Re: sauropods and abelisaurids

[Stan Friesen <swf@ElSegundoCA.ATTGIS.COM>]

>From: BPC.APA@email.apa.org (Considine, Blaise)
 > 
 > I have 2 questions; 1 from me and 1 from my son that I could't answer.
 > 1) can someone provide me with a sauropod lineage? Who came first sort of 
 > thing. This is a result of browsing through dinosaur books with my son 
 > and he noted that frequently different types of sauropods are shown 
 > together. While this is most likely for convenience, what is the timeline 
 > for sauropods? 

Well, not necessarily, there are several different lineages of
sauropods, and some places (and times), such as those represented
by the Morrison and Tendaguru formations, had many species of
sauropods.

The aproximate lineages are something like the following:

Barapasaurids (early, fairly generalized forms, mostly Early Jurassic).
    Cetiosaurids  (later, but still fairly generalized forms)
    Brachiosaurids (very large, tall, forms, mostly Late Jurassic).
    Camarasaurids  (mid-sized forms, mostly Late Jurassic)
    Euhelopodids  (forms from Asia, Late Jurassis and Early Cretaceous)
    Diplodocids   (very long forms, mostly Late Jurassic)
        Titanosaurids (poorly known forms, mostly Late Cretaceous)

Within each main lineage there were subordinate lineages, and thus
many forms could coexist.

For the Morrison Formation (Late Jurassic, in the Rocky Mountain
states of the USA), I remember the following genera as being known:

     Brachiosaurus (probably includes Ultrasauros)
     Camarasaurus
     Diplodocus (probably includes Amphicoelias and Supersaurus)
     Apatosaurus
     Seismosaurus
     Dicraeosaurus

and perhaps others.

Thus, all of the above listed types actually did occur together.

 > 2) can someone explain more about the abelisaur(ids) mentioned by Stan 
 > and others while discussing S American dinos? They were related to the 
 > ceratosaurs, which were an early line of theropods...were abelisaurs the 
 > last in this line, more advanced, or what? 

Well, as they probably survived right up to near the extinction
of the dinosaurs, I would say they were probably the last of the
ceratosaurs.

They were certainly more specialized than the earlier ceratosaurs,
but I hesitate to say "more advanced", as this term is really not
well-defined, and is of little meaning in evolutionary discussions.

As in the sauropods, there were several major lineages of theropod
dinosaurs, the two largest being the ceratosaurs and the maniraptor-
like group (technically, the coelurosaurs).  In addition there were
groups like the megalosaurs and allosaurs that seem to be pretty much
seperate lineages of their own.

The abelisaurids were a late, mostly southern hemisphere, subgroup
of the ceratosaurs.  They were large theropods which often had
prominant ornamental crests or horns on their heads.  One particularly
odd form is called Carnotaurus, which had a pair of largish horns
above its eyes.

[Actually, the ceratosaurs in general seem to have been prone to
develope large head ornaments, given that the group includes
both Ceratosaurus, with its nasal crest, and Dilophosaurus with
its double-helmet].

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.