First Unequivocal Record of the Hybodont Shark Egg Capsule Palaeoxyris in the Mesozoic of North America

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/232807915 First unequivocal record of the hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America Article in Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen · April 2010 DOI: 10.1127/0077-7749/2009/0028 CITATIONS READS 17 75 3 authors, including: Brian Axsmith Sidney Ash University of South Alabama University of New Mexico 50 PUBLICATIONS 714 CITATIONS 92 PUBLICATIONS 1,248 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Investigations of the Chinle-Dockum flora of the desert southwest View project Fishes from the Cretaceous of Saxony View project All in-text references underlined in blue are linked to publications on ResearchGate, Available from: Brian Axsmith letting you access and read them immediately. Retrieved on: 10 November 2016 N. Jb. Geol. Paläont. Abh. 2010, vol. 255/3, p. 327–344, Stuttgart, March 2010, published online 2009 First unequivocal record of the hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America Jan Fischer, Freiberg, Brian J. Axsmith, Mobile, and Sidney R. Ash, Albuquerque With 7 figures and 3 tables FISCHER, J., AXSMITH, B. J. & ASH, S. R. (2010): First unequivocal record of the hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America. – N. Jb. Geol. Paläont. Abh., 255: 327–344; Stuttgart. Abstract: The hybodont shark egg capsule Palaeoxyris humblei n. sp. is described here from four specimens collected from flood plain deposits in the Blue Mesa Member of the Chinle Formation of Late Triassic (Norian) age in Petrified Forest National Park, Arizona. This find is the first unequivocal record of Palaeoxyris in the Mesozoic of North America. The species differs from previously known taxa, especially other Triassic forms in size and banding. It also is one of the smallest species assigned to the genus. This find offers the rare opportunity of plausibly assigning these egg capsules to the hybodont nonmarine shark Lonchidion humblei as the most probable source since its disarticulated remains (teeth, fin spines) have been found at a closely adjacent locality. Originally, these eggs were deposited in special spawning grounds in the river that deposited the Newspaper Sandstone Bed. There they became attached by tendrils to a piece of drift wood or perhaps the stem or branches of a horsetail such as Neocalamites or Equisetites that grew in the shallow waters of the stream. However, the stream overflowed its banks and the egg capsules together with masses of plant debris and various invertebrates were washed onto the adjacent floodplain where they were buried and eventually fossilized. Key words: Palaeoxyris, shark egg capsule, Hybodontoidea, Lonchidion, Norian, Late Triassic, Chinle Formation, Arizona, spawning grounds. 1. Introduction (VIALOV 1984) with a puzzling gap in the record during the Permian (SCHNEIDER & REICHEL 1989; The genus Palaeoxyris was first described by FISCHER et al. 2008b). The greatest diversity of forms BRONGNIART in 1828 from the Middle Triassic (Ani - occurs in the Late Paleozoic where they are most sian) of the Vosges, France. Since that time knowledge common in siderite concretions from the Westphalian- of the variety of shapes, the geographical distribution Stephanian (Late Pennsylvanian) of North America and the stratigraphical range of this extraordinary and Great Britain (e.g., LESQUEREUX 1870; 1880; fossil has increased greatly. Among the three morpho- KIDSTON 1886; MOYSEY 1910; LANGFORD 1958). logically similar fossil egg capsule groups Palaeo - Several Mesozoic species are known from Europe, xyris, Fayolia RENAULT &ZEILLER, 1884 and Veta - Asia and Australia (e.g., SCHMIDT 1928; CROOKALL capsula MACKIE, 1867, Palaeoxyris is the most 1930; MÜLLER 1978) and there is also a doubtful common type. It is found in brackish and freshwater record from the Late Cretaceous of Kansas, USA deposits that range from the Visean (Late Mississip - (CROOKALL 1930; BROWN 1950). pian) (SCHNEIDER et al. 2005) to the Late Cretaceous DOI: 10.1127/0077-7749/2009/0028 0077-7749/09/0028 $ 4.50 © 2009 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart 328 J. Fischer et al. Fig. 1. A, Stratigraphic section of the lower part of the Chinle Formation in the southern part of Petrified Forest National Park, Arizona, showing the approximate position of the locality that contained the fossils described here (Locality PFP 004) and the position of the two localities that contain the teeth attributed to the hybodont shark Lonchidion humblei (Localities PFV 122, 124). The small index map shows the location of Petrified Forest National Park east of Holbrook in east-central Arizona and the location of the study area shown in B. B, Map of the Tepees – Puerco study area in the southern part of Petrified Forest National Park, Arizona showing the localities that contained the fossils described here (Locality PFP 004) and the two localities that contain teeth attributed to L. humblei (Localities PFV 122, 124). Stratigraphic section adapted from PARKER 2006, fig. 2) and the maps are based on the Adamana 72 minute topographic quadrangle (U.S. Geological Survey, 1982) and data supplied by W. G. PARKER. The affinities of Palaeoxyris have long been a parable to that of extant heterodont shark capsules, source of controversy (FISCHER & KOGAN 2008). As allometric properties, the absence of cuticles, and also implied by the generic name, BRONGNIART (1828) the rare co-occurrence of Palaeoxyris and skeletal considered the type species, P. regularis an inflore - remains of sharks on the same bedding plane at some scence similar to those of the extant angiosperm Xyris. localities. Consequently, Palaeoxyris is now generally Based on overall appearance and frequent occurrence accepted to be a shark egg capsule by nearly all in fossil plant assemblages, many early paleobotanists paleozoologists and paleobotanists (e.g., BROWN also regarded Palaeoxyris and the similar genera 1950; MÄGDEFRAU 1953; ZIDEK 1976; MÜLLER 1978; Fayolia and Vetacapsula as plant fossils (e.g., PRESL SCHNEIDER & REICHEL 1989; RÖSSLER & SCHNEIDER 1838; SCHIMPER & MOUGEOT 1844; ETTINGSHAUSEN 1997; SCHULTZE & SOLER-GIJÓN 2004; FISCHER & 1852; LESQUEREUX 1870; LANGFORD 1958). Further- KOGAN 2008). Although, fossil egg capsules have to more, speculations on the exact systematic position be regarded as form genera because of their am - within the plant kingdom have included nearly every biguous orthotaxonomic position (ZIDEK 1976; major vascular plant group as well as the charophy - MÜLLER 1978), they are typically treated under the cean algae (see complete reviews in CROOKALL 1932 International Rules of Zoological Nomenclature and FISCHER & KOGAN 2008). (RÖSSLER & SCHNEIDER 1997). However, other early workers (e.g., SCHENK 1867; In this contribution, the first unequivocal Palaeo - RENAULT & ZEILER 1888) noted the similarity of xyris species from the Mesozoic of North America is Palaeoxyris to the egg capsules of the living chon- described in detail from a small collection obtained drichthyan fishes. Several later studies (e.g., ZEILLER by one of the authors (SRA) from the Late Triassic 1890; MOYSEY 1910; CROOKALL 1932; MCGHEE Jr. (Norian) Blue Mesa Member of the Chinle Formation 1982; SCHNEIDER 1986; FISCHER et al. 2008a) in Petrified Forest National Park, Arizona (Fig. 1A). provided additional evidence about the affinities of This work expands on a preliminary account of this fossil. This evidence included the spiral morpho- the Chinle fossils published earlier by AXSMITH logy and parallel striae on the fossils, which are com- (2006). The hybodont shark egg capsule Palaeoxyris in the Mesozoic of North America 329 2. Geological setting 2006) (Fig. 1B). The mudstone facies of the News - paper Rock Bed contains most of the well-preserved The Chinle Formation is widely exposed on the leaf and stem compressions in the park and possibly Colorado Plateau where it has a maximum thickness beyond its borders. Although plant compressions of about 400 m. It was deposited under humid to occur at other horizons, they are not as common nor as semiarid conditions (WOODY 2006) in a variety of well preserved as in this facies which contains many nonmarine environments including floodplains, palynomorphs (LITWIN et al. 1992) and approximately stream channels, lakes, small swamps, etc. Most of the 24 named plant species based on plant megafossils deposition occurred in a succession of incised paleo- such as leaves, stems, and cones. Thirteen of these valley cut and fill complexes (DUBIEL et al. 1999). As species are closely associated with the new Palaeo - a consequence, the formation consists of a number of xyris at locality PFP 004 (Fig. 1, Table 1) and several discontinuous lithologic units that have been given unidentified forms based on plant megafossils occur a variety of names since the beginning of geologic at the locality and are now under study. The mudstone research in the region in the 19th Century (see facies also contains a variety of invertebrate fossils summaries in ASH 1970 and WOODY 2006). In Petri - including the remains of conchostracans, clams, cray- fied Forest National Park and vicinity the Chinle For- fish, adult insects, and larval cases of caddis flies, mation has a thickness of about 300 m and includes although none of these are as common as the plant many of the major subdivisions recognized elsewhere fossils (MILLER & ASH 1988; AXSMITH 2006). Most of on the Colorado Plateau although the nomenclature of the logs in the Petrified Forest as well as the verte brate some of the units in the lower part has been revised fossils are found in the strata above the Newspaper recently by PARKER (2006). We follow PARKER’s Rock Bed, particularly in the upper part of the Blue recommendations in this article. Mesa Member of the Chinle Formation (PARKER The new Palaeoxyris fossils were collected from 2006). the mudstone facies of the Newspaper Rock Bed in Typically the fossils in the mudstone facies are the Blue Mesa Member of the Chinle Formation irregularly distributed and oriented, and few if any of (Fig.

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