Minute Trace Fossils Offer Major Implications For Extinction Recovery

Large body fossils of extinct creatures capture our imagination.  It’s understandable.  These were fascinating behemoths, and we can see something of their life in the bones that remain. While our collective attention might be focused on these very big things, researchers published a paper this past November that centered on some very tiny things.  And what they found has enormous implications for our understanding of ancient life.

Fossi leaf with insect damage - Michael Donovan

Insect feeding damage on a fossil leaf, including holes and a leaf mine (bottom right), made by a larval insect that fed on tissue within the leaf. The fossil is 67-66 million years old and from the Lefipán Formation in Patagonia, Argentina; photo and caption courtesy of Michael Donovan.


The authors Michael Donovan, Ari Iglesias, Peter Wilf, Conrad Labandeira, and N. Rubén Cúneo studied trace fossils of insect feeding damage on over 3000 fossil leaves from Patagonia (an area that encompasses the southern part of Argentina and Chile).

Remarkably, fossil leaves number in the tens of thousands in the Western Hemisphere alone.  But studying them for insect damage during the end Cretaceous and early Paleocene is relatively new.  Keep in mind that the end Cretaceous marked the last mass extinction this planet has known thus far.  The early Paleocene marks the time when life was, however slowly, working its way back into existence.

There is a preponderance of fossil leaves in the western interior North America (WINA) from this time period, and they have been studied.  In “Rapid recovery of Patagonian plant-insect associations after the end-Cretaceous extinction” published in Nature Ecology and Evolution, the authors compared the relatively smaller number of fossil leaves in Patagonia to the much larger numbers of such leaves from WINA.

What interested them was the diversity of insect damage to these Patagonian plant leaves.


Tiny insect piercing and sucking marks on a fossil leaf from the fossil locality Palacio de los Loros 2 in Patagonia, Argentina (approximately 64 million years old). Piercing and sucking damage is made by insects that use their straw-like mouthparts to feed on fluids from within plants; photo and caption courtesy of Michael Donovan.


Close up of the picture above; photo and caption courtesy of Michael Donovan.

The type of insect damage—the different ways insects fed upon a leaf–relates to the diversity of insects. That diversity of herbivorous insects, in turn, relates to a much larger food web.  In other words, the traces these ancient insects made indicate that there was a growing population of different types of insects. That growing population suggests a growing, thriving food web.  Life in Patagonia, after the last mass extinction, may have been returning at a much faster rate than its northern counterpart.

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“If we’re just looking at the raw numbers, there are way more fossils, but less insect-damage diversity,” explained Michael Donovan in a phone interview referring to the WINA fossil leaf damage.  “In the Western US, there’s around almost 20,000 leaves included in those data sets. Maybe a little less.” He chuckled. “And that’s compared to the 3,646 [fossil leaves] in Patagonia. So, it’s a big difference!”

“We can’t always say exactly what insects were making the damage,” he wrote earlier in an email.  “During this study, we found many different kinds of damage representing the work of a wide range of plant-eating insects. Some types of damage can be made by a variety of insects. For example, many different kinds of insects with chewing mouthparts, such as beetles or grasshoppers, can create holes in leaves by feeding through the plant tissue. Other types of insect damage provide more specific information about the culprit. Leaf mines, for example, are made by larvae of some species of moths, flies, wasps, and beetles. The mines act as a detailed record of the behavior of the insect, which we can use to infer the type of insect that may have made the mine.”


View of an excavation at the Palacio de los Loros 2 fossil plant locality in Chubut, Patagonia, Argentina. The fossils there were formed in the early Paleocene around 64 million years ago;photo and caption courtesy of Michael Donovan.


Michael was the one responsible for studying these 3,646 fossil leaves to see if any had any damage to begin with, and then to see whether that damage may have been insect-related.  (In a nod to how I may have organized such things, I wondered whether museum collections separate out fossils with traces of damage.  They do not. Or rather, as Michael explained, “How they are organized usually depends on the collector or museum. The collections used in this study are organized by plant morphotype/species. To collect the data, I inspected all of the leaf fossils under a microscope for insect damage.”)

But how can one determine the difference between disease-related traces and insect-related traces in a fossil leaf?

“One good thing to look for is reaction from the plant to the insect damage,” he answered.  “So, for example, if an insect chews through a leaf and makes a hole, [scar] tissue [will form] around the edges of the hole. On the fossil, it looks like a little dark area surrounding the hole.  That’s where the plant healed itself after the damage was made, and that shows that [the insect ate the leaf] when the plant was still alive. If it happened when the leaf was dead, it wouldn’t form that scar tissue. So if there’s something like a tear that was made when the leaf was already dead, reaction tissue wouldn’t form. Then some other types of damage are very distinctive, such as leaf mines, and look very similar to damage we see on modern leaves.”


Skeletonization (feeding on leaf tissue between leaf veins but leaving the veins intact) caused by a plant-feeding insect. The leaf is from the Palacio de los Loros 2 fossil plant locality in Patagonia, Argentina (approximately 64 million years old); photo and caption courtesy of Michael Donovan.


Their research determined that there is a greater diversity of insect-damage to fossil leaves in Patagonia, and that this diversity occurred 4 million years after the meteorite crashed into Earth at Chicxulub, Mexico.  Contrast this to the western interior North America, in which insect-damage indicates that same recovery took 9 million years.

“The fossil plant collections that we studied were collected relatively recently by my coauthors (Ari Iglesias, Peter Wilf, and Rubén Cúneo) and other scientists as part of a larger research program on Patagonian fossil floras from the end of the Cretaceous through the Eocene,” Michael described. “The Paleocene floras have been dated with a variety of methods, which show us that the fossil sites were formed during three time slices in the early Paleocene. Using these dates, we were able to observe how plant-insect associations in Patagonia recovered in the 4 million years after the end-Cretaceous asteroid impact.”

Co-authors Conrad Labandeira and Peter Wilf were part of a 2014 study published in PLOS One (“Insect Leaf-Chewing Damage Tracks Herbivore Richness in Modern and Ancient Forests,” also by Mónica R. Carvalho, Héctor Barrios, Donald M. Windsor, Ellen D. Currano, and Carlos A. Jamarillo) in which extant insect leaf damage was correlated to the larger food web of two tropical rainforests.  The variety of insect traces on today’s leaves represents a healthy variety of insect species.  Like keystone species in any ecosystem, these traces indicate a thriving web of life.

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How remarkable to then extrapolate that insects so many millions of years ago, simply eating the leaves available to them in the Southern Hemisphere, can offer important clues to the state of life after the devastation our planet endured.  The traces of these tiny creatures—and the fragile plants that survived fossilization—are extraordinarily significant.

“It was pretty exciting to see what was happening in another part of the world,” Michael enthused.

When asked why fossil leaves and insects interested him, he responded, “Plants and insects are the most diverse multi-cellular organisms on Earth, and their interactions are important components of food webs on land. By studying insect feeding damage on fossil leaves, we can learn how insects and plants responded to major environmental changes in the past and have a better idea of how they may be affected in the future.”

“This is what I’m interested in continuing doing. This is a relatively newer field within paleontology, so there are lots of projects to pursue, lots of periods of time in the ancient past where we don’t know much about how insects and plants were interacting.”

“The Cretaceous-Paleogene extinction was a major event in the history of life and the most recent of the big mass extinctions. The plants and animals that we see today are all descended from organisms that survived this asteroid impact. We observed a faster recovery of plant-feeding insects in the Southern hemisphere—in Patagonia—compared to the Northern hemisphere—[in WINA.]  These patterns from the early Paleocene may be related to biodiversity patterns that we see today.”



Leaf mine made by a larval insect that fed on tissue within the leaf. The fossil is ~65 million years old and from the Palacio de los Loros 1 fossil site in Patagonia, Argentina; photo and caption courtesy of Michael Donovan. 


An absolutely ENORMOUS thank you to Michael Donovan for making so much time to answer my questions, both in email and by phone.  The number of pictures he sent, and their detailed captions, was AMAZING.  I did not include them all here. I encourage you to read the paper done by him and his colleagues to see how many and beautiful they are. THANK YOU, MICHAEL!!



  1. Donovan, M. P., Iglesias, A., Wilf, P., Labandeira, C. C. & Cúneo, N. R. Rapid recovery of Patagonian plant–insect associations a er the end-Cretaceous extinction. Nat. Ecol. Evol. 1, 0012 (2016).
  2. Carvalho MR, Wilf P, Barrios H, Windsor DM, Currano ED, Labandeira CC, et al. (2014) Insect Leaf-Chewing Damage Tracks Herbivore Richness in Modern and Ancient Forests. PLoS ONE 9(5): e94950. doi:10.1371/journal.pone.0094950
  3. Monocots versus Dicots, University of California Museum of Paleontology
  4. Museo Paleontológico Egidio Feruglio, Trelew, Argentina
  5. Check out more research done in Patagonia! Patagonia Paleofloras Project


Museo Paleontológico Egidio Feruglio

Museo Paleontológico Egidio Feruglio, home to the fossil leaves used in this paper and many other exciting fossils; photo by Pedrochubut (Template:MEF Photo) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons


Researching Fossil Ungulate Communities


Alces alces (moose), Porkkala, Finland; photo courtesy of Juha Saarinen

In their paper “Patterns of diet and body mass of large ungulates from the Pleistocene of Western Europe, and their relation to vegetation,” published this past September in Palaeontologia Electronica, Juha Saarinen, Jussi Eronen, Mikael Fortelius, Heikki Seppä, and Adrian Lister investigate fossil ungulate communities found in England, Ireland, and Germany.

Not fossil ungulates, fossil ungulate communities.

The variety of fossils studied is just one of the exciting elements of their research.  Rather than focusing on a single species—which, given the limitations of the fossil record, is usually the case—they studied groups of fossils from at least 14 different ungulate species from the Middle to Late Pleistocene.

“[W]e are now at a point,” wrote Juha Saarinen, lead author of the paper, in an email, “where enough fossil material of ungulates and pollen records have accumulated to enable such a large scale quantitative comparison of body size and diets of ungulate with local vegetation patterns in the past as we did. Comparing vegetation proxies and mammal ecometrics from fossil data using such quantitative statistical analyses as we did has, to our knowledge, never been attempted before, so that is probably the most novel achievement of this study.”

The ungainly name of ‘ungulate’ refers to hooved animals: even-toed and odd-toed (Artiodactyla and Perissodactyla, respectively). Examples include horses, deer, moose, rhinoceros, bison, pigs and hippopotamuses.


Brontops tyleri (a type of brontothere and a Perissodactyl) at the Beneski Museum at Amherst College, Massachusetts.   Brontotheres survived until the Eocene, an era that ended approximately 30+ million years BEFORE the Pleistocene, so this animal–although an ungulate–was not part of this study. Picture taken by the author of this blog


Using mesowear on the fossil teeth, they were able to determine information about their diets (from browsing to grazing), and by comparing this data with the pollen record associated with the areas in which these fossils were found, they were able to tell whether they ate more browse or grass in either open or closed environments. Body mass for these fossils was calculated and then compared to the diet of these animals.

They were searching for answers to how these species adapted to the environment in which they lived.  How did their body size relate to the vegetation available? Was their body size influenced by possible predators or by other members of their species? (In other words, were they bigger to intimidate predators or were they smaller because they lived in expansive herds?) Or was thermoregulation the single determining factor in how big these animals became, as has been proposed in earlier studies?


Beneski - Irish elk

Megaloceros giganteus (otherwise known as Irish Elk and an Artiodactyl) in between a mastodon and a mammoth fossil at the Beneski Museum at Amherst College, Massachusetts; picture taken by the author of this blog


It interested me to learn that they relied on what I rather simplistically referred to as the ‘physical observation’ of fossils.

Mesowear analysis looks at the wear and shape of fossil teeth.  Various plant material affects tooth-wear in distinctly different ways, which can be seen both on the teeth themselves and in the way the teeth have evolved.

To be clear, “this is specifically wear-induced shape, not the original shape of the unworn teeth,” Juha added. “In other words, mesowear is the change in the shape of the teeth as they get worn, and different food items cause different worn shape to develop (browse maintains high and sharp features on the tooth surface, whereas grass “grinds” them down leading to them to progressively wear down lower and more blunted the more there is grass in the diet).”


Examples of a mammoth tooth — used to eat mostly grasses and sedges — and a mastodon tooth — used to eat trees and shrubs. Notice the very different shape of these teeth for very different types of vegetation. Proboscideans such as mammoths and mastodons were once grouped in with ungulates, but this has changed. Picture taken at the Harvard Museum of Natural History by the author of this blog.


Obtaining data about the pollen record (non-arboreal pollen percentages, or NAP %) meant researching published information and connecting that information with the related fossil sites.

The mathematical work behind all of this–determining mesowear, animal body size, and then relating this to the available pollen record—is staggering.

Surely, I thought, isotopic analysis would have been a much easier way to obtain information about each fossil’s diet at least.  Especially given that the pollen record isn’t always available, or—in one case—runs the risk of being skewed by the defecation of Pleistocene hippopotamuses that grazed in the area.  Why, I wondered, did they rely on methods that seemed considerably more labor-intensive and potentially (to my understanding) less accurate?

“There are a number of reasons for this,” Juha explained. “First, we wanted to obtain as much palaeodietary data as possible, comprising as complete ungulate communities as possible, and this meant dealing with very large samples of fossil molar teeth. Taking isotope samples from all those teeth would have been laborious, time consuming and expensive, not to mention also slightly destructive to the fossil specimens.


Cervus elaphus (Red Deer, Artiodactyl) at Richmond Park, London; photo courtesy of Juha Saarinen. Red Deer are one of the most extensively studied animals today. You can read about another study that references Red Deer in this post.


“Second, stable isotopes work best at resolving herbivore diet compositions in tropical areas where carbon isotope composition reflects roughly the proportions of C4/C3 –photosynthesizing plants (roughly grass vs. browse) in diet, but outside tropical areas all plants, grasses included, are C3 photosynthesizing and the carbon isotope composition varies also considerably according to so called canopy effect (open vs. closed environment), not just according to diet, and thus isotopes would not have allowed us to estimate the amount of grass vs. browse in the Pleistocene European ungulates as consistently and quantitatively as we could with mesowear analysis.

“Third, mesowear has been specifically shown to reflect average grass vs. browse compositions in the diets of ungulate populations, without being significantly obscured by other environmental variables, such as climate or environmental openness (e.g. Louys et al. 2012, Kaiser et al. 2013). Even if mesowear is a ‘physical observation’ as you say, it has been shown to specifically reflect the amount of abrasive dietary items (mostly grass) in herbivore diets.”

The authors focused on fossil-rich sites, where they could study between 3 – 10 fossils of each species.  They made sure to include species that were browsers, grazers and mixed-feeders.


Screenshot of Figure 1 from “Patterns of diet and body mass of large ungulates from the Pleistocene of Western Europe, and their relation to vegetation.” Palaeontologia Electronica19.3.32A: 1-58


“I owe thanks to my co-authors who knew much of the available European Pleistocene mammal collections already, having experience on working on them for many years,” Juha responded when asked how they knew of or had access to so many fossils.

Adrian Lister from the Natural History Museum of London in particular has a huge amount of knowledge and experience about Pleistocene mammal collections.

“I was also in contact with the curators of the museum collections, who gave me valuable information about the how much and what kind of material they have. Also, information about important fossil finds and numbers of specimens found have often been published before in scientific journals.

“The authors of this paper represent different fields of research experience on the various aspects of the study. I started to work on this research as a part of my PhD work, and I originally planned it with my PhD thesis supervisors Mikael Fortelius, Jussi Eronen and Heikki Seppä from the University of Helsinki.

“During the work, I visited the Natural History Museum of London, where I worked together with Professor Adrian Lister, whose expertise on British Pleistocene mammals, the NHM fossil mammal collections and mammal palaeoecology in general were very important for this work.”


Image of Professor Adrian Lister, Natural History Museum of London, with the mummified baby mammoth, Lyuba; photo courtesy of the Natural History Museum of London for this post.


This work was not without its challenges.  As with any study of fossils, there are limits to the number of fossils available.  While pollen record availability has increased, there is still so much more to be discovered.  And although some species–based on extant examples–do not exhibit sexual dimorphism in body size, the sex of most of the fossils they studied was indeterminate.

“Indeed, these were some of biggest challenges in this study,” Juha acknowledged, “but they were expected and nothing much could be done to completely avoid them. I would add that it was often challenging to connect the fossil mammals with associated pollen records, especially when the fossil pollen was not obtained directly from the mammal fossils. To succeed in this study, it was important to analyze lots of data in order to overcome these problems, and to ensure that the main results and conclusions of this study are robust despite of them.”

The authors of this paper considered numerous variables in their research, and they suggest that ungulate size has a lot to do with a number of factors.  This might seem obvious, but such has not been the result of past studies.  In particular, Bergmann’s rule, which stipulates that body size corresponds largely to thermoregulation (i.e.: big body size is the result of living in colder environments), has been supported before.


Bison bonasus (Artiodactyla), Kraansvlak, Netherlands;photo courtesy of Juha Saarinen. 


“[T]here has been a lot of discussion as to what ultimately explains the tendency of some (but not all) organisms to be larger in cold climate. This was actually one of the main questions I discussed in my PhD thesis,” wrote Juha. “Already in 1950s some researchers (e.g. Scholander 1955, Irving 1957, Hayward 1965) pointed out that increase in size alone would not give a large enough benefit for thermoregulation in cold climates, especially considering that mammals have far more effective mechanisms of keeping warm, such as thick fur.

“Since then, many authors have noted that while there is a tendency of mammals being larger in higher latitudes, there are a number of exceptions to this ‘rule’ and heat conservation alone would not explain it.

“However, body size in mammals does correlate with food quality and availability and this seems to explain most of the body size patterns observed in mammals (e.g. Rosenzweig 1968, Geist 1987, Meiri et al. 2007, McNab 2010). For example, many herbivorous mammals tend to be larger at higher latitudes because food quality is better there (e.g. because of fertile soils created by glacial erosion and because plant defense mechanisms are lower), and thus predators eating them also tend to be larger there, but for example brown bear body mass does not correlate with latitude but with distance to nearest salmon spawning areas. On the other hand, population density also affects body size through resource availability: individual body size has been noted to decrease in many species of mammals when population densities are high leading to increased intraspecific resource competition (e.g. Wolverton et al. 2009).”

The authors of this paper argue that environment–climate, open or closed vegetation, food availability and quality–and species social structure–large or small herds–affect body size.

“[T]here are many (often interconnected) factors which together affect body size,” Juha explained. “This makes it quite complicated and challenging to study what ultimately regulates body size in mammals (and other organisms).

“In fact, our results do not support Bergmann’s rule as such, because even if our analyses show that larger sizes seem to occur in some species in open environments, this is not because of low temperature, as some of the open environments were in fact quite warm. Also, we often see that when one species was particularly large in an environment, another species was particularly small under those same conditions. E.g., we found out that red deer (Cervus elaphus) tends to be large in open environments, but wild horse (Equus ferus) tends to be small in those same environments. Thus, our results do not support the assumption of Bergmann’s rule or any other “single-cause” explanation for ungulate body size variation.

“What ultimately regulates ungulate body size is primarily food quality and availability, which is affected by the interplay of vegetation structure (regulated by environmental temperature, precipitation and soil fertility), interspecific resource competition (depending on the presence of competing species) and intraspecific resource competition (depending on population density). For example, species with large population densities in open environments, such as reindeer, bison and wild horses, could be small under those conditions because of increased intraspecific resource competition, whereas species with smaller population densities in open environments, such as red deer are large under such conditions, e.g. because of abundant, high-quality food and diminished plant defense mechanics. This is also the main conclusion concerning our results of Pleistocene European ungulate body size variation.”

“I think that studying how mammals in the past interacted with their environments is important for understanding how these interactions work in general,” he concluded. “At present, environments and their mammal faunas are so heavily influenced by human activities, and they have lost so much of their original diversity, that I believe that we simply need to study fossil mammals and their palaeoenvironments to better understand how these things have worked and ‘should usually work’ in nature.”


Equus ferus (Mongolian wild horse and Perissodactyl), Lippeaue, Germany;photo courtesy of Juha Saarinen. 

It was a great honor and pleasure connecting with Dr. Juha Saarinen!  Reading this paper and gaining more insight about it from him was absolutely fascinating!  An enormous thank you to him for all of his generous help!!

Additionally, Dr. Saarinen was extraordinarily kind and helpful in clarifying points about the research that I had misunderstood.  That is always appreciated.  THANK YOU!!


  1. Saarinen, Juha, Eronen, Jussi, Fortelius, Mikael, Seppä, Heikki, and Lister, Adrian M. 2016. Patterns of diet and body mass of large ungulates from the Pleistocene of Western Europe, and their relation to vegetation. Palaeontologia Electronica 19.3.32A: 1-58 palaeo-electronica.org/content/2016/1567-pleistocene-mammal-ecometrics

Fossil plant defenses and the rise of African savannas


Endangered Rothschild Giraffe bending over eating the leaves from a small Acacia tree in Lake Nakuru, Kenya, Africa – notice the thorns!; photo: David Gomez, from Getty Images


We are still a long way from understanding the animals* around us, but in many regards, it’s a lot easier to infer the emotions and actions of other mammals than it is to grasp anything about plants.

I know, for example, when my cats want attention, when they’re hungry, and—especially when one of them ambushes my legs with her furry paws—when they want to play.

I can’t say the same for my plants.  I’m not sure I ever think of them in terms of having emotions.  Am I concerned with their growth? Absolutely.  Do I make sure to water and feed them appropriately?  Yes.

But I suspect most of us think of plants in a completely different way than we think of animals.

This particular view of life on our planet was expressed in “Jurassic Park.”  After their initial introduction to the dinosaur park created by John Hammond and his team, the invited scientists gathered for lunch.  Mathematician Ian Malcolm (played by Jeff Goldblum) expressed his doubts and concerns about the park.  This led the others to offer their opinions as well.  Paleobotanist Dr. Sattler (played by Laura Dern) stated:

“Well the question is: how can you know anything about an extinct ecosystem?  And, therefore, how could you ever assume that you can control it?  You have plants in this building that are poisonous. You picked them because they look good, but these are aggressive living things that have no idea what century they’re in, and they’ll defend themselves. Violently, if necessary.”

Ellie Sattler (Laura Dern) - Jurassic Park - Universal Studios

Dr. Ellie Sattler (played by Laura Dern), Jurassic Park, 1993, Universal Studios

That very statement (albeit in a movie) challenges the conventional view of plants on this Earth.  Rather than simple sedentary life forms, it suggests that plants are more complex, engaging in the world around them, just as we know animals do.

And once you start thinking about plants defending themselves—taking an active part in the world around them rather than simply existing and having things done to them—it changes how you look at everything around you.

Scientific research into the realm of extant plant communication, defense and even participation in community is relatively new.  Dispersal of that scientific knowledge to the general public is even newer.

Remarkably—given how much we have yet to learn about existing plants—scientists from South Africa, Canada and the United States published research regarding the possible origin of African savannas, an origin that has roots** in plant defense millions of years ago.

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An example of an African savanna: Mt Kilimanjaro & Mawenzi Peak, clouds, grassland, and Acacia; photo: 1001slide, from Getty Images


A significant amount of land in the Miocene belonged to savannas, pushing forests to recede where they once flourished.  Some have attributed this to climate change; others to a change in the amount of carbon dioxide in the atmosphere.

The authors of “Spiny plants, mammal browsers, and the origin of African savannas”, published in PNAS this September, found a striking correlation between savannas, the evolution of plant spinescence, and the rise of ancient bovids.

“Savannas grow in climates and on soils that also support closed forests. So there is no ‘savanna climate’ uniquely predicting where they occur. Their rather abrupt appearance in the Miocene implies the emergence of new ecological processes favouring grasses at the expense of forest trees,” wrote Dr. William Bond of the University of Cape Town, one of the co-authors of the paper.

But how to even begin?  The fossil record, in general, doesn’t contain everything scientists would need to completely recreate any particular ancient ecosystem.  Where one might find animal fossils, that same rock may not preserve plant fossils, and vice versa.

The authors drew upon knowledge of today’s African megafauna, how it impacts existing ecosystems, and compared that with information about African fossils from the Miocene.  Elephants, for example, are known to knock down trees.  Antelopes, sheep, deer and other browsers  maintain open ecosystems today. Could their ancient ancestors have done the same?

“We had worked on fire as a major factor promoting [the spread of savannas,]” explained Dr. Bond. “We used a marker, underground trees, of fire-maintained higher rainfall savannas to explore their origins. Our dates of the emergence of ‘fire savannas’ in Africa were remarkably convergent with dates for ‘fire savannas’ in South America (cerrado) and also consistent with the sparse fossil record (Maurin et al 2014, New Phytologist and Pennington and Hughes, same issue with a commentary on our paper). In drier savannas, grasses do not build up enough fuel to burn regularly.  We wondered whether mammal browsing may help maintain open savanna vegetation where fire is less important. We needed a marker of savannas with high herbivore pressure and chose spiny plants.”
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A sparrow sits amongst the large white thorns of an Acacia tree, Kenya; photo: Richard du Toit, from Getty Images


In other words, fire was originally thought to be the reason behind the rise of savannas.  Evidence of fire has been found in fossil charcoal,  in paleosols and in fossil teeth.  The authors of this paper expanded their research to include fossil mammals.  Knowing that today’s savanna plants defend themselves with thorns from browsing mammals, the authors wanted to see if these same defenses occurred in fossil plants.

They had an incredible tool to help with this task: the African Centre for DNA Barcoding.


Types of thorns - Supplemental info, Charles-Dominique et al

Fig. S1. Types of spines. (A) Prickles: Zanthoxylum davyi. (B) Straight stipular spines: Vachellia robusta. (C) Straight stipular spines and stipular hooks: Ziziphus mucronata. (D) Straight thorns: Gymnosporia harveyana. (E) Hook thorns: Scutia myrtina. (F) Straight stipular spines and stipular hooks: Vachellia tortilis. (G) Stipular hooks: Senegalia nigrescens. Es, epidermic spine; L, leaf; Ls, leaf scar; Ss, stipular spine; T, thorn (i.e., branch with a sharp tip); from Charles-Dominique et al. http://www.pnas.org/cgi/content/short/1607493113


What they discovered was that savannas existed before the large-scale evidence of fire, rather than simply because of it.  Thorns didn’t appear until well after the rise of proboscideans and hyracoids, indicating that neither of these species triggered the need for that specific physical defense.  Interestingly, the rise of ancient bovids (and possibly ancient giraffoids) corresponds to the emergence of thorns in the Miocene.  Ultimately, they found that spinescence evolved at least 55 times.

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Browsing impala — a type of modern antelope (bovid); photo by: annick vanderschelden photography, from Getty Images

“One might think that spines are a general defence against an archetypal mammal herbivore,” Dr. Bond wrote. “So we were most surprised at the late emergence of spines in African trees. We speculate that spines don’t work to limit food intake by proboscideans (a reasonable guess based on extant elephant feeding) and also hyracoids. But just why hyrax don’t select for spines is an intriguing puzzle. Observations on the remaining few hyrax species may be informative.”

“Physical plant defences are far less studied than chemical defences. They seem to resemble more plant-pollinator or plant-disperser interactions in being adapted to particular types of herbivore with particular modes of feeding. Spines don’t work for monkeys, for example, with their ability to pluck leaves with their fingers and manipulate branches. I have also worked on plant physical defences against extinct giant browsing birds (moas in New Zealand, elephant birds in Madagascar). They are utterly different from spines and exploit the limitations of beaks and the ‘catch and throw’ swallowing mechanism of the birds.”

“Molecular phylogenies dated with fossils were our main tool for exploring the past,” he continued. “Molecular phylogenies for mammals have been controversial tending to give much older dates for lineages than the fossil evidence. We used a recent phylogeny for bovids produced by Bibi (2013, BMC Evol Biol) using many more fossils than usual for calibrating the molecular phylogeny. Christine Janis, in an early e-mail exchange, kindly pointed us to the excellent book on Cenozoic mammals of Africa (Werdelin, Sanders 2010), among others, for help in reconstructing herbivore assemblages at different times.”


Spiny species distribution - Charles-Dominique et al PNAS

Screenshot of species distribution and environment correlates; from Charles-Dominique et al. http://www.pnas.org/cgi/content/short/1607493113


The sheer size and scale of the African continent is overwhelming.  This recent paper doesn’t focus on part of it; it encompassed the entire continent. When I asked Dr. Bond if this project was as enormous as it seemed, he wrote, rather amusingly, “Yes! Very daunting for me. People used to publish papers analyzing environmental correlates of single species distributions. Our team did the analyses for 1852 tree species. The mammal data was also enormous. Seems the younger generation is used to these vast data sets. I was amazed at the speed at which results became available.”

The list of websites cited in this paper (http://www.ville-ge.ch/cjb/; http://www.theplantlist.org; http://www.naturalis.nl/nl/; http://www.gbif.org; http://www.fao.org/home/en/) and the information those websites provide prompted me to ask whether it was fair to say that this paper could not have been written at an earlier point in time (without that online data). I also wondered if it was fair to say that science (in instances like this, where researchers share data online and make it accessible to others worldwide) is becoming more cooperative or team-oriented.

He responded: “You are absolutely right about ‘more cooperative and team-oriented’. The availability of massive data sets, and the tools to analyze them, has made analyses such as ours possible. Our team included people with diverse skills and knowledge. Hard to see how one or two researchers could have pulled this off.”

“The study is the outcome of several years of collaboration between systematists led by Prof Michelle van der Bank of the University of Johannesburg, ecologists working with me at the University of Cape Town, and a phylogenetic specialist, Prof Jonathan Davies from McGill University in Canada and an old friend of Michelle.

“Michelle, who heads up a DNA barcoding unit, had invited me to work with her group on ecological questions that could be addressed with molecular phylogenies. It has been a wonderful collaboration.

Tristan Charles-Dominique worked with me as a post-doc bringing new skills in the French tradition of plant architecture. He made great strides in understanding plant traits of savanna trees. His work on physical defences against mammal herbivores is the most original and important contribution since the 1980s in my view.

Gareth Hempson,  also an ex post-doc with me, had spent a great deal of effort compiling a map of African mammal herbivore abundance, and species richness, as it would have been ~1000 years ago (Hempson, Archibald, Bond 2015, Science). He combined mammals into functional groups which helped enormously in simplifying ecological functions of different groups. His participation allowed us to link the key mammal browsers to concentrations of spiny plant species.”

“It’s a rare combination of people to address a big question.”

Embed from Getty Images

Gerenuk, or giraffe antelope (Litocranius walleri) feeding from a bush; photo: 1001slide, from Getty Images



*including our own species!

**an unintended pun

It was a great honor and a great pleasure connecting with Dr. William Bond, who–despite a very busy schedule and an unfortunate stay in the hospital–responded so quickly to my inquiries!  Thank you so much, Dr. Bond!  The research by you and your colleagues has opened a fascinating door for me!!



Spiny plants, mammal browsers, and the origin of African savannas,Tristan Charles-Dominique, T. Jonathan Davies, Gareth P. Hampson, Bezeng S. Bezeng, Barnabas H. Daru, Ronny M. Kabongo, Olivier Maurin, A. Mathuma Muaysa, Michelle van der Bank, William J. Bond (2016), PNAS, vol. 113 no. 38. DOI: 10.1073/pnas.1607493113

What Plants Talk About, Nature, PBS, 2013

Savanna fire and the origins of the ‘underground forests’ of Africa, Olivier Maurin, T. Jonathan Davies, John E. Burrows, Barnabas H. Daru, Kowiyou Yessoufou, A. Mathuma Muaysa, Michelle van der Bank, William J. Bond (2014), New PhytologistDOI: 10.1111/nph.12936

Jurassic Park, (movie) Universal Studios, directed by Steven Spielberg, 1993


How Trees Talk to Each Other - Dr. Suzanne Simard TED


Further FASCINATING information on contemporary plants

How Trees Talk to Each Other, Suzanne Simard, TED talk, June 2016

Published papers by Suzanne Simard, University of British Columbia

The Hidden Life of Trees, Peter Wohlleben, 2016, Greystone Books

How Trees Fight Back, Dave Anderson, Chris Martin, and Andrew Parrella, “Something Wild,” NH Public Radio, September 23, 2016

The Herbivore Elicitor-Regulated1 (HER1) gene enhances abscisic acid levels and defenses against herbivores in Nicotiana attenuate plants, Son Truong Dinh, Ian T. Baldwin, Ivan Galis, Plant Physiology,162, 2106-2124, 2013. doi:10.1104/pp.113.221150.

Plant Kin Recognition Enhances Abundance of Symbiotic Microbial Partner, Amanda L. File, John Klironomos, Hafiz Maherali, Susan A. Dudley, PLOS One, September 28, 2012.

Fitness consequences of plants growing with siblings: reconciling kin selection, niche partitioning and competitive ability, Amanda L. File, Guillermo P. Murphy, Susan A. Dudley, Proceedings of the Royal Society B, vol: 279, issue 1727, 2012. doi: 10.1098/rspb.2011.1995


Hidden Life of Trees - Peter Wohlleben