[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: More on Argentavis

> The problem here is the lack of fossils. There are
> no known Paleogene 
> ratites except for rheas (*Diogenornis*, Paleocene)
> and a few flightless 
> birds from the Eocene of Europe, at least some of
> which could be ostriches 
> (notably *Palaeotis*).
> Incidentally, if at least *Palaeotis* is an ostrich,
> it probably fits the 
> proposal by Cooper et al. (2001) that the ostriches
> evolved in India in the 
> Paleocene, then reached Laurasia at the
> Paleocene-Eocene boundary, and then 
> entered Africa around the Oligocene-Miocene
> boundary.

Probably earlier, if _Struthio coppensi_ (or
_Struthioolithus coppensi_) is good: Namibia, 20 mya,
osteologically rather "modern".

Fossil record of ostrich bones and ostrich-like eggs
in Eurasia considerably younger. Don't know if due to
lack of reseach, but are 30-20 Ma-old
Konzentrat-Lagerstätten from semiarid to semihumid
habitat *that* rare in SW Asia? If ostrich remains
occur in a lagerstätte, it's usually not a big effort
to find them if a site is worked (if the Pliocene
record is any indication, where at least ostrich
eggshells are rather common in alluvial and/or aeolian
concentrates across Africa and (Eur)asia).

Kurochkin summed up the Asian record in 1976
(Smiths.Contrib.Paleobiol.27) and here he lists 5
sites that I'd call reasonably good candidates based
on date and location alone*, notably a good Middle
Oligocene record. Ratites? Not even a bit of eggshell.
Ergilornithids, ecologically somewhat convergent?

Interestingly, the bone fossils show ostrich
autapomorphies several MA before the eggshell fossils,
which until mid-Miocene remain of the (probably
plesiomorphic) "aepyornithid" type (But then, a
similar morphotype was possibly shared by
osteodontorns, so make of that what you will)


* The current state of paleogeography has the supposed
dispersal route into Africa as an uplifting
subtropical island arc for most of the crucial time.
Good for _Cypselavus_, good for _Jungornis_, probably
sucked for ostriches to disperse. A solid land bridge
into Africa is a bit too close for comfort to the
Oligo/Miocene boundary if _S. coppensi_ is indeed a
full-blown albeit basal ostrich.

      __________________________________  BE A BETTER INTERNET-GURU: Jetzt 
Frage stellen und einen von 44 iPods gewinnen! www.yahoo.de/clever