According to new research led by Dr. Nathan Jud of William Jewell College, angiosperm (also called broad-leaf, hardwood or deciduous) trees approaching 6.5 feet (2 m) in diameter were part of the forest canopies across southern North America by the Turonian stage of the Late Cretaceous epoch, approximately 92 million years ago — nearly 15 million years earlier than previously thought.
An illustration of the finds made by Jud et al. Image credit: Sae Bom Ra, Adelphi University.
Dr. Jud and colleagues found a whealth of plant and terrestrial vertebrate fossils — including a large petrified log of angiosperm tree — in deposits of the Mancos Shale Formation in Utah, the United States.
The fossils date to the Turonian, a severely underrepresented interval in the terrestrial fossil record of North America.
“A large silicified log, 36 feet (11 m) in preserved length with a maximum diameter estimate of 5.9 feet (1.8 m), is assigned to the genus Paraphyllanthoxylon,” the paleontologists said.
“It is the largest known pre-Campanian angiosperm and the earliest documented occurrence of an angiosperm tree more than 3.3 feet (1 m) in diameter.”
Map of Turonian localities in western North America with angiosperm woods over 3.9 inches (10 cm) in diameter and stacked area curve showing the contribution of this discovery (indicated by star) to the global record of Cretaceous angiosperm woods. Ages are midpoint estimates. The gray area indicates the maximum observed angiosperm diameter through the Cretaceous. Dashed box indicates Turonian occurrences shown in the map above. Inset shows the new angiosperm log in the field. During much of the Late Cretaceous, the Western Interior Seaway divided North America into Appalachia in the east and Laramidia in the west. Image credit: Jud et al, doi: 10.1126/sciadv.aar8568.
Aside from the petrified log, they also found fossilized foliage from ferns, conifers and angiosperms, which confirm that there was forest or woodland vegetation 90 million years ago in the area, covering a large delta extending into the sea.
“Until now most of what we knew about plants from the Ferron Sandstone came from fossil pollen and spores,” Dr. Jud noted.
“The discovery of fossil wood and leaves allows us to develop a more complete picture of the flora.”
The scientists also found turtle and crocodile remains as well as part of the pelvis of a duck-billed dinosaur.
Previously, the only known vertebrate remains found were fish teeth, two short dinosaur trackways, and a pterosaur.
“These discoveries add much more detail to our picture of the landscape during the Turonian period than we had previously,” said co-author Dr. Michael D’Emic, a researcher at Adelphi University, the Burpee Museum of Natural History and Stony Brook University.
The research appears in the journal Science Advances.
_____
Nathan A. Jud et al. 2018. A new fossil assemblage shows that large angiosperm trees grew in North America by the Turonian (Late Cretaceous). Science Advances 4 (9): eaar8568; doi: 10.1126/sciadv.aar8568
