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An artist’s conception of Poebrotherium (an early camel)
Camelids are believed to have originated in North America. From there they spread down into South America (after a land bridge connected the continents) where they are represented by llamas, alpacas, vicuñas, and guanacos. Ancient camels also left North America via land bridge to Asia. The dromedary and Bactrian camels are descended from the creatures which wandered into Beringia and then into the great arid plains of Asia. Yet in their native North America, the camelids have all died out. This strikes me as a great pity because North America’s camels were amazing and diverse!
An illustration of the size of Gigantocamelus
At least seven genera of camels are known to have flourished across the continent in the era between Eocene and the early Holocene (a 40 million year history). The abstract of Jessica Harrison’s excitingly titled “Giant Camels from the Cenozoic of North America” gives a rough overview of these huge extinct beasts:
Aepycamelus was the first camel to achieve giant size and is the only one not in the subfamily Camelinae. Blancocamelus and Camelops are in the tribe Lamini, and the remaining giant camels Megatylopus, Titanotylopus, Megacamelus, Gigantocamelus, and Camelus are in the tribe Camelini.
That’s a lot of camels–and some of them were pretty crazy (and it only counts the large ones—many smaller genera proliferated across different habitats). Gigantocamelus (as one might imagine) was a behemoth weighing as much as 2,485.6 kg (5,500 lb). Aepycamelus had an elongated neck like that of a giraffe and the top of its head was 3 metres (9.8 ft) from the ground. Earlier, in the Eocene, tiny delicate camels the size of rabbits lived alongside the graceful little dawn horses. This bestiary of exotic camels received a new addition this week when paleontologists working on Ellesmere Island (in Canada’s northernmost territory, Nunavut) discovered the remains of a giant arctic camel that lived 3.5 million years ago. Based on the mummified femurs which were unearthed at the dig, the polar camel was about 30 percent larger than today’s camels. The arctic region of 3.5 million years ago was a different habitat from the icy lichen-strewn wasteland of today. The newly discovered camels probably lived in boreal forests (rather in the manner of contemporary moose) where they were surrounded by ancient horses, deer, bears and even arctic frogs! Testing of collagen in the remains has revealed that the camels are closely related to the Arabian camels of today, so these arctic camels (or camels like them) were among the invaders who left the Americas for Asia.
Aepycamelus (painting by Heinrich Harder)
The bones are a reminder of how different the fauna used to be in North America. When you look out over the empty, empty great plains, remember they are not as they should be. All sorts of camels should be running around. Unfortunately the ones that did not leave for Asia and South America were all killed by the grinding ice ages, the fell hand of man, or by unknown factors.
An artistic reconstruction of the newly discovered Arctic camels
Agriculture is almost unknown in the natural world. Human beings are the only vertebrates known to grow crops or keep livestock (with the possible exception of damselfish which carefully tend little algae gardens). And yet we were not the first animals to invent the concept. Ants have farmed fungi within their tunnels for tens of millions of years. Ants also keep aphids in captivity in order to “milk” them of sugary secretions–or to eat them outright. It is possible that beetles, termite, or snails came up with the concept first, but most evidence points to ants as the first farmers.
An Ant Milking Aphids
Ants do not have a shabby operation either. Leaf cutter ants form the largest and most complicated animal societies known on Earth (other than our own) and a single colony can have over 8 million individuals. Leaf cutters are an ideal example of how adept ants are at farming fungi. Four different castes of worker ants work together to bring back leaf fragments and integrate them into huge fungal gardens. Different species of leafcutters cultivate different fungi from the Lepiotaceae family. Certain bacteria with antifungicidal and antibacterial properties grow within the metapleural glands of the ants. The worker ants use these bacteria to “prune and weed” dangerous or unproductive organisms out of their gardens. Older (more expendable) worker ants carry waste products from the hive to a waste pile where they stir the hive wastes together to aid in decomposition. The waste-management job brings the danger of fungal or bacterial contamination and contaminated ants are exiled to certain death in order to keep the gardens safe. Additionally dead ants from within the hive are carefully placed around the waste pile so as to protect the hive from their decomposition.
Leaf Cutter Ants at the Cameron Currie Lab arrange cut-up leaves into their fungal garden.
According to geneticists who study the rates of mutation within the various fungal cultivars, ants began their farm relationship with fungi around 50 million years ago in the warm Eocene epoch (an era which saw many of the critical relationships in modern ecosystems begin).
Digital Cut-away of an underground leaf-cutter nest
Scientists are also beginning to understand the means by which ants herd their little flocks of aphids. The aphids are smaller insects which feed on the saps and juices of plants (which they suck out by means of specialized mouthparts called stylets). The ants prevent the aphids by flying away by tearing off their wings. The feet of the ants produce chemicals which tranquilize and subdue the aphids and keep them from escaping the “pastures” near the ant colonies. It is believed that aphids also derive certain benefits from this arrangement since the aggressive ants protect them from many of their natural predators.
An Ant with a “herd” of Aphids
For years naysayers belittled the farming achievements of ants suggesting they were little more than symbiotic arrangements. However as entomologists study the ants more carefully they increasingly discover just how complicated and sophisticated those relationships are (involving as they do numerous symbiotic relationships with bacteria in order to produce the chemicals necessary for agricultural control). Additionally, what are humankind’s relationships with our crops and animals if not huge harrowing examples of symbiosis?
A human (black), an African Elephant (gray), a Mastodon (french blue) and a Paraceratherium (sky blue)
The largest land animal alive today is the mighty African elephant, however even the largest adult bull elephants were dwarfed by the largest land mammal ever to exist. The giant herbivore Paraceratherium stood 5.5 metres (18 ft) tall at the shoulder. When standing upright the creature’s head (which was approximately the same size as character actor Danny Devito) was about 8 metres (26 ft) above the ground. Although debate continues about how much the beast weighed, reasonable estimates suggest it could have massed from 15 to 20 metric tons which means that the animals were as large as mid-sized sauropod dinosaurs from the previous era. Partial skeletons of Paraceratherium were discovered by different scientists at different times–which has confusingly resulted in three different names for the genus: 1) Paraceratherium which means”near horn animal” in Greek; 2) Indricotherium which was derived from a mythical Russian progenitor-monster called the Indrik-Beast; and 3) Baluchitherium which means “Baluchistan beast”, in honor of Baluchistan, an arid portion of the Iranian plateau, where a fossil specimen was unearthed. Paleontologists prefer to call the genus “Paraceratherium,” however, thanks to TV specials and museum shows the name “Indricotherium” remains popular with the public.
Artist’s Conception of Paraceratheriums Migrating (from asecic.org)
Paraceratheriums were perissodactyls. The giant creatures were most closely related to the living rhinoceroses (although they shared ancestors with tapirs and horses as well). Paraceratherium’s immense size allowed it to eat the branches and leaves of large trees. They ranged across what is now Central Asia across Iran, India, Pakistan, Mongolia, Kazakhstan, and China. The various species of Paraceratherium had long graceful necks somewhat like that of Okapis. Additionally they possessed nimble elongated upper lips with which to strip leaves off of branches. These lips were no quite trunks but probably resembled the long grasping snout/lips of tapirs. Although Paraceratherium was closely related to rhinoceroses, they lacked the rhino’s characteristic horns—their giant size meant they did not need them. The genus originated in the Eocene and flourished during the Oligocene—a golden age of perissodatyls. However as the global cooling became more pronounced in the late Oligocene, the great creatures gradually vanished.
Fossil Paraceratherium skeleton in a museum
Antarctica Seen from Space
Imagine standing high above planet Earth and looking down at the blue and white band of seas surrounding Antarctica. You are looking at one of the most important features of the Earth’s surface. The turning of the planet and strong westerly winds drive the cold deep waters of the Southern Ocean into the planet’s largest and most powerful current system, the Antarctic Circumpolar Current (ACC). The clockwise current isolates the frozen continent into its own self-replicating climate. Since there are no great land masses lying in the ring of open water at these latitudes, the ACC also forces waters from the ocean depths up to the surface. This upwelling brings rich nutrients from the depths and causes immense blooms of phytoplankton (which in turn nurture life throughout all the world-ocean). Additionally the current stirs the circulation of the Atlantic, Pacific, and Indian Oceans.
The ACC has been known to sailors for centuries. A sailing ship can travel west along the current with great speed (if the sailors have the bravery and stamina to confront the fierce winds of “the roaring forties”). The “clipper route” was the fastest sailing route around the world, but it was dangerous. The three great capes (Cape Horn, the Cape of Good Hope, and Cape Leeuwin) all claimed innumerable lives as did wind, ice, and storm. Today the clipper route has been abandoned as self-powered ships bring their cargoes of plastic junk straight across the ocean from China (and then cut across the Panama Canal) but sailing enthusiasts still recognize the fastest way to ride the wind around the planet. The major circumnavigation sailboat races all travel the clipper route.
“Roaring Forties” (Gordon Frickers, oil on canvas)
The true history and significance of the ACC vastly exceeds the paltry recent concerns of navigation and world trade. Geologists estimate that the ACC current began spinning around 34 million years ago at the end of the Eocene epoch as Antarctica split from Australia and drifted further south. When still connected, Antarctica and Australia had been a place where cold southern water and chill weather mixed together with tropical warmth—thus causing the whole planet to warm up. However when Antarctica drifted south, it started a series of climate feedback loops. The oceans around the continent began to freeze and ice started to build up on the mountains. An entire continental ecosystem began to change in the cold. The tropical forests (which had been filled with strange marsupials) began to die and become tundra. As the Oligocene progressed and Drake’s Passage widened, the rivers–once filled with catfish–turned to ice. The landmasses of Antarctica became crushed down under immense glaciers. Antarctica died in the cold. By 15 million years ago it was as it is now, home to only tardigrades, lichen, and a handful of visiting birds and seals.
The Transantarctic Mountains (photo by John Goodge)
Even now the Antarctic Circumpolar Current still isolates the continent from the warmth of the rest of the world. Yet through upwelling of iron and other nutrients, the current bolsters an immense fecundity of phytoplankton–the great primary producer of the ocean. Masses of copepods and krill feed on the algae and the diatoms and they in turn are eaten by fish, mollusks, mammals, birds, filter feeders…everything. The great southern oceans are among the most diverse and strange habitats for living things. It is there that the largest mollusk on the planet is found—which is the subject of an upcoming post.
Model of a Moeritherium
Our story takes us back 37 million years ago to the hot moist swamps of the Eocene (again). In the swamps of Africa lived a long low wallowing mammal 3 meters (9.8 feet long) and 70 centimeters (2.25 feet) tall. This swamp dweller occupied the same sort of niche now taken by pygmy hippos and capybaras—it was an amphibious grazer which lived on soft water plants and could slip into the water to avoid land predators (and vice versa). The animal was named Moeritherium, a genus consisting of several similar species, all now long extinct.
Moeritheriums (painting by Heinrich Harder)
Moeritheriums mostly had peg like teeth for grinding up vegetation, but the creatures’ second incisor teeth were elongated like daggers for display, defence, and rooting. So Moeritherium was really another saber toothed creature (like walrus, Smilodon, and Odobenocetops), but we never think of their closest living relatives as saber-toothed so it is hard for me to think of them that way. In fact Moeritherium’s closest relatives overshadow all the details about the low-slung swamp-dwelling creature entirely because they are one of the most magnificent and intelligent orders of creature on planet Earth. The Moeritheriums wallowing in the African swamps long ago were among the very first Proboscideans–an order of mammals including elephants, mammoths, mastodons, and gomphotheres.
An artist’s conception of a Moeritherium
Moeritheriums probably did not have a long trunk like today’s elephants, but they did have a long flexible upper lip like tapirs. Their eyes and ears were high up on their head so they could submerge themselves but still watch the surrounding landscape. They were not direct ancestors of the elephants and mammoths but instead descended from a common ancestor, Eritherium, a rabbit sized progenitor, which was rather like a hyrax. Moeritheriums were highly successful in their day, but they disappeared as the Eocene climate dyed up and cooled down. Fortunately several other families of proboscideans like the paleomastodons and the Phiomias were there to carry on the magnificent order of Proboscideans.
Paleomastodon (painting by Heinrich Harder)
Wadi Al-Hitan, Egypt
In the desolate desert 150 kilometers southwest of Cairo there is a fearsome arid valley (wadi) of cliffs, carved buttes, and sandblasted erratic boulders. The bleached landscape has an otherworldly emptiness as though it were located on a lifeless alien planet, though if you look closely, the desert is filled with austere furtive life like dorcas gazelles, tiny sand colored lizards, cobras, scorpions, and fennec foxes. The name of the place is even more otherworldly—“Wadi Al-Hitan” which is Arabic for “valley of the whales” and although the great smooth rocks buckling out of the sand might momentarily be taken for the backs of huge whales, the utter absence of the ocean (or of water of any kind) makes the name seem fanciful. The nearby Mount Garet Gohannam (which means mountain of hell because of the way it glows like flames at sunset) seems to be more aptly named.
Whale fossil at Wadi Al-Hitan
However the name of Wadi Al-Hitan is remarkably literal–for the valley contains the remains of hundreds of huge ancient cetaceans which died in the Eocene and were fossilized in the yellowish sandstone. Forty million years ago the valley was a marine lagoon. Although the remains of numerous sirenians, sawfish, sharks, rays, sea turtles, marine crocodiles, sea snakes, and even swamp dwelling moeritheriums have been discovered in the wadi, the valley takes its name from the most spectacular and numerous fossils which belong to four different species of primitive whales. The most commonly discovered fossils belong to Dorudon, which was 3-5 meters long (9-15 feet) and fed on fish and mollusks, and to Basilosaurus, which was 15-22 meter (50-72 foot) and fed on everything else in the ocean.
Basilosaurus was first discovered in Louisiana in the early 19th century. Its immense size and serpentine form initially convinced naturalists that it was a marine reptile and they misnamed the creature Basilosaurus (which means “king lizard”). The mistake soon became obvious and Basilosaurus was classified among the Archaeoceti, a paraphyletic suborder of the cetaceans, however the giant kept its dinosaur name. Different species of Basilosaurus flourished in oceans worldwide during the wet, tropical Eocene and, even though they were obviously very adept at ocean living (indeed rising to the top of the food chain) the creatures betray vestiges of terrestrial living which modern whales have entirely dispensed with. Not only do Basilosaurus fossils have teeth and jaws which retain reatures from their artiodactyl ancestors, they also have tiny vestigial back legs a mere half meter in length (which would scarely help a 22 meter animal get around). Additionally Basilosaurus was different from modern whales in that it probably moved with eel-like horizontal thrashing of its long tail (modern whales move their flukes vertically). Basilosaurus probably did not dive very deeply, but moved about near the surface of the oceans hunting for smaller marine animals.
Basilosaurus from “Life in the Ancient Seas Exhibit” at the Smithsonian Institution, National Museum of Natural History
Although Wadi Al-Hitan was discovered by Europeans in 1902-1903, some archaeologists and anthropologists have speculated that it was known long before that and have been irresistibly drawn towards comparing basilosaurus with the giant crocodiles and earth spanning serpent gods which populate ancient Egyptian cosmology.
Detail from painting (Life in the Ancient Seas Exhibit: Smithsonian Institution, National Museum of Natural History)
Andrewsarchus Skull at the American Museum of Natural History
In the summer of 1923, Kan Chuen Pao, unearthed an enormous skull from the baking Gobi desert of Mongolia. Pao was a member of a paleontology expedition led by Roy Chapman Andrews, a world famous explorer, adventurer, and naturalist who, during the course of his career, rose from being a janitor at the American Museum of Natural History to being its director. The skull they found was an enigma—the creature was a mammal with immensely powerful jaws but blunt peg-like teeth. No substantial bones were found other than the skull sans jaw (nor have any further specimens ever been discovered). The skull was discovered in sediments deposited during the late Eocene, the sweltering summer epoch when most extant mammalian orders evolved, so it is probably 36 to 40 odd million years old. Andrews was immediately of the opinion that it was a huge carnivore, but what sort of creature was it really?
A toothy hairy model of Andrewsarchus
The creature was named Andrewsarchus mongoliensis in honor of Adrews and his expedition. Andrewsarchus may have been the largest mammalian carnivore ever (although short faced bears might have been larger). The one skull, currently in New York, measures 83 cm (33 inches) long and 56 cm (22 inches)wide–which suggests the animal may have been 3.4 meters (11 feet) long and nearly 2 meters (6 feet) tall at the shoulders. Such a creature could weigh more than 1000 kg (2200 lb).
A drawing of Andrewsarchus with a large ninja to explain scale (Picture Credit: Everything Dinosaur)
But Adrewsarchus may not have been a carnivore: ever since the beginning of the jazz age, Paleontologists have argued about the monster’s diet. Andrewsarchus lived along the coast of the eastern Tethys Ocean, a sea which was dried out and destroyed when the Indian subcontinent barreled into Asia during the late Eocene/Early Oligocene.
A Delightful Andrewsarchus model/toy produced by Bullyland
Some scientists believe the creature was a hunter who captured the giant land animals of the time. Other scientists believe the animal was a scavenger which lived on the rotting carcasses of primitive whales and beached sea turtles. Another group feels that the creature fed on huge beds of shellfish, and a final school holds that the animal was even larger than believed and was at least part-herbivore!
An unpainted model of an athletic hunting Andrewsarchus (as envisioned by Paleocraft)
The taxonomy of Andrewsarchus is equally confusing. The great skull was initially classified as a giant creodont (an extinct order of alpha-predators which share an ancestor with today’s carnivore). The first scientific paper about the creature by great paleontologist and…um eugenicist Henry Fairfield Osborn states, “An outline sketch of the skull was sent in a letter to the Museum, from which Dr. W. D. Matthew immediately observed its real affinity to the primitive Creodonta of the family Mesonychidae.”
Later scientists have been less certain about lots of things than Osborn was and Andrewsarchus’ place in the mammalian family is now uncertain. A consensus is emerging that the great creature shared common ancestors with the artiodactyls (like hippos, deer, and pigs). Perhaps its heritage provides insights into the link between the artiodactyls and their close (yet oh so distant) cousins the whales.
A digital Andrewsarchus pensively gnawing a bone beside the Eastern Tethys (from BBC's "Walking with Beasts")
Whatever the case is, these giant hoofed creatures with their immense powerful maws must have been amazing and terrifying to behold. Their fate seems to have been sealed as the Tethys closed and the Gobi basin dried out, but whenever I think of the harrowing deserts of Mongolia and China, I imagine their fearsome toothy spirits towering over the other strange ghosts of that haunted place.
An Iridescent Wasp on a Linen Tablecloth
Today I would like to start a brand new animal category concerning the most gifted of the social insects, the superorder Hymenoptera, which consists of wasps, bees, ants and sawflies (along with some other oddballs which are less frequently mentioned). Hymenoptera are arguably among the most successful creatures on the planet. Their behavior can be almost embarrassingly humanlike and they are famous for building elaborate constructions, going to war, taking slaves, farming fungi, and crafting rigid city-like social hierarchies. However, of all life forms on earth, the hymenoptera are some of the most vividly alien: cuttlefish do seem downright cuddly when compared to the horrifying digger wasps. A sociologist could happily draw parallels between a bee hive and a city until he looked at the details of bee reproduction, at which point he would probably break down and weep.
The Hymenoptera are not as ancient as either the mollusks or the mammals (if it is fair to compare an order with a phylum or a class). They originated in the Triassic and did not develop the successful social organization which is now such a defining feature until the late Cretaceous. The first hymenopterans were the xylidae, a family of sawflies with a minimal presence on earth today but with a long pedigree. These first sawflies fed on the pollen and buds of the conifer stands beneath which the first dinosaurs developed (and under the roots of which the first mammals cowered). The rise of the flowering plants in the Cretaceous led to a leap-forward for these pollen-eaters: complex flowers then evolved in tandem with the hymenopterans. It was also during the Cretaceous that the ants and termites split from the vespoid wasps. The earliest honey bees of the familiar genus Apis evolved at the end of the Eocene bt they were preceded by all sorts of hymenopteran pollinators.
A Sawfly Fossil (Hymenoptera: Symphyta)
I mentioned above that, for all of their familiarity to us, the Hymenoptera are disturbingly alien. In fact as I have been writing this comparatively tame post, a dreadful sense of formication has stolen over me and I find myself brushing phantom ants from my limbs and feeling the terrible pang of yellowjacket stings from childhood. The hymenoptera are frequently the basis of the extraterrestrial enemies in science fiction. Although people are occasionally stung to death by wasps or ripped apart from within by driver ants, it is something larger and less tangible which makes the hymenoptera such reliable villains. I have watched the soldier bees snip the wings off of wasps trying to invade my grandfather’s bee hive and then toss the invaders’ writhing bodies from the painted ledge—all while a river of worker bees went out and came back laden with pollen. There is an alarming touch of civilization to these social insects: a hint that they are utilizing the same kinds of organization and communication which have made humans such a success. And, in fact, the social insects are a huge success—ants alone are estimated to constitute a substantial portion of the animal biomass of earth (to say nothing of termites, bees, wasps and the rest).
Yellow Jackets on a Coke Can (photo by the fearless Alan Cressler)
Of course this success has broad ramifications. The hymenoptera are everywhere in nature and they also play a huge part of human culture. Indeed the very name of this blog is a play on words between my surname and the noble art of aviculture. Without the bees, we would not have much in the way of fruit or vegetables. Not only would this be a disaster for human farming—just contemplate how many other creatures rely on those fruit! Similarly the ants bulwark an entire portion of the ecosystem by scavenging the tidbits out of fields and forests, while the despised termite breaks cellulose down into a form which can be reintegrated back into the food chain. Writing about the hymenoptera may be an itchy, antsy business but it is a well-merited study. This group of insects is pivotal to life on dry-land as we know it. The biblical promised land was one of milk and honey. There would be no milk without mammals, but there would be no honey (and precious few mammals) without the hymenoptera.
A beekeeper completely covered with swarming honey bees in a “bee man” cantest in China
Obdurodon--A Miocene Platypus which flourished 15 to 20 million years ago
Ferrebeekeeper has an abiding interest in monotremes including both the poisonous platypus and the enigmatic echidnas (with their advanced frontal cortex). But sadly that is about it as far as it goes for the extant egg-laying mammals: there are only two living families of monotremes (with a scanty total of five species split between them). To learn more about these animals one must turn to paleontology. Unfortunately even in the fossil record, monotremes are extremely rare.
Based on genetic evidence, biologists believe that the first monotremes made their advent in the history of life about 220 million years ago during the Triassic era; however the earliest known fossil monotreme so far discovered was a fossil jaw from the early Cretacious era about 120 million years ago. The bones belonged to Steropodon galmani, which seems to have been a beaked swimmer about 50 cm (20 inches) long which lived in Australia. Steropodon was apparently a giant among Cretacious mammals–most of which seem to have been shrew-sized (so as to better avoid attention from their contemporaries, the dinosaurs). Reconstructions of Steropodon all seem to resemble the platypus, and most paleantologists would probably concede that it was a sort of platypus—as apparently were other Mesozoic fossil monotremes such as Kollikodon and Teinolophos (platypuses and these platypus-like forbears are called the Ornithorhynchida). During the Cretaceous era, the land which is now Australia was in the South Polar regions of the world (approximately where Antarctica is today). Although temperatures were much warmer during the Cretaceous, monotremes must still have been able to deal with terrible cold: it is believed that the extremely efficient temperature control and the deep hibernation mechanism which these animals continue to display first evolved during that time.
An artist's reconstruction of Steropodon
The only monotreme fossil which was not found in Australia was from another platypus-like creature named Monotrematus sudamericanum. The creature’s remains were found in a Patagonian rock formation from the Paleocene era (the era just after the fall of the dinosaurs). Monotremes probably flourished across South America and Antarctica, as well as on Australia, but evidence is still scarce. There are most likely many interesting monotreme fossils throughout Antarctica, but, for some reason, paleontologists have not yet discovered them. Additionally, unlike the marsupials (which still quietly flourish throughout South America), the poor monotremes were wiped out on that continent.
Another artist's vision of Steropodon galmani--Notice how peeved the poor creature looks!
Last week I wrote about the Eocene era and the great proliferation of mammalian types which took place during that warm and fecund time. Although most families of mammals alive today first appeared on the scene during the Eocene, obviously the monotremes were already incredibly ancient. The Eocene does however seem to have been significant time for the monotreme order: the aquatic platypuses were apparently the ancestral monotremes, and echidnas (the Tachyglossidae) probably split off from them during the Eocene. Unfortunately we have no Eocene monotreme fossils so this conclusion is based on genetic evidence and on the suffusion of Miocene monotremes which include representatives of both Ornithorhynchida and Tachyglossidae. Some of these latter creatures are spectacular, like Zaglossus hacketti the giant echidna from the Pleistocene which was about the size of a ram! As Australia dried up so did the monotremes and now there is only one species of platypus left…
The Giant Echidna (Zaglossus hacketti) which lived until 20,000 years ago...
Well, that’s a cursory history of the monotremes based on what we know. I wish I could tell you more but unfortunately there is no fossil evidence concerning the first half of the order. Sometimes I like to imagine the first monotremes—which were probably clunky, furry platypus-looking characters with an extra hint of iguana thrown in. These creatures fished in the alien rivers of the Triassic world in a time when dinosaurs and pterosaurs were also still evolving.
The Eocene (Illustration by Bob Hynes for the Smithsonian Institution)
The Eocene epoch (which lasted from 56 million ago to 34 million years ago) was hot! Temperate forests ran all the way to the poles. Steamy tropical jungles grew in the latitude where Maine is now and the equatorial regions of earth were (probably) sweltering. Tropical reefs formed in the coastal waters around a heavily forested and ice-free Antarctica. Since there was not year-round ice at each pole, the sea levels were much higher.
A Global Map of the Early Eocene (map by Dr. Ron Blakey)
The Eocene was a time when most of the contemporary mammalian orders first appeared. The earliest artiodactyls, perissodactyls, rodents, bats, probiscideans, sirenians, and primates all originated during this time. Of course mammals were not the only story: the Eocene was also a time of great diversification for birds and many familiar orders of avians developed then. Reptiles begin to put the setbacks which marked the end of the Cretaceous behind them and several giant new species emerged including an immense tropical ur-python and a host of crocodiles and turtles. It is harrowing to think that the first wee dawn horses and cute little early atiodactyls were forced to contend with a 13 meter long super snakes and giant crocodilians (which flourished in the great hot swamps of Alaska), but such is the case.
Titanboa with Ancient Crocodilian (painting by Jason Bourque)
The high temperatures of the Eocene are perplexing to scientists. By contrast, the temperatures of the Paleocene (which was the first era of the Cenezoic and had directly preceded the Eocene) were much more temperate. In fact the temperature spike of 56 million years ago seems to have ended the Paleocene and brought about the diversification of Eocene life. The rapid warming is known as the Palaeocene-Eocene thermal maximum and scientists have been vigorously debating what caused the climate change. An immense amount of carbon seems to have entered the atmosphere at this time, which in turn led to greenhouse warming. It remains controversial as to how such a large quantity of carbon got into the atmosphere. Comet/meteorite impact, massive peat fires, and volcanic activity have been suggested as triggers, however supporting evidence is lacking. The release of globally significant quantities of hydrocarbons–which had been trapped in undersea clathrates seems like a more feasible hypothesis, as does the idea that the earth’s orbit brought the planet closer to the sun for a time.
Phenacodus, a goat-sized grazer of the Eocene era (painting by Heinrich Harder)
The end of the Eocene was also linked to the carbon cycle. Reduced carbon dioxide in the atmosphere seems to have led to global cooling and newly evolved varieties of grasses began to invade large swaths of the world. Additionally two massive meteor strikes in Siberia and Maryland combined with substantial volcanic activity to finish off the long hot summer. But during the Oligocene, the era which followed the Eocene, the world was a much more familiar place inhabited by orders of animals which are still here with us today (or are us–since primates first evolved during the Eocene).
