93
(2005) suggests that the purported unprecedented accumulation of fungal spores
after the global plant die-off at the end of the Cretaceous would have altered the
usual balance of power, namely by delivering such massive concentrations of spores
into the lungs of the dinosaurs that their immune defenses were overwhelmed. If the
body temperature of dinosaurs was lower than that of mammals, then these reptiles
might well have been susceptible to fungal infection, perhaps giving an advantage
to early mammals to survive the KT-extinction event. While there are numerous
censures surrounding this hypothesis, including the debate as to whether the spores
that accumulated indeed are fungal in origin (Hochuli 2016) and the ongoing discussion of whether dinosaurs were warm- or cold-blooded (e.g., Grady et al. 2014),
it nevertheless opens an interesting and thought-provoking new perspective on the
end of the age of dinosaurs.
3.4 Concluding Remarks
Deciphering the roles of fungi colonizing other organisms in natural environments
today is challenging because of the difficulties in making field observations (Jeffries
1995). Even more challenging is the analysis of fungal relationships from the geologic past. The lack of information that can be used to safely assign fungal fossils
systematically is one of the principle problems exacerbating the assessment of fossil
fungal associations (Krings et al. 2016). As we have tried to exemplify in this chapter, however, there are also persistent uncertainties with regard to determining the
fungal nutritional modes that are connected to the inherent limitations of the fossil
record (Fig. 3.5). Based on the examples of (assumed) fungal parasitism from the
fossil record presented throughout the sections of this chapter, certain patterns
nonetheless begin to emerge:
1. Sublime preservation (e.g., in amber or chert) is a precondition to identify direct
features such as fungal mycelia spreading along consistent pathways in intact
plant tissue, and indirect evidence such as host responses or death-grip scars in
fossils that can be attributed to fungal parasitism.
2. Host responses currently represent the most reliable fossil evidence in support of
fungal infection of a living host, albeit not necessarily of a parasitic nutritional
mode of the intruder.
3. In the absence of host responses, the presence of certain structural features regularly seen in extant fungal parasites (e.g., haustoria, endobiotic rhizoidal systems, and holdfasts) can provide hints at parasitism in fossil fungi (see
Karling 1932).
4. Fossils that can be attributed to present-day parasitic fungal families and genera
with confidence are suggestive of fossil parasitism even if information on the
hosts is not available. Unfortunately, fungal fossils older than Cretaceous cannot
normally be attributed to modern families and genera with confidence.
3 Fungi as Parasites: A Conspectus of the Fossil Record
(2005) suggests that the purported unprecedented accumulation of fungal spores
after the global plant die-off at the end of the Cretaceous would have altered the
usual balance of power, namely by delivering such massive concentrations of spores
into the lungs of the dinosaurs that their immune defenses were overwhelmed. If the
body temperature of dinosaurs was lower than that of mammals, then these reptiles
might well have been susceptible to fungal infection, perhaps giving an advantage
to early mammals to survive the KT-extinction event. While there are numerous
censures surrounding this hypothesis, including the debate as to whether the spores
that accumulated indeed are fungal in origin (Hochuli 2016) and the ongoing discussion of whether dinosaurs were warm- or cold-blooded (e.g., Grady et al. 2014),
it nevertheless opens an interesting and thought-provoking new perspective on the
end of the age of dinosaurs.
3.4 Concluding Remarks
Deciphering the roles of fungi colonizing other organisms in natural environments
today is challenging because of the difficulties in making field observations (Jeffries
1995). Even more challenging is the analysis of fungal relationships from the geologic past. The lack of information that can be used to safely assign fungal fossils
systematically is one of the principle problems exacerbating the assessment of fossil
fungal associations (Krings et al. 2016). As we have tried to exemplify in this chapter, however, there are also persistent uncertainties with regard to determining the
fungal nutritional modes that are connected to the inherent limitations of the fossil
record (Fig. 3.5). Based on the examples of (assumed) fungal parasitism from the
fossil record presented throughout the sections of this chapter, certain patterns
nonetheless begin to emerge:
1. Sublime preservation (e.g., in amber or chert) is a precondition to identify direct
features such as fungal mycelia spreading along consistent pathways in intact
plant tissue, and indirect evidence such as host responses or death-grip scars in
fossils that can be attributed to fungal parasitism.
2. Host responses currently represent the most reliable fossil evidence in support of
fungal infection of a living host, albeit not necessarily of a parasitic nutritional
mode of the intruder.
3. In the absence of host responses, the presence of certain structural features regularly seen in extant fungal parasites (e.g., haustoria, endobiotic rhizoidal systems, and holdfasts) can provide hints at parasitism in fossil fungi (see
Karling 1932).
4. Fossils that can be attributed to present-day parasitic fungal families and genera
with confidence are suggestive of fossil parasitism even if information on the
hosts is not available. Unfortunately, fungal fossils older than Cretaceous cannot
normally be attributed to modern families and genera with confidence.
3 Fungi as Parasites: A Conspectus of the Fossil Record