Channel Islands National Park: Paleontological resource inventory (public version)

Channel Island National Park (CHIS), incorporating five islands off the coast of southern California (Anacapa Island, San Miguel Island, Santa Barbara Island, Santa Cruz Island, and Santa Rosa Island), has an outstanding paleontological record. The park has significant fossils dating from the Late Cretaceous to the Holocene, representing organisms of the sea, the land, and the air. Highlights include: the famous pygmy mammoths that inhabited the conjoined northern islands during the late Pleistocene; the best fossil avifauna of any National Park Service (NPS) unit; intertwined paleontological and cultural records extending into the latest Pleistocene, including Arlington Man, the oldest well-dated human known from North America; calichified “fossil forests”; records of Miocene desmostylians and sirenians, unusual sea mammals; abundant Pleistocene mollusks illustrating changes in sea level and ocean temperature; one of the most thoroughly studied records of microfossils in the NPS; and type specimens for 23 fossil taxa. Paleontological research on the islands of CHIS began in the second half of the 19th century. The first discovery of a mammoth specimen was reported in 1873. Research can be divided into four periods: 1) the few early reports from the 19th century; 2) a sustained burst of activity in the 1920s and 1930s; 3) a second burst from the 1950s into the 1970s; and 4) the modern period of activity, symbolically opened with the 1994 discovery of a nearly complete pygmy mammoth skeleton on Santa Rosa Island. The work associated with this paleontological resource inventory may be considered the beginning of a fifth period. Fossils were specifically mentioned in the 1938 proclamation establishing what was then Channel Islands National Monument, making CHIS one of 18 NPS areas for which paleontological resources are referenced in the enabling legislation. Each of the five islands of CHIS has distinct paleontological and geological records, each has some kind of fossil resources, and almost all of the sedimentary formations on the islands are fossiliferous within CHIS. Anacapa Island and Santa Barbara Island, the two smallest islands, are primarily composed of Miocene volcanic rocks interfingered with small quantities of sedimentary rock and covered with a veneer of Quaternary sediments. Santa Barbara stands apart from Anacapa because it was never part of Santarosae, the landmass that existed at times in the Pleistocene when sea level was low enough that the four northern islands were connected. San Miguel Island, Santa Cruz Island, and Santa Rosa Island have more complex geologic histories. Of these three islands, San Miguel Island has relatively simple geologic structure and few formations. Santa Cruz Island has the most varied geology of the islands, as well as the longest rock record exposed at the surface, beginning with Jurassic metamorphic and intrusive igneous rocks. The Channel Islands have been uplifted and faulted in a complex 20-million-year-long geologic episode tied to the collision of the North American and Pacific Places, the initiation of the San Andreas fault system, and the 90° clockwise rotation of the Transverse Ranges, of which the northern Channel Islands are the westernmost part. Widespread volcanic activity from about 19 to 14 million years ago is evidenced by the igneous rocks found on each island.

Causes of mortality in northern elephant seal pups on San Miguel Island, California

In February 2015, we conducted a field study of causes of mortality of northern elephant seal ( Mirounga angustirostris) pups on San Miguel Island, California. Autopsies were performed on 18 freshly dead pups. Ages of pups ranged from stillborn to 6–8 wk. Gross and histologic lesions included trauma (9 of 18 pups), multifocal necrotizing myopathy (8 of 18), starvation with emaciation (7 of 18), congenital anomalies (3 of 18), bacterial infections (3 of 18), and perinatal mortality (stillbirths and neonates; 2 of 18). Trauma and emaciation or starvation were the most significant contributors to death. Bacterial infections included hemolytic Escherichia coli isolated from the lungs of 2 pups with pneumonia. Additionally, non-hemolytic Streptococcus sp. and hemolytic E. coli were isolated from the liver of an emaciated pup that had mild multifocal suppurative hepatitis. Other lesions, including a previously described necrotizing myopathy, congenital anomalies, and bacterial infections, were detected concurrently in cases with starvation and/or emaciation or trauma.

Multifocal Necrotizing Myopathy in Northern Elephant Seal (Mirounga angustirostris) Pups, San Miguel Island, California

A field study addressing causes of mortality in freshly dead northern elephant seals ( Mirounga angustirostris, Gill, 1866) was conducted on San Miguel Island, California, in February 2015. Necropsies were performed on 18 pups ranging in age from stillbirths to approximately 7 to 8 weeks. The primary gross diagnoses in these pups included trauma, myopathy, starvation/emaciation, infections, congenital anomalies, and perinatal mortality. However, 6 (33%) had a previously unrecognized myopathy characterized by multiple white streaks that were most obvious within the inner layer of the abdominal wall and the small innermost ventral intercostal muscles. Following histological examination, 2 more pups from San Miguel Island and 6 pups from The Marine Mammal Center (Sausalito, California) were found to have similar lesions. Histologically, the lesions within the skeletal muscles were characterized by a multifocal polyphasic, mild to severe, acute to subacute necrotizing myopathy with mineralization. Acute necrosis and degeneration characterized by pyknotic nuclei, eosinophilic cytoplasm and cytoplasmic vacuolization were found in smooth muscle myocytes within the urinary bladder and digestive system. Degeneration of myocytes was present in the tunica media of a few small- to medium-sized vessels and was characterized by a vacuolar degeneration and occasionally necrosis. This condition has been termed multifocal necrotizing myopathy. A cause of this myopathy was not identified.

A tale of two mice: A trans-Holocene record of Peromyscus nesodytes and Peromyscus maniculatus at Daisy Cave, San Miguel Island, California

Rats and mice are among the most successful mammals on earth, with some of these species thriving in and around human settlements or areas disturbed by human activities. Here, we present morphological, taphonomic, and chronological data on two mice ( Peromyscus nesodytes [extinct] and P. maniculatus [extant]) from a trans-Holocene sequence at Daisy Cave, San Miguel Island, California. We explore the colonization history of each species, species abundance through time, taphonomic history, and the causes and timing of the extinction of P. nesodytes. P. maniculatus were probably introduced by humans to San Miguel Island ~11,000 years ago, 1000 years earlier than previous estimates, and P. nesodytes does not occur in Daisy Cave deposits after ~8000 years ago, some 7000 years earlier than reported at adjacent Cave of the Chimneys. Island P. maniculatus form a distinct morphological group from all other North American subspecies. These data highlight the importance of morphological analyses of archaeological and subfossil rodent specimens for understanding the evolution and natural history of island endemic species and their interactions with humans.