The third episode of Prehistoric Planet takes viewers away from the scorching sands, and into freshwater environments.
The opening scene of “Freshwater” focuses on a trio of Velociraptor as they ambush a pterosaur, which may be an homage to Planet Earth‘s stunning footage of snow leopards. It also appears to reference a fossil discovery in which a pterosaur bone was discovered as part of the stomach contents in a Velociraptor fossil, though the paper makes clear that this instance was likely a case of scavenging, due to the size of the pterosaur.
Prehistoric Planet then returns to North America, and to T. rex. This scene sets out to obliterate some misconceptions about the world’s most infamous dinosaur. The first is that Tyrannosaurus was a scavenger, as this male T. rex is shown to have killed (off-screen, for the children) a Triceratops. The binary of hunter vs. scavenger is largely a human conception — few terrestrial carnivores will pass up a free meal, and even animals characterized as scavengers, like the spotted hyena, will do quite a bit of hunting.
Furthermore, a study by Thomas Holtz showed that late Cretaceous ecosystems of Asia and North America dominated by tyrannosaurs lacked many of the mid-sized carnivores that were in earlier ecosystems (so there weren’t any other carnivore species to scavenge from). The implication is that younger tyrannosaurs would have occupied the ecological niches normally filled by mid-sized carnivores.
The second misconception is that female Tyrannosaurus were larger than males. That might have been true, but it’s nearly impossible to determine the sex of an extinct dinosaur, and harder still to get a substantive enough dataset to determine if females were larger as a rule, or it’s just that larger female individuals fossilized. That being said, there’s one way to try to determine if a dinosaur was female — by examining the medullary cavity in the bone.
In birds, the medullary cavity will fill with calcium in preparation for laying eggs. This only occurs when the bird is pregnant, but if you find a fossil with the medullary cavity filled, this could mean that you’ve got a female that wass pregnant. Such an examination was done on a Tyrannosaurus specimen, which found fossilized tissue that appeared consistent with medullary bone, suggesting the specimen was female, but there’s still more work to be done before anything like a sex-size correlation can be determined.
As far as mating behavior goes, a 2017 study did show that a relative of Tyrannosaurus, Daspletosaurus, had scales along its face that showed a strong correlation with the facial sensory organs of crocodilians, so a pair of nuzzling Tyrannosaurus rex is pretty reasonable.
Prehistoric Planet then returns to Central Asia, but this time to a flooded delta and the truly amazing Deinocheirus mirificus. Hailing from the Nemegt formation in Mongolia, Deinocheirus was described in 1970 by Halszka Osmólska et al from a pair of massive arms, eight feet long from shoulder to finger. From these arms, it was determined that this was a theropod, but the exact nature of the animal was unknown. And it remained that way for over 40 years.
But in 2012, it was announced that much of the original specimen had been found, and in 2014, the description of the animal was published. The result is the bizarre animal depicted in Prehistoric Planet, a giant ornithomimid (like Gallimimus) with an oddly proportioned skull, and elongated spinal vertebrae that may have supported a fatty hump. While we don’t know definitively if the massive Deinocheirus was covered in feathers as depicted in the show, two of its tail vertebrae were fused together in a manner resembling the pygostyles from relatives like therizinosaurus. Pygostyles in birds help support feathered tail fans, suggesting that Deinocheirus also had a fan of feathers along its tail.
The last stop in this episode of Prehistoric Planet takes viewers to southern Africa, and one of the more speculative depictions in the show thus far. The scene begins with the giant azhdarchid Quetzalcoatlus arriving. Quetzalcoatlus is not known from remains in Africa; in fact, the only conclusive fossils of Quetzalcoatlus are from the United States, but azhdarchids have long been believed to be quite efficient flyers and thus able to travel long distances via thermal soaring.
One of the beauties of science is that it keeps moving, and new analyses keep arriving, and published just this year was a study by Yusuke Goto et al that called into question the soaring capabilities of azhdarchids like Quetzalcoatlus, and concluded they were likely short-range fliers. That lack of efficiency doesn’t necessarily mean that they couldn’t cover greater distances, though, and given the diverse range of azhdarchids, it’s possible that southern Africa may have had its own local pterosaurs, as well. For those interested in reading more scientific literature on Quetzalcoatlus, the Journal of Vertebrate Paleontology published a massive special edition on them last year, and it’s all open access.
The next animal viewers are introduced to also helps peg down where in southern Africa we are — Masiakasaurus knopfleri is known from the Maevarano formation in Madagascar. The depiction of Masiakasaurus also features a piece of speculation, in that it’s depicted with fine, delicate feathers between its scales. This is interesting because Masiakasaurus is only distantly related to the coelurosaurs (the group that includes tyrannosaurs, dromaeosaurus, ornithomimids, alvarezsaurs, therizinosaurs, oviraptorosaurs, troodontids, and birds, all of which have direct evidence of feathers).
Masiakasaurus is actually a noasaurid, a type of ceratosaur, and thus a member of a more basal theropod lineage. Outside of the coelurosaurs, it’s unclear how widespread feathers were in dinosaurs. Animals like Psittacosaurus and Kulindadromeus both had integument that might have been feathers, which would make feathers an ancestral trait for all dinosaurs.
Furthermore, an April 2022 study of the fluffy pycnofibers that covered pterosaurs showed that those structures may also have been feathers, which would push the structure’s origin back to well before the dinosaurs. This doesn’t mean that all dinosaurs had feathers, but it does mean that we might see them in species we might have otherwise assumed lacked them.
Prehistoric Planet‘s poor Masiakasaurus hatchling is attacked by the giant frog Beelzebufo ampinga, which has been found in the Maevarano formation with Masiakasaurus. It’s important to remember that we’re dealing with small animals here — Beelzebufo was large for a frog, but it wasn’t a monster. Recent estimates having its snout-to-vent length as 245 mm (or just over 9.5 inches).
The final scene of “Freshwater” depicts a group of elasmosaurs swimming through the brackish waters near the shore. No elasmosaur fossils have yet been found in Madagascar but, as mentioned in the breakdown of episode 1, elasmosaurs as a group had a global distribution, so they almost certainly would have been prowling the seas off the island. And while elasmosaurs are most well known from marine sediments, animals like Fluvionectes have been found in non-marine environments, so seeing some of these reptiles in rivers is possible, too.
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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