GEOL 104 Dinosaurs: A Natural History

Fall Semester 2006
Life on Land before the Dinosaurs

Surface of the Earth (and even position of continents) changed radically over Earth history:

First organisms on land would have been various forms of algae back in the Precambrian. Plants colonized land in early part of Paleozoic; arthropods (arachnids, millipedes, insects) followed.

Why should vertebrates colonize land?

Some of the problems with living on land:

Vertebrate solutions to some problems:

1rst Amniote Radiation – Basal Synapsids:

  • Early Permian Epoch of the Paleozoic Era
  • Basal synapsids once placed in a paraphyletic group "Pelycosauria", the "fin backs"
  • All quadrupeds, all had sprawling gait
  • Most advanced basal synapsids had teeth differentiated between front of mouth and back of mouth

    Anapsids and diapsids were present, but minor component of ecosystem.

    Basal synapsids evolved themselves to extinction: were replaced by their own descendants, the Therapsida.

    2nd Amniote Radiation – Therapsids:

  • Late Permian Epoch of the Paleozoic Era into Early Triassic Epoch of the Mesozoic Era
  • Once called “mammal-like reptiles”, but NOT part of Reptilia
  • Therapsids had many specializations:

    The end of the Permian Period (and thus the Paleozoic Era) and the beginning of the Triassic Period (and thus the Mesozoic Era) (boundary at 251 Ma):

    Anapsids and diapsids still present, but relatively minor components. However, one type of diapsid becoming more important in Early Triassic:

    One of the two branches of Archosauria, Pseudosuchia, becomes more important throughout Early Triassic.

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    Last modified: 14 July 2006