Presenter: Dr. Nick Pyenson
Institution: Smithsonian Institution's National Museum of Natural History
Series: Fossil Fridays
This presentation covered the evolution of whales and how they uncovered this information. Whales have ancestors dating back to over fifty million years ago. One of these ancestors is the Basilosaurus, which is a whale caught somewhere in between the modern whale and its land ancestors. Like other mammals, they had four different kinds of teeth, arms that bend at the elbow joint, and hind limbs. Another ancestor is the Pakicetus. They had weight bearing hind and forelimbs and the chemical signatures of their teeth revealed that they lived some of their time in the water. The family tree of whales shows that the earliest whales stopped using their hind limbs to propel themselves and became more tail driven slowly over time. More recently on the tree are hippos, which DNA revealed are the closest living relative to whales. The two types of whale today are Odontoceti, which use echolocation to hunt, and Mysticeti, which are filter feeders that have baleen.
A major tool in discovering all this information is fossils. One way scientists find these fossils is by searching at locations where tectonic plates meet and push up layers that otherwise would be buried deep under the crust. Once they find fossils, they can use 3D scanning to make a digital copy and transport them to a research facility to be studied. Although there are some questions about the past that can only be answered by looking at scenarios from today. One of the questions was why there were mass deaths of whales at varying times in the same area. By looking at similar events today they hypothesized that harmful algal plumes might be the cause. The large amounts of iron at the excavation site, a fuel source of harmful algal plumes, supports this hypothesis. Since whales spend ninety-nine percent of their time underwater, it is difficult to study the modern whale. Technology is a large part of this endeavor. This includes drones used to track the behavior of whales.
I found Dr. Pyenson’s evolution of whales convincing since his explanations match up with what I have learned in previous science courses. In middle school I learned vestigial structures as a part of the biology curriculum. These are components of organisms, such as organs or bones, that no longer have any functional purpose. Instead they demonstrate how the organisms once depended upon these components but have evolved to no longer need them. In whales, this was displayed as elbow joints and bone structures that closely resemble those in the limbs of land animals. They also used DNA testing, which is a highly developed technology, to show that whales are closely related to a mammal that spends time on land and in water, the hippopotamus. Concerning the classification, there are two whales that come to mind that fit perfectly. For the Odontoceti, the beluga whale is known for using echolocation. For the Mysticeti, the blue whales are known for their baleen used to filter organisms such as krill. In middle school I also learned about tectonic plates and the supercontinent of Pangaea as a part of the geology curriculum. The land mass ended up breaking apart due to the movement of magma underneath the plate in the Earth’s mantle. This continues to cause the movement of the tectonic plates. This leads to collisions in certain areas that push up older layers of the Earth’s crust closer to the surface or even above the surface. As a result, paleontologists such as Dr. Pyenson have access to fossils that are older than they normally do. Since Dr. Pyenson excavated a location in South America where two tectonic plates meet,it is reasonable that he and his team found mass amounts of whale fossils which span layers of the crust that represent varying time periods. He also did not jump to conclusions concerning the cause of death of the whales spanning a large timeline. When he found that it resembled the same effects of harmful algal blooms and discovered a fuel source for these blooms in the excavation site he did not push away all reasoning and claimed his was the only true one. Instead, he made a hypothesis off of this connection and admitted that it might not be the right answer. He then touched on other possible hypotheses to highlight that his hypothesis was not the definite answer.
Overall, Dr. Pyenson is a distinguished paleontologist who specializes in paleobiology. His work has been published in countless scientific journals including Science and Nature. He also is the lead curator, chair, and curator of Fossil Marine Mammals at the National Museum of Natural History which is a part of the Smithsonian Institution. Dr. Pyenson’s achievements in the field of paleontology and the wide acceptance of his work by other scientists makes him a reliable source of information concerning his subject of expertise.
Presenter: Dr. Briana Pobiner
Institution: Smithsonian Institution's National Museum of Natural History
Series: Fossil Fridays
This presentation briefly covered the family tree of early humans and the groups they fall into. Although they know these groups are related, the common ancestor linking all the groups together has not been discovered. Out of the twenty or so species of early humans, the only species that remains is Homo sapiens. Otherwise known as the modern human, this species only dates back to three-hundred thousand years ago. While the known history of humans dates back six million years ago, Dr. Pobiner specifically studies one million to three million years ago. This time period holds the earliest evidence of humans being meat eaters.
Dr. Pobiner and other paleoanthropologists know this and other deity habits of early humans by looking at five pieces of evidence. The first piece of evidence comes from looking at close relatives of early humans. Today, chimpanzees and bonobos are the closest relatives to modern humans. They eat fruits , nuts, seeds, leaves, insects, birds, eggs, honey, and occasionally small animals. By examining this, it can be inferred that other relatives, that is early humans, had a similar diet. The next piece of evidence comes from analyzing the teeth and skulls of fossils. If the early human had sharp teeth it most likely means that they were a carnivore, if the early human had flat teeth with large surfaces it most likely means that they were a herbivore. A mix of both indicated that they were an omnivore. Larger molars relate to more chewing. The patterns of pits or scratches can tell paleoanthropologists if the food they were eating was tough or soft. The chemistry of their teeth can also point to the type of food they were eating. Plant microfossils have even been found on teeth from becoming trapped in plague. The shape of their skulls is also a sign of their diet, since some early humans formed crests on the tops of their head to make room for chewing muscles. The third piece of evidence comes from fossilized feces. The plant and animal matter they ingested can be preserved in this form. The fourth piece of evidence comes from their compost or scraps. Specifically, the bones they leave behind have marks which point to tools when they are narrow, deep, and straight. When the marks are more irregular it points to teeth. Lastly, the fifth piece of evidence comes from the tools they used. These stone tools can be found shaped into knives, hammers, fish hooks, and spear points. In some cases the tools have traces of plants or animal blood. All of these pieces of evidence help to create a picture of how early humans ate and lived.
I found Dr. Pobiner’s explanation of how paleoanthropologists analyze fossils to determine the dietary habits of early humans convincing. It is unreasonable to compare the highly processed diet of the modern Homo sapiens to that of early humans. So by comparing the diet of Homo sapiens closest living relatives, the chimpanzee and bonobo, to that of early humans, Dr. Pobiner makes a reasonable connection since they both share similar characteristics. In addition, species that fall into a family today exhibit similar diets. An example of this is seen in Felidae, otherwise known as the feline family. While lions, tigers, panthers, and jaguars are different species, they share similar characteristics and are all carnivorous. It is also reasonable to assume the diet of early humans by their teeth. Looking at modern animals, their diet, and their teeth, there is a correlation between the shape of their teeth and whether or not they are carnivores, herbivores, or omnivores. For example, cows have flat teeth with large surfaces that are able to grind and break down plant matter, and they are herbivores. Wolves have sharp teeth that can rip apart other animals, and they are carnivores. Modern humans have a mix of flat and sharp teeth and they are omnivores. While these claims are convincing, using feces as evidence is not entirely convincing. Dr. Pobiner only mentioned how feces can preserve traces of food, which is convincing since it is the remnants of food from digestion. Although she did not bring up how they know whether or not the feces they find belong to early humans. Since I have no additional knowledge on the area I can not say that this piece of evidence is convincing. Dr. Pobiner did properly address a similar issue that arises when studying bones of prey. Instead of making the assumption that the marks in bones were caused by tools right away, she first ruled out the possibility that the marks were caused by the teeth of other animals. She does this by analyzing the bones of prey of modern day predators in Africa, including lions. From this Dr. Pobiner is able to determine that the marks in bones could not have possibly been from another predator and that tools were used by early humans to butcher their food.
Dr. Pobiner overall is a reliable source since she earned her Ph.D. in anthropology at Rutgers University. In addition to this she has countless articles published in scientific journals such as Journal of Anthropological Archaeology and Historical Biology. Dr. Pobiner is also an education program specialist of human origins at the National Museum of Natural History which is a part of the Smithsonian Institute. Her achievements in the field of paleoanthropology and the wide recognition of her work by renowned organizations make her a reliable source on the evolution of human diets.
