Tag Archives: archosaur

Illustration of Antarctanax shackletoni sneaking up on an early titanopetran insect. Credit: Adrienne Stroup, Field Museum.

‘Lizard king’, an early dinosaur ancestor, ruled over lush Antarctica more than 250 million years ago

About 250 million years ago, Antarctica wasn’t the barren frozen landscape we know today but rather a lush landmass covered in forests and rivers. Naturally, all sorts of wildlife lived here, among them a newly identified iguana-like ancestor to crocodiles and dinosaurs.

Illustration of Antarctanax shackletoni sneaking up on an early titanopetran insect. Credit: Adrienne Stroup, Field Museum.

Illustration of Antarctanax shackletoni sneaking up on an early titanopetran insect. Credit: Adrienne Stroup, Field Museum.

Technically, Antarctanax shackletoni — the genus means “Antarctic king” while the latter name denoting the species is a tribute to polar explorer Ernest Shackleton — is an archosaur. These were the direct ancestors of the dinosaurs and crocodiles, evolving from more primitive reptiles in the Triassic, following the Permian mass extinction. The evolution of archosaurs signifies an important milestone in the history of terrestrial life, and fossils such as A. schackletoni, which is one of the first members of this group, help paint a broader picture of how dinosaurs evolved and spread.

Radiocarbon dating suggests that the lizard-like archosaur lived only two million years after the Permian mass extinction event that wiped out 90% of all animal life. In the aftermath of cataclysmic volcanic eruptions and subsequent climate change, most ecological niches were left blank and opportunistic lineages soon stepped up to fill the voids. Archosaurs were one of the groups that profited the most from Earth’s biggest mass extinction, rapidly colonizing the whole planet. Before the event, the group was mostly confined to areas around the equator.

The incomplete fossilized specimen was described by a research team led by Brandon Peecook, a Field Museum researcher. Despite missing bones, the researchers could tell from the fused vertebrae that their specimen was an adult measuring about 4 to 5 feet (1.2 to 1.5 meters) in length. Other, more subtle hints provide insight into the animal’s ecology. For instance, the shape of its limbs suggests it lived on the ground and did not climb trees or burrow.

However, the most interesting thing about this reptile is where it lived. It suggests that Antarctica was a thriving environment for the rapid evolution and diversification of life after the mass extinction.

“The more we find out about prehistoric Antarctica, the weirder it is,” said Peecook in a statement. “We thought that Antarctic animals would be similar to the ones that were living in southern Africa, since those landmasses were joined back then. But we’re finding that Antarctica’s wildlife is surprisingly unique.”

“Antarctica had a combination of these brand-new animals and stragglers of animals that were already extinct in most places—what paleontologists call ‘dead clades walking.’ You’ve got tomorrow’s animals and yesterday’s animals, cohabiting in a cool place.”

The findings appeared in the Journal of Vertebrate Paleontology.

Crocodilians use sticks to attract prey

  • Two distinct groups of crocodilians have been reported to use tools for hunting
  • They balance sticks on their snouts, baiting birds who want to use the sticks for nests
  • Crocodiles actively search for the sticks (which are usually rare) and do this more often during the birds’ mating season

Mugger crocodile (Crocodylus palustris) at Madras Crocodile Bank, Tamil Nadu, India, with sticks on its head. Image credits: Dinets et al. (2013).

It’s been known for quite a while that the usage of tools isn’t restricted to humans. Monkeys (of course) also use tools, but this type of behavior has also been reported in other species, including crows, dolphins, elephants and otters. Now, a new study has reported that crocodiles and alligators also use sticks to attract prey.

In recent years, reptile research has provided some stunning results, showing that they are not only cold-blooded efficient killers, but that they exhibit a myriad of remarkable behaviors. Play behaviour, complex social interactions, gaze recognition, pair-bonding and monogamy, social hunting, speedy learning abilities and good memories – they have all been reported in reptiles.

Now, another very interesting unexpected adaptation has been demonstrated across these groups: tool usage.

As described by Dinets et al. (2013), Mugger crocodiles Crocodylus palustris in India and American alligators Alligator mississippiensis in the USA have been observed to lie, partially submerged, very close to birds they want to hunt, with sticks balanced carefully on their snouts. Birds want to take the sticks to use them in their nests and… let’s just say it usually has a very bad ending for the birds.

But what’s remarkable is that this occurrence of stick usage by crocodilians isn’t random! Stick displaying took place consistently more often with crocodiles living closer to rookeries, and it also took place more often during mating season – when birds are more inclined to construct nests. It’s also noteworthy that sticks are pretty rare in this type of environment – the reptiles actively search for them, especially during the birds’ mating period.

Baiting behavior was demonstrated before in archosaurs (the big group of species which includes crocodiles, birds and all extinct dinosaurs). Green herons (Butorides virescens) often do it: they use feathers, twigs and even berries and bits of bread to attract fish, while burrowing owls (Athene cunicularia) use mammal dung to attract dung beetles. Also, anecdotal reference suggests that crocodiles also use fish fragments to attract birds. But the fact that this has been consistently reported in two separate groups seems to suggest that this type of behavior is mainspread.

If you think about it, crocodiles have been around for over 70 million years – since the Cretaceous. They are incredibly well adapted to the environment, being able to live as scavengers and survive for months without food. They can even go into a state of hibernation when conditions aren’t favorable, waking up when things are looking up. So it makes sense that they learned a trick or two about hunting.