dinosaur taxonomy

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MattDP - 14 Dec 2004 13:11 GMT

Hi,

I've become very confused by the detailed taxonomy of dinosaurs in the
sense that the terms being used to describe the various taxa seem to
vary an awful lot from place to place.

For example, I've seen the taxon name "dinosauria" described variously
as being a SuperOrder and a SubClass. The taxon "theropoda" I've seen
described as an Order, a SubOrder and an InfraClass.

The differences I've seen are on a variety of internet pages, and I
presume they've arisen from a misunderstanding of modern cladistic
analysis which can include animals in "un-named" clades. Annoyingly,
the more realiable internet sources such as the dinosauricon and the
UCMP sites don't have any information which helps unravel this problem.
So can anyone point me at a reliable source for this information?

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John Harshman - 14 Dec 2004 20:32 GMT

> Hi,
>
[quoted text clipped - 12 lines]
> UCMP sites don't have any information which helps unravel this problem.
> So can anyone point me at a reliable source for this information?

Pick your favorite. There is no official taxonomy, so any source is as
good as any other.

This all comes from the problem that Saurischia is traditionally an
order, and Aves is traditionally a class. Since Saurischia includes
Aves, if you change to any form of cladistic taxonomy, you can't
maintain the traditional ranks. This is why so many people are going to
a rank-free classification. Clades get names, but not ranks.

There are several suggested solutions for maintaining ranks and group
monophyly at the same time, and you appear to have enountered a couple
of them. I suggest that the rank-free solution works best: Dinosauria is
a clade and Theropoda is another clade nested within Dinosauria, and we
don't worry about superorders, infraclasses, or any of that stuff.

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MattDP - 16 Dec 2004 09:43 GMT

Thanks for the information.

I subscribe wholly to the theory that evolutionary relationships are
best constructed through cladistic analysis, but I was hoping to try
and find some sort of Linnean equivalent so I could better describe
some dinosaur relationships to people not familiar with the technique.
It becomes tiresome to constantly have to explain that Theropoda is a
group within Saurischia, which is a group within Dinosauria which is a
group within Archosauria and so on. Much neater if we could just put a
label on it, however scientifically inaccurate it may be :)

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John Harshman - 16 Dec 2004 14:38 GMT

> Thanks for the information.
>
[quoted text clipped - 6 lines]
> group within Archosauria and so on. Much neater if we could just put a
> label on it, however scientifically inaccurate it may be :)

Two points:

Cladistic analysis, cladistic classification, and rank-free
classification are all separate and mutually independent concepts that
could be freely mixed and matched if you wanted to.

If you want rank labels, pick your favorites. It's all arbitrary. I
don't know of any ranked classification that has resolved the central
contradiction that Class Aves lies within Order Saurischia.

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Gautam Majumdar - 14 Dec 2004 22:51 GMT

> I've become very confused by the detailed taxonomy of dinosaurs in the
> sense that the terms being used to describe the various taxa seem to
[quoted text clipped - 3 lines]
> as being a SuperOrder and a SubClass. The taxon "theropoda" I've seen
> described as an Order, a SubOrder and an InfraClass.

The problem is that there is no definitive way of defining a "grade" in
the Linnean system. So the same taxon can be put virtually to any grade.
Dr Robert Bakker suggested that Dinosauria should be a Class. If
Dinosauria is defined as a Superorder, how does one include Avis within
that grade ? In Linnean system Avis is a Class.

Linnean system was developed before the theory of evolution & for extant
organisms. Applying that to palaeontology would inevitably cause all sorts
of problems. It is best to avoid Linnean grades altogether and stick to
the cladistic system where everything, named or unnamed, is a clade.

> The differences I've seen are on a variety of internet pages, and I
> presume they've arisen from a misunderstanding of modern cladistic
> analysis which can include animals in "un-named" clades. Annoyingly, the
> more realiable internet sources such as the dinosauricon and the UCMP
> sites don't have any information which helps unravel this problem. So
> can anyone point me at a reliable source for this information?

They don't have any information regarding the grades because they do not
use the Linnean system.

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Gautam Majumdar

Please send e-mails to gmajumdar@freeuk.com

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Natural Science Forum / Biology / Paleontology / December 2004

dinosaur taxonomy