# Prehistoric marine reptiles and the facts of life **URL:** \ **Category:** Factual Questions\ **Created:** [August 27, 2001, 7:35am UTC](https://boards.straightdope.com/t/prehistoric-marine-reptiles-and-the-facts-of-life/78295 "2001-08-27T07:35:42Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![choosybeggar](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@choosybeggar](https://boards.straightdope.com/u/choosybeggar)\ **Post date:** [August 27, 2001, 7:35am UTC](https://boards.straightdope.com/t/prehistoric-marine-reptiles-and-the-facts-of-life/78295/1 "2001-08-27T07:35:42Z")
[Pleisiosaurs,](http://prehistoricsillustrated.com/pg_elasmosaurus_01.html)[ul][/ul][pliosaurs,](http://www.oceansofkansas.com/pliosaur.html) and[ichthyosaurs](http://www.hunterian.gla.ac.uk/HuntMus/dinosaur/images/ichth.jpg) are three classes of prehistoric marine reptiles. My question is where did they lay their eggs? I am under the impression (misimpression??) that reptillian eggs must be incubate on land. None of these prehistoric creatures looks capable of hauling themselves out of the ocean for reproduction. Is it believed that they did? What is the evidence? Is this a good example of the power of love? ---
**Author:** ![Tamerlane](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tamerlane/32/7602_2.png) [@Tamerlane](https://boards.straightdope.com/u/Tamerlane)\ **Post date:** [August 27, 2001, 7:45am UTC](https://boards.straightdope.com/t/prehistoric-marine-reptiles-and-the-facts-of-life/78295/2 "2001-08-27T07:45:19Z")
> [@](#): > > \*Originally posted by choosybeggar \* > > I am under the impression (misimpression??) that reptillian eggs must be incubate on land. None of these prehistoric creatures looks capable of hauling themselves out of the ocean for reproduction. Is it believed that they did? What is the evidence? Is this a good example of the power of love? I don’t know what evidence there is for prehistoric reproductive systems, but I’ll note that not all reptiles lay eggs 🙂 . A number are viviparous/ovoviviparous. Including all seasnakes 😉 . - Tamerlane ---
**Author:** ![mmmiiikkkeee](https://avatars.discourse-cdn.com/v4/letter/m/edb3f5/32.png) [@mmmiiikkkeee](https://boards.straightdope.com/u/mmmiiikkkeee)\ **Post date:** [August 27, 2001, 8:07am UTC](https://boards.straightdope.com/t/prehistoric-marine-reptiles-and-the-facts-of-life/78295/3 "2001-08-27T08:07:29Z")
Some of these marine reptile gave birth to live young in the water… with the ichthyosaur they’ve found a fossil of one with a baby inside - I’ve seen the picture in many dinosaur books, so it shouldn’t be hard to find on the net. I did a quick search and found [this](http://lupus.northern.edu:90/natsource/earth/Marine1.htm)site that had some info on different types of marine reptiles and their supposed methods of reproduction (well two of them anyway). Wait, [this](http://www.esc.cam.ac.uk/new/v10/museum/exhibits/ichthyosaur.html)site has the pic I mentioned… it’s too small but there it is! ---
**Author:** ![Fern\_Forest](https://avatars.discourse-cdn.com/v4/letter/f/71c47a/32.png) [@Fern\_Forest](https://boards.straightdope.com/u/Fern_Forest)\ **Post date:** [August 27, 2001, 8:08am UTC](https://boards.straightdope.com/t/prehistoric-marine-reptiles-and-the-facts-of-life/78295/4 "2001-08-27T08:08:14Z")
There is a really famous fossil of a … pleisiosaur I believe, which was pregnant when it died and sunk to the floor. Really pregnant, like shortly about to give birth. Both her and her baby died and as they decomposed the baby was partway expelled and this is how they found the fossils. With the baby half in and half out. So these gave live birth, and since we never find eggs for the other species, maybe that’s because they never laid eggs? ---
**Author:** ![Fern\_Forest](https://avatars.discourse-cdn.com/v4/letter/f/71c47a/32.png) [@Fern\_Forest](https://boards.straightdope.com/u/Fern_Forest)\ **Post date:** [August 27, 2001, 8:09am UTC](https://boards.straightdope.com/t/prehistoric-marine-reptiles-and-the-facts-of-life/78295/5 "2001-08-27T08:09:31Z")
_kicks self_ not only did he beat me, but he wrote a better post, sigh ---
**Author:** ![Duck\_Duck\_Goose](https://avatars.discourse-cdn.com/v4/letter/d/50afbb/32.png) [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)\ **Post date:** [August 27, 2001, 5:15pm UTC](https://boards.straightdope.com/t/prehistoric-marine-reptiles-and-the-facts-of-life/78295/6 "2001-08-27T17:15:50Z")
Garter snakes give birth to live young, as do some sharks. The dividing lines tend to blur. “Reptiles” don’t always incubate eggs on land; “fish” don’t always expel millions of eggs into the water. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [August 27, 2001, 5:44pm UTC](https://boards.straightdope.com/t/prehistoric-marine-reptiles-and-the-facts-of-life/78295/7 "2001-08-27T17:44:23Z")
> [@](#): > > \*Originally posted by choosybeggar \* > \*\*[Pleisiosaurs,](http://prehistoricsillustrated.com/pg_elasmosaurus_01.html)[ul][/ul][pliosaurs,](http://www.oceansofkansas.com/pliosaur.html) and[ichthyosaurs](http://www.hunterian.gla.ac.uk/HuntMus/dinosaur/images/ichth.jpg) are three classes of prehistoric marine reptiles. My question is where did they lay their eggs? > > I am under the impression (misimpression??) that reptillian eggs must be incubate on land. None of these prehistoric creatures looks capable of hauling themselves out of the ocean for reproduction. Is it believed that they did? What is the evidence? Is this a good example of the power of love? \*\* First, the main groups of Mesozoic marine reptiles were **plesiosaurs** (these are further broken down in to long-necked **elasmosaurs** and short-necked **pliosaurs** ), **mosasaurs** (most closely related to varanids, the most famous member of which is the Komodo Dragon), **nothosaurs** (intermediate between terrestrial reptiles and plesiosaurs), and **ichthyosaurs** (the most “fishy” looking of the bunch). Now, for the easy one, we have evidence that ichthyosaurs gave live birth (as is mentioned in the site **mmmiiikkkeee** linked to). For plesiosaurs, we have no evidence one way or the other. For mosasaurs, calculations were made in 1986 (by paleontologist Gordon Bell) which indicate that their limbs were far too weak to have been able to support them on land; thus egg-laying is not likely. In 1996, Bell found fossil evidence supporting live-birth on mosasaurs. Two baby mosasaur skeletons were found within the pelvic region of a larger one. However, there was no evidence of eggshell fragments or digestion, so the most reasonable explanation is that mosasaurs gave live birth, and that this particular mosasaur died before giving birth.