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John Ostrom started it all - at least the 'recent history' phase of the enquiry into bird origins - with his discovery of, and eventual monograph on Deinonychus, which although coming from near the middle of the Cretaceous (abbreviated to K), and about 40mys (million years) after Archaeopteryx (Archae) was similar enough for a close relationship to spring to mind.
Dinosaur workers were particularly interested in the ancestors of birds , so Deinonychus, and its close relative Velociraptor, were auditioned with this role in mind, and not some other less interesting one...
Velociraptor is now quite well known to the public and many know it is a bird-like dinosaur. If it looks intermediate between birds & dinos, why not call it the dinosaur that gave rise to birds? Ok, perhaps it might be, but is there some way we can be more certain? One way some people use to try to clarify understanding is...
CLADISTICS
Using Cladistics , we can generate "Cladograms" such as the one below, if we want to (ignore the red squiggle for the time being):
Cladogram by Prof Kevin Padian from Nature - June '98, showing the currently 'conventional' view of the bird-dino relationship:
But why shouldn't we want to?
Well, if we were trying to fit a fossil animal with two toes into a line of prehistoric creatures which decreased their toes through 5, 4, 3, 2 & 1 over time, most people could make a pretty good guess at where it should go!...
REVERSALS
...But biology is full of reversals. Maybe toes don't increase in number (and maybe they do!) but other things definitely DO go back. For example, whales went back to having flippers. Before that they had proper legs; but long ago, when fish first crawled out of the water, they had had flipper-like structures. We are sensible enough to understand this, in the light of all the other evidence, as a reversal.
RECURRING SUITES OF CHARACTERISTICS IN UNRELATED TYPES
Whales began to resemble fish in a few other ways, some of which ichthyosaurs and marine lizards shared. In the same way, when a bird species loses its power of flight, very many changes happen all at once, and every time, certain characteristic changes tend to be involved. Everyone knows that when birds lose their flight their wings tend to get smaller. There are numerous other changes that:
Do cladistic methods pay any attention to this special phenomon? No. They blindly tip everything into the machine in the hope that the program is magic enough to sort it all out. As a result, all the flightless forms tend to appear on the cladogram as if they were closely related (all with short wings, stout legs etc etc) and all the flying types clump together too.
These changes happen together - in other words they are not independent. This is where the cladistic system falls down because the statistical process requires that they are. When the material is plentiful or friendly we can sometimes get away with treating slightly dependent data as if they were truly independent, but the phylogeny of early flight is one aplication whre we can't.
This is the central problem when using cladistics for deciding bird/dino relationships. But it is made worse because the early birds were still very similar to their dino ancestors: They still had quite good hands, with claws on them, they still had teeth, and they still had long bony tails! (Modern birds' tails have only feathers except right at the base). This means that flightlessness beckoned more appealingly to them than later birds, and it is reasonable to assume that a great many "early birds" would readopt the suite of flightless characteristics.
That is one reason we may be rather worried about cladistics, and here is another:
TEMPORAL PARADOXES
Remember the red squiggle in the cladogram? That's TIME going backwards as soon as Archaeopteryx enters the frame. Four central nodes in a row along the spine of the cladogram are traversed in reverse temporal order. That is not a cool feature to have in your family tree. Don't think the animal types are just side branches and not meant to be ancestral to each other; cladograms always have the types off to one side, and some of the forms must surely be considered fairly close to the direct line. And if anyone ever tells you "Cladograms are meant to show relationships of characters rather than creatures" ask them what's the point in doing them if they're not meant to suggest true relationships? They certainly have a way of transubstantiating from theory into 'fact', in far too many people's minds (and writings).
Now we may ask "How can Velociraptor be ancestral to Archaeopteryx if it came after it?"
Well, because of the many gaps in the fossil record, fossils don't always show up 'on time'. For example a recently discovered partial fossil from the Late Cretaceous of Madagascar, Rahonavis, seems to be a cross between birds and something like Velociraptor, but appears 60mys too late. No-one however says its late appearance is evidence against its being a missing link, it may just have lasted a long time. Such examples are called "Ghost Lineages"; we assume these animals existed earlier when we have probable ancient ancestors for them a long way back, and perhaps possible descendants back then too.
So we don't necessarily criticise the conventional theory: "Velociraptor -> Archaeopteryx", just because our Archaeopteryx fossils are older, but...
...how do we decide whether an animal was hiding, or just wasn't there?
HIDING OR ABSENT?
Sometimes, if you have reason to believe you are 'looking properly', you can say "There is only a very small chance (eg 1%) of finding no examples, if there were at least (some number) really there." (Manufacturers often have to use statistical methods such as these in quality control, as do naturalists looking for rare/extinct species.)
But it's not just Velociraptors that weren't there! ...because our theory goes way beyond them!
SECONDARY FLIGHTLESSNESS
Indulge your imagination for a moment. Follow on from an original suggestion by Gregory S. Paul [a reference page here###], and say Archaeopteryx went flightless. After 100,000 generations, how would you know such a creature wasn't just any other carnivorous dinosaur that had never flown? That is a hard and important question. And here's another: what do you think it would look like?
Well, it would probably still have long arms, if it used them at all - and if it was still a predator (probably Archaeopteryx ate prey, a bit smaller than itself) it could make good use of such arms. However, its tail, evolved down to little more than a long, feathered, segmented toothpick for flight purposes, might have changed back a bit. It's legs and head would be more heavily built; in the case of the head, which is a much more complex structure than the legs, the changes might be hard to understand. Who can say for sure exactly why a bird's head is built as it is?! As flightless carnivorous dinosaurs often ate prey as big as or bigger than themselves, and Archaeopteryx seems as likely to have been insectivorous as anything else, it would have a new diet, which might well affect the head. Of course, it might still have feathers; no flightless birds today have lost their feathers, though some (eg ostriches) are thought to have been flightless for over 50,000,000 years.
There were a lot of theropod dinosaurs wandering about the Cretaceous that we might see differently in the light of this. In fact, as that period wore on, more and more dinosaurs began to show [an eerie similarity to birds - fullish details of these similarites###]. In some strange way, it looked like dinosaurs were evolving 'towards birds'. This is odd because evolution doesn't aim towards something in that way, accumulating features one by one which don't work well until the whole set has been collected. And besides, birds had already evolved!
Here is a list of these particularly 'bird-like' dinosaurs, with an approximate number of finds alongside each:
Oviraptors: 20
Protarchaeopteryx + Caudipteryx.: 4+
Deinonychs (inc. Veloci's & Droms's): 25
ARCTOMETATARSALIA:
Tyrannosauroidea: 70
Troodonts: 28
Ornithomimos: 24
Total: 171 (Not including avimimids, Rahonavis, alvarezsaurids, therizinosaurs or Archaeopteryx itself.)
(The Arctometatarsalians are grouped together because of their similar ankles. All the others are often called the Maniraptorans.)
And not one of these birdlike forms seems to have preceded Archaeopteryx! Are we sure? and does it matter?
The best pre-Archaeopteryx evidence for any of these consists of a femur (thigh bone) from the Morrison formation (in N.America) - said to be definitely maniraptoran. However it cannot be ascribed to any of the Cretaceous forms. Teeth similar to those of many of these types have been found in a coal mine in Portugal, but loose teeth aren't always very diagnostic - they can be similar across two or more species, and are very easily swept in from strata of a different age.
HIDING OR ABSENT AGAIN - FIGURES
What does the fact that they all come after Archaeopteryx tell us? There are at least 171 good examples of the maniraptora and arctometatarsalia after Archaeopteryx and none before. Is this meaningful? Maybe
THE RIGHT SUSPECT AT THE RIGHT TIME
The sharply defined starting line for these birdish forms is suggestive; so is their progressive radiation. Many of them seem to have been very successful. Wouldn't we expect the point of origin of a supremely successful group to have something rather special about it? Archae is extraordinary enough, and perfectly timed.
THE FIRST FEATHER
Feathers are much less likely to be fossilised than bone is, and the fact that we have no examples of them in the fossil record before Archaeopteryx may not be particulalry significant. But it is a fact. It is also a fact that even though we find pterosaurs sprinkled through the Jurassic and later parts of the Triassic (Pterodactylus for example was found in the same quarry as Archaeopteryx) we find no birds there. Of course, the pterosaurs aren't stacked up like groceries in a supermarket, but it is odd that no birds at all have been found alongside them - unless of course they weren't there!
Another odd thing is the fairly sudden disappearance of small pterosaurs from the fossil record. Guess when that happened? Right! This is another watershed in prehistory punctuated by Archaeopteryx. Just about the time the maniraptorans and other bird-like dinos started appearing, the small pterosaurs vanished. Actually, Pterodactylus accompanied Achaeopteryx, but in the Cretaceous which followed very shortly afterwards small pterosaurs quickly disappeared. The presence of Pterodactylus is another piece of evidence for the notion that Archaeopteryx was the first bird. #### find out what pteros accompany the chinese birds ###
One argument sometimes used to support BAMM is that birds always lose
flight through the mechanism of becoming more 'child-like' - in other words,
certain aspects of their development, including the development of the flight
apparatus, are arrested. This is called "Paedomorphosis", and it is claimed
that this is the only mechanism by which birds are capable of becoming
flightless. As the types "2F" claims to be flightless are not paedomorphic,
the paedomorphosis argument says they cannot be ex-flying. But since
evolution so often demonstrates a variety of different
ways of achieving the same end, it would be very surprising indeed if
a certain facility could only be lost through one particular genetic
mechanism; besides, on close examination, certain modern flightless birds
appear to have quite a few features which seem to be the opposite of
paedomorphic, even amongst some of the flight-related
systems. I will not go into it any further as this argument brings a
feeling of great weariness to me; suffice it to say, it's been well covered
on the Dinosaur List
So - reasons for believing 2F and not BAMM:
Reasons for disbelieving BAMM (Birds Are Modified Maniraptorans): Disbelieve cladistics Unconvincing design philosophy Untested particularly in this type of domain [Output unbelieveable (see bad BAMM points) (Valid on its own, this becomes circular when embedded in other arguments)] Temporal paradox of all manis. pre-Archae Unconvincing account of evolution of birdlike features espec feathers Insufficient numbers of ex-flying forms advocated Paedomorphosis argument invalid Reasons for believing 2F (Secondary Flightlessness): Convincing account of evolution of birdlike features Especially origin/time of first feather explained Types with/without feathers explained (as identified) Rise of maniraptorans explained Fall of small pterosaurs explained Order of ancestry of birds/manis. explained Sudden J/K development of birds explained