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AW: how many bird-species right after the K-T ?

> Is there any estimate of how many
> species of our feathered friends might have survived the big
> high-five from space, say, within a million years (or less)
> afterwards?  

Recent studies are "at least a dozen species" to "several dozen species" order 
of magnitude. Sounds reasonable to me. Within a million years, the number 
probably got higher, possibly even doubled or more; the absolute cladogenesis 
(in this case, essentially "speciation") rate after such an event was probably 
somewhat higher than at other times. Also, those that made it through the first 
100 years after were probably hardier than the average bird, so their 
extinction rate was unlikely to have been above-average. 

But a million years or less is not much, if you can judge by modern standards 
ar least: Lineages of birds where it is reasonably well known generally 
branched zero times to three times within the last Ma. And in most of these 
cases, it probably was zero to one times.

> Is it known for a fact which known groups of birds did not
> pull through, thus lost to descendants alive today?

Depends on the definition of "bird".

The least one can say is "a few species".

Using a strict definition of "bird", there are no known remains of lineages 
that definitely ceased then. There are a few fragmentary fossils which due to 
their disparate locations imply that not all of the handful of relatives found 
in various places all over the globe can have survived.

What can be reasonably well assumed, in layman's terms, probably is closer to 
"a few dozen genera and perhaps a few families of palaeognaths and fowl, and a 
number of species and probably a few genera of waders and oceanic birds". In 
penguins for example, perhaps a handful of species of proto-penguins at most - 
one survived (we know that because there are penguins today), and the "penguin" 
lineage was probably only distinct for a short evolutionary time. Judging from 
the known and inferred penguin biodiversity at any one point or very short 
episode in time, it cannot have been branched very often between its inception 
and the end of the Mesozoic.

(Molecular studies imply, once again (sigh...), that the penguin lineage was 
distinct shortly after _Archaeopteryx_, but AFAIK one one or two 
paleontological research groups, who handle the actual material evidence, are 
seriously pondering that idea.)

Among what is usually considered a bird - Ichthyornithes, Hesperornithes, some 
other minor lineages of close relatives of modern birds. 

Then, Enantiornithes and perhaps a few minor lineages related to them (though 
they might rather have been outcompeted by their successful relatives before 
the impacts).

The "other" early bird lineages - those of _Confuciusornis_, _Sapeornis_ , 
_Archaeopteryx_ of course, and their close relatives, probably all went extinct 
long before the end of the Mesozoic.

Among those animals opnly considered birds anymore by a minority (some would 
say fringe minority), _Rahonavis_, which was perhaps the last time a dinosaur 
lineage evolved close to looking like a "bird". Also some other paravian 
theropods - but most of those probably never evolved more than a handful 
features typical of birds today. Mind you, as soon as Enantiornithes got off 
the ground, it became suddenly very much harder to evolve bird flight if yu 
didn't have already.