendages (comment # 18): it’s called Allen’s Rule. What I’m saying is that Allen’s Rule might partially or wholly explain tail reduction in stem-pinnipeds, this meaning that they (and other cool-climate endothermic swimmers) were perhaps less likely to become tail-propelled swimmers. Is this the entire explanation as to why pinnipeds became limb-propelled swimmers? No – pinniped limbs would (based on analogy with other swimming mammals) become enlarged and webbed anyway, regardless of the tail, but… does it contribute to the fact that pinnipeds came to rely on the limbs and not the tail? I still see this as a reasonable hypothesis, so long as Allen’s Rule really applies, and so long as stem-pinnipeds really did have reduced tails compared to related carnivorans.

    This hypothesis entails a set of predictions: that other cool-climate swimmming endotherms will also have reduced tails and rely more on their limbs than do tropical swimming endotherms. Without running stats or anything.. . it seems to work for sea otters, but I’m not sure about other mammals. I need to check the Carl Zimmer book to see what that says about the hypothesis.

    Link to this
  26. 26. vdinets 5:07 am 06/13/2014

    Allen’s rule works in martens (Siberian sable has the shortest tail of them all), but apparently not in bears (it looks like the polar bear is re-evolving longer tail). Is their any difference in tail length between northern and southern populations of widespread river otters, i. e. Eurasian and North American?

    Link to this
  27. 27. DavidMarjanovic 11:21 am 06/13/2014

    Also, there has been a very dubious publication of an Eocene pinniped. I wrote a critical review of the paper here:

    http://coastalpaleo.blogspot.co.nz/2012/04/an-eocene-pinniped-critique-of-diedrich.html

    …Diedrich. No comment.

    I left a comment on your post, though, regarding the identity of the supposed institution that supposedly houses the specimen.

    I don’t know how sirenians and cetaceans “figured out” how to turn the embryo around so that it’s born tail first

    Nothing more than natural selection on present variation. My grandmother was pulled out by her legs; hippos give birth either way, both on land and in the water; IIRC, whales still occasionally give headfirst birth.

    Um, you missed the turn, Darren. The nearest living relative of whales, is of course, the hippo. Which is amphibious.

    It’s also under strong selection for being too round for crocodiles to bite.

    the sea otters give birth in the water, apparently tail first

    Link doesn’t work.

    the comments section at Tet Zoo remains the most active place on the whole SciAm network, so far as I can see…

    The other blogs get almost no comments, unless they mention climatology, in which case the denialists descend upon it and ask in droves how scientists dare pretend the climate is warming just so they can impose less-than-Republican policies on everyone – no, seriously.

    it looks like the polar bear is re-evolving longer tail

    Huh.

    Link to this
  28. 28. DavidMarjanovic 11:44 am 06/13/2014

    Oh, forgot:

    monophyletic clade

    Brought to you by the Department of Redundancy Department. :-)

    Link to this
  29. 29. Heteromeles 12:51 pm 06/13/2014

    @David: perhaps I’m too simplistic, thinking that tail-first birth is necessary for an underwater delivery? I keep forgetting that human kids get born into the water too (google waterbirth). Still, I suspect there’s a reason why more amphibious mammals don’t give birth underwater, and perhaps it drove pinniped evolution?

    Here’s the sea otter link:
    https://www.youtube.com/watch?v=2ONOJqhHM-A

    As for shortening tales as part of becoming aquatic in northerly climates, I’m still unconvinced. We’ve got a reduction of a tail and massive expansion of webbed feet. Was there a net loss of surface area at any step in this process?

    Link to this
  30. 30. naishd 1:21 pm 06/13/2014

    Heteromeles: nobody’s trying to “convince” you — it’s a hypothesis (but.. as goes net loss of surface area – note that it’s harder to rewire tails with counter-current heat exchange networks than it is the distal parts of limbs).

    Link to this
  31. 31. Heteromeles 4:46 pm 06/13/2014

    @Darren: Counter-current heat exchange is harder. My understanding is that whales have countercurrent exchanges in all fins and flukes (ref: Scholander and Schevill. 1955. Counter-Current Vascular Heat Exchange in the Fins of Whales Journal of Applied Physiology 8:279-282.). Perhaps I’m wrong? That doesn’t seem like it’s that hard to set up.

    Link to this
  32. 32. irenedelse 6:02 pm 06/13/2014

    “What I’m saying is that Allen’s Rule might partially or wholly explain tail reduction in stem-pinnipeds, this meaning that they (and other cool-climate endothermic swimmers) were perhaps less likely to become tail-propelled swimmers. Is this the entire explanation as to why pinnipeds became limb-propelled swimmers? No – pinniped limbs would (based on analogy with other swimming mammals) become enlarged and webbed anyway, regardless of the tail, but… does it contribute to the fact that pinnipeds came to rely on the limbs and not the tail? I still see this as a reasonable hypothesis, so long as Allen’s Rule really applies, and so long as stem-pinnipeds really did have reduced tails compared to related carnivorans.”

    Now, it would be interesting to see what was going on with the the tail of Amphicynodon and other early ursoids. Do we have enough caudal vertebrae in the fossil record to get an accurate enough picture? And did they evolve in cold climates too when they reduced their tail?

    What I’m thinking is: in addition to Allen’s rule, simple lack of usefulness may have contributed to the state of the pinniped tail. In other words, the sequence of events may have been reversed: stem pinnipeds started to evolve limb-powered swimming and in the process their tail became less useful, which in turn made said appendage more prone to reduction in a cold climate, as Allen’s law would predict.

    Link to this
  33. 33. paalexan 8:18 pm 06/13/2014

    My $.02:

    “the cladogram is arguably odd in showing the name Pinnipedia as being attached to the entire clade rather than just to the crown-group… which isn’t shown on the tree”

    Crown-group vs. entire clade: the new and still inappropriate way of recognizing paraphyletic groups. :-) The -only- reason you would want to make this distinction between “entire clades” and “crown-groups” is to talk about the taxa included in the former but not the latter–i.e, to weasel your way around to recognizing paraphyletic groups. Instead of giving them formal names, we recognize paraphyletic groups by referring to them as the members of the entire clade but not the crown. It amounts to accepting cladism as an empty formalism while ignoring its conceptual substance.

    If the members of the entire clade aren’t “Pinnipedia”, what are they? Just give those not-really-pinnipeds-but-members-of-the-clade-that-includes-pinnipeds a name. At least we could then talk about this paraphyletic assemblage openly and honestly–as some artificial, unnatural grouping–rather than through some indirect, dissembling nomenclature that seeks to recognize them as a real group while admitting somewhere under the table that they -aren’t-. Either it’s a taxon or it isn’t. Choose one.

    Link to this
  34. 34. Boesse 8:30 pm 06/13/2014

    Paalexan – Some background on pinniped taxonomy/cladistics is necessary to understand the context of Darren’s quote. Berta and Wyss (1994) and a couple of earlier papers by Berta proposed Pinnipedia for the most exclusive clade including all modern pinnipeds, and Pinnipedimorpha for a more inclusive clade including Enaliarctos; the proposed Pinnipedimorpha + Puijila + Potamotherium clade of Rybczynski et al. 2009 thus should be something even larger than Pinnipedimorpha, and not equated with crown Pinnipedia.

    A. Berta and A. R. Wyss. 1994. Pinniped phylogeny. Proceedings of the San Diego Society of Natural History 29:33–56.

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  35. 35. vdinets 2:08 am 06/14/2014

    David (#27): all modern bears have shortened tails, but in the polar bear it is noticeably longer, even compared with very closely related brown bear. It might be covering the anogenital area from stormy winds…

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  36. 36. irenedelse 4:11 am 06/14/2014

    Anyone here follows the Tumblr LolMyThesis? Seals were mentioned recently… ;-)

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  37. 37. Heteromeles 11:16 am 06/14/2014

    Another thing I realized is that we’ve got an extant sample size of N=3: sirenians, cetaceans, and pinnipeds. Two are tail propelled, one is flipper propelled.

    For the true null hypothesis, let’s assume that flipper propelled and tail propelled locomotion are assigned effectively at random, due to a conglomeration of mutations and prior structures, with Allen’s rule (and reproductive structures, and gross environmental cues) playing no role at all. Assuming all possible permutations of random assignations of propulsion (8 possible outcomes, all permutations of 2 states and three clades), there’s a 3 in 8 probability that you’ll see two lineages with tail-driven propulsion, one lineage with flipper-driven propulsion, which is exactly the same probability as seeing the reverse, two flipper-driven clades and one tail-driven clade.

    While it’s fun to argue, I’ve got to point out that we can’t eliminate this null hypothesis with the data we have.

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  38. 38. irenedelse 1:20 pm 06/14/2014

    Heteromeles:

    “I keep forgetting that human kids get born into the water too (google waterbirth).”

    Which makes sense in the light of the Aquatic Ape Hypothesis, obviously… @__@

    “we’ve got an extant sample size of N=3: sirenians, cetaceans, and pinnipeds. Two are tail propelled, one is flipper propelled.”

    If we count the sea otter, where propulsion is mostly assured by the webbed feet, then N=4 for fully aquatic marine mammals, and it looks even better for your null hypothesis (2 clades out of 4 using limb propulsion). But I don’t know if it should be counted since Enhydra lutris descends from other otters already partially adapted to aquatic life…

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  39. 39. Heteromeles 3:17 pm 06/14/2014

    Ah yes, the aquatic ape hypothesis. I prefer the sweaty jogger hypothesis myself, so this is simply to point out that babies don’t necessarily drown at birth if they come out head first, even if they come from a species that exhibits no, erm, uncontroversial adaptations to aquatic life.

    Of course, if I understand it properly, Allen’s Rule works best when it’s calculated against the average temperature at which females incubate their young (RL Nudds, SA Oswald. 2007. An interspecific test of Allen’s rule: Evolutionary implications for endothermic species. Evolution), so one can handwave away just about *any* Allen’s Rule role in strongly seasonal environments, so long as pregnancy takes place in the warm season. One could make also the argument that being pregnant in the ocean would drive Allen’s Rule-type adaptations, but that causes trouble for any deep diving organism, no matter whether it’s got flippers or flukes. By the way, how does a fetus survive deep diving?

    I should also point out that seals use their vertebral column as their primary propulsive power, and their leg muscles and bones appear to be highly reduced. In propulsive terms, seal feet are equivalent to cetacean flukes, regardless.

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  40. 40. DavidMarjanovic 4:33 pm 06/14/2014

    perhaps I’m too simplistic, thinking that tail-first birth is necessary for an underwater delivery?

    Probably. It has even been argued (I think in connection with Maiacetus) that the reason why whales are generally born tail-first is just that it’s much easier to press on the round, robust head.

    Thanks for the link!

    If the members of the entire clade aren’t “Pinnipedia”, what are they? Just give those not-really-pinnipeds-but-members-of-the-clade-that-includes-pinnipeds a name.

    Why? It’s not like we’re restricted to Linnaean hierarchies. It’s possible to be a pinnipedimorph without belonging to any taxon smaller than that.

    David (#27): all modern bears have shortened tails, but in the polar bear it is noticeably longer, even compared with very closely related brown bear. It might be covering the anogenital area from stormy winds…

    Makes sense, thanks!

    By the way, how does a fetus survive deep diving?

    The lungs are already collapsed, so there’s no problem in increasing the internal (blood etc.) pressure in keeping with the water pressure.

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  41. 41. irenedelse 4:44 pm 06/14/2014

    ‘Aquatic Ape’ jokes aside, the late 20th and early 21st century fad with waterbirth can actually illustrate a few of the challenges with the adaptation of mammals to an amphibious or aquatic life. Though some traits of H. sapiens make our species particularly ill-suited for a return to water.

    The troubles with water birth in humans don’t stop at drowning. Because human neonates are born at such an early stage of development compared to other mammals, their kidneys can’t handle large quantities of freshwater, so the baby can go into hyponatremia from ingestion of too much water (waterbirth enthusiasts rarely think about things like electrolytes, and rarely go as far as delivering in the ocean). Human neonates also don’t have good thermoregulation, so they are prone to hypothermia in a tub of lukewarm water. (Btw, any new parent is well acquainted with the the importance of temperature for bathing a baby.) And then there’s the risk of the baby getting pneumonia an infection from fecally contaminated water (of course all sorts of things get out during contractions, and the huge size of baby H. sapiens‘ head leads to internal pressure on the colon and bladder during the descent of the baby in the birth canal).

    Hypothermia, water ingestion (in freshwater), drowning, infections… several challenges for any tetrapod going for live birth in the water. In addition to water carrying far and long the the scent of blood to attract predators. I don’t know about sirenians, but both sea otters and cetaceans give birth to big babies, able to swim on their own and regulate their temperature. But such babies are an expensive investment on the part of the mother and limit the number of descendants she can have in her life.

    Pinnipeds going back to land to give birth and raise babies may well have had less to do with their mode of locomotion than with the ability to give birth to smaller, less energetically expensive babies.

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  42. 42. irenedelse 4:50 pm 06/14/2014

    @DM:

    It’s possible to be a pinnipedimorph without belonging to any taxon smaller than that.

    Non-Pinnipedian Pinnipedomorphs! If this gets discussed in the podcast, I can already hear John Conway groan. :-D

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  43. 43. Heteromeles 6:03 pm 06/14/2014

    @Irene: you beat me to it, thanks (genuinely, not sarcastically). I was just about to propose that the difference between pinnipeds, cetaceans, and sirenians comes down to relative development at birth, plus the constraints required by water movement.

    In reverse order, I’d suggest that hydrodyanmics are a bigger constraint than Allen’s Rule: cetaceans (and probably pinnipeds) develop countercurrent systems on fins, flukes, and possibly even tongues, not just to keep the cold in, but also to avoid overheating. They can dump heat as well as retain it. Blubber insulation is pretty darn efficient, and I’d say Allen’s Rule isn’t a huge factor.

    However, being an air breathing endotherm in an ocean that’s mostly a nutrient desert puts a huge premium on having a hydrodynamically efficient shape, e.g. a torpedo (something similar is seen in things like tunas and sharks). Since these animals need more food than a comparably sized ectotherm, they also need to cover more territory and do it with as few breaths as possible, and that has shaped their bodies far more than Allen’s rule ever will. Sea otters are a partial exception to this rule, but they’re also limited to nutrient rich kelp forests. A sea otter would starve in Hawaii, for example, but monk seals made a go of it there.

    The challenge of the torpedo shape is that it needs to taper at the rear, but it generally needs decent propulsive fins in back (excepting sea lions here, which have AFAIK higher nutrient requirements than seals or cetaceans and correspondingly more limited habitats). This requires reduction of the hindquarters, whether feet are modified into flippers or not. Pinnipeds reduced their hips and legs, cetaceans and sirenians eliminated them and went with modified tails and “the life aquatic.” Why?

    Here’s where I was thinking what Irene already said: pinniped pups and otter pups are typical carnivoran pups, born relatively less developed and more helpless. They need to learn to swim. Sea otters get away with having their pups in the ocean by swaddling them in kelp on the surface until they learn to swim, but pinnipeds have to rear their pups on a solid surface until they can swim, and that means they have to be able to move on land.

    Cetaceans and sirenians come from lineages with with relatively more altricial offspring. For example, here’s video of a hippo calf being born in the water and swimming immediately afterward: https://www.youtube.com/watch?v=pGxi-ZNMsaU . While precocious offspring don’t force a lineage to develop tail-based propulsion and become fully aquatic (witness the hippo above), this characteristic does allow it to happen in a way that isn’t possible for lineages that have altricial offspring.

    While sea otters have figured out a way to become mostly aquatic with altricial pups, they pay a huge price for it, because they are tied to kelp forests. Pinnipeds, by giving birth on land or on ice, are much more adaptable, which is why there are so many species of pinnipeds around the world than there are sea otters. Cetaceans are more versatile still, and the only thing I can say for sirenians is that being an air-breathing aquatic herbivore is a fairly specialized niche.

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  44. 44. AndrewD 6:14 pm 06/14/2014

    Help!(and off topic) It is (counts on fingers) 42 years since I looked at systematics in any detail and that was as part of my first degree, the applied Zoology bit. Since then I have spent the 42 years as a Process Development Chemist. David @40 has confused me even more than normally (with his comment on Linnaean taxonomy) SO…Is there a simplish book on current systematics say “Cladistics for Dummies” that the commentators here could recommend? If not could someone, (Darren or David) write one please? Wikipedia can only take one so far.

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  45. 45. Heteromeles 6:49 pm 06/14/2014

    @Andrew: I don’t know of any simple books for cladistics, but I will say that learning it’s a lot like learning algebra: it a set of fairly simple concepts and terms, but it takes repeated exposure and working out some examples by hand for it to sink in. In other words, don’t expect any book or teacher to enlighten you. You need to practice it a little (draw some trees, map some characters, that sort of thing) for it to make sense.

    My experience in this was TAing for a number of years. I watched teachers in senior level systematics classes cover cladistics exactly the same way it was covered in freshman-level general classes. The difference was that the students in the senior-level classes understood cladistics. They naturally said that the senior-level teachers were better than those teaching the freshman classes. Having TA’ed both, I’m pretty sure that this wasn’t the case. What was the case was that the students had seen cladistics two or three times by that point, and it finally sank in and made sense.

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  46. 46. John Harshman 8:34 pm 06/14/2014

    Moderately simple guide to cladistics: Tree Thinking: An Introduction to Phylogenetic Biology.

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  47. 47. Jenny Islander 1:22 am 06/15/2014

    In other tetrapod news, the first California condor sighting in San Mateo County since 1904:

    http://blog.sfgate.com/stew/2014/06/13/california-condor-spotted-in-san-mateo-co-for-first-time-in-110-years/

    According to the article, this is a bigger deal than California condors naturally expanding their range would already be because nice big fat elephant seals breed a short flight from where this condor was spotted, and “marine mammals were historically an important food source for condors, which began to disappear when the the populations of sea lions and other marine mammals plummeted.” This is news to me. Anybody with more knowledge of the subject care to weigh in?

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  48. 48. BrianL 4:26 am 06/15/2014

    Regarding cetaceans and sirenians evolving from ‘ungulates’ and this driving the evolution of their body shape, I’d like to throw a spanner in the works by mentioning desmostylians. Those too were marine or at least semi-marine mammals descended from hoofed ancestors with presumably precocial young, yet they went the pinniped way: A very short tail and robust hindlimbs. What to make of that? Presumably they would have given birth to very precocial young too?
    Also, where does *Thalassocnus* the marine sloth come in in this discussion? Any idea as to how it adapted its pelvic region to a marine lifestyle and how they would have given birth?

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  49. 49. naishd 6:43 am 06/15/2014

    Thanks to everyone for the further comments — so many interesting thoughts here on pinniped evolution, Allen’s Rule, and which factors may, or may not, have contributed to body shape in these animals. I have a few more points to make.

    Evolution is complicated, and factors of several kinds presumably influenced the early evolution of stem-pinnipeds and the ‘direction’ they took as goes swimming style and body shape. Their ancestral body form and swimming style has to be taken into consideration: they evolved from reasonably long-tailed, mustelid-like animals that most likely used dog-paddle-style swimming, and their reproductive biology has to be taken into account too, since they would have produced (and still do produce) babies that are less precocial than those of some other mammal groups that took to life in water.

    Some mammal groups took to life in water and already had short or reduced tails that were useless from a locomotory point of view, ergo there’s little reason to think that they ever had the chance to develop long tails used in swimming. Examples include hippos, amphibious rhinos, and perhaps desmostylians, alleged amphibious or aquatic hyraxes and some swimming voles. However, some of the animal groups we’re talking about here entered the water with an approximately similar overall body shape: compare silhouettes or outlines of the very earliest members of the pinniped, cetacean and sirenian lineages and you’ll see that they’re very similar, cetaceans being the most different because of their proportionally long limbs. There are other mammal groups we should probably consider here too, including swimming sloths and opossums (yapoks), desmans, otter shrews, beavers, muskrats and platypuses.

    I just dug out Zimmer’s At the Water’s Edge and see that the idea of Allen’s Rule playing a role in tail ‘destiny’ comes from Frank Fish, a familiar name when it comes to the study of aquatic locomotion in mammals. I still think there might be something going for this hypothesis, especially when we bring in the data from other swimming mammals: otter shrews, muskrats and beavers all have tails that are especially important in swimming, and all evolved in tropical or subtropical climates, for example. Desmans are mostly foot-propelled but have a large, paddle-like tail, and evolved predominantly in subtropical and temperate climates. Sirenians appear to be deeply nested within an afrotherian clade where the tail, ancestrally, is neither especially long nor especially muscular (this partly explains why recent reconstructions of stem-sirenians give them fairly feeble tails: less proportionally big and bulky than those of extant otters), and yet still they enlarged the tail.

    Finally, I want to emphasise that I never meant to imply that thermoregulation provides the One True Factor that ‘controlled’ tail ‘destiny’… if anything is clear from this discussion, it’s that several or many factors of biology, reproduction, behaviour and environment likely contributed to the eventual swimming style and body shape of these different mammal groups. Nevertheless, it still seems that Allen’s Rule might have played a role – in other words, the hypothesis that it did play a role in the evolution of these animals remains a reasonable one that matches predictions.

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  50. 50. DavidMarjanovic 6:53 am 06/15/2014

    David @40 has confused me even more than normally (with his comment on Linnaean taxonomy) SO…Is there a simplish book on current systematics say “Cladistics for Dummies” that the commentators here could recommend?

    Here’s a very good basic introduction.

    However, cladistics is just phylogenetics, it has nothing (a priori) to do with nomenclature. What it seems you’re actually asking about is phylogenetic nomenclature, and as long as I haven’t repaired and updated the Wikipedia article on that subject, the best I can do is send you here.

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  51. 51. DavidMarjanovic 6:58 am 06/15/2014

    Frank Fish, a familiar name when it comes to the study of aquatic locomotion in mammals

    Chapter headline in Carl Zimmer’s At the Water’s Edge: “Frank Fish learns to swim”.

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  52. 52. gentle lemur 10:04 am 06/15/2014

    I can try to answer Jenny Islander’s question. As a regular visitor to the large colony of grey seals at Donna Nook NNR, I have seen many avian scavengers consuming the glut of afterbirths and the occasional stillborn pups. I imagine that an elephant seal colony would provide a seasonal feast for a condor, which might be extended if other species breed at different times of the year.

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  53. 53. Heteromeles 10:23 am 06/15/2014

    But only if the condors have room to take off. I’m totally fine with condors scavenging dead whales. I’m not so sure how condors would get in among the elephant seals to scavenge dead pups and afterbirths. After all, alpha male beachmasters are a bit testy about humans getting close enough to photograph, and condors need to run a few steps (on sand, no less), to get airborne. I’ve only seen one elephant seal colony, but IIRC, they’re pretty closely packed. Scavenging around them may suit ravens more.

    California condors are probably following the big ranches. That’s where most of the megaherbivores are these days.

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  54. 54. Jerzy v. 3.0. 10:38 am 06/15/2014

    @condor
    I think california condor biology in 19. and early 20. century is known only from scattered anecdotal reports. Too little to seriously propose a link between pinniped decine and condor decline. I imagine all wild mammals in N America were hunted down in the early 20. century, so all sources of carrion (except whales) were becoming scarce.

    BTW, what makes cetacean embryo develop in position tail-first, and other embryos head-first?

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  55. 55. John Scanlon FCD 10:46 am 06/15/2014

    Speaking of early seals and Cajus Diedrich, he’s got a new paper proposing that the Carcharodon (White Shark) lineage was already specialising on seals 50 mya. I can’t help being reminded of these lines of Plato’s Euthyphro that I read earlier today:
    “Soc: … Tell me, for the love of Zeus, whether you really believe that [these stories about the gods] are true.
    “Euth: Yes, Socrates; and things more wonderful still, of which the world is in ignorance.”

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  56. 56. naishd 10:59 am 06/15/2014

    One quick comment on condors and pinniped colonies… for a deep-time perspective, look at Chamberlain et al.’s Pleistocene to recent dietary shifts in California condors. Carbon and nitrogen isotopes show that Pleistocene California condors were routinely exploiting marine mammal carcasses and associated resources.

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  57. 57. Gigantala 11:32 am 06/15/2014

    @On desmostylians: Based on Hayashi 2013, they were fully marine mammals like cetaceans and sirenians, incapable of terrestrial locomotion like pinnipeds, so they must by default have given birth at sea. Based on this, relatively precocial young were probably the norm.

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  58. 58. irenedelse 11:32 am 06/15/2014

    “Finally, I want to emphasise that I never meant to imply that thermoregulation provides the One True Factor that ‘controlled’ tail ‘destiny’… if anything is clear from this discussion, it’s that several or many factors of biology, reproduction, behaviour and environment likely contributed to the eventual swimming style and body shape of these different mammal groups. Nevertheless, it still seems that Allen’s Rule might have played a role – in other words, the hypothesis that it did play a role in the evolution of these animals remains a reasonable one that matches predictions.”

    Talking of throwing a spanner or wrench in the works: how about Pinnipeds’ toes? Allen’s rule also predicts shorter toes and fingers, but seals and sea lions developed long, webbed, flipper-like feet and hands. Which ties in to the discussion of counter-circulation earlier in the thread. Would it have been much more problematic for stem Pinnipeds to have such adaptations in their limbs only or also in their tails? I’d suggest that a way to test the “tails you lose” hypothesis (the role played by Allen’s rule here) would be get insight from embryology. How do seal pups develop in utero? And cetaceans? Do carnivoran embryos get ‘locked’ into developing powerful paws, perhaps, making it less likely to reduce their hind limbs, like cetaceans did?

    And talking of lower body evolution: I can’t help but go back to the precocial/altricial issue. Surely, it’s easier for a female placentary mammal to give birth to a big precocial calf (sirenians and cetaceans) if her pelvic girdle is already gone, or vestigial. Fewer obstetrical issues, for sure. But if you rely for locomotion on a kind of modified walk, like phocids, you retain your pelvis and are more likely to keep producing relatively small, altricial babies, and hence more like to have to breed on land. Or at least it makes sense if we consider evolution as a ‘package deal’ involving the whole body.

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  59. 59. irenedelse 11:44 am 06/15/2014

    @Gigantala:

    Desmostylians were occupying the same kind of niche than today’s sirenians, then? Fully aquatic littoral herbivores? Fascinating.

    Jerzy:

    “BTW, what makes cetacean embryo develop in position tail-first, and other embryos head-first?”

    I don’t know about cetaceans, but other mammals’ embryos (including humans) don’t *develop* in a particular position, but they turn at the end of gestation to present head first (or in ungulates, head and forelimbs first) for delivery.

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  60. 60. naishd 11:50 am 06/15/2014

    Irene – there’s a lot of neat literature on desmostylians, much of it very recent. No time to point you to any of that, but see the Tet Zoo ver 2 comments on the group included in this article.

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  61. 61. naishd 11:53 am 06/15/2014

    Oh, something tells me we’re over the 23 comment threshold…

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  62. 62. irenedelse 12:12 pm 06/15/2014

    @Darren:

    Cool, thanks :-)

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  63. 63. Tayo Bethel 3:50 pm 06/15/2014

    How do phocids move in the water exactly? I’ve seen several references to phocids swimming with sideways movements of the hindlimbs but employ dorsoventral flection of the body when on land. Or amI missing something?

    BTW many arctoids seem to have reduced their tails as their lineage becomes more specialized over time, so pinnipeds might simply befollowing a phylogenetic blueprint for tail reduction. The comment on polar bears evolvinglonger tails seems strange inlight of this.

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  64. 64. Gigantala 4:39 pm 06/15/2014

    “Desmostylians were occupying the same kind of niche than today’s sirenians, then? Fully aquatic littoral herbivores? Fascinating.”

    According to the study I mentioned, yes, at least as litoral/coastoal herbivores. There’s probably many nuances we’re missing, though.

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  65. 65. Gigantala 4:39 pm 06/15/2014

    *fully aquatic littoral/coastoal herbivores.

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  66. 66. gentle lemur 7:15 pm 06/15/2014

    How do phocids move in the water exactly? I’ve seen several references to phocids swimming with sideways movements of the hindlimbs but employ dorsoventral flection of the body when on land. Or am I missing something?

    On land, phocids generally prop themselves on their front flippers as they crawl by flexing their spines dorsoventrally; but if a seal is lying on its side it can easily move a few metres just by lateral movements of its spine, without bothering to turn onto its belly. This is quite similar to swimming, but in slow motion and without using the flippers at all. I have seen it most when grey seals are very fat at the start of the breeding season.

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  67. 67. Allen Hazen 1:52 am 06/16/2014

    Darren has mentioned desmans, but there are a lot of other comparatively small (comparatively, that is, when compared to Pinnipeds and Cetaceans) mammals that do a lot of swimming: aquatic rodents, such as muskrats and beavers. Interestingly, the ones I know of seem to use their tails a lot, even though some are (now at least: I don’t know when/where beavers adopted an aquatic lifestyle) denizens of fairly cold climates. (There’s a reason the beaver, Castor canadensis, is a Canadian icon, not a U.S. or Mexican one!)

    Thought: maybe rodents have a use for long tails (balancing when jumping around trees?), and so kept them even in cold climates, so had them available when they became aquatic.

    On the other hand, just to complicate things even further, Cetaceans went through a phase in which they used hind legs for swimming: Ambulocetus had whomping big hind flippers, and its locomotory style (both on land and in water) has been compared to sea lions. Despite which later Cetaceans reduced the hind limbs and developed flukes on their tails.

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  68. 68. Tayo Bethel 2:20 am 06/16/2014

    So do phocids swimwhile lyingontheir sides, then?

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  69. 69. DavidMarjanovic 5:43 am 06/16/2014

    BTW many arctoids seem to have reduced their tails as their lineage becomes more specialized over time, so pinnipeds might simply befollowing a phylogenetic blueprint for tail reduction.

    Evolutionary tendencies can’t be inherited, they’re not genetic. They exist as long as directional selection makes them exist; as soon as selection goes elsewhere, the trend stops.

    Ambulocetus had whomping big hind flippers, and its locomotory style (both on land and in water) has been compared to sea lions.

    …In water, sea lions fly with their front flippers, and the hind flippers are just for steering. They look like penguins. Ambulocetus swam by wagging the rear half of its body up and down, and that happened to include the hind flippers. Broadening the tail to fill the gap between them was an advantage, and once that had happened, the legs were superfluous.

    maybe rodents have a use for long tails

    I’ve read the assertion that the tail is used to dump excess heat; beavers being much bigger than mice, their tail needs to have a larger surface to compensate for the decreased surface-to-volume ratio.

    Keep in mind that beavers don’t swim by wagging their rather stiff tails. They use their hindlimbs; the tail is mostly just dragged along.

    So do phocids swimwhile lyingontheir sides, then?

    No. They swim like fish, with the feet playing tail fin. More precisely, on a stroke to the left the left foot is folded, while the sole of the spread right foot pushes water to the left and back; then the right foot folds, the left one unfurls, and a stroke to the right begins.

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  70. 70. Jerzy v. 3.0. 7:19 am 06/16/2014

    @condors – happy to be corrected, thanks.

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  71. 71. Heteromeles 11:23 am 06/16/2014

    Yes, a better model for Ambulocetus is a sea otter, which ironically show tail reduction, rather than tail expansion. I think Irene’s comments up-thread, about whether all tails are capable of producing flukes, or whether they’re limited to certain lineages (excluding carnivorans?), is relevant here.

    As for seals, they can be a little sloppy about folding their feet on the backstroke, which may be why their hind feet are close to isomorphic in shape (same on both sides). See this video of a Mediterranean Monk Seal swimming, although there are lazier ones out there:

    http://www.arkive.org/mediterranean-monk-seal/monachus-monachus/video-06.html

    Not being a degreed specialist, I tend to prefer the idea that whales, sea otters, and manatees swim with a modified gallop, while seals swim with a modified walk. The idea is that walking in a long-bodied animal involves lateral flexing of the spine, while galloping involves dorsoventral flexing of the spine. Sea lions fly with their forelimbs, but when they engage their hindlimbs, it seems to be more often in dorsoventral flexing, rather than lateral flexing.

    The interesting thing is that all of these engage their spines and trunks in swimming. Compare that with, say, a dog swimming underwater, who uses legs alone:

    https://www.youtube.com/watch?v=F3tKnLz9YyE

    Now, if someone can just post a picture or video of a Potamogale swimming, I’ll be happy. It looks like they’ve gone for gator-style lateral tail flexing?

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  72. 72. vdinets 1:09 pm 06/16/2014

    Muskrats, which live all the way to the Arctic, use their long tails for propulsion, and they have evolved from voles, which have relatively short an weak tails by rodent standards. But it’s possible that they have originally evolved in warmer climate, since the sister species is almost endemic to Florida. Desmans mostly use their hind legs for propulsion, as far as I remember (I’ve only seen a desman swim for a few seconds).

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  73. 73. Heteromeles 2:11 pm 06/16/2014

    Muskrats use tails for propulsion? I’d always thought they paddled with their hind feet, as do beavers. There’s an example here (starting at 2:03 into the video):
    https://www.youtube.com/watch?v=ADrtyKHnl_A
    It’s nice because there’s a slow motion rerun at the very end.

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  74. 74. vdinets 4:43 pm 06/16/2014

    They swim with rapid undulation of the tale, as can be seen here: https://www.youtube.com/watch?v=ppcjsk1Rm4s
    I’ve never seen them from underwater, so I don’t know how much the feet are involved when they swim in a direct line.

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  75. 75. vdinets 4:44 pm 06/16/2014

    Here’s a marginally better video: https://www.youtube.com/watch?v=ygH21jSMHpo

    Link to this
  76. 76. irenedelse 10:11 am 06/17/2014

    @vdinets:

    The second video really makes it look like “alligator style” lateral tail ondulations is at least a component of propulsion for the muskrat. Wikipedia tells us that their laterally compressed tail is unique among rodents, and that according to W. Voelker’s The Natural History of Living Mammals (Medford, New Jersey, Plexus Publishing, Inc., 1986), though the partially webbed hind feet help in swimming, the tail is the main factor of propulsion.

    Link to this
  77. 77. naishd 10:18 am 06/17/2014

    I really should finish that Tet Zoo article on muskrats (part of the vole series I started earlier in 2014).

    Link to this
  78. 78. DavidMarjanovic 10:41 am 06/17/2014

    whales, sea otters, and manatees swim with a modified gallop, while seals swim with a modified walk

    I think that’s correct.

    Link to this
  79. 79. Dartian 4:15 am 06/18/2014

    Vladimir:
    all modern bears have shortened tails, but in the polar bear it is noticeably longer, even compared with very closely related brown bear

    Huh? According to DeMaster & Stirling (1982), the polar bear’s tail length is 76-127 mm, whereas according to Pasitschniak-Arts (1993), the brown bear’s tail length is 65-210 mm. Where does your information come from?

    Muskrats [...] use their long tails for propulsion

    That’s what it may superficially look like, but actually they do not, at least not to any significant effect. This has been studied by the already mentioned Frank Fish, the go-to guy when it comes to knowledge of mammalian swimming kinematics. Fish (1982) showed that the muskrat’s undulating tail movements only provide ca. 1-2 % of the total thrust power; most of the power comes from the muskrat’s hindlimbs. (The muskrat’s tail probably isn’t a totally insignificant aid in its swimming, as Fish found that a muskrat with an amputated tail accelerated a bit more slowly than normal muskrats. But the main function of the muskrats tail, Fish (1982) suggests, seems to be improvement of maneuverability, not the increase of speed or stamina.)

    References:

    DeMaster, D.P. & Stirling, I. 1981. Ursus maritimus. Mammalian Species 145, 1-7.

    Fish, F.E. 1982. Function of the compressed tail of surface swimming muskrats (Ondatra zibethicus. Journal of Mammalogy 63, 591-597.

    Pasitschniak-Arts, M. 1993. Ursus arctos. Mammalian Species 439, 1-10.

    Link to this
  80. 80. Heteromeles 10:13 am 06/18/2014

    Thanks Dartian. That’s what I thought I was seeing, but people seemed so certain that the tail movement was propulsive that I kept silent.

    This seems reflected in the muskrat skeleton (see image here)
    which doesn’t seem to have the enlarged spine processes that would indicate that the tail is highly muscular. Conversely, those hind limbs are rather large.

    Conversely, an alligator skeleton, even a small one (see image here) seems more obviously adapted for tail-driven propulsion.

    Link to this
  81. 81. CraigYork 5:36 pm 06/18/2014

    it looks like the polar bear is re-evolving longer tail sounds like a perfect lead in to a SpecZoo piece, if you don’t mind my saying. ( Great White Whale-Bears anyone?)

    As for Muskrats, I’d think the tail contributed a measure of hydrodynamic efficiency, reduced drag, rather than contributing to thrust.

    Link to this
  82. 82. irenedelse 8:30 am 06/19/2014

    @Dartian, Heteromeles:

    Thanks for the references and pics. The comparison of skeletons is illuminating.

    @CraigYork:

    “Great White Whale-Bears anyone?”

    I think we have the answer to the bear-versus-shark conundrum at last! :-D

    Link to this
  83. 83. vdinets 6:51 pm 06/19/2014

    Polar bear tail:

    brown bear tail:

    There’s plenty of photos online, see for yourself.

    Link to this
  84. 84. vdinets 6:53 pm 06/19/2014

    Sorry, images don’t get inserted. Here are links:
    1. http://www.bearsoftheworld.net/images/bears/polar_bear_fishing.jpg
    2. http://www.planetozkids.com/images/animals/grizzly-stump-tail-full-bea.jpg

    Link to this
  85. 85. Dartian 3:32 am 06/23/2014

    Vladimir: I presented actual, published biometrical data from the technical literature; your response to that is to suggest that I google pictures of bears and try to subjectively guesstimate their tail lengths instead. (Without being able to account for the possibility that the polar bear’s tail only looks longer because it has longer hair in general than other bears.)

    see for yourself

    I suggest you do the same: polar bear skeleton vs. brown bear skeleton. The polar bear’s actual tail looks damn short to me.

    Link to this
  86. 86. vdinets 6:19 pm 06/24/2014

    Dartian: I’ve handled a few skins of polar and brown bears, and I assure you that polar bear tails are longer than those of brown bears. You can check for yourself next time you are in a zoo. The difference is not due to hair length (I am not sure it differs much between the two spp.), but it could be just soft tissue rather than the skeleton. I have an zoologist friend who guides trophy hunting tours to Siberia and has probably seen more brown bear carcasses than most people alive – I’ll ask him what he thinks.

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  87. 87. Yodelling Cyclist 10:12 pm 06/24/2014

    Yes everybody these are the Tetzoo comments, where the mean tail length of polar bears is grounds for passionate debate and long held beliefs regarding the locomotion of muskrats are ruthlessly smashed. It’s a strange little social world, but quite wonderful.

    I hope that when, and if, Tetzoo volume 2 is published, some of the better (including more whimsical) posts are retained.

    Link to this
  88. 88. Dartian 1:37 am 06/25/2014

    Vlad:
    polar bear tails are longer than those of brown bears

    The important thing here is whether they are longer in proportion to body size. If the polar bears’ tails are longer than those of other bears’ simply because the polar bear is, on average, the largest bear species, that observation is pretty trivial. Tail length allometry (positive, in this case) would be biologically interesting; isometry, not so much.

    Besides, according to the sources that I cited in my earlier comment, there is significant overlap in the (absolute) tail lengths of brown and polar bears. In fact, the greatest recorded brown bear tail lengths would seem to exceed those of polar bears’. It’s admittedly hard to judge that information without more detailed knowledge about sample sizes, ranges of variation, the exact brown bear subspecies involved, etc. But still, that’s what the literature says. If there are any published comparative studies on the relative tail lengths of bears out there that are relevant to the present discussion, now would be the time to bring them to attention.

    You can check for yourself next time you are in a zoo.

    No, no, no! Subjective assessments won’t do here. This has to be measured. (Preferably by using bear skins and/or skeletons. Trying to measure live bears’ tails can be a bit… impractical.)

    Link to this
  89. 89. vdinets 2:36 am 06/25/2014

    Dartian: the only kind of tail length you can get from a photo is relative to body size. Published papers are useless in this situation because the way tails are routinely measured is from the base to the tip of the last vertebra, this gives you skeleton length but not soft tissue length. Also, they never mention the length relative to body size.

    Link to this
  90. 90. irenedelse 2:49 am 06/25/2014

    Allow me to muddy up the polar bear tail debate a little further: what about Kodiak bears? And other populations of brown bears from cold climates? How do their tails compare with those of more temperate regions? How does Allen’s rule fare in bears?

    Link to this
  91. 91. Dartian 4:29 am 06/25/2014

    Vlad:
    the only kind of tail length you can get from a photo is relative to body size

    So which one of those two specific bears in the photos that you linked to in your comment #84 has the larger body size, then? (Expressed as either body mass or, preferably, body length.) If you can’t first answer that basic question, you can’t make any meaningful comparison of their tail lengths either.

    the way tails are routinely measured is from the base to the tip of the last vertebra, this gives you skeleton length but not soft tissue length

    And why are you making the assumption that tail vertebrae length would not be a good proxy measurement for total tail length of ursids? Do we have the necessary information to assess this question? In comment #86 you claimed that tail hair length does not differ between brown and polar bears but, paradoxically, you also admitted that you’re “not sure” if polar bear and brown bear tail hair lengths actually differ or not! And you further said that tail length “could” be affected by amount of soft tissue. In other words, you/we do not possess enough information of either of these two matters (i.e., bear tail hair length and amount of soft tissue in bear tails) to be able to make any factual statements about them. Which only serves to illustrate the point I’m trying to make: one needs actual comparative data to address these issues – there is no way around that.

    they never mention the length relative to body size

    If that is indeed the case then it, too, only supports my point: that we don’t, at present, have enough information to make any definitive claims about whether polar bears really have longer tails than brown bears. (Everyone is, of course, free to have their personal opinions on that matter – just as long as they remember not to present their opinions as facts.)

    Link to this
  92. 92. Yodelling Cyclist 11:22 am 06/25/2014

    This is turning into one of those academic arguments that starts with bald statements of fact, escalates through the available literature, progresses to museum specimens and calipers before culminating in exhaustion, hypothermia and bear attack.

    Just be sure to take enough data points to make it statistically meaningful, or we’re going to have to go around the loop yet again.

    Link to this
  93. 93. irenedelse 1:15 pm 06/25/2014

    @Yodelling Cyclist:

    Crowdfunded bear tail measuring expedition, anyone? ;-)

    Link to this
  94. 94. Yodelling Cyclist 3:32 pm 06/25/2014

    Sure, you measure, and I’ll record your findings.

    From way the hell back here.

    Link to this
  95. 95. vdinets 3:26 am 06/26/2014

    OK, I asked a few people who handle a lot of bears, and here’s what I learned:
    1. Polar and brown bears have roughly the same length of the tail vertebra.
    2. However, brown bears normally have more fat deposited around the base of the tail. So the part of the tail actually protruding from the body is shorter.
    3. On top of this, the hair on their tails are different: brown bears have softer, more curly tail hair, while polar bears have straight tail hair that makes the tail look even longer.
    I hope this important issue is now clarified.

    Link to this
  96. 96. Heteromeles 11:11 am 06/26/2014

    If you need to see polar bear butts in action, here’s a GoPro video. Someone somehow strapped a GoPro on a female polar bear and she swam off with a couple of other polar bears. Note that you get to see them swim as well.

    Link to this
  97. 97. Jenny Islander 7:45 pm 07/23/2014

    Re waterbirth: I have known midwives since I was a teenager (get off my lawn) and I have heard of only one case of a newborn taking in water in the birth tub. He choked and coughed, and had to be monitored for potential pneumonia. That was it.

    Waterbirth is wonderful for laboring parents because the water supports you. That’s why it’s such a long-lasting “fad;” it’s a way to reduce stress, and therefore pain and the further stress that results from pain, hence increasing the likelihood of a good outcome. It appears to be as safe as non-waterbirth for neonates. It seems that there is a reflex that prevents most neonates from breathing until they actually feel air on their faces, and they nearly always keep their mouths closed as well.

    Link to this

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