Gansuyaena megalotis, a small-bodied hyaenid that lived in what is now the Chinese province of Gansu between 15 and 12 million years ago (Miocene epoch), represents the closest morphological link to the termite-eating aardwolf (Proteles cristatus) to date.
An artist’s reconstruction of Gansuyaena megalotis. Image credit: Mick Ellison.
“Aardwolves are hyenas, but they are really the strangest of hyenas because they don’t do what other hyenas do, either living or extinct,” said Dr. Jack Tseng, a researcher at the University of California, Berkeley, the American Museum of Natural History, and the Natural History Museum of Los Angeles County.
“They are termite specialists, which couldn’t be any further away from the other hyenas in terms of their ability to crunch bones or cut through meat.”
“So, the aardwolf has always been a really curious mammal that ecologists and paleontologists alike have tried to learn more about.”
Hyenas originated about 22 million years ago, and the aardwolf apparently emerged about 15 million years ago, based on an analysis of their genetic divergence from the three other living hyena species.
But the only recognizable aardwolf fossils are from, at most, 4 million years ago.
Two fossilized skulls of Gansuyaena megalotis may shed light on this mystery.
According to the team, the ancient hyena’s skulls have a broad palate, like the aardwolf, possibly to accommodate a larger, more muscular tongue with which to slurp up termites.
The teeth have wider spacings, also like the aardwolf, suggesting that Gansuyaena megalotis was moving away from a meat-carving diet.
In addition, its middle ears have spacious, dome-shaped chambers, or bullae, that are found in animals, such as some desert rodents and aardwolves, that evolved to increase hearing sensitivity — perhaps to detect the hum of a termite colony.
“Relative to skull size, the bullae are very much enlarged in Gansuyaena megalotis, compared to modern hyenas,” Dr. Tseng said.
“Similar to the extant aardwolf, the fossil also has larger eye sockets for its size than other hyenas.”
While they are not claiming that Gansuyaena megalotis was a direct ancestor of the aardwolf, the researchers conclude that the ancient animal is the closest fossil yet to the aardwolf, showing signs of having diverged from a meat-and-bone lifestyle to something closer to insectivory.
The age of the fossil also fits nicely with the molecular clock estimate of the origin of the aardwolf about 15 million years ago.
“With these fossils, we can really start to get at the question, ‘How does an otherwise very specialized lineage for eating meat have a member, a weird cousin, that started down this totally different path of becoming a specialized insectivore, a termite specialist?’” Dr. Tseng said.
“Now, we have the starting point and ending point, which is today.”
“The next step is to figure out what happened in the intervening 10 million years of this lineage.”
The findings were published in the journal Vertebrata PalAsiatica.
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Henry Galiano et al. 2022. A new aardwolf-line fossil hyena from Middle and Late Miocene deposits of Linxia Basin, Gansu, China. Vertebrata PalAsiatica 60 (2): 81-116; doi: 10.19615/j.cnki.2096-9899.211025
Source link: https://www.sci.news/paleontology/gansuyaena-megalotis-10911.html
