Updating the Fossil Record of Whales


Publication Date: 29 November, 2019

Stefano Dominici, Silvia Daniseb, Simone Cauc, Alessandro Freschic

Summarized by Jacob T. Booe. Jacob is in his senior year at the University of South Florida pursuing a B.S. degree in Geology. Growing up on the east coast of Florida near Kennedy Space Center, science and engineering has surrounded him for much of his educational career. While Jacob’s current trajectory is geared towards Earth Sciences, at the time of high school graduation, Jacob had no clue what his future career path was. Therefore, he enrolled in his local community college, Eastern Florida State College, where he graduated with his A.A. degree. However before obtaining an A.A. degree, Jacob found himself as an avid musician, pursuing the idea of acoustics and audio engineering. It wasn’t until his last year before receiving his A.A. degree that Jacob decided to take an intro to geology elective. After that course Jacob found himself committed to a career in geology transferring to USF in Spring 2020.

What data were used: The research team began with the analysis of 719 records of fossil whales, whose first origins are in the Cenozoic Era, across the Miocene, Pliocene, and Pleistocene epochs, approximately 11,000 to 23 million years ago (Figure 1). Researchers also used fossil whale occurrences to supplement their dataset from the Paleobiology Database (PBDB), which is a public database of global fossil occurrences that researchers update with new fossil finds. Along with the fossil occurrences, researchers collected information about the characteristics of rocks (i.e., their lithology). in which the fossils were found, where in the world they were found, and the time at which they lived. 

Methods: Researchers created six categories of lithology based on composition and grain with carbonate (like limestone) and siliciclastic rocks (like sandstone); these can be considered to represent the environments they likely have lived in. The skeletal system of the whales was categorized into four parts: skull, teeth, limbs, and spinal column. In addition, each fossil was graded on its quality of preservation. These data were analyzed to determine what relationships these variables shared. Other data, like measurements of the whale bones, were used to determine growth patterns of the organisms.  

Results: The majority of whale fossils that have currently been described originated in the Northern hemisphere. The team compared their findings to that of the existing PBDB and found that the PBDB had a more global sampling, with more even coverage between the north and south hemispheres. Researchers note that more exploration for fossils in the southern hemisphere must continue; other areas for further research include West Africa and Antarctica. In regard to lithological findings, results show that whale fossils are mainly found in fine-grained siliciclastic rocks while carbonates contribute considerably fewer occurrences. This differs from the PBDB, where carbonate lithologies had more occurrences than fine-grained siliciclastic. In terms of the growth of an organism, the team compared the fossil whales against the growth of a modern whale, the river dolphin. The results showed that in ancestral whales, skull size increases while the tympanic bulla (an ear bone) decreases; however, modern whales show skulls that increase concurrently with the tympanic bulla, with a special type of growth called “isometric growth”. 

The figure shows a global map projection denoting whale fossil finding by colored dots. Each dot is assigned a color based on its region locality. Regions are classified into nine groups as follows: 1) Western coast of Central and North America, 2) Western Coast of Southern America, 3) Eastern Coast of North America, 4) Eastern Coast of South America, 5) Western Coast of Europe and North Africa, 6) Mediterranean, Central and Eastern Europe, and Asian Near East, 7) Eastern Coast of Asia, 8) Oceania, 9) Indian Ocean and Austral Africa. The figure visually identifies that most samples are present in regions of North America (regions one and three), Europe (regions five and six) and Japan/Eastern Asia (region seven); or simply put the Northern Hemisphere.
Figure: The figure above displays the various distributions of whale fossil findings. The team grouped together nine regions showcasing which areas have been sampled. This also shows which areas are under sampled and could provide excellent locations for future studies.

Why is this study important: The current information used to study whales and their evolution is incomplete and biased towards known fossil localities in the northern hemisphere. In order to fill in the gap of whale fossils, this study shows some trends towards what environments is more likely to hold preserved whale fossils. 

The big picture: In this study, the authors tried to determine the quality and quantity of fossil data of whales. Identifying the gaps in our knowledge, and discovering why those gaps currently exist, can have an impact on how scientists approach whale paleontology moving forward. As the authors point out, places like West Africa are under-sampled, which leads to biases in our dataset. It is critical to determine whether under sampled areas of the world are due to a lack of fossil record or if scientists are not approaching the search for fossils globally. 

Citation: Dominici, S., Danise, S., Cau, S., & Freschi, A. (2020). The awkward record of fossil whales. Earth-Science Reviews, 205, 103057.https://doi.org/10.1016/j.earscirev.2019.103057