Coast Geological Society

Ventura, California

Please Join CGS on Tuesday February 19th, 2019

Jonathan Hoffman, Ph.D., from the Santa Barbara Museum of Natural History, will give his talk titled:

Fossil Megafauna from Santa Rosa Island, Channel Islands National Park

Fossil Megafauna from Santa Rosa Island, Channel Islands National Park


Abstract: 


The fossils of Channel Islands National Park demonstrate the dynamic nature of southern California’s tectonic and climatic history. In particular, Santa Rosa Island (SRI) gives us a look at the contrasting worlds of two different fossil megafauna: the sea cow and Pygmy Mammoth.


The fossils of these distantly related mammals are found in geologic units on SRI that are separated by at least 20 million years. As a result of southern California’s famous tectonic history, these animals also lived at different latitudes. Fossils of the first known SRI sea cows were excavated by the Santa Barbara Museum of Natural History in 2017 and 2018. The animals had lived, died, and were buried near modern-day San Diego in a warm, nearshore environment similar to that of most living manatees and dugongs. The sea cow fossils on SRI are currently estimated between 20 to 25 million years ago (Ma). Around 20 Ma, the region of continental crust containing the sea cow bones detached from the North American Plate and began rotating while travelling northwest along the San Andreas fault system. At about 5 Ma, this slab started being compressed by Baja California, which had also detached from the North American Plate and began travelling northwest. The compression resulted in folding, faulting and uplift of the Channel Islands and Western Transverse Ranges.


Sea cow fossils were likely already exposed on the interior of the superisland Santa Rosae when Columbian Mammoths arrived on its shores as early as 200,000 years ago. The northern Channel Islands formed Santa Rosae during glacial maxima and corresponding sea level lowstands. During the lowstands, the Santa Barbara Channel was less than 6 miles across and a manageable swim for pioneering Columbian Mammoths on the mainland. Over successive generations, the island population of Columbian Mammoths (average of ~14 feet at the shoulder) underwent insular dwarfism, resulting in the Pygmy Mammoth (average of ~5 feet at the shoulder). Additionally, the Pygmy Mammoth adapted its limb morphology to scale steeper slopes and access more of the mountainous interior than its larger ancestors. The Pygmy Mammoth went extinct about 13,000 years ago, near the end of Pleistocene glaciation.



Jonathan Hoffman, Ph.D.
Bio:

Jonathan Hoffman came to the Santa Barbara Museum of Natural History in 2017 after receiving his Ph.D. in Geology from the University of Wyoming. He earned his Master’s in Geology from the University of Florida and Bachelor of Arts in Geology from Occidental College. His dissertation focused on the utility of fossil mammal teeth as paleoecological tools to recreate ancient landscapes. His research interests have led him to unconventional studies not commonly associated with vertebrate paleontology, such as fecal analyses of modern bison herds (including on Santa Catalina Island) and controlled feeding trials with sheep. He has worked field sites across the United States, including California, Florida, Kansas, Oregon, Utah, and Wyoming.

As the Dibblee Collection Manager of Earth Science, Dr. Hoffman is responsible for the Museum’s geology and paleontology collections. He has placed a strong emphasis on reanimating the fossil collecting program and growing the Earth Sciences Collection to fully represent the Central Coast’s paleontology and geology. Channel Islands National Park is a key component to this goal. The SBMNH is the official repository for Channel Islands National Park and Jonathan has been working with the Park Service to protect and recover fossils from the Islands. These fossils include the first known sirenian, or sea cow, from the Channel Islands. In 2017 and 2018, Dr. Hoffman led the first SBMNH excavation crew in decades to stabilize and excavate the specimen and he is the Principal Investigator for the multi-institutional research team studying the sirenian locality.

Headline

The monthly CGS meeting is held at the Poinsettia Pavilion in Ventura!

Meeting Schedule:

6:00 - 7:00 PM: Social Hour - Snacks and Beverages 

7:00 - 7:30 PM: Dinner Service

7:30 - 8:00 PM: Announcements & Raffle

8:00 - 9:00 PM:  Main Presentation


CGS is proud to be affiliated with the PSAAPG