Researchers have uncovered the oldest known fossil of a viviparous snake. Fossils of Messelophis variatus found in the Messel Pit show that this species existed 47 million years ago. According to the fossil, the boa was pregnant with at least two young at the time of its death. Her offspring had settled in the back of her body and were already grown.
Not far from Darmstadt, the Messel Pit is often visited for its well-preserved snake fossils. Evidence that ancient snakes had infrared vision and the oldest known python were discovered here by paleontologists.
In the Messelboa Messelophis variatus, paleontologists have discovered the bones of at least two juveniles (shown by orange).
There are still many unanswered questions about the evolution of snakes. These include the time when snakes began to give birth to live young instead of eggs. At that time, many snake species preferred live births to egg-laying, which is the norm for most reptiles today. Like us, they carried their young inside them until they were ready to be born, where they were raised in safety. Until today, it was not known when snakes first started using this tactic.
Fossilized Pregnant Snake
Thanks to the efforts of a team led by Mariana Chuliver from the Fundación de Historia Natural in Buenos Aires, Argentina, this enigma is about to be solved. The pregnant boa fossil was found by paleontologists in the 47 million-year-old Messel Pit sediments. It is the first time a live snake has been documented in the fossil record. According to the researchers, only two other viviparous reptile fossil records have been found globally so far, and neither of them was a snake.
The new description relates to Messelophis variatus boa, which is about 50 centimeters long and one of the most common fossil snake species found in the Messel Pit. Some of the skull bones in the fossil were identified as belonging to small boas no longer than 20 centimeters. These bones are located well back in the stomach; if they had been the snake’s prey, they would have decomposed so far back in the gut that they would be unrecognizable. The snake, which was too far along to lay eggs, was carrying at least two young.
Live Birth Despite the Environment
But the science team is baffled by the snake: Viviparity among modern reptiles occurs almost exclusively in cold environments. The embryo is better protected from the cold if the mother’s internal temperature is more stable than the ambient temperature. But the Messelophis snake did not have to deal with cold temperatures because of the environment in which it developed. Typical temperatures in the Messel region were around 20 degrees Celsius and never dropped below freezing, even in the middle of winter.
Although scientists cannot explain why the Messel pit boa gave birth to live young, they suggest that there may have been advantages for the offspring beyond protection from the cold. Perhaps other fossils found in this region can help people answer this riddle.
