
In
paleontology
Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure ge ...
, a fern spike is the occurrence of unusually high
spore
In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
abundance of
fern
The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...
s in the
fossil record
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
, usually immediately (in a
geological
Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth s ...
sense) after an
extinction event
An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp fall in the diversity and abundance of multicellular organisms. It occ ...
. The spikes are believed to represent a large, temporary increase in the number of ferns relative to other terrestrial
plant
Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
s after the
extinction
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
or
thinning
In agricultural sciences, thinning is the removal of some plants, or parts of plants, to make room for the growth of others. Selective removal of parts of a plant such as branches, buds, or roots is typically known as '' pruning''.
In forestry ...
of the latter. Fern spikes are strongly associated with the
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the extinction event, mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event cau ...
,
although they have been found in other points of time and space such as at the
Triassic
The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
-
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
boundary.
Outside the fossil record, fern spikes have been observed to occur in response to local extinction events, such as the
1980 Mount St. Helens eruption.
Causes
Extinction events have historically been caused by massive environmental
disturbances, such as meteor strikes. Volcanic eruptions can also wipe out local ecosystems through
pyroclastic flow
A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...
s and
landslide
Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...
s, leaving the ground bare for new
colonization
475px, Map of the year each country achieved List of sovereign states by date of formation, independence.
Colonization (British English: colonisation) is a process of establishing occupation of or control over foreign territories or peoples f ...
.
For a population to recover and thrive after such an event, it must be able to tolerate the conditions of the disturbed environment. Ferns have multiple characteristics which predispose them to grow in those environments.
Spore characteristics
Plants generally reproduce with spores or seeds, meaning those will be what
germinates in a disaster's aftermath. But spores have advantages over seeds in the environmental conditions produced by a disaster. They are generally produced in higher numbers than seeds, and are smaller, aiding
wind dispersal
Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal') and the movement from one breeding site to another ('breeding dispersal' ...
.
While many wind-dispersed pollens of
seed plants
A seed plant or spermatophyte (; New Latin ''spermat-'' and Greek ' (phytón), plant), also known as a phanerogam (taxon Phanerogamae) or a phaenogam (taxon Phaenogamae), is any plant that produces seeds. It is a category of embryophyte (i.e. la ...
are smaller and farther dispersed than spores, pollen cannot germinate into a plant and must land in a receptive flower. Some seed plants also require animals to disperse their seeds, which may not be present after a disaster. These characteristics allow ferns to rapidly colonize an area with their spores.
Fern spores require light to germinate. Following major disturbances that clear or reduce plant life, the ground would receive ample sunlight that may promote spore germination. Some species' spores contain
chlorophyll
Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...
, which hastens germination and may aid rapid colonization of clear ground.
Environmental tolerance
After the eruption of
El Chichón, the fern ''
Pityrogramma calomelanos'' was observed to regenerate from
rhizome
In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and Shoot (botany), shoots from its Node (botany), nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from ...
s buried by ash, even though the plants' leaves were destroyed.
The rhizomes tolerated exposure to heat and sulfur from the volcanic matter. Their survival suggests resilience of ferns to the harsh environmental conditions imposed by certain kinds of disasters, and rhizome regeneration may have been a factor in fern recovery after other environmental events.
Ecology
Fern spikes follow the pattern of
ecological succession
Ecological succession is the process of how species compositions change in an Community (ecology), ecological community over time.
The two main categories of ecological succession are primary succession and secondary succession. Primary successi ...
. In the past and in modern times, ferns have been observed to act as
pioneer species
Pioneer species are resilient species that are the first to colonize barren environments, or to repopulate disrupted biodiverse steady-state ecosystems as part of ecological succession. Various kinds of events can create good conditions for pi ...
.
Eventually, their abundance at a site decreases as other plants such as
gymnosperm
The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...
s begin to grow.
Spore availability
Fern spikes cannot occur without ferns already existing in the area, so spikes occur primarily in regions where ferns are already a prominent part of the ecosystem. At the Cretaceous-Paleogene extinction event, a fern spike occurred in the New Zealand area, where ferns made up 25% of plant abundance pre-extinction. After the event, fern abundance increased to 90%.
Detection
Prehistoric fern spikes can be detected by
sampling sediment. Sources include sediment that has been accumulating in a lake since the event of interest and
sedimentary rock
Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...
s such as sandstone.
Because sediment accumulates over time and thus shows
superposition
In mathematics, a linear combination or superposition is an expression constructed from a set of terms by multiplying each term by a constant and adding the results (e.g. a linear combination of ''x'' and ''y'' would be any expression of the form ...
, layers can be assigned to certain times. Spore concentration in a layer can be compared to the concentration at different times, and concentration of other particles such a pollen grains. A fern spike is characterized by a suddenly higher abundance of fern spores following a disaster, generally accompanied by a decrease in other plant species as indicated by their pollen. Eventually fern abundance will decrease, hence the term "spike" describing the pattern.
Modern fern spikes can simply be directly observed, and allow for observation of factors contributing to the spike that may not be detectable otherwise, such as rhizomes persisting in ash.
Significance
Because fern spikes generally coincide with certain disasters such as meteorite strikes and volcanic eruptions, their presence in the fossil record can indicate those events. A fern spike is believed to support a meteorite impact as cause of the
Triassic-Jurassic extinction event, similar to the one later causing extinction at the end of the Cretaceous period.
Known events
A fern spike followed a fungal spike after the
Permian–Triassic extinction event
The Permian–Triassic extinction event (also known as the P–T extinction event, the Late Permian extinction event, the Latest Permian extinction event, the End-Permian extinction event, and colloquially as the Great Dying,) was an extinction ...
(252 Ma). It has been observed in Australia.
After the Triassic-Jurassic extinction event (201.3 Ma), ferns drastically increased in abundance while seed plants became scarce. The spike has been detected in eastern North America and Europe.
A very widespread fern spike occurred after the Cretaceous–Paleogene extinction event (66 Ma).
The spike has been predominantly observed in North America, with just one observance outside the continent in Japan.
Fern spikes today are often observed after volcanic eruptions. The areas affected by the eruptions of
Mount St. Helens (
May 18, 1980) and
El Chichón (March—April 1982) exhibited such a pattern.
See also
*
Ecological succession
Ecological succession is the process of how species compositions change in an Community (ecology), ecological community over time.
The two main categories of ecological succession are primary succession and secondary succession. Primary successi ...
*
Paleoecology
Paleoecology (also spelled palaeoecology) is the study of interactions between organisms and/or interactions between organisms and their environments across geologic timescales. As a discipline, paleoecology interacts with, depends on and informs ...
*
Pioneer species
Pioneer species are resilient species that are the first to colonize barren environments, or to repopulate disrupted biodiverse steady-state ecosystems as part of ecological succession. Various kinds of events can create good conditions for pi ...
References
{{DEFAULTSORT:Fern Spike
Extinction
Extinction events
Fossil record
Paleontological concepts and hypotheses
Ferns
Paleobotany