On August 17th, 2017 we learned about

Chilesaurus diegosuarezi’s plant-digesting gut and the origins of ornithischian dinosaurs

When we first heard about Chilesaurus diegosuarezi, the unusual dinosaur was being labeled as a rare, herbivorous theropod. The creature’s leaf-shaped teeth just didn’t look up to the task of tearing meat compared to the pointed and sometimes serrated chompers seen in most theropods. The was speculation that this strange hodgepodge creature was a weird hiccup in theropod history, but new analysis suggests that C. diegosuarezi wasn’t a plant-eating theropod, but a bipedal ornithischian. If correct, this dinosaur may represent beginnings of the family tree we now associate with Stegosaurus, Ankylosaurus, and various duck-billed dinosaurs like Edmontosaurus.

C. diegosuarezi’s interest in eating plants isn’t being questioned. If anything, it’s thought to be an important factor in why his body has some more ornithischian traits. The big deliminator between theropods and ornithischians is usually the shape of their hip bones. Theropods, both before and after C. deigosaurezi, have what’s been called a “lizard” hipbone, because the pubis bone faces forward like on modern lizards. In contrast, ornithischians have “bird” hips, where the pubis faces backward. It’s all a bit confusing, because modern birds are actually theropods, even with that ornithischian-looking hip bone. With C. deigosaurezi being classified as an ornithischian too, it means that a rear-facing pubis bone must have evolved at least twice— once when the ornithischians first branched off the theropods, then again when with the development of birds.

What pressures moved the pubis bone

This may seem like a lot of arbitrary changes in anatomy, but there are explanations for why they would help each lineage survive. The plant eating of ornithischians would require bigger, more complex guts to digest than chomped flesh would, and so they’d literally need more space their abdomens. A forward facing pubis probably didn’t leave enough room for their digestive demands, giving an advantage to herbivores with “bird” hips.

While we now have birds that eat plant-based foods like nectar and seeds, digestion probably isn’t the reason a crow or sparrow ended up with a rear-facing pubis. In that case, the evolutionary pressure may have been balance. Modern birds don’t have the thick, muscular tails older theropods had, and so as their tails were reduced to the feather-covered stumps we know today, their center of gravity shifted. To avoid tipping over too much, the pubis bone evolved to face backwards, taking a bit of weight with it.

Obviously, C. deigosaurezi’s hips weren’t putting it on the road to flight, but were making room for a bigger tummy. Combined with a mouth well-suited for eating plants, it suggests that adapting to an herbivorous diet was a driving factor in the split between theropods and ornithischians. This then raises questions about what was happening in these creatures’ environment to make plant-eating so enticing that such transitions would occur. Changes in the continents were likely leading to more moisture on land, making the world a much more attractive salad bar, providing options to creatures that were trying out eating more than meat.

Source: One of the Most Puzzling Dinosaurs Ever Discovered Just Got a Major Rebrand by George Dvorsky, Gizmodo

On August 10th, 2017 we learned about

Scans of Moschops’ skull suggest that thick bone protected a small brain from headbutting

Over 100 years ago, a fossilized skull was excavated from South Africa. The creature was dubbed Moschops, and it was one of many bones that have since been found in the region. The initial examination found that the heavy-set herbivore probably grew to as long as 16 feet, weighing up to two tons. The creature was nearly all chest and shoulders, with thick legs but a relatively small, bulbous head. And that’s just about where the story would end if not for CT scanners that have now allowed researchers to peer inside this petrified skull to see some of Moschops inner workings, however small they may be.

CT scans, also known as CAT scans, are basically specialized x-rays that allow us to look at internal structures of dense objects. In the case of Moschops, researchers were able to differentiate which minerals were originally skull and which parts of the hard lump were once soft tissues like the brain. This allowed them to gain a much more detailed understanding of the animal’s anatomy, leading to hypothesis about the behavior of this long extinct creature.

Little brain in lots of bone

The most exciting aspect of Moschops‘ brain was how small it was. The rhino-sized animal only had a brain the size of a chicken egg, meaning most of the skull’s domed cap was actually six inches of solid bone. This kind of armor suggests that the brain was being protected for a reason, with speculation immediately pointing to head-butting activity like that seen in modern rams and deer.  Beyond the brain, other sensitive structures, like the inner ear and nerves connecting to sensory organs in the face, were equally protected. In fact, the positioning of the inner ear indicates that Moschops regularly kept its snout pointed to the ground and its forehead pointed forward. This contrast to the positioning of say, a dog, may another indicator that this creature was adapted to crack heads, although it probably also helped with grazing behaviors as well.

Funnily enough, the protection of this tiny bit of gray matter may indicate a considerable amount of sophistication in Moschops behavior. If these herbivores did bang heads like modern rams or deer, it means they had social contact within their species that valued such interactions. These social relationships require a degree of cognitive prowess to pull off, even if you’re impressing your friends by smashing your heads together.


My four-year-old said: It looks like a baby long-necked dinosaur with no neck yet.

The thick build of a Moschops torso and small head is somewhat reminiscent of a sauropod dinosaur like Brachiosaurus, but Moschops wasn’t a dinosaur. It was part of a group called therapsids that predated the dinosaurs by around 30 million years. Also that stubby neck probably would have been better suited for head-butting compared to the hollowboned necks sauropods perched their heads upon.

Source: New insights into the survival techniques of a prehistoric beast by Julien Benoit, The Conversation

On August 9th, 2017 we learned about

Fossils reveal evolution’s earliest examples of the “flying squirrel” body plan

Who knew gliding between trees on giant armpit pouches was so popular? While this kind of tree-hopping has been proposed as a starting point for winged flight, it’s apparently a successful enough strategy to have evolved repeatedly in the history of four-limbed animals. The two latest examples originate from the Jurassic period in what is now China, and were discovered in fossils so well-preserved the outline of the animals’ skin flaps were visible in the surrounding rock. At first glance, these creatures strongly resembled a modern flying squirrel, but closer examination reveals that they weren’t direct relatives of any modern glider.

The skeletons of Maiopatagium furculiferum and Vilevolodon diplomylos both featured anatomy that indicated they were gliders, even outside the skin flap impressions they were found with. They probably didn’t spend much time on the ground at all, as they had very long limbs and fingers. These wouldn’t have been great for outrunning a predator on the ground, but would have allowed these creatures to grasp and possibly hang from branches like bats without much trouble. Both creatures had a decent amount of hair, all of which makes them seem like a good blueprint for our modern gliding mammals.

A key difference between the two species was their diets. Simpler teeth in M. furculiferum indicate that it was a fruit eater, while more ridged crowns found on V. diplomylos‘ teeth point to that animal being a seed eater. The other big difference was their sizes— M. furculiferum was around ten inches long, close to the size of a modern flying squirrel, while V. diplomylos was more of a flying mouse, only growing to three inches in length. We’re not sure if these species were actually contemporaries of each other, but if so, these differences in size and diet would have helped them avoid competing for the exact same resources in the trees.

Not exactly an ancestor

For all of their similarities to modern gliding animals, we’re sure that neither M. furculiferum nor V. diplomylos were ancestors of today’s gliders because neither were actually mammals. The species were eleutherodonts, a parallel offshoot from the family of animals that also includes modern mammals. They were similar to mammals in most ways, with differentiation being noted in tooth formation, among other details. Eleutherodonts and other mammaliforms in the Jurassic and Cretaceous periods actually showed a lot of diversity between species, especially compared to the shrew-like creatures that represent “true” mammals from the same time periods.

For better or for worse, all these specializations, including gliding between trees, didn’t save this lineage from extinction. When the dinosaurs were devastated by the asteroid impact that ended the Mesozoic era, these mammaliforms went extinct too. Eventually, mammals would pick up the gliding lifestyle again, rediscovering it around 50 million years ago.

Source: These Jurassic "squirrels” were the first creatures of their kind to go airborne by Brian Switek, Earth Touch News Network

On July 27th, 2017 we learned about

Corythoraptor jacobsi appears to connect the cassowary’s head crest to the Cretaceous

An extinct species of dinosaur discovered in China has a lot people thinking about it’s living relative. The fossil remains of Corythoraptor jacobsi were remarkably well-preserved, allowing paleontologists to describe it as something similar to an ostrich and more importantly, a cassowary. In the Cretaceous period, the animal would have stood around five-and-a-half feet tall, topped off with an impressive half-foot of bony crest on its head.  That crest is so similar to what’s on modern cassowaries that researchers have even raised the possibility that the two dinosaur species may be part of a single lineage.

Possible proto-ratite

So what would an ancient, ostro-cassowary be like? Even if C. jacobsi turns out to be a cousin rather than an ancestor to these modern birds, we can still deduce a lot about its life from the fossils alone. This particular specimen was probably eight-years-old, although it wasn’t fully grown yet. It was part of the oviraptorid family of dinosaurs, a group of dinosaurs that generally sported beaks, strong legs and feathers. Those feathers may have never been used in flight though, as they were much fluffier and fringed than the plumage required to fly. Like modern ratites like ostriches, emus and yes, cassowaries, these creatures’ feathers most likely helped with showing off to peers, camouflage, and insulation against heat and cold.

Interestingly, there’s a chance that the tall, flat crest on C. jacobsi’s head served some of those purposes as well. Like a modern cassowary, the crest, or more specifically, casque, wasn’t a solid lump of bone. It was composed of various layers that would have allowed for empty cavities, blood circulation and more. These features suggest a range of uses, including a way to vent heat like a toucan’s bill, show off to potential mates or rivals, and possibly even emit low-pitched vocalizations. Much of this speculation isn’t due to mysteries specific to C. jacobsi’s casque, but that we’re not actually sure what cassowaries do with their heads either.

Figuring out the casque’s function

Cassowaries aren’t easy to observe in the wild, partially thanks to their small ranges in Australia and New Guinea that are difficult to traverse, much less follow occasionally dangerous, six-foot-tall birds. It’s been suggested that their casques protect them from falling fruit, possibly help them dig through loose soil, and vent heat. Their striking appearance is hard to ignore, even among brightly colored plumage and wattles, which begs the notion that they’re a display feature of some sort. Casques are found on males and females, although they tend to be bigger on females which supports the idea of some kind of sexual selection at work. Male cassowaries help with child-rearing, and so both sexes may have reason to be choosy about the health and stature of their partners. Finally, cassowaries are famous for emitting deep, booming vocalizations, and their crests may help them make or possibly hear those calls across long distances.

Understanding the casque on cassowaries and C. jacobsi may end up advancing a few different ideas about dinosaurs. If the value of a good casque can be pinned down, it may help us better understand crests on more distantly related species as well. While head crests were not uncommon among oviraptorids, they’re also found on other groups of dinosaurs, like “duck-billed” hadrosaurs. Of course, there might be more than one use for a huge lump on one’s head, but the resemblance between C. jacobsi and cassowaries raises hopes of a more direct comparison.

Source: Newfound Dino Looks Like the Creepy Love Child of a Turkey and an Ostrich by Laura Geggel, Live Science

On July 20th, 2017 we learned about

Identifying a pterosaur from a pelvis evolved for walking and leaping

Identifying flying animals by their hip bones isn’t easy. Generally, heads and wings are the big points of interest, as they give clues about maneuverability, diet and more, but we don’t get to choose which parts of an ancient skeleton get preserved. A recent example of this challenge started in 2015, when a strange bone was found in Alberta’s Dinosaur Provincial Park. The bone was in good enough shape to show specific structural features like muscle attachment points, but the overall shape was so odd it took extensive efforts to even be sure it was from a pterosaur rather than a dinosaur. However, the family of pterosaurs that has now been identified was actually very dependent on specialized hips, as they probably spent a huge amount of their time walking on the ground.

Identified as an azhdarchid

To help identify this walking, flying creature from the Late Cretaceous period, researchers enlisted the help of pterosaur expert Liz Martin-Silverstone. The team had done comparative analysis to rule out the chance that this strange pelvis was from a theropod dinosaur, but further work was needed to narrow down which kind of pterosaur would have hips so similar to animals that spent their time walking on the ground. Introducing information about the hindlimb helped a lot, as it showed extensive muscle attachment points for a very strong leg. The owner of the hips had been a azhdarchid, a family of pterosaurs noted for their big heads, long necks, and body orientation that would have let them look a giraffe in the eye when walking around.

Azhdarchids were likely the largest flying animals on Earth. The most famous member of the family is the enormous Quetzalcoatlus northropi, a creature that probably had a wingspan close to 33 feet across. The 550-pound predator was likely an able flyer, casually cruising through the sky at around 55 miles per hour. Those wings were probably saved for bigger trips though, since the animal’s specialized hips and legs, as well as fossilized tracks, all suggest that azhdarchids spent much of their time walking around on all four limbs, more like a giant stork or hornbill than a soaring falcon or pelican.

Time spent stalking

This model for azhdarchids’ ecology has been called ‘terrestrial stalking.’ These pterosaurs would fold their wingtips back, so their final digit on their hand pointed upward while their other fingers hit the ground. This positioning would be helped thanks to changes in wing proportions— shoulders and upper arms were bigger, while the wing fingers were shorter than you’d find on other pterosaurs. Long necks and heads would allow them to quickly strike downwards to eat smaller prey, and in some regions this anatomy was so robust that azhdarchids were likely the local apex predator.

This isn’t to say that azhdarchids were somehow giving up on flight though. One of the reasons researchers are excited with the hip bones out of Alberta is that they’ll provide more details about how these large pterosaurs could launch themselves into the air. Strong legs would have helped for stalking the land, but it’s been calculated that quick, anaerobic movement in those leg muscles would have allowed azhdarchids to basically leap into flight in a single motion. By studying the muscle scarring on the new hip bone, we’re getting a better picture of the balance between launching and walking, er, stalking.

Source: Paleontologists solve pterosaur pelvis puzzle, Phys.org

On July 13th, 2017 we learned about

Ouanosaurus showed its age with a set of full-sized sail spines

Young Ouanosaurus may have been cute, but they were fairly nondescript dinosaurs. They probably weren’t as rotund their cousins Lurdusaurus, and maybe had smaller hands than Iguanodons, but from a distance there probably wasn’t a lot that stood out about these herbivores. That changed as they aged though, and analysis of fossils has revealed the timeline for Ouanosaurus growth, particularly as it pertains to the development of the large sail that grew from adults’ backs.

While Ouranosaurus nigeriensis generally followed the iguanodont body plan, the 27-foot-long herbivore’s most striking feature was the row of bony spines growing on its back. Not every spine has been found, but it’s presumed that large, flat spines grew from the top of every vertebrae past the shoulder blades. The longest spine stood over two feet tall, indicating that a substantial structure sat on this animal’s back when it was alive. The details of that structure are still subject to debate though, with ideas ranging from a thin, sail-like membrane for thermoregulation, like jackrabbit ears, to a fatty growth to store food, like a camel or bison’s hump.

Small clues in big bones

To dig into the spines’ potential purpose, researchers have been examining the texture and structure of each bone. The first thing they found was what wasn’t there. The spines didn’t have the rough texture you find for muscles to attach, nor did they have openings for blood vessels that would presumably be needed to carry warmed or cooled blood in and out of the sail if it were needed to control the dinosaur’s temperature. One thing the spines, and the rest of the skeleton, had were lines of arrested growth (LAGs). LAGs are layers of bone that grow around dinosaur bones in correspondence with the amount of nutrients available to the animal. Like the rings of a tree, they can be used to calculate the growth rate and age of a particular animal, including when individual bones were grown.

Based on this data, researchers determined that Ouranosaurus nigeriensis grew up fast, and was fully mature in under ten years. In fact, the dorsal spines of the specimen in question started growing when that animal was only three, but continued to grow larger each year. By age seven when that individual died, the sail seemed to be fully matured. While a juvenile body might not need the heat dissipation or calorie stockpile of an adult, it’s hard to ignore the idea that sail growth corresponded with maturity. This lends itself to the last hypothesis about O. nigeriensis’ spines, which is that they were used to hold a display structure.

Showing off with a sail

There are many examples of animals sporting otherwise extraneous anatomy in order to impress their foes, their competitors, and their potential mates. In many species, these structures are also different depending on the sex of the animal, such as the amazing plumage on a male peacock vs. the brown feathers of a peahen. We don’t know if the fossils we have were from males or females, but it there is growing evidence that these spines, and the sails they likely supported, where fairly impressive markers of maturity among these dinosaurs.


My four-year-old said: That looks like the toy we have, but without the crest.

While I thought he’d be fixated on the animal’s sail, it’s fitting that a four-year-old wasn’t yet concerned with such things. Instead, my son was referring to a toy Parasaurolophus, a hadrosaur noted for it’s large, bony crest.

Like these hadrosaurs, Ouranosaurus nigeriensis had a wide, beak-like mouth, although the two species weren’t directly related. O. nigeriensis predated Parasaurolophus by close to 50 million years, and the resemblance is largely due to convergent evolution, where that particular mouth shape was simply a successful way to eat a variety of plants for both dinosaurs.

Source: Sail-back dinosaur got flashier with age by Pete Buchholz, Earth Archives

On July 6th, 2017 we learned about

Colossal crocodilian was built to be the top predator of Jurassic Madagascar

While the name may suggest otherwise, the Age of Dinosaurs was not always ruled by actual dinosaurs. Some ecosystems were instead dominated by other lineages, with crocodilians most often giving dinosaurs a run for their money. As distantly related members of the archosaur family tree, these animals often adopted similar predatory strategies as the theropod dinosaurs we normally think of as apex predators. This kind of convergent evolution ended up producing some amazing species, such as the recently named Razanandrongobe sakalavae.

Once glance at R. sakalavae would make it clear that this reptile wasn’t a modern crocodile. While the basic shape of the body looked crocodilian, that body walked on upright legs, allowing considerable ground-clearance and mobility. Its snout was wide and robust, carrying six-inch serrated teeth. When these factors are combined with an overall size that may have reached over 40 feet long, it starts to make sense why R. sakalavae would be compared to other apex predators like Tyrannosaurus rex. All these pieces of anatomy set the creature up to tear flesh and break bones with impunity in its local ecosystem.

Origins unknown

All these features beg the question of where R. sakalavae has been all this time? We don’t have any complete skeleton of this animal, with the few fragments that have been recovered coming from Madagascar. R. sakalavae was part of a crocodilian lineage called Notosuchia, and indeed R. sakalavae seems to be the oldest and largest member of that branch of the crocodilian family tree. However, Notosuchia is just as mysterious as this new reptile, as all known members appear after the start of the Jurassic period 174 million years ago. With no immediate way to trace how Notosuchia came to be, paleontologists refer to the sub-order as a ghost lineage, appearing in the fossil record without any clear ancestors to get them there.

R. sakalavae does help answer some of these questions. The large predator’s presence in what is now Madagascar adds to a hypothesis that Notosuchia  got its start in southern Gondwana, the super-continent that once included all of today’s continents in a single landmass. As exciting as a new giant, upright crocodilian with giant teeth may be, R. sakalavae’s real bigger importance may end up being that of a stepping stone towards uncovering its ancestors.

Source: Gigantic crocodile with T. rex teeth was a top land predator of the Jurassic in Madagascar, Phys.org

On July 5th, 2017 we learned about

Ecological opportunities awaited survivors of Mesozoic mass extinctions

Mass extinctions can apparently be great, as long as they’re someone else’s extinction. The odds aren’t favorable in the case of an ecological collapse that could lead to the total destruction of a huge range of life forms at once, but like any long-shot, the payoff can be big. Surviving lineages can spread to new territories, diversify into new species, and essentially rule their dominions for millions of years… at least until the next mass extinction.

Dinosaurs enriched by volcanic eruptions

The extinction event usually associated with dinosaurs is the one that wiped them out at the end of the Cretaceous period, but they had previously survived a different collapse earlier in their history. The first dinosaurs evolved around 240 million years ago in the Triassic period, but they didn’t immediately dominate their world. Moderately sized spices like Nyasasaurus parringoni lived in the shadow of predatory Rauisuchians, a group of reptiles that closely resembled dinosaurs, but didn’t survive the disaster that shook the world 200 million years ago.

Recent samples of mercury in rock layers around the world suggest that the Triassic period ended with enormous volcanic eruptions all around the super-continent, Pangea. Intermittent eruptions flooded around 4.2 million square miles of terrain with lava, but it was the accompanying smoke and ash that likely caused ecosystems to collapse. Smoke could have done everything from hiding sunlight for plants to raising the acidity of the oceans, all of which proved too difficult to survive for as many as 76 percent of the world’s species. Among the survivors, dinosaurs were able to take over new niches, eventually taking over the world as everything from feathered birds to mountainous herbivores.

Dinosaurs were able to enjoy the opportunity presented by the Triassic’s period of volcanic activity for millions of years, but nothing lasts forever. Famously, an asteroid struck the Earth near the Yucatan Peninsula 65 million years ago, creating waves of devastation fairly reminiscent of the extinction event that first put the dinosaurs on top of the food chain. In this case, the only dinosaurs to carry on were the precursors to today’s birds, but they weren’t the only survivors. While mammals arguably benefited from the end of dinosaurs’ reign the most, researchers recently confirmed that frogs were also big winners.

Families formed from a few surviving frogs

Genetic studies of modern frog species found that 90 percent of today’s frogs evolved from just three lineages. That genetic bottleneck was traced to the same extinction event that wiped out the non-avian dinosaurs. However, frogs were apparently well positioned to take advantage of the newly-reset ecologies, and quickly diversified into new niches and species. For instance, some families of frogs moved into trees for the first time, while others evolved to live most of their lives on dry land, giving up the tadpole stage of their development.

Researchers are digging into the three lineages that survived the asteroid’s impact 65 million years ago in order to see what got them through that difficult time. Frogs are already known to become dormant underground when resources are stressed, but it’s not clear if that was what got them through fire, brimstone, cold, and worse. They want to know if there was some shared trait that made those frogs extinction-proof, and how well that resilience may have stuck with our amphibians today.

Source: How Frogs Benefited From The Dinosaurs' Extinction by Merrit Kennedy, The Two-Way

On June 29th, 2017 we learned about

Fossil teeth fill in details on hippos’ expansion across ancient Africa

The average modern hippo spends most of its day in the water. In rivers all over Africa, these huge mammals dominate their local waterways, although they’re not there for the fishing. Most evidence suggests that water functions as a way to beat the African heat while facing less competition for territory. It’s a niche this family of animals has only come to dominate in the last eight million years, and even then, it probably only began because of grass.

Hippos started specializing as a family around 55 million years ago. Like the cetaceans they were parting ways with, they spent their lives on land alongside many other Eocene animals in from southern Europe to to Africa to India. They generally had more slender heads than a modern Hippopotamus amphibius, balanced by slighter bodies as well. The latest fossils from Ethiopia suggest that the big transition to the bulbous, river-dwelling animals we know today started eight million years ago. Within a relatively short one-and-a-half million years, African rivers all over the continent were well stocked with hippos, each biding their time for the nightly visit to the salad bar.

A tale told in teeth

The key fossils from this recent Ethiopian excavation relate to the newly named species, Chororatherium roobii. While known primarily from its teeth, C. roobii seems to be a sort of missing link between earlier ancestors like Kenyapotamus and more modern animals. Tooth sizes fit neatly between the smaller and larger members of the family, demonstrating the evolutionary scaling up that led to today’s 3,300 pound behemoths. More importantly, the teeth also show transitional features in the the shaping of cusps on lower molars. While not yet definitive, this change in shape would have helped C. roobii eat grass, closely resembling the dentry of H. amphibius.

This specialization in lawn mowing was probably a big step in hippo history. Based on how many hippo fossils are found in different layers of rock, the transition represented by C. roobii was a bonanza for these mammals. Hippos usually constitute six percent of the fossils found in older Miocene rock layers, but they constitute as much as 30 percent of fossils found after the rise of species like C. roobii. Researchers hypothesize that this is because grasses were spreading across Africa at that point, supporting hippos along the way. C. roobii was then part of this expansion, eventually planting hippos all over the continent, much to the chagrin of the crocodiles who were there first.

 

Source: Teeth tell tale of hippo’s quick spread across Africa by Traci Watson, Nature News

On June 28th, 2017 we learned about

Pierced sea shells allow researchers to quantify how predators have scaled up over time

It seems like common sense to assume that over time, bigger predators can dominate their local ecosystem more than smaller ones, but common sense isn’t enough for scientific study. To really prove this idea, researchers needed a consistent mode of predatation that could be compared over time, encompassing a variety of hunters, so that size was the primary variable being tested. Flashy attacks like shark bites or lion claws would therefore be hard to quantify in this way, but the patient, slow attacks of sea snails on shelled prey turned out to be the perfect way to test if bigger is better.

Specifying predators’ changing sizes

Predatory snails, forams, octopuses and more have been drilling holes in shelled prey since the Ordovician Period,  488 million years ago. Animals like brachiopods, clams and mussels have all been found in the fossil record with small, precise holes, bored into them by the aforementioned predators in order to extract the softer bodies that lived inside. This strategy is still in use today, and modern predators prove that larger attackers leave larger holes. With all these reference points, researchers could then quantify just how much predators did or did not change in size over millions of years, based on the size of the holes they left in the fossilized shells.

It turns out that the data backs up the initial hypothesis. The average hole was 0.35 millimeters 450 million years ago, but is now up to 3.25 millimeters— an increase of over 900%. This doesn’t mean that modern snails are 900% bigger than their ancient ancestors, but it is a safe bet to say that evolution favored their larger family members.

Persistent methods of predation

As much as the point of attack has gotten bigger, the exact mechanics behind boring into a shell aren’t thought to have changed all that much. Marine snails, for instance, switch back and forth between excreting enzymes to soften their prey’s shell, then drilling into it with the abrasive teeth that line their “tongue,” better known as a radula. Once the hole is made, the squishy, nutritious body of the clam or mussel is sucked out to be devoured, only now that can happen through a larger hole.

Interestingly, some of this increase in predator sizes may have been promoted by prey. The early brachiopods had less meat in their shells hundreds of millions of years ago, but they were later eclipsed by clams and mussels, both of which offer more nutrition to a predator. This meant that the slow process of piercing a shell was actually more profitable, enabling predators to grow larger more easily. The main catch would be that as these boring predators grew larger, they probably put themselves on the menu of other predators, like fish and crabs. So while bigger may be provably better from one perspective, it seems to have come with its own set of compromises.

Source: Marine predators bulked up over eons to dominate their prey by Robert Sanders, Berkeley News