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One ancient predator turns out to have been able to eat much larger prey than we thought was possible, and a baby titanosaur skull gives us clues about what changes took place as sauropods grew up.

Hosted by: Hank Green

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Sources:
Ichthyosaur: https://doi.org/10.1016/j.isci.2020.101347
Titanosaur: http://dx.doi.org/10.1016/j.cub.2020.07.091
https://www.geosociety.org/GSA/Education_Careers/Geologic_Time_Scale/GSA/timescale/home.aspx

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[♩INTRO].

Figuring out what ancient creatures ate and therefore, what role they played in their ecosystem, isn’t easy. But thanks to a study published this month in the journal iScience, we have a pretty solid idea about at least one ancient predator one that ruled not the land, but the sea.

The specimen was found in 2010 in the Guizhou Province of southwestern China, dating back to the Middle Triassic Period, about two hundred forty million years ago. It’s a five-meter-long ichthyosaur named Guizhouichthyosaurus, part of a group of fish-shaped reptiles that dominated Triassic oceans. And they may have been far more impressive predators than we thought.

See, inside this ichthyosaur’s belly are the remains of another marine reptile named Xinpusaurus. This was a thalattosaur, which was a predator of smaller marine animals like fish or shelled creatures. Only about half of the smaller reptile is preserved in the predator’s stomach, but it would have been about four meters long.

Remember, our ichthyosaur was only a meter longer than that. So this was one big snack, and way more so than we thought possible. It’s really rare to find stomach contents for ancient marine reptiles like these, and what we do have doesn’t add up to much.

So paleontologists typically infer these animals’ diets by their body size or tooth shape. Big animals with sharp teeth are more likely to have hunted large prey. But ichthyosaurs like Guizhouichthyosaurus had blunt teeth that are thought to be best suited for grasping soft prey like squids.

This new discovery is strong evidence that these animals were megapredators at least some of the time, they ate very large prey. We don’t know for sure whether this was a case of hunting or scavenging, but the authors of the study think this predator probably caught its meal alive. That’s because the fossilized stomach remains contain the body and legs of the prey, but without the head and tail.

Animal carcasses decomposing at sea tend to lose their legs before their head and tail detach, so we wouldn’t necessarily expect to see legs if the meal were scavenged. What’s more, a disembodied fossilized tail was found about twenty-three meters away from this fossil! The tail matches the size and shape of the consumed thalattosaur, and if it’s really part of the same animal, then it must have been torn apart, probably by the same bite-and-shake method we see marine predators use today.

It paints a fearsome picture, but it’s also a huge clue that there may be more to prehistoric marine reptile diets than we thought. And while we’re on the subject of surprising fossil finds, another new study in the journal Current Biology provides a rare glimpse at a dinosaur embryo! No matter how big they eventually got, all dinosaurs started out as hatchlings.

But for many dinosaurs, we don’t know very much about how they grew and developed. This new study describes a single skull, less than three centimeters long, found within a fossil eggshell from Argentina. Based on its anatomy, researchers identified the skull as a sauropod, one of those dinosaurs with the long necks and pillar-like legs.

More specifically, this was a type of sauropod called a titanosaur, some of which were truly enormous -- meaning this specimen could have grown into one of the largest dinosaurs ever to live. Incredibly, this tiny skull is one of the best-preserved titanosaur skulls ever found. And it has a lot to tell us about the changes that took place as sauropods grew.

Based on the developmental features of the skull, the researchers estimated that it was about three quarters of the way to hatching. And it had already developed enough adult facial features to be identified as a titanosaur. But it also had some pretty striking differences from adults.

For one thing, its eyes were more forward-facing than in adult titanosaurs, suggesting these babies were good at seeing what was ahead of them, but became more sensitive to what was off to the sides later. The embryonic skull also had an unusual projection of bone sticking off its snout, which appears to be a single small forward-pointing horn. Now, that sounds a lot like an egg tooth the temporary tooth that some animal hatchlings use to break out of their eggs.

But egg teeth are lost after hatching. This little horn was built into the upper jaw bone and would have stuck around for a while before the babies lost it later in life. So even if this horn was used in place of, or alongside, an egg tooth, we don’t know what else the babies might have used it for.

All this tells us that baby titanosaurs probably had very different lives compared to adults. The researchers don’t know what species this embryo belongs to, and in fact, they don’t even know for sure where it came from. The specimen was illegally exported out of Argentina before eventually being brought to the scientists.

It’s now been repatriated to its home country, but without any data on where it came from, it’s hard to know more about its ancient habitat or possible family members. Fortunately, there are many more dinosaur eggs known from Argentina. With some luck, this little specimen might end up being part of a series that cracks open the mysteries of the earliest days of the largest dinosaurs.

Thanks for watching this episode of SciShow News, and a titanosaur-sized thanks to our patrons for helping to make it happen. A grown titanosaur, not a baby one. Biggest one you can imagine.

If you’re interested in joining our community of supporters, check out patreon.com/scishow. [♩OUTRO].