On February 15th, 2018 we learned about

Fossil footprints suggest that lizards have long been able to run on only two legs

110 million years ago, a small lizard near the coast of what is now South Korea was being pursued by a pterosaur. To better evade the predator’s attack, the lizard appears to have reared up, sprinting on its back legs across the moist sand. This upright-sprinting not only gave the lizard a boost in speed, but probably helped the lizard’s maneuverability, making it that much harder for the pterosaur to catch.

My third grader asked: Wait, the lizard ran upright? Like a human?!

Well, not exactly like a human, as lizards’ legs are angled out to the sides of their bodies, rather than under them. Looking at the 50 species of living lizards that can also pull off this maneuver, they don’t look a whole lot like humans as they run. In some cases it’s almost supernatural looking, as when the basilisk or “Jesus Lizard” (Basiliscus basiliscus) sprints across the surface of water.

My third grader said: Oh, like Dash from The Incredibles.

Ok, they’re not quite that fast, but the lizards that run on their hind legs today to move pretty quickly. That speed may even help explain how they started running this way to begin with— one hypothesis is that as a lizard with smaller front legs picks up speed, their center of gravity effectively moves back to their hips. They can then tip up over their hips, making turning easier compared to running on all four legs. However, that uses a lot of energy for a cold-blooded animal, which is probably why they’d save it for critical moments instead of becoming bipedal all the time.

Scientists aren’t actually sure how, or when, this behavior got started. Small lizards don’t get fossilized as often as bigger animals, so we don’t have tons of examples of every intermediate form that would hint at changes in the reptiles’ gait. Fossilized footprints aren’t common either, and these particular tracks aren’t only the first record of a bipedal lizard’s movement, but of any lizard at all.

My four-year-old asked: How are they sure the tracks are from the back feet only?

The tracks are clear enough to preserve specific details about the feet that made them, right down to toe and claw placement. There are a couple of prints that appear to be from the lizard’s front feet towards one end of the trackway, which help contrast from the back feet as well, particularly in their size. Combined with the distance between each foot, it all matches what might be expected when a small lizard was making a quick dash on its back legs.

Of course, it’s hard to be absolutely certain about something like a footprint. There is always a chance that the lizard was walking on all four limbs, but that the smaller front legs just weren’t making impressions in the soil. There’s not a lot to suggest that that’s the case, but it’s good to keep in mind that footprints alone aren’t giving us the whole story.

My third grader asked: So are we sure it was a lizard? How do they know it was being chased by a pterosaur?

The feet do match the anatomy of a lizard, and there’s no doubt that this type of animal was alive 110 million years ago. What motivated this particular critter to take off running is much more speculative— Yuong-Nam Lee, the paleontologist who discovered the tracks, was originally searching in those rocks for pterosaur prints. At first, he barely paid attention to the lizard prints once he realized they weren’t from a pterosaur. So while pterosaurs likely lived in the vicinity of the sprinting lizard at some point, there’s no direct evidence that these tracks were made to avoid being eaten.

Source: Lizards ran bipedally 110 million years ago by Hang-Jae Lee, Yuong-Nam Lee, Anthony R. Fiorillo & Junchang Lü, Nature

On February 8th, 2018 we learned about

Ancient arachnid appears to be an amalgam of spiders and scorpions

Arachnids have apparently been experimenting with limbs for the last 400 million years. While modern arachnids’ eight legs may seem weird enough, what we live with today is relatively tame compared to what was scuttling around during the Mesozoic era. Specimens recovered from ancient amber have revealed other offshoots of the arachnid family tree, some of which are almost an amalgam of spiders and scorpions, complete with long, whip-like tails. There’s no evidence that those tails delivered venom, but it does give us a better sense of the wide spectrum of spidery creatures that left us with the arachnids we know today.

The latest specimen has been named Chimerachne yingi, as it’s body looks like it combines features from both spiders and scorpions. Like it’s modern kin, the “chimera spider” sported eight legs, as well as function, silk-producing spinnerets. These critical organs are actually highly specialized limbs, and weren’t present on older arachnid ancestors. Combined with an age of 100 million years, C. yingi is probably one of the closest relatives to modern spiders ever found, even though it’s not thought to be a direct ancestor of what lives today.

Defined by differences

This is where C. yingi’s differences become relevant. Its exoskeleton is structured more like a scorpion than a true spider, with segmented plates along its abdomen that would have made its rear end more flexible. Even more dramatically, C. yingi sported a tail longer than its tiny, 0.07-inch body. That tail was thin and probably fairly flexible, evolved from yet another limb structure. It probably didn’t get used like a scorpion’s tail though, as researchers suspect it acted more like a rear-mounted antenna, allowing arachnid to probe its surroundings. Like other specific behavior, this can’t be completely confirmed from the specimen trapped in amber, but the overall structure looks more like a sensory tool than any kind of weapon or leg.

In the end, C. yingi wasn’t technically a spider. It was classified as an uraraneid, which was an order of arachnids that likely diverged from the modern spider lineage hundreds of millions of years ago. Their common ancestor likely sported the signature limbs and spinnerets, possibly along with tails too. It’s thought that the arachnids that eventually became our modern spiders must have then lost their shared tail and solidified their abdomens, diverging from both the uraraneids and arachnids like scorpions. So while this tailed creature wasn’t a direct relative of today’s spiders, its unusual anatomy is still helping us understand how spiders evolved.

Source: Part spider, part scorpion creature captured in amber by Elizabeth Pennisi, Science

On February 1st, 2018 we learned about

Small titanosaur answers big questions about ancient African geography

Mansourasaurus shahinae was only the size of a bus, probably weighing around five tons when it was alive 80 million years ago. That’s nothing to sneeze at, but it’s certainly not a record-breaker among its titanosaur relatives. Like other dinosaurs in this family, it sported a small head, long neck and small bony osteoderms on its back. Nonetheless, the discovery of M. shahinae is turning heads, not because of any unusual anatomy, but because of the place where it was found. It’s the seventh titanosaur from Africa, and only the sixth dinosaur species ever discovered in Egypt. As such, these fossils represent a relatively huge expansion of our understanding of African ecology in the late Cretaceous period.

M. shahinae was found in the Sahara desert, but certainly was not the only dinosaur living there. While Africa was habitable throughout the Mesozoic era, little is known of the animals that lived there thanks to a dearth of fossils. Much of the continent lacks the crisp, cliff-filled geology paleontologists benefit from in areas like the South Dakota Badlands, which often expose fossils from ancient layers of rock. Instead, much of Africa is covered in vegetation, making excavations much trickier get started.

No signs of African isolation

Fortunately, the fossils the team from Mansoura University found were in good condition. While there wasn’t a full skeleton, enough of the animal was preserved to clearly place it in the titanosaur family tree. As it turns out, M. shahinae’s closest known kin weren’t from Africa. The morphology of the available bones indicates that this dinosaur was more closely related to dinosaurs from Europe, not southern counterparts like Shingopana songwensis of Tanzania. M. shahinae, or rather its ancestors, must have had some way to access Europe.

This relationship then confirms a long-held hypothesis that Africa was connected to Europe and Asia by the Cretaceous period, similar to the geography of today. This may seem obvious from our modern perspective, but geologists know that the world’s continents were being considerably reshaped throughout the Mesozoic. Earlier on, most of the Earth’s land masses were clumped together in a huge super-continent known as Pangea. As the continents broke apart, it wasn’t clear when an animal living in Africa would necessarily have access to places like Europe, leaving a definite chance that dinosaurs like M. shahinae would have actually been geographically isolated. The similarities to European dinosaurs found in M. shahinae‘s fossils then provide critical evidence for this question, certainly making it a bigger discovery than the simple sum of the animal’s parts.

Source: New Egyptian dinosaur reveals ancient link between Africa and Europe by Ohio University, Phys.org

On January 18th, 2018 we learned about

Survey of species parses the prerequisites for a wielding a weaponized tail

It’s hard to fight with your rear end. Aside from a creature like a horse chasing away flies with its tail, few creatures can be said to be more intimidating from behind. There are exceptions to this rule, and they’re unusual enough that researchers have studied every tail-swinging tough-guy to see why those species evolved to fight with their rears instead of their claws or faces. Even though using one’s head or limbs would seem perilous in its own way, the number of anatomical requirements needed to make a tail weapon functional may have curtailed (ahem) their popularity in both living and extinct animals.

There’s obviously some variety to how a weaponized tail can operate. Dinosaurs like Stegosaurus carried spiked thagomizers, while some ankylosaurs ended up with bludgeoning clubs. Living species are generally a tad less ornamented, but the quills on a porcupine or the speedy snap of a monitor lizard’s tail can still make a foe think twice about attacking. Once a list of 286 species was assembled, researchers categorized them by an array of traits, from diet to size to the presence of bone or spikes on the tail’s tip. At that point, the data could be sorted and sifted to find what common threads united the reptiles, mammals and dinosaurs that have ever purposely backed into a fight.

Two traits proved to be universal among all the tail-swingers. Every animal that did battle with its rump was an herbivore, and as such these weapons weren’t being used for hunting. Most living species with dangerous derrieres only use them defensively, although exceptions, like rainbow agama lizard, pick fights to compete for mates. Still, it seems that teeth and claws have an edge (sorry) for predatory activities, beating out clubbed behinds as the anatomy of choice for predators around the world.

Other traits that were tied to tail weapons weren’t quite as obvious. Creatures with enlarged tail tips, like Ankylosaurus, Glyptodon or Shunosaurus, were all huge, with specially formed vertebrae in their tails. Stiff tails seem to require a smaller minimum body size, but shared a likelihood for osteoderms, or bony skin armor. Tail spikes, such as those found on a Stegosaurus or meiolaniid turtles, were tied to more head ornamentation, wide hips and some kind of bony but discontinuous armor on the torso. All the extinct species were also found to share osteoderms enveloping their tail tips, as well as an unusually stiff trunk, possibly to provide better leverage for lateral tail-swings. Living backside-battlers still follow many of these rules, although the minimum size requirements have shrunk down to around three feet in length since the age of dinosaurs.

Putting these parts in perspective

This may seem like a very roundabout way to describe animals we already know of, but organizing these traits helps bring a few things into focus. Requirements like stiff bodies and protective skin covering had to evolve before tails were weaponized, since a tail club or spike is the less common feature, and there’s evidence that anatomy like osteoderms actually fused together to create those weapons in the first place. However, most large herbivores found other ways to protect themselves before actually developing a rear-mounted defense mechanism. This isn’t to say that tail weapons were ineffective at their jobs, but that they require so many other anatomical conditions first, they’re very unlikely to evolve in the first place.

It also seems that, as cool as a tail bludgeon or thagomizer may have been, the complete package of bulk, armor and bone didn’t necessarily out-compete other forms of defense once they were assembled. Instead, brawling with one’s butt remains a bit of a niche adaptation that evolution keeps playing with, but rarely fully commits to.

Source: Where did all the tail clubs go? by Victoria Arbour, Pseudoplocephalus

On January 11th, 2018 we learned about

Wear and tear on fossilized teeth used to update assumptions about pterosaur diets

Puffins have a deep, almost domed beak that they use to retrieve fish from the sea. When feeding offspring or a mate, they often carry around 10 fish at a time, clearly demonstrating how well-suited their mouths are for handling seafood. From this reference point, it would seem reasonable to assume that other animals with similarly shaped mouths would also use them to hunt fish, which is how paleontologists once concluded that the pterosaur Dimorphodon macronyx was a piscivore back in the Jurassic period. The catch is that no other anatomy on this ancient creature really aligned with the rest of a puffin’s lifestyle, starting with its teeth.

An absence of corroborating evidence

Unlike birds, pterosaurs had mouths full of teeth, although figuring out what they used them on hasn’t always been easy. Some teeth are highly specialized, with flesh-slicing serrations, or baleen-like density, but pterosaurs like D. macronyx leave more to the imagination. Since pterosaurs have lightweight, hollow bones, few of their skeletons have been well preserved as fossils to say nothing of the handful of stomach contents that survived the test of time. As such, this has left researchers with a limited range of evidence to figure out what pterosaurs once ate, forcing them to rely on things like mouth shapes and the environment where the fossils were found.

Dimorphodons did have a rather puffin-esque mouth, but its body didn’t really live up to a fully pescatarian lifestyle. Most estimates of the small pterosaur’s flying ability haven’t been terribly optimistic, suggesting that D. macronyx wouldn’t have been able to gracefully soar over the water’s surface to snatch fish out of the sea. Even other species that were likely adept at air travel have raised questions about their buoyancy and ability to take off from a watery start. Fortunately, a new line of evidence has finally been opened up in the form of an infinite-focus microscope, which is finding new clues written in the pterosaurs’ teeth.

Dental details in 3D

The images compiled from the infinite-focus microscopes allowed researchers to not only look closely at the small scrapes, scratches and chips in a fossil’s teeth, but also to produce 3d models of them to better display those markings. Once a clear pattern was identified, it was compared to living animals with familiar diets, such as crocodiles, bats and lizards. After scanning the wear and tear on D. macronyx’s teeth, it became clear that they weren’t sushi lovers, but instead lived off of small vertebrates and insects, which seems to be a much better match for a non-marine predator. Other species’ diets have been amended as well, all without the need to excavate new fossils.

This doesn’t mean that no pterosaurs lived off of seafood, or that mouth morphology can’t be used to understand how extinct animals lived. Even if D. macronyx wasn’t carrying fish, it probably couldn’t use its short snout to chew tough plants either. But tooth damage does provide a widely-shared reference point that will hopefully help build richer, and more accurate, pictures of extinct animals’ ecology.

Source: Tooth scratches reveal new clues to pterosaur diets by John Pickrell, Nature News

On January 10th, 2018 we learned about

The world’s oldest proboscis appears to predate the first flowering plants

It’s an odd question to have to ask, but what good is a drinking straw without a drink? A skinny tube, such as the long, nectar-sucking proboscis found on moths, flies and butterflies, is generally only used to obtain liquefied nourishment. In some cases, proboscises can be so specialized that they only work with specific flowers, which makes the discovery of some 200-million-year-old butterfly fossils quite mysterious. What would that ancient insect be eating if it evolved before the world’s first nectar-filled flower even existed?

The fossils in question were found in Germany, dug out of what was once an algae-covered bog. The low oxygen levels of that bog water helped preserve some amazingly delicate scaled wings off of what is now the oldest-known member of Lepidoptera, the group of insects that includes moths and butterflies. Aside from being tiny, the scales were hollow, requiring that they be removed from the surrounding soil with a “pick” tipped with a single human nose-hair to avoid damaging them.

From old wings to early diets

The structure of these scales was crucial to this study though, as it greatly narrowed what lineage this insect came from. Today, hollow scales are found in moths and butterflies in the suborder Glossata, a group also noted for their flexible probosices. When this anatomy is compared to the timeline of flowering plants, it becomes clear that this Triassic-aged butterfly had no nectar to drink anywhere, since the fossil record can only confirm the first flower’s existence 70 million years later.

So what does this say about the proboscis this insect probably had? There isn’t much evidence to work with, but the current hypotheses are that this early butterfly or moth was using its elongated mouth to hydrate itself in the Triassic’s arid climate, or pick sweet pollen out of sap. There’s precedent for the latter option, as kalligrammatid lacewings, an extinct line of insects that were the spitting image of a modern butterfly, were also thought to pick up pollen with their elongated mouthparts around 125 million years ago. Since there even flies toting proboscises of their own today, it seems that there has been an evolutionary advantage to elongated, flexible mouths for quite a long time.


My third-grader asked: How did they know it had a proboscis if they didn’t see its head?

It’s a guess, but a guess based on a number of types of evidence. Members of Glossata all have proboscises , and while the owner of these wing scales may have possibly bucked that trend, that anatomy is a defining feature of the group. It’s also not the only specimen that’s rewriting Lepidoptera’s origins. Another fossil from 190 million years ago was found in England, helping to establish that these insects were fairly well established by the Triassic period. This doesn’t mean that a better preserved fossil can’t overturn this hypothesis, but right now everything is pointing in that direction. At least until we find fossils from the true first flower, which may be even older than any of these bugs.

Source: 'Butterfly Tongues' Are More Ancient Than Flowers, Fossil Study Finds by Rebecca Hersher, NPR

On January 4th, 2018 we learned about

Fossilized microbes show surprising biodiversity from 3.4 billion years ago

Most rocks on the Earth’s surface don’t last more than 200 million years before erosion or other forces get the best of them. Sure, that’s older than any dinosaur, but it’s only a tiny slice of our planet’s 4.5-billion-year history. Thankfully, rocks and crystals from the Earth’s early days do turn up here and there, helping us understand what our planet once looked like, and even more intriguing, who first called it home. That latter point is being revealed by 3.4-billion-year-old rocks from Australia, which have been found to not only contain fossilized microorganisms, but evidence of a surprisingly diverse ecosystem at a time when our planet was just beginning to be habitable.

Combing through fossils for traces of chemistry

The fossilized microorganisms weren’t multicellular animals of course, so these ancient rocks offered no bones or organs to study. Instead, researchers studied each singled-celled organism with secondary ion mass spectroscopy (SIMS). This technology allowed researchers to compare variations of carbon atoms, or isotopes, in the fossils and surrounding stone. The ratios of carbon-12 to carbon-13 was then be used to determine how each microbe functioned when it was alive, as those isotopes will accumulate differently in different metabolic conditions.

Differences in these early prokaryotes‘ metabolisms suggest that even 3.4 billion years ago, life had evolved a few different ecological niches. One group was apparently a methane producer, while another powered its metabolism by consuming methane. A third fossil showed signs of primitive photosynthesis that, unlike today’s plants, didn’t produce oxygen (which would have been toxic to these organisms). A microbe from an earlier study rounds out the bunch, as it relied on sulfur as its primary food-source.

Is life less unusual than we assumed?

This version of Earth certainly wouldn’t be habitable by today’s standards, but it’s an amazing degree of sophistication for a planet that had probably only had solid ground for 600 million years. This suggests that either the Earth was intensely lucky at an early age, or that life may be a bit more tenacious than we once thought. If it’s the latter, researchers suspect that this aggressive microbial timeline may have played out on other planets as well. It wouldn’t mean that other planets have the same complex organisms we do here, but that getting some microbes growing in the first place isn’t such a long-shot.

Until we get probes out to places like Europa, Titan or Enceladus, the best location to find extraterrestrial microbes may be Mars. This wouldn’t be to find microbes alive today, but to look for traces of similar fossils from the days when Mars was likely a more habitable planet.

Source:

On December 21st, 2017 we learned about

The difficult task of deciphering the world’s first known digging dinosaur

Sometimes the fossil that makes sense of a long extinct species isn’t a bone at all. This was the case with Oryctodromeus and it’s relative, Orodromeus. The strange dinosaurs found in Idaho and Montana just didn’t seem to add up when scientists first found them. Their anatomy was a confusing mish-mash of large and small proportions, with oversized shoulders and oddly robust hips. Once they could finally be placed in the proper context, these strange theropods suddenly made sense as the world’s only known burrowing dinosaurs.

No obvious ecology

One of the first discoveries of Orodromeus was understandably misleading. Researchers had thought they’d discovered a nest, complete with eggs and the strangely proportioned skeleton of the yet-unnamed species. Careful study discovered that this site was somewhat of a red herring though, as the eggs were from a larger Troodon, meaning the Orodromeus skeleton was probably the there as leftovers from the predator’s lunch

The eight-foot-long dinosaurs kept turning up in Idaho, which was also unusual, as the environment in that area 75 million years ago didn’t have much of the soft sand and silt that is better at fossilizing remains. Nonetheless, Oryctodromcus and Orodromeus remains were being found in multi-aged groups, suggesting that they lived in some kind of family unit, not unlike modern rabbits or prairie dogs. Hmm…

Answers in the shape of the sand and silt

The key that finally unlocked the puzzle wasn’t exactly a Oryctodromcus skeleton, but the solidified sand around it. Adults and two juvenile dinosaurs were found in what was clearly a filled-in burrow. The burrow was around six-and-a-half feet long, and sophisticated enough to include two 90 degree bends towards its center. Once researchers understood the space where these specimens had been buried, the dinosaur’s anatomy all started to make sense. These animals needed strong arms and shoulders to claw at the earth, with robust hips to help provide leverage in tight spaces. This also explained their abundance in Idaho, as they’d most likely been buried in holes that they themselves dug, increasing the odds of fossilization in a place where most creatures weren’t preserved.

While hindsight may be 20/20, it’s understandable that these Oryctodromcus‘ digging would have been hard to recognize. No other dinosaur was known to dig burrows up to that point, and so this kind of behavior simply wasn’t expected by anyone. Since that time, a species from South Korea, Koreanosaurus, has turned up as another potential burrowing dinosaur. Burrows from the early Cretaceous period have also been found in Australia, but in those cases no occupants were found at that site. Apparently burrowing wasn’t the most popular lifestyle for a dinosaur, but at this point it’s hard to say for sure how widespread digging one’s own hoe really was around the world.

Source: The dinosaurs that dug their own grave by Pete Buchholz, Earth Archives

On December 14th, 2017 we learned about

Portable scanners promise to expose the places where poached fossils were originally excavated

When a fossil is removed from the ground, some of the context of its original burial is necessarily lost in the process. Unless a dig site is carefully documented as the fossils are excavated, details about a fossil’s resting place are essentially lost to the ages. These problems are exacerbated when poachers strip sites of fossils to sell on the black market, as they’re usually more concerned with the commercial value of specific anatomy rather than advancing our understanding of the ancient world. As a result, specimens that might offer new insight into extinct animals like dinosaurs can’t be considered reliable, either due to a lack of context or even being a possible fake. Fortunately, portable x-ray fluorescence scanners are now being adopted to help identify these lost fossils’ original homes.

Identifying the source of illegitimate specimens

X-ray fluorescence is essentially a way to quickly identify the precise mix of minerals that can be found in any given location. First, an x-ray is fired at a soil or fossil sample, pumping energy into some of the targeted atoms’ electrons. As those electrons calm down again, they release a specific frequency of light, which the scanner can then detect and identify as a belonging to a specific mineral. En masse, the ratios of different minerals and elements can be combined to create a geochemical ‘fingerprint,’ unique to a specific site. In the field, this can be used to compare soil or rock samples from particular locations against fossils of unexplained origin. These readings are only useful if you have stone and soil samples for comparison, but now that x-ray fluorescence scanners are portable enough to take into the field, paleontologists are building a library of reference points for fossil poaching hot spots.

Of course, knowing where stolen fossils originated doesn’t prevent poaching on its own. However, as the technique has more and more successful identifications, it may deter poachers and buyers wary of having their purchases get reclaimed by their countries of origin. For example, actor Nicholas Cage made headlines when a Tarbosaurus skull he purchased was identified as being the product of poaching, compelling him to return the fossils to their rightful home in Mongolia. As identifying the origins of black market fossils gets easier and easier, this kind of corrective verification will hopefully become commonplace enough that poachers won’t bother excavating in the first place.

Restoring origins to archived specimens

Beyond making life harder for folks profiting off the theft and destruction of the world’s history, x-ray fluorescence may fill in more benign gaps in our records as well. Museum collections have plenty of specimens that were collected under the best intentions, but not the best documentation. Fossils are sometimes mislabeled, or archived with only minimal data for future scientists to reference, which makes them hard to use in comparative studies. As more geochemical data is gathered with around the world, more details about these archived specimens can be recovered. With this contextual data, paleontologists may be able to restore scientific value that was otherwise lost at the dig site.

Source: Thieves Are Smashing Dinosaur Fossils. Science Is Fighting Back. by John Pickrell, National Geographic

On December 7th, 2017 we learned about

Elephant feet provide context in studies of extinct sauropods’ footprints

To understand how extinct dinosaurs functioned in the world, paleontologists often look to living animals for examples of how similarly built creatures put their modern anatomy to use. For example, the thick, columnar legs of an elephant seem like a good reference point for how ancient sauropods might have lumbered around.  Looking beyond bones, researchers are thinking that modern elephants can also be a reference point for trace fossils, like footprints made back in the Mesozoic era. While sauropod dinosaurs haven’t shared a direct ancestor with elephants for over 100 million years, the hope is that the similarity in their ecological niches as giant herbivores will carry over into other aspects of each animal, right down to the bottom of their feet.

In South Korea, a fossilized footprint revealed a very specific similarity between elephant and sauropod feet. The trace fossil footprint was covered in a sort of honeycomb-shaped pattern, as soft mud crept into the cracks of the dinosour’s feet way back in the Cretaceous period. The resulting texture shows the dinosaur’s feet were covered in hexagonal scales across their soles, looking strikingly similar to the natural tread found on an elephant’s feet. It’s hard not to assume that this was a case of convergent evolution, with both large herbivores evolving the same “solution” to keeping thick, heavy limbs from slipping as they walked through soft soil or wet mud.

Inferring size from a foot’s impression

A second study looking at sauropod footprints wasn’t focused on the texture of the dinosaur’s soles as much as what those prints could tell us about the animal as a whole. Starting with the simple premise that heavier animals will make deeper footprints, researchers measured fossilized tracks and then simulated the forces that would be needed to make different sizes of footprint. Once a match could be made between simulated feet and the depth of actual fossilized prints, researchers could then calculate just how much the original sauropod must have weighed to sink that far in the soil.

To validate this method, they turned to elephants as the closest living approximation for extinct sauropods. Researchers used the same techniques developed around fossilized prints on fresh elephant footprints, since they could then verify the living elephant’s weight. In the end, the simulated footprints weren’t perfect, but with a margin of error of around 15 percent, they were at least as close as other methods for estimating dinosaur mass. For example, estimates for a dinosaur’s size may be made calculating the animal’s volume based on bone sizes, which in turn is often based on living animals as reference points. The hope is that estimates based on footprints can be refined to become more accurate, particularly in regards to the physics that control soil movement.

Restraint in using elephants as reference points

Other researchers question the validation aspect of this technique though, since we can’t be sure if elephants really are the best reference point for animals that could grow to be close to 100 feet long and probably weigh ten times more than the largest living pachyderm. Differences in leg movement, for instance, could change how weight is distributed across a dinosaur’s heels and toes, which could affect how deep a foot presses into the dirt. These critics aren’t advocating that giraffes or rhinos would necessarily be a better model organism, but that we should be careful about assuming too much about how sauropods were built and moved, even if their feet now seem so familiar.

Source: Can fossil footprints reveal the weight of a dinosaur? by David Moscato, Earth Magazine