Research published in the Journal Evolution revealed an astonishing finding in frogs. Around 230 million years ago, the progenitors of contemporary frogs permanently lost the teeth along with their bottom jaws. However, this Guenther's marsupial frog was discovered to have teeth.
Daniel Paluh, a herpetologist and a PhD candidate at the University of Florida, performed the study in collaboration with colleagues at the Florida Museum of Natural History. He examined the skulls of six G. guentheri species maintained in alcohol for decades using a micro-CT scanner.
Findings
The findings demonstrate that these teeth are legitimate, produced by bone tissue called dentin and clad in enamel, debunking the possibility that these formations were "pseudo-teeth."
From 230 million years to the present, evolutionary researcher John Wiens used fossil records to recreate the evolutionary connections between 170 species of amphibians and frogs. He discovered that the teeth were lost approximately 20 million years ago and re-evolved around 20 million years ago.
"It's not as if teeth have to be re-evolved from scratch," Wiens explains. "It's simply a matter of relocating them to a location they haven't been in 200 million years."
These data suggest that Dollo's Law of Irreversibility, which states that once a characteristic is lost in a group of organisms, it is lost for good, is inaccurate. According to this logic, a creature cannot re-evolve what its progenitor lost, like human tails.
A researcher at the University of Michigan-Dearborn, John Abramyan, has explored the genes coding for enamel in toads that lost their teeth 60 million years ago. Over millions of years, the genes had degraded into pseudogenes.
How did it regain its lower teeth?
Paluh says that frogs' preference for tiny insects and the use of sticky tongues to catch food reduced the importance of teeth for some species. But G. guentheri eats huge prey like lizards and frogs.
The hefty "Pacman" frogs of South America have sharp teeth along their lower jaws to capture food. Fangs are bony expansions of the jaw that lack dentin and enamel.
An evolutionary researcher named Alexa Sadier believes comparing G. guentheri embryos to other frog species' embryos will reveal how genes control tooth production. She anticipates researchers to uncover more proof of teeth that vanish throughout development if they scan embryos.
G. guentheri hasn't been seen since 1996, and it was rarely examined before that. Less than 30 specimens of the creatures are known to survive in museum collections worldwide. This paucity of research has left many unanswered.
Paluh hopes Guenther's marsupial frog returns as well—not least because living specimens of this amphibian will be critical for knowing more about their teeth and addressing this evolutionary mystery.
