Paleontologists have discovered the fossilized jawbone of a previously unknown ancient animal in a dry riverbed deep in a forest near the Brazilian Amazon. As the excavation continued, the team discovered eight more similar jawbones, each about 6 inches long. However, no additional bones apparently consistent with a complete skeleton were recovered.
Still, these isolated jaws revealed something remarkable. This fossil belongs to a species that lived about 275 million years ago, and would have been considered a “living fossil” even then. The jaw was also very unusual and had a twisted shape. Some of the teeth are oriented outward and sideways, and the inner surface is lined with rows of small teeth. This structure suggests that this animal may have been one of the earliest of its kind to grind plant material.
name a strange new species
In a study published in Proceedings of the Royal Society Bresearchers formally described this species and named it Tanica amnicola. The name Tanica comes from the indigenous Guaraní language, meaning “jaw”, and Amnicola means “living by the river”.
“Tanika belongs to an ancient lineage that we didn’t know survived until now, and it’s also a very strange animal. It has a strange twist in its jaw that drove us crazy trying to figure it out. We’ve been scratching our heads for years wondering if this is some kind of deformity,” says study lead author Jason Pardo, who worked on the project during a postdoctoral fellowship at Chicago’s Field Museum. “But so far, nine jaws have been taken from this animal, and they all have this twist, including some that are really well preserved. So it’s not a deformity, it’s just the way this animal was made.”
ancient branch of tetrapod
Tanica belongs to the broad group of vertebrates known as tetrapods, which includes all four-limbed animals with backbones, such as reptiles, birds, mammals, and amphibians. The earliest tetrapods, called pedunculated tetrapods, eventually split into two large branches. One group evolved to lay eggs on land, leading to reptiles, birds, and mammals. The other group continued to lay eggs underwater, giving rise to modern amphibians such as frogs and salamanders.
Even after this split, some tetrapods continued to exist alongside their more recently evolved relatives. Tanika was a holdover from an old family line.
A similar pattern is seen in mammals. Early mammals laid eggs, but later groups evolved live births. Most modern mammals reproduce by giving birth, but some species, such as the platypus, still retain the trait of laying old eggs.
“Tanika is a bit like the platypus in the sense that it is a remaining member of the stalked tetrapod lineage, even after the evolution of newer, more modern tetrapods. It was really a living fossil back then,” says Pardo, who is now a researcher at the Field Museum and a postdoctoral researcher through Vilnius University in Lithuania.
What did Tanika look like?
Much about Tanika remains unknown, especially her general shape. “We found these jaws on their own, and they’re really strange and very distinctive. But until we find one of those jaws attached to a skull or other bone definitively associated with that jaw, we can’t say for sure that the other bones found nearby are Tanica’s,” says Ken Angielczyk, curator of paleo-mammals at Chicago’s Field Museum, who served as Pardo’s advisor during his postdoctoral research. There, and co-authors of the paper.
Based on comparisons with related species, researchers believe Tanika may have resembled a salamander with a slightly longer snout. Its size is unknown, but estimates suggest it may have reached up to 3 feet in length. Surrounding rocks indicate that it probably lived in a freshwater environment, such as a lake.
Jaws made for crushing plants
Although the rest of the body remains a mystery, the jaw provides a clear clue as to how Tanika fed.
If you run your tongue along your bottom teeth, you’ll notice that they point up toward the roof of your mouth. With Tanyka, this arrangement was completely different. Its lower jaw was twisted, with teeth facing outward instead of upward. At the same time, the inner surface of the jaw, facing the human tongue, was pointing upwards.
This inner surface was covered with tiny teeth called denticles, which formed a rough grinding area similar to a cheese grater. Scientists believe that the upper jaw likely had a similar structure.
“We suspect that the teeth in the lower jaw were rubbing against similar teeth on the upper side of the mouth. The teeth were rubbing against each other, creating a relatively unique feeding method,” Pardo said.
This type of tooth and tooth grinding is usually associated with animals that process plant material. “Judging by its teeth, Tanica is probably a herbivore, eating plants at least at some point in time,” said study author Juan Carlos Cisneros of Brazil’s Federal University of Piauí (UFPI). The researchers note that this is surprising since most quadrupeds are thought to have been carnivores.
Bridging gaps in ancient ecosystems
Tanika’s discovery will help scientists better understand early Permian life. About 275 million years ago, the area that is now Brazil was part of Gondwana, a vast supercontinent that included South America, Africa, Australia, and Antarctica. Fossils from this time and place are relatively rare compared to fossils from regions of the Global North.
“Brazil’s Pedra de Fogo Formation is one of the only windows into the fauna of Gondwana during the early Permian period of Earth’s history, and Tanica tells us how this community actually worked, how it was structured, and who ate what,” Angielczyk said.
This study is co-authored by Jason Pardo (Vilnius University Open-Air Museum), Claudia Marsicano (University of Buenos Aires, CONICET), Roger Smith (Iziko South African Museum, University of the Witwatersrand, Johannesburg), Ken Angielczyk (Open-Air Museum), and Jörg Fröbisch (Natural Fur Museum — Leibniz Fur Institute). Evolution and Biodiversity), Christian Kammerer (North Carolina Museum of Natural Science), and Martha Richter (Natural History Museum, London).
