The research, published in Current Biology, was led by Kiersten Formoso, an assistant professor in the Department of Ecology, Evolution, and Natural Resources in the Rutgers School of Environmental and Biological Sciences. Her team reconstructed the bodies of four kinds of mosasaurs from their nearly complete fossil skeletons and then applied principles of physics to estimate how quickly each animal could surge forward with a single, powerful sweep of its tail. The answer, she says, helps explain how these predators caught their meals and, in turn, how ancient ocean ecosystems functioned.

At the heart of the study is a movement the researchers call a slam-start. An animal curls its tail to one side and then forcefully sweeps it back, pushing against the water and driving its body forward. Formoso compares the initial surge to a swimmer pushing off the wall of a pool. It is the tail itself pushing off the water, she said. That single burst of acceleration could mean the difference between a successful ambush and a meal that swims away, or between life and death for a smaller animal trying to escape a larger hunter.

The scientific question began with an observation about the fossils themselves. Two major branches of the mosasaur family tree had differently proportioned tails, and Formoso wondered whether those anatomical differences affected how quickly the animals could launch an attack. Previous research on swimming reptiles had largely focused on cruising, the steady type of swimming in which an animal beats its tail repeatedly to move through the water. Burst performance, the sudden acceleration that helps a predator seize prey, had gone largely unquantified.

The nearly complete fossils provided detailed information about body size and tail shape, but one crucial ingredient was missing: muscle. To reconstruct the tail muscles that no longer exist, the researchers drew on the anatomy of living lizards, including the Komodo dragon, one of the closest things the modern world offers to a giant predatory reptile. With bodies and musculature estimated, the team modeled the physics of the slam-start for each of the four mosasaurs, calculating how quickly each could surge forward with one powerful tail stroke.

The calculations produced striking results. A particularly large Tylosaurus, one of the animals modeled, could have reached about 15 miles per hour with a single tail stroke. That estimate describes a brief burst rather than a speed the animal could maintain over distance, and the researchers caution that exact speeds remain uncertain. What matters more, they say, are the differences among the animals. Across the tested conditions, two species, Platecarpus and Tylosaurus, achieved faster lunges for their body size than Mosasaurus and Plotosaurus, with Platecarpus emerging as the fastest of the four.

The advantage came largely from a longer, more flexible section of the tail, which allowed Platecarpus and Tylosaurus to curl their tails farther before sweeping them back. In the models, how far the tail could curl had a much larger effect on the resulting speeds than any other variable the team tested. To make sure the findings were robust, the researchers ran the numbers across a range of assumptions about muscle power, tail flexibility, and resistance from the water. The pattern held up under all of them: the animals with the most curlable tails were the ones best built for a lightning first strike.

Such an advantage, the researchers said, would favor ambush hunting in shallow seas, where a predator could lie in wait and explode toward prey before it could react. Mosasaurus and especially Plotosaurus appear to have been better suited to a different strategy, pursuing prey across the open ocean. That does not mean Plotosaurus was slow, Formoso said. Its tail was built for sustained, tuna-like swimming rather than sudden bursts. In other words, the mosasaur family tree contained specialists in two very different hunting styles, much as modern predatory fish divide the water between sprinters and endurance swimmers.

The findings also agree with other independent clues to how mosasaurs lived. Studies of bite force, patterns of tooth wear, and the chemical makeup of fossils have all been used to reconstruct mosasaur diets and habitats, and the new burst-swimming results fit comfortably alongside that earlier evidence. The study additionally carries a New Jersey connection: alongside the four main reconstructions, the team modeled exceptionally large animals, including a Mosasaurus based on a fossil from New Jersey held by the New Jersey State Museum in Trenton, a reminder that the remains of these ocean giants lie beneath some surprisingly familiar ground.

To the authors’ knowledge, this is the first study to put numbers on burst swimming performance in any marine reptile from the age of dinosaurs, and the team is making its tools freely and publicly available so other researchers can apply the approach to additional extinct swimmers, including animals with no close living equivalent. For Formoso, whose broader research examines how animals with land-dwelling ancestors evolved to live in water, the work rests on a simple and powerful premise: the physical rules that govern swimming today also applied millions of years ago. Physics is physics, she said, and by applying those unchanging rules to fossil bones, scientists can watch long-extinct predators move again, one tail stroke at a time.

Subject of Research: Burst swimming performance and hunting strategies of mosasaur marine reptiles based on tail morphology

Article Title: Some of those ancient sea predators were built for surprise attacks

Article References: Some of those ancient sea predators were built for surprise attacks. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: mosasaurs, marine reptiles, burst swimming, tail morphology, ambush predation, Current Biology, Rutgers University, paleontology, Cretaceous seas, biomechanics, Tylosaurus, Plotosaurus

The study, published in Geological Magazine by Cambridge University Press, was conducted by Dr Dirk Knaust, a palaeontologist who specialises in the trace fossils left behind by invertebrates. Over the past three decades, Knaust has examined several thousand metres of drill core samples drawn from North Sea wells operated by Equinor ASA, the Norwegian energy company that employs him. Much of the fossil vomit material he analysed came from cores collected during the development of a subsea CO2 storage site near the Troll gas and oil field. The investigated material originates from Middle to Upper Jurassic shallow- and marginal-marine deposits on the Horda Platform offshore Norway, including the Krossfjord, Fensfjord, Heather and Sognefjord formations of the Viking Group, in quadrants 31 and 32 of the Troll Field area. What began as routine commercial core logging turned into one of the most detailed behavioural portraits ever assembled for an extinct marine reptile.

The pellets themselves are striking objects. Ranging in size from a walnut to a mango, and in some cases reaching ten centimetres or more across, they are dense clumps of compacted skeletal debris bound together in a matrix that once consisted largely of mucus. Inside them, Knaust identified bivalve shells, serpulid shells — the hard, tube-like dwellings constructed by filter-feeding worms — crinoids, the stalked invertebrates that anchored themselves to the sea floor, and belemnites, the hard internal remains of squid-like cephalopods. This mixture points decisively toward an animal that specialised in devouring hard-shelled and exoskeleton-bearing prey from the sea floor. Crucially, the producing animal also had to be large enough to expel regurgitated clumps of this size, immediately narrowing the field of candidate culprits.

The behavioural interpretation rests on a subtle but powerful ecological paradox. The shellfish identified within the vomit required the stable salinity of open marine water to survive. Yet the deposits in which the pellets were fossilised formed in a river delta, an environment where incoming freshwater continually altered salt levels, rendering it impossible for such salinity-sensitive creatures to live there. The shellfish could not have inhabited the delta, so their remains could not have been vomited there by an animal that had just fed in place. The logical conclusion, Knaust argues, is that the predator hunted in deeper offshore waters, consumed shelled prey from the sea floor, and then swam toward shore — into the delta environment — before vomiting up the compacted, indigestible material. The behaviour parallels that of modern fur seals and marine crocodiles, though with one important distinction: while those animals haul themselves onto land, plesiosaurs, constrained by their weight and body shape, probably remained submerged in shallow water as they regurgitated.

Understanding why such fragile traces survived at all requires appreciating the taphonomic odds stacked against them. Vomit, unlike bone, is soft, dispersed and rapidly destroyed. As Knaust explains, these pellets endured partly because they were so densely compacted and coated in mucus, but even so, most would have been completely broken apart by waves and tides. The exceptional specimens recovered from the cores survived because clusters were quickly buried by sediment delivered by the rivers feeding the delta. Others came to rest in burrows abandoned by crustaceans on the sea floor, where the shelter of the sediment-filled structures allowed them to be partially preserved and ultimately fossilised. Without these fortuitous burial events, the entire record of this behaviour would have dissolved back into the mud.

Distinguishing fossilised vomit from fossilised faeces — coprolites — is its own technical challenge, and Knaust approached it systematically. Regurgitalites contain a higher proportion of undigested food remains, show scattered and irregular shapes rather than the coherent form of faecal masses, and display a distinctive mineralogy. Throughout the research, he compared the Norwegian specimens with previously studied vomit fossils documented over the last century across Europe and North America. This comparative framework matters, because most recent research into fossilised regurgitations has focused on vertebrates eating other vertebrates. According to Knaust, this is the first time plesiosaur vomit, and the shellfish preserved within it, have been identified, making the material an unusually direct window into the diet and digestive physiology of these animals, which lacked the crushing teeth needed to process shell and skeletal material and instead compacted it in the stomach for expulsion, much as owls do today with their pellets.

Identifying the culprit demanded an exercise in systematic exclusion. Knaust began with invertebrate suspects such as cephalopods, the group that includes squid, octopus and cuttlefish, but the size and composition of the vomit did not match. Among vertebrates, fish regurgitations would have been far too small. Moving up the food chain, he evaluated sharks and crocodiles, both abundant in the region during the Jurassic. One coprolite found near the vomit in a core likely came from a crocodile, and one tantalising clue — a bone recovered just centimetres from the fossilised vomit and coprolites — initially appeared to be from a dinosaur. CT scanning revealed instead that it belonged to an ichthyosaur, a group of dolphin-like marine reptiles unrelated to plesiosaurs. That discovery briefly raised the possibility that the vomit and faeces belonged to an ichthyosaur, but many other marine animals had to be considered, and the composition of their vomit differs. Crucially, Jurassic sharks and crocodiles hunted fish rather than grazing the sea floor for shellfish, and no fish skeletons appeared in the fossilised vomit. The plesiosaur, Knaust concluded, most closely matches both the size and the feeding profile of the vomit producer.

The identification carries particular weight because of what plesiosaurs represent in the history of life. Measuring anywhere from two to thirteen metres in length, they rank among the most successful marine reptiles ever to have evolved, surviving more than 140 million years and weathering multiple extinction events. The specific group implicated in the Norwegian vomit, the cryptoclidid plesiosaurs, grew between four and eight metres long and lived from the Middle Jurassic to the Early Cretaceous, roughly 174 to 100.5 million years ago. Earlier research into plesiosaur anatomy and movement had already suggested that these long-necked reptiles angled their heads downward to collect shellfish from the sea floor. The vomit pellets now provide behavioural confirmation of that feeding strategy, and they do so from an environment — a river delta — rather than the open marine settings where most plesiosaur fossils are found.

There may be wider implications for fossil hunters closer to home. Plesiosaur skeletons have been recovered across the world, but the United Kingdom stands out as a particular hotspot, and Knaust, an enthusiast for collecting along England’s Jurassic Coast, believes the same shoreward-vomiting behaviour could have occurred around Britain and many other coastlines. During Jurassic times, the offshore location of the well that yielded the fossils and the rock outcrops along the cliffs of southern England lay within the same narrow sea, an arm of ocean comparable to the North Sea today. That shared palaeogeography means the Norwegian cores may effectively preview what similar deposits in southern England could hold. Meanwhile, the delta itself was a lively place: while dangers lurked in the deeper water, two-legged predatory dinosaurs and long-necked herbivores roamed the delta lands nearby, and Knaust and his colleagues have identified parts of their footprints in some of the extracted cores, adding a terrestrial counterpoint to the marine story preserved just metres away.

For Knaust, the findings represent less an endpoint than an opening. The research adds a new category of evidence — direct digestive traces — to the anatomical and sedimentological clues that palaeontologists use to reconstruct how extinct animals behaved, fed and moved through their worlds. It demonstrates that seemingly mundane commercial core material, drilled for energy infrastructure, can preserve subtle biological interactions over stretches of time measured in tens of millions of years. And it shows that even the least glamorous of fossil traces, the compacted leftovers of an ancient meal, can carry genuine behavioural information: where an animal hunted, where it rested, and how it managed the indigestible consequences of a shellfish diet. As Knaust himself notes, this is still just the beginning, and there is a great deal more to learn from picking through what extinct animals threw up after dinner.

Subject of Research: Fossilised plesiosaur regurgitalites from Jurassic delta deposits offshore Norway revealing shoreward vomiting behaviour in marine reptiles

Article Title: Queasy sea monsters swam to shore to vomit, Jurassic fossils reveal

Article References: Queasy sea monsters swam to shore to vomit, Jurassic fossils reveal. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: plesiosaurs, regurgitalites, fossilised vomit, Jurassic, coprolites, marine reptiles, North Sea, cryptoclidids, palaeontology, river delta deposits, shellfish prey, Geological Magazine