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Owen, Department of Biological Sciences, Texas Tech University, Lubbock, Texas 79409-3131, (806) 742-3232. AFFILIATED ORGANIZATIONS Texas Section, American Association of Physics Teachers Texas Section, Mathematical Association of America Texas Section, National Association of Geology Teachers American Association for the Advancement of Science Texas Society of Mammalogists The Texas Journal of Science (ISSN 0040-4403) is published quarterly at Lubbock, Texas U.S.A. Second class postage paid at Post Office, Lubbock, Texas 79402. Postmaster: Send address changes, and returned copies to The Texas Journal of Science, Box 43151, Texas Tech University, Lubbock, Texas 79409-3151, U.S.A. THE FOSSIL BIRD ICHTHYORNIS IN THE CRETACEOUS OF TEXAS DAVID C. PARRIS AND JOAN ECHOLS Bureau of Natural History, New Jersey State Museum, CN-530, Trenton, New Jersey 08625-0530, and Department oj Earth Sciences, East Texas State University, Commerce, Texas 75428 ABSTRACT.—Four avian fossils from the Cretaceous of Texas are referred to Ichthyornis. Two specimens identified as /. dispar (Marsh, 1872) are from the Ector Chalk (Coniacian) of Fannin County. One specimen referred to /. antecessor (Wetmore, 1962) is from the Pflugerville Formation of Travis County, and another is from the Roxton Member of the Gober Chalk of Fannin County, both Campanian. The Texas specimens can be correlated with greater precision than most material of Ichthyornis and span a period essentially equal to that during which the Niobrara Formation, source of the classic specimens, was deposited. Key words: Ichthyornis; Cretaceous; paleontology; geology; bird. Since it was first described, the avian genus Ichthyornis has been among the taxa most associated with the classic chalk strata of North America. The six species described by Marsh (summarized in Marsh, 1880) from the Niobrara Formation (Coniacian-Campanian) established Ichthyornis as one of the notable toothed birds of the Cretaceous of Kansas, a genus familiar to anyone with a basic knowledge of vertebrate paleontology. Interest in Ichthyornis has increased in the last few decades (Walker, 1967; Stewart, 1990; Stewart et al., 1990). Descriptions of better specimens than those available to Marsh have reinforced knowledge of the anatomy of the genus (Gingerich, 1972; Martin and Stewart, 1977). The geologic and geographic ranges have been greatly expanded in other published reports (Olson, 1975; Lucas and Sullivan, 1982; Martin and Stewart, 1982; Fox, 1984; Zinsmeister, 1985; Nesov, 1986). As yet, however, no comprehensive taxonomic review of the genus has been published, although such a study is much to be desired. Ichthyornis was reported from the Cretaceous of Texas by Marsh (1877). The Yale University specimen (YPM 1796), the only published report of an alleged Cretaceous bird from Texas, was designated the type of a distinct species, Ichthyornis lentus (originally referred to the genus Graculavus). The specimen was attributed to the Austin Chalk near Fort McKinney (now McKinney), Collin County (misprinted as Colling County in Brodkorb, 1967). The taxonomic identity and geologic age of that specimen have been questioned, however (Shufeldt, 1915; Martin and Stewart, 1982). Despite skepticism about /. lentus, the genus Ichthyornis would be expected to occur in the chalk horizons of Texas. In fact, two well-documented Texas specimens of Ichthyornis have been known since 1940, although they apparently have not been described. Their existence presumably was noted in organizational reports 202 THE TEXAS JOURNAL OF SCIENCE—VOL. 44, NO. 2, 1992 and they were studied by leading authorities on the genus. Unfortunately, reviewers of Cretaceous faunas (Russell, 1988) generally were unaware of these specimens. We describe here four Texas specimens of Ichthyornis, the two noted above and two that have been collected more recently. All are from the Austin Division of Young (1986), a single transgression-inundation event (Fig. 1). Texas specimens of Ichthyornis are of particular importance because of their intermediate geographic position between records from Kansas and Alabama, and because the well-studied biostratigraphy of Texas (especially ammonite zonation) enables a high degree of age resolution for them. Institutional collection prefixes used here are: ET, East Texas State University; TMM, Texas Memorial Museum; USNM, National Museum of Natural History (Smithsonian Institution); YPM, Yale University (Peabody Museum of Natural History). SYSTEMATIC PALEONTOLOGY Order Ichthyornithiformes Marsh, 1873 Family Ichthyornithidae Marsh, 1873 Genus Ichthyornis Marsh, 1872 Ichthyornis dispar (Marsh, 1872) Holotype.—YPM 1450, an incomplete postcranial skeleton from the Smoky Hill Chalk Member of the Niobrara Formation in Section 1, Township 6 S, Range 19 W, Rooks Co., Kansas. Referred specimens.—TMM 31051-24, a complete right humerus (Fig. 2), and TMM 31051-25, a right wing with complete humerus, partial ulna, partial radius, and portion of carpometacarpus (Fig. 3), both specimens from the Ector Chalk Formation of the Austin Group at the Savoy Pit, Fannin Co., Texas (Ector 7.5' Quadrangle). For descriptions of the locality and Bureau of Economic Geology collecting projects, refer to Springer (1957) and Bardack (1968). Collected by Bureau of Economic Geology field party (Gregory) in 1940. Description.—The specimens are well preserved except for minor breakage and crushing, and include the conspicuous pectoral crests of the humerus that are diagnostic of the genus. Pending a generic revision, the best means of species determination remains comparison of measure­ ments to specimens described by Marsh himself. As shown in Table 1, the TMM humeri are similar to the Marsh specimens of Ichthyornis dispar, including the type. Other species of the genus for which the humerus is known differ significantly in dimensions. Both of the referred specimens from Texas are prepared in relief on blocks of matrix, somewhat limiting the views available for detailed description. However, the shaft is ICHTHYORNIS FROM THE CRETACEOUS OF TEXAS 203 FIGURE 1. Part of northeastern Texas with primary outcrop area of Austin Group (after Oetking, 1959). Localities of specimens are Gober (G) and Savoy (S) in Fannin County, and Austin (A) in Travis County. Inset shows relationships of Austin Division rocks (after Young, 1986). relatively robust in both of the distal ends of the humeri, a characteristic of /. dispar noted by Olson (1975). Length of the ulna as preserved is 63.5 mm. Discussion.—Although a revision of the genus probably will result in a reduction in the number of species of Ichthyornis, the validity of the 204 THE TEXAS JOURNAL OF SCIENCE—VOL. 44, NO. 2, 1992 FIGURE 2 (upper). TMM 31051-24, Ichthyornis dispar, right humerus, oblique view of anconal side. FIGURE 3. TMM 31051-25, Ichthyornis dispar, semiarticulated partial right wing, oblique view of distorted humerus. species /. dispar likely will be sustained. Although it was the second species of Ichthyornis to be described, it was the first to be directly attributed to the genus, and is, therefore, considered the type species (Brodkorb, 1967). It is certainly the most appropriate name in this case, because the type specimen is adequate for diagnosis and includes skeletal elements that are directly comparable. The type of /. anceps (the only species of Ichthyornis described prior to /. dispar) is too fragmentary to be useful for most specific diagnoses, being merely the distal end of a ICHTHYORNIS FROM THE CRETACEOUS OF TEXAS 205 TABLE 1. Measurements of Ichthyornis humeri (mm). /. dispar /. dispar YPM 1450 YPM 1730 TMM 31051-24 TMM 31051-25 Length 58.0 62.5 63.8 62.5 Greatest proximal diameter 13.0 15. - - Distal width 9.6 9. 9.6 8.2 Humerus distal depth 5.0 - - - Ulnar condyle diameter - 5. 4.6 5.2 Measurements of YPM specimens published by Marsh (1880). carpometarcarpus. However, it seems distinct from /. dispar based on size, as noted by Marsh (1880), who published dimensions of the types. Stratigraphy.—The Ector Chalk is the basal formation of the Austin Group and is the lowest unit of the Austin Division in the lithogenetic classification of Young (1986). It is within the Peroniceras haasi Zone of Young (1963) and correlates with the lower Coniacian Stage. The type specimen of Ichthyornis dispar is from Rooks County, Kansas, from a locality mapped in the combined zones of Cladoceramus undulatoplicatus and Platyceramus platinus by Stewart (1988),—his Protosphyraena Zone D. Thus it probably correlates with the Santonian Stage. Ichthyornis antecessor (Wetmore, 1962) Holotype.—USNM 22820, the distal end of left humerus from the Mooreville Formation (Selma Group) at Hewletts Farm, Greene Co., Alabama. Referred specimens.—TMM 42522-1 (Figs. 4 and 5), distal end of left humerus from the Pflugerville Formation at the Little Walnut Creek-Old Sprinkle Bridge Locality in Austin, Travis Co., Texas (Austin East 7.5' Quadrangle). For description of the locality, see Young (1977). Obtained by A. Busbey in 1985. ET 4396 (L85-6), the proximal end of a left carpometacarpus (Figs. 6- 8), from the Roxton Limestone Member of the Gober Formation at East Texas State Locality 36, "Dig 2," obtained by D. Galbraith, J. Echols, G.