Eric G. Ekdale, Ph.D.
BALEEN WHALE EVOLUTION
Generalized cladogram of mysticete cetaceans (baleen whales) with mapped characters associated with filter feeding. (Photo: Gatesy et al. 2022. Journal of Mammalian Evolution.)
Baleen whales (Mysticeti) are the largest animals to have ever lived on planet Earth. The fossil record of baleen whales extends to before the Eocene/ Oligocene boundary (~34 million years ago), and the evolutionary affinities among extinct and extant taxa are unresolved. I am collaborating with colleagues primarily from the San Diego Museum of Natural History, American Museum of Natural History, and the Smithsonian to reconstruct the phylogenetic relationships of baleen whales by combining novel genetic data (DNA) with classical and novel morphological information. By determining the relationships among whale species, we can reconstruct how the biology of whales, such as hearing and other feeding behaviors, has evolved through time.
Professional collaborators: Annalisa Berta (San Diego State University), Tom Deméré (San Diego Natural History Museum), Joseph El Adli (Bargas Environmental), John Gatesy (American Museum of Natural History), Agnese Lanzetti (Natural History Museum, London), Michael McGowen (Smithsonian National Museum of Natural History).
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THE EARS OF WHALES
Whales (Cetacea) are some of the most charismatic and beloved denizens of Earth's oceans. Whales are divided into two groups based on structures in their mouths - "toothed whales" (Odontoceti) have teeth and "baleen whales" (Mysticeti) have plates of baleen in lieu of teeth. Beyond the physical differences between toothed and baleen whales, the two groups of whales differ physiologically in that toothed whales are sensitive to high frequency sound waves (above 20 kHz), whereas baleen whales likely are sensitive to much lower soundwaves (~20 Hz or lower). My colleagues and I have identified anatomical evidence from an early whale ancestor indicating that low frequency sensitivity is an ancestral physiology that was retained by baleen whales, and high frequency sensitivity was newly derived along the toothed whale lineage. In addition, the morphology of the middle ear (bones referred to as the petrosal and auditory bulla) are phylogenetically informative for extant species.
Professional collaborators: Rachel Racicot (Vanderbilt University), Mark Uhen (George Mason University), Tom Deméré (San Diego Natural History Museum), Annalisa Berta (San Diego State University), Ted Cranford (San Diego State University)
Inner ear endocast (cochlea and semicircular canals) of extinct "archaeocete" whale (Zygorhiza kochii). (Photo: modified from Ekdale and Racicot, 2015, Journal of Anatomy.)
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GRAY WHALE ANATOMY
Rostral blood vessels and vascular canals of a gray whale neonate (Eschrichtius robustus). (Photo: modified from Ekdale et al., 2015, Anatomical Record.)
The California Gray Whale (Eschrichtius robustus) is a welcome and familiar visitor to most Californians, but there are many fundamental aspects of the biology of this magnificent animal that are yet to be discovered and understood. I and several colleagues from San Diego State University and the San Diego Natural History Museum coordinated a team of interdisciplinary scientists from multiple institutions across the country to complete a series of detailed studies of the carcass of a newborn female Gray Whale, which had stranded on a beach in northern California and subsequently was dissected at SDSU. Our novel research was published as a special thematic section in the scientific journal The Anatomical Record, and our results revealed interesting new information about the anatomy and physiology of the baby whale that was not previously known for a juvenile of the species at such an early stage of development.
Student collaborators: Joe El Adli (University of Michigan), Sarah Kienle (San Diego State University), Meghan Smallcomb (San Diego State University), Nick Zellmer (San Diego State University), Will Ary (San Diego State University), Mary Alice Chollas (San Diego State University).
Professional collaborators: Annalisa Berta (San Diego State University), Tom Deméré (San Diego Natural History Museum), Joy Reidenberg (Mount Sinai Hospital).
Dissection of the tongue of a gray whale neonate (Eschrichtius robustus). (Photo: E.G. Ekdale)
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EVOLUTION OF THE MAMMALIAN EAR
The auditory system of mammals rises above that of other tetrapods in that most mammals can process sound vibrations above 10 kHz. The overall bandwidth across which mammals are sensitive is broad – some toothed whales are sensitive to frequencies around 150 kHz and above, while elephants are sensitive to frequencies below 20 Hz. Much of my research career has focused on the anatomies associated with auditory perception, and I have used computed tomography (CT) extensively in my research. This includes studies of intraspecific variation in both marsupial and placental mammals, as well as broad scale studies of interspecific variation among placental mammals as a whole.
Inner ear endocasts of four mammals in approximate anterior view. (Photo: modified from Ekdale, 2015, PLoS ONE.)
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MESOZOIC MAMMAL EVOLUTION
Skull reconstruction of Late Cretaceous mammal (Kulbeckia kulbecke) from Uzbekistan. (Photo: Archibald et al., 2001, Nature.)
Mammals are the dominant terrestrial vertebrates of today, but they certainly held their own amidst the giant dinosaurs of the Mesozoic Era. The origin of placental mammals is controversial - living clades either appeared in the Cretaceous Period (alongside non-bird dinosaurs), or else in the earliest parts of the Cenozoic Era (after their way was paved by the great end-Cretaceous extinction). Some of my research with colleagues at San Diego State University and the Russia Academy of Science has aimed to elucidate such questions. In addition, I am actively collaborating with scientists from the University of Washington to research the lifestyles of Mesozoic mammals, which indicate that the earliest mammals were not small creatures hiding in the shadows of their giant reptile contemporaries.
Professional collaborators: J. David Archibald (San Diego State University), Alexander Averianov (Zoological Institute, Russian Academy of Sciences), Greg Wilson (University of Washington).