Birds: are they dinosaurs, or not?

Linnaeus

Hello! My username is Linnaeus, and that name says it all. I am an amateur palaeontologist of the good old Linnaean school. Honestly, I see no reason to discard this scientific method of classification. So many so-called experts today are using cladistics, but I believe that the original system of taxonomy remains the best and most logical. Take the case of birds. Once upon a time, any palaeontologist worth his salt knew how to define our feathered friends, and realized quite well that, whatever their genetic origin may have been, they belong together in a specific class called Aves. But nowadays, birds are seldom considered to be anything other than highly derived dinosaurs, in spite of the obvious fact that, in the process of evolution, they have lost practically all the characteristic features of their theropod ancestors.

Followers of cladistics tend to ignore this, claiming that birds are closer anatomically and physiologically to "avian" dinosaurs than to any other creatures; according to this viewpoint, ergo, birdlike theropods and true birds must be lumped together into one clade.

But this is essentially like saying that, as a human being is more similar to a chimpanzee than to any other animal, we folks are nothing but monkey's grandchildren after all.

Please, I'd appreciate comments on this. No raging polemics, just lively civil discussion. Thanks.

Adam Khor

Hi, Linnaeus, welcome to the board

I'm afraid I can´t give much of an opinion since I am not sure I can even call myself an "amateur paleontologist"- here's hoping someone more knowledgeable will join in.

Personally, I too grew up with the Linnean system - when I was a kid, my father would test me by asking me the classification of random animals at random times. Even today I find it less confusing. But when it comes to birds, I do love the idea of them being bona fide dinosaurs and living amongst us today. As for humans being "nothing more than monkey's grandchildren" as you put it... I don´t see why that would be a bad thing? If you study human behavior you will find countless evidence that we're nothing but well-dressed apes. Try thinking of this next time you have a job interview; you will be less nervous and will smile more. :B

Rubecula

I do think of birdies as dinos myself. But it is only my own opinion.

As for us being apes, why yes of course, we certainly are. Just a little less pronouncedly hirsute.

Linnaeus

Dear Adam and Rubecula,

Thank you for responding to my post.

I'd like to expand a bit on the thoughts which I expressed in it.

There's virtually no doubt in my mind that birds are descended from certain theropod dinosaurs, just as Homo Sapiens is descended from certain apes. But descent does not necessarily imply identity: in all evolutionary processes there is a gradual transformation of life forms up to the point where new families, genera, orders and classes emerge. Once the descendant of any given ancestor enters into a DISTINCT classification, it is no longer identical to this ancestor, although externally and internally it may still bear resemblance to its immediate forebears. This is especially true when a creature makes the crossover into a new, significantly different CLASS. Thus, we see certain types of prehistoric amphibians slowly evolving, becoming more and more reptile-like, until one fine day a mutant is hatched and becomes the first genuine reptile. We can observe the same process from synapsids and cynodonts to mammals, as well as from theropods and the so-called "feathered dinosaurs" to true birds. Yes, I know it's fun to think of ourselves as "less hirsute apes", or birds as authentic living dinosaurs. What palaeontology lover would not be delighted to cuddle a real live miniature dino? Yet, although we may call our children "little monkeys" and our pet parrots "wee dinosaurs", science simply does not bear this out. Both man and the birds have evolved so far from the ancient ancestors as to constitute separate, unique groups: Aves in the case of birds, Homo for the human race. Birds are CLOSE DIRECT DESCENDANTS of certain dinosaurs: granted. But this does not signify that they, themselves, are dinosaurs.

I welcome comments from members of this group.

Adam Khor

You say "in all evolutionary processes there is a gradual transformation of life forms up to the point where new families, genera, orders and classes emerge", but families, genera, orders etc are determined by certain scientists and accepted by their community. The creatures themselves do not change- the definitions do. Humans and apes, birds and some dinosaurs, they do share enough traits to be considered different varieties of the same thing in my totally non-professional opinion.

Linnaeus

Hello Adam,

Here we disagree. You are speaking from the cladistic point of view; I, from the Linnaean. Both systems exist today, side by side; palaeontologists take their choice, or construct other, hybrid systems.

You say that "the creatures themselves do not change". Oh, but they do! Not just as varieties...like the breeds of cats, which are all still clearly and completely feline...but also as new groups which are patently distinct from that which went before. It may be convenient for cladistics to place different families into broad categories just because these bear similarity one to another. And there's nothing wrong with that, as long as one accepts the differences existing in this extended genealogy. I have no problem in accepting the fact that Archaeopteryx is a feathered theropod, not a bird. But I will never agree that the sparrows chirping in my garden are runty dinosaurs, not birds.

Adam Khor

You misunderstood me. Of course creatures change over time- but it matters little for the ones currently existing whether we classify them one way or another.

I guess what I'm trying to say is, to a layman (like me), this isn´t really much of a big deal.

Capt'n Midnight

snakes are very different to turtles but we still regard both as reptiles
perhaps a bad example given what else could be included as reptiles

it's handy when you can lump stuff together, but what we do if the platypus had scales instead of hair or what happens if we find a more cold blooded one ?


And there's the whole argument about whether there's no such thing as a fish

http://www.bbc.co.uk/nature/animals/by/fish


And what of Ring Species ?
At what point do you draw the line ? And what if the middle species goes extinct ? Because over time that has happened a lot and the end species go their separate ways.

Yes we are related to chimps, I'd like to think we are closer to bonobos. But we're all cousins , distinct from the most recent common ancestor.



One thing is reasonably certain though the egg was in use by the chickens ancestors.

Linnaeus

Hello Capt'n Midnight,

Yes, turtles and snakes certainly do not resemble each other very much on the outside; but they do share certain essential physiological characteristics which pertain to Class Reptilia and only to that class.

In my posts, I have made reference mainly to life forms which CROSS OVER from one order or class to another.

I believe we may draw the line when a mutant descendant of one type of animal can no longer breed with its ancestral type. This would indicate a genetic difference sufficient to cause reproductive incompability. Birds are surely directly derived from reptiles, but cannot produce offspring with them. Dogs, cats and bears all have the same remote ancestor, but are unable to interbreed.