The family of spiders Lagonomegopidae is now extinct, but spiders have a long history and appeared during the Carboniferous period between 359 and 299 million years ago.
One “shows a female lagonomegopid spider grabbing an egg sac containing eggs about to explode (small pre-hatches can be seen inside the egg sac),” said study author Paul Selden, Distinguished Professor Emeritus of Gulf-Hedberg at the University of Kansas, in an email. “It’s exactly the appearance of a live female spider lying in a crevice in tree bark (in this case, just before it was flooded with tree resin).”
Other pieces of amber show a group of tiny spiders that had just hatched. This shows that a female lagonomegopida spider protected the egg sack from harm. Once the spiders came out, they stayed together and were guarded by their mother, as evidenced by the Lagonomegopidae leg fragments of the same piece of amber.
This suggests that the spider creatures probably clung to their mother for some time after birth.
The researchers were pleasantly surprised by “how everything fit very well in place. We had about three copies that all corroborated each other in history,” Selden said.
The researchers used computed tomography to detect tiny eyes and other features that revealed the identity of the spider and the tiny spiders in 3D detail.
Lagonomegopidae spiders can be distinguished because they had a large pair of eyes located in the anterior corners of the head. Other known fossils of these spiders have been revealed to have reflective tapetum in their eyes, similar to other nocturnal creatures; think of the way a cat’s eyes flicker in the dark.
These now extinct spiders look similar to modern jumping spiders, but 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 their beginnings, however, it’s great to have real physical evidence of the fossil record about 100 million years ago,” Selden said.
But what does maternal care really mean, observable in many species of living spiders today?
“Parental care refers to any investment made by parents that improves the adequacy of their offspring and often to a cost for the future survival and reproduction of the parents,” the researchers wrote in the study. “Their evolution represents a breakthrough in the adaptation of animals to their environment and has significant implications for the evolution of society.”
Other arthropods that present this type of care include insects and crustaceans.
Selden and his colleagues will continue to look for “other cases of behavior frozen in time.”