Download Geo-evolution Background Information

Geo-Evolution
Background Information
The southeastern United States within the boundaries of the Southeastern Fishes Council (SFC Constitution)
has the most diverse regional aquatic fauna of North America. Several fundamental factors are responsible for
the tremendous diversity in the region of aquatic insects, mollusks, crayfishes, fishes, and other aquatic
organisms. First, the region has experienced relatively long climatic stability; the southeast was a sanctuary
from the great ice sheets that covered much of northern North America during the global climate changes in the
Pleistocene. Secondly, the inherent geological, topographic, and hydrologic complexity of the region is the
underlying basis for the great wealth of habitats and environments. The aquatic landscapes of the southeast
are ancient and have changed vastly over time; geologic and hydrological processes that transformed the
landscape affected the evolution, composition, and distribution of aquatic faunas. In comparison to the
glaciated regions of eastern North America, the southeast is a landscape dominated by rivers. Natural lakes
occur on the lower Coastal Plain, river mainstem oxbows, and throughout peninsular Florida, but few natural
lakes occur in the southeast’s interior. Examples are Mountain Lake, formed from an ancient caldera in Virginia
and Tennessee’s Reelfoot and Isom lakes, formed by the New Madrid earthquake in 1812.
Across the tapestry of topography and time, a veritable cornucopia of aquatic diversity evolved in the southeast
producing the rich diversity of freshwater fishes and other aquatic biotas. The fish fauna includes archaic fishes
such as sturgeons, paddlefishes, and gars whose ancestors shared the super continent Pangaea with
dinosaurs. However, most fishes are members of a more modern fauna, thought to have evolved from about
the late Miocene to the Pleistocene (about 11 million to 10 thousand years before present). Evolution is a
dynamic, ongoing process; the fish we see today are but a contemporary snapshot of organisms occupying the
southeast for tens of thousands of years or longer.
Most southeastern fishes are “primary” or obligate freshwater fishes, implying intolerance of seawater, but
many species can tolerate dissolved ion concentrations up to 20 or 30% of full strength saltwater. These
include familiar fishes such as minnows, catfishes, sunfishes and basses, and perches. However, a few fishes
encountered in inland streams are clearly marine species. These marine species can move between saline and
freshwater environments, and some may venture hundreds of kilometers inland. Examples of marine species
that occur in fresh waters are the striped mullet Mugil cephalus, Atlantic needlefish Strongylura marina, and the
curious hogchoker Trinectes maculatus. Some coastal springs have enough dissolved minerals to enable
marine fishes like mangrove snappers Lutjanus griseus to school with freshwater species like the bluegill
Lepomis macrochirus.
A subset of southeastern fishes evolved complex lifestyles that depend on both freshwater and marine realms
(diadromy). Two common types of diadromy are anadromy, fishes that live in marine realms as adults but
ascend creeks and rivers to spawn, and catadromy, fishes that spawn in saltwater but the young must enter
and remain in fresh water until near adulthood. Gulf sturgeon Acipenser oxyrinchus desotoi and striped bass
Morone saxatilis are examples of southeastern anadromous fishes. The only catadromous example is the
American eel Anguilla rostrata. In the following list, marine fishes that readily enter freshwater and diadromous
fishes are indicated by a parenthetic ‘M‘or ‘D’ after the common name, respectively.
During the time of the continental collisions that formed the ‘Supercontinent of Pangaea’, some 350
million years ago, there were already what we would have recognized as fish in the freshwater lakes and
streams of the future southeastern US. This was the ‘Age of Fishes’, the Devonian Period. The Corals,
Mollusks and bryozoans had already been present for nearly 150 million years (Ordovician Period). The
Amphibians wouldn’t arrive for another 50 million years or so and reptiles 50 million years after that.
As the mountains rose, streams were forced to flow down one side or the other, depending on their
location. Isolated pools formed as the streams became blocked by earth and rock pushing upward in the
collision. Small lakes were formed as springs were exposed along the altered terrain. And through all of
this, fish did as fish still do, they spawned. With every generation the conditions in these isolated lakes
and streams became a little less like the ones in the past and also less like the others in the region. As
the generations passed, the species, fish and otherwise, in those waters began to respond in diverse
ways to the various conditions in their respective locations. Soon these variations became so in depth
that not only did new species develop, but entire families (in the Linnaean sense…) evolved. Today we
still see the remnants of these early systems. Fish such as gar, bowfin, paddlefish and sturgeon shared
the earth with the dinosaurs and are still found in our waters. (The Agnathans, the jawless fish, are only
represented by lamprey and hagfish today and were never in our waters.) These ancient fish have many
physiological peculiarities that set them apart from more modern fishes. Among them is a swim bladder
that is open to the esophagus. These fish take air from the surface and use the bladder as a ‘lung’.
MONOTREMES
There are only five living monotreme species: the duck-billed platypus and four species of echidna (also
known as spiny anteaters). All of them are found only in Australia and New Guinea. The oldest fossil
monotremes come from the Lightning Ridge opal fields of New South Wales, Australia. An opalized
lower jaw fragment of Steropodon galmani more than 100 million years old (middle Albian, Cretaceous)
was found containing three distinctive teeth remarkably similar to those of the juvenile platypus. From
the size of the jaw, it is estimated that the living animal was about the size of a cat, making it one of the
largest Mesozoic mammals known. This find (Archer et al. 1985) marked the first known Australian
mammal from the Mesozoic. A second jaw, described as Kollikodon ritchiei, was found in 1995 from
deposits of similar age, suggesting that monotremes had already diversified by the Early Cretaceous.
During the 1970s, the first Tertiary monotreme fossils were uncovered in southern Australia. Over
several years, a jaw, a pelvis, and teeth of the Miocene platypus Obdurodon insignis were discovered.
Cast of Obdurodon teeth are pictured at left. More recently, a skull with a nearly full complement of
teeth has been found in New South Wales (Archer et al. 1992). This new species, O. dicksoni,
demonstrates that unlike the modern platypus, Obdurodon kept its teeth at maturity. Like the platypus,
however, Obdurodon had an elongated snout, though straighter than in its modern relative. Opinions
differ on whether Obdurodon may have been aquatic, based on its association with numerous terrestrial
marsupials. The Australian fossil record of monotremes also includes some quite good Miocene and
Pleistocene fossils of giant echidnas. Three species are known, two assigned to the genus
Megalibgwilia (Griffiths et al. 1991). Several nearly complete skulls of M. ramsayi have been recovered
from caves in South Australia. The largest of the giant echidnas, Zaglossus hacketti, is known only from a
few bones found in Western Australia; it ranks as the largest monotreme ever to have lived. The time
and place of monotreme origin is still largely unknown. Most fossil monotremes have been
found in Australia, though a Paleocene platypus tooth (Monotrematum) has recently been
recovered from Argentina (Pascual et al. 1992), suggesting they were once distributed across
southern Gondwana.
Marsupial Mammals
The short gestation time is due to having a yolk-type placenta in the mother marsupial. Placental
mammals nourish the developing embryo using the mother's blood supply, allowing longer
gestation times. The only naturally occurring marsupial in the United States is the opossum,
Didelphis marsupialis. In the past, however, marsupials were quite common. During the
Mesozoic marsupials were very common in North America; more common, in fact, than
placental mammals. They persisted here until the mid- to late-Tertiary. In South America and
Australia, however, marsupials continued to be an important group of land mammals. Many
South American forms are similar to the North American opossum. The marsupials of South
America began to go extinct in the late Miocene and Early Pliocene when a land connection
with North America formed, allowing placental mammals to cross into South America. In
Australia, though, marsupials continue to be very diverse, and are the dominant native mammals.
They include kangaroos, koalas (above left), tasmanian devils, wombats (above right), and other
typical Australian mammals. Until recently, they also included the marsupial wolf, Thylacinus
(below). Like the quagga, the marsupial wolf is now extinct. The last individual was seen in
Tasmania in the 1950s. There are several cases of convergent evolution between
marsupials and placental mammals, in which the two animals have evolved to fill the
same ecological niche in different parts of the world. There are burrowing forms, grazing
forms, gliding forms, and even long-snouted ant-eating forms which have evolved
independently in the two groups.
Earth is 4.5 Billion years old.
4,500,000,000 years.
4.5 Years ago- Barack Obama was running against John McCain for president. (2008)
45 Years ago- Viet Nam war, and protests, are in full swing. Beatles release ‘Sgt. Peppers...’
1st super bowl, Curt Kobain born.
450 Years ago- The ‘age of the pirates’ begins in the Caribbean. The Mongols are loose…
4,500 Years ago- construction of the Pyramids and Stonehenge begins, first horses are tamed. (2nd
Century BC)
The Earths formation is over 1 million times more distant in time.
Shrew-like early ‘near placentals’.
The paper by a team of scientists led by Carnegie Museum of Natural History paleontologist Zhe-Xi Luo
describes Juramaia sinensis, a small shrew-like mammal that lived in China 160 million years ago during
the Jurassic period. Juramaia is the earliest known fossil of eutherians -- the group that evolved to include
all placental mammals, which provide nourishment to unborn young via a placenta. As the earliest known
fossil ancestral to placental mammals, Juramaia provides fossil evidence of the date when eutherian
mammals diverged from other mammals: metatherians (whose descendants include marsupials such as
kangaroos) and monotremes (such as the platypus). As Luo explains, "Juramaia, from 160 million years
ago, is either a great-grand-aunt, or a 'great-grandmother' of all placental mammals that are thriving
today."
Eomaia is not a placental mammal. It is an early, primitive representative of the lineage that
eventually led to placental mammals," said Weil. "Properly, it is called a eutherian mammal—a
mammal that is more closely related to living placentals than to living marsupials."
Eumaia was oldest known prior to discovery of Juramaia.
Chiroptera
The inability to link bats to any other mammalian group in itself suggests a very early origin. Some
fossilized eggs of noctuid moths, with the ability to detect echolocation calls of bats and trigger escape
responses , have recently been discovered dating back to about 75 MyBP5 implying that the bats
themselves arose substantially earlier, about 80 to 100 m.y.a.6. If so, they would have shared their world
with dinosaurs, watched their extinction at the end of the cretaceous and remained, relatively
unchanged, to this day. At the time bats are thought to have been evolving, the flowering plants were in
the first stages of their massive diversification. By the end of the Cretaceous, the insects supported by
these plants were abundant, and insectivorous mammals were becoming well established4. But so were
the predators of small mammals, posing a serious threat during daylight hours. For these reasons, it is
presumed early species of bat were nocturnal, evolving from small, arboreal mammals16. From here they
literally launched themselves into flight, becoming the highly successful aerial hunters we see today.
Lagomorpha
appeared with Paramyidae in the later Paleocene of North America and the earliest Eocene of
Europe [8]. Early rodents were, e.g. Tribosphenomys from the Paleocene of Central Asia [9].
Late Paleocene Heomys and Mimotona from China were considered to be close to the ancestral
stock of Rodentia and Lagomorpha, respectively [10,11]. Glires may share a common ancestry
with the Late Cretaceous Zalambdalestidae (Kulbeckia kulbecke, from the 85-90 my old
Dzharakuduk fauna, Uzbekistan [12])
Eocene Dawsonolagus antiquus from China [13], early Eocene Lagomorpha from Western India
[14]. Glires may share a common ancestry with the Late Cretaceous Zalambdalestidae [12].
Perissodactylids