It is 16 million years ago during the Miocene Epoch. Mammals have exploded in diversity and have spread across the world. The world has long since healed from the brutal extinction event that took out the dinosaurs 65 mya. However, a new global event is coming, one that will challenge these animals and plants and stress even successful animal families. The world is cooling, it is no longer the hot and wet world it once was, the Ice Age is coming.
Fortunately, there are still places in this changing world where animals can find refuge in their tropical paradise. One such location are the Greater Antilles, a group of Caribbean islands whose members include Cuba, Puerto Rico, Jamaica, and Hispaniola. The islands were once a part of the Americas but eventually separated and moved eastward around 60 million years ago. The landmass split off into many smaller islands and yet never became completely submerged. Animals and plants hitched a ride on these islands while others flew or swam to them from distant landmasses.
On Hispaniola the world is teeming with life. Tall trees that are green all year round dominate the canopy while various ferns, fungi and flowering plants flourish underneath their forest behemoths.
A lone, wandering male spider searches for his next prey. He delicately tiptoes his way across the moss-covered bark hoping to find a juicy katydid. It has been awhile since his last meal and he is ready to feast. He is alerted to a nearby insect, a distressed beetle, who seems incapable of moving. Perfect, it’s wounded, an easy prey. The spider scurries to the beetle but just before he reaches his helpless foe, he is suddenly stuck. His legs are glued to an aromatic, yellowish substance upon the tree’s bark. He can’t move. And now, he too struggles to free himself like his would-be prey. But no matter how hard he tries he is unable to escape.
And in his worrying state, the spider does not notice an even bigger threat. Another wave of the golden liquid is moving down the tree towards him. In minutes the wave engulfs him and the beetle and suffocates them. They are trapped, and over millions of years the liquid hardens into a solid and protects them from the elements. They are buried but are found again where they are appreciated for being among the best fossils in the entire world.
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Hello and welcome back to Fossil Bonanza, my name is Andy Connolly and this is a podcast focused on unusual fossil sites from around the world called Fossil-Lagerstatten. In the previous episode we talked about amber in general but now we’re focusing on one of the best amber deposits in the entire world, the Dominican Amber.
So quick geography lesson. The Dominican Republic is located in the Caribbean and is southeast of Cuba. It and its smaller, western neighbor Haiti reside on Hispaniola island which itself is part of the Greater Antilles region which includes the islands Cuba, Puerto Rico, Jamaica, and the Cayman Islands. The DR has a humid tropical climate with little variation in the temperatures round year but with noticeable rainy and dry seasons.
With that said, compared to other prosperous and well known amber sites, the Domincan amber is something of a sleeper hit. Its first written account was when good ol’ Christopher Columbus met the Taino people in the late 1400’s. In an initial effort to display good will, he offered a European-made amber necklace to the chief only to be surprised when the chief offered him amber-adorned sandals. Although to some extent the Taino people appreciated the amber and even buried people with amber necklaces, the Spaniards weren’t so invested and never looked into it (they had plenty of it back in Europe). (Penney 2010)
(And as a quick side note; if Columbus actually looked into it he may have stumbled upon the rarest type of amber yet. Blue amber. Although the Domincan mines produce the golden and sunset-tinged amber we’re familiar with, every now and then blue amber can be found. It is so rare that it can be hundreds of times the worth of gold.) (Atlantic article)
Now, for centuries, the amber went unnoticed until the mid-1900s when the first couple of scientific papers were published praising the amber and its inclusions. This caught the attention of a West Germany mining company who saw the high potential in it after their supply of Baltic amber was cut off by the USSR. They set up a deed and used locals to mine the amber and send it back to Germany unprocessed. It wasn’t long before the DR realized…hey…this is a pretty good source of income for us and we want it! So they cancelled the European company’s mining rights which forced them to go bankrupt! (Penney 2010)
The amber mining is now solely in the hands of the DR and has several export limitations. First, only local DR people can mine and process the amber. The only amber that leaves the country are ones that have been cleaned up. Even more importantly, any amber with inclusions can leave only if it has permission from the country’s National Museum of Natural History which is pretty cool in my book. (Penney 2010)
Most of the mines are located in the northern part of the country within the mountain range Cordillera Septentrional, just north of Santiago. The mines can be 800-1000 meters above sea level and the only access to them involves hiking steep trails. Mining the amber is a laborious process with very little machinery involved. The mines are hand dug and are only lit by candlelight. The mines themselves are not pleasant as they’re cramped and too short for a grown person to comfortably stand. The humid conditions make them quite slippery and there’s a high risk of flooding and collapse while excavating. This is a far cry from the Jurassic Park, Dominican Republic-mining scene where the film displays an easy stroll from a river to a large tunnel filled with electronic lights, rock saws, and plenty of room to comfortably stand and work. (Penney 2010)
Sometimes, the miners will go for weeks without finding a profitable seam of amber but every now and then they will strike highly productive areas and carefully remove the amber from the walls. Once the amber is removed the amber is cleaned and polished, sometimes by the miners themselves and sometimes by the people who own the mine and from there the amber begins its journey through middlemen, collectors, and scientists. Unfortunately, many of the finer and more extravagant amber inclusions are sold to rich private collectors who can outbid museums and scientific institutes. These amber pieces are lost to the scientific community but every now and then cherishable collectors will donate their pieces to museums free of charge. There’s actually a good Atlantic article I read recently focused on the darker aspects of amber collecting which partially features a former colleague of mine, Matthew Downen, and his experiences purchasing Domincan amber spiders. I will provide a link to the article on my website but please be aware there is some description of human suffering and death in relation to the Burmese amber. A very dark reminder that even Lagerstätten can be subjected to the effects of human greed, malice, and carelessness. (Penney 2008, Atlantic article)
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So there’s actually one more thing majorly wrong about that amber scene in Jurassic Park.
So Hammond, the old rich man who financed the park, uses the amber from the DR to resurrect his dinosaurs. The problem with this is that the Dominican Amber is no where near the age of dinosaurs. In fact, it is much, much younger and was formed after the dinosaurs died!
Now I should mention that dating amber can be very frustrating. You can’t radiometric date it and amber has a knack for remixing itself into younger rock layers. From what I understand, the Baltic Amber has been very difficult in pinning down its time period as it’s found in many different rock layers. The Dominican Amber is no different and I read papers from the 90s giving it a range from 45 to 15 million years old. Quite a range considering how relatively recent that is.
Thankfully Cuban Paleontologist Dr. Iturralde-Vinent wrote a groundbreaking paper in 2001 which firmly answered this question. By analyzing the rock layers, the amber, and insects he deduced that the Dominican Amber is about 15-20 million years old, possibly 16 mya, during the Miocene Epoch. Mind you this is a very simple retelling of his paper but I encourage you if you’re in the mood for good ol’ fashion paleontology detective work check it out, I’ll provide a link to an open access version of the paper on my website.
What was this ancient forest like? Well, the climate was actually quite similar to modern Hispaniola’s climate! Based on the fossilized plants and arthropods, this environment was a humid, tropical forest. Many of the animal and plant inclusions found are closely related to those found in tropical conditions of Central and South America. As such, I think it’s initially tempting to say that these two forests are one and the same with minor differences but that’s…a bit untrue. (Poinar and Poinar 1999)
Perhaps the biggest difference between the past and the present ecosystems is the complete extinction of the amber-producing tree itself, Hymenaea protera. Without this tree, none of the Dominican Amber would’ve happened. Although now extinct, Hymenaea protera is survived by many extant relatives, all of which live in the tropics. These evergreen trees can grow up to 24 meters or so, can exude a lot of resin and an abundance of dropped copal can be found at their bases. (Poinar 1991, Iturralde-Vinent 2001)
How do we know what type of tree the amber came from? Well, not surprising, we can find an abundance of Hymenaea leaves, pollen, and flower inclusions. This makes them highly likely to be trapped by their own resin. We can also look at the chemical makeup of the amber and compare it to other resins. The amber molecules have changed little since it was a resin so we can compare its chemical identity to modern tree resins. What’s interesting is that H. protera’s closest relative lives in East Africa even though there are a whole bunch of them living in Central America. Why the huge geographic distribution? Although this hasn’t been completely figured out, one explanation proposes the tree had an ancestor who floated across the Atlantic thanks to their water-proof seed pods. The seed pods landed on Hispaniola and grew from there. (Poinar 1991, Poinar 2010)
What’s nice is that we can find other plant inclusions in the amber and can partially reconstruct this ancient forest. Bamboo, locusts, algae, lichen, fungi and a host of canopy and understorey tree parts are found within the amber. Flowers still in bloom can also be found. We even find indirect evidence of figs and palms thanks to preserved insects whose modern relatives rely on the plants for survival and growth. Make no mistake that this was a forest that was alive and thriving! (Nudds and Selden 2008)
I think this thriving forest is fully emphasized in the animals preserved in it and man are there a bunch! Every year, new amber animals are described and trying to keep track of them all is formidable. I read an expert’s opinion from 2010 that over 1,000 extinct species of arthropods have been described and that was ten years ago!! (Penney 2010)
I will admit, when I tackled this episode I was dreading that number and wondered how the heck I would talk about these inclusions without making it a list of species that would last three hours. I’ll provide links on my website where you can find out more about the variety of species but for now I want to hit some broad group of animals as well as some cool behaviors captured in the amber.
Obviously, arthropods are incredibly numerous in our inclusions. They’re small, abundant, and many of them rely on the trees for shelter and food. Ants are by far the most common animal making up about 26% of the Dominican Amber inclusions. Their colony abundance and constant crawling up and down the trees makes them an easy resin-engulfing target. (Poinar and Poinar 1999)
In fact, the Dominican Amber shows us an important step in the evolution of ants. Compared to older amber deposits, it seemed that ants had an explosion of diversity going from a rare species during dinosaur times, to a successful, almost cosmopolitan group of animals by the Miocene. There’s even a great variety of ant species in the Dominican Amber such as leaf-cutter ants, pollen-harvesting ants, harvester ants, ants that farm aphids, and ants that eat nectar. (Nudds and Selden 2008, Penney 2010)
There are also tons of flies, midges, and gnats and a random sampling of inclusions found they made up about 35% of the animals. These insects, all of which are under the Diptera order, make up the most species rich group of organisms in the Dominican Amber. (Poinar and Poinar 1999)
Another common inclusion are the stingless bees which no longer live on the island. Interestingly enough, their inclusion commonality is more likely attributed to their lifestyle than their actual abundance. Modern stingless bees collect resin, mold it into an adhesive ball, stick it to their legs, and use it to make nests. Many of the stingless bee inclusions still have these resin balls on them. Perhaps these bees were careless or had an accident and got stuck while transporting the resin. Clearly these bees need some safety training to minimize work accidents! (Nudds and Selden 2008, Poinar 2010)
One of the more significant inclusions are the spiders. Spiders are generally rare in the fossil record due to their fragility and avoidance of burying conditions after death. In fact, over 90% of all known fossilized spiders are from amber inclusions which is incredible! The Dominican Amber alone has over 40 identified spider families which include the jumping spiders and the orb-weaver spiders. The web itself can even be preserved and still have the original victims trapped in them. (Nudds and Selden 2008, Penney 2010)
What’s really cool is we can find camouflaging insects in the amber. Obviously, walking sticks are among the most noteworthy of this bunch and if you’re lucky you can find inclusions with their eggs. Meanwhile, the funky tree-hoppers mimic plant thorns to discourage would be predators. There are even beetles that mimic ants to avoid predation and even crash their nests and steal their food like unwanted house guests! (Poinar 2010)
This actually leads us to a great talking point, symbiosis. Symbiosis is the relationship between two different interacting organisms. Generally speaking, there are three kinds of symbiotic relationships; parasitism, mutualism, and commensalism. Parasitism is when one organism harms another by stealing its nutrition, ticks are a common example of this as well as the aforementioned ant-mimicking beetle. Mutualism is when both organisms benefit from their relationship, like a bird who feeds off of ticks from a rhino. Commensalism is when one organism benefits from the relationship but the other is not affected at all such as a bird living in a hole of a tree. The Dominican Amber displays all three of these relationships in one form or the other and helps us reconstruct this ecosystem.
Let’s start with parasitism. One sample had an entombed mite still feeding on a lizard’s scales. Another sample had a clump of rodent hair and scat with a nearby tick. Because of their proximity, we can assume that this particular species of ticks fed on rodents. There are many samples of ticks and mites but we can get into especially creepy territory with the nematodes, also known as roundworms. Many nematodes grow up inside their hosts before they finally exit them, often killing them in the process. One midge sample had three large nematodes that already exited their host while a fourth still resided inside of its body. Another sample had a fly surrounded by a swarm of juvenile nematodes which is especially unsettling…(Poinar 2010)
For commensalism, when one organism benefits but the other is not affected, we find animals who are getting a free ride off of their partners. Mites and pseudoscorpions, which both are quite tiny, hitch a ride on large insects who transport them from tree to tree. Once transported to their new spot they let go of their carrier and start a new life looking for some fresh food. In this case, these vagabonds chose a horrible carrier as they flew right into some resin and drowned! Haha. (Poinar 2010)
Finally, for the organisms that benefit each other, or mutualism, we have the standard algae+fungi=lichen, a true classic, but we can find other examples as well. Fig wasps and their respective trees directly rely on each other for survival; the wasp pollinates the fig in exchange for the wasp grubs eating some of the fig seeds. In this case, there are amber inclusions of fig wasps with fig pollen still on them. FInally, we have a cool example between ants and Theope caterpillars. Based on their modern relatives, these caterpillars excrete a sweet liquid that the ants drink and in exchange the ants protect the caterpillar from predators and parasites. What’s interesting is that neither this caterpillar or its ant protector are found in modern Hispaniola suggesting their extinction may have been intertwined. (Devries and Poinar 1997, Poinar 2010, Compton et al. 2010)
We can find other cool amber inclusions that are not just behavior related. Sometimes, we can even find a microcosm of life trapped in the amber. A whole ecosystem in one stone. One example I found had a pseudoscorpion, which is small to begin with, surrounded by a swarm of tiny organisms. The pseudoscorpion would eat the mites and tardigrades which would eat the nematodes which would eat the fungi and bacteria. All of which are present in the amber. (Poinar 2010)
There’s one inclusion that has captured a fantastic moment in life, hatching insects. The sample contains 47 eggs with five assassin bug nymphs. Two of the nymphs were hatching when the resin submerged them. Although egg samples have been found in ambers, there are very, very few examples of hatching insects in the entire fossil record. (Hörnig, M.K., Fischer, T.C. and Haug, J.T. 2019)
Perhaps the rarest and most sought after inclusions are the vertebrates. For the most part, these backbone critters can escape the resin unharmed and the best we can usually find are feathers, hair, eggshells, scat, and scales but even these are quite rare. There’s only one instance of a feather, in this case from a woodpecker, while the lone eggshell sample was from a hummingbird. Nonetheless, these few traces can still tell us so much about this ancient world as we can even identify hair belonging to bats and scales to snakes. Very cool but we do have more robust inclusions as one amber had a shrew’s ribs and vertebrae, another had a frog, and there are some with geckos and anoles lizards but many of them are unfortunately in personal collections. (Nudds and Selden 2008, Poinar 2010)
The most recent addition to the vertebrates club is a salamander hatchling described in 2015. This is the first salamander preserved in amber ever which is incredible. Based on its morphology, it likely lived in the trees which is not unheard of as some modern salamanders do this as well. This leads to its unfortunate, traumatic birth; the preserved hatchling is missing an arm and it’s possible that right after it hatched it was attacked by a predator which took off its limb. The hatchling fled its predator but fell into the resin where it was quickly entombed, poor guy. What’s also interesting about all of this is that no known salamanders naturally live on modern Hispaniola or even the Greater Antilles region itself! They’re completely absent! Which is very strange…how did this salamander get to ancient Hispaniola? It was already an island during the Miocene. One hypothesis is that a population of the salamanders basically hitched a ride on the island before it separated from the main continents. The salamanders enjoyed a nice life there for a long time before things took a turn for the worse when the Ice Age struck and they went extinct. (Poinar and Wake 2015)
The salamander fossil also brings up the question, who else lived on this island? As amber preserves a very select group of fossils, what animals are here that we aren’t finding? Thankfully we can draw evidence from other nearby fossil deposits and do some reasonable inferences for this ancient ecosystem.
Fossils of tree-dwelling animals like sloths are found in nearby contemporaneous Cuba while Hispaniola monkey bones are found in recent cave deposits. Both of these animals would’ve found the ancient Dominican forests to be a suitable home for them. Parasites can also indicate who lives in this forest. A mosquito was discovered carrying a parasite called Plasmodium dominicana, who’s genus causes malaria. The parasite’s closest modern relative primarily infects Galliform birds which include chickens, turkeys, and a native Central American bird called chachalacas. Chachalaca fossils have been found in North America during this time period so it’s possible the birds lived on this island and then died out. This is still speculation though but it would be amazing if a chachalaca bird feather was found confirming this hypothesis. (Nudds and Selden 2008, Poinar 2010)
<beginning of the Can-Can dance>
Okay, so we don’t have time to cover all the amber animals so what better way to mention them then in a frenetic song! Aphids, paper wasps, orchid bees, little fleas, biting ticks, walking-sticks, snails and moths, butterflies, dragonflies, damselflies, centipedes, millipedes, mosquitos, woodlice, cicadas, roaches, katydids, roundworms, daddy-long legs, beetles, gnats, grasshoppers, leafhoppers, scorpions, termites, springtails, bristletails, true bugs, water strider. Phew! (Poinar and Poinar 1999, Nudds and Selden 2008).
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As I reflect on the Dominican Amber I’ve come to realize it’s a subtle symbol of our changing world. When we see the plants and animal inclusions, we see a world that was very similar to today’s Hispaniola. A humid tropical forest located on a Carribean island. It’s as if nothing has changed these past 16 million years.
But upon closer inspection we see the flaws of this idea. This Miocene world is different from our current world. Yes, we see many recognizable groups of animals and plants but yet, a lot of them are more closely related to animals living in the Americas than those who live in Hispaniola today which is interesting. What’s more, many of the amber families no longer live on Hispaniola like the salamanders or stingless bees and live in the Americas. Some of the relatives now live in a completely different part of the world like the Mastotermes termite which lives in Australia and the Halovelia water strider which lives in the Indo-Pacific region. Even, the resin tree itself, Hymenaea protera is extinct and its closest relative is in East Africa. Clearly, something happened that changed this ecosystem and killed off many of its species. (Poinar and Poinar 1999)
The Dominican Amber forest grew when the world was warm and wet. A world where rainforests flourished. But this came crashing down as the world became cooler and cooler. At first, the temperature changes were gradual but then, about 4 million years ago, they plummeted. The Carribean experienced a drop of about 5-6 degrees Celsius (or about 10 degrees Fahrenheit) across the region. The Polar Ice Caps grew tremendously and locked valuable sources of water. This was now a cold and dry world. (Poinar 2010)
Unfortunately, tropical creatures are so ingrained in their ecological niches that even small temperature or precipitation changes can push them into extinction territory. The Dominican animals and plants were no exception; even their paradise was not immune to a changing world. The only way they could survive was to move towards the equator where tropical conditions persisted. But their island isolation deprived many of them of this option. With nowhere to go the ecosystem began to collapse when the resin tree and other tropical plants died out. This caused a severe chain reaction; animals that relied on these plants like pollinators, herbivores, and stingless bees suffered total extinction. Predators and parasites who relied on these animals starved and followed suit. The Amber Forest was no more. (Poinar and Poinar 1999)
What was this new, Ice Age ecosystem like? It honestly was probably like the southeastern U.S. today, with hot summers and mild winters. That may not sound like a huge difference but to many lifeforms it was just too much. Survivors in this new subtropical world would have to persist. Animals that could eat different foods like spiders flourished in their new, cooler home. Animals and plants that could withstand the cooler temperatures would eke out a living until the Ice Age subsided. Once the Ice Age ended, the organisms began their road to recovery in a now depleted world. (Poinar and Poinar 1999)
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To this day, the Dominican Amber continues to produce new inclusions that get recognized every year. Just last year in 2019 it produced its first inclusion with hatching insects and 2015 saw its first salamander. Who knows what else will be discovered to fill our still incomplete ecosystem? I’m personally hoping for more feathers that will expand our knowledge of ancient birds! Whatever it is, it will be amazing, there’s no doubt about that.
References
–Compton, Stephen G., et al. “Ancient fig wasps indicate at least 34 Myr of stasis in their mutualism with fig trees.” Biology letters 6.6 (2010): 838-842.
–DeVries, P. J., and G. O. Poinar. “Ancient butterfly–ant symbiosis: direct evidence from Dominican amber.” Proceedings of the Royal Society of London. Series B: Biological Sciences 264.1385 (1997): 1137-1140.
–Gammon, Katherine. The Human Cost of Amber. The Atlantic, 2019.
–Hörnig, Marie K., Thilo C. Fischer, and Joachim T. Haug. “Caught in the act of hatching–a group of heteropteran nymphs escaping from their eggs preserved in Dominican amber.” Palaeodiversity 12.1 (2019): 123-134.
–Iturralde-Vinent, Manuel A., and R. D. E. MacPhee. “Age and paleogeographical origin of Dominican amber.” Science 273.5283 (1996): 1850-1852.
-Penney, David. Dominican Amber Spiders: a comparative palaeontological-neontological approach to identification, faunistics, ecology and biogeography. Siri Scientific Press, 2008.
-Penney, David, ed. Biodiversity of fossils in amber from the major world deposits. Siri Scientific Press, 2010.
–Poinar, G.O. Hymenaea protera sp.n. (Leguminosae, Caesalpinioideae) from Dominican amber has African affinities. Experientia 47, 1075–1082 (1991).
–Poinar Jr, George. “Palaeoecological perspectives in Dominican amber.” Annales de la Société entomologique de France. Vol. 46. No. 1-2. Taylor & Francis Group, 2010.
-Poinar, George O., and Roberta Poinar. The amber forest: a reconstruction of a vanished world. Princeton University Press, 1999.
–Poinar Jr, George., and David B. Wake. “Palaeoplethodon hispaniolae gen. n., sp. n.(Amphibia: Caudata), a fossil salamander from the Caribbean.” Palaeodiversity 8 (2015): 21-29.
-Selden, Paul, and John Nudds. Fossil ecosystems of North America: a guide to the sites and their extraordinary biotas. CRC Press, 2008.
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