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FAMILY TREES



TWO COMPETING THEORIES
In reading the various dinosaur books, there seem to be two competing
theories of the development of the dinosaurian group. While details
vary, the basic branches of the tree look something like this:
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
COMPETING THEORY #1: BRANCHING TREE
>.................................+--Theropods-->---->---->---->--Birds
>................................/
>..................+SauroThero--+..................+-Segnosaurs
>................./..............\................/
>................/................+Prosauropods--+
Ancestorsaurus--+.................................\
>................\.................................+-Sauropods
>.................\
>..................\................./-Stegosaurs->-Nodo->-Ankly
>...................+-Ornithiscians-+--Iguanodons->-Duckbills
>....................................\-Pachys-->--Ceratopians
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
COMPETING THEORY #2: THE ONE-SIDED TREE
Ancestorsaurus--+--Theropods-->---->----Coelosaurs---->----Birds
>................\
>.................+----?---->---->-----?---->---->---->--Segnosaurs
>..................\................../
>...................+--Prosauropods--?-->--Sauropods
>....................\
>.....................+--Iguanodons-->--Duckbills
>......................\
>.......................+--+-Stegosaurs-->--Nodosaurs-->--Anklyosaurs
>........................\..\-----------/?\-----------/
>.........................\
>..........................+-+-->--Pachycephalosaurs
>.............................\------->---->---->--Ceratopians
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Now, a few things. These are FAMILY TREE things, not 'cladograms'.
I'm specifically trying to understand ancestor/descendant relationships
here, rather than just grouping characteristics.
I'm curious as to what you all think about these theories. Maybe you
have another one. (Family trees please, not cladograms.)
Some of the lower (right end) elements of both trees are sort of
controversial, and I don't want to see your analysis of the main
(leftward) parts of the tree buried in the minutae of the last leaves.
I stipulate my ignornance and mean no offence. Specifically....
1. The origin of segnosaurs isn't resolved and isn't totally critical.
2. The ancestor/descendant relationship of iguanodons and duckbills seems
relatively clear, it's not entirely clear how things inside that branch
of the tree shake out, but they are all one branch.
3. Same thing applies to the shield-bearers. I think that Nodos are
ugly kids of a Stegosaur who grazed on some uranium-laden grass, but
I'm willing to consider that they came from someplace higher on
the branch. The point is that the branch IS a branch, and I want to
know what you guys think of where the branches go.
4. I have probably mis-spelled a few of those.