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X-ray analysis of fossil whale baleen

Modern baleen XRD map

Elemental map of a cross-sectional view of the modern minke whale baleen. Image: Mark Goodwin.

Two years ago I approached UCMP Assistant Director Mark Goodwin and asked if he had any room for some student help in his research. I had no previous experience in paleontology, just a passion for learning about dinosaurs and biology. Now, as a third-year graduate student in the Department of Materials Science and Engineering, I work on a variety of projects with Mark and the UCMP. For my own research, I study the micro- and nano-scale features in fossil bone with electron microscopy. I have always enjoyed interdisciplinary work, and the opportunity to use cutting edge X-ray and electron microscopy techniques to uncover new knowledge about the preservation of fossilized structures is very exciting to me.

The Lawrence Berkeley National Laboratory, which sits overlooking the UC Berkeley campus from atop the Berkeley hills, offers many amazing opportunities to conduct state-of-the-art science. In particular, the Advanced Light Source (ALS) offers a variety of techniques for analyzing material properties, for studying the structure of biological specimens or molecules, or for investigating chemical reactions in real time. All of these techniques use X-ray light, which is a higher-energy form of light than the visible light that our eyes can see.

UCMP Assistant Director Mark Goodwin has been using several techniques at the ALS to study a variety of fossil and modern samples. Most recently, Mark investigated the elemental composition and physical structures of a sample of 5.8 million-year-old fossil whale baleen and then compared it to a sample of modern minke whale baleen.

Baleen whales don’t use teeth to catch and chew their food; instead they use hair-like baleen to strain microscopic organisms from the water. The hair-like structures of baleen are actually small tubules composed of concentric, alternating layers of keratin and hydroxyapatite. Keratin is the same tough protein found in fingernails, and hydroxyapatite is the same mineral that makes bones strong. Just as fossilized bones are altered from their original state, in fossil baleen the keratin and hydroxyapatite can be replaced by other minerals.

That’s where the X-ray absorption techniques at the ALS come in. Because whale baleen has such a large protein component, like muscle or skin, it usually is not preserved during fossilization. The fossil whale baleen that Mark analyzed, with the help of ALS scientists Sirine Fakra and Matthew Marcus, is an incredibly rare sample. Two techniques were used to study the preservation of this remarkable fossil whale baleen, including (1) elemental analysis to spatially map where a variety of different elements are in the baleen and (2) X-ray Absorption Near Edge Structure (XANES) to discern the chemical structure of the elements present. In both cases, the data must be compared to the modern minke whale baleen, or the standard, to assess what has actually changed during fossilization.

An example elemental map of a cross-sectional view of the modern minke baleen can be seen in the figure. The colors each represent a different element present in the baleen and they highlight the concentric circular structure of the baleen tubules. The maps show us that the keratin protein rings in the fossil baleen have largely been replaced by mineral. The original hydroxyapatite rings are still there, too, although some elemental substitutions have occurred in the mineral structure.

From this data we now know the secret behind the preservation of this amazing, rare fossil baleen discovery! The keratin was replaced by mineral, which preserved the three-dimensional structure of the original whale baleen – the mineral prevented the tubules from flattening under pressure in the rocky fossil bed. Measuring the characteristics of the three-dimensional structure, like tubule diameter and thickness, Mark was able to determine that this fossil whale is evolutionarily related to the modern minke whale. This one piece of fossil baleen, therefore, has taught us two lessons: (1) how baleen fossilizes to preserve its original structure and (2) that this extinct whale is related to the modern minke whale.

CT scan of fossil baleen, courtesy of Mark Goodwin.

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