The end-Permian mass extinction 252 million years ago was by far the worst in the entire history of the world; an apocalypse by any other name. Over 90 percent of all life on Earth died, including a terrifying 96 percent of all marine species. It was a true evolutionary bottleneck, one that the survivors barely managed to get through.
It is colloquially and appropriately known as the Great Dying, and the infamous dinosaurian extinction event 66 million years ago simply pales in comparison. A long-held assumption among many paleontologists was that during this time of epic prolonged volcanism, rapid climate change and dramatic sea level fluctuations, the rate of the evolution of new marine species was relatively slow.
However, a new study describing a peculiar new fossil throws this theory into some disrepute. This bizarre marine reptile, named Sclerocormus parviceps, is a type of ichthyosauriform, which were beasts that generally resembled contemporary dolphins but belonged to a distinct evolutionary lineage.
Living from 250 million years to around 90 million years ago, they were particularly abundant during the early Jurassic period (201 to 174 million years ago). This new specimen was found in a Chinese geological formation just over 248 million years old, meaning that this ichthyosauriform is one of the most evolutionarily primitive ever found.
A different ichthyosaur, the Shonisaurus. Catmando/Shutterstock
“We don't have many marine reptile fossils from this period,” Dr. Olivier Rieppel, a researcher and curator at the Field Museum in Chicago and co-author of the paper, said in a statement. “This specimen is important because it suggests that there's diversity that hasn't been uncovered yet.”
As described in the journal Scientific Reports, this newly discovered species looked entirely different from what paleontologists have come to expect. Most of these aquatic creatures had long beak-like snouts, streamlined hydrodynamic bodies, sharp conical teeth, and powerful tail fins.
This new 1.6-meter-long (5.25 feet) fellow had a shorter snout, smaller skull, and a long whip-like tail with a lack of large fins. Most distinct of all, it was toothless. Researchers think that it used its snout to suck up prey, like a biological syringe.
The fact that it is so very different from its descendants shows that the evolution of these apex predators was actually far more rapid than previously thought. Within the space of just 50 to 80 million years or so, they had diversified into a plethora of forms.
“Sclerocormus tells us that ichthyosauriforms evolved and diversified rapidly at the end of the Lower Triassic period,” Rieppel added. “Darwin's model of evolution consists of small, gradual changes over a long period of time, and that's not quite what we're seeing here. These ichthyosauriforms seem to have evolved very quickly, in short bursts of lots of change, in leaps and bounds.”
The new fossil, Sclerocormus parviceps. Da-yong Jiang
This remarkable find does more than just add resolution to the story of the ichthyosaurs, whose extinction was recently blamed on them becoming too specialized and ultimately losing their ecological niche to others. It also shows researchers how life responds to a mass extinction event, which in this case was the mother of all extinction events, immediately after the event itself.
Although this particular species of ichthyosauriform went extinct soon after it evolved, it beautifully showcases the types of aquatic features that natural selection deemed to be appropriate at a time of huge environmental change. Ultimately, though, this fossil raises more questions than it answers, most prominently of all being this: How was this line of marine reptiles able to evolve so incredibly quickly right after life on Earth almost ended?