page_title: Hell Creek Formation
section_title: Flora
hierarchical_section_title: Hell Creek Formation / Fossil content / Flora
caption_attribution_description: Volcan Llaima, Parque Nacional Conguillío, Chile
context_page_description: The Hell Creek Formation is an intensively-studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The formation stretches over portions of Montana, North Dakota, South Dakota, and Wyoming. In Montana, the Hell Creek Formation overlies the Fox Hills Formation. The site of Pompeys Pillar National Monument is a small isolated section of the Hell Creek Formation. In 1966, the Hell Creek Fossil Area was designated as a National Natural Landmark by the National Park Service.
  It is a series of fresh and brackish-water clays, mudstones, and sandstones deposited during the Maastrichtian and Danian by fluvial activity in fluctuating river channels and deltas and very occasional peaty swamp deposits along the low-lying eastern continental margin fronting the late Cretaceous Western Interior Seaway. The climate was mild, and the presence of crocodilians suggests a sub-tropical climate, with no prolonged annual cold.
context_section_description: The Hell Creek Formation was a low floodplain at the time before the sea retreated, and in the wet ground of the dense woodland, laurels, sycamores, beech, magnolias, and palm trees grew. Ferns and moss grew in the forest understory. Plant fossils from the upper early Paleocene of the Hell Creek Formation include the ferns Botrychium, Woodwardia, Osmunda, Onoclea and Azolla; conifers Metasequoia, Glyptostrobus and cupressaceous conifers; the monocot Limnobiophyllum (a relative of duckweeds); and the dicots Cercidiphyllum and Platanus. There are numerous types of leaves, seeds, flowers and other structures from Angiosperms, or flowering plants. The Hell Creek Formation of this layer contains 300 tablets or more of plants. Angiosperms are by far the most diverse and dominant flora of the entire population, about 90 percent. However, the evergreens included conifers, ginkgo, bald cypress, and cycads. Flowering plants included a variety of trees that no longer exist. Today Hell Creek's flora is hardwood forest mixed with deciduous and evergreen forest and apparently similar to then, but with a closer look, the current plant community is distinct. In sharp contrast to Montana today, the presence of palm trees meant the climate was warmer then.
  Dr. Kirk Johnson (Scientist) claims that there are no grasses, oaks, maples, or willows in the Hell Creek Formation. Ferns are uncommon in the majority of the formation, however there is a great increase in the abundance of fossil fern spores in the two centimeters of rock that directly overlies the impact fallout layer (the famous K-T boundary layer). This increase in fern spore abundance is commonly referred to as "the fern spike" (meaning that if the abundance of spores as a function of stratigraphic position were plotted out, the graph would show a spike just above the impact fallout layer). Johnson also found that the majority of the angiosperm genera in the Hell Creek Formation are now extinct. He also believes that, very roughly, 80% of the terrestrial plant taxa died out in what is now Montana and the Dakotas at the K/T boundary.
  Many of the modern plant affinities in the Hell Creek Formation (e.g., those with the prefix "aff." or with quotes around the genus name) may not in reality belong to these genera; instead they could be entirely different plants that resemble modern genera. Therefore, there is some question regarding whether the modern Populus or Juglans, as two examples, actually lived in the late Cretaceous.
  Compared to the rich Hell Creek Formation fossil plant localities of the Dakotas, relatively few plant specimens have been collected from Montana. A few taxa were collected at Brownie Butte Montana by Shoemaker, but most plants were collected from North Dakota (Slope County) and from South Dakota. "TYPE" after the binomial means that it is represented by a type specimen found in the Yale-Peabody Museum collections. "YPM" is the prefix for the Yale-Peabody Museum specimen number.
  Overview (from Johnson, 1997):
  190 plant morphotypes, including:
  1 bryophyte (mosses and liverworts)
  6 "pteridophytes" (A paraphyletic group: modern examples are horsetails, club mosses and ferns.)
  9 conifers
  2 ginkgo (uncommon)
  172 angiosperms (90% of all specimens collected, as well as 90% of all taxa found)
  Plants of the Hell Creek Formation
  various ferns and cycads
  Equisetum (Equisetaceae)
  Gymnosperms
  Platyspiroxylon (Cupressaceae)
  Podocarpoxylon (Podocarpaceae)
  Elatocladus (Taxodiaceae)
  Sequoiaxylon (Taxodiaceae)
  Taxodioxylon (Taxodiaceae)
  Araucaria (Araucariaceae)
  very widespread Mesozoic conifer group. All members are extinct (Cheirolepidiaceae)
  Ginkgos
  Baiera
  Ginkgo adiantoides
  Angiosperms
  Artocarpus (Moraceae)
  Barberry family (Berberidaceae)
  Cercidiphyllum (Cercidiphyllaceae)
  Dombeyopsis (Sterculiaceae)
  Laurel family (Lauraceae)
  Magnolia (Magnoliaceae)
  Palms (Arecaceae)
  Platanus family includes today's American sycamore or plane tree (Platanaceae)
caption: Although the first representatives of leafy trees and true grasses emerged in the Cretaceous, the flora was still dominated by conifers like Araucaria
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