The Cambrian Explosion, which took place 541 million years ago – give or take – was zoological artistry at its best. The fossil record back then records a dazzling array of ecologies and biotas emerging from the murk, paving the way for life on Earth as we know it today.
Predatory behaviors common to the world today also made their debut, but as a new study explains, it wasn’t just the adults chasing others around to gobble them up. Writing in the National Science Review, a team led by China’s Northwest University of Xi’an describe what are killer baby shrimp, in a manner of speaking.
The finding revolves around a species named Lyrarapax unguispinus. This little monster isn’t newly discovered: It made the news back in 2014, for example, when a separate group of researchers managed to examine the fossilized remains of its brain.
Back when it lived, during said explosion, life had not colonized the land, and some of the earliest predators – this one included – populated the oceans. It was a member of a group named Radiodonta, whose animals were typified by their massive, spiny grasping claws and their tooth-like serrations within their mouths.
This allowed them to engage in raptorial feeding, which generally refers to a predator’s ability to grasp its prey with claws or similar appendages. These beasties could grow up to a meter (around 3.3 feet) in length, and many were fearsome apex predators of their soggy ecosystems.
Not much was known about juveniles belonging to this group, though. What were they like compared to their adult forms – and how did they survive?
Fortunately, the unearthing of a magnificently well-preserved juvenile belonging to the L. unguispinus species from China solved this longstanding enigma. Remarkably, despite it being particularly tiny – just 18 millimeters long (0.7 inches), the smallest radiodontan individual known to science – its anatomy wasn’t that dissimilar from its adult equivalents.
“Its adult-like morphology – especially the fully developed spinose frontal appendages and tetraradial oral cone – indicates that L. unguispinus was a well-equipped predator at an early developmental stage,” the team explain in their study. They compare the overall life cycle of L. unguispinus to modern mantises, mantis shrimps, and arachnids.
Although it’s difficult to tell if the juvenile engaged in the same behavior as adults, it’s certainly a solid assumption to make based on these early-forming adaptions. In any case, if it’s correct, then it has wider implications: Namely, that raptorial feeding in (juvenile) Euarthropoda, a group including insects, arachnids, crustaceans and more, appeared very early on in their evolutionary history.
In fact, this may also influence our understanding of the Cambrian Explosion itself. Assuming it truly was an explosion of life and not a result of fossils being better preserved, it’s still not entirely clear what induced this so-called explosion to occur in the first place.
Although oxygen availability is frequently touted as a trigger, there’s also the idea that predatory adaptations may have been responsible. This would have encouraged prey species to quickly adapt to new ecological niches or face death, which would in turn force predators to evolve new tricks of the trade.
Did juvenile raptorial feeding also play its part? Perhaps – but it’s still one part of a gigantic, enigmatic, evolutionary jigsaw that we’re still scrambling to piece together.