On July 19th, 2018 we learned about

Even with extra atmospheric carbon dioxide, plant-eating dinosaurs probably didn’t struggle with nutritional deficiencies

If a mouthful of meat has more calories than the same volume of veggies, how could the world’s biggest dinosaurs manage as herbivores? Between having relatively small mouths and a diet we presume to be based around green, leafy material, it’s hard to imagine how a 33-ton Apatosaurus could find time to do anything but eat in order to power its enormous body. To further complicate things, scientists have long believed that the higher concentration of carbon dioxide (CO2) in the Mesozoic atmosphere would have encouraged plant growth but left them with less nutritional value. Unless these animals had some amazing metabolic trick unheard of in any of their living bird and reptile relatives, the simplest explanation would be for some of these assumptions to be… wrong.

Approximating the Mesozoic atmosphere

As one of the key building blocks of plant life on Earth, CO2 availability does make a difference in how plants grow. Since it’s hard to pull nutritional data from fossilized wood or leaf impressions, scientists conducted an experiment, growing various plants in different atmospheric conditions. The plants were all picked as approximations of the species that lived millions of years ago, and included things like dawn redwoods, monkey puzzle conifers, ginkgo, ferns and horsetails. Naturally, these plants have likely changed to adapt to modern conditions on Earth in the last 65 – 250 million years, but they could hopefully offer a sense of how CO2 would affect their nutrient levels.

Growing a tree or fern in 400 to 2,000 parts per million concentrations of CO2 is only step one though. To figure out how much one of these high-carbon plants might benefit a hungry dinosaur, researchers had to next come up with a fake digestive tract, which they created by fermenting the plants in cattle rumen fluid for 72 hours. By capturing the various byproducts of this process, this technique is used to figure out how easily digestible food is for livestock, and thus could give us a sense of how easy or tough any particular plant was to extract nutrients from. Chewing and other processing strategies like gastroliths weren’t really included in the ‘simulation,’ although since different species of dinosaur ate differently, that seems like a fair omission.

Everything a growing dinosaur needs

In the end, researchers found that the extra CO2 didn’t reduce the nutritional value of these plants as much as had been previously assumed. A 33-ton sauropod was calculated to have only needed 242 pounds of monkey puzzle leaves grown in the CO2-rich Triassic air. That’s certainly a lot of food, but since it’s at the low-end for an African elephant’s daily intake, it would have certainly been possible. If that weren’t good news enough for large herbivores, researchers also found that some plants showed no loss of nutrition at all. A dinosaur eating horsetails grown at three-times modern CO2 levels would only need 112 pounds of food a day, assuming they really liked horsetails.

The overall takeaway is that herbivorous dinosaurs likely had a more nutritious salad bar than we’d ever thought. The gap between these nutrition values and earlier estimates suggest that ancient flora could have fed 20 percent more herbivores than anyone thought, possibly requiring reconsideration of dinosaur population density in general. As exciting as more giant sauropods and hadrosaurs may sound, not every animal would have benefited from these CO2-soaked leaves. Herbivorous insects rely a lot on nitrogen in the plants they eat, which was one of the few nutrients that was definitely reduced in the experimental plants. It’s too early to say at this point, but it’s possible that insect populations suffered in the way we had previously assumed dinosaurs did.

Source: The real palaeo diet: the nutritional value of dinosaur food by Susannah Lydon, The Guardian

On July 12th, 2018 we learned about

Ingentia prima offers an alternate model for how dinosaurs could be so big

Being gigantic is obviously awesome, but that doesn’t mean it’s easy. Juggling growth rates, heat retention, reproduction and stuffing one’s face full of calories have long seemed like a difficult challenge for evolution. While there have been some wrong turns, paleontologists have been putting together the pieces of history’s largest dinosaurs, hoping to build a sort of anatomical formula for how to prosper as a huge animal. Many of those key traits seemed to have gotten their start 180 million years ago in the Jurassic period, when long-necked sauropods like Vulcanodon started paving the way for eventual giants like Brachiosaurus and Argentinasaurus. Of course, science is all about revisions, and a newly discovered dinosaur out of Argentina is making researchers rethink what was needed to be big, right down to when being big became a thing in the first place.

An earlier start for being big

Ingentia prima was a 32-foot-long herbivore that lived 215 million years ago, in the Triassic period. Since most of the early dinosaurs of this period were closer to the size of large dogs and turkeys, the fact that this creature likely grew up to 11 tons in that time period wasn’t really expected. Yes, there would have been a transition from smaller dinosaurs to the larger herbivores of the Jurassic, but I. prima predated those species enough that it’s not actually a direct relative of the sauropods that came later. This means that however specialized a long neck and barrel-shaped body may seem, scaling that anatomy up to ridiculous sizes was advantageous enough that evolution did it at least twice.

Different ways to develop limbs

That’s not to say that I. prima was a perfect predecessor of the sauropod cousins that would come later. Features that were thought to have been critical to these dinosaurs’ evolution apparently…wasn’t. For example, many large sauropods had straight, column-shaped legs that likely helped support the animals’ immense weight, even at the cost of mobility. These legs may have helped some later sauropods like Argentinasaurus reach their truly mind-boggling sizes, but I. prima apparently handled 10 tons of mass with relatively crouched knees and elbows.

In addition to a different posture, the growth of I. prima’s bones was different as well. The bone structure of most sauropods indicates that they grew at a regular, even pace. In contrast to this, I. prima may have handled its bulk by growing in quick fits and spurts. Cross-sections of the I. prima’s bones show that it’s bone growth looked a lot like tree rings in seasonal conditions, increasing immensely at certain times while being relatively static at others.

Shared air sacs in the spine

All this analysis of I. prima’s skeleton did find that the dinosaur did share one size-strategy with it’s Jurassic cousins, which is the inclusion of air sacs in its spine. Similar to the air sacs found in modern bird skeletons, these carefully located voids would have lightened the weight of vertebrae without sacrificing structural integrity while also helping with respiration and possibly temperature control. The fact that this trait later evolved again in large sauropods indicates that, unlike thick, even legs, taking a load off one’s back may have truly been a crucial piece of how these animals grew to such enormous sizes.

Source: Discovery of 'First Giant' Dinosaur Is a Huge Evolutionary Finding by Laura Geggel, Live Science

On July 9th, 2018 we learned about

Prehistoric pink pigments found in fossils of world’s most ancient organisms

Beauty, and by extension coloration, is only skin deep. It’s a frustrating fact for paleontologists, who can often only guess at what colors extinct creatures like dinosaurs may have been millions of years ago. Allowing for a few unusual exceptions, it’s just very unlikely for the color-producing pigments from an animal’s skin to be preserved as a fossil. Unless, apparently, that organism is so ancient and simple that there was never skin to worry about, in which case we can say with confidence that some of the world’s original organisms were all pink.

This conclusion is the result of oil drilling in the Sahara Desert. Some of the extracted shale was found to contain microscopic fossils from 1.1 billion years ago, well before any multi-cellular organism ever wriggled or swam across the Earth. When analyzed further, researchers realized that the fossilized cells were preserved well enough to carry molecules from the organisms’ pigmentation, and that that pigment would have given each cell a light pink hue. That pink was likely part of an early version of chlorophyll, which helped researchers identify exactly what kind of organism produced it.

Large numbers, tiny size

Cosmetic concerns aside, these fossils were identifiable as an ancient form of cyanobacteria. Their concentration was high enough to suggest that these tiny organisms likely dominated their ecosystem to such an extent that they may have been holding other forms of life in check. Until algae really spread throughout the oceans, an ecosystem flooded with minuscule cyanobacteria wouldn’t have provided much nutrition for larger, more predatory organisms. In fact, they’re so small many have been appropriated in to larger organisms’ cells, making up the chloroplasts found in plant cells today.

More complex organisms still had a long time to wait though. These tiny, pink cells would continue to dominate the planet for another 450 million years after this particular batch started becoming fossils.

My fourth-grader asked: What are cyanobacteria? What were they eating then?

Cyanobacteria were likely the first organisms on the planet, and they’re still alive today. They generally live in water, and produce their own food through photosynthesis, which is why some now live in plants as mentioned above. Thankfully for the rest of us, cyanobacteria’s primary waste product is oxygen, meaning their metabolism is actually the reason we have air to breath today.

Source: Scientists discover world's oldest colour – bright pink by Luke Henriques-Gomes, The Guardian

On June 28th, 2018 we learned about

Fossil record suggests that solitary primates regrew claws to help with grooming

No matter how badly you may want them, no matter how long you let you nails grow out, you will never grow claws. Humans and most other primates seem to have traded in proper claws for our flimsy nails around 56 million years ago. It might seem like we gave up some crucial anatomy in this trade, as claws can be used as everything from weaponry to climbing gear, although the fact that we now have touch screen-friendly fingers certainly helps. Nonetheless, paleontologists are now realizing that not every primate has been truly served by the loss of claws, which is why some genera have apparently regrown one on each hand, although not for the more adventurous uses listed above. The task they couldn’t give up was grooming, which raises questions about why our fashion-conscious species is able to get by with nails alone.

The long-standing assumption about primate claws is that they were lost to enable our ancestors’ mobility. As arboreal climbing, leaping and grasping became increasingly important to these animals, thinner, flatter nails likely provided an advantage over more pronounced hooks and knobs. Nails would be less likely to snag on small branches, allowing a hand to rotate around a branch as an animal swung through the trees in a way embedded claws just wouldn’t allow for. As far as anyone knew, once a common ancestor switched to nails, there was no going back.

Caring for hair with claws

Except, of course, for all the living primates that still sport a tiny grooming claw on each hand. Lemurs, lorises, galagoes and tarsiers all have a tiny claw on their second digits, enabling them to pick debris and parasites like like lice and ticks out of their thick fur. These claws aren’t exactly fierce, and they had long been thought to be a hold-over from an alternate branch of the primate family tree. A new survey of fossil fingers has started to unravel some of this model though, suggesting that some modern grooming claws have actually developed again, restoring anatomy previous lost to fingernails.

As researchers pieced together all the distal phalanges, or finger-tip bones, held in various collections, they realized a pattern was emerging that might help explain why some species needed a grooming claw while others didn’t. More solitary species, such as the modern titi and owl monkeys, need these claws to groom themselves. Primates that live in social groups don’t need that extra tool, because they can rely on each other to clean up their fur. This study can’t prove conclusively that this is why some primates have regrown their claws while others haven’t, but if this trend holds true, it opens up a new avenue for understanding extinct animals from their fossils alone. Because the grooming claw may be tied to the social structure of a species, finding the right bony digit could presumably reveal a lot more about how an animal lived than just the size of its fingers.

Source: Fossils show ancient primates had grooming claws as well as nails by Natalie Van Hoose, Phys.org

On June 28th, 2018 we learned about

Ancient organisms originally grew bigger to boost the distribution of their offspring

Long before any mammals, dinosaurs or even fish existed on Earth, the most advanced forms of life looked a bit like single fern leaves growing along the sea floor. These organisms, called rangeomorphs, literally stood out among more primitive life forms, growing larger and taller than most other life at the time. It’s easy to dismiss this difference as bigger being better, but that vague assertion doesn’t really provide insight into why these organisms would have ever started growing larger in the first place.

If not for the moving water of the ocean, the world of a rangeomorph would be pretty dull. Fossils of these 600 million-year-old organisms show no hints of mouths, organs or any anatomy that would enable mobility. They could apparently stand passively on the ocean floor, soaking up nutrients from the water around them without fear of being eaten or disturbed. This may sound a bit like plants growing in a modern forest, but that’s not really an accurate comparison- a sapling, for instance, will have to race its neighbors for access to sunshine, send out roots for water and soil nutrients, and avoid being killed by herbivores and parasites. As far as the fossil record shows, rangeomorphs worried for none of these things, making their varying sizes even weirder.

Size for the sake of their offspring

Fortunately for paleontologists, the lack of activity in the Ediacaran-era ocean has allowed entire communities of rangeomorphs to be preserved as fossils. This allowed researchers to not only compare sizes of each organism, but also the distributions of where each stalk grew. Once competition for resources or defensive positioning were eliminated, researchers took another look at where the tallest stalks grew in relation to their larger ecosystem.

What they realized is that being taller apparently helped rangeomorphs distribute their spores, suckers or whatever form of propagule they depended on to reproduce. By growing taller, individual rangeomorphs could reach slightly faster currents in the water that would then carry offspring out across a larger range of territory. Essentially, growing taller helped these rangeomorphs spread out faster than their shorter kin.

Source: Why life on Earth first got big, Phys.org

On June 24th, 2018 we learned about

Many dinosaurs’ hyoid bone left their tongues immobilized in their mouths

You’ve probably never worried about this, but paleontologists have finally confirmed that dinosaurs like Tyrannosaurus rex couldn’t french kiss. They couldn’t lick lollipops, nor could they do that trick where you tie a knot in a cherry stem in your mouth. However amazing their teeth or jaws may have been, analysis of a bone called the hyoid has found that T. rex, as well as most other dinosaurs, couldn’t do much with their tongues besides swallow. Lacking the articulation of many modern birds, snakes and lizards, this sheds light how tongues evolve to support different animals feeding habits.

Degrees of tongue articulation

The hyoid is a small bone that, millions of years ago, was a gill arch in our fish ancestors. As animals have evolved along different ecological paths, the hyoid has been adapted to support a variety of anatomical needs. In humans, it sits above the larnyx, connecting soft tissues to help us manage the passage of air and food in our throats. In many birds, the hyoid juts further into the mouth, often acting as a mobile attachment point for the tongue. This enables a variety of tongue movements, including extreme cases like the curling, tube-like tongue of a hummingbird. Beyond tongues, hyoids also enable modern reptiles like the Mata Mata turtle to stretch and open its throat to suck in prey underwater.

However, in most theropod and sauropod dinosaurs, hyoids weren’t quite so active. They were found to usually be a relatively simple pair of rods under the tongue, suggesting minimal possibility for movement. This arrangement most closely resembles the hyoids of modern crocodiles and alligators, which isn’t entirely surprising. These crocodilians can position their heads well enough to lop off hunks of food, only needing their tongue to help push that food back to be swallowed. Without other demands, their tongues can essentially be fixed along the bottom of the animal’s mouth by muscle and other soft tissues. Dinosaurs like T. rex could probably use this sort of feeding pattern as well, relying on their heads and teeth to get food into their mouths to be swallowed.

When to switch from simply swallowing

This doesn’t mean that hyoids only became complex in the last 65 million years though. Plant-eating ornithischian dinosaurs, like Stegosaurus or Triceratops, had more sophisticated hyoids than many of their compatriots. Pterosaurs were also found to have hyoids that would have facilitated more tongue waggling and lapping. Taken together, these ‘exceptions’ help prove what a mobilized tongue could be good for— if T. rex could simply aim its mouth at its food, Triceratops and pterosaurs likely had to use their tongues to grasp and manipulate their food before eating it. This could be necessary for grasping and chewing twiggy plants, or getting a hold of small prey with long, skinny beaks. In modern birds, this kind of tongue use is clearly demonstrated by parrots who use their tongues to pluck and hold nuts and seeds, almost like a finger built into their mouth.

To really make the point about what pressures push a species to develop a more complex hyoid, researcher noted the difference between tyrannosaurs and avian dinosaurs more directly related to modern birds. While both groups were theropods, the larger, bitier predators had the more crocodilian tongue arrangements. Flying theropods like microraptors had mouths that look much more like modern birds, showing that taking to the sky created a need for a more complex mouth.

Source: Tongue-tied: T rex couldn't stick out its tongue by Nicola Davis, The Guardian

On June 7th, 2018 we learned about

Ancient arthropods’ clawed appendages made these predators successful at any size

While they were only eight centimeters long, the top predators of the early Cambrian period were dangerous from birth. The radiodontan arthropods like Lyrarapax unguispinus looked a bit like a modern ray with claw-like appendages mounted on the front of its head that could gather food to put into their circular, serrated mouths. As arthropods, these relatives of crabs and insects, there was a chance that these predators would start life in some kind of larval form, needing to mature before they could successfully hunt for food. However, a tiny specimen from China seems to prove that these animals were well-developed predators from day one.

Claws over cognition

Despite being over 513 million years old, we’ve been able to piece together a significant amount information about these ancient predators. In addition to the eye-catching, spine-covered appendages and semi-toothed mouths, fossils have even given us a glimpse of L. unguispinus brain structures. These structures suggest that while these creatures’ bodies were quite specialized for gobbling up their neighbors, their brains were impressively straightforward. While we think of predators as often having to plan and outwit their prey, there’s a decent chance that L. unguispinus mainly got by with its physical strengths and, for its ecosystem, large size.

The newest fossil of a juvenile essentially had a miniaturized version of an adult body. Even at less than two centimeters in length, the well-developed claws and mouth of this specimen suggest that these traits were formidable even at a smaller size. This puts the tiny sea monster in company with some modern predators, like praying mantises, who are ready to hunt for themselves before they’re full size.

Predatory pressure

A mini-Lyrarapax unguispinus also has implications for Cambrian ocean ecology, since a tiny predator would have likely been hunting down tiny prey (versus scavenging or being fed by its parents). L. unguispinus would have then been an influential predator at any age, and their presence in an area would put pressure on all kinds of prey species to develop forms of defense or evasion. This then fits with what we know about ecosystems from 500 million years ago, as the so-called Cambrian Explosion saw a huge increase in the variety and diversity of species on Earth during this time. A claw-faced predator that chased down prey of all sizes very likely contributed to this diversification, since it was apparently hard to avoid being eaten by one of these spiny arthropods.

Source: Earth's first giant predators produced killer babies by Science China Press, Phys.org

On May 31st, 2018 we learned about

Ancient mammal relative in Utah refines our understanding of land bridges to Africa

It was not terribly glamorous to be a mammal in the Mesozoic era. Most of the furry critters looked like small shrews, scuttling about in the in the shadows of the dinosaurs that ruled the world at the time. To really drive that point home, a recently described mammal-relative, Cifelliodon wahkarmoosuch, was found literally buried beneath one of its massive dinosaur neighbors. However, C. wahkarmoosuch is proving to be quite significant, providing information on everything from the evolution of mammals and their relatives to the shape of the entire world as it existed 130 million years ago.

Clearer look at a haramiyidan cranium

One of the first things that stood out about C. wahkarmoosuch was how much it was able to stand out at all. Most fossils of mammals and their relatives are either reduced to jaws and teeth, or are flattened so much that they’re hard to work with. Possibly thanks to the the bulk of the dinosaur it was buried under, this particular specimen still had a three-dimensional skull, which allowed researchers to learn more about its brain case with CT scans. Among other things, this view of the creature’s interior structures revealed large olfactory centers in an otherwise small brain, which, when coupled with relatively small eyes, suggests that C. wahkarmoosuch navigated primarily by its sense of smell.

C. wahkarmoosuch was also unusually large for its time. While most mammal-like creatures in the Cretaceous were still mouse-sized, this species of haramiyidan likely grew to a whopping two-and-a-half pounds. While that’s nothing that your average house cat couldn’t handle today, it was certainly larger than most of its contemporaries.

Longer lasting land bridges

Most significantly, what really grabbed researchers’ attention was just how much C. wahkarmoosuch resembled other haramiyiadans and other mammal ancestors from other parts of the world. For most of the Mesozoic era, there was essentially one giant landmass on Earth, called Pangea. Pangea started to break apart as early as the late Triassic period, but most estimates expected that they were much more fractured by the time C. wahkarmoosuch lived 130 million years ago. However, C. wahkarmoosuch seems to share a number of features with fossils found in South America and Morocco, which has researchers rethinking this timeline. When coupled with a growing number of dinosaurs turning up with similar, cross-continental anatomy, C. wahkarmoosuch helps build the case that these continents may have broken up 15 million years later than we thought.

My third grader asked: Well, how do they know how old it was? What if it was buried 15 million years earlier than they thought?

In this case, researchers could look at the sediment layers they dug through to get these fossils, the other fossils buried in that layer, and most importantly, the amount of lead and uranium found in zircon crystals mixed in with the other rocks.

When zircon crystals are formed in underground magma, uranium is able to become mixed in due to chemical similarities between zirconium and uranium. That uranium is radioactive though, decaying into lead over time at a fixed rate of change. Since we know that rate of decay, researchers can compare the ratio of uranium and lead in zircon crystals to see estimate how old a particular zircon crystal is. Once multiple crystals are compared, this radioisotope dating technique can date a rock or fossil to within 200,000 years- a fairly precise measurement compared to the millions of years discussed above.

Source: Utah fossil reveals global exodus of mammals' near relatives to major continents by University of Southern California, Phys.org

On May 24th, 2018 we learned about

A look at modern quail ligaments suggests that pterosaur legs had a limited range of motion

It’s hard to study extinct animals with no surviving descendants, which is why researchers have had to use modern quail skeletons to prove that pterosaurs didn’t move like bats. It sounds silly, but is also somewhat appropriate for animals that are often confused with dinosaurs and were also strongly compared to flying mammals when their fossils were first discovered. Because pterosaurs also flew on wings made of skin that extended from the animals’ torsos to their specialized fingers, the assumption was that their hind legs would also splay out as if they were a bat. That idea may be falling out of favor though, and a recent study with modern quail corpses may narrow the range of possible poses even further.

Which poses were possible?

With very rare exceptions, fossils usually only preserve skeletal anatomy in an animal. We can learn a lot from bones alone, as they will generally be marked by specific textures where muscle once attached, as well as stress damage from the pull of strong tendons. Of course, not all wear and tear adds useful information to a fossil, and flattened or broken bones make it harder to know how a skeleton once interacted with softer tissues like muscles, tendons and ligaments. Just because a thigh bone could appear to fit in a hip socket in specific orientation doesn’t necessarily mean that we can be sure the animal actually held itself in that posture when it was alive.

To see just how much of a difference soft tissue can make, Armita Manafzadeh from the Brown University dissected and analyzed the femurs and hips of modern quails. She found that a few ligaments in particular greatly reduced the range of movement in the bird’s legs, ruling out close to 95% of the leg positions that the bones alone could adopt. Among those positions are the bat-like leg poses seen in early reconstructions of pterosaurs, suggesting that pterosaurs never flew this way. This doesn’t take a huge stretch of the imagination, since while bats and pterosaurs could have independently evolved this posture in a case of convergent evolution, they’re so distantly related from each other there’s no way one animal inherited the pose from the other.

How close are these connections?

On the other hand, pterosaurs aren’t closely related to just about any animal alive today, including the quail used in this study. Pterosaurs weren’t birds or even dinosaurs, and so they wouldn’t have a direct connection to modern bird anatomy, especially as far as flight anatomy is concerned. Instead, this research is relying on the idea of phylogenic bracketing, in which a trait is inferred in one species by looking for shared traits in nearby branches of their family tree. Since the key ligaments that limited leg movement are similar in both birds and modern reptiles like lizards, it’s somewhat fair to assume that pterosaurs would have inherited similar anatomy from these groups’ last shared ancestor. Of course, reptiles nor birds flew with elongated pinkies either or developed a pteroid, so there’s also a chance that pterosaurs had time to evolved their own, specialized version of a more flexible ligament.

At the very least, these more bird-like postures don’t necessarily conflict with some of the best evidence we have about pterosaur legs— their trackways. Many trace fossils of pterosaur footprints have been found, which has helped build the hypothesis that larger pterosaurs used their legs and arms to hop, jump and catapult themselves into the air. What their legs did once airborne may need to be debated a bit further though.

Source: Study casts doubt on traditional view of pterosaur flight by Kevin Stacey, News From Brown

On May 17th, 2018 we learned about

Various dimensions of how dinosaurs dealt with being too big to incubate their own eggs

Out of all the challenges a parent faces, at least we don’t have to worry about how to properly sit on our children. As mammals that gestate our young inside their mother’s endothermic bodies, humans can be pretty sure that there’s no upside to perching atop our offspring. It sounds a bit ridiculous, but even warm-blooded birds and dinosaurs had to likely grapple with how to best incubate their eggs at some point in their evolutionary history. In fact, multiple studies have been trying to figure out how and when these occasionally gigantic animals ever managed to incubate their eggs without smushing them in the process.

Rigid pelvises requiring petite eggs

A modern bird’s pelvis is flexible enough to allow the passage of a relatively large egg. This larger egg allows for incubating babies to be as large and robust as possible when the egg is first laid, giving them a bit of a head-start on their development. It also allows for a larger, stronger egg, which raises questions about avian dinosaurs long ago.

A study of various species’ fossils found that ancient pelvis bones were fused together more tightly than their younger counterparts. This would limit the size of an egg that could be laid, forcing creatures like Archaeopteryx to have a much daintier clutch of eggs than more modern birds of the same size. These eggs would likely be more fragile as well, possibly to the point where the relative bulk of their mother would be dangerous. If true, this suggests that birds couldn’t really sit and warm their nests before birds’ pelvises evolved to allow for relatively larger eggs, around 100 million years ago.

Leaving space for large moms to sit

A second study looked at maternal bulk from a different angle, starting with the clutches of eggs themselves, rather than mothers’ pelvises. There’s some evidence that oviraptor dinosaurs would sit on their nests for warm or at least some kind of protection, so researchers started comparing nests to see how these creatures managed their eggs. While modern bird eggs are reliably strong enough to handle their mother’s weight, some species of oviraptor grew to be at least 3,300 pounds, heavier than any egg could be expected to handle.

Looking across eggs from multiple species of oviraptor, a general strategy started to become apparent. The ostrich-like dinosaurs arranged their eggs in a circle, with each oblong-egg arranged to “point” outwards from a central point. The eggs were fairly precisely arranged, always leaving an empty space in the center of their circle. The size of that empty space was found to be disproportionately larger in larger species of oviraptor, which researchers believe was intentional. It would have allowed a heavier mother to sit and place the bulk of her weight on the ground in the middle of her eggs, allowing the perimeter of her feathered body and arms to actually cover the eggs. Smaller species could apparently rest more directly on their clutch, as the empty space in the nest was significantly smaller, even for a smaller mother.

Bury the eggs if you’re too big

So if a larger oviraptor likely left room for her body between her eggs, how did multi-ton behemoths like Argentinosaurus deal with its eggs? There’s evidence that they employed a less attentive approach to nesting, which meant digging holes with their back legs, then burying eggs in those holes. Clutches of sauropod eggs have even been found in extended lines, meaning each egg was left to its own devices (and a bit of insulating dirt.) This may sound neglectful when compared to the efforts most modern birds put into parenting, but there are some modern birds like the malleefowl that rely on elaborate mounds of dirt to incubate eggs while the parents leave the nest behind. In those cases, it’s not even that the parent bird is too heavy to incubate a clutch of eggs. The advantage is that a parent is then left to move on and find food and more mates for the future, leaving their offspring to figure out their temperature and nutritional needs for themselves.

Source: How 3,000-Pound Dinosaurs Sat on Eggs But Didn't Crush Them by Laura Geggel, Live Science