Resolve the Relationships of Occithrissops Is Sedis Category
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66 AMERICAN MUSEUM NOVITATES NO. 2796 versus the traditional or evolutionary meth- example, the Sundance endemic Occithris- od (e.g., Mayr, 1982). The first leads to un- sops willsoni is the earliest ichthyodectiform certainty, expressed in liberal use of incertae known, and could be treated as ancestral to sedis. The second leads to spurious certainty, other members ofthe group, or at least to the when phenetic or "adaptive" groupings are ichthyodectoids. Ancestry is thus one way of treated as real. interpreting the meaning of a monotypic tax- As for "detailed biogeographical work" on in a trichotomous cladogram like figure (Campbell's 1975 phrase), it begins for the 30C. One could then develop a narrative of cladist with the question "what is the sister- ichthyodectiform dispersal, with the Sun- group, and where does it live?" The question dance Sea as the center of origin. But just as is asked for many taxa in a diversified fauna. evolutionary systematics may lead to spu- In our Sundance/Wanakah assemblage, the rious certainty, so evolutionary biogeography question cannot be answered for any taxon, may lead to spurious stories. Our inability to and analytical biogeography cannot be start- resolve the relationships of Occithrissops is ed. For the traditionalist, biogeography can surely no basis for an inferred center oforigin. be sketched out with a broader brush. For APPENDIX: THE DISTRIBUTION OF JURASSIC FISHES A resume of Jurassic fish distribution has been Forcing all Jurassic fish localities into either a ma- included in this Appendix in the form of two ta- rine or a nonmarine setting involved some judg- bles, one for marine (table 3) and the other for ments that may be incorrect, but in our view that nonmarine (table 4), and by a series of paleogeo- possibility is preferable to lumping all occurrences, graphic maps (figs. 37-39) showing most of the or to introducing a third set of tables for indeter- areas in which Jurassic fishes have been found. In minable or possible brackish-water occurrences. our present state of knowledge, this compilation The basis for the classification is necessarily a must be regarded as tentative. The reasons for this combination of the "classical" and phylogenetic have been set forth in the preceding discussion, approaches. For the Chondrichthyes, the recent which emphasizes some ofthe problems that arise studies of Thies (1983), Maisey (personal com- in analyzing and comparing any fossil fish assem- mun.), and Patterson (1965) have been utilized. blages of about the same age from different areas The actinopterygian classification is mostly based or parts of the world. Our justification for includ- on Gardiner (1967) for the chondrosteans, on Pat- ing these tables is simply that no effort of this sort terson (1973) for the non-teleost neopterygians, has been attempted before, and that the tables will and on Patterson and Rosen (1977) for the teleosts. provide a summary of current information about Taxa of unknown or uncertain status are framed both the systematics and the distribution of Ju- by quotation marks or are placed in an incertae rassic fishes. sedis category. The preparation of worldwide taxonomic, The abbreviations in the marine and non-ma- stratigraphic, and geographic records ofextinct an- rine tables represent the stages of the Jurassic, as imals, such as are represented in these tables, nec- follows: essarily involves data compression and various Portlandian Po arbitrary decisions. If such compilations are un- Upper Kimmeridgian K critical, they cease to be informative. Doubtful or Oxfordian Ox questionable identifications, which are often per- petuated in tables such as these, can mislead the Callovian Ca specialist as well as the non-specialist. On the other Middle Bathonian Bt hand, to omit a record because of doubt about Bajocian (incl. Aelenian) Bj provenance or identification can also lead one astray. We have tried to steer a middle course, Toarcian T using specialist knowledge judiciously, checking Pliensbachian P1 specimens where possible, and omitting records Lower Sinemurian S only when we believe that they lack any real factual Hettangian H basis. The distinction between the marine and non- In some areas, and particularly for nonmarine marine tables has been based on the literature, on deposits, the Jurassic has been divided only into paleogeography, and on our own opinion and/or Lower (L), Middle (M) and Upper (U), and in a field experience of the associated fauna and flora. few places only a Jurassic age (J) has been recog- 1984 SCHAEFFER AND PATTERSON: JURASSIC FISHES 67 FIG. 37. A. Paleogeographic map showing approximate distribution of land and sea during the Hettangian and Sinemurian. B. Same for the Pliensbachian and Toarcian. Modified after Hallam (1975). Geographic areas in tables 3 and 4 are shown in figure 39. nized. In the Lower and Middle Jurassic, stages Bajocian. There are problems toward the end of are non-controversial, except that we have not dis- the Jurassic, where, as Rawson et al. (1978, p. 7) tinguished the Aalenian, including it as (Lower) put it, "Ammonite provincialism had reached such 68 AMERICAN MUSEUM NOVITATES NO. 2796 FIG. 38. A. Paleogeographic map showing approximate distribution ofland and sea from the Bajocian to the early Callovian. B. Same for the late Callovian to Kimmeridgian. Modified after Hallam (1975). Geographic areas in tables 3 and 4 are shown in figure 39. a peak ... that it is extremely difficult to correlate the Jurassic/Cretaceous boundary. Hence a three- the Tethyan and boreal ammonite sequences near fold stage terminology has evolved for the top of 1984 SCHAEFFER AND PATTERSON: JURASSIC FISHES 69 FIG. 39. Paleographic map showing approximate distribution ofland and sea during the Portlandian. Modified after Hallam (1975). Numbers refer to geographic areas in tables 3 and 4. the Jurassic: Tithonian for the 'standard' Tethyan Solnhofen, Cerin) appear as Kimmeridgian, and sequence and Volgian or Portlandian for the boreal the Lulworth Beds (formerly Purbeckian) appear regions." as Portlandian. There is also a problem with the Purbeckian, The earliest Cretaceous fish assemblages from traditionally regarded as the terminal stage of the Great Britain have also been included in the tables, Jurassic in Britain. We follow Casey (1973) and to emphasize their close identity with the Late Rawson et al. (1978) in taking the mid-Purbeck Jurassic ones, as follows: Cinder Bed as the base of the Cretaceous. The lower (Jurassic) half of the old Purbeckian is now Wealden and Purbeckian above the named the Lulworth Beds, and the upper (Creta- Cinder Bed (freshwater) We ceous) half the Durlston Beds. In attempting a Marine equivalents of Wealden Ne world survey of Jurassic fishes, our selection of The geographic subdivisions in tables 3 and 4 Upper Jurassic stage names is influenced by the are based on regional or paleogeographical con- fact that we have used the British Museum (Nat- siderations. The numbered paragraphs in the dis- ural History) collections, and their catalogues and cussion below refer to these subdivisions, as do records, as an up-to-date and verified list of Ju- the numbers in figure 39. The paleogeographic rassic taxa that will serve as a standard for the maps (figs. 37-39) should be examined in con- identification and composition ofassemblages from the remarks on occurrence. other areas. We have therefore followed the Upper nection with Jurassic correlation chart recently published by the Marine Occurrences Geological Society of London (Cope et al., 1980), (Table and used Kimmeridgian and Portlandian as the 3) last two Jurassic stages. 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