On May 28, 2020, Justin Reynolds and his daughter Ruby, then 11, were walking the foreshore at Blue Anchor in Somerset, England, when they spotted a gray, ridged fragment of bone sticking out of the mud. They had been fossil hunting along this stretch of coast for years and recognized it as something unusual: part of a jaw, and a large one. Over the following months they returned to the site and recovered additional pieces, eventually assembling 145 centimeters of a single bone called a surangular, part of the lower jaw of an ichthyosaur, a group of dolphin-like marine reptiles that patrolled Triassic and Jurassic seas.
The last fragment belonging to this specimen was collected on October 16, 2022, not by the Reynolds family but by Paul de la Salle, a fossil collector who had found a related jawbone of his own nearby in 2016. The completed bone, cataloged as BRSMG Cg3178 and housed at Bristol Museum and Art Gallery, comes from two pieces: a posterior segment about 99 centimeters long and an anterior segment of roughly 46 centimeters. Even combined, the fossil is incomplete. Based on the curvature and thickness of what survives, the research team estimated the whole surangular originally ran past 2 meters. A second, smaller surangular found by de la Salle at Lilstock in 2016 preserves about 96 centimeters and comes from the same rock unit, giving the researchers a second data point to check their reading of the Somerset bone against.
Scaling a Fragment to a Full Animal
A single jaw fragment cannot by itself tell you how long an animal was. To estimate body length, the team led by Dean Lomax, a paleontologist affiliated with the University of Manchester and the University of Bristol, compared the Somerset bones to the jaws of other giant ichthyosaurs, particularly the shastasaurids, whose relatively complete skeletons provide a ratio between jaw size and total body length. Applying that ratio, and factoring in the uncertainty of working from partial bones, the team arrived at an estimated length of roughly 25 meters, with a plausible range of 20 to 26 meters.
That would put the animal in the same size class as a blue whale, among the largest creatures known to have lived. It is also an estimate, not a direct measurement. No skull, spine, or limb bones belonging to this individual have been found, so the figure rests on comparative anatomy rather than a complete skeleton. Lomax and his coauthors are explicit about that uncertainty in their paper, and it is worth repeating here: the 25-meter figure describes a probable range, not a confirmed length.
Shastasaurids are a family of Triassic ichthyosaurs known mostly from North America and Asia, and their better-preserved skeletons are what make the ratio method possible at all. Without a reasonably complete relative to calibrate against, a jaw fragment this size could support almost any length estimate a researcher wanted it to. The method itself is standard practice in vertebrate paleontology when only partial remains survive, used for estimating the size of everything from theropod dinosaurs to extinct whales, but it works only as well as the comparative skeletons behind it, and giant Rhaetian ichthyosaurs have so far produced very few of those.
Naming Ichthyotitan severnensis
The Somerset jawbone and the earlier bone found by de la Salle at Lilstock, about 10 kilometers away, both come from the Westbury Mudstone Formation, a layer of rock dated to the Rhaetian stage of the Late Triassic, roughly 202 million years old. Their similarity in shape and internal bone structure led the research team to conclude they belonged to the same previously unnamed species. In a paper published in PLOS ONE on April 17, 2024, titled “The last giants: New evidence for giant Late Triassic (Rhaetian) ichthyosaurs from the UK,” the authors named the animal Ichthyotitan severnensis, meaning roughly “giant fish lizard of the Severn,” after the Severn Estuary where both bones were found.
The paper lists six authors: Lomax; de la Salle, affiliated with the Etches Collection Museum of Jurassic Marine Life in Dorset; Marcello Perillo, a graduate researcher at the University of Bonn in Germany; Justin and Ruby Reynolds, both credited by their home town of Braunton, Devon; and James Waldron, founder of the DWABA Museum in Orlando, Florida. Ruby, who was 15 by the time the paper appeared, became a named coauthor on a peer-reviewed paleontology paper as a teenager, a detail that drew as much press attention as the fossil itself.
Why the Rhaetian Record Is So Thin
Ichthyosaurs appear in the fossil record roughly 250 million years ago and largely vanish partway through the Cretaceous, but the Rhaetian stage at the very end of the Triassic is a notoriously sparse window for the group. Neil Kelley, a paleontologist at Vanderbilt University who was not involved in the study, has described this interval as something close to a black box for ichthyosaur evolution: sediments from the period are limited, and few skeletons survive intact enough to study. That scarcity is part of why two isolated jawbones, found six years apart by unrelated collectors, were enough to justify naming a new species and a new size class within it.
The Rhaetian stage also sits close to the end-Triassic mass extinction, one of the five largest die-offs in the fossil record, which followed shortly after. Whatever giant ichthyosaurs were doing in these seas, the window to find more of them is narrow on both sides: a thin band of rock, itself only fully exposed where tides and storms strip the Severn’s mudflats bare, bracketed by an extinction event that reshaped which marine reptiles existed afterward at all.
It also means the case for Ichthyotitan rests on modest physical evidence. Two jaw fragments are not a skeleton, and the researchers have been careful to frame their conclusions as provisional, pending the possible discovery of more complete remains. Other giant ichthyosaur fossils recovered from Aust, farther up the Severn, have produced informal size estimates as high as 30 meters or more using the same scaling method, but those bones are less complete than the Somerset specimens and have not been formally assigned to a named species, so the Ichthyotitan paper does not rely on them. Lomax has said he hopes further searching along the Severn Estuary’s exposed mudstone beds, an area regularly scoured by tidal erosion, will eventually turn up more of the animal. For now, the largest marine reptile candidate on record is known from little more than the fossilized rim of its mouth.
What Erosion Keeps Handing Over
The coastline around Blue Anchor and Lilstock has produced ichthyosaur fossils for more than a century, and the cliffs there continue to shed material as they erode. Ruby Reynolds has said she plans to keep looking for fossils along that same stretch of beach. Whatever specimen turns up next will still have to survive the same test this one did: enough bone, in the hands of people willing to notice it, before the tide takes it back.