The following was the script for the “Amber 101” episode for Fossil Bonanza.
Hello, my name is Andy Connolly and welcome back to another episode of Fossil Bonanza. This is a podcast where I look at fantastic fossil sites found across the world, called Fossil-Lagerstätten, and gush why these sites are so fantastic, what they can tell us about the ancient world, and how their fossils became preserved. This is a special episode for us as this is the first episode focused on amber! Amber! Yes, the almost fantastical substance who has played strong roles in both our cultural and scientific history. Not only has it been a part of our history for thousands of years, it continues to astound us to this day for the fossils they contain.
Fossils in amber, called inclusions, are among the best preserved fossils in the world. Amber’s unique properties are so amazing in halting decay that it seems the trapped insects are in stasis, ready to be woken again. The entombification of these creatures is so precise that you can find mummified insect organs, and even pollen and bacteria. Other, more “traditional” ways of fossilization can’t even approach the level of life-like quality that amber inclusions have obtained. Even in older times, many people were appreciative of these inclusions and a stanza I particularly like by 18th century, English poet, Alexander Pope goes
“Pretty! In amber to observe the forms
Of hairs, or straws, or dirt, or grubs, or worms!
The things, we know, are neither rich nor rare,
But wonder how the devil they got there.”
Wonder indeed! But we’ll learn in this episode how the devil the insects got into the amber and why they are in amazing condition. And for our first amber episode we’ll dive into the Dominican Amber and appreciate the animals locked in its golden tombs. We’ll see crawling spiders, terrifying parasites, and ants, ants, ants! Ladies and gentlemen…(in the voice of John Hammond)…welcome to Fossil Bonanza!
All amber is formed from resin, a viscous substance used by trees to patch open wounds. Whenever a tree may experience damage from high winds or an insect invasion, it exudes the resin to patch these wounds and ensure that no further damage or invaders take place. The resin works very well as an insecticide as not only can the chemicals be deadly but they suffocate any would be intruders from getting into the tree. The resin then hardens and acts as scab for the wounded tree. (Grimaldi 1996, Nudds and Selden 2008)
Immediately, we begin to understand why amber is an excellent way to preserve fossils. Not only is there a high opportunity for insects (invasive or not) to be entombed, but the resin’s solidifying properties means it can survive transport and burial.
It should be pointed out, before we go any further, that resin and sap are technically different from each other even though they both come from trees. Sap is a watery substance that is full of sugars. Trees use sap to deliver nutrients and sugars, produced in the leaves, throughout its body. Maple syrup is derived from the sap of maple trees. Resin on the other hand is made from a tree’s bark and is much thicker. In fact, if you ever go hiking through a conifer forest, it’s highly likely you have stumbled upon resin and even felt its highly sticky, pine-like aroma on the tree’s bark. The resin is made of terpene chemicals which give it its unique properties.
It actually takes awhile for the viscous resin to transform into an amber gem. The transformation immediately begins once the resin has left the tree and is exposed to the air. Many of the resin’s chemicals will slowly evaporate over time while the rest will begin to link together in a process known as polymerization. This polymerization is what hardens the resin into amber. (Grimaldi 1996, Nudds and Selden 2008)
Before the resin can fully become amber, it reaches a stage called copal which is sort of like a proto-amber. Copal is very similar to amber in that it’s hard and can contain inclusions but there are a few critical differences. For one thing, it’s still undergoing polymerization and as such can be melted at lower temperatures than amber. It also isn’t as hard as amber and it can be dissolved in many kinds of acids. Many people have been fooled into thinking they have an amber which in fact it’s just a disguised copal. Copal isn’t as useful for paleontologists because they are relatively young, usually less than 50,000 years old or so. Real amber takes much longer to form and although there isn’t a hard date of when the transformation is complete. When transformed, the amber is harder and can withstand higher temperatures and is more resistant to acids. (Grimaldi 1996, Nudds and Selden 2008)
However, if the resin is exposed to air for too long during polymerization it can degrade and crack. The resin needs to be safely transported and buried somewhere to continue its transformation. That is why a lot of amber sites have been found in delta and lagoon deposits. As the resin drips off the tree or falls down with a broken branch, it can be carried by a fast moving current to a river where it will eventually be buried by the sand and mud. The burying mud is air-sealed and allows the water-proof resin to continue its amberfication. (Grimaldi 1996)
There’s also another problem with amber that we need to take into account. The trees that produce it. You see, not every tree can produce resin and even the ones that do may not produce a lot of it. The trees that DO produce a lot of resin are usually found in tropical areas possibly due to the high amount of invasive insects and fungi and the prominence of tropical storms that can break branches. (Martínez-Delclòs et al. 2004)
As such, we are seeing very specific circumstances for our Amber-Lagerstätten to happen. There needs to be an abundance of trees that can produce a high amount of resin who live near a delta or a river which can quickly transport and bury the resin so it can become amber. These are very rare circumstances which seems fitting given these are among the best fossils in the entire world. We’ll briefly mention a few global amber sites that satisfy these conditions but I want to talk about one more important piece to our Lagerstätte puzzle and that’s our inclusions, the poor critters who got stuck in the resin.
So one of the running themes on this show is fossilization bias, that not every type of animal or plant in an ecosystem will get preserved. Fossilization usually favors animals with hard parts located near areas that can bury them. Even our previous Lagerstätten demonstrated some form of bias despite their amazing fossils. The underwater mudslide in Beecher’s Trilobite Bed only buried the animals living on the sea floor while the Posidonia Shale only fossilized creatures who could swim or float in the open waters. The same thing is true for our amber fossils.
Obviously, size is going to be the first factor here that eliminates who can become an amber inclusion. If you’re big enough, you can easily escape the resin if you find yourself semi-trapped by it. An absolutely huge proportion of animal inclusions are less than an inch long so it’s no wonder a lot of them are arthropods like insects, spiders, and millipedes. It’s very rare to find vertebrate inclusions and when you do it’s just a portion of them like a body part of a feather or scales.
Also, as mentioned before, the trees that are likely to produce amber are found in tropical rainforests. So you’re eliminating animals and plants that can be found in other habitats like grasslands even if the two habitats are nearby. Even then, the many micro-habitats that reside in tropical rainforests are outstanding. Animals may specialize to live in just the trees, solely on the ground, IN the ground itself, and anywhere in between. I encourage you all next time you’re in a park or in your own backyard to observe a tree for a few minutes and then observe the ground nearby and see how animals and plants differ even when they’re fifteen feet apart.
The Dominican Republic amber is a fantastic example of this. Even though there are over 800 species of butterflies and is the third most species-rich insect on modern Hispaniola, only 7 species are known from amber. This is probably because they just don’t regularly interact with the resin trees. Meanwhile, ants make up 26% of all the amber inclusions due to their frequent crawling up and down the tree. (Penney 2010)
Then you have to take into account geologic time. Although resin has been found dated to about 300 million years old, it didn’t become abundant until about 120 mya during the age of dinosaurs. Why the sudden rise? Although there is some discussion on the matter, it may have been tied to the evolution of wood-boring insects. More resin means less intruders! (Martínez-Delclòs et al. 2004)
All of this means we have a very, very focused lens on our inclusions. Yes, the animals and plants may not wholly represent the world they lived in but danget are they not the most wonderful fossils out there. Let’s dive into what it takes for an insect to be immortalized in amber.
In general, one of the best ways for an organism to become a fossil is to remove it from the environment as fast as you can. You want to minimize the time between an animal’s death to its burial so you can preserve as much of it as you can. For many burying environments, this can take several days to hundreds of years before the animal remains are submerged. Resin can do this in minutes. As an insect, say an ant, is crawling on a tree, it walks across the resin and almost immediately becomes stuck in the viscous substance. While struggling in its gooey deathbed, another wave of resin buries it completely and submerges it. The ant dies through either suffocation or dehydration and exhaustion if it’s only partially submerged. Immediately, the resin begins it amberfication and the ant begins its fossilization.
Resin is incredibly good for decay prevention. I already mentioned before that resin is waterproof but some resin have anti-fungal or anti-bacterial properties that prevent tiny microbes from infiltrating and growing in its golden walls. Not all resin have this though as I came across an example of fungi growing off of an insect inside of the amber! It’s likely that the fungi was already leeching on the insect by the time the resin submerged it. The fungi then immediately grew off of its now dead host before it succumbed to its oxygen-deprived, resinic environment. Very cool! (Martínez-Delclòs et al. 2004)
However, in some cases, resin may be too good at its entombification. If an insect is quickly submerged, it can go through a process known as autolysis. The insect’s own cells and bacteria begin to break down the internal cells and tissues. When the resin seeps into the insect, it reacts with the internal soupy fluids and creates a bubbly sphere around the insect. The resulting process leaves a 3-dimensional, hollow cast of its inclusion. (Martínez-Delclòs et al. 2004)
Fortunately, there is a way nature can prevent autolysis from happening. If the insect is only partially submerged and dies before another wave of resin buries it, it can dehydrate to the surrounding environment. The lack of water halts any kind of bacteria activity that may destroy the internal organs. Once the resin submerges it, the insect will be mummified with its internal organs still in place. (Martínez-Delclòs et al. 2004)
This is when amber’s astonishing potential of fossilization occurs. If the tissue compounds are relatively stable we can detect the likes of organs like a spider’s book lungs, liver, or spinning glands. We can even identify cell organelles like mitochondria, ribosomes, and cell nuclei which is absolutely insaaaaaaaane (Nudds and Selden 2008).
Which leads me to the T-Rex in the room, the million dollar question, can amber preserve DNA?! To give an unsatisfying answer…it likely does not. DNA is highly unstable and even in the best of best conditions it’s rare to find DNA that’s over 100,000 years old. In the 90’s, during the Jurassic Park hey-day, there were a number of publications saying scientists were able to extract DNA from insects millions of years old but these results have since not been replicated and were likely due to lab error. The history behind the DNA Holy Grail is quite complex but fascinating so I’ll leave it to a future amber episode to tell that story. (Austin et al. 1997, Martínez-Delclòs et al. 2004)
In fact, DNA, and other organic compounds like proteins, in general do not have a stable shelf life, even in the comforts of an amber home. The body constantly needs to update, fix, and mend broken and degraded molecules to keep itself functional. Many of those compounds just break down over time while others, like the hard exoskeleton of insects, remain strong and relatively unchanged for millions of years. So even amber, despite its near perfect conditions of delaying decomposition, can only do so much for its imprisoned inclusions. (Martínez-Delclòs et al. 2004)
As we have seen, amber deposits just go all in on having high quality fossils. They’re the definition of a Konservat-Lagerstätten or a fossil site with excellently preserved fossils. The trade off being that A. only certain kinds of organisms can become fossils and B. there are relatively few amber sites found throughout the world. Even profitable amber sites struggle to produce inclusions as a majority of the amber stones have nothing in them. (Martínez-Delclòs et al. 2004)
One source I’ve read dating from the 90s said there are hundreds of known global sites that produce amber but only in trace quantities. About 20 of them have an abundance of mined amber. Even then, these 20 or so, from what I can tell, are overshadowed by four sites that dominate the amber literature. They are known as the Lebanon, Burmese, Baltic, and Dominican Amber sites. These big four sites again and again are praised for their scientific significance and their amber abundance. The Dominican and Burmese sites in particular have seen a rush of new species identified every year and keeping up with them is almost impossible. The fossils all four of these sites contain are magnificent and give a critical look into our world’s evolutionary history. Their importance cannot be understated. (Grimaldi 1996)
In another time, we will look at the Lebanon, Burmese, and Baltic sites but for now we’re going to end the episode here and resume next time for the Dominican Amber! Hope to see you then.
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-Austin, Jeremy J., et al. “Problems of reproducibility–does geologically ancient DNA survive in amber–preserved insects?.” Proceedings of the Royal Society of London. Series B: Biological Sciences 264.1381 (1997): 467-474.
-Grimaldi, David A. “Amber: window to the past.” (1996).
-Martı́nez-Delclòs, Xavier, Derek EG Briggs, and Enrique Peñalver. “Taphonomy of insects in carbonates and amber.” Palaeogeography, Palaeoclimatology, Palaeoecology 203.1-2 (2004): 19-64.
-Penney, David, ed. Biodiversity of fossils in amber from the major world deposits. Siri Scientific Press, 2010.
-Selden, Paul, and John Nudds. Fossil ecosystems of North America: a guide to the sites and their extraordinary biotas. CRC Press, 2008.