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.”

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

 

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*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!!

 

References

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

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Stegodon: Does this ancient elephant have origins in Asia?

So much has been said in recent years about the wealth of fossils in China. Almost all of it about dinosaurs: exciting new species, feathered fossils, nest upon nest of dinosaur eggs.  There is no doubt that China holds exciting clues to the history of our planet; one has only to wait to hear of the next discovery.

Within the past few months, yet another exciting find was revealed, but this time about a little known mammalian ancestor: Stegodon.

 

Stegodon by artist Hannah Stephens

Painting of a Stegodon by artist Hannah Stephenshannahleestudio.com.

 

The name Stegodon, to me, evokes ‘dinosaur’, not ‘mammal,’ but this was, indeed, an ancient animal.  Its fossils resemble those of other similar mammals, from mastodons to mammoths to today’s elephants.

 

 

Alexandra van der Geer - shrinking elephants

Figure 1: Reconstruction of four insular dwarf proboscideans with their respective mainland ancestors. Mainland proboscideans: 1, Palaeoloxodon antiquus; 2, Mammuthus columbi; 3, Stegodon zdanskyi [stegodon found in China]. Insular proboscideans: 4, Palaeoloxodon ‘mnaidriensis’; 5, Palaeoloxodon falconeri; 6, Mammuthus exilis; 7, Stegodon aurorae [a type of dwarf stegodon found in Japan]. Based on skeletons at Museo di Paleontología, University of Rome, Italy (1), American Museum of Natural History, New York (2), Taylor Made Fossils, U.S. (3), Museo di Paleontología e Geología G.G. Gemmellaro, Palermo, Italy (4), Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt, Germany (5), Santa Barbara Museum of Natural History, Santa Barbara, U.S. (6), Taga Town Museum, Honshu, Japan (7). Photos 1–2, 4–7 George Lyras, photo 3 courtesy of TaylorMadeFossils.com, reproduced here with permission.

From The effect of area and isolation on insular dwarf proboscidea by Alexandra A. E. van der Geer et al; photo and caption courtesy of Dr. Alexandra van der Geer.

 

When Stegodon skulls with tusks attached have been found, many (but not all) of the tusks are close together–preventing the trunk (the ‘proboscis,’ from which this group gets its name; proboscis —> proboscidea) from hanging between them.

They lived in what is now Africa and Asia, causing continued debate over its place of origin. Until recently, the oldest known Stegodon fossil, a 6.5+ million-year-old partial molar from Kenya, was described by William J. Sanders in 1999.  That record changed this past December when Dr. Hong Ao and his colleagues published their results dating the sediment in the Lanzhou Basin, China, from which a number of fossils–including that of a Stegodon–were found.

And that Stegodon was found to be between 8 – 11 million years old.

 

GSA Geologic Time Scale - Neogene

Detail of the Geologic Time Scale, created by the Geological Society of America.  Stegodon is believed to have existed between the Miocene to the Pleistocene, a relatively small segment of time in Earth’s overall history, but still considerably longer than that of our own species!  (You can view the time scale in much better detail here.) 

 

The fossils of the Stegodon, along with at least 5 other species, were actually found in the 1980s by Professor Xing Zhang of Northwest University in China.  Given the length of time between the fossil excavations and the recent dating of these fossils, one might wonder why determining the fossil age took so long.

Dr. Ao, a scientist at the State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, and his colleagues state that western China does not have suitable material for radiometric dating, an oft-used method for this purpose.

When I asked why this was so, Dr. Ao replied by email, “Because volcanic activities are rare in western China during the late Cenozoic, it is difficult to find  in situ tephros or tuffs for radiometric dating (e.g., 40Ar/39Ar dating).”

Instead, they conducted a magnetostratigraphic study, one in which they determined the age of the rock through the polar reversal record.  Combining this with analysis of the fossils provided evidence that this Stegodon is 2 – 5 million years older than that of the Kenyan partial molar.

“We are indeed surprised by our dating results,” Dr. Ao continued, “which document that the Lanzhou Stegodon is the oldest Stegodon worldwide, although the Stegodon  fossil [was] not discovered by us. However, our dating results document it to be the oldest known Stegodon fossil.”

Dr. Hong Ao 1

 

Dr. Hong Ao 2

Dr. Hong Ao 3

Dr. Hong Ao 4

Images of Professor Yongxiang Li (from Northwest University) and his master student as well as several employed workers who helped to excavate mammal fossils, Lanzhou Basin, China; photos courtesy of Dr. Hong Ao.

 

indricotherine fossil

indricotherine fossil2

indricotherine fossil3

Images of indricotherine fossils found in Lanzhou Basin, China; photos courtesy of Dr. Hong Ao.

 

Dr. Ao himself has been working with fossils in the Lanzhou Basin for 5 years.  When asked how  he and his co-authors chose to work together on this recent paper, he wrote, “I have collaborated with them on broad subjects before, thus I [invited] them to join [in] this research.”

Finding information about this extinct species is difficult.  Unlike mammoths or mastodons, Stegodon does not appear to be a popular ancient animal.

Fortunately, Dr. Alexandra van der Geer–paleontologist, indologist, ethno-zoologist and author –has not only studied this species, she very generously made herself available for questions.  Currently, Dr. van der Geer is an Associate Researcher at both the National and Kapodistrian University of Athens and the Naturalis Biodiversity Center in the Netherlands. She is part of the Isolario project, a project that studies biodiversity and cultural evolution within an island context.

When I asked why there was such a dearth of information on Stegodon, she wrote, “We can think of several reasons for this.”

“First of all, stegodons typically are the elephants of Southeast and East Asia, where most countries did not have the resources and opportunities most Western countries had when it comes to scientific research and excavations. These activities are costly, and since they don’t have a direct use in the sense that they don’t advance the medical, technical or economic levels of a country, they have, understandably, a lower priority. Furthermore, because of this region, half the publications (especially before the 1990s or so) you can find are in Chinese or Japanese, which is not very helpful to the [English-speaking] world.

“Secondly, stegodons are forest elephants. Forest areas are very unlikely places for the long-term preservation of organic materials: everything is eaten, digested or otherwise broken down into smaller components in no time. The tropical (warm, humid) climate of these forests is not helpful either, as decomposition is much faster here. Stegodon remains only have a chance to be preserved when (1) they are covered fast, such as with river sediments, volcanic ashes etc., (2) or are in an oxygen-free environment, such as sunken deeply into a swamp, (3) or were deposited in a natural fridge such as limestone caves where they are gradually covered in clayish sediment or [travertines]. The same is valid for Palaeoloxodon, the Old World fossil elephant, but Europe has many limestone caves, which are excellent for preservation (for a nice [travertine]-preserved negative skull, see Stuttgart museum: skull cast SMNS nr. 32888 from Bad Cannstatt).

“As you can deduct from these preservation issues, it is more likely to find molars and tusks than skeletal material, which is much softer. The vast majority of proboscidean findings all over the planet consists of molars and tusks, and that is not for nothing. Inherently this means that there is much more information about their dentition and diet than about their bodies.”

I was interested in understanding why Stegodons are portrayed as hairless animals, so very similar to contemporary elephants.  Was this just an artistic guess?

“The hairlessness of stegodons is not an artistic guess but a scientific guess instead,” Dr. van der Geer answered.  “Very large animals with thick skins (pachyderms) in a (sub)tropical environment are unlikely to have a significant hair covering. Elephants lost their hairs secondarily. The information for hair growth is not lost, and baby elephants still have a thin, woolly coat. Woolly mammoths lived in the cold, temperate zones, and needed hair, so they were covered in a thick layer of hairs, and for this is evidence (mummies preserved in the permafrost), but the other mammoths (M. meridionalis, M. columbi, M. exilis, etc.), [did] not, and it’s generally assumed that they had a light coat fitting to the temperate zones.

“Tropical and subtropical stegodons almost certainly did not have any coat that’s worth mentioning. Stegodons of temperate zones, however, may have been more hairy. Indeed, the lack of hairs makes them look more like today’s elephants.”

 

Alexandra van der Geer - Stegodon ganesa-model-I.Vjdchauhan-SiwalikHills

Photo of the two life-size models of Stegodon ganesa;photo courtesy of Dr. Gerrit van den Bergh (University of Woolongong, Australia); special thanks to Dr. Alexandra van der Geer.

 

“Note, however, that the proboscis is carried very differently. Their tusks are set very close to each other, so the proboscis doesn’t fit in between as in modern elephants, Asian and African alike. This means that the mobility of their proboscis was more restricted, relative to their living relatives.”

 

Alexandra van der Geer - Flores-excavation-31-stegodon-florensis

Fossils of Stegodon florensis insularis, from Flores, Indonesia; photo courtesy of Dr. John de Vos (Naturalis, the Netherlands); special thanks to Dr. Alexandra van der Geer.

 

Alexandra van der Geer - stegodon-timorensis-mandible

Mandible (and holotype!) of  Stegodon timorensis; photo courtesy of Eelco Kruidenier (Naturalis, the Netherlands); special thanks to Dr. Alexandra van der Geer.  Anyone familiar with proboscidean teeth and jaws will recognize the similarities instantly.

 

But how do we know that Stegodon–a rather enormous animal–evolved into something smaller?

“[D]warfs and giants are relative. Something can be a dwarf, yet have a considerable size. When we speak of dwarf stegodons, we mean stegodons that are much smaller than their ancestors. For this, you have of course to have identical or otherwise similar elements from both the descendant and the ancestor in order to compare reliably,” she continued.

“The expectation is that dwarf stegodons must have existed on the islands, following the so-called island rule, according to which large animals get smaller in isolation. There is sound evidence that this rule still stands, and is even more pronounced for fossil species (see Lomolino et al., 2013, in Journal of Biogeography).

“Indeed, the many fossil molars from the Southeast Asian islands (‘Wallacea’) are all much and much smaller than the same molars from their mainland ancestors (see Van den Bergh, 1999). True, you first have to know what is the ancestor, and for this you need information about morphology, or how the molars, tusks, skulls and postcranial elements look like. After that, you compare the sizes.

“Note that if a molar is, for example, half the length of the same molar of its ancestral species, the body weight of that animal must have been a quarter of that of its ancestor! (the cubic law: linear reduction 50% means volume reduction 50% of 50%).”

Alexandra van der Geer - Flores-stegodon-florensis

Molar of Stegodon florensis; photo courtesy of Dr. Gerrit van den Bergh (University of Woolongong, Australia); special thanks to Dr. Alexandra van der Geer.  

 

“The most interesting dwarf stegodon is Stegodon sondaari, named after the Dutch palaeontologist Paul Yves Sondaar (1934-2003), expert in fossil insular mammals. This stegodon lived on the island of Flores about a million years ago, and weighted only about 15% of the weight of its ancestral species, S. elephantoides (see Van der Geer et al., 2016, in Journal of Biogeography, doi:10.1111/jbi.12743).

“Sondaar’s dwarf stegodon is not the smallest stegodon, that honour goes to the Sumba stegodon (S. sumbaensis), of only 8% of the original weight. Sondaar’s stegodon is interesting because it may have witnessed the arrival of early humans, possibly the ancestors of the Hobbit, or Homo floresiensis. Its fossils are contemporaneous with primitive lithic artefacts, dated to about a million years ago (see Brumm et al., 2010, in Nature 464, pp. 748–752).”

 

Alexandra van der Geer - Sumba-stegodon-sompoensis-holotype-in-Naturalis-Leiden-2

Molar (and holotype!) of Stegodon sompoenisphoto courtesy of Dr. Gerrit van den Bergh (University of Woolongong, Australia); special thanks to Dr. Alexandra van der Geer.  

 

“[R]ecently,” she concluded, “one of the island dwarf stegodons (S. timorensis of Timor) has been dated to about 130 thousand years ago (see Louys et al., 2016, in PeerJ 4:e1788). This excludes, according to the authors, an anthropogenic cause for its extinction, because humans had not yet arrived at the island.”

 

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So many people helped with this blog post!  (But please remember that any errors are my own.)

Many, many thanks to Dr. Hong Ao (Dr. Ao Hong) from the State Key Laboratory of Loess and Quaternary Geology (Chinese Academy of Sciences) for his fascinating responses and the great images of fossil excavations in the Lanzhou Basin.  I am thrilled that he was willing to answer questions about his research and that of his colleagues! It was a great honor and a pleasure connecting with him!

I am indebted to Dr. Alexandra Van der Geer, who very kindly (and so very quickly–despite everything else she has going on!!) answered specific questions about Stegodon that I could not find anywhere else and who provided pictures of dwarf Stegodon fossils.  It was an equally great honor and pleasure connecting with her!

A mastodon-sized thank you to the amazing Dr. Katy Smith for providing needed and hard-to-find material on Stegodon fossils!

And an enormous thank you to artist Hannah Stephens for her depiction of a Stegodon as it may have appeared in life.  I am particularly moved by the warmth of its intelligent-looking eyes, and I love the tones within its skin.  I adore this picture.  I am grateful to have it in this post;  I am thrilled to have the actual painting hanging on my wall!  Please be sure to check out her artwork at: http://hannahleestudio.com or http://hstephens.blogspot.com

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References from Dr. Alexandra Van der Geer:

  1. Brumm A, Jensen GM, van den Bergh GD, Morwood MJ, Kurniawan I, Aziz F, Storey M (2010) Hominins on Flores, Indonesia, by one million years ago. Nature 464, 748–752.
  2. Lomolino MV, van der Geer AAE, Lyras GA, Palombo MR, Sax DF, Rozzi R (2013) Of mice and mammoths: generality and antiquity of the island rule. Journal of Biogeography 40, 1427–1439.
  3. Louys J, Price GJ, O’Connor S. (2016) Direct dating of Pleistocene stegodon from Timor Island, East Nusa Tenggara. PeerJ 4:e1788
  4. van den Bergh GD (1999) The Late Neogene elephantoidbearing faunas of Indonesia and their palaeozoogeographic implications; a study of the terrestrial faunal succession of Sulawesi, Flores and Java, including evidence for early hominid dispersal east of Wallace’s line. Scripta Geologica 117, 1–419.
  5. van der Geer AAE, van den Bergh GD, Lyras GA, Prasetyo UW, Due RA, Setiyabudi E, Drinia H (2016) The effect of area and isolation on insular dwarf proboscideans. Journal of Biogeography, doi: 10.111/jbi.12743

References used in this blog post:

  1. New magnetochronology of Late Miocene mammal fauna, NE Tibetan Plateau, China: Mammal migration and paleoenvironments; by Hong Ao, Peng Zhang, Mark J. Dekkers, Andrew P. Roberts, Zhisheng An, Yongxiang Li, Fengyan Lu, Shan Lin, Xingwen Li; Earth and Planetary Science Letters; 1o December 2015
  2. Oldest record of Stegodon (Mammalia: Proboscidea); by William J. Sanders; Journal of Vertebrate Paleontology; Vol. 19, No. 4, Dec. 13, 1999, pp. 793 – 797
  3. Fossil elephantoids, Awash paleolake basins, and the Afar triple junction, Ethiopia; by Jon E. Kalb; Palaeogeography, Palaeoclimatology, Palaeoecology; 1995, pp. 357 – 368
  4. The effect of area and isolation on insular dwarf proboscidea; by Alexandra A. E. van der Geer, Gerrit D. van den Bergh, George A. Lyras, Unggul W. Prasetyo, Rokus Awe Due, Erick Setiyabudi, and Hara Drinia; Journal of Biogeography; 11 March 2016.
  5. Magnetostratigraphy – concepts, definitions, and applications, by Cor G. Langereis, Wout Krijgsman, Giovanni Muttoni, and Manfred Menning; Newsletter on Stratigraphy, Vol. 43/3: 207–233, April 2010
  6. Mammoths and Mastodons of the Ice Age, by Adrian Lister, Firefly Books, 2014
  7. Mammoths, by Adrian Lister and Paul Bahn, University of California Press, 2007
  8. The Proboscidea: Evolution and Palaeoecology of Elephants and Their Relatives, Edited by Jeheskiel Shoshani and Pascal Tassy, Oxford Science Publications, 1996
  • Stegodontidae: evolutionary relationships by Haruo Saegusa, pp. 178 – 190, The Proboscidea: Evolution and Palaeoecology of Elephants and Their Relatives
  • Palaeobiogeography of late Neogene African and Eurasian Elephantoidea by Jon E. Kalb, David J. Froehlich, and Gordon L. Bell, pp. 117 – 123, The Proboscidea: Evolution and Palaeoecology of Elephants and Their Relatives

Dick Mol – Renowned Mammoth Expert: Fossil Hunting in the Sea

‘Fossil-hunting’ often brings to mind remote locations filled with rocks, sparse vegetation and a bright, merciless sun.

But Dick Mol–an internationally renowned paleontologist–is part of a team that regularly uncovers fossils in an unusual place: the ocean.

Dick MolDick Mol holding Ice Age bison skull found in the North Sea, image courtesy of Rene Bleuanus and Dick Mol

 His expeditions take place upon the North Sea, a large expanse of ocean between the East coast of the United Kingdom and the coasts of several other European countries such as the Netherlands, Belgium, and Germany up through to Norway.

 

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“The North Sea is very rich,” wrote Dick Mol in an email. “Ever since 1874, fishermen have brought large quantities of bones and molars ashore.”

He himself has written articles about these finds, describing how the area is routinely dredged, enabling large ships passage on this navigational route. This dredging is what helps uncover fossils deposited there so many thousands of years ago. Coupled with trawling—a method of fishing that pulls weighted nets along the sea floor—these fossils are then brought to the surface.

“I learned about the Ice Age mammal remains, trawled by fishermen,” he explained, “from the curator of the Geological and Mineralogical Museum in Leiden, now the NCB Naturalis (Netherlands Center for Biodiversity). At that time, the attic of the museum was full of large bones of trawled mammoth bones, skulls and lower jaws. It was very impressive.”

Trawling boat, Stellendam harborFisherman preparing trawling nets as the ship leaves Stellendam harbor for the North Sea, image courtesy of Hans Wildschut and Dick Mol

“I remember,” he continued, “that in November 1992 I brought the late Dr. Andrei Sher, a renowned mammoth expert from Moscow, to the museum. When he entered the large attic, he didn’t believe what he was seeing: perhaps one of the largest collections of isolated mammoth bones in the world. This was recorded by a film crew making a documentary on mammoths in the Netherlands. Once in a while, I rewatch this brief documentary again, and it gives me very good memories of a longtime ago.”

“When he entered the large attic, he didn’t believe what he was seeing: perhaps one of the largest collections of isolated mammoth bones in the world.” — Dick Mol, describing the reaction of Dr. Andrei Sher to a collection of mammoth fossils from the North Sea at the NCB Naturalis in the Netherlands

Known to the world as Dick Mol, his name is actually Dirk Jan Mol, and he has been researching mammoths and other Pleistocene fauna for decades. One cannot study mammoths without becoming acquainted with his name and his work.

In response to what prompted his career in mammoths, he wrote, “I grew up on the border with Germany. Around the town of Winterswijk a lot of different geological sediments and fossils can be found from the Triassic, Cretaceous, Oligocene, Miocene, Pliocene and Holocene eras. In different quarries and clay-pits you could collect fossils, but none were of mammoths or remains of other Ice Age creatures.”

“I have been, since 1968, fascinated by mammoths. In the literature, you could read that these prehistoric animals stood up to 5 meters at shoulder (which was exaggerated, of course). I wanted to know more about mammoths and their ancestors. I wanted to find my own mammoths, but it seems that the mammoth has found me!”

“I wanted to find my own mammoths, but it seems that the mammoth has found me!” — Dick Mol

His enthusiasm for the topic has lead him to become a visiting scientist in 1990 and 1994 at the Mammoth Site in Hot Springs, South Dakota—part of the “Visiting Scholar” program designed by Dr. Larry Agenbroad. He has co-authored numerous papers over the years, and his books include Mammoths (published 1993) and, more recently, Mammoths and Mastodons of the Haute-Loire (published 2010), a bilingual book he co-authored with French paleontologist, Frédéric Lacombat.

Scientists and explorers from all over the world have invited him to help excavate their discoveries: some of the most notable finds include the Jarkov woolly mammoth in Russia (Mammuthus primigenius), the Nolhac steppe mammoth in France (Mammuthus trogontherii), and parts of a mastodon skeleton in Greece (Mammut borsoni), in which the longest tusks found to-date were uncovered (502 cm in length).

Queen Beatrix of the Netherlands knighted him for his work in paleontology in 2000. In addition, he is President of Mammuthus Club International and has been involved in the international conference related to mammoth research for years.

His family’s personal collection of fossils exceeds 30,000 specimens that have been used for educational purposes and scientific studies.

Today, he is a Research Associate at the following institutions:

For all of his accolades and accomplishments, Dick Mol is a very accessible and kind man. One witnesses his infectious enthusiasm in these two videos about his work in the North Sea:

 

Trawling for Mammoths: http://www.bbc.co.uk/programmes/p01q0gfr

A Mammoth Task: http://www.bbc.co.uk/programmes/p01q29mg

 

“Over the years, tons and tons of bones have been trawled by fishermen in their nets,” he reiterated. “Between 1997 and 2003, we weighed the mammoth bones: 57 tons, not including 8000 mammoth molars (!) of woolly mammoths. The southern bight of the North Sea between the British Islands and the Netherlands is very rich in Pleistocene mammal remains. It is a real treasure trove.”

“Between 1997 and 2003, we weighed the mammoth bones: 57 tons, not including 8000 mammoth molars (!) of woolly mammoths. The southern bight of the North Sea between the British Islands and the Netherlands is very rich in Pleistocene mammal remains. It is a real treasure trove.”–Dick Mol

“In the meantime, I have organized 43 mammoth fishing expeditions on the North Sea using big beam trawlers. Quite spectacular and always a good catch. Doing these expeditions gave us very good insight into those areas that are very productive and those areas in which Pleistocene fossils are scarce.”

Given the enormous number of fossils brought up from dredging, it doesn’t take a lot of imagination to wonder whether there might be exciting fossil discoveries just waiting to be found if one could go even deeper.

“Yes, for sure,” he agreed. “Most of the bones trawled by the fishermen have been washed out of the seabed by currents. The Eurogully area, off the coast of the province of South-Holland, was dredged from 13 to 40 meters below sea level. At approximately 23-26 meters, there is a rich layer with bones and teeth from the Late Pleistocene. Deeper, there is a layer containing an interglacial fauna (110.000-130.000 BP) including Hippopotamusses and straight-tusked elephants. This is true for the entire southern bight of the North Sea.”

Private collector with femur of the so-called straight-tusked elepahnt, North Sea

Private collector with the femur of the so-called straight-tusked elephant from the North Sea,image courtesy of Hans Wildschut and Dick Mol

But the cost of such an underwater excavation might be prohibitive.

“Once, I used a diver on one of the expeditions. Visibility was very poor, and it was not successful. But some divers in the past have found some mammoth remains. Amongst others, a diver brought up a complete mammoth tusk.”

Aside from the need to desalinate fossils found in the North Sea, they are not physically treated any differently than fossils one finds on land. And despite the wealth of fossils found thus far, Dick Mol does not have any favorites.

“For me,” he wrote, “every bone, bone fragment or remnant is unique and tells us a story….”

Mammoth tibia, freshly trawled, with fish... (1)

Mammoth tibia freshly trawled from the North Sea with fish, image courtesy of Hans Wildschut and Dick Mol

Keep in mind, however, that these fragments and bones are not found together.

Paleontology is like detective work: terrestrial excavations include mapping by grid, pictures, and notes related to where each bone is found. All of these details help paleontologists better understand what species it is and what happened to that animal before and after it died.

The bones found in the North Sea are pulled up individually in a mass of fish and other debris.

Without any of the clues available to someone digging on land, this begs the question: can one determine to which species a bone belongs in isolation?

“[A]fter spending more than 40 years of my life identifying isolated skeletal elements (we have never retrieved a complete skeleton from the North Sea bed) again and again, using comparative collections, it is possible to identify the specimens as soon as they are on the deck of the vessel.”

“Sometimes,” he added, “I need to use literature, but in most cases, an experienced anatomist can do it right away.”

And what about the isolated teeth that have been found in abundance?

“[A]t least three different species of mammoths are well-documented: from the Early Pleistocene the southern mammoth, (Mammuthus meridionalis); from the Middle Pleistocene the steppe mammoth, (Mammuthus trogontherii); and from the Late Pleistocene the woolly mammoth, the icon of the Ice Age, (Mammuthus primigenius). The molars of these species are quite different and easy to tell apart from each other by an experienced specialist.”

Grooves and marks upon the bones give rise to questions about who or what caused them: humans or other Pleistocene animals? And how can one tell the difference?

“Hyena gnawing marks and other predators are well-known and, in general, easy to recognize. Of course, you need some training and experience. Sometimes, especially in large bones, one can see the deep grooves in the so-called material spongiosa caused by hyena (pre)molars. Hyena gnawing marks are very often found in the skeletal remains of woolly mammoths and woolly rhinoceroses. The ice-aged hyena was very common on the Late Pleistocene mammoth steppe environment. Cut marks caused by human activity are completely different from those of predators.”

The “quality and quantity” of the fossils in the North Sea are two things that surprise him the most.

“We have huge collections, and we are constantly learning from them.”

Storage private collection Urk (1)

Private fossil collection storage, image courtesy of Hans Wildschut and Dick Mol (Dick Mol is pictured on the left)

Highlighting mammoth teeth

Please click on this (or any) image to see it in more detail, image courtesy of Hans Wildschut and Dick Mol; highlighting by author

“Recently, many collectors are also focusing on small mammal remains (micro-mammals like voles and lemmings). These remains can be found on the beaches of the North Sea where Pleistocene sediments have been added to strengthen the coastline. Some collectors have hundreds and hundreds of small molars of the entire small mammal fauna. These small mammal remains provide very interesting data to complete the picture of the woolly mammoth and its Ice Age world. In other words, it gives us a window into the small animal community that coexisted with the megafauna.”

“These small mammal remains provide very interesting data to complete the picture of the woolly mammoth and its Ice Age world. In other words, it gives us a window into the small animal community that coexisted with the megafauna.”–Dick Mol

There are two questions that come to mind regarding the volume of fossils collected so far: where are these fossils stored and how long does it take to catalog and study such collections?

“It is a continuous process,” he stated, referring to the length of time needed to catalog and study the fossils.

But in terms of where they are stored, he wrote, “[t]he NCB Naturalis (Netherlands Center of Biodiversity Naturalis in Leiden) has a huge collection of fossil bones from both the North Sea, as well as from dredging operations in the floodplain of our rivers like Rhine, Meuse and IJssel. Really, a huge collection.”

“Using about 200 skeletal elements of mammoths of almost the same size, same age and same gender, we compiled a skeleton for museum display, a huge male individual. Another extensive collection is housed at the Natural History Museum in Rotterdam. Here, a huge collection of Pliocene and Pleistocene marine mammals is stored. Most of these marine mammal remains have been trawled from the seabed as well, and some of these animals coexisted together with terrestrial mammals like mammoths and other large animals. The marine mammals were living in the paleodeltas.”

Compilation skeleton woolly mammoth, NCB Naturalis Leiden (1)

 

Woolly mammoth skeleton at the NCB Naturalis Leiden Museum, the Netherlands, composed of individual fossils found within the North Sea, image courtesy of Hans Wildschut and Dick Mol

“And there are some private collections. Some of them are very well documented. They are like professional collections, and they are available and often used for scientific studies.”

“The co-operation between non-professional and professional paleontologists is extremely good in the Netherlands. For more than three decades, both groups have been working closely together on mammoths and mammoth fauna, scoring very interesting results like 14C, stabile isotopes, new species, etc.”

Dick Mol himself posed the final question: “What can we learn from the mammoth bones trawled from the North Sea between the British Islands and the Netherlands?

“The rich terrestrial mammal remains trawled teach us that the North Sea between Britain and the Netherlands was once dry land,” he explained. “The British Islands were connected with the mainland of Europe during the entire Pleistocene or Ice Age (2.580.000 – 11.500 BP). That area was inhabited by different faunas.”

“In the Early Pleistocene, it was a savannah-like environment, dominated by the southern or ancestral mammoths, (Mammuthus meridionalis). In the Middle Pleistocene, it was a steppe-like environment dominated by the steppe mammoth, (Mammuthus trogontherii), and in the Late Pleistocene, it was a cold, dry and almost treeless steppe dominated by woolly mammoths, (Mammuthus primigenius).”

Dick Mol - compilation skeleton

Woolly mammoth skeleton at the Hellevoetsluis Museum, the Netherlands, composed of individual fossils found within the North Sea, image courtesy of Hans Wildschut and Dick Mol

“At the end of the Pleistocene, this landscape disappeared, caused by dramatic change of climate. It became warmer and warmer, and ice–which blanketed the northern hemisphere–started to melt. Melted water filled up lower countries, and the vast plain became ocean. We know this area today as the ‘North Sea’, and it reached its present sea level about 8,000 years ago. The mammoth steppe disappeared and the mammoth fauna became extinct. This extinction is what we need to accept; it is not dramatic.”

“These events—of which we can learn from the North Sea fossils–show us that we are on a living planet and extinction belongs to it.”
————-

A Mammuthus trogontherii-sized THANK YOU to Dick Mol for his generous and detailed answers to my many, many questions; for his time, his wisdom and his thoughtfulness! What a truly great honor and a great pleasure!!

Dick Mol

 

Dick Mol, image courtesy of Hans Wildschut and Dick Mol

Dick Mol’s papers and research: http://hetnatuurhistorisch.academia.edu/DickMol

The Eurogeul—first report of the palaeontological, palynological and archaeological investigations of this part of the North Sea:  http://www.sciencedirect.com/science/article/pii/S1040618205000649

For fascinating pictures and in-depth descriptions of mastodons and mammoths, Mammoths and Mastodons of the Haute-Loire is a great book (published 2010, in English and in French):  http://www.amazon.fr/Mammouths-Mastodontes-Haute-Loire-Dick-Mol/dp/2911794974/

If you are interested in seeing more of Hans Wildschut’s exciting work, here are links provided by Dick Mol:

Trawling and fossils:

Hans Wildschut – trawling for fossils

Hans Wildschut – fossil finds

Hans Wildschut – trawling for fossils, December 2010

Hans Wildschut – exciting fossil finds and collection (Urk)

Remie Bakker and the creation of the life-sized model of the Mastodon of Auvergne:

Hans Wildschut – Remie Bakker’s work