A fossil that sat in a museum collection for over a century is a previously unknown species of predatory dinosaur, researchers have found. The discovery could help scientists solve a longstanding mystery about how some of the Cretaceous period's most formidable hunters spread around the globe.

The dinosaur lived on what is now the Isle of Wight in southern England about 120 million years ago. It belonged to a group of two-legged carnivores called megaraptors, which are related to tyrannosaurs. But unlike tyrannousars, megaraptors are thought to have relied on their powerful arms and large curved claws to attack prey and defend themselves.

The newly identified species was described in an Oct. 14 study in the journal Royal Society Open Science. It is the first megaraptor identified in Europe, filling an important gap in the fossil record of a group whose evolutionary history remains poorly understood.

"It is a real mystery that this fossil was overlooked for so long, sitting in a drawer for nearly 100 years," study first author Cassius Morrison, a researcher in the Department of Earth Sciences at University College London (UCL) said in a statement. "Lots of bones are found on the Isle of Wight — who knows what else is waiting to be discovered."

Unconquered female warrior dinosaur

The discovery of the megaraptor began in 1924, when an amateur fossil collector discovered a dinosaur skull fragment on the Isle of Wight. The specimen eventually entered the collections of London's Natural History Museum, but it was largely forgotten.

Recently, researchers revisited the fossil as part of a study on dinosaur braincases. To identify the animal, the researchers used micro-CT scanning to examine the fossil's internal structure and build detailed 3D digital models of the space that once held the dinosaur's brain.

The researchers then compared the animal's anatomy with that of other meat-eating dinosaurs, including tyrannosaurs, spinosaurs and other theropods (the group of two-legged, mostly meat-eating dinosaurs). Several features differentiated the unknown specimen, including an almost oval opening where the spinal cord entered the skull and an unusual, hourglass-shaped ridge at the back of the braincase.

Computer-based evolutionary analyses placed the fossils within the Megaraptora family tree, supporting the idea that the skull represented a never-before-seen species. The researchers named the dinosaur Invictibellatrix amberina, combining the Latin words "unconquered" and "female warrior" for the genus name, while amberina refers to amber found in the rocks associated with the fossil.

Megaraptors lived between roughly 125 million and 66 million years ago and varied considerably in size. While early members were relatively small, some later species became enormous predators. Maip macrothorax, discovered in Argentina, may have reached up to 33 feet (10 meters) long and weighed as much as an elephant. Based on comparisons with related dinosaurs, I. amberina was much smaller, likely around 10 to 13 feet (3 to 4 m) long and standing roughly 5 feet (1.5 m) tall. The researchers estimated it weighed around 440 to 660 pounds (200 to 300 kilograms), making it one of the smallest known megaraptors.

"It was not the apex predator of its time, but for humans this dinosaur would have been more dangerous than a T. rex," Morrison said. "We would have been perfectly sized prey, about a third of their body weight. They definitely would have chased us."

Although the newly described fossil doesn't preserve the animal's arms or claws, its closest relative suggests that its claws may have measured around 4 to 8 inches (10 to 20 centimeters) long. The researchers also suggested I. amberina may have been feathered, though that feature can't be determined directly from the specimen.

A missing link in the dinosaurs' globetrotting

Scientists have long suspected that megaraptors originated in Asia before spreading to other parts of the world, eventually becoming the dominant predators across the southern supercontinent Gondwana, which included present-day Africa, South America and Antarctica. But a lack of European fossils left an important gap in verifying this migration route.

The new study's evolutionary models suggest that I. amberina descended from Asian megaraptors that dispersed into Europe around 130 million years ago. From there, members of the group may have moved through what is now Africa and further into Gondwana via temporary landbridges and temporary land connections across the shallow Tethys Ocean.

"This new species is the first proof we have that megaraptorans were also present in Europe and that they reached Gondwana this way rather than island-hopping further south," study co-author Charlie Scherer, a doctoral student at UCL Earth Sciences, said in the statement.

However, the specific route these animals took over millions of years is still unknown. The researchers also cannot yet explain why megaraptors disappeared from northern areas, but changes in climate or competition with other predatory dinosaurs may have contributed. More research on other megaraptor fossils like I. amberina could help uncover more clues.

"Work like this shows the exceptional value of working with historical museum collections where there are still many discoveries to be made," study co-author Paul Barrett, a researcher of dinosaur evolution at the Natural History Museum in London, said in the statement.

Paleontologists in China have discovered a small Jurassic bird that was likely a land-based predator — like a carnivorous pheasant with killer claws. It had some features of birds and others of dinosaurs, suggesting that the earliest birds had a greater diversity of lifestyles than previously recognized.

Jurassic birds first emerged 150 million to 148 million years ago, and fossils of them are rare, so experts are just starting to understand how early birds diversified and evolved the ability to fly.

The researchers discovered the newly identified Yuezhuornis yangyuanensis in 2024, in the fossil assemblage known as the Upper Jurassic Zhenghe Fauna in southeastern China. It lived 150 million to 148 million years ago, roughly when birds started to appear in the fossil record. The team published their findings Wednesday (Oct. 14) in the journal Nature.

Analysis of the fossilized skeleton revealed the animal was small and weighed about 1.8 pounds (0.8  kilograms). "It was probably as large as a crow," Min Wang, a researcher at the Chinese Academy of Sciences, told Live Science via email.

Y. yangyuanensis had a mix of features seen in birds and predatory Deinonychosauria dinosaurs, such as Velociraptor, which are known for their sickle-shaped toe claws. It had deinonychosaur-like hyperextensible toes, with forelimbs that were roughly one-third shorter than its hind limbs. This is odd because modern birds and many other Jurassic paravians — the group that includes bird-like dinosaurs, including the ancestors of birds as well as modern birds themselves — have long forelimbs, linked to giving wings more lift force for taking off.

Y. yangyuanensis also had slender cranial elements and sparsely spaced teeth. These features, alongside the curved claw-like toes that were capable of securing prey, suggest that the animal's diet included meat.

"Its key anatomical features are the combination of dinosaurs' and birds' features: for instance, its teeth, pectoral gird, and especially the hyperextensible, 'sickle-clawed' second pedal digit are similar to that of dinosaurs," Wang said. Meanwhile, he said its slender cranial bones and bird-like pelvis are comparable to early birds.

This combination of features suggests that "the morphological gap between birds and dinosaurs is much smaller than we thought," he added.

Comparisons with 377 living bird species showed that the limb proportions of Y. yangyuanensis were most similar to those of terrestrial birds.

Wang suggested that Y. yangyuanensis was a flightless bird, but not one specialized to live in trees or wade in the swamps in the region. It was a small carnivore, with similar proportions to a pheasant, that was well adapted for running. "I think there are no directly comparable modern birds," he said.

The mosaic of features hints that Y. yangyuanensis may have occupied an ecological niche that was rarely utilized by early birds, and that there wasn't a systematic progression toward flight optimization, Wang said.

Despite being flightless, Wang and his colleagues place Y. yangyuanensis closer in the evolutionary tree to modern birds than to Archaeopteryx, one of the world's first proto birds, which lived about 150 million years ago and is thought to have been able to fly.

This adds to evidence that "the ability to fly arose not once, but several times among disparate groups of carnivorous dinosaurs that are closely related to birds," wrote Fernando Novas, a paleontologist at the Felix de Azara Natural History Foundation in Buenos Aires, Argentina, who wasn’t involved in the study, in an accompanying article in Nature. This includes flight evolving in early birds and in scansoriopterygid dinosaurs, which had membranous folds like the wings of bats, and the four-winged microraptors. Y. yangyuanensis seems to have taken a different road, eschewing the flying ways of its relatives.

"It highlights the extraordinary breadth of ecological and morphological diversification that took place close to the origins of avialans," Wang said.

A newly discovered platypus-like creature is the largest-known mammal relative from the entire Jurassic period, a new study finds — although it still only weighed as much as a Chihuahua.

The critter, which hunted salamanders in the freshwater lakes and rivers of what is now Inner Mongolia, China, lived during the mid-Jurassic between 168 million and 163 million years ago. It seems to be the earliest known mammal-type animal that lived a semiaquatic life.

Researchers unearthed the delicate and detailed fossil in 2016, which revealed that the animal likely weighed about 2.2 to 4.4 pounds (1 to 2 kilograms). It was large for a mammal relative during the Jurassic, but its name, Megacauda sungei, was inspired by its tail: Megacauda means "big tail." The discovery was detailed in a study published on Wednesday (Oct. 7) in the journal Nature.

The furry predator had a mix of features seen in modern-day animals, with a broad, flattened tail that marks it as a powerful swimmer, and short hind legs with relatively long feet.

"It's like a chimera," study co-author Zhe-Xi Luo, a paleontologist at the University of Chicago, told Live Science. "The back half of this animal is very much like a platypus. As are the limbs, which would be capable of swimming or digging tunnels in river banks."

But the teeth "are definitely not like a platypus," Luo said. It possessed robust canines and shearing cheek-teeth that would cut and chew meat in a different way from modern carnivorous mammals. "It's a predator with gigantic and very specialized canines," Luo said. "So, it's partly otter-like and partly platypus-like."

A revealing fossil

Tiny bits of vertebrate bones found in what would have been the animal's stomach and the surrounding fossil beds hint that M. sungei dined on salamanders, Luo said.

He added that M. sungei may have sheltered in burrows on land in the temperate plant-filled climate, and hunted in lakes and rivers for fish and invertebrates.

Another notable aspect of the fossil is its throat. Modern mammals, including humans, have hyoid bones in the throat arranged in a "U"-shaped saddle. These help us use throat muscles to swallow chewed food one chunk at a time, instead of gulping down huge bites or whole prey. The structures also enable babies to suckle their mother's milk.

M. sungei seems to have had the apparatus needed to do this, study co-author Thomas Martin, a paleontologist at the University of Bonn in Germany, told Live Science.

"This is an incredibly important evolutionary innovation," Luo said, adding that this capability is one of the things that helped early mammals diversify into carnivores, insectivores, herbivores or omnivores to take advantage of all sorts of foods.

Finding this in M. sungei suggests that the apparatus needed for suckling milk and swallowing had already evolved by the Middle Jurassic (around 174 million to 164 million years ago), Martin said.

This is before marsupials like kangaroos and placental mammals like primates and bears are thought to have diverged from each other 160 million years ago, after descending from an egg-laying common ancestor that lived approximately 180 million years ago.

"Now we push the history of it back to before the split of modern marsupials and modern eutherian [placental] mammals," Luo said.

"Neonatal suckling behaviour was previously thought of as being a hallmark of advanced mammals, but it now appears to have evolved well before then, in the common ancestor of docodontans and mammals at least 165 million years ago," said Sue Hand, a vertebrate paleontologist at the University of New South Wales in Australia who wasn’t involved in the study.

M. sungei is from an extinct lineage of docodonts, which are relatives of mammals from the dinosaur-dominated Jurassic and Cretaceous periods, living between about 200 million and 120 million years ago.

Docodonts adapted to a wide variety of habitats. For example, there was the Jurassic tree-dwelling shrew-like docodont called Microdocodon gracilis, and Docofossor brachydactylus, a tunnel-digger with shovel-like paws. Luo was also part of the team that described a semiaquatic "Jurassic beaver", Castorocauda lutrasimilis, which lived 164 million years ago.

"It seems that an aquatic lifestyle arose often in early mammal-like species," said Tim Flannery, a mammalogist at the Australian Museum Research institute who wasn't involved in the work.

If anything, the newly described "spectacular fossil" shows that docodonts were wide-ranging during the dinosaur age, Hand told Live Science in an email.

"This very detailed study adds to accumulating evidence that mammaliaforms occupied a wide range of ecological niches long before the evolution of living mammals," Hand said.

Mammals first appeared on Earth over 200 million years ago, scuttling around alongside the dinosaurs as little mouse-sized creatures. But after the asteroid hit 66 million years ago, it was their time to shine ‪—‬ and the Age of Mammals began.

But the path to understanding our own branch of the animal kingdom hasn't been straightforward. In this excerpt from "The Story of the Mammals in 25 Discoveries" (Columbia University Press, 2026), author Donald R. Prothero looks at a time when philosophers and early naturalists believed giants roamed the Earth and explores the idea that extinction was heresy.

Many cultures around the world have a mythology that includes legends about gigantic races of humans that lived on Earth in the dark mysterious past. They may have fought against the gods, or they may have been destroyed by floods. These stories were reinforced by the discovery of gigantic bones, much larger than those of any living human, all over the Mediterranean and Europe.

The Greek philosopher Empedocles (492-432 BCE) reported gigantic bones from Sicily, supposedly remnants of a race of giants. The Roman historian Pliny the Elder (23-79 CE) mentioned fossil ivory in the ground, and according to the Roman historian Suetonius (69- 122 CE), Emperor Augustus owned a collection of large bones that had been found on the island of Capri, near Pompeii. The skulls of elephants, with their huge central opening in front (for the trunk), were thought to be the skulls of the one-eyed cyclops.

In the Middle Ages, these huge bones were again attributed to gigantic humans or other monsters (Genesis 6:4) that were drowned in Noah's flood. Giant tusks from Siberia were thought to be the horns of the mythical unicorn or the tusks of dragons. In some places gigantic teeth or vertebrae of mammoths were revered as relicts of saints. Nearly every possibility was suggested except that they were the bones of extinct elephants.

In the early seventeenth century, some giant bones dug up in a sand pit near Langon in southeastern France were exhibited around France as the remains of the giant Teutons, Germanic tribes that once roamed Gaul and were defeated by the Romans in 101 BCE.

But in 1613 the famous anatomist Riolan attacked the prevailing interpretation, suggesting that they were the bones of an elephant. This generated a raging controversy between physicians and anatomists and the barber-surgeons who called them gigantic human bones. Others thought they were hoaxes or generated by mysterious "plastic forces" (vis plastica in Latin) that percolated through Earth. Still others attacked the anatomists for questioning the biblical account of giants on Earth. The controversies died down in 1618 without being resolved, and for the next two centuries most people continued to interpret new finds as gigantic humans.

The giant bones that kept turning up in the New World were also a source of much mystery and consternation. The Native American tribes usually attributed them to giant monsters fought by their ancestors and incorporated them into their folklore. When these bones were first seen by European settlers, they were thought to be the bones of gigantic humans that roamed the earth in biblical times. Others thought that the giant tasks so revered by the Native Americans were the works of Satan, placed there to tempt the believer.

In 1519, the Spanish explorer and conquistador Hernan Cortez received a bone of a "giant," a gift from the friendly Tlascalan tribe of Mexico during the conquest of the Aztecs. He sent it back to the King of Spain as proof that giants at once lived in the New World. In 1706, the Reverend Cotton Mather of the Massachusetts Bay Colony pronounced them to be "the remains of godless giants drowned in Noah's Flood." He sent some bones to the Royal Society in London to have them certified as evidence of this "wicked giant" because biblical scholars were calculating Adam's height at 123 ft. 9 in.

The Royal Society never pronounced an opinion on these bones, although by that time many members were becoming skeptical of the literal interpretations of Genesis. The stifling effect of religious dogma about giants and Noah's flood was complicated by another idea: the notion of Divine Providence. An omnipotent, benevolent God would never allow any of his creatures to become extinct. As the poet Alexander Pope wrote in An Essay on Man (1734), "who sees with equal eye, as God of all, a hero perish, or a sparrow fall."

The prevailing concept was that of a "great chain of being" that linked the animals to man to the angels to God. Breaking any link in that chain implied the destruction of the whole chain. In the same poem, Pope also wrote: "Where, one step broken, the great scale's destroy'd; From Nature's chain whatever link you strike, Ten or ten thousandth, breaks the chain alike."

By the late 1700s, however, it was becoming more and more apparent that many of the recently discovered fossils had no living counterparts. Remote corners of the world were being explored, and although many new and surprising beasts were discovered, clearly the gigantic beasts were not hiding in South America or Africa or the East Indies. Many strange fossils, such as the bones of hippopotami in Paris and London, were clearly related to tropical animals, but it was assumed that these bones had been washed from the tropics during the Great Flood.

The notion of extinction was still blasphemous. The New World soon provided unequivocal evidence that these large bones were not simply gigantic humans. In 1739, Charles le Moyne, the second Baron de Longueil, left Montreal with French and Indian troops to fight the Chickasaw Indians along the Ohio River. Somewhere along the Ohio he found the remains of what appeared to be three elephants. When the war ended in 1740, le Moyne collected the bones and shipped them to New Orleans and ultimately to Paris, where they came to the attention of French naturalists.

In the 1740s and 1750s, English settlers in the region sent more of these bones from Big Bone Lick, Kentucky, off to England and also to Benjamin Franklin in America. Most of the bones (especially the tusks) were clearly like those of elephants and mammoths, but the teeth were puzzling. They were clearly unlike any living elephant, yet they were part of an animal of elephantine size. (We now know that these were specimens of the American mastodon, Mammut americanum.) Franklin speculated that the teeth were reminiscent of a carnivorous animal, although he and others later decided it was a vegetarian.

In 1769, the famous British anatomist William Hunter took the carnivory suggestion seriously and suggested this was not a true elephant but a "pseudelephant" or "American incognitum" (Latin for "unknown") that had independently developed ivory tusks:

"This monster, with the agility and ferocity of a tiger . . . cruel as the bloody panther, swift as the descending eagle, terrible as the angel of night. . . . And if this animal was indeed carnivorous, which I believe cannot be doubted, though we may as philosophers regret it, as men we cannot but thank Heaven that its whole generation is probably extinct."

This very precocious suggestion was still not accepted by naturalists of the time. Nevertheless, remains of the "incognitum" and also of the Siberian mammoth (including frozen carcasses with hair and skin) were turning up again and again. Georges Louis Leclerc, the Comte de Buffon (1707-1788), concluded in his Théorie de la terre in 1749 that although most of the supposedly extinct animals were hiding somewhere in an unknown region, it was likely that the large terrestrial mammals such as the mammoth and "incognitum" had actually perished.

By 1778, Buffon was relating their disappearance to his ideas of violent cataclysms in Earth's early history. During this time the climate was warmer and polar regions had once been tropical, so "elephants" (meaning mammoths) could live in Siberia. This implied a nonbiblical Earth of much greater antiquity. Buffon suggested it was as much as 75,000 to 3,000,000 years old, rather than the 6,000 years demanded by most literalist biblical scholars.

Naturally, such revolutionary ideas were not popular with the theologians in the Sorbonne. Buffon was protected by the king, however, so he was not persecuted for his heresy, although his ideas were not widely accepted either. The fact of extinction was finally proved by one of the greatest scientists of all time, the Baron Georges Cuvier (1769-1832).

Jean Leopold Frederic Georges Cuvier was an impressive man. Tall of stature, he had a "massive" head crowned by a large mane of hair. One admirer wrote that his head "gave to his entire person an undeniable cachet of majesty and to his face an expression of profound meditation." After his death, scientists weighed his brain and found that it was a massive 1830 grams [4 pounds], more than 400 grams [14 ounces] above average, and 200 grams [7 ounces] heavier than any brain ever measured at that time.

More important, he was one of the most brilliant men of his time, with a command of many subjects, some of which he invented all by himself. Before Cuvier, natural history was a field that resembled stamp collecting, with many amateur naturalists compiling long lists and descriptions of new species without analyzing the similarities in their anatomy. Cuvier almost single-handedly revolutionized natural history by dissecting many different animals and discovering their underlying similarities and differences.

This became the foundation of comparative anatomy, a subject that has been fundamental to biology ever since. Naturalists and explorers sent him their fossil bones, and he was the first to correctly describe many types of extinct animals. Cuvier solved the mystery of the puzzling fossil teeth called the "Great Incognitum" and recognized them as the teeth of the elephant-like mastodons. He also correctly deciphered the huge marine lizards we now know as mosasaurs.

For this reason, he is also considered to be the founder of vertebrate paleontology. Cuvier is most famous for his "law of correlation of parts," wherein he discovered that certain types of anatomical features tend to be associated. If you are a flesh eater, you will have sharp teeth and claws; if you are a plant eater, you will have flat grinding teeth and hooves; and so on. Using this law, paleontologists have been able to reconstruct whole animals from just a few key bones because the other parts of the anatomy are so predictable.

Excerpted from The Story of the Mammals in 25 Discoveries: Amazing Fossils and the People Who Found Them by Donald R. Prothero. Copyright (c) 2026 Donald R. Prothero. Used by arrangement with the Publisher. All rights reserved.

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Paleontologists have identified the first confirmed remains of Diplodocus — "Dippy," for short — outside the western U.S., revealing that the iconic long-necked dinosaur reached what is now Spain roughly 150 million years ago.

The findings show that the enormous sauropod didn't live only in North America, as was long thought. Instead, it may have rambled across a land bridge all the way to Europe, the new study suggests.

The discovery, made at the La Tejería site near the small village of El Castellar in eastern Spain, provides some of the strongest fossil evidence yet that dinosaurs could move between North America and Europe during the Late Jurassic, when the Atlantic Ocean was still in its early stages of opening after the breakup of the supercontinent Pangaea. The researchers published their findings Tuesday (Sept. 15) in the Journal of Vertebrate Paleontology.

"Paleontological studies like this one help us better understand the history of life on Earth, reconstruct ancient ecosystems, and understand how they changed through time," study first author Sergio Sánchez Fenollosa, a doctoral student who studies biodiversity and evolutionary biology at the Joint Paleontology Foundation Teruel-Dinópolis (Dinópolis Foundation), a paleontological research institution, told Live Science via email.

A sauropod in Spain

Dippy is one of the best-known dinosaurs. After its fossils made their grand debut at the Carnegie Museum of Natural History in Pittsburgh in the early 1900s, life-size fossil replicas of the towering herbivore were sent around the world, including to England, France, Spain, Argentina and Russia.

But until now, Diplodocus' Late Jurassic fossils were known only from the Morrison Formation in the western United States ‪—‬ and the latest discovery shows that Dippy wasn't a homebody.

The newly unearthed Diplodocus specimen consists of 14 well-preserved tail vertebrae and several chevrons ‪—‬ bones that helped support blood vessels and muscles within the dinosaur's tail.

Study co-author and managing director of the Dinópolis Foundation, Alberto Cobos, said it was a friend who "thought he had spotted some bones on a mountainside," Cobos told Live Science via email. "That very day, I went to the site near El Castellar (a village in the province of Teruel). Sure enough, we saw a couple of sauropod vertebral centers."

Although only part of the skeleton has been recovered, the bones show a series of characteristics associated with Diplodocus, including large cavities corresponding to where air sacs would have been, along with deep grooves running alongside the underside of the tailbones.

"It was an exciting and continuous process of seeing the pieces of the puzzle gradually fall into place," Sánchez Fenollosa said in a statement. "From the early stages of the osteological study, we noticed strong similarities with several diplodocine sauropods … With each new result, the picture became clearer: we were looking at a Diplodocus."

It's unclear which species of Diplodocus the new specimen is, but like others of its genus, it was a huge dinosaur with an extremely long neck and whip-like tail.

"The Diplodocus from El Castellar was approximately 25 meters [82 feet] long (comparable in size to its North American relatives), making it another of the giant sauropods of the Spanish Jurassic," Cobos said in the statement.

An ancient bridge

Between 195 million and 170 million years ago, the supercontinent Pangaea broke apart as the Atlantic Ocean opened. But the ocean was much narrower than it is today, and the continents were not necessarily as isolated as their modern geography is now.

Evidence indicates that temporary land bridges may have allowed some animals to move between the two regions. The most famous prehistoric land bridge is the Bering Land Bridge that humans used to move between Asia and what is now Alaska. Previous research showed the Bering Land Bridge also existed around 68 million years ago, and it may have allowed an Asian ancestor of Tyrannosaurus rex to trek into North America.

One possible route for Diplodocus into Spain may have been a land bridge that connected what is now Newfoundland with the Iberian Peninsula.

Geological conditions may have allowed dinosaurs like Diplodocus to move between continents, Sánchez Fenollosa told Live Science in an email. "This interpretation is supported not only by the fossil record but also by geological evidence," he said.

The newfound Diplodocus fossils also suggest that the distribution of giant sauropods was more complicated than the fossil record previously indicated.

"More complete specimens will be essential to understand this story in greater detail, particularly to determine which Diplodocus species inhabited Europe: whether it was one already known from North America or a previously unknown species," Sánchez Fenollosa said. "This discovery reminds us that even for such iconic dinosaurs, there are still many unanswered questions about their evolutionary history and biogeography."

An exceptionally well-preserved fossilized molar belonging to an adult Pacific mastodon has surfaced in a nature preserve near San Francisco.

Upon first glance, the ancient tooth looked like an "oddly shaped rock" to geologists who were conducting fieldwork in the area, according to a statement from the Midpeninsula Regional Open Space (Midpen), which runs the preserve. But the find was quickly unmasked as a valuable fossil from the last ice age and was sent to scientists at Stanford University for carbon dating.

"The tooth itself is in immaculate condition," Wayne Thompson, a paleontologist and the CEO of Pacific Paleontology, a consulting firm that carried out a preliminary analysis, said in the statement. "It's the most complete mastodon molar from our area, and the most spectacular mastodon molar that I've ever seen. I had chills and shivers up and down my spine."

Brigid Lynch, a geomorphologist with the California-based hydrology consulting firm Balance Hydrologics, found the molar this summer while surveying a creek bed. "As a geologist, I've gone out and seen stuff in the field, but definitely nothing as exciting as this," Lynch said in the statement.

Lynch's team was working on a habitat enhancement project to support the threatened California red-legged frog (Rana draytonii) inside the preserve, which is located on the San Francisco Peninsula in San Mateo County. The fossil was a complete surprise and dates to at least 10,000 years ago, when the Pacific mastodon (Mammut pacificus) is thought to have gone extinct.

The Pacific mastodon was first recognized as a species in 2019. It was closely related to the American mastodon (Mammut americanum). Both elephant-like creatures lived in North America during the Pleistocene epoch (2.6 million to 11,700 years ago), but the Pacific mastodon inhabited regions farther west than its cousin, roaming parts of present-day Mexico, California, Oregon and the northern Rocky Mountains of the western U.S., according to the statement.

Pacific and American mastodon fossils reveal slight differences between the species, including a narrower third molar, thicker hind-leg bones and occasionally absent lower-jaw tusks in the Pacific mastodon, according to the Royal Alberta Museum.

The newfound tooth is "another puzzle in the Ice Age saga that we can put into place," Thompson said. To get a precise date for the fossil, Midpen donated it to Stanford University's Doerr School of Sustainability in July, the Los Angeles Times reported.

Researchers will produce a 3D copy of the molar that Midpen plans to use for public outreach and education, according to the statement.