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Plate Tectonic Reconstructions

The Cretaceous* saw the first appearance of flowering (Angiosperm) plants. Marine life flourished, with many groups achieving their peak abundances and diversity. This Period saw the emergence of the largest of all land predators known, Tyrannosaurus Rex. Reptiles dominated the land (dinosaurs), the sea (mososaurs and the giant turtle, archelon) and the air (pterosaurs). The Cretaceous ended with a great extinction so severe it also marks the end of the Mesozoic Era, Dinosaurs, pterosaurs, mososaurs and ammonoids, just to name a few, were among the groups lost at this time. The now emptied ecosystems allowed the evolution of a largely new fauna in the coming Cenozoic Era.

The Cretaceous saw a rise in sea levels, leading to vast shallow continental seas and huge deposits of chalk from the skeletal remains of marine organisms.  Undersea volcanism and spreading-ridge formation enhanced middle-Late Cretaceous super-greenhouse conditions. The Cretaceous extinction event is delineated by the famous K-T boundary. The end of this Period correlates with a huge meteor impact on what is now the Yucatan peninsula. This impact is thought by many to have caused the demise of the Dinosaurs, as well as many other organisms at this time.

*Cretaceous comes from the “Terrain Crétacé” established by d’Omalius d’Halloy in 1822 for the chalk [Latin creta] deposits of the Paris basin.

Cretaceous Animal (Metazoan) Fossils
Crustacea (ToL: Arthropoda<Ecdysozoa<Bilateria<Metazoa<Eukaryota)
	Lobster (Decapoda) fossils, for example Hoploparia browni, are relatively rare in Cretaceous deposits.
	Crabs (Decapoda), such as Avitelmessus grapsoideus, which had appeared in the Jurassic, became more abundant.
Echinoderms (ToL: Echinodermata<Deuterostomia<Bilateria<Metazoa<Eukaryota)
	Echinoids (Echinoidea [sea urchins and relatives]), such as Epiaster whitei and Micraster sp. were common.
Vertebrates (ToL: Vertebrata<Chordata<Deuterostomia<Bilateria<Metazoa<Eukaryota)
	The sharks (Chodrichthyes), one of the two major modern fish families, are represented here by a group of fossil sharks teeth.
	Bony Fish (Osteichthyes): Ray-finned teleost fish, for example Rhacholepis buccalis, which dominate modern groups, appeared first in the Jurassic. In the Cretaceous they first outnumber the earlier fish types.
	Reptiles (Reptilia). The display includes fossils from two major groups of dinosaurs (Dinosauria [Birds and Dinosaurs]). The Ornithischia (bird-hipped plant eaters) are represented by a Hadrosaurus tooth plate and Hadrosaurus teeth.
	The Theropods (predatory bipedal dinosaurs, such as Tyrannosaurus and Birds) are represented by a tooth from an Albertosaurus sp. (note the serrated edges. The display also includes an unidentified reptile egg.
Mollusks (ToL: Mollusca<Lophotrochozoa<Bilateria<Metazoa<Eukaryota)
	Bivalves (Bivalvia) were very common and important in this Period. One group, the rudist bivalves have an unusual form in which one valve is cone shaped, much like rugose corals of the Paleocene. During the Cretaceous they built huge reefs, cementing themselves together as they grew upward. The rudists became extinct at the end of the Mesozoic. Other bivilves also flourished including the oysters, such as Actinostrea travisana , and extinct oyster relatives. Extinct oysters sometimes had unusual forms with one valve snail-shaped (pyritized fossil), or twisted into a spiral. In each case a second valve covered the opening as seen (partial) in this second spiral example.
	Gastropods (Gastropoda) are represented by two assemblages: a slab with Goniobasis chrysalis and a rock with freshwater snails exposed. The neogastropods, the most advanced of the marine gastropods, appeared in the Creatceous, while the older mesogastropods remained numerous.
	Cephalopods (Cephalopoda): The ammonoids, for example Scaphites nodosus were diverse and abundant during the Cretaceous, to be completely lost at the end of this Period. A non-ammonoid cephalopod, Exiteloceras jennyi., is also displayed.
Sponges (ToL: Porifera<Metazoa<Eukaryota)
	Sponges; The museum displayes two cup-shaped Rhaphidonema farringdonense sponges in this case (a and b).
Cretaceous Plant Fossils
Vascular Plants (ToL: Embryophytes [land plants] <Green Plants<Eukaryota)
	Cycads are a largely unbranched, woody plant resembling a pine. Cycads flourished during this Period, though they are nearly extinct today.  A trunk showing obvious leaf-scars is on display.
	Conifers, represented here by a Spruce cone (Picea), continued to dominate the flora of the Cretaceous.
	Angiosperms: The angiosperms, or flowering plants, first appeared and became abundant in the Cretaceous. Fossils of the cones" of an alder, Alnus, and the fruit of a fig, Ficus ceratops, are shown. .

The engravings are from Dana, James D. (1870) Manual of Geology, Le Conte, Joseph (1898) A Compend of Geology, Shimer, Harvey Woodburn (1914) An Introduction to the Study of Fossils,or McMurrich (1894) Invertebrate Morphology.

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Last modified 29 January 2007 | ©1998, HSU NHM