Wednesday, November 6, 2013

Belated Halloween post: Top Ten Scariest Prehistoric Environments

Sorry this took so long!  I was hoping to get this done by Halloween, but it took a week to get this one out. Next time I’ll do monster posts like this one in installments. Today we’re going for another lighthearted one-yes, we’re going to do a top ten list today. This one’s been inspired by the documentary series Sea Monsters, where host Nigel Martin took the audience through the “top 7 deadliest seas”. In the same spirit, I’ve chosen the top 10 Deadliest Terrestrial faunas, based on the number of large predators. If I missed any that deserved to be on this list, please let me know. This isn’t based on any particular grade, but based on the number of large predators present in the fauna.

First, we’ll go to Texas, in the Sakmarian age, about 290 million years ago. The environment consists of low, open wetland, like river deltas today. There’s a great variety of aquatic life and vegetation that can support a large variety of wildlife. These were the first big land animals. Now, in terms of predators ,you could divide them into three areas-terrestrial, amphibious, and aquatic.  
In the terrestrial realm, we’ve got Dimetrodon. Yep, that classic pelycosaur that people think is a dinosaur. It’s got nasty teeth and a huge sail on its back, but more related to whoever’s reading this (even if it’s an office cat) than a dinosaur. They were calculated to get up to 500 lbs and 14 feet long. Body was fairly low to the ground, but that’s also true of monitors and crocodilians, and they’ve killed people quite brutally.  

Predator #2 is Sphenacodon, which is a smaller version of Dimetrodon with a much lower sail. The distribution of fossils suggests that the Dimetrodon preferred the wetter east while the Sphenacodon was found in the drier west. The head’s very similar-slicing incisors, large canines, and a battery of smaller slicing teeth along the side, a heterodont dentition similar to modern mammals
In the amphibious realm, we’ve got a third big pelycosaur (primitive ancestors of mammals). The body is long and heavy, roughly the same as Sphenacodon and Dimetrodon, but the skull is deeper and longer. What makes this animal different is the teeth-the name Ophiacodon is Greek for snake teeth.  These teeth weren’t broad sabers like in Dimetrodon, but narrower and pointed for catching fish, small reptiles amphibians, and large insects. Not quite as formidable as Dimetrodon, but still a powerful predator

The other amphibian is actually an amphibian. You should recognize this one-big broad head with eyes on the top, fat wide body with armored skin and short tail, and many long sharp teeth, with huge curved fangs on the palate.  This guy is Eryops-a bit of a combination of frog, crocodile, and salamander. Besides Dimetrodon, it’s an iconic Permian predator. The chest and hips had evolved to support its weight on land, but the small limbs point to a very slow gait and an aquatic habitat, something like a snapping turtle or crocodile today.  While half as big as the pelycosaurs, a 2-foot skull full of teeth is nothing to sneeze at. 

In the water, things don’t improve. There’s Archeria, a salamander-come-muskellunge the size of a sea lion related to my old friend Diadectes. And there’s Orthocanthus, 10 foot, double-fanged moray-eel-shaped sharks that prowled freshwater rivers, lakes and streams. Neither would be a great white or saltwater crocodile in proportions, but if you’ve seen an episode of River Monsters, you’d have a feeling of what kind of big nasty aquatic predators existed in the Permian. 

Our second fauna is South Africa, part of the Karoo beds. This is the Wuchiapingian era, transitioning from the middle to the late Permian.  In this period, it is therapsids (basal synapsids, ancestors of modern mammals and their relatives) that rule the earth.. The biggest is the tubby omnivore Jonkeria, up to 15 feet long. The long skull has  large canines and incisors, capable of shearing off both flesh and plant material. Think of a giant pig or hippopotamus.  Pretty formidable animal, but it isn’t the apex predator of the time.

There is a faunal turnover at the time-big headed dinocephalian (like Jonkeria) predators was being replaced by saber-toothed predators called gorgonopsids. Dinocephalian predators include Anteosaurus and Titanosuchus. Anteosaurus has a long body, short limbs, and a huge fanged head. Titanosuchus is slightly older and smaller, but has  the very similar body plan. These animals have thickened skulls, suggesting head-butting as a social activity. 

A more primitive but still large predator group is the Biarmosuchids. The last and largest is present. The crest-headed Lophorhinus is smaller than the other predators, but still the size of a bull terrier and a formidable, big-toothed predator.

The most successful group consists of newcomers. These are the gorgonopsians. They’re big, long legged, short-tailed, saber-toothed, and long-snouted for scenting prey.  The smallest one is Aelurognthaus, slightly bigger than Lophorhinus with a bigger head and huge fangs. Arctops was slightly bigger in turn, with a low, foot-long skull. Still bigger was Gorgonops, which had six species with different shaped and sized skulls. Some were smaller than Arctops, others much bigger, the size of a Great Dane. Bigger still is Dinogorgon, with a heavy, robust skull. Finally, the biggest is the 10-foot Rubidgea, with a 1.5 foot skull and  8 inch fangs.  The gorgonopsids had smaller heads and lighter bodies than the dinocephalians, but their saber teeth, razor incisors, and long limbs made them even more dangerous.

The Permian extinction brought these guys down, though. They were replaced by all sorts of archosaurs-scaly, fully erect, fast moving animals that lacked the saber teeth but had batteries of broad, curved flesh-rending slicers. This particularly dangerous one is Silesia, in the Norian, about 210 million years ago. The Triassic period has allowed for the archosaurs to diversify into all sorts of forms and by the end of the period, as we’ll see, there’s quite a few kinds of predators. You should remember these from my Teratosaurus writeup. 

I guess I’ll start with the nastiest. This is a twenty foot predator with two foot skull filled with four-inch curved serrated teeth, named Smok after the legendary dragon of Warsaw. It had a long body and long tail with long front and very long back feet, long enough for it to be reconstructed in a bipedal post. It has yet to be completely described, so it’s uncertain whether it’s a rauisuchid, dinosaur, ornithosuchid, or basal archosaur is. What definitely are rauisuchids, big armored erect animals that look like a cross between a crocodile and a predatory dinosaur, are Polonosuchus and Teratosaurus. These animals are only subtly different, and probably inhabited different regions of Europe.

Smaller is the first large predatory dinosaur, Liliensternus. This German theropod weighs 400 lbs compared to the rauisuchids 700 lbs, but is much faster, with a long flexible neck and two long hind legs perfect for running. They eat smaller prey, but that would still include animals the size of humans. In a similar position is the slightly smaller non-dinosaur cousin Ornithosuchus, from Scotland. This animal is more basal, much more like a crocodilian, but still capable of bipedal running in times of need. It’s shorter than Liliensternus, but more heavily built and with a larger head on a short neck, so it would be an ambush predator of smaller prey.

In the water, there are phytosaurs-distant relatives to crocodiles that occupy the same ecological niche. In Europe, the species Termatosaurus, Rileyasucuchus, Rutiodon, Paleorhinus and Mystriosuchus swim the rivers, hunting mostly fish and amphibians, but also preying on whatever ventures too close to their freshwater streams. They share this niche with giant amphibians, similar to Eryops with weaker limbs, much longer bodies and tails, and slightly narrower skulls. Like the phytosaurs, they play the crocodile role as predators of the shallows, lying in the mud until prey wanders too close. The two in Europe are frog faced Metoposaurus and the more gator-shaped Cyclotosaurus, and they are not picky eaters-if prey goes close enough, it’s gone in a quick powerful snap.

Now we’re in more familiar times, the time of dinosaurs. One of the richest fauna is the Morrison formation, in today’s Utah and Colorado. Dinosaurs by this point diversified into big spiky stegosaurs, ornithopods like Dryosaurus and Camptosaurus, and a whole plethora of huge sauropods. With all this meat, the predators are likewise big and menacing.  The environment consists of long rivers and wide floodplains, interspersed with huge, dense forests. First things first, let’s deal with some waterway predators. The amphibians and phytosaurs were wiped out by the Triassic extinction, and now they’re replaced by crocodiles.  These crocodiles belong to the genera Eutretauranosuchus and Goniopolis, and they’re roughly the same physically as modern crocodiles and live the same way.
The land predators are all theropod dinosaurs. The smallest is a Megalosaur, Marshosaurus. Marshosaurus is about 15 feet long,  the size of the rauisuchids and early theropods of the Triassic, but far more advanced. The skull’s about two feet long, and filled with the curved serrated teeth that make the hallmark of the predatory theropods. Big enough to eat a human, but it’s a pygmy compared to the other Morrison theropods and is very obscure and rare.

 Bigger still is Ceratosaurus, from its own group of theropods, the Ceratosauria. Ceratosaurus is distinct for the small four-fingered hands, a long bony ridge on its back, hornlets over the eyes, and a large flat horn on the nose. The horn is long and deep, for social display. Ceratosaurus ranges from the size of Marshosaurus to about twice the size at about a short ton in weight and 25 feet in length.  It is rarer than the bigger Allosaurus (more on him later), and has a distinct dentition of huge teeth in front of the maxilla and shorter ones elsewhere.  Paleontologist Robert Bakker, in an essay in the book Feathered Dragons: Studies on the Transition from Dinosaurs to Birds, speculates that Ceratosaurus might have been a wetlands specialist, using its muscular tail to swim in the shallows hunting fish, turtles and crocodiles but not above scavenging or attacking dinosaurs.

The most common predator in the Morrison is the famous Allosaurus. Allosaurus ranges from 25-40 feet long, big enough to easily overpower the ornithopods, menace the well –armed Stegosaurs, or even take on a sauropod. This dinosaur has powerful arms tipped with large curved talons, rows and rows of serrated, curved teeth and a deep head and a wide jaw gape. This suggests that it used not bone-crushing bites or claw slashes to dispatch prey, but instead struck using its open mouth as a weapon. The teeth would create long, deep bloody wounds,  and the prey would go into shock from blood loss. This is ideal for taking down giant sauropods-too big to overpower, so bleedout would be the best chance to take them down. 

Even bigger than the Allosaurus is Torvosaurus, a megalosaur similar to Marshosaurus. Torvosaurus is very likely a descendant of Megalosaurus, and a rival to Allosaurus. Two species live in the Morrison Formation, and like Ceratosaurus, both are rare and associated with riverine parts of the ecosystem. It would probably avoid going too far inland or risk confrontation with the other predators., but would easily be Allosaurus’ match in a confrontation, or be able to take down a small sauropod.  Torvosaurs, Allosaurs, and Ceratosaurus also lived in Portugal’s Lourinha Formation as well, in a similar environment and eating the same kind of prey. 

The largest of the Morrison predators is no doubt a sauropod hunter, and the first in a long line of giant carnosaurs specializing in bringing down huge prey. This is Saurophaganax, sometimes considered a  species of Allosaurus, and a truly formidable predator. It is even larger than Allosaurus and Torvosaurs, at about 40 feet or more, the size of a Tyrannosaurus rex. This animal is the state fossil of Oklahoma, but much rarer than Allosaurus fragilis. Perhaps Allosaurus is more versatile a predator, or perhaps it compensates for smaller size with social behavior. Nonetheless, it is the top predator, the largest in the world for millions of years, and the first of a long, terrifying legacy of giant allosaurs. 

This next fauna, however, has only the giant allosaur. The megalosaurs and ceratosaurus are extinct in North America, and the allosaurs with follow them, but there is one last monster. This is Acrocanthosaurus. At 40 feet and 7 tons, it would not be surpassed by other theropods on the continent until Tyrannosaurus itself. Instead of lacrimal crests like Allosaurus, it has a 2-foot sail along the neck, back, and tail. Like Allosaurus, it’s armed with large claws and teeth and also specializes in hunting sauropods. There have been tracks found showing Acrocanthosaurus chasing down sauropods.  Sauropods would be the ideal prey, as Acrocanthosaurus is bigger than any of the iguanodonts, even the huge Iguanocolossus, and Gastonia was an armored dinosaur covered with nasty spikes.

Iguanodonts like Hippodraco, Eolambia, and especially Tenontosaurus would be prey for the next largest predator. At the Morrison formation, the only maniraptoran dinosaur was the tiny Palaeopteryx. However, by this time, they’ve spread, diversified, and grown to formidable size. The largest of these dromeosaurs is Utahraptor. Remember the “Velociraptors” from Jurassic Park? Remember that big one that seemed to be in charge? She was roughly the size of a smaller Utahraptor.  Utahraptor are the size of bears, armed with the usual teeth, claws, and a huge curved talon on each foot. To make matters worse, dromeosaur footprints have been found in groups, suggesting that they are social hunters as well.  The large claws on the hands and feet could be used to slashing or stabbing blood vessels, grappling to subdue, or just hanging on while tearing at the prey with its teeth. A human would be simple prey.

Human-sized prey would be vulnerable to Deinonychus, roughly half the size of Utahraptor. A group of subadult Deinonychus has been found with the body of a Tenontosaurus-scavenging turned feeding frenzy? Teenage gangsters biting off more than they can chew? Attempt at scavenging from adults or bigger predators gone horribly wrong? If they were pack hunters, they could take on larger prey. Deinonychus is faster and more agile than Utahraptor, but still an ambush predator, too slow to outpace most of its small prey. 

About the same size is Nedcolbertia, a long but slimmer coelurosaur that must be a specialist in small prey, but a faster runner than the dromeosaurs.  There’s also Geminiraptor, a slightly smaller relative of Deinonychus. Finally there’s the troodont Yugovectia. Troodonts are smaller and more gracile than dromeosaurs, but faster and smarter. They must have the best claw-eye coordination, and probably eat small, fast prey but their sickle toe claws also suggest hunting larger prey.

Our next fauna is across the Atlantic and a few million years later. No dromeosaurs here, but some old tribes in new forms. This is the wet delta of North Africa, stretching from Morocco and Niger to Egypt.  The environment, and the fauna, is not too different from the Morrison. No stegosaurs, but they’ve been replaced by iguanodonts. While the sauropods are not as diverse as before, they’re just as abundant and huge. The armored sauropod Paralititan weighs over 60 tons. Even the fish are big-the coelacanth Mawsonia, sawfish Onychopristis, the bichir Bawitus, and lungfish Neoceratodus all reach sizes of almost 20 feet. 

The smallest predator is a ceratosaur, and fulfills a similar role as its ancestor. Rugops has a lightly built skull with a short snout, wide curved teeth, and a number of crests and rugosities on its face for display. The small size, light skull, stubby claws, and short teeth make it less of a sauropod hunter and more of fisher, scavenger, and chaser of baby dinosaurs. The environment’s wetness provides plenty of crocodiles, fish, frogs, and carcasses for Rugops.

Rugops would have to give way to one crocodile rival, however. Kaprosuchus, the boar crocodile is the same size as Rugops, but more than a match. Armed with a horned 2-foot skull and an array of teeth growing up to 5 inches, it can a meal out of any ornithopod or small sauropod that wanders to close to its place of ambush. The eyes in most crocodiles are laterally situated so they have a wide field of vision, but Kaprosuchus has eyes oriented forward like a dinosaur for judging depth. Unlike the conical teeth of its relatives, its teeth are flattened to form sharp edges and long enough to pierce deep into the flesh of dinosaurs. This animal lurks by waterholes, ambushes prey, and with a rush, tears them apart with its powerful jaws.

The next bigger theropod was also a ceratosaur. Deltadromeus’s skull is as of now unknown, but the arms and legs are long and powerful, and the animal is about 25-30 feet in length. That suggests that it hunts the faster iguanodonts rather than sauropods, and so doesn’t compete with either the fish-eaters or the giant predators. Unfortunately, teeth or skull material associated with the known remains are yet to be found, so the specializations are yet to be entirely established.
Another mysterious predator which may be the same as Deltradroemus is Bahariosaurus. So far, only the ribs and vertebrae have been found. To make matters worse, the material was destroyed by Allied bombers in the total war of mutual extermination called World War 2. The material suggests a huge but gracile animal, possibly a ceratosaur or carnosaur the size of Tyrannosaurus itself. No teeth or claws have been found, so only the vertebral form and pubis suggest that it’s a theropod in the first place. I would bet on it being a big ceratosaur myself, but it’s one of those mysterious dinosaurs. Perhaps someday we’ll find the rest.

Fortunately, we do have existing material for the next three giants of the fauna. This next one is a relative of Allosaurus but only known from the top of the skull. ThThe piece is high and thick, but recognizably allosaurian. Allosaurs all had tall ridges on top of their eyes, but this one is particularly thick. This feature on the eye led to the brilliant name Saurinops, after the restless eye of Tolkien’s Sauron. Like other allosaurs, it would be a specialist in ripping open sauropods with its teeth. The aforementioned adaptation is evolved probably for head-butting, suggesting a kind of social structure. These features, along with trackways of carnosaurs moving in groups, leads to a terrifying conclusion: they hunted in groups.

What did the rest of Saurinops look like? Fortunately, we have a relative from the same formation. Like Bahairiosaurus, it was discovered by Ernst Stromer in the 1930s and the holotype lost in the war.  Unlike Bahariasaurus, additional material has been found, and now we have a very good idea of it. Carcharodontosaurus weighs in at almost 10 tons, more than 40 feet, and with a 5-foot head. Everything I said about Saurophaganax is true here, except that Carcharodontosaurus has much smaller, weaker forelimbs. Like its allosaur predecessors, Carcharodontosaurus has a large head armed with broad, serrated teeth for inflicting bloody wounds on giant sauropods. This dinosaur is a giant-killer.

The biggest theropod here, in fact the largest of all time, is a bizarre one. You see, since the rise of the allosaurs, the megalosaurs declined, and from their stock came a new group of giant predators-the Spinosaurs. These animals have long limbs and huge claws, long narrow snouts, tall vertebral spines, and long conical teeth. They’re also huge.  

Spinosaurus is the most spectacular-more than 12 tons and more than 50 feet, bigger than any other theropod. Like Bahariasaurus and Carcharodontosaurus, its holotype was destroyed in the same bombing, and  only recently has been known well. Now, the freakish size is odd enough, and if it looked like the carnosaurian reconstruction used for years, it would be even stranger for the 6-foot tall fin on its back. However, recent discoveries have shown the head is just as strange- almost 6-feet long, narrow, and armed with smooth, sharp, and conical teeth. If you looked at the skull, you would immediately think of a crocodile. Indeed, the connection based on morphology has been supported recently by an isotope study showing a similar diet to crocodiles. Remember the giant fish I told you about? Spinosaurus would be ideal for their predation. In addition, it could easily overpower the small ornithopods, or scare off all but the largest and most determined rivals from kill sites with sheer size coupled with the size-magnifying fin.  It probably would never be able to bring down a sauropod, but it didn’t have to-just let a carcharodontosaur or abeliosaur do it for it and then chase them off.  The other, smaller theropods seem to be specialists, but Spinosaurus’ unspecialized teeth and huge size suggest a jack of all trade, preferring aquatic fare but easily subsisting on smaller dinosaurs.

Spinosaurs never made it to Asia and North America, though. Our next fauna shows the triumph of the coelurosaurs. This is Mongolia, 77 million years ago. The Bayan Shireh, Iren Dabasu, and Djadochta Formations show streams and lakes only miles away from barren desert, much like Egypt or Texas today.  No sauropods-ornithopods like Bactrosaurus, therizinosaurs like Erlikosaurus and Segnosaurus, and ankylosaurs like Pinacosaurus and Talauurus were the main herbivores, with amphibians, lizards, birds and mammals providing a rich small-animal fauna.

The largest predator here is a theropod, but not a strict carnivore. You see, one of the many coelurosaur lines of the Cretaceous are the beaked oviraptors, perfectly capable of shearing through flesh or plant material with their powerful jaws. This is the largest oviraptor-Gigantoraptor. 2 tons of feathered fury, with a two-foot beak and foot-long hand claws, this is the grizzly bear of Cretaceous Mongolia. It can easily overpower most of the smaller animals of the day, and the beak would equally be suited for breaking the back of a Protoceratops, tearing into the corpse of a hadrosaur, or stripping a tree to the bare wood. 

Nearly as big is a Tyrannosaur, a smaller version of the late Cretaceous titan. Alectrosaurus was smaller and more primitive than Tyrannosaurus, but still a fast-running, powerful-jawed predator. All that has been discovered is a leg, foot, and some body elements, but not the skull. Still if it’s anything like the other Tyrannosaurs, it’s a truly formidable predator.

The Dromeosaurs are still here. Remember Utahraptor? A slightly smaller relative, Achillobator, is here, big enough to bring down most of the prey dinosaurs in the area. Three dog-sized relatives share the fauna-the infamous Velociraptor and its sister taxa Tsaagan and Linheraptor. If they were social predators, they could take down larger prey. They certainly consider Protoceratops a food item-the ceratopsian has been found in a fossilized death struggle, fighting to the death with a hungry Velociraptor.  Gigantoraptor, too, has smaller relatives here. While Citipati is not nearly as big as Gigantoraptor, it’s almost the size of a human being and no doubt a formidable animal. Finally, there’s Troodonts-they’ve been successful little predators. The largest one here is the nasty Saurornithoides.

While the next 60 million years have had their share of predators, from Tyrannosaurs to Hyeanodonts to big predatory birds to terrestrial crocodiles to giant omnivorous pseudo-pigs. However, carnivore diversity finally reached its apex in the Miocene epoch.  Where we’re looking at is France in the Asteracian age, about 16 million years ago. The huge array of bovids, horses, apes, rodents, and pigs led to a similar flourishing of predator diversity. 

Cats have finally evolved. There are two species here-the lynx-sized Pseudaelurus loreti and the puma-sized Pseudaelurus quadritentatus. By now, cats have evolved their winning characteristics: powerful muscles, short jaws, long canines, amazing eyes and ears, long whiskers for hunting by touch, and fast reflexes for ambushes. P. quadritentatus probably hunts the local apes the same way leopards do…including humans. 

There’s also false cats, the nimravids. There is only one now, the leopard-sized Prosansanosmilus, but it will soon be followed by the bigger, burlier Sansanosmilus and almost bearlike Barbourofelis. They’re almost identical to big sabertooth cats, but they have much lower, longer bodies and shorter legs. 

There’s a very old group here. The creodonts, distant relatives of Canivorans, used to be the main predator for 20 million years. This is the last of them- Hyainailuros. Like all Hyaenodonts, it has a long body, short legs, and a huge head armed with large bone-crushing teeth. It’s also one of the largest, the size of a grizzly bear. Only in Africa and Western Europe has the once great order survived, being succeeded by false cats, true cats, bears, dogs, and bear dogs. 

Bear dogs are the top predators of the day, combining doglike predation with bearlike strength and size. They range from the dog-sized Pseudarctus and Cynelos to the massive Amphicyon and Pseudocyon, both reaching the size of a brown bear or a Siberian tiger. In between are Euramphicyon and Agnotherium. These six genera dominate the middle Miocene as apex predators, being bigger and more formidable than any other predator. Ambush predators, they can quickly run down and overpower prey with lionlike forelimbs and huge powerful jaws. 

They do have rivals, though; the late Miocene is one of the most diverse periods in mammalian prehistory, both in prey and in predators. The big hyenas have made their debut with Percrocuta, larger than a spotted hyena today and just as deadly a predator.  There are also some primitive bears, Hemicyon and Plithocyon-they resemble their amphicyonid neighbors, but are bears that are still doglike in form and more carnivorous than modern bears. They would share the same roles as the cats, false cats, and bear dogs. At the size of black bears, they’re powerful predators but still overshadowed by Amphicyon and Hyenailuros.

Fast forward 8 years and go back to North America. It’s the Hemphillian age, and it’s a period of faunal turnover. Species are going extinct, some are arising and some are arriving from Asia.  The natives include bear dogs and true dogs, but bears and sabertooth cats are coming to displace them.
The biggest, baddest predator of the age is Agriotherium. Agriotherium is a bear, but a super bear as well. Big an as Alaskan grizzly, its skull has evolved to withstand incredible stress, especially around the carnassials and canines. This suggests that unlike modern bears, it eats more meat than vegetables. Agriotherium has been found on every continent but Australia and South America, dispossessing the bear-dogs and finishing off the hyeanodonts. The species will only die out with the onset of the ice ages.

There is another intruder,  Machairodus. This is the first of the sabertooths, and the first big true cat. The sabers are shorter and studier than later saberteeth, but still powerful enough to pierce flesh and sever arteries.  Machairodus is as big as a tiger, and like Agriotherium has conquered most of the world and will last until the ice age. These two predators have cut down the bear dogs and nimravids, and forced the dogs and hyenas to secondary roles.

There is still some of the old guard left, however. Barbourofelis is the last and largest of the Nimravids; as long as a leopard but built like a bear and bearing huge saber canines. This predator has been fine bringing down tapirs, horses, and rhinos for the past 5 million years, but its time have come to an end with the invasion of Machairodus.

Likewise, the bear dogs are displaced. The last American bear dog is Ischyrocyon, the size of Machairodus but lacked the powerful sabers. Ischyrocyon has always kept Barbourofelis in its shadow, but against these two new predators, it’s obsolete and will not survive for much longer.
The dogs are not beaten yet, however. About 16 million years before the present, dogs became big predators, placing pressure on the nimravids and bear dogs and even overmatching them with their social hunting. They adapted to hunting large prey by developing bone-crushing jaws, making them very much the hyenas of America.  The oldest and most successful genus, Aelurodon, is down to its last species, and it’s almost extinct. The largest, in fact the largest dog that ever lived, is Epicyon Haydeni.  This dog is the size of a St. Bernard or Newfoundland, and armed with massive jaws and bone-shattering teeth. In packs they are unstoppable. Only Machairodus and Agriotherium now bring its downfall. 

There’s a smaller species of Epicyon, E. saevus, and this species is always found alongside its giant cousin. Right now, it’s doing poorly, being replaced by the new species of bone crushing dog, Osteoborus. Epicyon will linger on, but it will perish along with Barbourofelis as Machairodus takes over.  The dogs are falling, but not out. The coyote sized Canis lepophagus is the first of its kind, but it will grow and rise and conquer. By the end of the ice age, Canis will have reached every continent., and when it is paired with a new social predator of African descent, it will rule the world.

Now, originally I was going to do Pleistocene Australia, but then I realized I already covered that. Here’s the link-
So instead I’m going to Los Angeles around 100,000 BC. While humans are inventing culture and technology across the Old World, the Americas are full of powerful predators.

Cats by now have spread and diversified to an extreme extent. By now, America has lynx and bobcats and all sorts of big cats. Pumas have already evolved, and by now they’ve covered both North and South Americas and become a very successful midsize predator.  Jaguars have likewise spread, ranging from Philadelphia to Seattle to Buenos Aires. Both of these are present at La Brea, but they were shadowed by the bigger, stranger cats.

Miracinonyx is a close puma relative evolved to become a cheetah. While being the size of a puma, the spine, tail, skull and limbs have all evolved to a cheetahlike lifestyle. Pronghorns today are by far the fastest mammal outside of Africa, begging the question why considering how easily they can outpace even wolves and cougars. This is why-antelope-eating cheetahs require the antelope to speed up in turn. 

There’s also a relative of the lion here, Panthera atrox. Lions and tigers have spread from Africa to every continent but Australia and Antarctica, competing and eventually succeeding the sabertooths. This particular species ranges from Alaska to Peru. Up to 800 lbs, they are much bigger than their African relatives.  The lion is more common than jaguars and pumas, but less common than the sabertooth at the Tar Pits, and lives in small groups of 4 to 2, much smaller than African lion prides.  The brain is larger than the sabertooths, suggesting it was smarter.  It’s also more of a cold weather cat as well.

Another cold-weather cat that is also rare in the Tar Pits is Homotherium, the scimitar tooth cat. Homotherium weighs as much as a lion, but a meter at the shoulder and less than two meters long. The front legs are long and high, while the back legs are much shorter but very powerful. They share every habitat that lions do, but target very different prey. Lions hunt horses, deer, antelope and bovids. Scimitarteeth , however , specialize in picking off elephant and rhino babies. They will take whatever they can find, but they prefer to run in small gangs to surround herds of mammoths and mastodon, and quickly strike down and kill vulnerable infants.

Of course, the biggest sabertooth and by far the most common feline at the pits is Smilodon. This is a North American species, ranging from Oklahoma to Peru, smaller than its southern relative. The northern sabertooth is shorter and smaller than the lions, but incredibly heavily built and reaching 600 lbs. They take horses and camels as prey, but also big dangerous animals like sloths and bison. Isotopes show a preference for camels and bison. Hunting in packs, they surround and ambush prey. They don’t run as fast as scimitars or cheetahs, but gang up on the herds, overpower them with their incredibly muscular and heavy forelimbs and claws, and then cut their prey’s throat with a bite.  The fact that the sabers are so long shows the size of their targets.

Cats aren’t alone. There are dogs-red fox, coyote and wolves live the same way they do during the human occupation of the continent. There is one particular species of wolf, however, that is unique to the time and to the American continent.  Dire wolves are big-the size Canadian and Russian wolves today or larger. The brain is smaller than the grey wolf, but the skull is sturdier and legs are shorter. The teeth are big, and carnassials have long blades. While the grey wolves hunt deer and smaller prey, dire wolves hunt bison, camels, horses, and other megafauna. The skull is adapted for crushing bone, and they compete with sabertooth cats the same way Hyenas do with lions in Africa.  Big bad wolf, indeed.

Finally, there are bears. Now, this area is relatively flat, so black and brown bears are uncommon. Instead, the bear of the plains is Arctodus simus, the northern short-faced bear. This bear is the size of an Alaskan brown bear, but with a shorter snout and longer front legs.  Ranging from Alaska to Texas, this bear ate more meat than vegetation, unlike its extant spectacled bear cousin.  There are three opposing theories in paleontology on how it gets its meat. One postulates that its gracile build makes it a fast runner to chase down horses and deer. The second argues that it’s too heavy to run and instead overpowers slower sloths and bison with brute strength. Finally, there’s a party that argues that it’s too slow to run and too weak to fight, and so is a scavenger that uses sheer size to intimidate other predators. I’m of the opinion that it does all three to some extent. It can’t outfight a mastodon or outrun a pronghorn, but it can bring down most animals in between. And, like all carnivores, would never hesitate to take a carcass, and a long-distance giant (remember Spinosaurus?) could quickly find and take whatever dead meat is available.  With its size and strength, it can win a fight against most adversaries, even sabertooth cats.

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