Cycads are plants that are often referred to as “living fossils” because they have a geologic time range of early Permian to recent. They belong to an ancient group of seed plants known as gymnosperms. Even though they resemble short, stout palms, they are not palms.
Two photos of the same cycad plant. The first image was taken in 2009, and the second image was taken in 2023, 14 years later. There has been noticeable growth but not much!
Starting in the Cretaceous, cycads gradually were replaced by angiosperm plants (the flowering plants). Today, there are 9 to 10 genera left of cycads and about 100 species. They are tropical to subtropical and very slow-growing. They require about 15 to 20 years to mature. Under the right growing conditions, they can reach up to 60 feet high, but many remain short/thick throughout their lives.
They are easy to grow and many gardeners cultivate them. They are, however, expensive to purchase because their forest habitats are vanishing. The fact that they are expensive is the reason why they are commonly stolen from gardens.
Cycads are poisonous because they contain a toxin called cyasin. Cycad nuts are extremely poisonus, especially to dogs. Also, cycad fronds, which soon become stiff after sprouting in the middle of the plant, have very sharp tips that easily penetrate animal skin and cause slow-to-heal wounds.
When the female cycads mature, they produce “flowers.” These "flowers" have very specialized pollinators, usually a specific species of beetle. The seed-bearing cones are borne on nearby, separate male plants. When the males mature (it can take a long time), they produce, thick solid cones that resemble pine cones but are referred to as sarcotesta, which are brightly colored, fleshy, fruitlike structures. Enclosed within the sarcotesta, which is sugary, are kernels (nuts).
This figure is of a sacrotesta “fruit” structure of the cycad Cycas circinalis, in the Washington, D.C. area. Image taken by Raul654 on May 7, 2005. This image is allowed to be used by GFDL Licensing, Creative Commons Attribution-Share Alike, courtesy of en.wikipedia.org
Late Paleozoic and Mesozoic herbivorous reptiles (including some dinosaurs) undoubtedly fed on cycads. In fact, they co-evolved: both flourished during the Mesozoic, and when the dinosaurs died out at the end of the Mesozoic, cycads declined greatly. Dinosaurs most likely had color vision and the brightly colored sacrotesta of the cycads would have been easily detected. The kernels (nuts) within the sarcotresta could have just passed through a dinosaur’s digestive tract without releasing their poisonous interiors--as along as the kernels were swallowed whole and not chewed up. This technique of seed dispersal was very an effective means of widespread geographic dispersal of cycads (Mustoe, 2007).
Hadrosaur dinosaurs had grinding teeth, thus they could not successfully feed on the cycad seeds without risking death.
It should be mentioned that herbivore dinosaurs could have fed also on other land plants: ferns, ginkgo leaves, pine trees, lichens, club mosses, and Equisetum (see one of my previous posts).
The Fossil Cycad National Monument was created in 1922 in order to “protect” a Cretaceous (120 million years old) cycadeoid forest in the Black Hills of southwestern South Dakota. It was the third national monument specifically created to protect fossils in the United States. The first was the Petrified Forest National Monument in northern Arizona, and the second was the Dinosaur National Monument located on the Colorado and Utah border.
Hundreds of specimens of a cycad-like cycadeoid, known as Pennettitales to paleobotanists, were exposed at the ground surface at the Fossil Cycad National Mounument. This made for easy collecting, and unfortunately, over-collecting and outright rampant theft resulted in all of the specimens “disappearing.” Thus, in 1957, the federal government deauthorized this national monument, and it no longer exists.
REFERENCES USED:
Mustoe, G.E. 2007. Coevolution of cycads and dinosaurs. The Cycad Newsletter, v. 30, no. 1, pp. 6–9. [An excellent treatment of the topic, and the pdf is free].
en.Wikipedia.org 2023
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