Since heavy snow still covers most of the Front Range trails, we opted for a visit to the Denver Museum of Nature & Science today. Long famous for its wildlife dioramas, this magnificent institution has recently received kudos for its recovery of numerous Pleistocene fossils from a lake bed near Snowmass, Colorado; the skeletal remains of mammoths, mastodons, ancestral camels, ancestral bison and numerous other animals were unearthed last summer before the reservoir was refilled.
Today, we arrived just in time to see an IMAX film produced by National Geographic and narrated by the renowned naturalist, David Attenborough. Given the odd title of The Flying Monsters, apparently chosen to attract young visitors, this 3-D film covered the natural history of pterosaurs, from their initial appearance in the Triassic, some 200 million years ago, until their disappearance at the end of the Cretaceous, 65 MYA. Thought to have evolved from lizards that used webbed limbs to glide between trees, pterosaurs had an elongated digit on each forefoot which was connected to the ipsilateral leg by a thin membrane. Early pterosaurs were not much larger than lizards while giraffe-sized pterodons had appeared by the late Cretaceous; through the course of their evolution, pterosaurs lost their long tails and developed a limited ability to walk on their hands (located at the bend of each wing) and feet, offering some capacity to feed on land as well as in the air. Some pterodons, equipped with a large head fin, also may have preyed on fish, sailing across the surface of the sea.
While pterosaurs disappeared with terrestrial dinosaurs, at the end of the Cretaceous, the film suggested that their demise may not have been solely related to a massive meteor strike; rather, the rise of birds, more agile on land and in the air, may have sealed their fate. Though pterosaurs were extinct for almost 65 million years before humans appeared, the film provided a splendid introduction to those fascinating creatures and, through the magic of 3-D photography and computer animation, allowed the audience to fly with them.
Rabu, 08 Februari 2012
Selasa, 07 Februari 2012
Snow on Snow
Leaving a nearly snowless winter in Missouri, we arrived at our Littleton farm and found it adorned with more than 15 inches of white powder; fortunately, my Tacoma pickup was able to navigate the long, uphill driveway and it was just a short trudge to the backdoor.
Out on our property, Townsend's solitaires, robins and bushtits feasted on juniper berries while chickadees, flickers and house finches moved among the bare deciduous trees, undaunted by the heavy snow. Our resident fox and raccoons may den up for a few days but we'll soon see their tracks across the blanket of white. Down on the South Platte, ducks and geese crowded the river, feeding along and beneath the relatively warm, open waters.
Another cold front passed through Colorado overnight and, though only a dusting was expected, five more inches were left behind. Enjoying a snowy winter landscape for a change, my wife and I took a walk through the residual flurries as the clouds began to dissipate and patches of blue opened above the Front Range. Milder, sunny weather is forecast for the rest of this week and the intense Colorado sun will soon take a toll on our beautiful gift of the season.
Out on our property, Townsend's solitaires, robins and bushtits feasted on juniper berries while chickadees, flickers and house finches moved among the bare deciduous trees, undaunted by the heavy snow. Our resident fox and raccoons may den up for a few days but we'll soon see their tracks across the blanket of white. Down on the South Platte, ducks and geese crowded the river, feeding along and beneath the relatively warm, open waters.
Another cold front passed through Colorado overnight and, though only a dusting was expected, five more inches were left behind. Enjoying a snowy winter landscape for a change, my wife and I took a walk through the residual flurries as the clouds began to dissipate and patches of blue opened above the Front Range. Milder, sunny weather is forecast for the rest of this week and the intense Colorado sun will soon take a toll on our beautiful gift of the season.
Senin, 06 Februari 2012
High Plains Upslope
On my frequent travels between Missouri and Colorado, I have often noticed that, following a snowstorm, the Wakeeney, Kansas, area receives more snow than areas to its west or east on I-70. Assuming this must represent an upslope phenomenon, a reflection of the local topography, I examined a map of the region after yesterday's journey reinforced my past observations.
In fact, Wakeeney sits on the east edge of the High Plains at the west end of a topographic wedge in which the elevation is gradually rising from east to west. A prominent ridge just south of Hays, Kansas, is an erosional remnant of the High Plains, dividing the watersheds of the Smoky Hill River, to its south, from that of Big Creek to its north. In similar fashion, though not as visible from I-70, another eastward extension of the High Plains divides the Big Creek watershed from that of the Saline River, to the north of that ridge. Both of these ridges merge near Wakeeney and the rolling terrain between them climbs from 2000 feet at Hays to about 2450 feet at Wakeeney, yielding an upslope terrain that concentrates its orographic precipitation near the latter city; this scenario develops whenever easterly winds sweep Gulf moisture westward toward the High Plains.
Upsloping air cools and condenses, dropping its cargo of rain or snow. Such orographic weather events are common along mountain ranges, producing vital snowpacks in many regions and moist, forested retreats in the "sky islands" of desert areas. The upsloping terrain near Wakeeney is repeated at many other sites across the Great Plains, where a series of escarpments produce stair-like transitions from the lower, tallgrass zone on the east to the higher, shortgrass ecosystem of the High Plains. In addition, similar escarpments border the High Plains to the north, west and south, yielding upslope funnels in those regions as well; examples include the Pine Ridge Escarpment of western Nebraska and the Palmer Divide in eastern Colorado.
In fact, Wakeeney sits on the east edge of the High Plains at the west end of a topographic wedge in which the elevation is gradually rising from east to west. A prominent ridge just south of Hays, Kansas, is an erosional remnant of the High Plains, dividing the watersheds of the Smoky Hill River, to its south, from that of Big Creek to its north. In similar fashion, though not as visible from I-70, another eastward extension of the High Plains divides the Big Creek watershed from that of the Saline River, to the north of that ridge. Both of these ridges merge near Wakeeney and the rolling terrain between them climbs from 2000 feet at Hays to about 2450 feet at Wakeeney, yielding an upslope terrain that concentrates its orographic precipitation near the latter city; this scenario develops whenever easterly winds sweep Gulf moisture westward toward the High Plains.
Upsloping air cools and condenses, dropping its cargo of rain or snow. Such orographic weather events are common along mountain ranges, producing vital snowpacks in many regions and moist, forested retreats in the "sky islands" of desert areas. The upsloping terrain near Wakeeney is repeated at many other sites across the Great Plains, where a series of escarpments produce stair-like transitions from the lower, tallgrass zone on the east to the higher, shortgrass ecosystem of the High Plains. In addition, similar escarpments border the High Plains to the north, west and south, yielding upslope funnels in those regions as well; examples include the Pine Ridge Escarpment of western Nebraska and the Palmer Divide in eastern Colorado.
Sabtu, 04 Februari 2012
Human Hybridism
While evangelicals will surely stick to their Adam and Eve story, DNA technology has greatly advanced our understanding of evolution and, in recent years, has uncovered the fact that most humans are hybrids. The last (to date) in a long line of hominids to walk the Earth, our species appeared in Africa about 130,000 years ago and began to disperse from that Continent about 80,000 years ago. However, earlier hominids had colonized Eurasia long before we left our homeland.
About 600,000 years ago, the lineage that would lead to humans split from one that would culminate in Neanderthals and their close cousins, the Denisovans. Based on DNA studies, these hominids diverged genetically and geographically about 350,000 years ago as Neanderthals spread into Europe and Western Asia while Denisovans occupied Eastern Asia, from Siberia to Indonesia. The latter group was unknown until a few fossils were discovered in a Siberian cave just two years ago; cool conditions within the cave served to protect DNA within the two bones and one tooth and subsequent studies demonstrated their close relationship to Neanderthals.
Of even more interest, DNA analysis of various human populations has demonstrated that early human migrants interbred with Neanderthals and Denisovans as they dispersed from Africa. While the latter two hominids became extinct about 30,000 years ago, we continue to carry some of their genes; 5% of the genome in humans of Eurasian descent is of Neanderthal origin and various populations of Southeast Asia, Melanesia and Australia have genomes that contain 4-5% Denisovan genes. The persistence of these genes in our DNA indicate that they conferred some benefit to early humans and were thus retained through the process of natural selection; only humans who are descendants of African populations do not possess this hybridism. Racist, white evangelicals may be interested to know that African Americans are pure Homo sapiens while they, themselves, are part Neanderthal.
About 600,000 years ago, the lineage that would lead to humans split from one that would culminate in Neanderthals and their close cousins, the Denisovans. Based on DNA studies, these hominids diverged genetically and geographically about 350,000 years ago as Neanderthals spread into Europe and Western Asia while Denisovans occupied Eastern Asia, from Siberia to Indonesia. The latter group was unknown until a few fossils were discovered in a Siberian cave just two years ago; cool conditions within the cave served to protect DNA within the two bones and one tooth and subsequent studies demonstrated their close relationship to Neanderthals.
Of even more interest, DNA analysis of various human populations has demonstrated that early human migrants interbred with Neanderthals and Denisovans as they dispersed from Africa. While the latter two hominids became extinct about 30,000 years ago, we continue to carry some of their genes; 5% of the genome in humans of Eurasian descent is of Neanderthal origin and various populations of Southeast Asia, Melanesia and Australia have genomes that contain 4-5% Denisovan genes. The persistence of these genes in our DNA indicate that they conferred some benefit to early humans and were thus retained through the process of natural selection; only humans who are descendants of African populations do not possess this hybridism. Racist, white evangelicals may be interested to know that African Americans are pure Homo sapiens while they, themselves, are part Neanderthal.
Jumat, 03 Februari 2012
A Spring Storm in Mid Winter
Here in central Missouri, we awoke to clear skies and temperatures in the low 40s (F), with light southeast winds. But to the west, a wall of dark clouds stretched across the horizon, the leading edge of a massive storm system that is centered over the Southern Plains. Ahead of the storm, Gulf moisture is flowing northward across the Heartland and, as the system approaches, bands of rain will move in from the west, a product of lift, atmospheric moisture and the clash of air masses. Rain should develop in central Missouri by early afternoon and is expected to persist for 24 hours or more, a welcome development for our parched landscape.
On the northwest side of this storm, the Gulf moisture is being whipped toward the Front Range as counterclockwise winds swirl around the central low. These upsloping winds cool as they rise in elevation and heavy snow is falling across Metro Denver, the foothills and the adjacent plains; up to 20 inches are expected in the city with higher amounts on the east slope of the Front Range. Since the primary jet stream remains up in Canada, the air will not be extremely cold (remaining in the 20s F) but the associated strong winds are producing blizzard conditions and parts of several Interstates have been closed.
As the storm pulls on to the east, this upslope effect will be lost and snow will be very limited in the Upper Midwest; here in Missouri, all precipitation is expected to arrive in the form of rain. Once again, the high riding jet stream will spare most of the U.S.; while we enjoy a mild winter, Alaska, eastern Europe and Russia, caught above the jet stream, have been dealing with heavy snow and frigid air. Indeed, our mild winter has nothing to do with global warming but, rather, reflects a stagnant weather pattern across the Northern Hemisphere.
On the northwest side of this storm, the Gulf moisture is being whipped toward the Front Range as counterclockwise winds swirl around the central low. These upsloping winds cool as they rise in elevation and heavy snow is falling across Metro Denver, the foothills and the adjacent plains; up to 20 inches are expected in the city with higher amounts on the east slope of the Front Range. Since the primary jet stream remains up in Canada, the air will not be extremely cold (remaining in the 20s F) but the associated strong winds are producing blizzard conditions and parts of several Interstates have been closed.
As the storm pulls on to the east, this upslope effect will be lost and snow will be very limited in the Upper Midwest; here in Missouri, all precipitation is expected to arrive in the form of rain. Once again, the high riding jet stream will spare most of the U.S.; while we enjoy a mild winter, Alaska, eastern Europe and Russia, caught above the jet stream, have been dealing with heavy snow and frigid air. Indeed, our mild winter has nothing to do with global warming but, rather, reflects a stagnant weather pattern across the Northern Hemisphere.
Kamis, 02 Februari 2012
Natural History of Elephants
Sixty million years ago (MYA), a common ancestor gave rise to three orders: Sirenia (represented today by manatees and dugongs), Hyracoidea (represented by the hyrax) and Proboscidea, which encompasses all extinct and living species of elephants and their close relatives. Moeritherium, a pig-sized mammal that lived in North Africa about 50 MYA, is the earliest known proboscidean and the Deinotherium line diverged 10 million years later; this lineage culminated in a massive elephant-like creature that spread throughout Eurasia and Africa during the Miocene and became extinct by the onset of the Pleistocene (2 MYA).
The Paleomastadon line emerged in North Africa about 34 MYA; Gomphotheriums split from this primary lineage about 25 MYA, giving rise to the Mastadon line about 20 MYA. The main group of Gomphotheriums died out by the end of the Pliocene (2 MYA) but the mastodons lived through the Pleistocene, occupying Africa, Eurasia and North America. Primelephas, the first member of the Family Elephantidae, appeared in North Africa about 7 MYA and this lineage would eventually give rise to mammoths and our modern elephants. The African and Indian elephant lines diverged very early in the history of this family; African elephants would then split into savannah and forest species (some say subspecies since they can interbreed) about 4 MYA and, during the same period, mammoths would split from Indian elephants. While the latter split occurred in North Africa, both species would leave their home Continent; Indian elephants spread across southern Asia (giving rise to Indian, Sumatran and Sri Lankan subspecies) while mammoth species colonized Eurasia and, during the Pleistocene, North America.
Here in North America, our elephant heritage is limited to mastadons and woolly mammoths that crossed the Bering land bridge during the glacial periods of the Pleistocene (2 MYA to 10,000 years ago). Like our ancestral bison, they were pursued by human hunters who likely colonized our Continent by 20,000 years ago. This predation, combined with the warming climate of the late Pleistocene and early Holocene led to the demise of our North American elephants; the last woolly mammoths are thought to have died out in the Arctic about 8000 years ago. Though we have lost the company of these large, sociable and intelligent creatures, we still have the manatees, their very distant cousins.
The Paleomastadon line emerged in North Africa about 34 MYA; Gomphotheriums split from this primary lineage about 25 MYA, giving rise to the Mastadon line about 20 MYA. The main group of Gomphotheriums died out by the end of the Pliocene (2 MYA) but the mastodons lived through the Pleistocene, occupying Africa, Eurasia and North America. Primelephas, the first member of the Family Elephantidae, appeared in North Africa about 7 MYA and this lineage would eventually give rise to mammoths and our modern elephants. The African and Indian elephant lines diverged very early in the history of this family; African elephants would then split into savannah and forest species (some say subspecies since they can interbreed) about 4 MYA and, during the same period, mammoths would split from Indian elephants. While the latter split occurred in North Africa, both species would leave their home Continent; Indian elephants spread across southern Asia (giving rise to Indian, Sumatran and Sri Lankan subspecies) while mammoth species colonized Eurasia and, during the Pleistocene, North America.
Here in North America, our elephant heritage is limited to mastadons and woolly mammoths that crossed the Bering land bridge during the glacial periods of the Pleistocene (2 MYA to 10,000 years ago). Like our ancestral bison, they were pursued by human hunters who likely colonized our Continent by 20,000 years ago. This predation, combined with the warming climate of the late Pleistocene and early Holocene led to the demise of our North American elephants; the last woolly mammoths are thought to have died out in the Arctic about 8000 years ago. Though we have lost the company of these large, sociable and intelligent creatures, we still have the manatees, their very distant cousins.
Rabu, 01 Februari 2012
Nature & Government
While I am a social liberal, I am a fiscal conservative and I actually agree with many Republicans that our government is bloated and inefficient. I support simplification of the tax code, elimination of earmarks and enforcement of term limits. Unlike many conservatives, I also favor an end to corporate welfare and strongly support efforts to cut our outrageous defense budget.
On the other hand, history is replete with evidence that the federal government plays a crucial role in the protection of both civil rights and the health of our natural environment. Big business, driven by greed and focused on profits, has not demonstrated the capacity to protect either the consumer or the environment without oversight by federal agencies. From a naturalists point of view, governmental regulations have been vital to the welfare of natural ecosystems throughout this country and across the globe.
Too often, Americans jump on the bandwagon of anti-government rhetoric without giving proper consideration to the consequences. It is not until they are personally affected by mining disasters, oil spills, polluted water or tainted food that they recognize the need for federal mandates. If we let the corporate world run our environmental policy, we place the health of our citizens and that of our vital natural ecosystems at significant risk.
On the other hand, history is replete with evidence that the federal government plays a crucial role in the protection of both civil rights and the health of our natural environment. Big business, driven by greed and focused on profits, has not demonstrated the capacity to protect either the consumer or the environment without oversight by federal agencies. From a naturalists point of view, governmental regulations have been vital to the welfare of natural ecosystems throughout this country and across the globe.
Too often, Americans jump on the bandwagon of anti-government rhetoric without giving proper consideration to the consequences. It is not until they are personally affected by mining disasters, oil spills, polluted water or tainted food that they recognize the need for federal mandates. If we let the corporate world run our environmental policy, we place the health of our citizens and that of our vital natural ecosystems at significant risk.
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