Bones of Contention: What Whale Skeletons Reveal About Their Hidden Lives
A museum collection of cetacean bones is unlocking secrets of where these ocean giants feed and how we can protect them, one skeletal element at a time.
By Marine Science Research Team | Published in Frontiers in Marine Science
For centuries, the magnificent skeletons of whales and dolphins have been preserved in museum collections, standing as silent monuments to creatures we rarely see alive. Today, scientists are listening to the stories these bones have to tell, and the message is revealing a surprising truth: not all bones are created equal. Groundbreaking research is uncovering that different bones from the same animal can tell different stories about its life, a finding that is crucial for conserving these often-endangered marine mammals.
Did You Know?
Cetaceans (whales, dolphins, and porpoises) have been evolving for approximately 50 million years, adapting from land-dwelling ancestors to become masters of the marine environment.
The Science of Stable Isotopes: Reading the Diaries in Bone
Imagine if every meal you ate wrote a tiny entry in a personal diary kept in your body. This is essentially what happens with stable isotope analysis, a powerful scientific technique that allows researchers to decipher the diet and habitat use of animals by examining the chemical signatures locked in their tissues5 .
Stable isotopes are different forms of the same chemical element that have slight variations in their weight. For example, carbon comes in a lighter form (12C) and a heavier form (13C). Similarly, nitrogen has light (14N) and heavy (15N) isotopes. As an animal eats, these isotopes from its food are incorporated into its body tissues in predictable ways.
Act like a GPS tag, providing clues about the foraging location or the type of habitat where an animal has been feeding3 .
Function like a trophic level indicator, revealing an animal's position in the food chain—what it's eating, and how high up the predator ladder it is3 .
Bone tissue is especially valuable because it acts as a long-term diary. Due to its slow turnover rate, it doesn't record last week's meal, but rather provides an integrated record of an animal's feeding habits over several years3 . This makes it perfect for understanding long-term patterns, a critical need in conservation science, which often must act quickly to protect species at risk of extinction1 .
A Landmark Study: Sampling the Museum's Archives
To understand just how different the stories from various bones can be, a team of researchers turned to the extensive osteological collection of the National Museums Scotland1 . Their mission was ambitious: to measure the carbon and nitrogen isotope values in multiple bones from the same individual animal.
The Experimental Blueprint
Specimens
The team sampled 72 cetacean skeletons from 14 different species.
Methodology
From each skeleton, they drilled a small sample of bone powder (about 1 gram) from the same eight specific skeletal elements. These included the mandible (lower jaw), humerus (upper arm bone), and several others.
Lab Processing
In the laboratory, the bone samples underwent a meticulous process to extract pure collagen, a protein that preserves the isotopic signature. This involved removing lipids and minerals and then freeze-drying the resulting collagen.
Isotope Analysis
The final collagen samples were analyzed using an isotope ratio mass spectrometer, which precisely measures the ratios of heavy to light carbon and nitrogen isotopes.
This systematic approach allowed for a direct, apples-to-apples comparison of isotope values across different bones from the very same animal.
Cetacean skeletons in museum collections provide valuable research material. (Credit: Unsplash)
The Surprising Results: A Single Animal, Many Stories
The findings, published in Frontiers in Marine Science, were striking. Researchers discovered far more variation between bones than anyone had anticipated1 .
Intraskeletal Isotope Variation in Cetaceans
| Isotope | Intraskeletal Range Observed | Percentage of Skeletons with Range >1‰ | Percentage of Skeletons with Range >2‰ |
|---|---|---|---|
| Carbon (δ13C) | 0.4‰ to 7.6‰ | 84.7% (61 of 72 skeletons) | 55.5% (40 of 72 skeletons) |
| Nitrogen (δ15N) | 0.4‰ to 5.2‰ | 59.7% (43 of 72 skeletons) | 15.3% (11 of 72 skeletons) |
This data reveals a startling fact: if a scientist were to analyze only the humerus of one dolphin and the mandible of another from the same population, they might wrongly conclude the two animals had vastly different diets or lived in different habitats. In reality, they might be looking at a chemical discrepancy that exists within every single individual.
The study also identified that not all bones are equally representative. The humerus and mandible, for instance, showed the most consistent and largest deviations from the skeleton's average isotope value. The researchers therefore advise against using these bones alone for stable isotope analysis in cetaceans1 .
Why Do Bones from the Same Animal Tell Different Stories?
| Underlying Cause | Ecological Explanation | Impact on Isotope Values |
|---|---|---|
| Differential Bone Turnover Rates | Bones remodel and regenerate at different rates based on their function, density, and mechanical stress. | A bone with a fast turnover rate will reflect a more recent dietary period, while a slower-turnover bone provides an older, more averaged record. A change in diet or habitat is therefore recorded on different timelines in different bones. |
| Ecological Shifts | An animal's life is dynamic—it may change prey, migrate, or shift habitats over its lifetime. | The variation seen across the skeleton is not just "noise"; it is an ecologically relevant record of these past shifts, locked in a patchwork of bone turnover rates. |
Using different bones from different individuals can lead to misleading conclusions about population dietary patterns and habitat use.
For cetaceans, the rib is often a good candidate for analysis, as it was found to be less biased than the humerus or mandible.
The Scientist's Toolkit: Key Materials for Isotopic Ecology
What does it take to conduct such research? Here are some of the essential tools and reagents that scientists use to read the isotopic diaries in bone.
Essential Research Toolkit for Bone Isotope Analysis
| Tool or Reagent | Function in the Research Process |
|---|---|
| Isotope Ratio Mass Spectrometer | The core analytical instrument that makes highly precise measurements of the stable isotope ratios in a prepared sample. |
| Handheld Drill | Used to carefully remove a small amount of bone powder from museum specimens, minimizing damage to the precious skeleton. |
| Chloroform-Methanol Solution | A solvent used in the lipid extraction process to remove fats from the bone powder, which can skew carbon isotope results. |
| Hydrochloric Acid (HCl) | A weak acid solution used to demineralize the bone sample, dissolving the mineral component to leave behind the protein-based collagen. |
| Sodium Hydroxide (NaOH) | A mild base used to rinse the sample and remove potential contaminants like humic acids. |
"The variation we found within individual skeletons was much greater than expected. This has profound implications for how we design future stable isotope studies and interpret existing data."
A Ripple Effect in Conservation
This discovery has immediate and important implications for protecting whales, dolphins, and other species. When scientists use specimens of opportunity—bones from stranded animals or historical museum collections—they often have to work with whatever bones are available. This research sounds a clear warning: the choice of bone matters.
Risk of Misinterpretation
If conservationists ignore intraskeletal variation, they risk drawing dangerously incorrect conclusions about habitat use and dietary patterns.
Improved Conservation
Using consistent bone elements across studies ensures accurate data for identifying critical habitats and recognizing genuine threats.
If conservationists ignore this intraskeletal variation, they risk drawing dangerously incorrect conclusions. They might mistakenly think that animals in a population are using vastly different habitats, when in fact the difference is just in their bones. This could lead to misidentifying critical habitats or failing to recognize genuine threats to a population1 .
The solution is elegantly simple. Future studies should strive to analyze the same specific bone from every animal in a study. For cetaceans, the rib is often a good candidate, as it was found to be less biased than the humerus or mandible. This simple step ensures that comparisons between individuals are valid and that the conservation actions based on this science are effective.
The silent skeletons in our museums have found a new voice.
By learning to listen carefully to the distinct stories told by each bone, scientists are ensuring that the lives of these ocean giants are accurately understood and protected for the future.
The research highlighted in this article is based on the original study: "Cetacean Skeletons Demonstrate Ecologically Relevant Variation in Intraskeletal Stable Isotopic Values" (Frontiers in Marine Science, 2020).