The Coastal Paleontologist: Coastal Paleontology in the News: recent press coverage, new publication in Geodiversitas

It's been about four weeks since I posted something on here last, but I've got some new stuff coming up. To kick it off, I have finally gotten around to submitting a press release about my new publication in Geodiversitas (in all actuality, published on December 27 of last year). What took me so long? I needed a suitable image for the press release, so I waited until I had completed a new piece of artwork. More on that below.

The new paper in Geodiversitas is concerned with a fossil assemblage of marine mammals from a relatively young section of the Purisima Formation. Most marine mammal fossils from the Purisima Formation are a bit younger, being from the latest Miocene; few well-preserved specimens are known from the Pliocene sections. Plenty of other latest Miocene marine mammal assemblages in California and Baja California exist, including the Capistrano and San Mateo Formations of Orange and San Diego Counties, and the Almejas Formation of Cedros Island off the Baja California Peninsula. However, pretty much only one Pliocene marine mammal assemblage exists for comparison - the San Diego Formation.

With this in mind, I began digging up marine mammal fossils over two two-year periods, each covered by a paleontological collections permit from California Parks and Rec. It took years to complete preparation, curation, and study the hundreds of fossils uncovered during this study, but ultimately this project produced three separate publications. The first covered the sharks, bony fish, and marine birds, while the second reported on the youngest fossil of a bony toothed bird from the Pacific basin. Although titled "A new marine vertebrate assemblage from the Late Neogene Purisima Formation in Central California, part II: Pinnipeds and Cetaceans", technically speaking the pelagornithid article was really the second part, but my coauthor Adam Smith wasn't too keen having such a long title.

One fossil in particular, the skull that would eventually become the holotype specimen of Balaenoptera bertae named in this paper, was collected when I was 19 years old. It was my first real excavation, and the first time I had ever made a plaster jacket. I'll have a longer post about the collection of the holotype later on down the line.

The fossil assemblage eventually yielded 21 marine mammals, for a total of 34 marine vertebrates. The assemblage includes fur seals (Callorhinus), walruses (Dusignathus), a "river" dolphin (Parapontoporia sternbergi) related to the recently extinct (ca. 2007) Baiji, several porpoises (Phocoenidae, unnamed genus 1, unnamed genus 2, cf. Phocoena sp.), a delphinid dolphin, a globicephaline pilot whale, two species of dwarf baleen whales (Herpetocetus bramblei, Herpetocetus sp.), the archaic balaenopterid "Balaenoptera" portisi, a possible Balaenoptera, the new species Balaenoptera bertae, and two right whales (Eubalaena spp.). Curiously absent from the fossil assemblage are tusked odobenine walruses and beluga-like monodontids (both present in other Pliocene sections of the Purisima, and will likely be found after further sampling) and hydrodamaline sirenians (e.g. Hydrodamalis cuestae), also absent from other Pliocene sections of the Purisima but abundant in coeval rocks further south in California, as well as basal late Miocene strata of the Purisima. Sirenian bones have an extraordinarily high preservation potential thanks to their large, pachyosteosclerotic (super dense) bones, and the complete absence of their fossils amongst hundreds of other marine mammal fossils suggests that this is a true absence, as their absence cannot really be argued from a taphonomic perspective. In other words, the same biases exist against other marine mammal groups, and even in intense taphonomic conditions sirenian bones are still just as common - if not more common - than cetacean bones.

The curious thing about this assemblage is that it shows that the marine mammal fauna of the Pliocene North Pacific was quite a bit different from the modern fauna. It includes numerous archaic species, such as "Balaenoptera" portisi, Herpetocetus, and a delphinid-like porpoise with a primitively asymmetrical skull, marine mammals with strange adaptations such as the as-yet unnamed "skimmer" or "half-beaked" porpoise with the elongate, edentulous "chin" that protruded beyond the upper jaw, the double-tusked walrus Dusignathus, and Herpetocetus (which counts again in this category as it had a strange feeding apparatus adapted for benthic filter feeding). The remaining marine mammals include species that are far removed with respect to modern relatives, such as Parapontoporia, the sister taxon to the recently extinct Yangtze river dolphin (Lipotes), and beluga-like monodontids and tusked odobenine walruses such as Valenictus (with modern relatives now restricted to the arctic), and early species within modern lineages, such as the newly described Balaenoptera bertae, the fur seal Callorhinus gilmorei, and an early harbor porpoise, Phocoena sp. (the Cuesta sea cow, Hydrodamalis cuestae, also counts towards this as it is known from other localities and is an early record of the recently extinct Steller's sea cow, Hydrodamalis gigas).

What explains the persistence of such a strange fauna, while modernized marine mammals were already abundant in the Atlantic? A warm-water equatorial barrier lay to the south, with the recently closed Panamanian isthmus to the east; the Bering strait had not yet opened, restricting dispersal to (and from) the north. After the Pliocene, climatic deterioration and associated oceanic cooling permitted dispersal across the equator, and the Bering strait opened up, allowing marine mammals to disperse through the arctic.

Life restoration of Balaenoptera bertae, a Pliocene species of rorqual from the Purisima Formation of Northern California. Artwork by RW Boessenecker.

Thursday, February 6, 2014

Coastal Paleontology in the News: recent press coverage, new publication in Geodiversitas

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