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The big-eyed spiders were likely guarding their egg sacs and possibly tending to the already hatched spiders when they were trapped in sticky tree resin around 99 million years ago. This resin has hardened, enclosing these arachnid moms in four pieces of amber recently mined in Myanmar, and now considered the oldest evidence of spider mothering, according to the researchers.
While the find is not unexpected, given that many spider mothers take care of their offspring these days, “it’s nice to have real physical evidence through these little snapshots in the fossil record,” studies Co-researcher Paul Selden, a distinguished professor emeritus in the Department of Geology at the University of Kansas, told Live Science.
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Of the four pieces of amber, the most extraordinary is a piece holding a large female spider with part of an egg sac under it, Selden said. This spider’s facial appendages, thornless legs and trichobothria, or “sensing hairs,” indicate that it is part of the Lagonomegopidae family, a now extinct group of spiders that lived in the northern hemisphere. during the Cretaceous period (145 million to 66 million years ago). The mother’s protective position on her egg sac suggests maternal care, Selden said.
“The female holding an egg sack with tiny little spiders inside – this is exactly the position you would find female spiders guarding their eggs in,” which may also have helped keep the eggs warm. , Selden told Live Science. “So, this is really typical female spider behavior captured in an instant by this process of fossilization.”
Amber even preserved the silk thread that enveloped the spider’s eggs. Some scientists believe that spiders originally used silk to group their eggs, and then later used it for other purposes, such as webs, Selden noted.
The other three specimens contain spiders – one with 24, another with 26, and a third with 34 hatchlings – as well as a few silk spider threads, arthropod legs, and a wasp. It is likely that each room contains a unique group of spider siblings, as the hatchlings in each specimen are roughly the same size. They also have characteristics of Lagonomegopidae, including two large eyes at the front of the head, much like jumping spiders today, the researchers said. These large eyes indicate that the lagoonomegopid spiders were probably free hunters rather than website builders, because spiders that make webs usually have poor vision.
One of the amber specimens with hatchlings contains pieces of detritus entwined with spider silk, which may have been part of a nest the mother built to keep her egg sac. This suggests that the hatchlings stayed with their mothers in the nest after the hatch, rather than immediately dispersing, the researchers said.
However, these spiders encountered a sticky end when they got trapped in the tree resin, which eventually hardened to amber. The newborns likely died soon after emerging from their eggs, and some of the arthropod appendages kept next to them could be their mother’s legs, the researchers said.
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Ethical considerations
The four pieces of amber were mined in Tanai, a village in northern Myanmar before 2017, when the Myanmar armed forces, known as Tatmadaw, took control of the country’s amber mines and began to pocket the profits. Scientists are strongly discouraged from studying the amber fossils mined after the takeover, to avoid funding the Tatmadaw, which took control of the whole country of Myanmar (not just the mines) in a coup. ‘Military status in February 2021, according to a letter from the Society of Vertebrate Paleontology.
The four amber specimens are now housed at the Key Laboratory of Insect Evolution and Environmental Changes, College of Life Sciences at Capital Normal University in Beijing, China, where study co-investigator Dong Ren is curator.
The study will be published online Wednesday (September 15) in the journal Proceedings of the Royal Society B: Biological Sciences.
Originally posted on Live Science.
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