Tag Archives: Megalodon

Otodus megalodon. Credit: Flickr, Elena Regina.

Cold oceans may have helped Megalodon reach gargantuan proportions

Megalodon was the uncontested marine predator of its time. Being about the size of a bus — twice as long as the second-largest shark in history — this fierce sea monster must have been a sight to behold. But according to a new study, the extinct species of shark, which lived from the early Miocene to the end of the Pliocene, from 23 to 2.6 million years ago, these truly huge Megalodons may have only been found in higher latitudes, where the water is much colder. Around the equator, the size of Megalodons was less impressive, though they were still a force to be reckoned with.

Schematic showing general body size distribution of Otodus megalodon, with body size increasing towards cooler waters at higher latitudes. Credit: Kenshu Shimada.

Like all sharks, Megalodon’s skeleton was mostly made of cartilage. This means that only its teeth and vertebrae have survived in the fossil record. But this seemingly limited fossil evidence can reveal a wealth of information about the intimate lives of ancient sharks, such as what they ate, how they bred, and much more.

In early 2021, Kenshu Shimada—a professor of paleobiology at DePaul University in Chicago — analyzed growth bands in Megalodon specimens, showing the fierce sharks gave live birth to the largest babies in the shark world, measuring about 2 meters (6.6 feet) in length. This study also estimated that Megalodon had a life expectancy between 88 and 100 years. 

In a new study published today in the journal Historical Biology, Professor Shimada took a new look at Megalodon teeth, re-examining their geographical occurrence and corresponding estimated body sizes to see whether water temperature may have had any notable influence on ancient sharks’ development.

The idea for this new study originated while Shimada was out on a family fishing trip to the Florida Keys with Martin Becker, a professor of environmental science at William Paterson University in New Jersey.

“After my daughter’s ‘big catch,’ we started to discuss where large fish live, leading to a conversation about different populations of Megalodon,” Shimada told ZME Science.

The researchers employed previously published data, some of which offered possible Megalodon nursery areas judging from the presence of much smaller teeth relative to other locations. But there is another possible explanation — the new study found that these supposed nursery areas were concentrated close to the equator, and this could have had a major impact on the size of these prehistoric sharks.

The ocean receives most of its heat along the equator, where incoming solar radiation is about double that received at the poles. Hence, sea surfaces are much warmer along the equator than at the poles.

Larger animals tend to thrive in cooler climates — an empirical observation known as Bergmann’s rule — because their size helps them retain heat more efficiently. So given the data they had at their disposal, the researchers think that the smaller Megalodon teeth found close to the equator might not necessarily all come from juveniles. It could just be that Megalodons in this region attained a much smaller individual body size as a result of the warmer water — and the differences may have been quite striking.

“Generally speaking, the new study found that Megalodon populations towards the equator were small, roughly 6.5 meters (21 feet) on average, while those away from the equator measured 11 meters (36 feet) on average.  While individuals that exceeded 15 meters (50 feet) must have been uncommon, the new study suggests that those that could have reached 20 meters (65 feet) must have lived more commonly in cooler environments away from the equator,” Shimada said.

These findings suggest that the most menacing Megalodons were concentrated closer to polar regions, although their geographical distribution must have evolved dramatically over the ages during their nearly 20-million-year-old history. Whether or not Megalodon’s propensity for following Bergmann’s rule had any impact on its eventual demise some 2.5 million years ago is still an open question, but as climate change today is pushing marine animals increasingly towards the poles, perhaps there’s a cautionary tale hidden in these prehistoric patterns that we ought to be paying close attention to.

“To our knowledge, Bergmann’s rule has never been recognized for sharks previously, but our research team contends that the lack of modern examples should not be taken as evidence for our idea to be false, especially because of the fact that there is no comparable modern shark to Megalodon.”

“The cause for the extinction of Megalodon is still uncertain, but one hypothesis states that competition with the rising great white shark could be the reason.  Even if that is the case, where climate change may not have been the direct cause for the demise of Megalodon, such climatic changes could have affected the availability of food sources for Megalodon as well as the success of competitors that could have indirectly contributed to its extinction,” Professor Shimada concluded.

Megalodon gave birth to newborns as large as adult humans

Megalodon reconstruction at the Museo de la Evolución de Puebla in Mexico. Credit: Wikimedia Commons.

Perhaps the fiercest shark that ever swam the world’s oceans was Otodus megalodon, an extinct species of shark that lived from the early Miocene to the end of the Pliocene, from 23 to 2.6 million years ago.

Megalodon was the uncontested marine predator of ancient times, reaching 15 meters (50 feet) in length — twice as long as the second-largest shark in history. Not surprisingly, Megalodon’s babies were also on the hefty side. According to a new study, Megalodon newborns were larger than most adult humans.

The study led by Kenshu Shimada—a professor of paleobiology at DePaul University in Chicago and research associate at the Sternberg Museum in Kansas—is one of the first that examined growth bands in Megalodon specimens.

Like all sharks, Megalodon’s skeleton was mostly made of cartilage. This means that only its teeth and vertebrae have survived in the fossil record. But these seemingly limited fossils can reveal a wealth of information about the intimate lives of ancient sharks, and even how they breed.

Megalodon’s vertebrae grow in incremental, distinct layers, analogous to tree rings. Each layer or growth band reveals information about the animal’s characteristics, such as its girth and body size at the time of deposition.

Identified annual growth bands in a vertebra of the extinct megatooth shark Otodus megalodon along with hypothetical silhouettes of the shark at birth and death, each compared with size of typical adult human. Credit: DePaul University/Kenshu Shimada.

Shimada and colleagues, who included Matthew Bonnan of Stockton University, New Jersey, and Martin Becker and Michael Griffiths of William Paterson University, New Jersey, used CT scanning techniques to examine the growth bands of a 9-meter Megalodon fossil.

The fossil’s 46 growth bands mean the shark died at age 46. By analyzing how each band formed in the giant vertebrae, the researchers could calculate the shark’s body length during each year of its life, including at its birth.

“Because no one has examined ‘growth bands’ in Megalodon vertebrae using a CT scanner in the past, I was not sure if the approach would work. The detection of the very fine growth bands is literally the breakthrough of this study,” Shimada told ZME Science.

This back-calculation suggests that Megalodon gave live birth to the largest babies in the shark world, measuring about 2 meters (6.6 feet) in length. But that’s not the study’s most interesting conclusion.

Researchers also revealed how Megalodon’s embryos developed, how it gave birth, and even provided one of the most accurate estimates of Megalodon’s lifespan.

Like modern Lamniforms, one of the most well-known groups as it includes famous species and feared hunters, like the Great White Shark, Basking Shark, and Mako (Shortfin and Longfin), Megalodon also gave birth to live young. And like modern sharks, these baby Megalodons were killers well before they left their mum’s womb.

“Lamniform sharks don’t lay their eggs outside of the body, but instead eggs hatch inside the mother that eventually gives live birth to young pups. A very interesting fact is that ‘early-hatched embryos’ will begin to eat surrounding unhatched eggs and at least in sandtiger sharks occasionally even feed on other hatched siblings for nourishment,” Shimada told ZME Science.

“The consequence is that only a few pups will survive and develop, but each of them can become considerably large in body size at birth. Although energetically costly for the mother to raise such large embryos, neonates have an advantage as ‘already-large’ predators with reduced chances of getting eaten by other predators.”

Concerning Megalodon’s lifespan, the researchers found that the ancient predator grew at a rate of about 16 centimeters (6.3 inches) per year or at least for the first 46 years of its life based on the only sample the researchers studied thus far. According to a growth curve model based on the vertebrae growth bands, the researchers estimate that Megalodon had a life expectancy between 88 and 100 years. These estimates, however, may change dramatically as the researchers analyze more Megalodon fossils.

“While the new study has given us a pretty good idea about the growth pattern between birth and ‘middle-age’ for Megalodon, the exact growth pattern past 46 years old, including its inferred life expectancy of at least 88-100 years, remains rather theoretical and needs further investigation,” Shimada said.

The findings were reported in the journal Historical Biology.

Megalodon’s giant size was truly unprecedented among all sharks ever

Schematic drawing showing the distribution of maximum possible sizes of all known 70 non-planktivorous genera (groups) in the shark order Lamniformes, comprising modern (in gray) and extinct (in black; with hypothetical silhouettes) members and in comparison with an average adult human (in red) as scale. Megalodon clearly stands out. Credit:  Kenshu Shimada, DePaul University.

Sharks are among the most amazing creatures there are. Not only are they older than mammals and dinosaurs, their 450-million-year-old evolutionary history means that they even preceded trees! Perhaps the fiercest shark that ever swam the world’s oceans was Otodus megalodon, an extinct species of shark that lived from the early Miocene to the end of the Pliocene, between 23 to 2.6 million years ago.

If there’s one defining feature that Megalodon is remembered for, that would be its size. Huge is really an understatement. Although its exact size is still a matter of contention among paleontologists and shark experts, the fossil record suggests that Megalodon could exceed 15 meters (50 feet) in length. And, according to a new study published today in the journal Historical Biology, no other shark came close to it.

Megalodon: the uncontested king of the sharks

Famed fossil hunter Vito Bertucci with a megalodon jaw, measuring 3,4 m. (11 ft.) across and almost 2,8 m. (9 ft.) in height. It took her almost 20 years to reconstruct the jaw.

Like all sharks, Megalodon’s skeleton was mostly made of cartilage. This means that only its teeth and vertebrae have survived in the fossil record. But these are enough to infer many qualities about this fascinating ancient marine beast.

For more than two decades Kenshu Shimada, a professor of paleobiology at DePaul University in Chicago and research associate at the Sternberg Museum in Kansas, has been studying Megalodon teeth and gathering data from the scientific literature. Shimada’s aim was to plot Megalodon’s size and compare it to other sharks. What he found was truly shocking.

“The initial goal of this new study was to investigate the size distribution of sharks in the order Lamniformes over geologic time by developing a logical method to estimate the body, jaw, and dentition lengths from their teeth. We did expect Megalodon to be gigantic based on my previous study,  but what surprised us was actually seeing in our data a 7-meter-gap [23-foot-gap] between the size of Megalodon and the size of the next largest non-planktiviorous (i.e. carnivorous sharks that don’t eat plankton) lamniforms not directly related to Megalodon in the entire geologic history,” Shimada told ZME Science in an email.

“The significance of this new study is that it represents the first collective analysis surveying the body sizes of all major lamniform shark lineages including both extinct and living forms. It demonstrates Megalodon was uniquely gigantic relative to other non-planktivorous sharks,” he added.

A comparison between a megalodon (black) fossilized tooth and two great white shark teeth.
Image via Wikimedia.

Shimada estimated the size of various species of extinct lamniforms from the fossil record based on measurements taken from present-day, living non-planktivorous lamniforms. Also known as mackerel sharks, lamniforms include some of the most familiar species of sharks, such as the great whites.

After the tally was made, the researchers were amazed to find that the next runner up behind Megalodon was very far behind. While Megalodon’s size could exceed 14.1 meters (46 feet), all other sharks, including extinct species, generally capped at 7 meters in length (23 feet).

Some plankton-eating sharks came close to Megalodon, such as whale sharks and basking sharks, however, carnivorous sharks were far behind. The exact reasons why are yet unclear.

“There are still so many fundamental questions about Megalodon scientists are still trying to answer. While Megalodon bite marks on marine mammal bones are known, whether they represent predatory attacks or scavenging activities are still unknown. Related to our new study, exactly how large Megalodon could have reached remains uncertain where, at present, the scientifically justifiable maximum length estimates are in the range of 14.1-15.3 meters (46-50 feet). The validity of a recent study on the body form of Megalodon also needs to be tested or substantiated. This does mean that individuals larger than 15.3 meters did not exist, but simply the existence of such over-sized individuals has not been substantiated in the realm of science yet. Among many other questions, exactly why Megalodon became extinct also remains to be a big unanswered question,” Shimada said.

According to the study, lamniformes were well represented in the late Mesozoic-Cenozoic fossil record, a time during which they showed remarkable diversity and specialization. And since most of them were carnivores, the researchers assert that these ancient lamniforms must have played a major role in the evolution of marine ecosystems throughout geological time.

“The fossil record is a window into the evolution of ecosystems, and understanding why species become extinct, and how their rise and demise affected their ecosystem is critical to today’s oceans for issues like conservation of organisms, habitat preservation, and sustainable marine natural resources. Elucidating ecological variables as simple as the body size of organisms, especially carnivores like sharks in our new study, is the first step. While much of the attention has been given to the question, “Why Megalodon evolved to be so large?”, our new study has provided another way of thinking about the issue for future scientific studies, that is to ask ‘Why all other non-planktivorous lamniforms have had a general size limit of 7 meters [23 feet]?'” Shimada concluded.

Megalodon.

Megalodon’s teeth evolved over 12 millions years, researchers find

These “ultimate cutting tools” were a long time in the making.

Megalodon.

Teeth are the only reliably identifiable fossils from Carcharocles megalodon. They’re also damn huge.
Image credits Kristen Grace / Florida Museum of Natural History.

The teeth of megalodon (Carcharocles megalodon), the largest shark ever to prowl the oceans, look like daggers. They’re up to 7 inches (18 cm) long and shaped like blades. But it took them millions of years to evolve into their final shape, new research reveals. The findings created more questions than they answered, as we still don’t know why the process took so long or why it started in the first place.

Big fish, bigger bite

“This transition was a very long, drawn-out process, eventually resulting in the perfect cutting tool — a broad, flat tooth with uniform serrations,” said study lead author Victor Perez, a doctoral student in geology at the Florida Museum of Natural History.

“It’s not yet clear why this process took millions of years and why this feature [serration] was lost.”

Megalodon has to be one of the most awe-inspiring and mysterious animals out there. It was the largest shark ever seen on Earth, but the only trace they’ve left is their teeth. Which is quite fitting for a shark.

But these teeth, according to Perez’s team, evolved over 12 million years. The researchers analyzed the evolutionary path of megalodon teeth and those of its immediate ancestor, Carcharocles chubutensis. Their study revealed a surprisingly slow and gradual process, in which they shifted from large teeth flanked by cusplets to regular, cusplet-less teeth.

The team performed a “census of teeth,” analyzing 359 fossils along with the precise location of their retrieval at the Calvert Cliffs on the western shore of Maryland’s Chesapeake Bay — an area that used to be an ocean in C. chubutensis and megalodon’s day.

Megalodon’s earliest ancestor, Otodus obliquus, boasted three-pronged teeth (i.e. teeth with cusplets) that acted more like forks, the team writes. This suggests that O. obliquus dined on fast-moving (but not too large) fish, and it needed teeth to pin them in place. This species effectively forms the baseline from which later megatooth shark species derived.

The fossil record at Calvert Cliffs spans from about 20 to 7.6 million years ago, so they overlap with both C. chubutensis and megalodon. Perez’s team found a consistent decrease in the number of teeth with lateral cusplets over this timespan. About 87% of teeth from 20 to 17 million years ago had cusplets, falling to about 33% roughly 14.5 million years ago. By 7.6 million years, no fossil teeth had cusplets.

But here’s where the results start getting muddy. While the team notes that adult C. chubutensis had cusplets, and adult megalodon did not, they also caution that this feature is not a reliable identifier of which species a tooth belonged to — juvenile megalodon could have cusplets, making it virtually impossible to discern whether a tooth with cusplets came from C. chubutensis or a young megalodon. Furthermore, some teeth analyzed for the study had tiny bumps or pronounced serrations where cusplets would be. A set of teeth from a single shark even had cusplets on some, no cusplets on others, and replacement teeth with reduced cusplets.

While definitely interesting from a paleontological and biological point of view, such specimens make it virtually impossible for the team to draw clean lines between different species. They can’t pinpoint when megalodon first appeared or when C. chubutensis went extinct.

“As paleontologists, we can’t look at DNA to tell us what is a distinct species. We have to make distinctions based off of physical characteristics,” says Perez. “We feel it’s impossible to make a clean distinction between these two species of sharks. In this study, we just focused on the evolution of this single trait over time.”

So what can the study, then, tell us? Well, it does help to flesh out our understanding of how later megatooth species (such as megalodon) lived, how they hunted, and a bit or two about how they handled disease.

Megalodon fossils have flat teeth, often with serrated edges. Based on their shape, they likely performed a different job than that of its earliest ancestor: that of killing (or at least, mortally wounding) large, fleshy animals like whales or dolphins. Megalodon likely hunted in a single-strike manner: it charged at its prey and chomped down hard. Whatever didn’t die on the spot was left immobilized or too crippled to run away, and bleeding heavily.

“It would just become scavenging after that,” says Perez. “A shark wouldn’t want to grab and hold onto a whale because it’s going to thrash about and possibly injure the shark in the process.”

Lateral cusplets may have been used to grasp prey, according to Perez, which could explain why they disappeared as these sharks shifted to a new hunting style. It’s also possible that the cusplets kept food out from between the sharks’ teeth — so they helped prevent gum diseases. But, frankly speaking, the team simply doesn’t have enough information to know why these structures evolved out of the shark’s teeth.

“It’s still a mystery,” Perez says. “We’re wondering if something was tweaked in the genetic pathway of tooth development.”

One point I found particularly interesting was how important ‘beachcombers’ were for this study. The team says that vast majority of teeth they analyzed were discovered by amateur fossil collectors and donated to museum collections.

“This study is almost entirely built on the contributions of amateur, avocational paleontologists,” Perez notes. “They are a valuable part of research.”

The paper “The transition between Carcharocles chubutensis and Carcharocles megalodon (Otodontidae, Chondrichthyes): lateral cusplet loss through time” has been published in the Journal of Vertebrate Paleontology.

A supernova explosion may have triggered radiation exposure in Megalodon and countless other ancient marine megafauna. Credit: NASA Goddard Photo/Wikimedia Commons.

Exploding stars may have wiped off large ocean life 2.5 million years ago

A supernova explosion may have triggered radiation exposure in Megalodon and countless other ancient marine megafauna. Credit: NASA Goddard Photo/Wikimedia Commons.

A supernova explosion may have triggered radiation exposure in Megalodon and countless other ancient marine megafauna. Credit: NASA Goddard Photo/Wikimedia Commons.

About 2.6 million years ago, nearly a third of the world’s large marine species mysteriously disappeared from the world’s oceans. Among them were huge apex predators, such as Carcharocles megalodon, which ruled the seas for over 20 million years. Climate change played an important role in the demise of Megalodon and other creatures like it, but it alone doesn’t seem to explain the magnitude of the Pliocene marine megafauna extinction. Now, a new study suggests that the extinction event may have a cosmic origin — a supernova, or possibly a string of supernovae, may have bombarded the oceans with radiation that decimated the largest marine creatures.

Death from above

In a new study led by Adrian Melott, professor emeritus of physics and astronomy at the University of Kansas, researchers describe evidence of nearby supernovae, whose explosion coincided with the onset of the Pliocene megafauna die-off.

When a star is ready to drop the curtain, it goes out with a bang — a titanic explosion known as a supernova. Although it might sound dramatic, these highly energetic events are quintessential to seeding new stars and solar systems, as they expel and distribute matter throughout the universe. Thus, understanding supernovae is key to demystifying the grander astronomic picture — how the cosmos evolves and how we all came to be.

Supernovae can also be destructive if something happens to cross their path. Melott and colleagues claim that a series of such explosions occurred between 8.7 million and 1.7 million years ago, at about 325 light-years from Earth. That’s far away enough not to cause catastrophic damage but close enough to bombard Earth with cosmic radiation. And this radiation may have been powerful enough to triggered mutations that led to cancer among Earth’s megafauna. The larger an animal was during such conditions, the more radiation it would absorb, thereby making them more vulnerable to the supernova-sourced radiation. The researchers estimate that the cancer rate would have gone up by about 50% for something the size of a human, but it would have been much worse for something as big as an elephant or whale.

“I’ve been doing research like this for about 15 years, and always in the past it’s been based on what we know generally about the universe — that these supernovae should have affected Earth at some time or another,” said Melott, in a statement. “This time, it’s different. We have evidence of nearby events at a specific time. We know about how far away they were, so we can actually compute how that would have affected the Earth and compare it to what we know about what happened at that time — it’s much more specific.”

Scientists know that such supernovae have occurred and pointed towards Earth due to iron-60 isotopes that have been engraved on the seafloor. These isotopes have a half-life of about 2.6 million years, so if they formed with the Earth, they would have been long gone. But instead, such isotopes can still be found in sediments drilled from the bottom of the seas and oceans. This can only mean evidence of radiation bombardment from one or multiple supernova events.

Specifically, muons may have been the culprit for the Pliocene marine extinction. The muon is an elementary subatomic particle similar to the electron but 207 times heavier. Muons are all around us, the products of cosmic radiation interacting with the atmosphere. However, the supernova radiation may have triggered extra muon exposure — much more than life can normally tolerate.

“The best description of a muon would be a very heavy electron — but a muon is a couple hundred times more massive than an electron,” Melott said. “They’re very penetrating. Even normally, there are lots of them passing through us. Nearly all of them pass through harmlessly, yet about one-fifth of our radiation dose comes by muons. But when this wave of cosmic rays hits, multiply those muons by a few hundred. Only a small faction of them will interact in any way, but when the number is so large and their energy so high, you get increased mutations and cancer — these would be the main biological effects. We estimated the cancer rate would go up about 50 percent for something the size of a human — and the bigger you are, the worse it is. For an elephant or a whale, the radiation dose goes way up.”

But if that were the case, why didn’t land animals go extinct at a similar rate? Radiation from the sun and the cosmos typically can’t penetrate more than a couple of feet of water, thereby shielding marine life. However, the shielding doesn’t work for muons. Suddenly, creatures that had adapted to a low-radiation environment for millions of years become exposed to a lot of it. Land animals, on the other hand, were adapted to radiation exposure and weren’t as affected as marine life.

And as if supernova radiation wasn’t scary enough. Around the same time, 2.6 million years ago, the planet’s magnetic poles reversed, which opened the floodgates for muon bombardment. The final nail in the coffin was climate change — around the same time a new Ice Age started, greatly diminishing coastal food supplies.

All of these factors form a complex, but a plausible picture that may explain the extinction of Earth’s marine giants.

“There really hasn’t been any good explanation for the marine megafaunal extinction,” Melott said. “This could be one. It’s this paradigm change — we know something happened and when it happened, so for the first time we can really dig in and look for things in a definite way. We now can get really definite about what the effects of radiation would be in a way that wasn’t possible before.”

You can read the entire study here.

Otodus megalodon. Credit: Flickr, Elena Regina.

Megalodon may have been warm-blooded — and this may have ultimately doomed the huge predator

Otodus megalodon. Credit: Flickr, Elena Regina.

Otodus megalodon. Credit: Flickr / Elena Regina.

The extinction of the largest fish to have ever swum the world’s oceans is shrouded in mystery. Megalodon dominated the oceans for millions of years during the Miocene and Pliocene epochs until it abruptly disappeared before the onset of a massive ice age 2.6 million years ago. A new study suggests that the iconic extinct shark was significantly warmer than its modern cousins, which may have sped up its demise in the face of cooling waters due to climate change.

An active metabolism that needed a lot of food

In comparison to Megalodon (Otodus megalodon), the Great White Shark seems like a guppy. The extinct shark achieved lengths up to nearly 20 meters and weights exceeding 20,000 kg — and if its formidable size wasn’t enough, the huge fish also had razor sharp teeth, each as long as 18 centimeters (about the size of a human hand).

Credit: Wikimedia Commons.

Credit: Wikimedia Commons.

The earliest Megalodon fossils — almost exclusively comprised of teeth — suggest the marine predator first appeared about 23 million years ago. A 2014 study performed by Swiss researchers found that all signs of the creature’s existence ended 2.6 million years ago. It’s not clear what brought Megalodon’s demise but a new study presented at the annual meeting of the American Geophysical Union (AGU) suggests that thermoregulation may have played a major role.

The team of researchers at William Paterson University (WPU), the University of California Los Angeles, and DePaul University employed a novel geochemical method called clumped isotope thermometry (CIT). By analyzing the concentrations of oxygen-18 (18O) and carbon-13 (13C) isotopes within the carbon dioxide (CO2) of tooth enamel, it’s possible to tease out an animal’s body temperature. A lower concentration of clumped isotopes means that the enamel was formed at a higher body temperature

In order to verify the method, the researchers first worked with teeth from aquarium-reared and wild-caught sharks from areas with known temperature records. The method proved quite accurate.

Next, once the method was calibrated, the researchers analyzed the teeth of Megalodon and other ancient shark species, showing that the huge marine creature was a bit warmer than its coexisting shark species and modern sharks such as great whites.

The ancestors of sharks like makos and great whites lived alongside Megalodon millions of years ago, and likely had a temperature of about 20 to 30 degrees Celsius (68 to 86 degrees Fahrenheit), whereas Megalodon had a body temperature as high as 35 to 40 degrees Celsius (95 to 104 degrees Fahrenheit). That’s about the same body temperatures as whales, which are endothermic (warm-blooded).

Perhaps, Megalodon may have also been warm-blooded, although that is quite an assumption, judging from enamel isotopes alone. The relatively high body temperature, however, may be a sign of an active metabolism that required lots of prey and frequent feeding. When the planet went through a particularly tough ice age, Megalodon may have been too big for its own good, with too little prey to spare in order to sustain its high body temperature. Coupled with competition from other predators, such as toothed whales, Megalodon went on a downward spiral.

“While still preliminary, these results may provide clues as to what may have led to the demise of O. megalodon during the Pliocene. For example, one hypothesis is that O. megalodon consumed large quantities of prey in order to maintain such a high body temperature. However, cooling of ocean temperatures during the Pliocene would have constrained the species to lower latitudes where ocean temperatures were warmer, whilst its preferred prey (e.g., whales) evolved traits to adapt to cooler temperatures of the higher latitudes. Therefore, large climatic shifts combined with evolutionary limitations may provide the “smoking gun” for the extinction of the largest shark species to ever roam the planet,” wrote the researchers.

Next, the authors plan to analyze other isotope ratios in megalodon teeth, such as calcium-44/calcium-40 or oxygen-16/oxygen-18. The former can reveal more details about a creature’s diet, such as if a certain prey was more abundant, whereas the latter ratio can record information like seawater chemistry and temperature. Together, all of these methods could help paint a bigger picture of Megalodon’s demise.

Megalolamna paradoxodon had grasping-type front teeth and cutting-type rear teeth likely used to seize and slice medium-sized fish and it lived in the same ancient oceans megatoothed sharks inhabited. (Image by Kenshu Shimada)

New ancient car-sized species identified by paleontologists. It was related to Megalodon

Megalolamna paradoxodon had grasping-type front teeth and cutting-type rear teeth likely used to seize and slice medium-sized fish and it lived in the same ancient oceans megatoothed sharks inhabited. (Image by Kenshu Shimada)

Megalolamna paradoxodon had grasping-type front teeth and cutting-type rear teeth likely used to seize and slice medium-sized fish and it lived in the same ancient oceans megatoothed sharks inhabited. (Image by Kenshu Shimada)

Some 20 million years ago, both the Atlantic and the Pacific were haunted by a huge shark the size of a car. The new species, called Megalolamna paradoxodon, was just discovered and researchers think it was related to the biggest shark that ever lived, Megalodon.

It’s very difficult to find shark fossils and it’s not that surprising if you know they’re made of cartilage, not bones. Paleontologists sometimes can find fossils of those parts of the shark made of denser cartilage like the centers of the vertebra, jaw cartilage, and the rostral node in a shark’s snout. However, maybe 99% of all known shark fossils are the teeth. In the case of  Megalolamna p., five tooth samples collected from California, North Carolina, Japan, and Peru were all that scientists had at their disposal.

Shark teeth, however, are enough to learn an awful lot. Each sharks species’ teeth have a unique shape — in the case of Megalolamna p., these are shaped in a mosaic-like pattern. It helped that both front and rear teeth were found, the former used for grasping while the latter for slicing.

The geographical distribution of the new ancient shark's teeth. Credit: Kenshu Shimad

The geographical distribution of the new ancient shark’s teeth. Credit: Kenshu Shimad

Megalolamna p. lived in the Miocene period, about 20 million years ago, and likely ate medium-sized fish. That’s judging from its estimated size, about 12 feet long. The researchers from DePaul University in Chicago who were responsible for the find compared the teeth to those belonging to other extinct and currently living species to come with this estimate.

“The fact that such a large …shark with such a wide geographic distribution had evaded recognition until now indicates just how little we still know about the Earth’s ancient marine ecosystem,” said Kenshu Shimada, the lead author of the study and a paleobiologist at DePaul University in Chicago.

Its size makes the ancient the shark actually smaller than the great white shark, which can grow between 15 and 20 feet in length. However, at this point, it’s very difficult to judge just how big Megalolamna p. could grow. A shark might have smaller or bigger teeth in its jaw which might not reflect the true size of the fish. More fossilized teeth might help settle it.

Megalolamna p.’s cousin, the beast of the ancient high seas called Megalodon, could grow to 60 feet in length and its bite was more powerful than T-Rex’s. Megalodon seemed to have disappeared about 65 million years ago, so that makes the two species 45 million years apart. We know little to nothing about what happened in between this time frame, how Megalodon evolved, what it turned into etc. There are a lot of unanswered questions which only more fossil findings might help settle.

Findings appeared in the journal Historical Biology.

megalodon.

Megalodon extinction paved the way for whale development

Megalodon is quite possibly the most dangerous predator to ever live in the Earth’s waters in the recent geological history – roaming the seas between 28 to 1-3 million years ago. We’re still not sure why it went extinct, but a recent study suggests that its extinction paved the way for whales to grow more and more, reaching the enormous sizes we see today.

Today’s biggest whales. Credit: Smithsonian Institution

The blue whale is the largest creature ever on Earth. At 30 metres (98 ft) in length and 170 tonnes, it is also the heaviest. But it’s not the only huge whale around – the finback can measure over 24 meters (80 feet), while the sperm whale and the right whale can both reach 18 meters (60 feet). But why are whales so big, especially in a geological period where life forms tend to be smaller than what was going around in the Jurassic, for example? Paleontologists believe this has a lot to do with the Megalodon.

The Megalodon was the largest shark to have ever lived, reaching a maximum length of 18 meters (60 feet), and having 18 cm long teeth (7 inches)! It was one of the most powerful and robust predators in vertebrate history, shaping basically entire ecosystems around it. Megalodon had enough adaptability to inhabit a wide range of marine environments (i.e. coastal shallow waters, coastal upwelling, swampy coastal lagoons, sandy littorals and offshore deep water environments), and exhibited a transient lifestyle. Throughout its existence as a species, it faced an incredibly competitive environment, but it was no doubt on top of the food chain for over 20 million years. Juvenile Megalodon preferred habitats where small cetaceans were abundant, and adult Megalodon preferred habitats where large cetaceans were abundant – in other words, the Megalodon’s preferred food was whale.

megalodon.

Megalodon relative size. Image via Wiki Commons.

In a new study published in the journal PLOS One on Oct. 22, researchers looked at the records of 42 of the most recent fossils of the ancient shark and employed a technique known as Optimal Linear Estimation (OLE) to determine when this animal went extinct. What they found was that Megalodon was contemporary to some of today’s whales; they also found that as Megalodon went extinct, whales started to grow more and more, reaching the dimensions we see today.

This makes a lot of sense. A 18 meter long Megalodon could easily eat a bigger whale, even one much larger than it. The size of the whale would have actually made it a more desirable prey, so whales had no reason to grow more and more.

“Our results suggest that C. megalodon went extinct around 2.6 Ma.,” the researchers wrote. “Furthermore, when contrasting our results with known ecological and macro-evolutionary trends in marine mammals, it became evident that the modern composition and function of modern gigantic filter-feeding whales was established after the extinction of C. megalodon.”

The thing is, we still don’t know why the shark went extinct (and this goes for several other top predators), and this research might help us paint a picture of what happened.

“When you remove large sharks, then small sharks are very abundant and they consume more of the invertebrates that we humans eat,” Pimiento said. “Recent estimations show that large-bodied, shallow-water species of sharks are at greatest risk among marine animals, and the overall risk of shark extinction is substantially higher than for most other vertebrates.”

Journal Reference: Catalina Pimiento, Christopher F. Clements. When Did Carcharocles megalodon Become Extinct? A New Analysis of the Fossil Record. DOI: 10.1371/journal.pone.0111086