Sauropod question...

[darylj]

I have been looking into various theories... and i keep coming across the idea that sauropods laid lots of eggs at one time... then left there eggs to hatch and the hatchlings to fend for themselves until they were large enough the herd....
it seems that herds of sauropod footprints have been discovered with no sign of junveniles....

my problem with this is that i cannot think of any comparable animal of a considerable size that does anything like this...
I mean, whales, elephants, giraffes, etc...

now im fully aware that none of the above creatures lay eggs... and that sauropods are infact archosaurs... so i agree that we should really compare them to modern relatives like crocodiles, komodo dragons, tortoises etc...?
or should we? I mean crocs, dragons etc are carnivorous... which i would say points towards a very different method of reproducing.
tortoises are a good reference, however a juvenille tortoise has protection, from day one pretty much.

another reference of course could be birds, which would suggest more of a nest laying theory, but that just doesnt seem plausible.

the questions I have are...
do we KNOW that suropods laid eggs and did not infact give birth to live young.
did young sauropods, fresh from the egg have any kind of defense... im sure there is no evidence that would suggest so, but they MUST have had something in place to prevent them all being devoured.... unless...
did sauropods just lay so many eggs... like turtles on a beach... that thousands of new born sauropods litterelly ran for cover as soon as they were hatched???

what are peoples thoughts?

[amargasaurus cazaui]

I would suggest that sauropod eggs are fairly well established as being a known. Consider the massive nesting grounds found in south american containing thousands of sauropod eggs, hatched and unhatched as well as embryonic remains.  There are other sites, one in France I believe and another in Spain which also lend themselves to sauropod egg nesting sites. I would have to say we have considerable evidence that sauropods as a genus did lay eggs. That much has been established. I own a sauropod egg myself.

[darylj]

thanks... i in no way dispute that they laid eggs.. i jsut wasnt aware there was hard evidence.

now i know

[amargasaurus cazaui]

There are known eggs, with embryonic Titanosaurs, that were so well preserved the skin texture was visible. I believe there are also other known types of saurpod found within an egg shell, but I am certain of the south American material. So I would state yes, there is some serious hard evidence to prove sauropods did in fact lay eggs.
    I am aware of a few bone beds that were monospecific as well as age specific being found for sauropods. I know Horner described finding a rather large bone bed of juvenile Apatosaurus in one of his books. This might suggest the young formed their own social groups away from the larger animals.
    Based on the trackways at Glen rose texas, Bob Bakker had suggested the tracks proved a herding method for the sauropods with the young located in the center of the grouping. This has since been debunked with at least one study showing there is no clear method for determining if the tracks were all laid in a single grouping or as seemed more likely, the accumulation over time of groups of sauropods passing this same spot.
    Myself I tend to accept the example you provided of mass egg laying, and while some of the young would be taken by predators, enough would make it through to insure the continuity of the species.

[CityRaptor]

As for the issue of protection: Protection in this case is large numbers. Because there are so many, it is unlikely that all die.  Same for turtles ( their armor does not offer protection at that point ).
Them not caring for their young can be attested to the size difference. There is always the danger of being accidently squished or falling into a track, which is like a death trap.

As for Vivparity: While Bakker is often associated with it, the theory goes far more back, when people assumed them to be aquatic.

[Gwangi]

I think the logic behind them abandoning the eggs rest mostly with their size. It would be very difficult for an animal the size of a sauropod to take the time out from feeding in order to watch its nest. A herd of any sauropod species would destroy the local vegetation if they remained in one place long enough for the eggs to hatch. Also sauropod chicks were very tiny, I doubt the parent could pay any close attention to them let alone avoid stepping on them. The main defense of the babies would have been their numbers and I'm sure a lot of them got eaten, much like sea turtles. There is also at least one bird species I'm aware of that abandons their nest, the Australian brush turkey. Other birds like the North American cowbird are nest parasites that abandon their chicks in the nests of other birds in part because they lead a nomadic lifestyle.
I should mention however that I believe there are sauropod trackways that contain juvenile tracks as well as adults. I'm not certain on this. I know there are also trackways that consist only of animals in a certain age range.

[CityRaptor]

I remmber reading that aswell.
Perhaps Quarry 5 of the Morrison Formation. There also seems to be evidence that Saurpod Hatchlings could run on their hindlegs, moving twice as fast:
http://paleopastori.deviantart.com/art/quot-Speedy-quot-the-Sauropod-200310190
http://paleopastori.deviantart.com/art/quot-Speedy-quot-the-sauropod-208214273


Also, is it wrong that I had to think of the Carnegie Apatosaurus when I read about the viviparty part during my recent read of "The Dinosaur Heresies"?

[amargasaurus cazaui]

     Bakker is indeed on record for translating the site at Glen Rose as an age structured herd. The concept might go back further than his comments, but he did in this incidence state the evidence was suggestive for such a structure in a herd, and was the first to do so for this particular site.
     And yes Gwangi, you are correct, that very site does offer both juvenile tracks associated with adult tracks. The area that is problematic is what order they were all made...were they a single group passing by or random groupings? Was there an adult herd followed by a younger one? These are questions the tracks cannot definitively offer answers for.
    The bone bed that was explored by Horner containing juvenile Apatosaurus, seemed to be a beachfront depost, perhaps a mud bog that had trapped the group. Even then the arugment is made that perhaps the larger animals were able to pull themselves free leaving only the young and smallest members entrapped to die.

[Gryphoceratops]

Its tricky trying to decide which modern animals to use as models when imagining dinosaur behavior.  Like you said the only animals remotely (i stress remotely) close to sauropod size today are mammals.  Sauropods loosely filled the same niche that things like elephants and giraffes fill today.  These mammals indeed for the most part care for their babies but remember, their babies are far fewer per birth and also much larger compared to the mother than a sauropod dinosaur.  When it comes to sauropods it seems (according to what fossils are known) they went with the turtle strategy- lots and lots of babies that go off on their own.  Many get eaten.  A few survive to become giants. 

I think Walking with Dinosaurs did a good job portraying this honestly. 

[darylj]

Thanks for all the information.
The only two points I struggle with are,

Comparing to turtles is - turtles are small, andd they live in the sea. I know that's obvious, but what I mean is... Baby turtles all hatch and dart for the ocean. They are in danger from predators for five minutes? Then those predators are gone. And they are in the ocean, where there is a lot of space, especially for the turtles size.
a young sauropod however doesnt reach an equivalent arearead like thethe ocean where the immediate dangers become void. And a wood full of thousands of young sauropods just wouldn't offer the same space and vastness to avoid predators in the way the ocean does for tinytiny turtles.

Also - I still think there must be something that the sauropods would have or be able to do to for defense... The only thing that clicks is protection from family members...

Is the bipedal thing generally considered possible?

[Gwangi]

Sea turtles face plenty of danger in the ocean. They're so small that they serve as food for a host of fish and sharks, sea birds, invertebrates. Aside from the open ocean anywhere near shore is generally pretty busy and keep in mind that sea turtles need to breath air so they have to surface often and that alone makes them a target. A lot of baby sea turtles actually end up hanging out in floating mats of sea weed which is not so much different from a baby sauropod hanging out in some thick vegetation.

Also keep in mind that freshwater turtles also abandon their young and those offspring have to contend with a host of terrestrial, avian and aquatic predators. Terrestrial tortoises also abandon their young and those babies are forced to find protection strictly on land like a young sauropod would. I can easily envision baby sauropods living in thick vegetation and undergrowth hiding from the larger carnivores.

[amargasaurus cazaui]

I think your argument is flawed to some degree by the perception that once the turtles reach water they are safe. There are just as many if not more predators waiting for them in the water as on land. All they are doing is exchanging one set of potential predators for another. The water does offer them better ability to maneuver and hide, but it is still beset with danger.
    The young sauropods face a similar thing, the woods might offer more cover and hiding places, but in the end some will perish . Hence the reason for so many baby dinosaurs to start with. If a herd has ten females, and each female lays fifty eggs, you have five hundred baby sauropods. If even fifty or ten percent make it to maturity, the population is still going to increase or at least never decline.

[Gryphoceratops]

Fishing boats that catch large fish like dolphin fish for instance commonly find baby turtles inside their bellies.  That being said, the baby turtles aren't safe once they hit the water.

Yes sauropods are very large but everything is relative.  Large tortoises use this strategy as do most lizards and snakes.  When it comes to defenses, plain and simple, numbers.  Yes, absolutely, most of the babies from any one of these animals will get eaten.  Many predators rely on them for food.  Maybe they can utilize camouflage to a degree but as grim as it sounds it looks like nature intends at least some of them to be eaten.  Its a really common reproductive strategy actually. 

[darylj]

sorry, Im not sure i was clear... what i meant was, baby turtles have all these dangers once they hatch, then they hit the water, and the birds or lizards hunting them down back off... then they are in the sea - sure there are more dangers in the sea... i get that.
the problem i have with sauropods is... say theres a nest site... a load of predators are waiting for them to hatch... bang, they hatch... the predators (lets say some raptors and some pterosaurs) swoop in... they feast... there is nowhere for the baby sauropods to get to, escape to, run to, where the predators will suddenly have to back off. (like the sea)... thats my only problem.
they arent small enough to hide in a burrow... they dont escape to the water... they have no protective shell... they dont fly away...

try and picture 100 eggs in africa with giraffes in them... lions, hyenas and secratary birds are waiting.
the giraffes hatch... realisticaly how many giraffes are gonna survive the first 5 mintues???
then.. where are they gonna go... what are they gonna do???
its just doesnt seem plausable...

stick some adults in the mix... and it all seems more likely... in my opinion.

[amargasaurus cazaui]

The thing you have to remember is animals generally do not kill just to kill. This idea, which exists in nature is called parsimony. Animals either kill to eat, defend their territory or their young. They do not just slaughter for the love of it. So even if you have a pack of raptors, or other predators close by and they each snatch one hatchling as the others escape into the forest, you still only lose a small percentage to predators. The larger predators would not be likely to waste their time on such a small biomass unless other resources are scarce. A single baby saurpod might feed two Pterodactyles for instance, or three .
    The problem with your example is they do have places to go. As was depicted in the WWD series they ran for the forest, where they could blend in. The close spacing of the trees tends to become problematic for larger predators in this sense. The forest also offers plenty of niches to hide in. And generally most dinosaurs would not likely sit around waiting for eggs to hatch. They would either eat the eggs themselves if that were their diet, or pass on looking for something that could be smelled, heard or hunted. The idea they would sit there waiting for the eggs to hatch so they could eat the chick are somewhat unlikely.
    Finally, i think as gryph stated quite well, to some degree they cannot be all expected to survive. If they did, the species would become overbalanced and eliminate their resources , creating a mass die off. In a larger sense it is likely many were born and intended to supplement other animals diets, as a sort of natural checks and balances type pattern.
   If you examine some of the nesting sites, there seem to be different strategies. Horner excavated a site he felt was a nesting place on an island, which would offer the hatchlings some protection. The nesting colonies in south america seem to be massive hatchery areas. It is not impossible the larger adults patrolled the edges of that area, protecting the boundaries, if not the actual hatchlings.
   The problem you have with a freshly hatched sauropod a foot or two long , let alone hundreds of them running around is size of the young versus adults. A fully grown sauropod might weight thirty tons and have a footprint the size of a tree trunk. You would find the chicks constantly being crushed accidentally in that scenario.

[Gryphoceratops]

Lets keep using turtles as our model here to compare to sauropods.  Sea turtles for instance will all emerge from the nest typically at night.  Nighttime there are far fewer predators on land that are willing to get them.  There will still be predators, just fewer.  Also, they all emerge at the same time.  Many many many of them.  There are more babies than the predators can eat really. 

So imagine a nesting site of sauropod eggs.  Lets say they hatch at night so there are fewer predators.  Hundreds of them coming out of the nests all at once.  Yes they are small and helpless and yes many of them probably will get nabbed by birds or troodontids or whatever kind of predator is appropriate for the place/time scenario but there will probably still be more sauropods than the predators' stomachs can hold.  Lets say some of them find cover in some plants.  They use camouflage (speculation!!!!) and hunker down and freeze.  I bet many predators will walk right by them in all the commotion without even knowing they are there (again I think there is a scene in WWD like this with diplodocus and ornitholestes).  Its not uncommon for only one in hundreds to survive into adulthood but one adult sauropod makes a dent in the ecosystem for sure! 

[wings]

the problem i have with sauropods is... say theres a nest site... a load of predators are waiting for them to hatch... bang, they hatch... the predators (lets say some raptors and some pterosaurs) swoop in... they feast... there is nowhere for the baby sauropods to get to, escape to, run to, where the predators will suddenly have to back off. (like the sea)... thats my only problem.
they arent small enough to hide in a burrow... they dont escape to the water... they have no protective shell... they dont fly away...

try and picture 100 eggs in africa with giraffes in them... lions, hyenas and secratary birds are waiting.
the giraffes hatch... realisticaly how many giraffes are gonna survive the first 5 mintues???
then.. where are they gonna go... what are they gonna do???
its just doesnt seem plausable...

stick some adults in the mix... and it all seems more likely... in my opinion.

Perhaps you would prefer an animal that doesn't escape to some kind of barrier (in this case, you are referring to the water for the sea turtles), what if the example is on Brush-turkeys? Their chicks are superprecocial (which means the chicks become independent as soon as they are hatched). They could fly but I highly doubt that they could out fly the predatory birds (i.e. hawks, kites or eagles). But their main enemies appear to be terrestrial animals like monitor lizards, snakes, foxes, or domestic cats (http://www.ehp.qld.gov.au/wildlife/livingwith/brushturkey.html), if that is true then it seems they don't fly that well. From the same article they also said that their survival rate is about 1 in 200...

Brush-turkeys only lay about 20 odd number of eggs in each nest and sauropods probably in general lay quite a bit more (http://labmem.unsl.edu.ar/Publicados/Lucas_10.pdf). Perhaps statically this would also make their (sauropods') survival rate higher somewhat than the Brush-turkeys.

I'm not saying that sauropods don't have parental cares, they might very well do. I just don't see how you can say the idea of non-parental care doesn't seem plausible because it obviously does work for some terrestrial egg laying animals (i.e. most reptiles). As for now we have evidences which support both scenarios (i.e. Trackway that shows a herd of juvenile sauropods traveling together in Cabo Espichel, Portugal, or fossil remains of mixed age sauropods at the Morrison Formation).

[darylj]

the turkey example is very good... and has pretty much turned my whole view... i do understand that predators only kill to eat etc. i just thought that, if sauropods applied this technique of mass egg laying for millions of years... surely eventually, the predators are gonna catch on and turn up to feast... but still... the turkey example is a good reference.
thankyou all for the opinions.
the island theory is extremely interesting! ive never heard of it before... *picturing brachiosaurs crossing with there long necks above water to reach nesting islands...

but yeah, the most sense is the mass egg laying idea...

[amargasaurus cazaui]

I forget which of Jack Horners books the reference was, but he stated one of their sites was either a small island in the middle of a large lake or lagoon, or very possibly a slender penninsula surrounded by water. He mentions finding several types of eggs during this book, but I am fairly certain the ones he established reliably were not sauropod eggs, however i mentioned it as another possibility. I think the dinosaurs likely used many different strategies for egg laying , nesting, and building populations. I do agree with Wings, Gryph and Gwangi that the answer used by sauropods was simply producing so many eggs that it would insure some would make it through to maturity.
    One reference you might find useful is to locate any books on the South American egg sites. They document a site that is massive and also appears to have been used annually for egg laying. The eggs are spread out over a large horizon, and also layers deep. They all seem at this point to be monospecific, the same species of Titanosaur. It is one of the largest dinosaur "rookeries" in the world known.

[tyrantqueen]

The thing you have to remember is animals generally do not kill just to kill. This idea, which exists in nature is called parsimony. Animals either kill to eat, defend their territory or their young. They do not just slaughter for the love of it.

the turkey example is very good... and has pretty much turned my whole view... i do understand that predators only kill to eat etc. i just thought that, if sauropods applied this technique of mass egg laying for millions of years... surely eventually, the predators are gonna catch on and turn up to feast... but still... the turkey example is a good reference.

I'd just like to point out this is NOT true. Many modern animals have been observed killing for pleasure. It is known as surplus killing. Wolves, weasels, orcas, foxes, spotted hyenas, brown bears, lynx, dolphins, spiders, and minks are all an example of this.

House cats do it too when they bring in dead animals as "presents".