A Fossil Skull of the Extant Blue Marlin (Makaira nigricans Lacapà ̈de, 1802) from the Late Miocene of Orange County, California

—A nearly complete fossil skull, including the rostrum, of blue marlin, Makaira nigricans Lacepède, 1802 (Perciformes: Xiphioidei: Istiophoridae), was collected from the Oso Member (latest Miocene) of the Capistrano Formation, Mission Viejo, Orange County, California. The specimen is compared with extant and fossil istiophorids, and 19 of its 20 morphological variables are within the range of values observed for extant M. nigricans, whereas only 13 or less variables are within the observed range of other extant istiophorids. Because extant M. nigricans usually inhabits a water column with a height of about 200 m or more and is the most tropical of all xiphioid species, its presence supports the hypotheses that the Oso Member was deposited at upper bathyal depths or greater and that the coastal paleoclimate of southern California was warmer during the late Miocene than at present. The extant blue marlin, Makaira nigricans Lacepède 1802, (Perciformes: Xiphioidei: Istiophoridae) is an important commercial and recreational fish species that inhabits the tropical and temperate Atlantic, Indian, and Pacific oceans, various strata within a water column of about 200 m or more and average sea surface temperatures of approximately 24uC (Nakamura 1985). The blue marlin is rarely observed off the coast of southern California (Eschmeyer et al. 1983). According to Fierstine (2006), the blue marlin or blue marlin-like xiphioids (M. cf. M. nigricans) are the most common fossils of the Family Istiophoridae. The earliest records are from the late Miocene where M. nigricans was identified in two rock units in southern California, the Monterey and San Mateo formations (Fierstine and Applegate 1968; Fierstine and Welton 1988; Fierstine 1998, 2001), and M. cf. M. nigricans was identified in three late Miocene rock units, the Eastover Formation, Virginia, U.S.A. (Fierstine 1998), Gatún Formation, Panama (Fierstine 1999), and Pietra leccese, Italy (Carnevale et al. 2002). In addition, blue marlin and blue marlin-like specimens also were described from the Trinidad Formation, Baja California Sur, Mexico, but because the age of the deposit ranges from late Miocene to late Pliocene (Fierstine et al. 2001), the specimens may or may not rank among the earliest known records of M. nigricans. The specimens from the two southern California localities were originally identified only to genus (Makaira sp.) (Fierstine and Applegate 1968; Fierstine and Welton 1988), but were re­ identified by Fierstine (1998, 2001) after more comparative material became available. In 1980, Hugh Wagner, during a paleomitigation project for the Mission Viejo Company, collected a nearly complete skull of M. nigricans, OCPC 31001 (Orange