Pamela J. W. Gore, 1995, 2010
Georgia Perimeter College
Includes many extinct taxa, plus many important modern taxa which had just appeared.
Most Cretaceous top carnivores were not "modern".
symmetrical tails, round scales, specialized fins (ray finned)
(dominant group of marine + fresh water fish today)
|Xiphactinus audax, a ray-finned fish, the largest bony fish of the Cretaceous. |
Typically 18-20 feet long. Niobrara Chalk, Lane County, Kansas.
Plesiosaurs (up to 35' long)
|Plesiosaur. Elasmosaurus platyurus, Pierre Shale, NW Kansas.|
(Ichthyosaurs & large marine crocodiles had become rare.)
Mosasaurs (up to 50' long) probably top predators; attacked ammonoids.
|Mosasaur, Tylosaurus poriger.|
78 m.y. old, 26 ft long.
On display at Georgia Southern University, Statesboro, GA.
|Mosasaur fossil skeleton from Greene County, Alabama|
Red Mountain Museum, Birmingham, Alabama
|Mosasaur chasing turtle. Clidastes propython|
Smallest mosasaur in North American seas
|Ammonite showing bite marks from a mosasaur.|
Unique group of large pelecypods appeared (the rudists).
Rudists were important reef formers; up to 1 m tall; (extinct at end of Cret.)
Fossil rudists. On display at the Smithsonian Institution, Museum of Natural History, Washington, D.C.
New mode of predation not seen before.
Modern pelecypods with holes drilled by predatory gastropods.
Unidentified flower fossil.
Today there are 200,000 flowering plant species & 550 modern conifer species
Cycadeoidea marylandica, a gymnosperm that produced both pollen and seeds in a flowerlike structure. Diamond-shaped leaf scars are present on its trunk, arranged in spirals. Small whorls mark the position of the flower-like structures. May be a precursor to the evolution of the angiosperm. Cretaceous. 105 m.y. old, Prince Georges County, Maryland. On display in the U.S. National Museum, Smithsonian Institution.
Angiosperm leaf, similar to modern sweet gum. Late Cretaceous Dakota Formation, central Kansas.
More species & individuals of herbivorous dinosaurs. Few carnivorous dinosaurs (top of food chain/web).
Trend toward evolution of large body size.
Drastic reductions with few survivors:
Animals both on land and in the sea were affected.
On land, only SMALL (less than 50 lb) animals survived.
Many groups that died out declined gradually, and others disappeared suddenly.
Many hypotheses about these extinctions:
sea level change?
climatic change? hot? cold?
meteorite impact? comet impact? (iridium)
volcanic eruptions; dust in atmosphere
change in CO2 levels?
change in O2 levels?
appearance of angiosperms changed food chain/web
spillover of freshwater cap onto world oceans from Arctic Ocean melting?
This page copyright Pamela J. W. Gore
Georgia Perimeter College, Clarkston, GA
November 15, 1995
Last modified November 10, 1997
Updated October 19, 1999
Images added March 21, 2003 and April 9, 2003
Images added February 7, 2006 |
Links updated August 15, 2009