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Titanosaurs—those long-necked, herbivorous sauropods that walked on four legs—are one of the most iconic groups of dinosaurs. I mean, when you think dinosaur, it's pretty much either them or T. rex.

And they don't just dominate dino pop culture—they were pretty dominant in their time, too. They're thought to be the biggest animals to have ever walked on land, and by the end of the Cretaceous, they were all over the place. We've found their fossils on every continent except for Antarctica.

But their early years are still kind of a mystery. And that's why paleontologists are excited about a new fossil described this week in the journal PLoS ONE. Not only is the titanosaur over 100 million years old, they found a lot of bones from the same animal, and it's already providing intriguing insights into titanosaur evolution.

We have plenty of fossil evidence that tells us titanosaurs reached peak diversity in the late Cretaceous era between 100 and 66 million years ago, but we don't know all that much about how they got started. The vast majority of what we do know comes from South America. And scientists have also found a handful of titanosaurs in Africa, which suggests the lineage started when the two continents were part of one supercontinent.

But it was thought that the creatures in what's now sub-Saharan Africa were kind of isolated from the rest of the world at the time, and therefore can't tell us much about major groups like titanosaurs. But this new fossil suggests otherwise. It was found in a quarry along the Mtuka River in southwest Tanzania.

They're calling it Mnyamawamtuka moyowamkia. That's a combination of Swahili words which roughly translate to “beast of the Mtuka with tail hearts.” That last bit references the heart-shaped structures in the tail vertebrae they found. And the best part is, they found well-preserved partial remains of every body region, including numerous vertebrae, ribs, limbs, and teeth.

That makes it one of the most complete titanosaur fossils ever found. All of that means it could shed some much-needed light on how this group of dinosaurs first evolved and diversified. For example, its teeth seem to be intermediate in shape between earlier sauropods and the peg-like teeth found in titanosaurs later on.

Small details like these can help scientists piece together the relatedness of different fossils to make an evolutionary tree. And the tree in this paper suggests this region of Africa wasn't as cut-off as paleontologists thought, and was likely a prominent area of early titanosaur evolution. That means more secrets may lie waiting for discovery in places like Tanzania.

So hopefully, future expeditions in Africa can paint an even clearer picture. And this is just one of two new sauropods in the news. The second one has sparked a bit of controversy since it was published in the journal Scientific.

Reports on February 4th. It's a roughly 140 million-year-old dicraeosaur, part of a family of sauropods that had their heyday around the late Jurassic and early Cretaceous periods, just before the titanosaurs really took over. They're smallish sauropods—you know, only like 20 meters long.

But their real claim to fame lies in their forked vertebrae, which give them a ridge of spines down their necks. Hence, the name of the new discovery: genus Bajadasaurus, because it was discovered in the Bajada Colorada region of Argentina, and species pronuspinax, which means “forward facing spines.” This specimen wasn't as complete as the titanosaur— they found most of the skull and jaw bones and one neck vertebra. But that neck vertebra has some glorious spines: a pair of them, reaching 58 centimeters in length, which researchers believe arched toward the animal's head.

They say that suggests this dinosaur had a huge, spiky, front-facing mohawk that ran all the way down its neck. That might seem weird, but remember, spiny vertebrae are what these dinos are known for. Just look at Amargasaurus, who sported its own respectable set of neck spines.

The mystery here is what those spines were there for. Some think they could be for a pair of sails that helped regulate temperature, kind of like the spines in Dimetrodon. Others think they might have supported fatty humps like you see in bison and camels.

And of course, there's always the possibility that they were some kind of mating display. Maybe a couple of padded crests were their version of a tricked-out Tinder profile. But the researchers behind this study are backing a different theory: they say they were there to defend against predators.

When they lowered their heads to graze, the spines might have stuck out at just the right angle to skewer any attackers. And the idea isn't completely random. There is at least one living species that has pointy neck bones that are also thought to be protective: the potto, a slow-moving African primate.

But the researchers' conclusions have received a fair bit of criticism. One problem is that it's not clear the animals had protection anywhere else. So predators could, you know, just attack from behind.

Also, the spikes are very close to the spinal cord, so they'd have been risking paralysis every time they impaled something that thrashed around. But perhaps the most obvious complaint is that the authors made sweeping conclusions about their necks based on very little data. Remember, all we have is one vertebra bearing one pair of spikes.

To conclude that this species had a full set of forward-facing spikes and that it used them for protection might be pushing it a little. That's one of the biggest challenges to studying a long-dead species. Paleontologists often have to piece together an entire animal's biology and behavior from a few bones encased in rock.

Fossils can tell us some really incredible things. But they keep their secrets sometimes, too. It's impossible to be 100% certain how the vertebral spikes were used without going back in time to see them firsthand.

But, if we find a lot more fossils of this species and its relatives, we might be able to rule out some ideas. The good news is that we're finding more new dinosaur species than we ever have before, at a rate of around 50 a year. So, who knows what evidence is waiting to be unearthed!

Thanks for watching this episode of SciShow News! And an extra special thanks to our President of Space, Matthew Brant. Matthew, we think you're pretty DINO-mite!

And we really appreciate your continued support. If you want to be President of Space, or just support us so we can keep making videos like this one, head on over to Patreon.com/scishow to learn more about becoming a patron. And be sure to swing by every Friday to keep up to date on the latest science news! [♪ OUTRO].