OFFICIAL27 What did researchers conclude from their study of sauropods and gastroliths?

[00:00.00]NARRATOR: Listen to part of a lecture in a zoology class.[00:03.35]FEMALE PROFESSOR: Your reading for today touched on dinosaur fossils from the Mesozoic era [00:10.79]Today, we'll be discussing the sauropods.[00:13.68]I think our discussion of sauropods will illustrate what we can learn by comparing the fossil record to [00:21.65]By "fossils,"we mean traces of prehistoric animals–such as bones, which become mineralized ...or impressions of bones or organs that're left in stone...[00:31.30]Now, sauropods were among the largest animals to exist, ever. [00:35.45]They were larger than blue whales, which are the [00:39.78]they weighed up to 100 tons–20 times as much as elephants. [00:45.01]Also, they were an [00:48.49]there's evidence of sauropods in the fossil record for an [00:55.51]So: Why were sauropods so successful?
[00:58.89]Biologically speaking, sauropods shouldn't have been successful. [01:03.52]Large animals–like [01:11.83]this makes maintaining a population harder. [01:14.93]The largest animals today don't live on land,
[01:18.27]but [01:26.13]and they give birth only once every few years. [01:28.93]We also know that body heat–that ...uh, well ...large [01:37.14]but for an ocean-going whale, that's not a problem; [01:40.33] for a 100-ton land animal, it can be.
[01:43.61]For years we've assumed it was the abundant plant life of the Mesozoic that allowed these giants to [01:50.58]However, we now know that, since oxygen levels were much lower in the Mesozoic than we'd [02:01.78]So now? well, we're looking at other–we...we're-we're trying to understand the biology of sauropods, comparing their fossils to the [02:15.51]What we've found is that sauropods were experts at conserving energy.
[02:21.81]They had enormous stomach capacity–the ability to digest food over a long period...converting it to energy at a slower [02:31.71]For animals with small stomachs, it takes lots of energy to constantly [02:38.04]with larger stomachs and slower digestion, you don't need as much [02:45.01]MALE STUDENT: Does ...mm, do scientists actually know about [02:59.36] ... and comparisons between animals that lived millions of years apart–[03:03.41]w-well, it just seems ...more like guessing.
[03:06.89]FEMALE PROFESSOR: [03:11.12]There's always guesswork when studying extinct animals; but [03:17.05]we "test" the hypothesis, by [03:21.03]then some questions are answered, which may lead to new question...[03:25.65]For example: Let's look at one of these comparisons?
[03:29.34] We know sauropods couldn't chew food–[03:32.72]their skulls show they had no chewing muscles. [03:35.41]Lots of modern animals–like birds and [03:40.48]they need to swallow it whole. [03:42.33]But modern animals have an interesting aid for [03:46.66]They swallow stones ...stones that're used to help grind up the food ...before it's actually [03:54.67]These stones are called "gastroliths."[03:57.85]Gastroliths make food easier to digest, [04:06.06]Over time, gastroliths inside the animal are ground [04:12.19]Now, sauropod fossils are commonly found with smoothed stones...[04:17.11]for years, [04:19.87]they looked just like gastroliths, and were found in the area of the [04:24.54]A recent study measured the gastroliths in modern animals–in ostriches ...[04:30.72]and the study showed that [04:37.24]But we've been able to determine [04:47.14]So now, we're not quite sure what these sauropod stones were used for. [04:51.77]It could be they were [04:58.88]Other [05:06.83]So, the original hypothesis–that the stones found with sauropods were gastroliths–even though it