Prehistoric Life 18

March 21, 2011 at 6:29 am (birds, botany, ecology, mammals, paleontology, Prehistoric Life series)
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by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Pliocene Epoch (5.2-1.64 million years ago)

The Pliocene Epoch, literally “more recent,” originally was defined (1833) by the percentage of then known fossil mollusk species still living (35-95%). Its end is marked by the beginning of the glacial times.

Life on Earth. In the Pliocene, grazers became largely supplanted by more generalist herbivores as savannas became widespread in Eurasia and North America. The dominant groups were camels, antilocaprids (e.g., pronghorn “antelope”), and Equus horses (which, like most horses, originated in North America). Opossums diversified in South America, mammoths appeared in Africa (early Pliocene), the North American rhinoceroses vanished (middle Pliocene), and Sorex shrews appeared in the late Pliocene.

Sorex shrews like our short-tailed shrew of today made their evolutionary appearance in the Pliocene Epoch.

Land bridges finally allowed camels to spread into South America and Asia in the Pliocene (a camel survived in North America into late Pleistocene times). In the middle Pliocene, continued connection to Asia brought immigration of more carnivores, deer, and the elephant Stegomastodon. From North America to Eurasia went a rabbit, a squirrel, the beaver, and Equus.

The world’s lynx and cheetahs first appeared in North America, crossing to the Old World via the Bering Sea land connection.

In the late Pliocene, new appearances were pocket gophers, the white-tailed deer genus Odocoileus, raccoons, the giant beaver, bobcat (Old World lynxes, and also cheetahs, trace their ancestry to the New World where their groups first appeared), the New World porcupine family, eastern mole, and masked shrew.

Modern deer made their appearance in the Pliocene.

In the meantime, the first hominids were beginning to walk upright in Africa 3.8-4 mya (million years ago; Science 307:1545). Upright walking may have begun in the trees, as a hand-assisted way of negotiating thin, flexible branches (Science 316:1328 ). “Lucy,” Australopithecus afarensis (3-3.6my ago), regarded as a human ancestor or close to it, has been tied to the older A. anamensis (4mya), which in turn may have come from the still older Ardipithecus ramidus (4.4mya). Fossils of all three species were found in the same African river valley (Science 312:178). Ardipithecus significantly was a woodland dweller; apparently upright walking was not a product of a grassland habitat (Science 326: 64). Genus Homo had evolved by the late Pliocene, with species from Africa to Asia. Homo habilis and H. erectus are two earlier species which apparently overlapped considerably in time, so that it is uncertain whether the latter descended from the former (Science 317:733). Examination of limb structure points to habilis being arboreal while erectus was terrestrial, so a connection by descent is unlikely (Science 320:609).

The New World chickadees evolved from a single species that emigrated from Eurasia in the Pliocene.

Birds also were dispersing, and our modern species began to emerge. At least some modern songbirds had evolved by the early Pliocene (Auk 124:85). The chickadees and titmice, which had appeared in Eurasia originally, came over to North America in the Pliocene. The first crested species (titmouse) came over around 4 mya, and a single non-crested (chickadee) founder species around 3.5 mya. Subsequent evolution led to the 3 modern titmouse species and about 7 chickadees in the Americas. One terror bird species, in genus Titanis, reached North America from South America 2-3 million years ago, but was extinct by the end of the Pliocene.

Local landscape. Cooling and increased seasonality continued in the Pliocene (the middle Pliocene was the last time that Earth temperatures were warmer than at present).  Climate in the early Pliocene was significantly warmer than today; the major difference apparently was that the El Niño pattern of Pacific Ocean currents was permanent rather than episodic as it is today. The re-establishment of such a pattern is a possible outcome of global warming (Science 312:1485). Woodlands were more open in the Pliocene, perhaps savanna-like in places in our area. Elsewhere in North America, the continent developed its first near-modern boreal forest, as well as the first deserts, tundra and permafrost areas.

The Pliocene brought increasing seasonality, and extensive savannas replaced much of the Miocene grasslands.

The nearest Pliocene deposits are tiny areas in southern Indiana, and extensive areas in eastern Nebraska. By the Pliocene, much of northeast Illinois was draining eastward into the river that ultimately was enlarged by Pleistocene glaciation to become Lake Michigan. This happened when the relatively erosion-resistant and eastward-sloping Niagaran dolomite beneath us was brought close to the surface. Today, surface waters are directed by much more recent glacial deposits on top of that bedrock, and all ultimately flow into the Des Plaines-Illinois River system, ending up in the Gulf of Mexico rather than the North Atlantic.

Local life.  There is a likelihood that the camels, antilocaprids and horses (including Equus, the genus that includes modern horses) were represented locally. Deer, rabbits, beavers, raccoons, sabertooth cats (including Meganteron, an ancestor of the famous Smilodon), bears, the scavenging “hyaenoid dog” Borophagus, otters, and skunks are other likely species at that time.

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Prehistoric Life 17

March 14, 2011 at 6:23 am (birds, botany, ecology, geology, mammals, paleontology, Prehistoric Life series, Uncategorized)
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by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Neogene Period (23.3 million years ago-present), Miocene Epoch (23.3-5.2 million years ago)

The Neogene Period (named in 1853) defines a time when a significant portion of fossil species (or at least very close relatives of them) still are in existence. The Miocene Epoch (established 1833), literally “few recent,” originally was defined by the percentage of then known fossil mollusk species still living (17%).

Life on Earth. Warming but continued dry conditions prevailed through most of the Miocene, giving way to renewed cooling in the late Miocene. This cooling was caused at least in part by the continuing growth of the Antarctic ice sheet. The resultant drop in sea level established land bridge connections from North America to South America and Asia. Continental growth, and also the rise of major mountain ranges, increased the seasonality of climate, and changed ocean circulation patterns, with upwelling zones probably setting up the conditions favoring pinniped (sea lion, etc.) evolution in the middle Miocene.

Harbor seal. Pinnipeds underwent a significant radiation in the Miocene.

Grasslands spread in the Miocene. The Perissodactyla had been the dominant ungulates, with their diversity peaking in the Eocene, but in the Miocene they declined (though rhinoceroses remained prominent throughout the epoch), while the Artiodactyla increased. The latter ungulates’ advantage may have been their ruminant digestive tract and complex high-crowned teeth, good for grazers (this was true of the larger division of artiodactyls; the pigs and hippopotami lack these specializations). Camels were very diverse in the Miocene, a remarkable example being the 12-foot-tall, giraffe-like browser Aepycamelus.

Bactrian camels, Brookfield Zoo. The camels, which had their start in North America, were very diverse on our continent in the Miocene.

The deer family appeared early in the Miocene in the Old World. By the middle Miocene, the diversification and evolution of horses was represented in part by the first one-toed species, Pliohippus of North America. Horses did not develop high-crowned molars until 4 million years after the grasses replaced trees as the dominant vegetation in the Great Plains, but their limb structure changed more quickly, so that they were able to survive by efficiently traveling longer distances between suitable habitat patches (Science 306:1467). Ungulate diversity peaked in the mid-Miocene, perhaps because frequent disturbance by the large proboscideans (gomphotheres and mastodons, which migrated into North America at that time) diversified the grassland savanna that had developed. Toward the end of the Miocene, however, much of the savanna gave way to grasslands, and there were extinctions of many of these ungulates and proboscideans.

Prairies and other grassland ecosystems spread into North America and became important here in the Miocene.

The departure of forests from much of North America is associated with the vanishing of primates from this continent.  Miocene land connections to South America and Asia resulted in significant immigrations and extinctions. Sabertooth cats and other Felidae first immigrated from Asia in the middle Miocene (ending the so-called “cat gap”).  Other new Miocene arrivals from Asia included bears, skunks, and badgers; from South America, ground sloths. There was a diversification of canids (dog family), mustelids (weasel family) and amphicyonids, though in the late Miocene the amphicyonids became extinct. The American white-footed mouse genus Peromyscus first appeared in the Miocene, and Spermophilus ground squirrels in the middle Miocene. Flying squirrels had their start in Asia in the early Miocene, with the split between Old World and North American flying squirrels happening in the late Miocene. The dominant carnivores in South America were marsupials in the Tertiary through the Miocene. The first member of the opossum genus, Didelphis solimoensis, showed up in the fossil record of Brazil in the latter part of the Miocene. Marsupials went extinct in North America in the Miocene, however.

Bears evolved in the Old World, and crossed the Bering Sea land bridge into North America in the Miocene.

Modern bird families were established in the Miocene, and the land bird orders other than the passerines underwent their great diversification. The passerine (perching birds) explosion began in the late Miocene. The first modern genera of birds began to appear in the Miocene, as well.

Local landscape. Subtropical forest of the early Miocene gave way to warm temperate to cooler temperate forests. The Texas gulf coast was swampy, so our climate very likely was at least as moist as today. We were between known areas of forests in New England that were warm temperate (hickories, chestnuts, hollies, mulberries, gums, oaks, buckthorns, elms, grapes) and shrubland-savannas on the Plains (invaded by grasses and prairie forbs as the Miocene progressed). The closest Miocene deposits are in western Nebraska, south central South Dakota, central Mississippi and SW Maryland.

Local life. Throughout the Miocene, browser-grazer pairs of rhinoceroses were found all over North America in savanna environments (the most common genera were Aphelops and Teleoceras, respectively; Teleoceras appears to have been a herding, and possibly semiaquatic species). If our area was more forested, we may have had only a browsing species. Rhinos became extinct in North America at the end of the Miocene. It seems likely that our area witnessed the transition from perissodactyl to artiodactyl dominance. Forms of rhinos (5 genera), tapirs (2 genera), horses (14 genera), dromomerycids (an extinct group of deer-like woodland browsers with horned males) and camels (5 genera, including the giraffe-like Aepycamelus) probably were here. The oreodonts were a diverse group of pig-like herbivorous artiodactyls, with at least 4 genera probably here in the Miocene. Carnivora would have been the dominant predators (diverse dogs, weasels, the large bears Indarctos and Plionarctos, “bear-dogs,” large cats, and the saber-toothed nimravid Barbourofelis), but there was also the entelodont Dinohyus. The Miocene also saw the arrival of the first proboscideans, or elephant relatives. These may have had a significant impact, killing the trees that they fed on and thus disturbing the vegetation so as to create more habitat diversity. There likely were 3 genera here, including two that were relatively elephant-like, and one that had shovel-like lower tusks that it probably used both to scoop up aquatic plants and to scrape bark from trees.

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Prehistoric Life 16

March 7, 2011 at 7:53 am (botany, ecology, geology, mammals, paleontology, Prehistoric Life series)
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by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Oligocene Epoch (35.4-23.3 million years before present)

The Oligocene Epoch (named in 1854), literally “little recent,” was divided from the Miocene of which it originally was part, based on fossils in Germany.

Life on Earth. The first grassland ecosystems appeared in Asia in the Oligocene, a profound step in the history to follow.

At the beginning of the Oligocene there was a big diversification of North American mammals, with only a quarter of the Eocene genera continuing. Change was slow for the rest of the epoch. This rapid change, preceded by a wave of extinctions, is associated with a time of climatic cooling. Relatively little is known about the Oligocene, because its general lack of change after the beginning has interested few researchers.

Those peculiar derived artiodactyls, the whales, continued their slow evolution through the Oligocene.

The oreodonts were a diverse North American artiodactyl (even-toed ungulate) group in the Oligocene; they declined to extinction at the end of the Miocene. The early Oligocene was the time when the browsing perissodactyl titanotheres (brontotheres) peaked in North America and Asia. Another perissodactyl, the giant rhinoceros Paraceratherium of Asia (also known as Indricotherium or Baluchitherium), is the largest known land mammal ever. It lived in the Oligocene and Miocene, was 18 feet high at the shoulder and could reach twigs and leaves 20 feet off the ground with its 5-foot-long head.

The ground sloths evolved in South America, the first ones appearing in the Oligocene fossil record.

Early in the Oligocene the first beavers appeared (in North America), the first procyonids (raccoon family) in North America and Europe, the first peccaries in North America. The Middle Oligocene brought the Canidae (dog family). Paleosciurus tree squirrels first appeared in the early Oligocene in Europe (Science 299:1568).

Peccaries, another artiodactyl group, evolved into existence in the North American Oligocene.

The hyaenodontids and nimravids became extinct in the late Oligocene, resulting in the “cat gap,” a lengthy period of time in which the North American carnivore fauna was dominated by larger canids and amphicyonids, and smaller mustelids (weasels), but nothing resembling a cat. The first ground sloths evolved in South America in the Oligocene.

Local landscape. A turning point in post-Cretaceous times was the separation of Australia from Antarctica in the late Eocene. The consequent establishment of a permanent cold current around the latter continent in the Oligocene brought a cooling to the global climate that impacts us to this day. Brief but intense glacial episodes, set off by changes in Earth orbital characteristics and made possible by the cold south polar currents, happened both at the beginning and end of the Oligocene (Science 314:1894). The cooling trend continued until our local climate became temperate in the Oligocene. Deciduous dry forests passed from semi-tropical to temperate.

Grassland ecosystems still were in North America’s future, but they had their start in the Oligocene, in Asia.

The oak family became more important both east and south of here. In the Plains to the west, hackberry was common, and that region may have been a low-rainfall scrubland (remember, no grasslands were here yet). The closest Oligocene deposits are in south central South Dakota and western Nebraska.

Local life. One or more species of the carnivore-like creodont Hyaenodon probably occurred here in the Oligocene. Oreodonts also were diverse, then, and likely were represented here. There were widespread, hippolike rhinoceroses called amynodonts in North America and Eurasia. Horses in the genus Mesohippus also were likely here.

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Prehistoric Life 15

February 28, 2011 at 7:12 am (birds, botany, ecology, geology, mammals, paleontology, Prehistoric Life series)
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by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Eocene Epoch (56.5-35.4 million years ago)

The Eocene Epoch, literally “dawn of the recent,” originally was defined by Lyell in 1833 according to the percentage of fossil marine mollusks in France’s Paris Basin still living today (3.5%).

Life on Earth. Reefs reappeared in the oceans 48 million years ago, as new species of reef-building corals evolved among the coelenterates (Science 312:857).

The greatest diversity of Cenozoic Era terrestrial plants in the New World tropics (greater even than today) occurred in the early to middle Eocene. Diversity across the era has correlated fairly well with climate, temperature in particular (Science 311:1893). In the Arctic, temperatures 55-50 million years ago were so mild that even in the darkness of winter they ranged from just above freezing to 70F. Large animals could live there without migrating or hibernating, subsisting on browse and evergreen material. Species in that region included brontotheres, early rhinoceroses, tapirs, alligators, turtles, snakes and flying lemurs.

Our area in most of the Eocene was a diverse tropical forest.

In the early Eocene, order Artiodactyla (even-toed ungulates) evolved, part of a large number of appearances of new mammalian groups and extinctions of older ones, associated with the global warming spike. This time produced the first North American true primates (2 families), didelphids (opossum relatives), perissodactyls and artiodactyls, and their numbers rapidly increased. The lagomorphs (the order containing today’s rabbits) began to diverge from the rodents early in the Eocene. A group called entelodonts, ancestors of pigs, lasted from mid-Eocene to late Oligocene. Camels originated in North America in the late Eocene. The perissodactyl rhinoceroses trace their ancestry to the early Eocene, as do the horses. The latter began with Protorohippus (= the less correct name Eohippus), with fossils in North America. (Europe’s Hyracotherium has been determined to be a different, non-horse, perissodactyl mammal). Perissodactyl brontotheres, which were rhinoceros-like ungulates, underwent much of their evolution through the Eocene. Uintatheres were primitive, Eocene ungulate-like animals, neither Perissodactyla nor Artiodactyla, in several genera, with tusks, horns and tiny brains. Mesonychids were still around, carnivorous species including the enormous Andrewsarchus of Asia and smaller Synoplotherium of North America. That group may have been the source of the whales, though recent evidence suggests that Asian artiodactyls were a more likely origin.

The opening environments of the late Eocene began the trend to increased herding and larger body sizes. The great diversification of artiodactyls and rodents began at the end of the Eocene. The squirrel family (Sciuridae) appeared in western North America at this time (Science 299:1568). The order Proboscidea (ultimately to include the elephants) appeared in the late Eocene in Africa. Whales, rabbits and hares appeared in the Eocene, and the late Eocene produced the first moles, and modern carnivore families. An impressive skeleton of a primate from the middle Eocene was reported in 2009. This individual was lemur-like, but may have been close to the line that led to us (Science 324:1124).

The first rabbits had evolved by the end of the Eocene.

Until the modern carnivore groups expanded, for most of the Eocene the creodonts remained the dominant predators. Hyaenodon was a diverse genus from late Eocene to the early Miocene, ranging from western North America through Europe to Asia and Africa, and with a size from small coyote to large grizzly bear. Sabertoothed carnivores of family Nimravidae appeared in the late Eocene, emigrating from Europe to North America. Felids appear at the Eocene-Oligocene boundary in North America and Eurasia. Other modern carnivore groups were represented by small, generalized forms.

Modern bird families did not exist through the Eocene, though many of the aquatic orders (e.g., Gruiformes, the order containing cranes) diversified. Diatryma was a 7-foot-tall North American flightless gruiform predator.

Local landscape. North America was isolated by the middle of the Eocene (and never again was connected to the east, though the western Bering Sea land bridge was to come and go several times). North America had no tundra, coniferous forest, grassland, desert, shrublands or savannas through the Eocene. There was a brief but intense global warming peak in the early Eocene, with much rain, then a cooling and drying to subtropical conditions in the late Eocene. The local environment made the transition from tropical forest to subtropical forest. The cause of the global warming peak is thought to be an episode of flood basalt eruptions (with attendant release of greenhouse gases) in the North Atlantic as North America and Europe split apart (Science 316: 587).

Local life. Bats probably have been here from the Eocene on, except during glacial times. Bats may have originated in North America, and they underwent a huge diversification in the early Eocene with all present-day families represented by the end of the period (Science 307:580). Primitive true primates likely were here in the Eocene, and possibly into the Oligocene (families Adapidae [lemur-like] and Omomyidae [tarsier-like]).

Bats diversified in the Eocene.

In the early Eocene, the first horse Protorohippus (“eohippus”) very likely was here. Coryphodon, the largest land mammal of its time, probably was here, as was the river-dwelling, hippo-like Metamynodon. The early browsing, running rhinoceroses, like Hyrachyus, were widespread in North America, Europe and Asia. Entelodonts, the predatory ungulates, had a likely representative in Archaeotherium. Condylarths still were around, with the rat-sized, squirrel-like Hyopsodus found all over the Northern hemisphere and lasting well into the Eocene, and the small, generalized Haplomylus also a likely local candidate. We probably had some artiodactyls and rodents by the end of the Eocene, as well as early carnivores (Miacis, Hesperocyon), and creodonts such as Prototomus or Hyaenodon. Crocodilians and turtles were on Ellesmere Island into the early Eocene, so presumably were here as well. The huge predatory bird Diatryma is another good possibility.

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