As children, one of my and my sister’s favorite rainy-afternoon activities was looking through our Mother’s jewelry box. The daughter of a forester and the wife of a teacher, my Mom didn’t have dazzling diamonds and sapphires, but she did have interesting things. An ivory and silver broach that belonged to her great Aunt, a ring she made from a quarter when she was a girl, a whole box of Mardi Gras beads from her childhood in New Orleans (back when they threw real seed bead strings and not the cheap plastic stuff you see now). But by far our favorite piece was her amber necklace. The beautiful smooth golden stones were so clear it was easy to see the tiny pieces of— something— trapped inside.
Anyone whose sister wanted to be (and now is) a geologist, will tell you that amber isn’t a gemstone, it is fossilized tree resin (think the sticky stuff on Christmas trees). And it turns out that amber has more to offer then just lovely and unusual jewelry. The arthropods and other organisms trapped in the fossilized resin (inclusions) act as well preserved reservoirs of information from the past. Combined with the amber itself, these gems can be used like thumb tacks in a timeline. And, as a paper published at the end of October in the Proceedings of the National Academy of Science highlights (1), sometimes they can extend a timeline back.
The authors of the paper used the recent discovery or a large deposit of Cambray amber that was found in lignite (brown coal) mines in the Gujarat state in India. For this study, around 330 pounds of amber was collected. Analysis of the chemical composition of the amber combined with fossil wood from the mine helped identify the botanical source as that of Dipterocarpaceae (family of broad leafed, tropical trees). Using shark teeth found in the shale deposits of the same mine, the amber was dated at ~50-52 million years old. This data suggest that the date of dipterocarp forest development in South-east Asia was not in the Miocene (~5-25 million years ago; 2,3) as previously thought, but instead was sometime in the Paleocene (~55-65 million years ago).
The unique properties of the Cambay amber allow the relative easy extraction of entire inclusions. The amber is poorly crosslinked and polymerized so it easily dissolves in toluene and chloroform. The extracted insects are incredibly fragile, but the authors were able to examine them using scanning electron microscopy. This examination reveled cuticle and ultrasctructural preservation that allowed submicron study of morphological characteristics. All this meant a great improvement in the phylogenetic identification.
The most common theory for how the continents formed has India breaking away from the super continent, Gadwana, around 160 million years ago, drifting as an island for around 100 million years before colliding with Asia (forming the Himalayans) around 50-60 million years ago. During this long period of isolation, you would expect that the insect and animal life to become endemic, much like what you currently see in Australia, which has only been isolated for around 30 million years. However, at the time of publication the authors had isolated over 700 arthropods representing 14 orders and more than 55 families, and they found little to suggest endemism in the paleobiota of India at or around the commonly held time of impact with Asia.
The arthropods from the Cambay amber have affinities to taxa from recent Autralasia, the Eocene of northern Europe and even the Miocene of tropical America. Interestingly there were no African or Malagasy connections identified.
So what does all this mean? It seems that there might have been some archipelagic connections between precontact India and Asia or India and Asia collided earlier in the Paleocene than previously believed. Either way, I don’t think I will ever look at amber jewelry the same way again.
- Rust J, Singh H, Rana RS, McCann T, Singh L, Anderson K, Sarkar N, Nascimbene PC, Stebner F, Thomas JC, Solórzano Kraemer M, Williams CJ, Engel MS, Sahni A, & Grimaldi D (2010). Biogeographic and evolutionary implications of a diverse paleobiota in amber from the early Eocene of India. Proceedings of the National Academy of Sciences of the United States of America, 107 (43), 18360-5 PMID: 20974929
- Ashton, P. and Gunatilleke, C.V. (1987) New light on the plant geography of Ceylon. 1. Historical plant geography. J. Biogeogr. 14, 249-285.
- Morley, R.J. (2000) Origin and Evolution of Tropical Rain Forests. Wiley, New York, NY.
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