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Simfish
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5 million years? 10 million years? I'm especially interested since the Pliocene was much warmer than today (with much higher sea levels), and it came only 5 million years ago.
Fossil records indicate that ancestors of modern sharks swam the seas over 400 million years ago, making them older than dinosaurs! Throughout time sharks have changed very little.
As the only marsupials found in North America, opossums have existed for 70–80 million years.
But there is no way of really knowing.For example, given normal extinction rates species typically exist for 5–10 million years before going extinct.[7]
Evo said:Well, sharks have existed for 400 million years.
Borek said:There will be an obvious problem - we don't have good definition of what a species is. This is of particular concern when we have to deal with a dynamic situation of species turning into other species - without knowing where and how to split the line, we can't say how many sections it has.
ryan_m_b said:It's not that we don't have a great definition of species per se, it's that there is no real thing. 'Species' is an arbitrary way for us to distinguish between organisms by placing them into groups.
Borek said:There will be an obvious problem - we don't have good definition of what a species is. This is of particular concern when we have to deal with a dynamic situation of species turning into other species - without knowing where and how to split the line, we can't say how many sections it has.
bobze said:Consider that if there wasn't extinction, we'd (collectively, all organisms on earth) be the same "species". Without the gift of hindsight and incompleteness in the fossil record, we would be unable to draw arbitrary lines in the sand and say "everything on this side is species one, everything on the other is species two".
ryan_m_b said:It's not that we don't have a great definition of species per se, it's that there is no real thing. 'Species' is an arbitrary way for us to distinguish between organisms by placing them into groups.
bobze said:More of this please :tongue2:. Its one of the hardest things for people to wrap their head around about evolutionary biology. Consider that if there wasn't extinction, we'd (collectively, all organisms on earth) be the same "species". Without the gift of hindsight and incompleteness in the fossil record, we would be unable to draw arbitrary lines in the sand and say "everything on this side is species one, everything on the other is species two".
In the study of sexually reproducing organisms, where genetic material is shared through the process of reproduction, the ability of two organisms to interbreed and produce fertile offspring of both sexes is generally accepted as a simple indicator that the organisms share enough genes to be considered members of the same species. Thus a "species" is a group of interbreeding organisms.
Phrak said:From http://en.wikipedia.org/wiki/Species#Definitions_of_species" is presented one amoung several definitions of species:
This seems to good fit the question as it appears to have been intended. Yet the answer to the question in this form is not yet testable. Without resurrecting a shark from fossilized DNA, how do we know that the 50 million year old shark could reproduce with a shark of today, for instance?
mishrashubham said:Sorry didn't get you.
Pythagorean said:Groups of a such a unispecies could get isolated from each other and after some time exhibit clear speciation without extinction.
To be clear, we're only talking about species right? Not kingdom, family, etc?
The average lifespan of a species is determined by studying fossil records and genetic data. Scientists look at the length of time a species existed in the fossil record and compare it to the estimated time of divergence from its closest living relative.
There are several factors that can influence the lifespan of a species, including environmental changes, competition for resources, and the ability to adapt to changing conditions. Other factors may include disease outbreaks, predation, and natural disasters.
Yes, certain types of species tend to have longer lifespans than others. For example, larger species such as elephants and whales tend to have longer lifespans than smaller species like mice and insects. Additionally, species with longer lifespans tend to have slower rates of reproduction and lower population sizes.
Yes, the average lifespan of a species has changed over time. In general, species have been able to adapt and survive longer due to advances in technology and medicine. However, there have also been periods of mass extinction events that have significantly shortened the lifespan of many species.
It is difficult to accurately predict the average lifespan of a species due to the many factors that can influence it. However, by studying the patterns and trends of past species, scientists can make educated estimations about the potential lifespan of current species.