In a complete reversal of environment from the Mesozoic coastlines, Prehistoric Planet‘s second episode, “Deserts,” takes viewers across some seriously dry landscapes at the end of the Cretaceous Period. This guide is again meant to help break down some of the science on display, so please watch the episode before reading!
“Deserts” opens dramatically in western South America, with the arrival of the mighty titanosaur, Dreadnoughtus schrani. Titanosaurs were the last surviving group of the long-necked sauropods, as many others such as the diplodocids (containing animals like Apatosaurus, Brontosaurus, and Diplodocus), the dicraeosaurids (containing the bizarre Amargasaurus), and rebbachisaurids (such as Nigersaurus) had gone extinct much earlier in the Cretaceous.
Titanosaurs were closely related to the brachiosaurids (containing Brachiosaurus and Giraffatitan), and were incredibly successful, with valid genera from every continent except Antarctica (and given their presence everywhere else, this is likely just a matter of discovery). In fact, every time sauropods are shown in Prehistoric Planet, we can be sure they are titanosaurs.
Dreadnoughtus itself made a splash with its discovery in 2014. With its imposing name, and the relative completeness of its skeleton (it’s hard to bury — and thus fossilize — big things), the genus has quickly become a staple in dinosaur media, having already appeared in the released “prologue” to the upcoming Jurassic World: Dominion, as well as several video games connected to the film franchise.
In Prehistoric Planet, the male Dreadnoughtus are depicted with rows of air sacs that fill as part of a mating display. We don’t know if structures like these were present in any sauropods, as soft tissues rarely fossilize, but given that such extravagant display structures have popped up in birds, lizards, and even mammals, it’s not unlikely that some sauropods could have had displays of their own, even if the exact appearance here is speculative.
Next, Prehistoric Planet takes viewers to Asia. Specifically, due to the animals on display, we can pretty safely say this is Mongolia. We begin with an ancient lizard chasing down flies around a group of sleeping Tarbosaurus bataar. A very close relative of T. rex, Tarbosaurus fossils have often been at the center of smuggling and the illegal fossil trade (if you’re interested in reading more on that, check out The Dinosaur Artist by Paige Williams).
David Attenborough’s narration mentions that temperatures here can soar to 60 degrees Celsius (140 degrees Fahrenheit), but I’m a bit unclear on how they got that number. Using chemical isotopes in Tarbosaurus fossil teeth, Krzysztof Owocki et al were able to examine the climate of the Nemegt Formation in Mongolia, and the conclusions led to a mean annual temperature of about 7-8 degrees Celsius, though the climate was marked by seasonal changes, so the temperatures in the dry season would have soared well above that. It’s very possible that the 60° C figure is correct, but I was unable to find the literature supporting it.
This scene also marks the first appearance of Velociraptor. Prehistoric Planet‘s model is far and away the most accurate screen representation of the animal, fully covered in feathers, hunting prey suitable for its relatively small size, and with its slender snout. I’ve written about the fossil evidence of pack hunting in dromaeosaurs (the group of dinosaurs that includes Velociraptor), or lack thereof, but I do want to say I find it a far smaller leap in speculation to say that Velociraptor hunted in pairs (as seen here) or triads, as opposed to full-blown packs.
I suppose now’s a good time to talk about feathers in non-avian dinosaurs. The first dinosaur to be found with direct evidence of feathers was a small compsognathid, Sinosauropteryx prima, and we’ve found plenty since, including the sizable tyrannosauroid, Yutyrannus hauli. Within dromaeosaurs, both Microraptor and Zhenyuanlong have been found with extensive feather covering, and in Velociraptor itself, quill nobs (places where feathers anchored into the arm bone) have been found, giving us direct evidence that Velociraptor was feathered.
The next animal shown is Mononykus olecranus, a member of a group of dinosaurs called alvarezsaurs. Alvarezsaurs have only recently been described, with Alvarezsaurus calvoi hitting the literature, thanks to the late Argentine paleontologist José Bonaparte, in 1991. Mononykus was initially described by Mongolian paleontologist Altangerel Perle et al as a flightless bird, though later studies proved it to be an alvarezsaur.
As depicted in Prehistoric Planet, alvarezsaurs are believed to have been insectivores, using their short, powerful arms to break into mounds. There’s no direct evidence of alvarezsaurs having the long tongue depicted here, but I also couldn’t find any record of a hyoid bone fossilization in alvarezsaurs, which would help give evidence to support or disprove a specialized tongue. If there’s one complaint I have about this depiction of Mononykus, it’s that the coloration and patterning of its feathers are a little too similar to its inspiration, fellow dinosaur Tyto alba.
The animals displayed here at the oasis all hail from Mongolia, specifically the Nemegt formation. The duckbilled hadrosaurs are Barsboldia sicinskii, the bizarre feathered dinosaurs with the giant claws are Therizinosaurus cheloniformis, the ankylosaurs in the background are either Saichania or Tarchia, and the smaller sauropods are … well, that’s where things get fun.
In the Nemegt formation, there are two named sauropods: Nemegtosaurus mongoliensis and Opisthocoelicaudia skarzynskii. Nemegtosaurus is only known from a skull, while Opisthocoelicaudia is only known from the post-cranial skeleton (that is, everything after the skull). Because we don’t have a body for Nemegtosaurus or a head for Opisthocoelicaudia, it remains to be seen if the latter is a valid genus or simply the missing body for Nemegtosaurus (in which case, the name Opisthocoelicaudia would be declared invalid).
However, as I mentioned in discussing Dreadnoughtus, titanosaurs were extremely successful, and elsewhere in the world, different kinds of titanosaurs have been discovered in the same environments, so it’s possible the Nemegt environment supported multiple genera, especially since the finds we have suggest that Nemegtosaurus and Opisthocoelicaudia weren’t necessarily massive (by titanosaur standards), at around 40 feet long. Recent work has also put into question their potential synonymity.
The massive “Mongolian titan” in this episode of Prehistoric Planet is (I believe) a speculative extrapolation of a find that made headlines in 2016, when a joint Japanese-Mongolian expedition discovered a massive titanosaur footprint. The animal that made the print is still unknown, so it’s possibly also Nemegtosaurus, but until we find actual fossils for the animal, it’s not something scientists can say with any certainty.
Here’s where I want to take a step away from the animals and talk about the scientists behind them. Paleontology is often thought of as a science exclusively for white men, but many Mongolian dinosaurs have been found and described by women. Halszka Osmólska and the late Teresa Maryańska described Barsboldia sicinskii, the name of which honors Rinchen Barsbold, a paleontologist from Mongolia who described Gallimimus bullatus of Jurassic Park fame (with Osmólska), and Wojciech Siciński, who worked as a technical assistant at the Institute of Paleontology in Warsaw, Poland.
Between them and their collaborators, Osmólska, Maryańska, and Barsbold described over 20 genera of dinosaurs still considered valid today, and greatly contributed to our understanding of the diversity of dinosaurs as a whole. This oasis scene would not exist so vividly without their work.
After the time spent in Asia, Prehistoric Planet returns viewers to Barbaridactylus in North Africa. Pretty much everything in this scene is completely speculative — the remains of Barbaridactylus grandis are quite fragmentary, so it’s impossible for us to know how this species would have behaved during mating season. The behavior seen here, with male animals that morphologically disguise themselves as female, is a process known as sexual mimicry, and is seen in a variety of vertebrates. Given that pterosaurs existed for about as long as the dinosaurs did, it’s likely that at least one species utilized similar tactics to what’s seen here.
The final sequence in this episode of Prehistoric Planet focuses on a herd of Secernosaurus koerneri. Hadrosaurs get a bad rap for being boring, so it’s nice that both Barsboldia and Secernosaurus get some attention here, especially since they lack the flashy headcrests of some of their relatives. Secernosaurus does have the “Roman nose,” a feature that identifies it as a member of kritosaurini, a group of hadrosaurs that all had that feature.
Another fascinating thing about Secernosaurus is that it’s from South America. It was long believed that hadrosaurs, who were common in fossil ecosystems in North America and Asia, had evolved after the northern continents had fully split from the southern ones. The discovery of Secernosaurus in Argentina expanded the range of the group considerably. Recent finds like Ajnabia in Morocco have further expanded the group, and it remains to be seen just how many hadrosaurs will be discovered on the continents that once formed Gondwana.
While we tend to think of astronavigation as a human accomplishment, recent research has looked at the various processes through which other animals use celestial objects to navigate. A study on fossilized hadrosaur braincasts does show they had adaptations to hear low frequency sounds, which likely would have helped them with long-distance communication. It’s not a stretch, then, to believe that hadrosaurs might have recognized the waves of the sea and used them to aid their navigation.
Robert Reed will be breaking down the cool scientific notes in each episode of Prehistoric Planet, so keep coming back every day this week!
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