A REVIEW OF OF FOSSIL BROWN MACROALGAE FROM SOUTHERN CALIFORNIA AND THE DISCOVERY OF NEW MACROALGAE FOSSILS FROM THE MIOCENE-PLIOCENE SISQUOC FORMATION

Macroalgae are of vital importance in both the local ecosystems they inhabit and support as well as on a broader, industrial and global scale. They directly and indirectly support innumerable species and have wide-reaching ecological influence. However, for all the importance of modern macroalgae, they are poorly represented in the fossil record. Only 26 specimens of fossil macroalgae from Cenozoic rocks of California have been described in the literature thus far, from 2 publications (Gardner, 1923; Parker & Dawson, 1965). Represented among these 26 fossils are 18 brown algae, 7 red algae, and 1 green algae. Several genera are present in these specimens — the most prominent of them being Paleohalydris and Paleocystophora. However, since the description of these macroalgae some 60-100 years ago, significant taxonomic rearrangements have occurred. Of most relevance is the consolidation of Cystoseira and Halidrys species along the West Coast of the United States into the Stephanocystis genus (Driasma et al., 2010). Furthermore, understanding of macroalgae morphology has evolved substantially in years since the discovery of the fossils described by Gardner, and later, Parker & Dawson. Following these developments, it is appropriate to return to previously described specimens and assign new taxa based on modern understanding and updated morphological guidelines.

Since 2021 numerous new macroalgae fossils have been recovered from the Jack and Laura Dangermond Preserve, in the vicinity of Point Conception, Santa Barbara County . These specimens, all found in the latest Mocene-earliest Pliocene Sisquoc Formation, more than double the number of known fossil macroalgae from California and have not yet been described. Numerous species are present within these samples, some of which are also represented in the specimens described by Parker & Dawson. These novel fossils, together with others collected in Southern California in recent decades, represent a wealth of untapped knowledge. Overall, the greater number of macroalgae species now available for study has significant scientific importance, particularly for understanding the evolutionary history of specifically brown algae along the West Coast of the US, which is not yet wholly understood. These new samples offer key glimpses into the timing of the evolution and ecology of brown algae along the West Coast over time.