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Aug 14 2011

Magnificent momma

This is one beautiful plesiosaur, Polycotylus latippinus.


(Click for larger image)

(A) Photograph and (B) interpretive drawing of LACM 129639, as mounted. Adult elements are light brown, embryonic material is dark brown, and reconstructed bones are white. lc indicates left coracoid; lf, left femur; lh, left humerus; li, left ischium; lp, left pubis; rc, right coracoid; rf, right femur; rh, right humerus; ri, right ischium; and rp, right pubis.

The unique aspect of this specimen is that it’s the only pregnant plesiosaur found; the fore and hind limbs bracket a jumble of bones from a juvenile or embryonic Polycotylus. It’s thought to actually be a fetal plesiosaur, rather than an overstuffed cannibal plesiosaur, because 1) the smaller skeleton is still partially articulated, and it’s large enough that it is unlikely it could have been swallowed whole, 2) the two sets are of the same distinctive species, 3) the juvenile is incompletely ossified and doesn’t resemble a post-partum animal, 4) the bones aren’t chewed, etched by acids, or accompanied by gastroliths. I think we can now confidently say that plesiosaurs were viviparous, which is what everyone expected.

There are other surprising details. The fetus is huge relative to the parent, and there’s only one — so plesiosaurs had small brood sizes and invested heavily in their offspring.


(Click for larger image)

Reconstructions of female P. latippinus and newborn young. Gastralia were present in both animals but have been omitted for clarity.

The authors speculate beyond this a bit, but it’s all reasonable speculation. That degree of parental investment in fetal development makes it likely that there would have been extended maternal care after birth, and rather more tenuously, that they may also have lived in larger social groups. The authors suggest that their lifestyle may have resembled that of modern social marine mammals — picture a pod of dolphins, only long-necked and lizardy.


O’Keefe FR, Chiappe LM (2011) Viviparity and K-Selected Life History in a Mesozoic Marine Plesiosaur (Reptilia, Sauropterygia) Science 333 (6044): 870-873.

(Also on Sb)

42 comments

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  1. 1
    Kevin Anthoney

    Do we know what type of viviparity they used?

  2. 2
    Zeno

    I’m sure that this new information “proves” that evolutionists were wrong about something, but I’ll wait for AiG or ICR or the Disco Institute to explain. (They really are parasitical lifeforms — aren’t they? — living off the scientific investigations of others, since they have none of their own.)

  3. 3
    Nerd of Redhead, Dances OM Trolls

    Saw this on one of the science sites last week. Very interesting.

  4. 4
    Drosera

    I think ‘latippinus’ should be ‘latipinnus’, which would mean ‘broad fin’.

  5. 5
    'Tis Himself

    This is why I keep coming back to this blog. Well, this and the references to bacon.

  6. 6
    David Marjanović, OM

    Indeed it’s P. latipinnus. Pinna = fin, lata = wide/broad.

    Tetrapod Zoology article here.

    it’s large enough that it is unlikely it could have been swallowed whole

    “Unlikely”? I see no way that baby could have fit between the adult’s jaw joints.

  7. 7
    Mak, acolyte to Farore

    Wow, that baby is huge. That’s pretty amazing.

    It’s so incredible what sort of data we’re constantly getting from these fossils. What an exciting field.

  8. 8
    Sili

    picture a pod of dolphins, only long-necked and lizardy.

    Like giant lake monsters, you mean?

  9. 9
    Steve L

    “which is what everyone expected” — you must mean “everyone who knows anything about them”. I, on the other hand, am very surprised. I guess nobody figured they could crawl out onto the beach like turtles, dig nests and lay their eggs. Comment 1 asks what kind of viviparity. I guess ovoviviparity? The kind where the egg breaks open upon birth? Er, I just looked it up. Apparently the terminology is different that when I studied it as a child.

  10. 10
    scarina

    Cute! Those were some of my favorite dinosaurs as a child. Now I know that they’re not considered dinosaurs, but they’re still my favorites. This is why I heart this blog.

  11. 11
    raven

    Comment 1 asks what kind of viviparity. I guess ovoviviparity?

    Could be a placenta. There are placental sharks and placental lizards.

    The data says it isn’t all that hard to evolve a placenta and it has happened a few times here and there.

    That fetus looks too big for ovoviparity.

    Wow, that baby is huge. That’s pretty amazing.

    That shows these plesiosaurs ate a forbidden fruit from a tree planted by a giant in a magic garden and were cursed to have difficult childbirths forever. Shoving a baby that size out of a cloaca looks a bit tricky.

  12. 12
    Francisco Bacopa

    This is really cool. I always liked plesiosaurs. It makes a lot of sense that they would have huge babies. They’d have to be born ready to swim with the group.

    Whales have pretty big babies, and whales have have the advantage of nursing their young. Plesiosaurs would have to be fully on solid food from day one and thus might need to be proportionally bigger at birth.

  13. 13
    Glen Davidson

    Died in the flood, is no doubt what AiG will say.

    Designed to go extinct is what the DI will say.

    No they won’t, they don’t tell us why God so carefully designed a host of phyla to go extinct very soon afterward, nor why nearly all species were “designed to die.” You’re not supposed to ask those questions, just be in awe at all of the “design.”

    As science, very cool, and things evolve and then get hit with calamities.

    Glen Davidson

  14. 14
    René

    Wow, interesting stuff here again. I do have a question to the palaeo-savvy around: Looking at the fins of these animals, are these on a branch that did not yet evolve fingers? Or might that be a reduction of previously existing fingers? I’m not even a biologist, but I’ll understand the answer, if you can please give me one.

  15. 15
    nemo the derv

    I normally think of dinosaurs as laying eggs. I sort of knew that not all of them did but it’s nice to be reminded.
    Wait, is this a technically dinosaur?

  16. 16
    Trebuchet

    Kene, since it has digit bones within the flippers, like modern pinnipeds and cetations, I’d say it evolved from a terrestrial creature with toes. (Not fingers, those are pretty much reserved for primates. And raccoons, I guess.)

  17. 17
    Trebuchet

    Aaargh! That’s “cetaceans”, not “cetations”.

    Nemo, I don’t think plesiosaurs are technically considered to be dinosaurs.

  18. 18
    René

    It is hard to recognize myself in “Kene”, Trebuchet, but I understand your answer as to mean that Plesiosaurs descended from land animals that had (separate) digits. (I should’ve thought of that term.) Thanks!

  19. 19
    Meregrotta

    Don’t be silly! There are no trees underwater forbidden or otherwise.

    It must’ve been the bladderwrack.

  20. 20
    WhiteHatLurker

    It’s been known for some time that Ichthyosaurs were viviparous. This discovery shouldn’t be that surprising, but it is still interesting.

  21. 21
    raven

    Don’t be silly! There are no trees underwater forbidden or otherwise.

    It must’ve been the bladderwrack.

    Good point.

    It must have been the forbidden seaweed from the kelp forest.

  22. 22
    joed

    Is this “live birth” possible new knowledge about plesiosaur or other ancient animals?
    What does this say about the origins of viviparous birthing?
    Is this info ground breaking for people that study plesiosaur?
    Can anyone give me an address for more info on this?
    And how does this affect knowledge of mammal evolution?
    Thank you

  23. 23
    ChasCPeterson

    Is this “live birth” possible new knowledge about plesiosaur or other ancient animals?

    Not really new, but positive confirmation of something strongly suspected for this lineage.

    What does this say about the origins of viviparous birthing?

    It’s confirmation of yet another independent origin among many.

    Is this info ground breaking for people that study plesiosaur?

    Not really. It is a very cool fossil, of course.

    Can anyone give me an address for more info on this?

    There are a few references listed at Tet Zool.

    And how does this affect knowledge of mammal evolution?

    Not even a little bit. Completely irrelevant.

  24. 24
    ChasCPeterson

    It’s been known for some time that Ichthyosaurs were viviparous.

    And seasnakes…but not turtles!

  25. 25
    joed

    @23 ChasCPeterson
    Thanks for the response.
    Amazing isn’t it that other types of aminals developed the same type of birthing. I assumed that mammal live birth was inherited from some snakes or some fishes that give live birth. Many many many years ago i learned the concept of covergent/divergent evolution in animals. Is this still a viable concept? I think it applise to my inquiries?
    Again thanks

  26. 26
    Mak, acolyte to Farore

    I assumed that mammal live birth was inherited from some snakes or some fishes that give live birth.

    Naw, mammals didn’t come from snakes or fishes*, so that wouldn’t have much effect. Since mammals laid eggs at one point (see: echidna and platypus for examples of those that still do) that was something that happened long after mammals branched off from the rest of the critters, I reckon.

    I think. I’m a layman at this too, lawl.

    *Depending on what one means by ‘fishes’, of course. Of the water-vertebrates-from-before-tetrapoda variety, yes, distant ancestors which eventually became mammals did. Of the bass, perch and shark variety, no.

  27. 27
    ChasCPeterson

    Yes, convergent evolution is exactly what we’re talking about. All mammals, birds, crocodilians, turtles, and lepidosaurs (lizards + snakes + tuatatras) are amniotes, descendant from a common ancestor that laid the distinctively complex amniotic egg. Live birth has evolved convergently from egg-laying ancestors many, many times in different lineages (but never in turtles, crocs, or birds). As you may recall, there are living mammals–perfectly good mammals, with fur, mammary glands, single dentary, etc.–that still lay eggs! There are also some living lizard species in which some populations are oviparous, others (ovo)viviparous.
    Of course, fishes do everything.

  28. 28
    Francisco Bacopa

    As a total layman I’m speculating that to grow a fetus that large in any reasonable amount of time would have required something like a placenta. Live bearing sharks (not that sharks are in any way an ancestor of plesiosaurs) have gas and waste exchange systems for their embryos, though almost all nutrients come from the yolk sac. This shows that it’s at least plausible that plesiosaurs had similar or more sophisticated systems.

    I think they must have had something at least almost as good as a placenta to get that baby so big. Biologists, is this a justified conjecture?

  29. 29
    Trebuchet

    @18, Rene! Aargh again, and sorry. I’m completely distypsic today! And yes, that was what I meant.

  30. 30
    WhiteHatLurker

    Live birth has evolved convergently from egg-laying ancestors many, many times in different lineages (but never in turtles, crocs, or birds).

    Just to be picky, we haven’t observed viviparity in those animals. I agree that it likely hasn’t happened. (How well would a pregnant bird fly?)

    Of course, fishes do everything.

    Chuckles agreement. You mean like eelpouts? Too be fair to the rest of us vertebrates, they’ve simply had more time.

  31. 31
    WhiteHatLurker

    @23 ChasCPeterson
    Thanks for the Tet.Zoo. pointer. That was an interesting read.

  32. 32
    llewelly

    Makyui | 14 August 2011 at 1:42 pm :

    *Depending on what one means by ‘fishes’, of course. Of the water-vertebrates-from-before-tetrapoda variety, yes, distant ancestors which eventually became mammals did. Of the bass, perch and shark variety, no.

    You were doing fine until you included sharks. Tetrapods are closer to teleosts (ray-finned fishes like bass and perch) than sharks are to either one. A clade that includes both teleosts and sharks necessarily includes tetrapods.

    Osteichthyes includes both tetrapods, which are within lobe-finned fish (Sarcopterygii), and ray-finned fish (Actinopterygii). But to include sharks you need to go all the way back up to jawed fish (Gnathostomata). Or so says wikipedia.

  33. 33
    llewelly

    WhiteHatLurker | 14 August 2011 at 6:07 pm :

    Just to be picky, we haven’t observed viviparity in those animals. I agree that it likely hasn’t happened. (How well would a pregnant bird fly?)

    As well as a pregnant bat?

  34. 34
    Mak, acolyte to Farore

    Llewelly:

    Spiff! Thanks for the correction. I had no clue sharks went back that far.

  35. 35
    Owlmirror
    Just to be picky, we haven’t observed viviparity in those animals. I agree that it likely hasn’t happened. (How well would a pregnant bird fly?)

    As well as a pregnant bat?

    Hm, I suspect not.

    I recall reading somewhere that bird development requires the developing embryo to move around a lot in order for the leg bones to develop properly (a bit of searching suggests that I’m thinking of the crest of the tibiofibula)(I hope David Marjanović, or someone, stops by to correct me if I got that wrong).

    I am not sure if that wriggling would be to a degree that would impair flight, but it’s a factor to take into consideration.

  36. 36
    Thomas R. Holtz, Jr.

    Nemo @#15: no, plesiosaurs are NOT dinosaurs! They are part of a different branch of the reptiles: Sauropterygia, which also includes more near-shore type animals (placodonts, nothosaurs, tiny pachypleurosaurs). At least some analyses place the ichthyosaurs as close relatives of the sauropterygians within a group Euryapsida, in which case most of the the marine reptiles of the Mesozoic form a single group.

    What is intriguing is that ichthyosaurs and pachylpleurosaurs were already known to have given birth live (and this may thus have been the ancestral state for all euryapsids), but they gave birth to many small young. What is curious here is that this plesiosaur had such a HUGE young: much more like a cetacean than a sea snake.

    If any of you find yourself in Los Angeles, stop by the Natural History Museum and check out the specimen: it is quite nice.

  37. 37
    David Marjanović, OM

    It makes a lot of sense that they would have huge babies. They’d have to be born ready to swim with the group.

    Except we don’t know whether there was a group.

    I do have a question to the palaeo-savvy around: Looking at the fins of these animals, are these on a branch that did not yet evolve fingers? Or might that be a reduction of previously existing fingers?

    Reduction? :-) The fingers and toes are extremely long. They were just bound together by soft tissue to form a continuous paddle, but skeleton-wise they’re there and really not reduced.

    Count them, too. There are five in each paddle.

    Wait, is this a technically dinosaur?

    No. In fact, it may be more closely related to the lizards than to the crocodiles plus dinosaurs. It’s a very different animal.

    And chances are very good that all dinosaurs have always laid eggs. After all, that’s what they all do today, and what their closest living relatives, the crocodiles, do; plus, their embryos take the calcium they need out of the shell (rather than the yolk), so there has to be a shell.

    Unfortunately, the reproduction mode of the extremely marine crocodiles (Metriorhynchoidea) is not yet known from direct evidence.

    @23 ChasCPeterson
    Thanks for the Tet.Zoo. pointer. That was an interesting read.

    (…psssst… the link was already provided in comment 6…)

    I recall reading somewhere that bird development requires the developing embryo to move around a lot in order for the leg bones to develop properly (a bit of searching suggests that I’m thinking of the crest of the tibiofibula)

    *lightbulb moment*

    Yep, the fibular crest on the tibia only forms when there’s enough kicking. No idea if that would hinder flight. Humans famously kick a lot at that stage, too, but bats are born before it, aren’t they?

    At least some analyses place the ichthyosaurs as close relatives of the sauropterygians within a group Euryapsida

    I don’t understand why Rieppel expanded Sauropterygia to encompass Placodontia, which hadn’t been considered a member since Owen in the late 19th century, and why whichever early-2000s paper proposed to use Euryapsida for a clade that included most of the traditional Euryapsida (Placodontia, Sauropterygia and – as people used to think till the 1990s or so – the terrestrial, Permian Araeoscelidia) and Ichthyopterygia. The name Enaliosauria, coined in the 19th century for a grouping of ichthyo- and plesiosaurs, had been available all the time. (It just so happens ichthyo- and plesiosaurs hadn’t been considered close relatives since then.)

  38. 38
    Thomas R. Holtz, Jr.

    David,

    Enaliosauria may indeed be returning as a node within Euryapsida. And I think the issue for not using Enaliosauria is that a lot of the late-80′s clado-clique just didn’t read a lot of the Victorian literature, and weren’t aware of the older names. They mostly drew upon names that were in use in the immediately more recent phase of taxonomy.

  39. 39
    PZ Myers

    I thoroughly checked the spelling in the Science article: it really is written “latippinus”.

  40. 40
    mo

    @ David Marjanović: Where are the radius/ulna fibula/tibula pairs in the plesiosaur limbs? Are they the two biggest bones proximal to the humerus and femur? In which case, what are those weird two smaller posterior bones?

    If P. latipinnus was published first, this name is correct, and the name in Science is wrong. The ICZN should be followed here, as it should be in most cases, except Sophopora, which is just stupid and hubistic of the people on their committees.

  41. 41
    mo

    Oh, and whales also have more finger bones (phalanges) than land mammals, which is convergent to plesiosaur limbs:

    http://fany.savina.net/wp-content/uploads/2010/06/HumpbackWhaleSkeleton.jpg

  42. 42
    Matt H

    I’m a non-biologist but am fascinated by this.

    In the diagram from above showing the relationship of bones to overall shape, bones which I’ll describe as the shoulder blades and the hip bones look absolutely enormous.

    Is the bone mass as big and heavy as it looks from above?

    If so, does it serve a ballasting function or something? (to balance the soft tissue that floats)?

    Those bones look as though they’d inhibit flexibility and slow the organism down….Now I really want to know how these things moved through the water. When I was a dinosaur-fascinated kid, I always envisioned them as moving like a water snake with flippers, but now I think that was wrong…

    Oh, and very cool. Viviparous giant swimming reptiles!!
    Thank you for posting.

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