Elaine Meinel Supkis
Another debate over the end of the age of dinosaurs and how quickly mammalian evolution branched out into all ecosystems. The latest theory is that all the major mammalian branches existed before the K-T boundary. I have always asserted that this is so simply because of the fact that before the collapse of the dinosaurs, Africa and South America had split yet we see the same basic lineages on both continents.
The mass extinction that wiped out dinosaurs and other life 65 million years ago apparently did not, contrary to conventional wisdom, immediately clear the way for the rise of today’s mammals.
In fact, the ancestral branches of most mammals, including primates, rodents and hoofed animals, emerged long before the global extinction and survived it more or less intact. But it was not until at least 10 million to 15 million years afterward that the lineages of living mammals began to flourish in number and diversity.
I am puzzled as to why this is news. During the long reign of the dinosaurs, South America and Africa were united but had two main features: the longest rift valley on earth which was very active and two lesser valleys, the Amazon and the Congo. The planet is split all the way from the North Pole to the Antactica by this giant rift which became the Atlantic Ocean.
At the end of the Cretaceous, in our own family, the early monkeys, we had already split from the lemurs. There are no lemurs in South America but there are in Africa, especially on the east coast. Madaggascar is home to a wide variety of these animals and this is due to its splitting off from Africa at the end of the Cretaceous.
We know that all big creatures perished quickly at the end of the Cretaceous. We also know that the climate was rapidly changing and the oceans were dropping which seems to me to mean it was getting colder. The earliest modern flowering trees appeared along with their cultivators, the bees.
The earliest mammals, I believe, mostly lived in the exotic rift valley that was opening up between Africa and South America. The thick mists on steep hillsides probably was their climate zone. It probably rained a lot. We see this sort of environment in jungles today. One characteristic of jungles is the abundance of feathers and fur both of which shed water while keeping the host animal warm.
There was this belief, I think based on wishful thinking, that dinosaurs were warm blooded and moved rapidly even in the cold. If this were so, when the earth cooled off during the run down to the K-T boundry, dinosaurs would have been just fine. But they were not.
Or rather, only the ancestors of birds did fine. We know they evolved in jungles and climbed about in trees. Most likely they were, like a number of bird species today, ominvores. Many people forget how many birds like to eat meat. I used to hate the roadrunner cartoons when I was a kid because I had roadrunner friends and they are ferocious hunters who love to eat meat. The cartoon stupidly shows this amusing desert survivor eating seeds.
I used to clean out the swimming pool filter and into it would fall the reptilian class of animals, namely lizards and snakes. I would hold them in the air and the roadrunners would hop up and down, croaking with joy, begging for goodies.
Heck, turkeys are omnivores. They love nothing better than snakes and frogs. They swallow them whole, betraying their dinosaurian roots.
From the NYT:
They said their analysis of more than 40 lineages of existing mammals showed that diversification rates “barely changed” in the aftermath of the extinctions at the boundary of the Cretaceous and Tertiary periods. The transforming changes started 10 million years later and lasted until about 35 million years ago.
Other scientists said the so-called “long-fuse model” opened a door to a better understanding of the evolutionary history of mammals and will force a re-examination of the ecological and other causes underlying the more recent proliferation of mammals.
Several things about mass extinctions: recovery takes a long time. The worse the extinction, the longer the recovery time. Complex animals like mammals can't occupy ecological niches is there are few or no plants, for example. There are not all that many animals above 12,000 feet, for example. On top of Mt. Everest, there are no mammals at all except foolish humans going there to yodel.
When great extinctions happen, the oxygen level evidently drops and there is lots and lots of muddy water because plants no longer cover much of the earth. This means river dwellers suffer, shallow seas get buried and the zone of life becomes very narrow, usually concentrated in these rift valleys.
In addition to primates, species in many other new orders were evolving. The first carnivores evolved in the Paleocene, though the order Carnivora did not thrive until the Oligocene. The forests supported a great variety of insects, resulting in a great deal of insectivores from this time period. Browsing animals (leaf-eaters) were also prevalent in the Paleocene, many of which have descendants that can be found in modern tropical and subtropical environments.
Before the disaster that killed of half of all living things and certainly, all large land creatures, there were plenty of insectivores. Insects were amoung the first animals to crawl out of the oceans and colonize dry land. When the population of most insect eaters collapsed, there was a short period when insects reigned. Sort of like it would be if we stupidly have WWIII. Cockroaches would be supreme.
Our distant ancestors were tree dwellers who were and still are, omnivores. When the world's ecosystems collapsed, our fur saved us from the deadly downpours that followed in the wake of the massive numbers of comets that crashed into the earth, one after the other. Being insect eaters, we could snatch a meal on the fly and with all the dead and rotting things around, the insects were in heaven and plentiful.
From the above story:
The Paleocene carnivorous mammals of Laurasia had to share their world with giant flightless birds of prey like Diatryma and it's cousins (order Diatrymiformes), which appear suddenly during the late Paleocene and continue through to the Middle Eocene. Standing 2 meters or more in height and weighing in at around 200 kg, these large-beaked birds were the biggest and fiercest animals on land for some five or ten million years. In South America similar giant predatory birds, the Phorusrhacids, are known from the Eocene but most probably likewise evolved during the Paleocene. These great birds were the last successors of the mighty theropod dinosaurs of the Mesozoic.
Birds also survived the foul weather because they sit on their eggs, indeed, perhaps this is why all birds sit on their eggs: the only ones to survive the massive die-off were the subspecies of birds that had this habit. Enough birds survived that they swiftly evolved into Kings of Creation. Not as large as the great predators of the dinosaurian age, they still were swift and voracious.
Anyone who has ever tangled with an angry rooster or goose knows that birds can be very quarrelsome. Eagles hunted our ancestors who feared them---and snakes---a lot. Indeed, all modern reptiles evolved from the few cold blooded scaled creatures we call 'reptiles': they probably were tree-dwellers or lived in burrows and only the ones living in the same rift valleys that was home to the mammals, survived.
But subsequent research found what many thought was "the smoking gun" - the Chicxulub Crater buried under Chicxulub on the coast of Yucatan. This crater is oval, with an average diameter of about 180km, about the size calculated by the Alvarez team. Its shape and location indicate further causes of devastation in addition to the dust cloud:
The asteroid landed right on the coast and would have caused gigantic tsunamis, for which evidence has been found all round the coast of the Caribbean and eastern USA - marine sand in locations which were then inland, and vegetation debris and terrestrial rocks in marine sediments dated to the time of the impact.
The asteroid landed in a bed of gypsum (calcium sulphate), which would have produced a vast sulphur dioxide aerosol. This would have further reduced the sunlight reaching the earth's surface and then precipitated as acid rain, killing vegetation, plankton and organisms which build shells from calcium carbonate (notably some plankton species and many species of mollusk).
The crater's shape suggests that the asteroid landed at an angle of 20° to 30° from horizontal and travelling north-west. This would have directed most of the blast and solid debris into the central part of what is now the United States.
Most paleontologists now agree that an asteroid did hit the Earth about 65 million years ago, but many dispute whether the impact was the sole cause of the extinctions.
One thing we know is that all living things pass through these series of eyes of needles: extinctions on mass scales. The more we look, the more craters caused by celestial objects are found. Since we know Mars was peppered by these things, there being not much recent geological activity to cover this up, since we know the moon is coated with meteorite strikes, it is obvious, our planet has been hit more than once. I'm betting most of the minor extinctions were ushered in by things falling from the heavens.
Several other craters also appear to have been formed at the K-T boundary. This suggests the possibility of near simultaneous multiple impacts, perhaps from a fragmented asteroidal object, similar to the Shoemaker-Levy 9 cometary impact with Jupiter.
Boltysh crater (24 km diam., 65.17 ± 0.64 Ma old) in Ukraine
Silverpit crater (20 km diam., 60-65 Ma old) in the North Sea
Eagle Butte crater (10 km diam., < 65 Ma old) in Alberta, Canada
Vista Alegre crater (9.5 km diam., < 65 Ma old) in Paraná State, Brazil
As our sun passes by other star systems, things can change rapidly. We move in this cloud of cosmic dirt, sort of like a fringe of boulders that can suddenly change orbit and fall towards the sun. On top of this, our planet is very active. During the K-T extinction, India was sailing rapidly into Asia and the Deccan Traps, a rift zone that disgorged a huge amount of lava, this probably changed the chemistry of the atmosphere. And if a dozen comets or meteorites hit too, this would really change the atmosphere and this, in turn, changes the climate.
And celestial objects disturb the sun and if our passage through the Orion Arm of the Milky Way Galaxy caused a distruption that sent a whole series of objects slamming into the earth, it probably caused the sun to flare up for the following age, the Eocene, was very warm. Deep oceans and lots of jungles for our monkey selves to swing around, eating bananas and bugs. To this day, the preferred home for monkeys and primates are the jungles.
Another thing about evolution: when populations are nearly destroyed, getting enough numbers to spread out and have different enough ecosystems to make former relations too distant to breed takes a long time. And as with the first sign of life on dry land, the plants have to come first. And they take their time. If there are no birds or animals to spread the seeds, there is only wind and water and we can see from the evolution of plants, they take great pains to attract insects, animals and birds. This is the best way to spread their own seeds.
Without this, it takes longer and isn't nearly as efficient. Once the plants finally created enough food for insects and other animals to survive, then evolution of varieties takes off.
And even then, evolution varies greatly. Monkeys on both sides of the ancient African/South American rift valley started out the same but in South America, they never evolved out of having tails while in the rift valleys of Africa, a small, very small group of monkeys were tail-less and from them sprang the Great Apes and humanoids.
When Africa banged into Europe and Asia, the many mammals that evolved on that continent headed north. Especially waves of Great Apes. Some of whom are now drastically altering the chemistry of the atmosphere.