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Re: emu history



Nancy, I don't profess to know much about fossil emus, but perhaps some
general comments would be helpful.

-----Original Message-----
From: Nancy Cavanaugh <nancy@lillypadsoftware.com>
>online as books about emus, at least in the public sector, in the US are
rare
>to non-existent) said anything about the emu being from a common ancestor
with
>the cassowaries. Who was the common ancestor? How did they evolve
differently?
>
>I had read in several places that it is believed that the emu has evolved
very
>little from its earliest form. One would assume, based on that information
and
>what you've said, that the cassowaries probably evolved very little from
their
>earliest form. Has that been the case?


Currently, cassowaries are restricted to the wet forest of North Queensland
and New Guninea, whilst emus have a much broader range that encompasses the
schlerophyll woodland and grasslands as well as the semi arid and desert
regions. Given that the general pattern here seems to be that the eastern
rainforest species (brids, reptiles, frogs, insects, trees) are the relict
(= i.e. closer to the ancestral form) types, and that their respective
relatives which inhabit of the eucalypt open woodlands to deserts are more
derived, I would imagine that the cassowary is perhaps 'closer' to the
ancestral form, and the the emu is a more recent derivitive (although keep
in mind all the caveats about the 'ancestral modern species' thing, as
discussed by Ron and Mike.).

The received wisdom in these parts is that Australian ecosystems were
largely wet forest domiated until the Miocene, and the deserts, semi arid
zones, and grass/woodlands that cover much of the continent today are mainly
post-Miocene in origin.  Given that these are the systems that the emu so
ably exploits, that would suggest a Pliocene origination of 'emus' at the
earliest.

>One specialist I spoke to suggested that I say that it is believed that the
>emus date back 80 million years ago but that there is more recent research
that
>suggests they may only be 45 million years old. Your suggestion is
basically
>the same so I think I will take that cue unless there is a further dispute
>about it.


I think even 45 Ma is a probably a huge overestimate - see above.  I
seriously doubt that any extant genus of bird, let alone species, was around
in the Oligocene.

>Sorry for the typo on Mr. Cracraft's name. The erroneous spelling is from a
few
>websites where I found the information about when the dating of the emu
>happened. When did Mr. Cracraft announce his findings for the dating of the
>emu? Was it '71 or '73?
>
>You forgot about the extinct Tasmanian Emu which is supposed to be a sub-
>species of the "mainland" emu. =) Did they ever live on the mainlanda? How
did
>they get to Tasmania?


Tasmania, King Island, and Kangaroo Island have all had, and continue to
have, plenty of 'subspecies' of mainland forms.  In most cases these date
only as far back as the last glacial maximum (lower sea levels - all of
these islands would have had extensive land bridges to the mainland in the
Pleistocene), and the difference between these island forms and the mainland
parent stock is usually only minor.  I am not aware of any examples of
succesful reinvasion of these 'subspecies' to the mainland, although the
Kangaroo Island koala may become a very recent example (and I still think we
should introduce the Kangaroo Island tiger snake to southern France...)

>-----Original Message-----
>From: Ronald Orenstein <ornstn@rogers.com>
>>
>> Of course there is no certain way to determine exactly when the modern
emu,
>> Dromaius novaehollandiae, first "appeared on earth" -- and, since it


  A third, perhaps more questionable, technique is to look at the
>> history of continental drift.  The argument would go, for example, that
the
>> emu lineage -- or at least the emu-cassowary lineage as separate from the
>> lineage is that lead to other large flightless birds such as ostriches --
>> must be at least as old as the point at which Australia broke away from
the
>> land mass of Gondwanaland.  That is where the 45 million-year-old figure
>> comes from, because that is apparently the time at which Australia and
>> Antarctica separated.  However, this does not tell us when emus and
>> cassowaries differentiated from each other, as they both occur in
>> Australia.  Presumably this happened later, but not necessarily as the
>> separation could have occurred before the birds became isolated on the
>> Australian landmass.  Obviously there are none left in Antarctica!


The separation of Australia from Anartica ocured in the Upper Cretaceous, as
far as I am aware.  By the K/T Australia was well and truely an island.
It's hard to put a date on the exact time of separation, but 80-85 Ma
probably wouldn't be too far off.

Ron is correct is stating that biogeographic arguments can be very weak, but
(weak) negative evidence for Cassuariiformes being a distinct lineage prior
to the seperation from Antarctica comes from the observation that they do
not (and never have) existed in New Zealand (remembering that Kiwiland split
from East Antarctica about the same time as Australia - important when
understanding the modern distribution of some cool-temperate fresh water
fishes such as _Galaxias_ (spelling?).  On the other hand, the presence of
_Casuarius_ in N. Queensland and New Guinea could mean that 1) cassowaries
were a distinct species prior to the seperation of New Guinea and Australia
(at a guess, this would be late Miocene / Early Pliocene), or 2) cassowaries
were part of the faunal interchange between Queensland and New Guinea during
the Pleistocene galcial maxima.

>> That said, and noting that Joel's name is "Cracraft", the Handbook of the
>> Birds of the World, Volume one, published in the 1992, notes that the
>> oldest fossils that can be ascribed to the living genus of emus are only
>> some 5000 to 10,000 years old, and belong to the King Island Emu which
has
>> since become extinct.  Obviously, emus as a lineage are older than
>> that.  however, the most recent book I have on the subject, a detailed
>> monograph called "Ratites and Tinamous" by SJJF Davies (Oxford, 2002),
>> casts doubt on any of the attempts to determine precisely how old these
>> groups of birds are, and does not suggest a date.


Overall, our Cenozoic record is pretty poor (thanks to a huge Miocene
weathering event), but it is good in some small patches (e.g. Riversleigh,
Naracorte).  New cave faunas from WA and Queensland might help improve the
picture for the Plio-Pleistocene, but these are only recently discovered and
are still being studied.  You might get in touch with Scott Hocknull at the
Qld Museum, or Alex Baynes at the WA Museum.  Alternatvely, why don't you
cross post your questions to the vrtpaleo list - you might pick up some of
the bone fide Cenozioc workers like Wroe or Archer, rather than Cretaceous
old farts like myself who tend to regard anthing post KT as overburden...

>> I would be inclined, given this, not to attempt to come up with an age
for
>> the emu family.  All that I think you can really say is that emus and
their
>> closest relatives, the cassowaries, have been separated from their
nearest
>> relatives ever since Australia drifted away from Antarctica and so,
>> together, must have been around in one form or another for at least 40 to
>> 45 million years.


I think Ron is giving you good advice here - stick to a date seperating the
Casuariiformes from their closest relatives (presumably the Kiwi + Moa
group?), or, if you can find it, a date for the split between emu and
cassowary.

Cheers
Colin

*****************
Colin McHenry
Geology Building
University of Newcastle
Callaghan  NSW 2308
Australia

Tel +61 2  4921 5404

******************
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Tel: +61 2 4920 7026
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