The Pliocene Adventure -- Herbivores (Grazers) Part 1

The diversity of the Herbivores in North America during the Pliocene rivaled that of modern Africa. In addition to animals familiar to modern people, including deer, antelope, peccaries, and prairie dogs, there were also camels, tapirs, ground sloths, and elephants. What is curious, however, is that more grazing animals eventually went extinct than browsing animals. Skimming this list reveals that, with one exception, all the big grazers died out while only the smaller ones survived (except for most of the the rabbits). This was superficially true of the browsers as well, but with the exception of the megafauna many of the big browsers survived while a fair number of the smaller ones went extinct. And the big ones that went extinct were probably out-competed by later more modern varieties.

Another interesting feature is that most of the grazers are large animals, especially megafaunal forms, while the browsers seemed roughly evenly divided between big and small animals, with fewer megafauanl forms, and most of those were megafaunal only in comparison with the other smaller creatures in their family. In other words, if marmots are normally only a foot long, a three-foot marmot would be megafaunal by comparison, even if it is dwarfed by normal-sized horses and camels.

However, this is to be expected, biologically speaking. Grazers obtain nutrition from the plants they eat by breaking down the cellulose that acts as skeletal tissue in plants. Animals have no metabolic means of doing this, but certain types of bacteria do, so grazers have special stomachs that contain these bacteria and act as fermentation vats, allowing the bacteria to break down the cellulose. These stomachs need to be big in order to be efficient, and foregut fermentators tend to grow big to provide that kind of room. Smaller grazers instead rely on hindgut fermentation, where the bacteria reside in the colon rather than the stomach. An interesting difference between foregut and hindgut fermentation is that foregut is more efficient, but hindgut is faster, and can better utilize food sources that are less nutritionally dense. As such, hindgut fermentation lends itself to fast active animals and large animal growth; the largest animals of all, the elephant family, are all hindgut fermentators, as are horses.

To increase efficiency, some grazers will re-ingest partially digested food to release more nutrients. Foregut fermentators will regurgitate solid material called the cud from their stomachs for rechewing; these animals are known as ruminants. Hindgut fermentators on the other hand will consume their own feces. These feces, however, have a high content of undigested plant material and look very different from feces that are finally excreted as more or less pure waste.

As a final note, it should be pointed out that some browsers are foregut fermentators, even ruminants, whereas some hindgut fermentators are grazers as revealed earlier, so the presence of one kind of fermentation over another is not a reliable indication of feeding mechanism, or vice versa.

Once again, the genus name for each creature is given in parentheses.

Ass (Equus cumminsii) -- This Species is extinct. The true ass is a different group of modern horses, but the body of this species was shorter and stockier than its cousins, so it seems reasonable that it occupied the same niche.

TG & Differel note that they prefer drier areas than other horses, with tougher vegetation, but still require access to water. They predominantly live close to the Aurora ridge, which is mostly scrubland, but well watered by rain runoff and springs. They tend to be aggressive towards predators and they live more solitary lifestyles than other horses. Some become quite friendly towards TG/Differel, leading Sunny to believe they could be domesticated like moderns asses.

Camels, Giant -- These Genera are extinct. Camels evolved in North America, first appearing 40-50 million years ago. The direct ancestor of all subsequent camels appeared some 20 million years ago, and looked more like a llama. When the Isthmus of Panama formed, camels migrated down into South America to evolve into llamas and guanacos and related groups. By the mid-Pliocene the North American camels had become a diversified group, including both megafaunal and smaller gracile forms. They had spread as far north as the Arctic, and subsequently crossed into Asia over the Bering Strait land bridge. They became extinct in North America at the end of the Pleistocene.

Even before the Pliocene, the true camels had shown a tendency to grow larger. By the mid-Pliocene all smaller gracile forms had become extinct in Colorado, leaving just three megafaunal forms. To fill the empty gracile niche, certain llamas evolved into running plains dwellers, but they also displayed a tendency to to produce megafaunal forms.

(Gigantocamelus) -- This was the second-largest camel to roam the Earth, standing 12 feet tall.

(Megatylopus) -- This was the largest camel to roam the Earth, standing 14 feet tall.

(Titanotylopus) -- This was the third largest camel to roam the Earth, standing at 11.5 feet tall. Its upper canines were larger than those of other camels, it had padded feet and toes like modern camels, and it had a hump for fat storage.

TG & Differel note that the limbs of all three Genera are long and massive, making them powerful runners. However, their size and mass makes them virtually invulnerable to all but the largest predators. They prefer the open grasslands, but also pass through the open-canopy savannas. They graze on grass but also any available foliage, including tree leaves and twigs. They are temperamental like modern camels and tend to be aggressive towards predators.

Capybara (Neochoerus) -- This Genus is extinct. This was the largest rodent to inhabit the Denver plain, larger even than the contemporary megafaunal beavers. In essence, it resembled a guinea pig with shorter fur and longer legs.

TG & Differel note that it prefers to live in closed-canopy woodlots and dense open-canopy savannas, but as close to water as possible, and are semi-aquatic. Hence they are common in the riparian zones along the rivers and the megafaunal beaver ponds. They graze on grass, aquatic plants, fruit, and bark. TG/Differel have observed them eating their own feces and regurgitating partially digested food to chew over again. A few have taken up residence around the beaver pond below the cave, but the trees there are not as dense as they prefer.

Gazelle-Horse (Nannippus) -- This Genus is extinct. This was the last of the pre-modern horses. It stood only 4 feet high at the shoulder, its body and limbs were thinner and more gracile, and its skull narrower and longer. It resembled a large gazelle and was probably a faster runner than modern horses of the same size. It had two extra toes rather than just one, but these were much smaller and did not touch the ground.

TG & Differel are rather surprised to discover these guys in the Denver plain, though they are represented by just one small herd. Though their affinity to horses is obvious, they look and act more like gazelles. They live on the grasslands and the more sparse sections of the open-canopy savanna. They eat mostly grass and other ground foliage, but they also take the leaves and twigs of young trees.

Glyptodont (Glyptotherium) -- This Genus is extinct. These were related to armadillos and essentially resembled turtles. They were heavily armored, with a tortoise-like body shell composed of boney deposits embedded in their skin. A boney cap covered the tops of their heads and their tails were surrounded by rings of bones. They were 6 feet long and weighed as much as a ton. Their armor had evolved to protect them from giant flightless carnivous birds, but when they became less common their shells still protected them from newer mammalian predators. Except perhaps a large bear, it's difficult to know what if anything could have preyed on them. They were slow because of their weight, and they were grazers, eating tough vegetation such as grasses.

TG & Differel first find a dead body being scavenged, then later find an extended family group on the grassland. As Differel later told Mabuse upon their return, they couldn't have been more surprised even if they had found a living dinosaur. The group does not follow any migratory path but instead wanders aimlessly. Even so, it stays in the grassland for the most part, though it does sometimes pass through the sparser open-canopy savannas.

Goat, Antelope (Sinocapra) -- This Genus is extinct. These guys were essentially wild goats that evolved more gracile forms adapted for a running life on the plains. They had fairly short straight horns, and while they most likely were grazers, their teeth indicated less wear, suggesting they may have eaten softer and less course vegetation.

TG & Differel observe a number of herds on the Denver area. They live in the grasslands, feeding within the sparser or along the edges of the denser open-canopy savannas. If threatened they either run away or seek shelter inside dense foliage, but a herd that lives along the Aurora ridge will head for higher ground along the steepest possible path.

Gomphotheres (Stegomastodon) -- This Genus is extinct. It was a contemporary of Cuvieronius the browser and was closely related. They even closely resembled one another, except that Stegomastodon's tusks were straighter and curved upwards. It stood 9 feet tall and was more robust than modern elephants. Its head was shorter and higher than Cuvieronius, suggesting its brain may have been larger, but the forehead was still long and low compared to modern elephants. Its teeth indicate that it ate tough plants such as grass.

TG & Differel discover a single herd that roams the grassland. They at first think it is just another herd of Cuvieronius, or perhaps a new herd of mastodons from the prairie beyond the Aurora ridge, but they manage to collect DNA from a stillborn calf and realize they had a different Genus instead.

Horses -- These Species are extinct. Like camels, horses evolved in North America, first appearing about 52 million years ago. The direct ancestor of all subsequent horses appeared about 13 million years ago, and looked more like the modern ass. The modern Genus Equus appears to have evolved about 4-6 million years ago. By the mid-Pliocene horses were already in the Old World, having crossed into Asia over an earlier incarnation of the Bering Strait land bridge. Equus was a diversified group with dozens of known species, but modern horses are limited to seven, of which one, the plains zebra, is the only wild horse that remains widespread and abundant. Otherwise, the most common horse species are the domesticated horses and the domesticated asses and donkeys. All horses became extinct in North America at the end of the Pleistocene.

Like a number of other Genera, horses showed a trend towards megafaunal forms; however, none of the known species became giants like the camels did. In fact, only a few species obtained any significant size bigger than modern horses, and most were smaller, though often more robust.

(Equus giganteus) -- This was the one true megafaunal form of the horse. It stood 6.5 feet at the shoulder and also had a larger head. Though individual modern horses have been taller (the current record is 7.2 feet), they tend to vary from 4.5 to 6 feet depending upon breed. It preferred open grasslands where it could use its speed and strength to escape predators.

(Equus idahoensis) -- This Species was descended from earlier more zebra-like horses (see Zebra in Part 2). It was larger than its ancestors, but it tended to be smaller than the modern domestic horse. It probably looked like a zebra but with a larger head. It most likely lived on grasslands or in open savannas.

(Equus scotti) -- This Species was also descended from earlier zebra-like horses. It was taller than its ancestors, as well as more robust with a larger head than other contemporary Species, but it was still smaller than the modern domesticated horse. It probably more closely resembled the modern kiang or onager. It was probably at home on both grasslands and scrublands, as well as savannas where trees existed.

TG & Differel discover that the Denver plain in the mid-Pliocene has a good many running herbivores, including camels, goats, llamas, and antelopes, but the horses are by far the most common, being as numerous as the antelopes of modern Africa, if not as diverse. The horses are primarily grassland, scrubland, and open-canopy savanna grazers, leaving the denser savannas and the closed-canopy woodlots and riparian zones for other herbivores, particularly browsers. Though the Species segregate themselves, the herds nonetheless graze in close proximity for better protection. TG/Differel even see horses among mastodons and the giant camels, both of which can deter even the largest, most ferocious predators.

Jackrabbit (Lepus) -- This is the contemporary Genus, and the Pliocene species are virtually identical to the modern species. These guys are actually hares instead of rabbits. They live solitary lives and build above-ground nests instead of underground burrows. They prefer grasslands and sparse open-canopy savannas, but can be found in more arid environments. Their young are born with fur and open eyes, and can move about and defend themselves shortly after birth.

TG & Differel note that the Denver plain supports a large population of jackrabbits, which serve as prey for a great number of carnivores, avian as well as mammalian, but mostly of small to medium size, and most for generalized rather than specialized predators. TG/Differel will hunt them with snares to augment their supply of rations.

Llama (Hemiauchenia) -- This Genus is extinct. As the camels evolved into megafaunal forms and the more gracile forms died out, they were replaced by their cousins the llamas. Though modern llamas are themselves specially adopted for mountain life, originally they were more generalized, and by the mid-Pliocene had become diversified. This Genus adapted to life on grasslands and in open-canopy savannas, becoming a runner like other plains-dwelling herbivores. Nonetheless, they too developed a large body with long robust limbs, both for greater speed and strength; they stood about 4.5 feet tall at the shoulder. They also had larger than normal heads so as to consume greater quantities of tougher grass and foliage. They probably emulated their living cousins and were aggressive towards predators. (In fact, modern llamas make better livestock guards than dogs.)

TG & Differel note that, after horses, llamas are the second-most common running grazers of the Denver plain. They confirm that they tend to be aggressive towards predators, even defending smaller herbivores that associate with them.

Continued in Part 2