How likely do you think it is that sauropod females had ovipositors?

[andrewsaurus rex]

Given that only some fish and insects have them it seems pretty unlikely to me.  But you never know.

There are 2 major problems sauropods faced when egg laying.  The height the egg dropped from and a huge sauropod being able to aim her tiny eggs into a (relatively) tiny nest.......i'm thinking of titanosaurs here.

An ovipositor would certainly solve both easily.  The height problem is gone because the ovipositor would presumably reach to ground level or very close and the female would just have to line up the ovipositor once, probably by looking back between her legs and once it's in the nest, well, let her rip.  The eggs could just slide out one by one into the nest while the female stands in a relaxed position, perhaps even grazing on a convenient tree that's close by.

The alternative, as I see it , would be to have eggs with super hard shells (that perhaps thin as time goes on as the embryo consumes some of the material in it) that could withstand the drop, or eggs with super rubbery shells that can take the drop and then perhaps harden over time.   The female would probably have to keep looking between her legs to ensure the eggs are all going into the nest and not bouncing all over the place.

A third possibility, is the female building a big cushion out of foliage, laying the eggs on that and then, one by one moving them into the nest with her mouth.  Quite a laborious process and you still run the risk of the falling eggs colliding with those already on the cushion and breaking. And  I wonder how long sauropods could keep their heads lowered before the blood pressure bursts some vessels in their brain?

Of the three, the ovipositor does seem the best method.  Of  course, that doesn't mean that's the way it was.

[Halichoeres]

It's not a completely crazy idea. Various eversions of the cloaca exist for various functions. The penis of ducks or the hemipenes of squamates are just cloacal eversions. Hyenas give birth through their clitoris, which looks a lot like how I would imagine a sauropod ovipositor to look. That said, what would stop them from simply squatting? I think that would solve most of their problems.

[thomasw100]

It's not a completely crazy idea. Various eversions of the cloaca exist for various functions. The penis of ducks or the hemipenes of squamates are just cloacal eversions. Hyenas give birth through their clitoris, which looks a lot like how I would imagine a sauropod ovipositor to look. That said, what would stop them from simply squatting? I think that would solve most of their problems.

There is a pretty nice discussion of the reproduction of sauropods in the book by Mark Hallett and Mathew Wedel (The Sauropod Dinosaurs). You probably know that one, but nevertheless I thought it worth to mention it. I am just reading it these days, and it is a wonderful book.

[andrewsaurus rex]

Squatting.  While I could see a female sauropod squatting a bit, to perhaps facilitate an ovipositor reaching all the way to the ground, or lessen the impact on the eggs to a degree, I can't imagine a 30, 40, 50 plus ton female squatting so low that the egg drop would be almost zero.  I just can't see her having the strength and more importantly, stamina to squat and hold that position while she lays several eggs.  And squatting once per egg would be just as taxing.  The strain on her  knees might be even more serious of a problem.  And she'd still have to be able to aim her eggs into the relatively tiny nest while holding this strenuous squat.

She could lie on her side and let the eggs slide out of her, but I think that impractical too.

[Halichoeres]

I'm not an expert in biomechanics, but I don't think a squat would be all that strenuous, especially since they could use their tail to brace themselves. It wouldn't have to take a large fraction of the weight, only add a point of stability. The eggs also were very small relative to their body size, so they probably didn't take all that long to lay (less time, than, say, a sea turtle). A cursory search hasn't yielded anything that obviously answers the question of 'could they squat,' but right now I'm not seeing a strong reason to think that they couldn't. At the same time, I don't see any reason to think a cloacal extrusion couldn't slow their descent. It might just be an unanswerable question currently.

It's not a completely crazy idea. Various eversions of the cloaca exist for various functions. The penis of ducks or the hemipenes of squamates are just cloacal eversions. Hyenas give birth through their clitoris, which looks a lot like how I would imagine a sauropod ovipositor to look. That said, what would stop them from simply squatting? I think that would solve most of their problems.

There is a pretty nice discussion of the reproduction of sauropods in the book by Mark Hallett and Mathew Wedel (The Sauropod Dinosaurs). You probably know that one, but nevertheless I thought it worth to mention it. I am just reading it these days, and it is a wonderful book.

I know of the book, but I haven't read it. Is there anything addressing the mechanics of egg laying?

[Cretaceous Crab]

Similar to what we saw on Prehistoric Planet season 2 with the Isisaurus...

How about:
1. digging up a nest of sorts, more or less piling up huge mounds of material,

2. then hollowing out a hole for the eggs to go into

3. Back up to where the cloaca is almost in line or close to the hole in the nest, with the tail stretching out over/above the nest

4. As the eggs are laid, they have a short distance and merely roll down into the interior of the nest

[andrewsaurus rex]

that's interesting.   Clever idea actually.    Some birds are very clever, maybe some dinos were too.   However it doesn't really mesh with what is known about Titanosaur nests, which were just holes dug into the ground with a back foot.  No mound building.

we'll probably never know the answer to sauropod egg laying and in truth, there may have been a variety of different strategies used by different species but it's fun to speculate about the behaviour of extinct animals that seem mysterious to us.  Like, how the heck did Kentrosaurus mate?. I know....carefully. 

[thomasw100]

I'm not an expert in biomechanics, but I don't think a squat would be all that strenuous, especially since they could use their tail to brace themselves. It wouldn't have to take a large fraction of the weight, only add a point of stability. The eggs also were very small relative to their body size, so they probably didn't take all that long to lay (less time, than, say, a sea turtle). A cursory search hasn't yielded anything that obviously answers the question of 'could they squat,' but right now I'm not seeing a strong reason to think that they couldn't. At the same time, I don't see any reason to think a cloacal extrusion couldn't slow their descent. It might just be an unanswerable question currently.

It's not a completely crazy idea. Various eversions of the cloaca exist for various functions. The penis of ducks or the hemipenes of squamates are just cloacal eversions. Hyenas give birth through their clitoris, which looks a lot like how I would imagine a sauropod ovipositor to look. That said, what would stop them from simply squatting? I think that would solve most of their problems.

There is a pretty nice discussion of the reproduction of sauropods in the book by Mark Hallett and Mathew Wedel (The Sauropod Dinosaurs). You probably know that one, but nevertheless I thought it worth to mention it. I am just reading it these days, and it is a wonderful book.

I know of the book, but I haven't read it. Is there anything addressing the mechanics of egg laying?

Sorry, by chance I just had started to read that chapter when I saw this discussion. Now I can say more. They actually speculate that indeed female sauropods would have had ovipositors and there is an illustration of that idea. But obviously soft-tissues are typically not in the fossil record, so it is hard to know. But they argue that it would have been difficult for large sauropods with their quadrupedal stance to get so close to the ground that the eggs would not break. From this they proceed to propose that they had ovipositors.

[Halichoeres]

Sorry, by chance I just had started to read that chapter when I saw this discussion. Now I can say more. They actually speculate that indeed female sauropods would have had ovipositors and there is an illustration of that idea. But obviously soft-tissues are typically not in the fossil record, so it is hard to know. But they argue that it would have been difficult for large sauropods with their quadrupedal stance to get so close to the ground that the eggs would not break. From this they proceed to propose that they had ovipositors.

I'll be damned. I wouldn't have thought it would be so difficult to bend their knees a little. Sounds like cloacal egg chute is the best hypothesis, then.

[andrewsaurus rex]

well they could have done both.......squat a bit and then use their ovipositor to reach the rest of the way to the ground.  It's nice to have some validation to the ovipositor idea.   Did the book discuss the possibility of super hard eggs that would be break resistant, or rubbery eggs that could withstand the drop?

[thomasw100]

well they could have done both.......squat a bit and then use their ovipositor to reach the rest of the way to the ground.  It's nice to have some validation to the ovipositor idea.   Did the book discuss the possibility of super hard eggs that would be break resistant, or rubbery eggs that could withstand the drop?

The latter gets into an interesting topic. They actually discuss egg sizes quite a bit and there is obviously an upper limit at approximately the size of the eggs of ostrichs or maybe a little bigger. If eggs would get much bigger, the shells would need to be much thicker to hold them together and making them withstand stresses during egg laying and other physical processes. But there is again a limit to the thickness of the shells, because of the need of gas exchange through the shell. So the oxygen for the metabolism of the growing embryo has to go in and the CO2 has to diffuse out. So shells could not get too thick and therefore the argument about the ovipositors is brought forward.

[andrewsaurus rex]

that's interesting.  I was thinking that the problem with thick eggshells was that the hatchling would have trouble breaking out but the solution for that would be to have the hatchling absorb many of the minerals in the shell to thin and weaken the shell prior to hatching.

But oxygen would need to be able to get inside the egg from the get go, so unless the shell developed to be both thick but still very porous, it would be a problem.   Did they mention soft shelled eggs at all?

Has anyone ever experimented with dropping a freshly laid ostrich egg to determine how much of drop it can withstand falling onto soft sand?   Would give an idea as to how far a sauropod female might have to squat or how close to the ground an ovipositor would have to come.  iirc ostrich females lie down to lay eggs, so the egg doesn't drop at all, it just slides out onto the ground.  Hard to imagine any female sauropod being able to duplicate that,, making specialized eggs or an ovipositor more likely in my view.

[Halichoeres]

In some cichlids the male collects the eggs in his mouth and guards them. I doubt sauropod males did anything similar but it's funny to imagine them grabbing them and then lowering safely to a furrow in the ground.

[stargatedalek]

I mean, sauropods were probably able to sit or lie down right? If the nests really were holes that were dug, why not just, sit flush to the ground and lay the eggs above the hole?

[andrewsaurus rex]

i'm not so sure sauropods were able to sit or lie down.   Their enormous weight could have caused major damage to internal organs and they many not have been able to breath properly.  It would not surprise me at all to discover adult sauropods spent their entire lives standing.   Horses rarely sit or lie down, usually only when they are sick or injured and even with horses that weigh 1/40 to 1/400 of an adult sauropod, it's bad for them to lie down too long.

Plus it would be difficult for an adult sauropod to sit/lie down then somehow scootch  her backside around to line up her cloaca with the relatively small hole she dug.

[edu]

But elephants are a lot heavier than horses and they can lay down without a problem! Thay can sleep both lying down or standing up.

[andrewsaurus rex]

true but sauropods are a lot heavier than elephants.  Most of the sauropod eggs and nest found have been titansoaurs, many of which were very large.  It's also possible that some species could sit and lie and others couldn't.

like most behavioral discussions with paleontology, we'll probably never know for certain and there can be good examples presented for all opinions.  Part of the 'fun' I guess.

[Newt]

A plausible alternative to an ovipositor would be an extended cloacal chamber running along the underside of the tail. This would place the vent somewhere along the length of the tail and permit the sauropod to lay her eggs at or near ground level merely by lowering her tail. A similar design (if for a different purpose) exists in turtles, where males of many species have an enlarged tail base which houses the penis, and the vent is placed well back along the tail (contra females, which have the vent in the traditional spot near juncture of tail and pelvis).

[Saarlooswolfhound]

I was going to mention turtles too. Some sea turtles have a tissue extension of the cloaca (I couldn't find a source to confirm it as an ovipositor directly) but that helps to lay eggs into the dug out nest. I don't see why it wouldn't be likely for sauropods. Especially since (as already mentioned) eggs have a limit to the shell thickness specifically because of gas exchange. Lastly, as for the rubbery vs hard shell debate; my understanding is that soft shell eggs (fish, turtles, and some reptiles) have rubbery eggs if they are an semi/fully aquatic species. Hard shells developed for water retention as animals moved into being terrestrial external egg bearers. So I would bet the eggs would be hardshelled, not soft. I am not sure how well soft shells preserve in fossilization conditions anyhow.

[andrewsaurus rex]

iirc many early dinosaurs are thought to have had soft shelled eggs and I don't think they supposedly laid their eggs in the water.  For sauropods, I was imagining the eggs coming out of the female, soft shelled, so they could withstand the fall to the ground, and then the shell hardening over the next few hours in reaction to being in contact with the air..  Not sure how realistic that is biologically.

the tissue extension of the cloaca is an interesting idea, but I don't know how much it would help in the case of sauropods.   The base of their tails are still pretty high off the ground, so unless this cloaca extension runs nearly half way the length of the underside of the tail, it would still be a long drop to the ground for the eggs.  Maybe a combination of the female squatting a bit and the cloaca extension might work?