Finding and studying fossils of Earth’s squishiest prehistoric creatures is a difficult task. The fossil record often tells the history of life through hard tissues. Bones, teeth, shells and other mineralized, durable parts of living things have a far better chance of being preserved as fossils than the softer tissues like muscle and internal organs. That’s a huge challenge for all paleontologists, but especially experts on ancient cephalopods—the fossil relatives of today’s nautilus, squid, cuttlefish and octopus that live from the shore to the dark depths. Mollusks have soft bodies that often decayed away before getting a chance to become fossils, leaving experts only with shells or beaks from what was once a complete animal. Yet the cephalopod fossil record is full of surprises, and experts have become ever more inventive in finding ways to visualize creatures that have been extinct for millions of years.
One of the latest surprises comes from an ancient relative of today’s vampire squid, a fossil relative called Vampyronassa. Vampyronassa was originally described twenty years ago. At the time, experts had to rely on what they could see with the naked eye. Paleontologists saw one of the cephalopod’s eyes and its sucker-lined arms, but much of its anatomy was obscured by the encasing rock. The outer details allowed researchers to categorize this strange cephalopod as a distant relative of the “vampire squid” that floats through the ocean depths today, but little more could be said of the animal’s biology. It seemed reasonable to assume that the fossil species lived much like it’s modern-day counterpart.
But advances in visualization technology and greater availability of micro CT scans allowed paleontologists to take a new look at the fossil. Especially when soft-bodied animals are preserved as fossils, there are often hidden aspects of their anatomy that can only be seen by looking beneath the surface of the fossil. “We chose to reanalyze these specimens as we now have access to non-destructive, powerful X-ray based imaging techniques that allow us to observe previously unseen internal structures,” says Sorbonne University paleontologist Alison Rowe, the lead author of a recent Scientific Reportsstudy redescribing the fossil.
Being able to look inside the fossil yielded unexpected results that couldn’t been seen just from the outside. Micro CT scans revealed parts of the gills, stomach, esophagus and other internal organs of this creature, the closest experts could hope to get to seeing this animal alive. “We were able to determine that the sucker attachment of Vampyronassa is the same type seen only in modern Vampyroteuthis,” Rowe says, though the shape of those suckers look like those of octopus. The shape of the suckers and the way they are anchored to the arms of Vampyronassa is a combination never seen before, what Rowe says “provides a small window on the diversity of character combinations that occurred in the Jurassic that are now lost.”
Looking closely did more than answer some anatomical questions, however. Today’s Vampyroteuthis has sometimes been called a living fossil, the assumption being that these cephalopods found a cozy home in deep, oxygen-poor waters and stayed there in a cozy niche, eating detritus that falls from above, since the Jurassic. But the new study of Vampyronassahas revealed something different. The arms and internal anatomy of the fossil cephalopod indicate that it was an active predator that pursued prey closer to the surface. Vampyronassa zipped around to hunt and nab prey with its sucker-lined arms, with its later relatives retiring to a deep sea existence sometime after 33 million years ago.
The fossil of Vampyronassa was a rare case. Fossils of cephalopods like ancient octopus and squid, which had very few hard parts, are difficult to find. Cephalopods such as the coil-shelled ammonoids are much more common, sometimes found in vast beds of empty shells. Such fossils have often been used to tell time in the fossil record as the evolution and extinction of ammonoid species was so rapid that particular species are often associated with particular rock layers–find an ammonoid and you can get a pretty good idea of where you are in the fossil record. Until recently, it seemed that the shells couldn’t tell us very much about how these animals lived. But paleontologists are an inventive bunch, and technological advances have allowed them to get closer to understanding how the beautiful and prolific ammonoid made a living during the deep past.
Case in point, paleontologists didn’t really know what ammonoids ate. The cephalopods were clearly an important part of ancient food webs from 66 to 450 million years ago, and were even fodder from marine reptiles like mosasaurs given some Cretaceous ammonoid shells are found with bite marks on them, but paleontologists were missing what ammonoids themselves ate. Only in 2011 did paleontologist Isabelle Kruta and colleagues announce that they were able to use high-powered X-rays to detect plankton inside the mouth of one particular ammonoid that was a little better preserved than others. Ammonoids fed on microscopic organisms floating in the water column. This became a critical realization. The last ammonoids went extinct about 100,000 years after the impact that wiped out the non-avian dinosaurs, during a time when oceans were struggling to rebuild their food webs from the bottom up. If ammonoids ate plankton, but also produced offspring that were so small they were part of the ocean’s plankton, the poor cephalopods may have practically cannibalized themselves into oblivion.
Prior to those final years, though, ammonoids came in a variety of shapes and sizes, up to species with shells the size of a Mini Cooper. How did these creatures swim, and why did evolution seem to favor some shapes over others? Scientists have turned to ammonoid robots to help answer those questions.
True ammonoids haven’t swum in the seas for about 66 million years, but their shells, at least, have been put through their paces in a college swimming pool. Starting with high-definition scans of ammonoid shells, University of Utah paleontologist David Peterman created three dimensional models of ammonoid shells that he then turned into swimming robots. These models mimic the swimming behavior of the extinct species, allowing experts to get a better idea of how these animals actually moved in the water. “Thanks to computation advances and 3-D prints,” Peterman says, “we were able to explore paleoecological and biomechanical questions with unprecedented levels of detail.” Scientists combined engineering and even video game software with scans of fossils tens of millions of years old, ancient and modern coming together to let ammonoids swim once again.
The tests in the pool have helped resolve some longstanding questions about these animals. Some prehistoric, shelled cephalopods have cone-shaped shells rather than whorls. Did these cephalopods swim in a horizontal position, vertical or crawl along the sea floor as in old museum dioramas? No one really knew. But the biomechanical tests revealed that these shells did best in a vertical position, meaning the cone-shelled cephalopods didn’t so much jet around in search of food but bobbed with the currents as they snagged what they could with their sucker-lined arms.
Frustrating as it might be that we lack as much detail on the soft tissues of prehistoric squid relatives as we might like, Peterman says, being able to scan, visualize and even replicate parts of these ancient creatures is telling us more than ever before. “These animals tell the remarkable story of how seafloor-dwelling critters evolved into living, jet-propelled submarines,” Peterman says, “leaving behind an unparalleled treasure trove of information.”