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

Re: Parahongshanornis, new Chinese Cretaceous bird (free pdf)




--- Tim Williams <tijawi@gmail.com> schrieb am Do, 2.6.2011:

> Von: Tim Williams <tijawi@gmail.com>
> Betreff: Re: Parahongshanornis, new Chinese Cretaceous bird (free pdf)
> An: dinosaur@usc.edu
> Datum: Donnerstag, 2. Juni, 2011 02:16 Uhr
> Mickey Mortimer <mickey_mortimer111@msn.com>
> wrote:
> 
> 
> >Agreed on point b, but II-2 being longer than II-1 is
> just a symplesiomorphy.
> 
> 
> >From an ecomorphological perspective, the retention of
> symplesiomorphic characters can often be quite
> significant.  Although
> I concur that, in the case of _Patagopteryx_, too much
> significance
> shouldn't be invested in this character.

Back in the phenetics days, this was a major source of error. Evolutionarily, 
such symplesiomorphies are widespread in the "living fossils" (in a loose 
sense) - the first successful members of the initial radiation of an eventually 
large and highly successful clade.

The main radiation will fill a particularly sustainable niche and diversify 
immensely. But first, there will be some Ma of lineages emerging polytomically 
or almost so, yet these wil not be completely "fine-tuned". They will be 
superceded by whatever lineage(s) from among them happens to evolve the missing 
trait refinements that will allow to monopolize that "good niche". Eventually 
only a few species-poor survivors from this initial radiation will remain. They 
are usually incredibly diverse character-wise (since they are "waifs and 
strays"), yet strong symplesiomorphies will in phenetic analyses often resolve 
them as a seemingly monophyletic group.

Cladistic analysis can fix this problem, but sometimes it is tricky.

For example, the bulk of the crown Accipitridae are "hawks", which are indeed 
monophyletic (provided you include some more unusual taxa, like true kites and 
sea-eagles) and are the sister group of eagles one might think. But not so fast 
- "eagles" are indeed *not* monophyletic; there is the main eagles radiation 
which is a clade, as well as a bunch of "grass" which may or may not be, and 
which consists mostly of the _Harpia_ group.

Is the _Harpia_ group a clade? I can't tell... yet. Many authors past and 
present have claimed they are, but I need to do the test - is _Macheiramphus_ 
the dwarf member of the basal hawk-and-eagle radiation, and does it clade with 
the rest of the _Harpia_ group? Molecular data are not able to resolve this 
clearly; they find a clade but support if all pertinent taxa are included is 
<0.8 ML bootstrap for RAG-1 which has good SNR at that level. I will need to 
put osteological data to the test (cf. the other discussion on-list at the 
moment).

At present the case is open on whether the "(usually) huge basal 
eagles-that-are-not-true-eagles" are a clade or whether they are better 
considered isolated surviving lineage from a (Eo-Oligocene?) radiation of 
accipitrids which otherwise yielded the "true eagles" and "expanded hawks" 
clades, whose success displaced the other basal members of this radiation.

FWIW, _Pithecophaga_ is probably not a member of this group. It is annoyingly 
LBAing molecularly (had to throw it out of some mol datasets; its presence 
tends to destruct otherwise good clades), but it seems to be too far outside 
the eagle s.l.-and-hawk s.l.-clade (Accipitrini auct.), clading with 
snake-eagles if it robustly clades with anything. To pit its osteological data 
against that of _Circaetus_ and _Harpia_ will be insightful.

In any case:

("harpiines"-para?, true eagles, (_Melierax_ clade, 
_Harpagus/Hieraspiza_-"grass", (_"Accipiter"-para+_Circus_), "buteonines" 
including _Milvus_ etc) )

Needs fossils to corroborate (I will eventually do this, but it's really the 
final step); in any case it's already reasonable if you take into account 
biogeography. The event that purged the presumed basal radiation, leaving only 
the 4(?) spp. of "harpiines" as survivors, may have been the Grande Coupure or 
similar contemporaneous events. It ties in with the fossil record (buteonine 
origin pre-Oligocene, "hawk" diversity increasing apparently from around 30 Ma 
onwards), and a ~35 Ma turnover especially in megafauna fits the profile of an 
event that killed off a lot of large-basal-"eagle"-but-not-true-eagle lineages.



Regards,


Eike