Tetrapod Tracks from the Mauch Chunk Formation (Middle to Upper Mississippian) of Pennsylvania, U.S.A Author(S): Matthew B
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Tetrapod tracks from the Mauch Chunk Formation (middle to upper Mississippian) of Pennsylvania, U.S.A Author(s): Matthew B. Vrazo, Michael J. Benton, Edward B. Daeschler Source: Proceedings of the Academy of Natural Sciences of Philadelphia, 156(1):199-209. 2007. Published By: The Academy of Natural Sciences of Philadelphia DOI: http://dx.doi.org/10.1635/0097-3157(2007)156[199:TTFTMC]2.0.CO;2 URL: http://www.bioone.org/doi/ full/10.1635/0097-3157%282007%29156%5B199%3ATTFTMC%5D2.0.CO%3B2 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. ISSN 0097-3157 PMROCEEDINGSISSISSIPPIAN OF THETETRAPOD ACADEMY T RACKSOF NATURAL SCIENCES OF PHILADELPHIA 156: 199-209 JUNE 2007199 Tetrapod tracks from the Mauch Chunk Formation (middle to upper Mississippian) of Pennsylvania, U.S.A. MATTHEW B. VRAZO AND MICHAEL J. BENTON Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, England E-mail: [email protected] EDWARD B. DAESCHLER Academy of Natural Sciences of Philadelphia, 1900 Benjamin Franklin Parkway, Philadelphia, Pennsylvania 19103-1195 U.S.A. E-mail: [email protected] ABSTRACT.— Evidence of tetrapods is scarce in the early Mississippian. Following Romer’s Gap, a time of some 15 million years at the beginning of the Mississippian when remains of tetrapods and other continental organisms are rare, only sporadic skeletal and footprint fossils are found. We report here on new specimens of the tetrapod ichnogenera Hylopus and Palaeosauropus from the middle of the Mauch Chunk Formation (middle to upper Mississippian) of Eastern Pennsylvania. These document walking and swimming behaviors by at least two basal tetrapod taxa, perhaps an anthracosaur and a temnospondyl, and show evidence for the beginning of the second period of tetrapod diversification. Key words: Carboniferous, Mississippian, tetrapod, trace fossil, ichnofossil, Mauch Chunk Formation. INTRODUCTION parts may be Viséan in age based on fossil plants (Jennings 1985). So, this unit probably immediately postdates Tetrapod trackways occur only sporadically in the Mis- Romer’s Gap (Ward et al. 2006). sissippian and yet such materials document the early stages Tetrapod tracks have long been known from the Mis- in the invasion of the land by vertebrates and can indicate sissippian of Pennsylvania (Lyell 1843; Lea 1849; Dawson aspects of the palaeobiology of early tetrapods. Fossil tracks 1863; Leidy 1879). Lea (1849) named the ichnogenus from the early Mississippian are especially important be- Palaeosauropus (Sauropus) from the Mauch Chunk For- cause of the rarity of skeletal fossils through that time. Tet- mation in Pennsylvania, but little else has been published rapods originated in the Late Devonian, and apparently di- from the state (Cotton et al. 1995). New trackway material versified to some extent, but their fossil record is especially from the Mauch Chunk Formation in Pennsylvania has re- weak for the first 15 million years of the Mississippian cently been added to the collections at the Academy of Natu- (Tournaisian and early Viséan; about 360-345 million years ral Sciences in Philadelphia (ANSP). The purpose of this ago). This time span is known as as Romer’s Gap, named paper is to describe the new material and to put it in con- for Alfred Sherwood Romer who first noted the hiatus (Ward text of the early radiation of tetrapods on land. et al. 2006). This interval was assumed to represent a time of poor preservation, but Ward et al. (2006) argue that the GEOLOGY gap was a time of genuine low diversity of tetrapods be- cause of unusually low atmospheric oxygen levels. Only after The Mauch Chunk Formation occurs in several drain- the recovery of oxygen levels 345 Ma did tetrapods begin age basins in Pennsylvania, Maryland and West Virginia, their terrestrialization phase in earnest. and for the most part is a monotonous sequence of 100m to Among tetrapods, this second phase of radiation is 1000 m thickness of red and grey siltstones, fine sandstones, marked by the appearance of several tetrapod lineages, the and shales that is largely unfossiliferous. Orogenic uplift basal Crassigyrinidae, Baphetidae, Colosteidae, and in the southeastern corner of the state during the late middle Adelogyrinidae, as well as the Aïstopoda, Microsauria, Mississippian created the Mauch Chunk delta, and by the Temnospondyli, and Anthracosauria, together representing late Mississippian this delta had prograded to the north- a major radiation of tetrapods that continued through the eastern corner of the state (Edmunds et al. 1979). The Mississippian (Ruta et al. 2003). The Mauch Chunk Forma- Mauch Chunk Formation has been subdivided informally tion of Pennsylvania is generally accepted as middle to up- into three members by Wood et al. (1969): the lower and per Mississippian (c. 320-340 million years ago), but lower upper members consist of alternating grey and red beds, 200 M. B. VRAZO, M. J. BENTON AND E. B. DAESCHLER and the middle member consists of greyish red beds. The The age of the Mauch Chunk Formation is debated. It upper member intertongues with the overlying Pottsville is usually dated as Mississippian, and most often middle to Formation, and the lower member intertongues with the upper Mississippian, because the underlying Pocono Sand- underlying Pocono Formation. The top of the formation is stone Formation is dated as middle Mississippian and the placed somewhat arbitrarily at the top of the last of the red overlying Pottsville Formation as Pennsylvanian. Edmunds beds, so there is some debate about whether the contact with (1996) notes the age of the Mauch Chunk Formation spans the Pottsville Sandstone is conformable or unconformable about half of the Osagean Age, the entire Meramecian and (Edmunds et al. 1979). Calcareous sandstone is found in Chesterian Ages, and a small part of the Morrowan Age some sections, and occasional limestone beds are found in based on intertonguing marine beds and determinations of the western part of the state where the formation is more age from marine fossils. This is confirmed by freshwater differentiated and has been subdivided stratigraphically bivalves in the Mauch Chunk Formation itself (Busanus and (Edmunds et al. 1979). Hoare 1991). The maximum age range, on this estimate, Coarsening-upwards fluvial cycles are seen through- corresponds to the time from Viséan to earliest Bashkirian out the Mauch Chunk Formation and have been interpreted on the international scale (Gradstein et al. 2004), suggest- by Griesmer (1980) as an indication of deltaic progradation. ing duration from 352 to 318 million years ago at most. The absence of large-scale cross bedding, the presence semi- Magnetostratigraphic evidence (Opdyke and DiVenere directional ripple marks and the presence of both walking 2004) confirms this and suggests that the entire Mauch and swimming traces indicate a shallow, semi-aquatic en- Chunk Formation spans more than 18 magnetozones repre- vironment. Barrell (1907) interpreted the whole of the senting some 16 million years. Jennings (1985) reported Mauch Chunk Formation as having been deposited in a sub- fossil plants that confirmed a Viséan age for the middle aerial/fluvial setting in a semi-arid climate. Desiccation member of the Mauch Chunk Formation, so it is still un- cracks and raindrop imprints throughout the formation in- clear whether the unit spans a long time interval or contains dicate a semi-arid climate, though it was never dry enough many gaps. The trackways all come from the middle mem- to produce evaporites. The footprint slabs described here, ber, equivalent to the late Meramecian/ early Chesterian time and field observations by MBV, confirm aspects of the sedi- interval (Edmunds 1996), and so perhaps some 340 Ma. mentology of the Mauch Chunk Formation. ANSP 22651 is a slab of medium/fine grained reddish-brown sandstone with SYSTEMATIC PALAEONTOLOGY a muddy, rough texture, and convex hyporelief raindrop imprints on the underside of the slab. ANSP 22652 and Ichnogenus Hylopus Dawson, 1882 22653 were found in situ at Tamaqua, Pennsylvania, where Ichnospecies Hylopus hardingi Dawson, 1882 the entire formation is only 115 m thick, in a bed some 20 m below the obscure contact between the Mauch Chunk Material.—ANSP 22651, a slab with 12 prints. and Pottsville formations. Bed thickness varies throughout Locality.—Banks of the Nescopeck Creek under an the section, but individual beds are some 60-100 mm thick. overpass of US I-80, near Hazleton, Luzerne County, Penn- The tracks are found near the top of a fining-upward fluvial sylvania. ANSP 22651 was found as float in an area under- cycle composed of fine-grained, grey sandstone overlaid lain by the Mauch Chunk Formation and the lithology is by red mudstone. There is an erosive contact at the base of consistent with Mauch Chunk lithofacies. the cycle, and the upper surfaces of some beds including Occurrence.—Hylopus is known from the Horton those with tracks, show shallow ripple marks, with those Group (Tournaisian to lower Viséan), Nova Scotia; Bluefield near the top of the section being more linguoid in shape. Formation (middle Mississippian), West Virginia and Mauch Shales at the top of the cycle show desiccation cracks, Chunk Formation (middle to upper Mississippian), Penn- raidnrop imprints, and rare plant impressions.