A Review of the Fossil Seabirds from the Tertiary of the North Pacific
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Paleobiology,18(4), 1992, pp. 401-424 A review of the fossil seabirds fromthe Tertiaryof the North Pacific: plate tectonics,paleoceanography, and faunal change Kenneth I. Warheit Abstract.-Ecologists attempt to explain species diversitywithin Recent seabird communities in termsof Recent oceanographic and ecological phenomena. However, many of the principal ocean- ographic processes that are thoughtto structureRecent seabird systemsare functionsof geological processes operating at many temporal and spatial scales. For example, major oceanic currents,such as the North Pacific Gyre, are functionsof the relative positions of continentsand Antarcticgla- ciation,whereas regional air masses,submarine topography, and coastline shape affectlocal processes such as upwelling. I hypothesize that the long-termdevelopment of these abiotic processes has influencedthe relative diversityand communitycomposition of North Pacific seabirds. To explore this hypothesis,I divided the historyof North Pacific seabirds into seven intervalsof time. Using published descriptions,I summarized the tectonicand oceanographic events that occurred during each of these time intervals,and related changes in species diversityto changes in the physical environment.Over the past 95 years,at least 94 species of fossil seabirds have been described from marine deposits of the North Pacific. Most of these species are from Middle Miocene through Pliocene (16.0-1.6 Ma) sediments of southern California, although species from Eocene to Early Miocene (52.0-22.0 Ma) deposits are fromJapan, British Columbia, Washington,and Oregon. During the historyof the North Pacificseabirds, thee were many widespread (global) and local (California Current)oceanographic events,but the underlyingphysical processes that affectedthe diversityof seabirds throughoutthe North Pacificwere tectonicchanges thatled to sequential stages of thermal isolation and refrigerationof Antarctica.Besides these broad-scale phenomena, the uplift of the Isthmus of Panama and the initiation and intensificationof coastal upwelling in the California Currentdirectly affected the diversityof seabirds in southernCalifornia. For the most part,Middle to Late Miocene and Pliocene seabird faunas fromCalifornia resembled Recent communities,but with several exceptions: (1) the extreme diversityand abundance, but subsequent extinctionof gannets(Morus) and flightlessalcids (mancallids); (2) the comparativelylow abundance and diversity of cormorantsand shags (Phalacrocoracidae) until the Late Pliocene; and (3) the absence of marine Laridae until the Late Pliocene. By affectingboth the physical and biological environments,geo- logical factorssuch as Antarcticglaciation, eustatic changes in sea levels, and local tectonicactivities influenced and will continue to influence the structureof seabird systemsin the North Pacific. KennethI. Warheit. Departmentof Ornithologyand Mammalogy,California Academy of Sciences,Golden Gate Park,San Francisco,California 94118-4599. Present address: Divisionof Birds,National Museum of NaturalHistory, Smithsonian Institution, Washington D.C. 20560 Accepted: December 23, 1991 Not only mightcommunity-level character- Pianka 1983; Roughgarden 1989). To this pur- isticsbear the stampof eventslong past ... pose, ecologists study organisms and popu- but so also mightthe variousproperties of lations; predation, herbivory, species-level componentspecies .... Yetsuch [past] events interactions,and Recent geographic distri- are surelyno less realfor having taken place butions are frequentlythe kinds of data col- beforethe ecologistarrives to observetheir lected. The implicit assumption here is that consequences; they are only less easily species diversity within Recent ecological studied.... communities can be understood in toto Cody (1989: p. 232) throughdata collected on extantpopulations and environments.To be sure, many ecolo- gistsare now realizing thatthe temporalcom- Introduction ponent of communitiesand ecosystemsmay One goal in the study of ecological com- extend beyond that of funding resources or munities is to identifyhow and why partic- even our own existences(as suggested by the ular species co-occur (see, e.g., Ricklefs1973 epigraph). And the haunting sounds of the C 1992 The Paleontological Society. All rightsreserved. 0094-8373/92/1804-0004/$1.00 This content downloaded from 152.3.102.242 on Sun, 8 Sep 2013 20:56:41 PM All use subject to JSTOR Terms and Conditions 402 KENNETH I. WARHEIT "ghost of competition past" (Connell 1980) communities measured temporally or spa- or the "ghost of extinction past" (Van De- tially may be the result of a combination of vender 1986) are frequentlyheard in studies these differentscale effects.I discuss these of ecological communities.However, despite scale effectsusing the California Currentsea- many exceptions(e.g., see papers in Diamond bird communitiesas an example. and Case 1986), the realization that historyis importantand the suggestion to incorporate Methods paleontological data into studies of Recent SeabirdsDefined. -My definitionof seabirds communitiesand ecosystems(e.g., Fowler and includes only the Procellariiformes (alba- MacMahon 1982; Janzen and Martin 1982), trosses, petrels, shearwaters,diving petrels, have inspired only a handful of ecologists to and storm-petrels),Pelecaniformes (pelicans, use geological data. cormorants and anhingas, sulids, frigate- Although researchon seabird communities birds, and tropicbirds),Alcidae (auks), Lari- has a historyof long-termstudies (e.g., Rich- dae (gulls), and Sphenisciformes(penguins), dale 1957; Belopol'skii 1961;Ainley et al. 1983; the last of which is unknown in the North Coulsen and Thomas 1985; Ainley and Boe- Pacific. I include in this analysis all taxa of kelheide 1990), few studies have attempted fossilseabirds fromthe North Pacificthat are to introduce data from the paleontological describedin the literature.Except for my work record.This is unfortunatebecause geological on the Sulidae (gannets and boobies), I do not factors,such as changes in sea level and tec- include unpublished seabird materialin these tonic events, have directly affectedRecent analyses. In addition to these seabird taxa, seabird systems through their effecton the gaviiforms(loons), podicipediforms(grebes), geography, circulationpatterns, and climate and marine anseriforms(ducks) have been of the oceans. Although these geological pro- described fromthe eastern North Pacific.Be- cesses may contributeto the structureof Re- cause these taxa have freshwateror terrestrial cent seabird communities,they operate on a habits, I did not include them in the follow- time-scalebeyond that of human experience. ing analyses (for listings of these taxa, see Therefore, those aspects of Recent seabird Howard 1983; Becker 1987). communities that are affectedby long-term SeabirdFaunas. -Seabird fossils are usually geological events, either directlyor through found in marinedeposits, and biostratigraph- their effectson short-termecological phe- ic time scales derived frommarine plankton nomena, cannot be explained adequately by (e.g., diatoms,foraminifera, radiolarians) and studying only Recent communities. molluscs are usually used to establish relative The purpose of this paper is to associate ages for the specimens. Typically,the strati- temporal changes in seabird diversityin the graphic informationfor the seabird-bearing North Pacificto changes in global geography, formationsare included by the authorsin their climate, and oceanography. To accomplish fossil descriptions. However, because many this, I provide a list of all species of fossil of these descriptions are fromthe older lit- seabirds from the North Pacific, and group erature, the stratigraphicdata provided by these species into faunas based on their rel- these authors is out-of-date.Therefore, to es- ative temporal occurrences. I also relate the tablish seabird faunas, I used both biostrati- changes in seabird diversitybetween succes- graphic and radiometricdata fromthe recent sive faunas to changes in continentalconfig- literature(see the Appendix for full discus- urations and physical featuresof the oceans. sion of literatureand methods). Using these I describe geological events in termsof their procedures, I described each fossil specimen scale effects.For example, large-scale events in termsof its relative or absolute age. Spec- (e.g., Antarcticglaciation) can affectthe entire imens are considered isochronous if they oc- North Pacific ecosystem,whereas other geo- cur within the same or close to the same strata logical events can be more local in their im- within the same formation,or fromanother pact (e.g., affectingonly the California Cur- formationcorrelated in time to the firstfor- rent system). Differences in seabird mation. This content downloaded from 152.3.102.242 on Sun, 8 Sep 2013 20:56:41 PM All use subject to JSTOR Terms and Conditions FOSSIL SEABIRDS FROM THE NORTH PACIFIC 403 CD) I recognized seven groups of seabird-bear- I cn < o LU n z ing formationsfrom the North Pacific, each o 0 C!) < produced during a single, but broadly de- Ma wL N < u Ma fined interval of PL > Irv time (fig. 1, Appendix). I o -L IV defined the assemblage of seabird fossils re- covered fromeach group of isochronous for- 5 5- mations as a seabird fauna. I thereforerec- 0 ognized seven seabird faunas fromthe North -J IU Pacific,each associated with one broadly de- z > fined time interval (fig. 1). The temporal se- w 0 quences of these faunas in California were 15 Luis~ 15 initially described