Paleo-girls and boys and their toys

There are a lot of cool toys out there.  Not just Research Institute Legos, Paleontology Barbie, and a new generation of Jurassic World figurines, but toys that are products of technological advancement. What's even cooler is that we have applied many of them to help advance our scientific knowledge.  Paleontology is no exception - technology toys are increasingly being adapted into research tools. To name a few examples: 3-D scanning and 3-D printing has hit the scene in the past few years, with applications from manufacturing to education to entertainment. Paleontologists have adopted 3-D scanning as a means for comparing shapes of bones (using 3D geometric morphometrics). 3-D printing is assisting with visualizations and analysis of brain evolution in extinct animals, improving our understanding of dinosaur biomechanics, providing fossil replicas for classroom education, and so forth. Technological advancements have lead to increased accuracy in radiometric age dating, helping us pinpoint absolute age dates for geologic events (like volcanic eruptions and extinctions). Even state-of-the-art medical equipment can help with anatomical diagnoses of fossils - not just living animals.

Skull of the type specimen of Tylosaurus kansasensis
at the Sternberg Museum of Natural History.

Tylosaurus kansasensis skeleton mounted at the
Rocky Mountain Dinosaur Resource Center

Recently, we took the skull of the type specimen of the mosasaur Tylosaurus kansasensis to the local hospital (thanks, Hays Medical Center!) to be CT scanned.  A type specimen is THE specimen used as the basis for naming a taxon. In this case, a new species. So all other specimens found will be compared to the type specimen to see if it is the same species or not.  Considering this, it's pretty important to know as much as possible about a type specimen.  CT (Computerized Tomography) scanning involves taking x-ray images from multiple angles to create image slices of the inside of an object. For humans, CT scans are used to examine hard and soft tissues within the body (this is especially useful for diagnosing internal injuries to muscles, tendons, ligaments, organs, etc.). Importantly for paleontology, CT scans produce 3-D images.  Because the skull of this specimen is crushed and flattened, it is difficult to see and understand how all of the bones fit together.  The shape, size, and placement of skull bones is very important to understanding what makes each species unique, and important to understanding how the skull and jaws functioned. So we took in our Tylosaurus kansasensis skull to generate 3-dimensional images of all the skull bones.

Check out our video for images and more information on CT scanning and paleontology research!

Technological advancements are exciting. And scientific advancements are exciting. So it's a welcome challenge to adapt the newest hot piece of technology into a tool for understanding extinct life and deep time!

Darwin Day: It's for the birds

Birds have played a large role in understanding the origin of species.  Birds are abundant and diverse, with some great examples of over-the-top plumage and behaviors. Knowing what we know now about evolutionary mechanisms, it's easy to see why birds continue to be model organisms for studying natural selection, sexual selection (a sub-category of natural selection), behavioral ecology, and ecologic health.   Birds also played a significant role in providing examples of change for early naturalists, like Charles Darwin, who were looking for the mechanisms to explain how organisms change through time.

Charles Darwin published On The Origin of Species by Means of Natural Selection in 1859 (Darwin removed "On" from the title after the first edition), revolutionizing the way we think about the natural world. He wasn't the first one to think that species slowly change over time, morphing from one form into the next; many naturalists who came before him were also searching for the secrets to "transmutation" (the term used before people understood what caused species to change). For example, Jean-Baptiste Lamarck (1724-1829) thought that characteristics changed between generations of organisms because of use or disuse; and these changes were heritable.  The classic example of Lamarkian evolution was a giraffe stretching its neck throughout its life to reach higher leaves, and the giraffe with the stretched neck had offspring with a longer neck. Essentially, Lamarck's idea of acquired characteristics stated that behavior could drive evolutionary change. Although Lamarkism has been falsified (though the new field of epigenetics may eventually vindicate Lamarck), his ideas are important because he was the first to come up with a mechanism to drive evolutionary change. It wasn't until decades later that the correct mechanism was identified: natural selection.

Mistaken Associations 

Natural selection is the process by which characteristics become more or less common in a population based on whether the characteristic provides an advantage or disadvantage to the survival and reproduction success of an organism in a specific environment. Darwin and his idea of natural selection are quickly associated with Galapagos finches. When Darwin was traveling aboard The Beagle, he spent time observing and collecting finch species on the various Galapagos islands.  Textbooks and popular science articles tell us that the differences in beak sizes and shapes between populations on various islands made a huge impact on Darwin when he was figuring out why species changed. However, finches are never mentioned in The Origin of Species. In fact, they're only passingly mentioned in his journals.  The truth is, Darwin never fully realized the importance of variation among Galapagos finches in light of natural selection. He actually didn't label his collections while on The Beagle and later had to figure out which birds came from where (a lesson on the importance of always keeping good field notes!). In fact, the term "Darwin's Finches" wasn't applied until 1936 (and made popular in 1947).

Despite the lack of realization on Darwin's part, Galapagos finches have played a large role in our understanding of natural selection. The huge bulk of work by Peter and Rosemary Grant (40 Years of Evolution and The Beak of the Finch are two great summaries of their research) demonstrate evolution in action.  Evolution is commonly touted as a process that takes place over long periods of time; those too long to be observed by individuals.  The Grant's research changes that idea. Rather, their life's work shows that variation in beak size and shape within a single finch population can change significantly from year to year based on environmental factors. The amount of rainfall influences the food supplies; beak size and shape determines which seeds and nuts can be eaten by an individual; so the survivorship of individuals in the population is based on who has the beak morphology that can crack the seeds that are produced, which varies depending on annual precipitation. These observations have been strengthened by the addition of genetic data - tracing gene flow and genetic variation within and between finch populations.

A Pigeon Fancier, You Say?

Birds still played an important part in Darwin's theory.  But it was a different group that influenced Darwin's ideas on natural selection: pigeons. Charles Darwin was a pigeon fancier. The Victorian Period (1830-1900) was known for it's Cabinets of Curiosities. These were for people to display their collections, and people loved to collect and display all sorts of natural history items - fossils, exotic skins and furs, artifacts, etc.  People extended their curios to live animals, as Victorian England also saw an increased interest in animal husbandry and breeding. Collections of cattle, dog, sheep, and pigeon breeds were common. But Darwin wasn't just a collector and keeper of pigeons, he turned his pigeons into an experiment.  He found that he could take one species, Columba livia, and, through selective breeding, breed hundreds of varieties.  By choosing which male pigeon mated with which female, he could study how variation could be introduced into a population, and how specific variable characteristics could be passed from one generation to the next.  It was these observations during pigeon breeding - artificial selection - that he could articulate how the environment could drive changes in the wild - natural selection.

From Chapter 1 of The Origin of Species: "Although an English carrier or short-faced tumbler differs immensely in certain characters from the rock-pigeon, yet by comparing the several sub=breeds of these breeds, more specially those brought from distant countries, we can make an almost perfect series between the extremes of structure."

Unlike finches, which never made it into The Origin of Species, pigeons made the cut and took center stage.  Darwin opens his book (or "abstract", as he put it since he intended to publish many volumes) with a chapter on domestication. The fact that his seminal work begins with domestication, not variation in nature, was a huge surprise to me the first time I read The Origin of Species, but it makes perfect, beautiful sense. Artificial selection is the key to Darwin convincing readers of his ideas. By the end of Darwin's book, he has laid out a series of logical steps that takes the reader from relatable experiences into the whole of nature:

1. Individuals in a population are not all identical.
2. This variation is heritable.
3. Variation affords different advantages and disadvantages to individuals in a population.
4. Through selective breeding, man can alter species.
5. If man can direct change (artificial selection), it can also happen in nature (natural selection).

Obligatory Discussion of Sex

An important aspect of natural selection is sexual selection - where reproductive success is a result of an individual's success in securing a mate (rather than avoiding death before reproducing). As Darwin states in Chapter 4 of The Origin of Species, 

"[Sexual selection] depends, not on a struggle for existence, but on a struggle between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring."

To emphasize this point, Darwin invokes examples from peacocks and birds of paradise. Birds are textbook examples of sexual selection. Many male species have flamboyant plumage and intricate courtship rituals they use to attract female partners.  In the case of birds of paradise, male plumage would obviously make them more obvious to predators, but it would seem that the drive for mate selection out-weighs pressures from predators.  Another example (perhaps a bit closer to home) is the cardinal. Males have evolved bright red plumage to help them attract mates, while the females are more drab to help with camouflage. If female cardinals are choosing mates with the brightest plumage (as a sign of their vitality), then the genes that control bright colors in males are being preferentially kept in the population.  Darwin expands on his ideas of sexual selection in The Descent of Man and Selection in Relation to Sex (1871).

A Celebration of Birds


The connection between Darwin and birds and his articulation of natural selection is undeniable.  Since 1859, evolutionary theory has grown.  While natural selection is still a driving force of change, we have added to that the knowledge of genetics and mutations. Despite additions to Darwin's original idea, birds have continued to play a significant role in the past 156 years of research supporting evolutionary theory.  And it's time to celebrate!

This year, 2015, we are excited to host our first Darwin Day celebration at the Sternberg Museum of Natural History!  Darwin Day is held on or around Darwin's birthday - February 12.   Choosing a theme for our first Darwin Day didn't prove to be as difficult as we feared. In this year's event, we are celebrating the huge impact birds and bird research has made on our understanding of evolutionary theory. Avian analogies are fantastic for hands-on lessons on natural selection, sexual selection, camouflage, ecosystem structure, sexual dimorphism, observing patterns in nature, and unique adaptations. And we can't wait to share this with the community!

You're doing WHAT to those bones?

Cross section through the femur of a fossil
bird called Hesperornis. Fossil bones
preserve many of the same structural features
that can be observed in modern bones. In this
image, the marrow cavity is the black portion
in the middle, and the bone tissue is the
golden/brown.

Fossils are not renewable resources.  While there is the potential that animals alive today may become fossils when they die, there are a finite number of T. rex and Smiledon (saber-tooth cat) fossils out there. Once an animal goes extinct, no more fossils of that animal can form.  This means that every fossil is precious to a paleontologist because it offers a unique glimpse into the biology, ecology, and evolutionary history of an extinct organism. Since people first understood that fossils are evidence of past life (which dates back to the mid-1600s and the work of Robert Hooke and Nicholas Steno), naturalists studied these biological remains by examining their size, shape, and similarities and differences to other fossil and living organisms. Given the scientific value of each specimen, it may be surprising to know that some researchers undertake destructive analysis (meaning they permanently alter bone) as part of their research methods. So why would paleontologists charged with preserving fossils into perpetuity do anything that would permanently alter a fossil? What information could be so important?

Histology is the study of tissue, and osteohistology is the study of bone tissue. Medical doctors and veterinarians study soft tissue and bone samples to look for disease, abnormalities, etc.  Paleontologists study bone tissue to look for evidence of the life history of an extinct animal. Only in the past few decades have paleontologists come to understand the wealth of information that can be gained from studying bone tissue. The internal microstructure of bone tells us about how an organism grew and how intrinsic and extrinsic factors affected how an organism grew.  Specifically, evolutionary relationships (phylogeny), age of the organism (ontogeny), how the animal used the bone (biomechanics), and environment directly influence bone growth. How an animals grows then tells us specifically about the life history of that animal: rate of juvenile development, age of sexual maturity, growth rate, etc.. To study bone tissue on a level that gives us useful information, one looks at just a thin sliver of the bone under a microscope.  This requires cutting a chunk out of the middle of the bone, gluing it to a slide, and grinding it thin enough so light shines through the bone. Of course we photograph, measure, and make replicas (molds and casts) of the bone before cutting, but this process obviously permanently alters a bone.

Schemtic drawing of internal bone structure showing
possible features that may be present.

Ultimately, justifying the time, effort, and destruction of cutting a bone is simple: looking at the internal structure of bone gives us information than we cannot gain just by looking at the outside of the bone (at least with current technology). Inside every bone is a network of vascular canals, osteocytes, collagen fibers, and other microstructures. Vascular canals contain vessels that carry blood and nutrients through the bone; these canals come in different shapes and sizes. Osteocytes are the cells that deposit new bone tissue; collagen fibers (made of proteins) are the organic portion of bone tissue and may vary in how well or poorly organized they are within the bone matrix.  Importantly, many of these features have been experimentally shown (using living species) to be related to growth rates. Other features like lines of arrested growth (LAGs) show when bone pauses growing and have been shown to be deposited annually.  And amazingly enough, these features are preserved during fossilization so that fossil bone microstructure can be studied just like modern bone microstructure. (It should be noted that actual osteocytes - the cells - are not fossilized, rather the space they occupy in the bone (termed osteocyte lacunae) are preserved.)

Cross section through a Gentoo Penguin femur under plain light (A) and polarized light (B). Under polarized light (B), collagen fibers become apparent (the light and dark regions show changes in collagen fiber orientation). Gentoo penguins were one of three modern penguins species used to help interpret fossil bird bone in a study I recently published. 

By studying how modern animals grow, and looking at their bone microstructure, we can understand how features like vascular canal density (canals/unit area), vascular canal orientation (radial, transverse, reticular, etc.), osteocyte density (osteocytes/unit area), osteocyte shape (globular or elongate), and collagen fiber orientation (well organized or poorly organized) relate to growth rates and metabolism. For example, high vascular canal density and unorganized collagen fiber orientations are associated with rapid growth rates; conversely, few vascular canals in well-organized collagen fiber matrix is associated with lower growth rates.  Using what we know about living animals to interpret and predict the biology, ecology, and behavior of extinct animals is an important aspect of paleontology. Armed with this knowledge of bone growth in living animals, paleontologists can begin to study the metabolism, effects of locomotion, effects of climate, and aging process of extinct animals. Bone histology is also the only way of knowing the age of an individual (extinct) animal at the time of death.

Histology is often the focus of studies pursuing a better understanding of ontogeny, paleoecology, and behavior. Even descriptions of new species often include bone histology. Knowing that an animal is an adult (and has completed development and growth) is important when describing a new species. Studying bone microstructure is the only way to determine if an animal had reached skeletal maturity by the time of death - in other words, whether the animal was an adult at the time of death. Because of all we can learn from fossils by cutting them open, histology is a rapidly growing field in paleontology. We are at a point where very few (at least in my experience) paleontology curators and collection managers (those who permit access to fossil for research purposes) don't permit researchers to section at least some bone for histology research.

Studying the internal microstructure of bone is a research trend that isn't going away any time soon - and this is a good thing.  There is too much valuable information yet to be uncovered that can come from studying bone growth. As one of my primary research focuses is on osteohistology, I sometimes find myself getting defensive when explaining my research to a lay audience. I feel that I need to justify why destructive analysis (or permanently altering bone, which sounds at least a bit more innocuous) is important. Luckily I have generally found that explaining the range and depth of information that can be gained from histology is very effective in relaying the significance of this research. Perhaps this research method doesn't seem so destructive when you consider how much information can only be gained by cutting open bone. Knowing that we make replicas of everything we sample also helps.

So while paleontologists work hard to preserve fossils, the goal of preserving them is to use these fossils for education and research.  Sometimes the quest for knowledge requires seemingly unconventional research methods. Histology has opened our minds to how extinct animals grew from hatching/birth to adulthood, how these animals responded to their physical environment, what their metabolism was like. It has also provided valuable information about the growth and development of modern animals! Bone microstructure has provided information that we could not imagine knowing just a few decades ago. It may seem paradoxical to alter bone to advance the science of paleontology, but in the case of bone histology, I feel it is clear that the ends justify the means.