Prehistoric spider that cared for its young was trapped in amber 99 million years ago

(CNN) – Nothing stands between a fiercely protective spider mother and her young. Resin dripping from the trees trapped the adult female spider and her little spiders about 99 million years ago, forever showing the maternal care of these arthropods, according to new research.

The Lagonomegopidae family of spiders is now extinct, but spiders have a long history, first appearing during the Carboniferous period between 359 and 299 million years ago.

The fossilized pieces of Burmese amber tell two different stories. A study detailing observations of amber samples was published Tuesday in the journal Proceedings of the Royal Society B: Biological Sciences.

One “shows a female lagonomegopid spider grasping an egg sac containing eggs about to hatch (you can see the tiny pre-hatchlings inside the egg sac),” said study author Paul Selden, Gulf-Hedberg Professor Emeritus at the University of Kansas, in an email. “This is exactly what a live female spider in a crack in the bark of a tree would look like (in this case, just before being drowned in tree resin).”

This illustration shows a female lagonomegopid spider protecting her egg sac in a Cretaceous forest.

Other pieces of amber show a group of tiny hatchlings that had just been born. This shows that a female lagonomegopid spider protected her egg sac from harm. Once the young hatched, they remained together and were guarded by their mother, as evidenced by fragments of Lagonomegopidae legs from the same piece of amber.

This suggests that the spider pups likely stayed close to their mother for a time after birth.

The researchers were pleasantly surprised by “how beautifully everything fell into place. We had three or more specimens that corroborated each other’s story,” Selden said.

The researchers used a CT scan to detect tiny eyes and other features that revealed the identity of the spider, as well as the tiny hatchlings in 3D.

Lagonomegopidae spiders can be distinguished by having a pair of large eyes located at the front corners of the head. Other known fossils of these spiders have revealed that they had a reflective mat in their eyes, similar to other nocturnal creatures; think, for example, of the way a cat’s eyes glow in the dark.

These now extinct spiders look like modern jumping spiders, but they are not related at all.

Spiders are known to exhibit maternal care, but fossilized examples of this are extremely rare.

“While we expected spiders to have maternal instincts from the beginning, it is nevertheless very nice to have actual physical evidence from the fossil record from about 100 million years ago,” Selden said.

But what does maternal care really mean, seen in many species of spiders alive today?

“Parental care refers to any investment by parents that improves the fitness of their offspring and often at a cost to the survival and future reproduction of the parents,” the researchers wrote in the study. “Its evolution represents a great advance in the adaptation of animals to their environment and has important implications for the evolution of sociability.”

Other arthropods that exhibit this type of care include insects and crustaceans.

Selden and his colleagues will continue to search for “other cases of behavior frozen in time.”