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Re: Ah ha! That's where therizinosaurs came from
I agree with both of your points. NZ is a tiny territory, most areas the size
of NZ have no fossils of either dromaeosaurs or ratites at all, I'm sure.
But I renew why question; why didn't any family of flightless ornithurine bird
spread globally? They've had at least 65 million years, and Samrukia was there
on Laurasia 80 million years ago, and it might have had grasping hands.
Gargantuavis also may have retained hands.
If, as you suggest, we should be cautious about comparing local to global
faunas then any comparison of ratites and dromaeosaurs is complicated and
possibly not meaningful.
In trying to compare the radiation of one group of Mesozoic diapsids with
another group of diapsids from the Cenozoic, we are always comparing apples
with oranges, aren't we? Most dinosaur fossils were deposited in
paleoenvironments that are incompletely understood. Take even Solnhofen -
where the debate still rages whether there were even trees there. It's hard to
say where the boundaries of Mesozoic islands such as Hateg were, or if they
even were islands or not and how they changed over millennia, and thus how
large the territory was when any given taxa evolved.
There will certainly not be any exact matches, considering the one-in-a-million
fossil record, climate and atmosphere shifts, continental drift, the gradual
domination of the flora by angiosperms during the Cretaceous, and repeated
global changes in faunal elements.
I'll try to state my point precisely now. Please tell me if my reasoning seems
correct to you, and please correct my logic if needed.
1) If Mr. Paul points to all manner of biological similarities between ratites
and dromaeosaurs as support for his hypothesis that both are secondarily
flightless, as he does, then I may point to the differences as evidence against
that hypothesis. In other words, if ratites can be compared to dromaeosaurs AT
ALL (despite being different taxa in different geologic eras and periods), and
if they can be compared in order to support Mr. Pauls's hypothesis (the
"neoflightless" hypothesis for non -avian maniraptorans), then their
differences can be weighed in the balance of evidence against that hypothesis.
In other words, I hope we don't say that all the similarities count and then
dismiss all the differences. That would seem to be working from preconceptions
rather than an open - minded search for the truth.
I didn't know Tennyson was a picture book, one of his papers cited it as an
authority on the total number of moa species. I'll try to check out Worthy. I
wonder how much has been learned about moas since 2002, since Tennyson
described the two miocene species in 2010.
On Aug 11, 2011, at 11:45 AM, Ronald Orenstein wrote:
> I agree with what you say, but note that it might not be fair to compare a
> localized fauna with a global one. More to the point would be how the
> diversity of moas compares with that of dromaeosaurs in a New Zealand-sized
> area elsewhere (even allowing for the fact that NZ was once larger than it
> is today). Also, I suspect that dromys had a bit more available evolutionary
> plasticity to hand as htey still had functionally grasping front limbs.
> Tennyson's is a very handsome picture book (I just picked one up in NZ
> earlier this year), but for details you should certainly get "The Lost World
> of the Moa" by Worthy and Holdoway (Indiana UP 2002). I believe it is now
> out of print (available at extortionate prices) but surely the AMNH library
> has a copy.
> Ronald Orenstein
> 1825 Shady Creek Court
> Mississauga, ON L5L 3W2
> From: Jason Brougham <firstname.lastname@example.org>
> To: Ronald Orenstein <email@example.com>
> Cc: firstname.lastname@example.org; DML List <email@example.com>
> Sent: Thursday, August 11, 2011 11:21:34 AM
> Subject: Re: Ah ha! That's where therizinosaurs came from
> Dr. Orenstein,
> Your note stimulated my curiosity about moas. I did some research on them and
> they are fascinating, I have ordered a book by Alan Tennyson and will be
> doing more reading on them.
> But I did want to report what I'd learned so far regarding the biological
> similarities and differences between moas and dromaeosaurs. My point is just
> to compare and contrast the two families, and assess their relative levels of
> diversity, in light of the hypothesis that both may be radiations of
> secondarily flightless maniraptorans.
> Moas seem to have achieved a diversity of probably only 9 species in 6
> genera, with possibly two more known from Miocene fossils. (Tennyson et al.
> 2010). Their body masses ranged from 20kg to around 240kg. Moas achieved
> this diversity in a minimum of 22 to 25 million years after NZ was inundated,
> though many suspect there were refugia that extended the moa lineage back
> much further.
> Dromaeosaurs have about 32 to 35 described species in maybe 30 genera. Their
> body masses range from 200 grams in Microraptor zhaoianus (Turner et al.,
> 2007) to 500kg in Utahraptor. They range from teeth known from the Middle
> Jurassic to end Cretaceous, so maybe 100 million years total.
> There are many similarities and differences we could tally. Most, but not
> all, ratites and other large flightless birds seem to have tended to become
> graviportal browsers. The dromaeosaurs may have ranged from sleek hunters to
> tiny gleaners. The large flightless birds seem to have been geographically
> restricted, while dromaeosaurs were cosmopolitan. Feduccia also reports that
> flightless birds tend to develop longer life spans. That could be tested in
> dromaeosaurs against basal avialans and Archaeopteryx to see if it was
> On Aug 9, 2011, at 5:45 PM, Ronald Orenstein wrote:
> > Leave out "achieved worldwide distribution" and the moas come pretty close.
> > Ronald Orenstein
> > 1825 Shady Creek Court
> > Mississauga, ON L5L 3W2
> > Canada
> > ronorenstein.blogspot.com
> > From: Jason Brougham <firstname.lastname@example.org>
> > To: email@example.com
> > Cc: DML <firstname.lastname@example.org>
> > Sent: Tuesday, August 9, 2011 4:57:17 PM
> > Subject: Re: Ah ha! That's where therizinosaurs came from
> > Yes, let's keep the point in mind: that no family of ratites or other
> > flightless crown group birds that I am aware of has become flightless,
> > achieved the morphological distinction of a new family, and then radiated
> > widely, diversified, achieved a range of body sizes spanning two orders of
> > magnitude, and achieved global distribution, in the way that dromaeosaurs
> > did, if we assume that BCF is true.
> > On Aug 9, 2011, at 4:26 PM, David Marjanovic wrote:
> > >> >> Secondly, failure of any recent group of flightless birds to
> > >> >> spread over the world is in part due to the recent positioning of
> > >> >> the continents (ie there are oceans in the way). Presumably
> > >> >> flightless birds have only dispersed over a land connection (I
> > >> >> can't think offhand of an example of a flightless bird spreading
> > >> >> by, say, rafting).
> > >> >
> > >> > Gondwana and Lauarsia were separated, but they shared several
> > >> > groups of maniraptorans in common.
> > >
> > > That separation only came about in the Late Jurassic and was rather
> > > intermittent. In contrast, I don't think there ever was a unitary
> > > Laurasia that wasn't cut in two by various seas through Europe.
> > >
> > >> >> Third, the fauna of mammalian predators and nest-robbers has been
> > >> >> quite different since the K-T from what it was earlier, and the
> > >> >> barriers to radiation of flightless birds on continents may not
> > >> >> therefore be identical to what they might have been in the
> > >> >> Mesozoic.
> > >> >
> > >> > Different, certainly, but there is no reason to think the
> > >> > differences were consequential. Mammals were feeding on dinosaurs
> > >> > in the Mesozoic, they could glide, they could swim, no reason to
> > >> > think they couldn't rob nests.
> > >
> > > Never mind nest robbers. It now seems that the flightless paleognaths
> > > became flightless in the early Paleocene on the continents as if they
> > > were islands -- due to the lack of big predators after the K-Pg mass
> > > extinction.
> > >
> > >> > But, in the case of rails, the morphological changes
> > >> > associated with flightlessness were so recent and superficial that
> > >> > the resulting species did not move into new families, unlike with
> > >> > the ratites. In maniraptorans we had, I guess, Troodontidae and
> > >> > Dromaeosauridae that Paul might say descended from Archaepterygids,
> > >> > though he may group them all in the same family.
> > >
> > > Isn't that just a matter of time? Let those flightless rails sit on their
> > > islands for 30 million years (...longer than most of the islands in
> > > question will exist, but never mind...) and then tell me what ranks you'd
> > > assign to them.
> > Jason Brougham
> > Senior Principal Preparator
> > American Museum of Natural History
> > email@example.com
> > (212) 496 3544
> Jason Brougham
> Senior Principal Preparator
> American Museum of Natural History
> (212) 496 3544
Senior Principal Preparator
American Museum of Natural History
(212) 496 3544