Cantwell Formation

The Cantwell Formation is a geologic formation in Alaska. It preserves fossils dating back to the Cretaceous period, it has also yielded numerous dinosaur tracks at Denali National Park. Contemporary therizinosaurid and hadrosaurid trackways in the formation indicate that the area was once a major point of immigration between Asia and North America during the Late Cretaceous for many families of dinosaur. Fossil plants of water lilies found in the same area suggest the presence of wetlands, ponds or other large standing bodies of water.
Footprints discovered in the formation include those of theropods, hadrosaurs, ceratopsians, pterosaurs and birds, notably the Magnoavipes denaliensis.

Description

The Cantwell Formation represents a Late Cretaceous fluvial succession in Denali National Park containing dinosaur trackways, invertebrate traces, and plant fossils. Sedimentary facies represent a lateral succession from alluvial fan and braided river deposits, to coastal fluvial and lacustrine environments with marshy overbanks, proximal estuary consisting of laterally avulsed distributary channels, intertidal estuarine deposits, and finally tidally influenced marginal marine environments.
A leaf analysis of the Sable Mountain flora was used to estimate a mean annual temperature of, a warm month mean temperature of, and a cold month mean temperature of. Growing season precipitation was estimated at over a period of 4.8 months. These results demonstrate a cool temperate, seasonal paleoclimate with short dry summers and cold wet winters. Dating of ash layers in the formation indicate this floral assemblage straddled the Campanian-Maastrichtian boundary, a period of rapid global cooling.

Taxa	Species	Locality	Material	Notes	Images
Alnites	A. sp.			Similar to extant Alnus.
Asplenium	A. sp.
Cf. Castaliites	cf. C. sp.		Leaf morphotaxon.
Cephalotaxopsis	C. sp.			Belongs to Taxaceae.
Corylites	C. beringianus			Similar to extant Corylus.
Cladophlebis	C. sp.
Cf. Craspedodromophyllum	cf. C. sp.			Belongs to Betulaceae.
Equisetum	E. arcticum
Glyptostrobus	G. sp.
Hammelidaceae indet.			Leaf morphotypes.	Belongs to Hammelidaceae.
Cf. Kenella	cf. K. sp.		Seeds
Larix	L. sp.		Needle bundles.	Originally described as Cf. Pseudolarix.
Metasequoia	M. occidentalis
Menispermites	M. septentrionalis			Belongs to Menispermaceae.
Menispermites	M. sp.			Another Menispermoid.
Cf. Nuphar	cf. N. sp.			Similar to extant Nuphar.
Parataxodium?	Indeterminate			In need of revision.
Cf. Phragmites	cf. P. sp.
Picea	P. sp.		Needles, ovuliferous cone.
Pinus	P. sp.		Needle bundles.
Pityophyllum?	indeterminate			Indeterminate Pinaceous needles.
Platanites	P. sp.			Belongs to Platanaceae.
Pseudoprotophyllum	P. sp.			Another Platanoid.
Cf. Sparganium	cf. S. sp.
Trochodendroides	T. richardsonii			Belongs to Cercidiphyllaceae.
Trochodendroides	T. sp.			A Trochodendroid.
Tumion	T. gracilis
Cf. Viburniphyll	cf. V. sp.			Similar to extant Viburnum.
Cf. Zizyphoides	cf. Z. sp.			Another Trochodendroid.