A 520-million-year-old fossil shows an ancient shrimp-like creature caring for its four offspring. It is the oldest ever example of a parent actively looking after its young after they hatch.
The tiny critter, Fuxianhuia protensa, is an arthropod, making it a possible ancestor of modern insects, spiders and woodlice.
There is little evidence of extended parental care in the fossil record. One of the few examples is a .
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We have more evidence of brood care – animals protecting their eggs. This behaviour has been reported in dinosaurs and in a 508-million-year-old . There are also fossils dating from 320 million years ago of fish carrying embryos inside their body. But brood care requires less commitment than parenting.
Fossil family
at the University of Cambridge and his colleagues analysed specimens from the in Yunnan province, China – a trove of marine fossils from the early Cambrian period.
“Fuxianhuia probably spent its days scuttering on the bottom of the sea searching for small animals to prey upon, or organic matter to eat,” says Ortega-Hernández – much like a modern crustacean.
The team had many Fuxianhuia fossils at different growth stages, so could see how F. protensa changed with age. “Juveniles are very similar to the adult, but… they are naturally smaller and have a more slender body,” says Ortega-Hernández.
Crucially, one of the fossils seems to be of a mature adult with four youngsters (pictured below). The juveniles are all a similar shape and size, and have the same number of body segments, suggesting they are the same age.
Because the remains are pristine, he argues the five animals died and were fossilised at the same time, rather than in the same place at different times. “We argue that they are basically siblings that were born from the same egg clutch and grew together, until they became buried and preserved in the fossil record,” says Ortega-Hernández.
It seems F. protensa lived with its young for some time before they became adults, perhaps to protect them from larger animals and predators.
The find is “as convincing a case as possible for the existence of parenting in the Cambrian”, says at the University of Kansas in Lawrence. It is one of the oldest, “if not the oldest, examples of extended parental care in the fossil record”.
The find pushes back the evolution of parental care to the Cambrian explosion around 540 million years ago. Before this, most organisms were simple and single-celled, but the event changed all that.
“The Cambrian is known to be a time when many of the major animal groups, or phyla, first appear in the fossil record,” says Lieberman. “Therefore, likely many of the distinctive behaviours that we see across the various animal groups today evolved during this time period, including parental care.”
It’s not clear why parental care evolved in Fuxianhuia and not in other arthropods of a similar age.
Previous studies found Fuxianhuia had and , comparable to some modern crustaceans. This could have allowed it to be more active and so care for its young. However, “many other arthropods may have had a similarly advanced brain at this time, yet don’t show evidence for this type of parental care,” says Lieberman.
Instead, Fuxianhuia may have had a different lifestyle to other arthropods. “There are certain environments or lifestyles where [parental care] would be favoured evolutionarily, and others where it wouldn’t be,” says Lieberman. “Parental care has not only evolved multiple times in the animal kingdom, it has also been lost multiple times.”
Reference: bioRxiv, DOI:
