GEOL 104 Dinosaurs: A Natural History

Fall Semester 2006
The Cretaceous-Tertiary Extinction IV: The Big Picture

What does the dinosaur record show?

Only a few spots on Earth have late Maastrichtian dinosaur record:

Only good, continuous record for late Maastrichtian and earliest Tertiary, and also earlier in the late Late Cretaceous is western North America.

The last two Ages in the Late Cretaceous Epoch are the Campanian and the Maastrichtian:
Age Absolute time range(Ma)
Maastricthian 71.3-65.51
Campanian 83.5-71.3

The Montana Group (late Late Cretaceous dinosaur-bearing rocks of western North America) spans the Campanian and Maastrichtian, and has earliest Tertiary rocks right above it. What does the dinosaur record of the Montana Group show us?

Throughout the Montana Group are the same basic groups of dinosaurs:

Currently, changes in these are best seen in hadrosaurids and ceratopsids; definite changes in tyrannosaurids, ankylosaurines, and pachycephalosaurs; other taxa too poorly sorted out at species level to be certain.

The Montana Group is often divided into four Land Mammal Ages (based on the land mammals, naturally). These are arranged stratigraphically one after the other, as follows:
Age "land mammal age"
late Maastrichtian Lancian
early Maastrichtian Edmontonian
middle-late Campanian Judithian
early Campanian Aqulian

The following describes some of the changes in the dinosaur community:




Pattern among big ornithischians:
Long snouted forms preferentially survive: link to vegetation change?

This pattern consistent with long-term (millions of year scale) change associated with Maastrichtian Regression (and possible vegetation change). However, no evidence that Lancian dinosaurs were declining WITHIN Lancian: might well have continued on to live in post-Lancian if not for Deccan Traps &/or Chicxulub impact.

So, what caused the dinosaurs to die out?

Three equally valid answers:

To Next Lecture.
To Previous Lecture.
To Syllabus.

Last modified: 14 July 2006