University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln U.S. Department of Agriculture: Forest Service -- USDA Forest Service / UNL Faculty Publications National Agroforestry Center 2012 Marine vertebrates from the Hartland Shale (Upper Cretaceous: Upper Cenomanian) in southeastern Colorado, USA Matthew Nagrodski DePaul University Kenshu Shimada DePaul University Bruce A. Schumacher USDA Forest Service Follow this and additional works at: https://digitalcommons.unl.edu/usdafsfacpub Part of the Forest Sciences Commons Nagrodski, Matthew; Shimada, Kenshu; and Schumacher, Bruce A., "Marine vertebrates from the Hartland Shale (Upper Cretaceous: Upper Cenomanian) in southeastern Colorado, USA" (2012). USDA Forest Service / UNL Faculty Publications. 161. https://digitalcommons.unl.edu/usdafsfacpub/161 This Article is brought to you for free and open access by the U.S. Department of Agriculture: Forest Service -- National Agroforestry Center at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USDA Forest Service / UNL Faculty Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Cretaceous Research xxx (2012) 1e13 Contents lists available at SciVerse ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes Marine vertebrates from the Hartland Shale (Upper Cretaceous: Upper Cenomanian) in southeastern Colorado, USA Matthew Nagrodski a, Kenshu Shimada a,b,c,*, Bruce A. Schumacher c,d a Department of Environmental Science and Studies, DePaul University, 1110 West Belden Avenue, Chicago, IL 60614, USA b Department of Biological Sciences, DePaul University, 2325 North Clifton Avenue, Chicago, IL 60614, USA c Sternberg Museum of Natural History, Fort Hays State University, Hays, KS 67601, USA d USDA Forest Service, 1420 East Third Street, La Junta, CO 81050, USA article info abstract Article history: The Hartland Shale Member of the Greenhorn Limestone was deposited in the middle of the Late Creta- Received 27 November 2011 ceous Western Interior Seaway of North America. Rock samples rich in micro-vertebrate fossils were Accepted in revised form 7 March 2012 collected from the lower part of the Hartland Shale (ca. 94.6 Ma: early Late Cenomanian) in southeastern Available online xxx Colorado, USA. Through acid treatment of the rock samples, 25 marine vertebrate taxa are identified including chondrichthyans, osteichthyans, and a reptile. Chondrichthyans are represented by seven species: Keywords: Ptychodus anonymus, Squalicorax curvatus, Carcharias saskatchewanensis, Archaeolamna kopingensis, Cenomanian Cretoxyrhina mantelli, Cretomanta canadensis,andRhinobatos incertus. Osteichthyan fishes consist of 17 taxa: Greenhorn Limestone Late Cretaceous Micropycnodon kansasensis,cf.Palaeobalistum sp., Caturidae indet., Protosphyraena sp., Plethodidae indet., Palaeoecology Elopopsis sp., Pachyrhizodus minimus,cf.Pachyrhizodus sp., Albulidae indet., Cimolichthys nepaholica, Western Interior Seaway Enchodus cf. E. gladiolus, E. cf. E. shumardi, Apateodus sp., and four unidentified teleosts. The only reptilian recognized is the small aquatic lizard Coniasaurus crassidens (Dolichosauridae). The taxonomic composition of the Hartland Shale fauna is similar overall to the extensively sampled, underlying mid-Cenomanian Lincoln Limestone fauna in Colorado and Kansas, although the occurrence of Apateodus and Cimolichthys from the Hartland Shale is notable as they represent geologically the oldest record for the two genera. The vertebrates identified are mostly carnivores that include piscivorous and durophagous forms, providing new insights into the trophic structure of the palaeocommunity. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction A fossil assemblage from the Niobrara Formation (Upper ConiacianeLower Campanian) in Kansas is arguably the best The Western Interior Seaway is an epicontinental sea that documented vertebrate fauna from the Western Interior Seaway extended from north to south through the middle of North America where over 70 fish and 40 tetrapod taxa have been recorded to date during the Late Cretaceous. It developed when the continent was (Russell, 1988; Everhart, 2005; Shimada and Fielitz, 2006). A recent flooded from the north (Arctic Ocean) and south (AtlanticeTethyan study (Cumbaa et al., 2010) shows that at least 70 vertebrate taxa seas), and merged in the midcontinent during the early Middle were present in the seaway during the mid-Cenomanian. This study Cenomanian (Kauffman and Caldwell, 1993). It served as habitat for also reveals that the time frame marked the onset of the “Niobrara a diversity of marine invertebrates including ammonoid cephalo- fauna” because the mid-Cenomanian fauna includes approximately pods and inoceramid bivalves as well as many marine vertebrates ten species that are represented in it (Cumbaa et al., 2010). including sharks, bony fishes, and tetrapods, such as plesiosaurs, The Hartland Shale Member of the Greenhorn Limestone (Fig. 1A) mosasaurs, sea turtles, and aquatic and shore birds (e.g., Everhart, in southeastern Colorado was deposited in the middle of the 2005; Cumbaa et al., 2010). Western Interior Seaway. It lies immediately above the Lincoln Limestone Member of the same formation where the composition of vertebrate taxa has been extensively studied previously (e.g., Liggett * Corresponding author. Department of Environmental Science and Studies, et al., 2005; Shimada et al., 2006; Shimada and Martin, 2008). þ DePaul University, 1110 West Belden Avenue, Chicago, IL 60614, USA. Tel.: 1773 Although a few fish and plesiosaur remains have been noted in the 325 4697; fax: þ1 773 325 7448. E-mail addresses: [email protected] (M. Nagrodski), kshimada@ Hartland Shale from Kansas (Hattin, 1975; Riggs, 1944; Shimada and depaul.edu (K. Shimada), [email protected] (B.A. Schumacher). Nagrodski, 2010), very little is known about the vertebrate fauna in 0195-6671/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.cretres.2012.03.007 Please cite this article in press as: Nagrodski, M., et al., Marine vertebrates from the Hartland Shale (Upper Cretaceous: Upper Cenomanian) in southeastern Colorado, USA, Cretaceous Research (2012), doi:10.1016/j.cretres.2012.03.007 2 M. Nagrodski et al. / Cretaceous Research xxx (2012) 1e13 Fig. 1. A, stratigraphy of the Upper Cretaceous Greenhorn Formation in southeastern Colorado and central Kansas. B, exposure of the Hartland Shale at the Bear Springs locality in southeastern Colorado; X marks the sample location in drainage just below visible level in this photograph; horizontal line ¼ boundary between Hartland Shale and Bridge Creek Limestone. this portion of the Greenhorn Limestone. In 2006, one of us (BAS) stratigraphic range than shown or the boundary between the Lincoln discovered a Hartland Shale exposure (‘Bear Springs locality’; Fig. 1B) Limestone and Hartland Shale needs to be lowered slightly to take on the Comanche National Grassland in southeastern Colorado that into account this diachronous contact in southeastern Colorado. contains a thin fossiliferous, calcarenite bed. Samples of the deposit Regardless, the fossiliferous calcarenite bed examined in our study is were sent to DePaul University, Chicago, Illinois, for examination of interpreted to be early Late Cenomanian in age (ca. 94.6 Ma). the composition of vertebrate remains. This study reports the find- Kauffman et al. (1993) radiometrically dated the C. cantiaurinum ings, which provide further insight into the palaeoecology and ammonite zone, which is immediately below the Dunveganoceras evolution of the Western Interior Seaway. problematicum ammonite zone, to approximately 94.6 Ma. This agrees with the work of Cobban et al. (2006),whichdemonstrates 2. Stratigraphy and geological setting that the D. problematicum ammonite zone is immediately above the D. pondi ammonite zone, dated as 94.71 Æ 0.49 Ma, but well below The Greenhorn Limestone disconformably overlies the Graneros the next younger radiometrically-dated zone (Vascoceras diartianum Shale and underlies the Carlile Shale (Fig. 1A). In Colorado, it ammonite zone), which is 93.99 Æ 0.72 Ma and middle Late Cen- consists of three lithostratigraphic members. In ascending order, omanian in age. As testament to this, a single specimen of Vascoceras they are the Lincoln Limestone, Hartland Shale, and Bridge Creek sp. (FHSM IP-1476) was collected about 3.2 km from the Bear Springs Limestone (Kauffman, 1969) where their lithology reflects a trans- locality within the lower portion of the Bridge Creek Limestone. gressive event termed the Greenhorn Cyclothem (Kauffman, 1977). Deposition of the Bridge Creek Limestone marks the maximum 3. Collecting method and specimen repository transgressive phase of this cyclothem, where the water column in eastern Colorado is thought to have been greatest in the deepest Rock samples containing noticeable fish remains (e.g., Fig. 2A) part of the Western Interior Seaway, estimated maximum depths were collected directly from the rock exposure. Apart from one rock being 0.6e0.9 km (Eicher, 1967). slab preserved for reference in an unaltered state, the sample slabs The fossiliferous calcarenite examined is located in the lower one- weighing approximately 2.3 kg (5 lbs) in total were submerged third of the Hartland Shale Member, roughly 4 m above the contact under household vinegar (i.e., 5% acetic acid solution) to dissolve with the underlying Lincoln Limestone