Over half a billion years ago, an early shrimp-like creature was swimming along the sandy floor of an ocean with its young in tow, before the whole group was buried in fine sediment.
Now, 520 million years later, the remains of the early arthropod – the group that includes crabs, spiders, centipedes, and butterflies – are providing some of the strongest evidence yet of the earliest parental care in the fossil record, according to a new study in preprint on bioRxiv.
The fossil was collected from the Chiungchussu Formation, in the Kunming region of South China. This site dates to the early Cambrian period when the oceans were dominated by soft-bodied animals, meaning life was less likely to be preserved in the fossil record. This is what makes the incredible number of fossils of marine creatures yielded from this formation so important.
Over the years, researchers have unearthed many Fuxianhuia protensa fossils in South China spanning a range of different growth stages, from smaller juveniles to larger, older adults, allowing those studying the fossils to build up an amazingly clear picture of how the ancient creatures aged. Curiously, surrounding the preserved body of one adult, scientists noticed four much smaller individuals.
From their morphology, the researchers can say with some confidence that they are indeed juvenile versions of the adult, and by counting the number of segments in their bodies, deduce that they were most likely the same age. This raises the possibility that all four of the young Fuxianhuia came from the same brood.
The fact that they were found with the adult – which the researchers are sure was buried and preserved at the same time rather than at an earlier or later date – suggests that it may have been the parent. Obviously this is impossible to prove with any certainty, but the researchers argue in their paper this is a convincing case from the fossil evidence that these early arthropods were indeed practicing parental care.
This might sound like a stretch for something that was basically an early shrimp, but we already know that 508 million years ago some early animals were carrying their eggs under their shell for protection. While we tend to think of it as something only "higher" animals undertake, parental care among arthropods is not actually that unusual.
Paternal care alone has evolved at least 13 times independently in the taxa, and there are many other examples of mothers looking after not only their eggs but also their newly hatched young. Spiders and scorpions will often carry their brood on their backs, while some male crustaceans will build burrows in which they can protect their offspring.
Why this particular animal evolved parental care so early on, is still not known, but likely related to the environment.
[H/T New Scientist]