Hibernation is a common defense mechanism where an animal moves to a state of minimal activity to survive tough winter months - and new fossil suggests that it occurred back in the Early Triassic period.
The latest research was conducted by Megan R. Whitney, postdoctoral researcher from Harvard University, and Christian A. Sidor, professor of biology from the University of Washington. Together, they reported fossil evidence suggesting the existence of an animal that went into a "hibernation-like" state. The Early Triassic animal lived in what is now Antarctica, about 250 million years ago.
Their findings were published in Communications Biology last August 27.
Evidence of Torpor from the Early Triassic
Researchers used its tusks to check stress differences between those who lived in polar environments as opposed to those who are in the warmer areas such as the African continent. They compared the frequency and patterns of growth marks in tusks of these non-mammalian Lystrosaurus, from those found in Antarctica to those from the Karoo Basic in South America.
The tusks were able to provide additional information because they can also record the time elapsed, similar to tree rings used in dating plants. They traced dentine, a major tissue that is hard, dense, and bony, deposited during two events: (1) regular incremental growth, as well as (2) in times of arrested growth, which reflects metabolic stress.
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Due to the lack of specific time period corresponding to each "growth mark," researchers adopted an "agnostic terminology" to reflect growth patterns, noting a baseline that will serve as their reference in dating the tusks.
Researchers were able to discover that prolonged stress was consistent among animals that experienced torpor - state of inactivity or torpor, such as hibernation. Those found in the lystrosaurus fossils are the oldest known instances of torpor drawn from fossil evidence.
"These preliminary findings indicate that entering into a hibernation-like state is not a relatively new type of adaptation. It is an ancient one," Whitney said in a UW press release.
Sidor explains that they looked at something that can fossilize, like the tusks, and that grows continuously through the animal's life, as is the case with the Lystrosaurus.
Limitations in the study restricted the confirmation of the Lystrosaurus case as "hibernation" as we know it in modern animals. Furthermore, the stress found in the tusks might be caused by another form of short-term torpor.
The Lystrosaurus
The fossils examined in the study belonged to an animal known as the lystrosaurus, or "shovel lizard." It was a herbivorous genus of therapsid - a group of synapsids that include the early mammals.
It is roughly the size of the modern pig, with tusks similar to elephants and a beak like those found in turtles. Its only teeth are its pair of tusks, with the turtle-like beak being used for biting off pieces of vegetation, which constituted the majority of its diet.
Lystrosaurus survived an extinction event some 252 million years ago, known as the Permian-Triassic extinction. Scientists in the study believe that this torpor among lystrosaurus might help explain their survival at the transition between the Permian and Triassic periods.
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