Named after the Atlas Mountains of Morocco where its fossil remains were discovered, Atlasaurus lived during the mid-Jurassic period, around 168-165 million years ago. While it wasn’t the strangest–lookingsauropod by any means, compared to other species its body proportions still show a particularly bizarre combination of features, with a slightly bigger head, unusually short neck, and very long slender legs that made up nearly half of its 9m height (29’6″).
It’s sort of the uncanny valley of sauropods. Everything about it is just a tiny bit wrong.
Its tall shoulders and sloping back resemble the body plan of brachiosaurids so closely that it was initially thought to be an early member of that group, but more recent studies suggest it may have been part of an earlier evolutionary branch of sauropods known as the turiasaurs – which would mean its brachiosaur-like shape was actually the result of convergent evolution.
But what was it doing with such weird proportions?
…We really don’t know. Other short-necked sauropods seem to have been adapted for feeding on lower vegetation only a couple of meters off the ground, but Atlasaurus’ leggy build would have made it a high browser like the brachiosaurids it was mimicking. Its long legs may also have allowed it to move faster, or given it some advantage navigating over rough terrain, but since no other sauropod ever seemed to evolve this way it must have been doing something particularly unique.
Or perhaps it was just an evolutionary fluke. Maybe part of a lineage that had started adapting to short-necked low browsing, then moved back towards the high browsing niche – and happened to end up lengthening their legs instead of their necks to get the necessary height back.
Originating from Japanese monster movies like Godzilla, the word “kaiju” is now often used to refer to giant creatures in general – and so it was only a matter of time before a huge sauropod dinosaur was named after the concept.
Kaijutitan maui* was a titanosaur living in Argentina during the Late Cretaceous, about 89-86 million years ago. It’s only known from fragmentary remains, so its full size is difficult to estimate, but it was probably somewhere in the region of 20m long (66′). Nowhere close to the largestsauropod, but possibly one of the heaviest since it does seem to have been rather chunkily built, with stout limbs and an estimated weight of 40-60 tonnes (44-66 US tons).
* Not named for the Polynesian hero, apparently, but for the initials of the Museo Argentino Urquiza.
Did you know butterflies weren’t the first insects to look like butterflies?
Lepidopterans (the group of insects containing moths and butterflies) have been around since the Late Triassic – but it wasn’t until the diversification of flowering plants during the Cretaceous that recognizable moths would have evolved, and true butterflies didn’t actually appear until the early Cenozoic.
Known as the kalligrammatids, these insects were giant members of the lacewing group, related to modern forms like antlions and owlflies. But unlike their predatory relatives the kalligrammatids were specialized pollinators, possibly having a mutualistic relationship with the flower-like cones of bennettitales or the pollination drops of some types of conifers. They seem to have originated in China and were found across Asia and Europe by the Late Jurassic, but a few fossils from South America suggest they were even more widespread and may just have a poor fossil record.
They reached wingspans of up to 16cm (~6″), comparable to some of the largest modern butterflies, and often sported conspicuous anti-predator markings on their wings such as stripes and eyespots – so it’s not surprising that they’re often nicknamed the “butterflies of the Jurassic”.
Rather ironically, the extinction of the kalligrammatids was probably linked to the rise of the flowering plants that the true butterflies would later be so dependent on. As flowers diversified and plants like the bennettitales declined, the kalligrammatids dwindled and disappeared, with the last known fossil record coming from the mid-Cretaceous of Brazil about 113 million years ago.
But while they were around, I do wonder if they also exhibited some similar behaviors – such as mud-puddling for extra nutrients, and specifically the habit of drinking the tears of larger animals that we see in some species. Perhaps some non-avian dinosaurs like this Dilong occasionally put up with kalligrammatids sitting on their faces!
For around 50 years some very unusual dinosaur tracks have been found in ancient desert sediments in South America: strange footprints showing the impression of only a single toe, a walking style never before seen in any reptiles.
And recently a fossil of what might be the track maker has actually been found.
Measuring about 1.5m long (~5′), Vespersaurus was fairly lightly built with legs proportioned for running – and its feet were absolutely unique. Although it had the standard three main toes of a theropod, it bore its weight entirely on the middle toe and held the other digits off the ground. The two raised toes on each foot also had large knife-like claws which may have been used during hunting, vaguely similar to the sickle claws on the feet of dromaeosaurs. But unlike dromaeosaurs these claws weren’t highly curved or pointed, suggesting Vespersaurus used more of a scratching and slashing technique rather than the raptors’ puncture-and-restraint strategy.
Much like ancient horses, it may have developed its single-toed stance as an adaptation for more efficient fast running, possibly to avoid larger predators or to chase down small fast-moving prey like hopping desert mammals.
The known one-toed fossil footprints are actually slightly older than the Vespersaurus fossil, and similar tracks in Argentina have been found dating back to the Late Jurassic (~150mya), so there may have been a long lineage of “one-toed” desert-dwelling noasaurids in South America that haven’t been found yet.
Many modern birds are capable of seeing into the ultraviolet regions of the electromagnetic spectrum, and some of their non-avian dinosaur ancestors might have had the same sort of vision. And much like their living relatives, that means various parts of their bodies and plumage may also have been UV-reflective and UV-fluorescent.
So here’s a Velociraptor with some speculative UV coloration – although this is just what it would look like to human eyes under a blacklight. What it would actually look like to a creature that can see extra colors is impossible to depict on a screen designed for trichromatic vision!
It had a chunkier build than its closest relatives, with a deep skull, a large beak, and a rotund body. Like other rhabdodontids it would have had powerful jaw muscles and ridged cheek teeth specialized for scissoring, adaptations for cutting up particularly tough plant matter.
It was also quite small, about 2.4m long (7’10”), although since the largest known fossils represent subadults this may not have been its full size. A second species in the same genus (Zalmoxes shqiperorum) lived on the same island and was actually slightly bigger, suggesting that Z. robustus represented a minor case of insular dwarfism.
At the very end of the Cretaceous period, between about 72 and 66 million years ago, tectonic uplift from the start of the formation of the Alps created an island in the area corresponding to modern-day Romania.
Known as Hațeg Island, after the region where fossils of the native species were found, it was similar in size to Hispaniola and was surrounded by deeper waters than most of the other European archipelago islands.
Magyarosaurus here was was a titanosaur living on this island, and was one of the smallest known of all sauropod dinosaurs at just 6m long (19’8″). Much of that length would have been in its neck and tail, and its body was only actually about the size of a horse.
Like some other titanosaurs it had bony osteoderm armor along its back, although since only one isolated piece has been found the exact arrangement isn’t known.
A layer of rock just above the deposit of Europasaurus fossils also gives us a clue about their eventual fate. Footprints of large carnivorous theropods – bigger than the mini-sauropods themselves – suggest that at some point the sea level dropped and predators from the mainland were able to reach the island.
Since there were no large predators on the island before then,the small Europasaurus had no defenses against these new giant invaders. They very likely were literally eaten into extinction.
Islands are natural sites for evolutionary experiments. Their isolation and limited resources put a lot of selective pressure on their native species, often resulting in spectacular and unique adaptations. Big animals become small, small animals become big, and ecological niches can end up being filled in unexpected ways.
From the dodo becoming the first well-known example of human-caused extinction, to Darwin’s Galápagos finches being influential in the development of the theory of natural selection, to famous-but-endangered living examples like the kiwi and marine iguana, island species are fascinating and often fragile examples of how diverse life can get even in restricted conditions.
In fact, this theme ended up containing so many species I wanted to feature that I can’t possibly fit them all into just a single month. So, for the first time, a theme is going to need two months – with part 1 happening right now, and part 2 coming later this summer.
For much of the Mesozoic Europe was an archipelago of islands in a shallow tropical sea. During the Late Triassic, about 205-201 million years ago, some of the paleo-islands in this region existed around southern Wales and South West England, near the city of Bristol.
Thecodontosaurus was actually one of the first non-avian dinosaurs ever named by modern science, discovered in the mid 1830s – several years before the term “dinosaur” was even created to classify the “great ancient lizards”.
It was an early member of the herbivorous sauropodomorphs, the group that would eventually include the largest ever land animals. But unlike its enormous later cousins it was short-necked and bipedal, and was particularly small compared to other contemporary “prosauropods”, measuring only about 2m long (6′6″). This would make it one of the oldest known examples of insular dwarfism.
Qianzhousaurus sinensis, a tyrannosaur from the Late Cretaceous of southern China (~72-66 mya). Measuring about 9m long (29′6″) it had an unusually long and slender snout for a tyrannosaur, leading to its nickname of “Pinocchio rex”.
The only other known long-snouted tyrannosaur was the closely related Alioramus from Mongolia – but since only juveniles of that genus have been found so far, it’s also possible that Qianzhousaurus was actually just a fully-grown species of Alioramus.