Associated with abundant bones, teeth and osteoderms of the giant eusuchian Deinosuchus rugosus are larger concretionary masses of consistent form and composition. It is proposed that these are crocodylian coprolites, and further, based on their size and abundance, that these are coprolites of Deinosuchus. The associated coprolite assemblage also contains additional types that may come from smaller crocodylians, most likely species of the riverine/estuarine genus Borealosuchus, which is represented by bones, osteoderms and teeth in fossil collections from the same site

Harrell, Samantha D.

Schwimmer, David R.

English

Columbus State University

209Milàn, J., Lucas, S.G., Lockley, M.G. and Spielmann, J.A., eds., 2010, Crocodyle tracks and traces. New Mexico Museum of Natural History and Science, Bulletin 51.COPROLITES OF DEINOSUCHUS AND OTHER CROCODYLIANS FROMTHE UPPER CRETACEOUS OF WESTERN GEORGIA, USASAMANTHA D. HARRELL AND DAVID R. SCHWIMMERDepartment of Earth and Space Sciences, Columbus State University, Columbus, GA 31907 USA, schwimmer_david@colstate.eduAbstract—Associated with abundant bones, teeth and osteoderms of the giant eusuchian Deinosuchus rugosusare larger concretionary masses of consistent form and composition. It is proposed that these are crocodyliancoprolites, and further, based on their size and abundance, that these are coprolites of Deinosuchus. The associatedcoprolite assemblage also contains additional types that may come from smaller crocodylians, most likely speciesof the riverine/estuarine genus Borealosuchus, which is represented by bones, osteoderms and teeth in fossilcollections from the same site.INTRODUCTIONThe Upper Cretaceous Blufftown Formation in western Georgiacontains a diverse perimarine and marine vertebrate fauna, including manysharks and bony fish (Case and Schwimmer, 1988), mosasaurs, plesio-saurs, turtles (Schwimmer, 1986), dinosaurs (Schwimmer et al., 1993),and of particular interest here, abundant remains of the giant eusuchiancrocodylian Deinosuchus rugosus (Schwimmer and Williams, 1996;Schwimmer, 2002). Together with bite traces attributable to Deinosuchus(see Schwimmer, this volume), there are more than 60 coprolites recov-ered from the same formation, including ~30 specimens that appear to beof crocodylian origin. It is proposed here that the larger coprolites arefrom Deinosuchus, principally because that is the most common largetetrapod in the vertebrate bone assemblage from the same locality, and itis assumed that feces scale to the producer (Chin, 2002). The additionalcoprolites of apparently crocodylian origin considered here are tenta-tively assigned to an indeterminate species of Borealosuchus, which isthe second most common crocodylian in the fossil assemblage.Age and PaleoenvironmentThe specimens in consideration come from a ~1.0-m thick bone-bed in the uppermost Blufftown Formation, a detrital sedimentary unitthat represents a mixture of marine coastal salt marshes, back-barrierembayments, and tidal estuaries along the southeastern coast of NorthAmerica during the Late Cretaceous (Reinhardt and Donovan, 1986).This geographic position is significant because it was then at the bound-ary of the Atlantic and Gulf Coastal Plains, although the Cenozoic growthof Florida places it now in the easternmost Gulf Coastal region (Frazierand Schwimmer, 1987). The locality sampled for all of the material hereis near the boundary of the States of Georgia and Alabama in the south-eastern United States (Fig. 1), along the banks of Hannahatchee Creek, amajor tributary to the Chattahoochee River, in Stewart County, westernGeorgia. The detailed site stratigraphy is presented in Schwimmer (1986),and the precise GPS coordinates are available by contacting DRS.At the sampling locality, the Blufftown Formation is dated to thelatest-early Campanian (78.0 + 1.0 Ma) by the co-occurrence of numer-ous index taxa, including oysters (Exogyra erraticostata), ammonites(Placenticeras dekayi), planktonic foraminiferans, and bylithostratigraphic correlation with regional chalk formations containingabundant calcareous microfossils (Schwimmer et al., 1994). The BlufftownFormation is overall approximately 125 m thick and ranges down to agesof approximately 84 Ma (Schwimmer et al., 1994); however, the speci-mens here are from the very top of the formation.COPROLITES ATTRIBUTED TO DEINOSUCHUSIdentifying the source of a Mesozoic coprolite can be a dauntingtask. Of the general categories of sedimentary masses found in associa-tion with numerous Deinosuchus fossils in the Blufftown Formation,the six largest of these have shapes and large size (Fig. 2) most parsimo-niously attributed to Deinosuchus. This attribution is based on severalfactors. First, Deinosuchus specimens extrapolated to 7-9 m total lengthare locally common and by far the most abundant larger tetrapods in thevertebrate assemblage from this site; indeed, this locality has the mostabundant known assemblage of Deinosuchus bones and teeth in theeastern USA (Schwimmer, 2002). Second, the overall external form ofthese presumed coprolite masses, as discussed below, is reasonably closeto crocodylian coprolites from other ages and settings (e.g., Sawyer,1981; Milàn, this volume). Finally, these are relatively large masses (rela-tive to other non-dinosaurian coprolites), and Deinosuchus is precisely alarge, non-dinosaurian tetrapod.These putative Deinosuchus coprolites are ellipsoidal and isopolar(sensu Thulborn, 1991), ranging from 9 to 11 cm in length (averaging10.25 cm), with the average width of 5.25 cm, ranging from 4.5 cm to 8.0cm. The six well-preserved masses are grossly uniform in being relativelywide in cross-section in proportion to length, but they range in outlineFIGURE 1. Locality map, showing the approximate position of thecollecting site for all specimens in study. The study area is in westernGeorgia, USA, within the valley of Hannahatchee Creek, a tributary to theChattahoochee River. The inset map of eastern North America shows theposition of the locality map within the southeastern continent.210from elongate cylinders to sub-ovals. All of these that are complete havetapering ends, but none show clearly-indicated sphincter marks. Struc-turally and sedimentologically they have many of the characteristics ofcommon septarian concretions (McBride et al., 2003), but with openvoids internally rather than the mineral-filled cracks found in septaria;however, we argue below that the origin of these concretions is fecal. Inthe discussion to follow, we divide the morphology of these putativecoprolites into three distinct regions: outer surfaces (Fig. 3A), corticesand cores (Fig. 3B).The outer surfaces of these presumed Deinosuchus coproliticmasses are mostly gray to tan, agglutinated quartz sand, carbonate clastsand mica, with invertebrate shell fragments, and osteichthyan and sharkteeth comprising ~5% of the surface material. The cortices (i.e., the outerzones between surfaces and cores) comprise approximately the outer0.8-1.0 cm volume in most specimens where they are visible, and containmaterials similar to the surfaces but with increased amounts of carbonateclasts, bone fragments and small fish teeth. One specimen (Fig. 4) in-cludes a well-preserved shark tooth (Squalicorax yangaensis) in thecortex.The cores of these coprolites consist of a slightly darker, finegrained matrix (Fig. 5A), which is composed largely of microcrystallinecalcite with a few, very small, empty vesicles, and minor inclusions of awide variety of materials, including opaque, presumably organic sub-stances. The notable feature evident in the cores of cut or broken speci-mens (Fig. 5B) is large fissures. These fissures are not as extensive as aretypically found in septarian concretions, but they do resemble closelythe radial fissure configuration present in some dinosaur coprolites(Thulborn, 1991). The presence of fissures in these presumed Deinosuchuscoprolites, versus the more typical small gas vesicles found in smallercrocodylian coprolites (see below), is explained as follows: in smallerfecal masses, numerous small vesicles occur from gas bubbles, which aresmall and abundant, and which may escape to the surface. In the largefecal masses of dinosaurs (Thulborn, 1991) and presumably Deinosuchus-size crocodylians, large volumes of gases (principally methane and am-monia) would instead be confined by the large size of the mass, produc-ing elongate voids, which would be preserved as radial fissures. It is alsonoteworthy that these fissures are generally open, rather than filled withcalcite crystals, as in typical septarian concretions.The mineralogical composition of the presumed Deinosuchus co-prolites is unusual. To explain their makeup, it is here hypothesized thatthese masses, which are obviously concretionary, developed around theoriginal Deinosuchus fecal masses, which are represented by the cores.Thus, the relatively homogeneous carbonate cores of the coprolites rep-resent the approximate size and shape of the feces, which is approxi-mately 7.0 to 10.0 cm long by ~ 5.0 cm diameter, whereas the “cortex” ofeach mass is mostly detrital sedimentary material that accumulated aroundthe original fecal mass. Bacterial films would naturally form around thefeces and would be sticky, attracting external material to the developingconcretions (Hendry et al., 2006). Although coprolites from carnivoresare typically mineralized by fluorapatite in terrestrial and freshwaterenvironments (Chin, 2002), they may also become the nuclei for concre-tionary growth (Thulborn, 1991). Formation of a carbonate concretionaround large feces in marine deposits may occur when the mass is buriedjust below the sediment-water interface in finer-gained, carbonate-richsediment. In this model, anaerobic decomposition produces abundantNH3, raising the local pH, and favoring precipitation of carbonate (Weeks,1957). We hypothesize that marine sedimentary conditions of theBlufftown Formation, and the relatively large size of these Deinosuchus-size masses, favored this mode of preservation of the cores of thesecoprolites.The distinctive cortices of these specimens are assumed to haveaccumulated well after the feces were excreted, during extensive marinetransport and redeposition. The upper 1.0 m of the Blufftown Forma-tion, where these coprolites are found, contains a concentrated bed offragmentary bones of many organisms (Schwimmer, 1986) and veryabundant, usually water-worn fish teeth (Case and Schwimmer, 1988).This type of sedimentary deposit is best explained as a marine transgres-sive lag concentration, where teeth and bones initially accumulated in thenearshore marine environment, and are subsequently carried by cyclicalhigh-sea stands into sediment-starved bays and estuaries along the ma-rine coast (Schwimmer, 2002). During the extensive transport and timesof accumulation, it is assumed the developing concretionary masses wouldroll around, pick up detritus and bone fragments, and accrete largely inwidth. It is notable that the cores extend well to the ends of the masses(Fig. 5B), whereas the cross-sections show thick annular accumulationof the cortex (Fig. 5A). Some of the fish teeth embedded in the corticesand on the surfaces may also represent coprophagous feeding by bonyfish and sharks (e.g., Fig. 4).FIGURE 2. Representative coprolites of Deinosuchus rugosus, both arefrom the uppermost meter of the Blufftown Formation, HannahatcheeCreek locality, Stewart County, Georgia (all specimens to be figured herefrom the same locality). All specimens are catalogued in Columbus StateUniversity Cretaceous (CSUK) collections: these are (upper left) CSUK-09-04-1 and (lower right) CSUK-09-04-2. Scale bars in all figures = 1 cm(except Fig. 7). Note the surface accumulations of carbonate shell debris,siliceous detritus, and minor (darker) vertebrate material.FIGURE 3. Largest (8.0 cm diameter) coprolite in the assemblage, CSUK-09-04-3, with one tapered end and broken surface showing distinctly separatecore and cortex. In this specimen the cortex is relatively asymmetrical(compare with Figure 5), and incorporates some larger shells and detrituswhich are assumed to have accreted onto the original fecal mass.211FIGURE 4. Deinosuchus coprolite including complete shark tooth (Squalicorax yangaensis), CSUK-09-04-4: A, overall coprolite morphology. B, brokenend separated and rotated to show shark tooth (arrow). Note that preservation of the shark tooth is very good, suggesting that the tooth was implantedin the coprolite after it was transported back to the final depositional site (i.e., the shark may have been feeding on the coprolite).ADDITIONAL COPROLITESATTRIBUTED TO CROCODYLIANSSmaller (relative to the above) coprolites in the Blufftown assem-blage are generally more typical of the sizes, shapes, and surface featuresgenerally assumed for crocodylian coprolites (Fisher, 1981; Sawyer,1981; Milan, this volume). These coprolites vary widely in size, averag-ing 4.0 cm in length by 2.2 cm width, and they are relatively dark andmore uniform in texture than the Deinosuchus coprolites discussed above.The overall shapes vary (Fig. 6), with some showing strong coiled orropy-textures, presumed to result from digestive compaction (Fig. 6A),which are quite typical of carnivorous tetrapod coprolites (Chin, 2002).Several of these smaller coprolites also show characteristic anisopolarmorphology (Thulborn, 1991) with one strongly tapered end (Fig. 6B),typical of terrestrial carnivore scat. Several smaller isopolar coprolites inthe assemblage have a J-shaped morphology (Fig. 6C), which may berepresentative of some smaller crocodylian feces (J. Milàn, pers. comm.).The internal composition of these smaller coprolites appears rela-tively uniform and is composed of darker, microcrystalline phosphaticmineral (collophane), with abundant, well-demarcated voids (Fig. 7),presumed to be formed by gas bubbles entrapped while the masses werenonmineralized. No evidence of preserved bone or any invertebrate ma-terials has been found either within or on the surfaces of these smallercoprolites. As discussed above, the associated Blufftown Formationvertebrate assemblage includes many types of tetrapod carnivores, whichcould hypothetically produce ~ 4.0 cm coprolites, ranging from smallertheropod dinosaurs (an indeterminate ornithomimisaur and cf.Saurornitholestes sp.), to mosasaurs, plesiosaurs, turtles, andcrocodylians. There are also large fish in the assemblage (e.g., the 4-m-long teleost Xiphactinus: Schwimmer, et al., 1997, and the similar-sizedcoelacanth Megalocoelacanthus: Schwimmer, et al., 1994), which con-ceivably could produce some of these masses. Assuming they arecrocodylian in origin, the fossil assemblage includes numerous teeth,osteoderms and a few vertebrae and jaw fragments attributed to an inde-terminate species of Borealosuchus, which would be the mostly likelysource of smaller crocodylian coprolites in this collection.FIGURE 5. Cut specimens of assumed Deinosuchus coprolites: A, CSUK-09-02-2, cross-sectioned and polished specimen, showing the distinct coreand relatively symmetrical cortex. B, CSUK-09-02-1, sagittally cut andpolished specimen. Note the extensive fissure visible in both sections, andthat the core in B persists close to the two ends.212FIGURE 6. Smaller, more typical tetrapod coprolites from the Blufftown Formation, same locality as the preceding figures: A, (left to right) CSUK-09-04-12, -13, -14, masses of generalized coprolitic morphology, notably with ropy surfaces suggesting digestive compaction; B, CSUK-09-04-10 completecoprolite with tapered unipolar morphology; C, (left to right) CSUK-09-04-10, -8, -9, J-shaped coprolites, notably with more complex surface sculptingand relatively uniform shape. SUMMARY AND CONCLUSIONSThe larger masses proposed here as Deinosuchus coprolites areatypical crocodylian coprolites, in that they are preserved as carbonate-cored concretions with differentiated concentric internal structure, in-cluding internal fissures and a large amount of accumulated sedimentarymaterial in the outer region. The explanation of all these unique character-istics is the combination of the large size of Deinosuchus feces and theirmarine depositional and transportation history. It is hypothesized thatthese Deinosuchus coprolites underwent some diagenetic processes moresimilar to the feces of dinosaurs rather than of smaller crocodylians, buttheir occurrence in nearshore marine environments favored replacementwith calcite rather than the more typical mineralization by apatite. Thesmaller coprolites in the same deposit are typical of those from average-sized crocodylians, and derive from Borealosuchus or a similar-sizedreptilian carnivore.ACKNOWLEDGMENTSWe thank Christopher Stanford of Columbus State University, forassistance in field collecting and laboratory preparation of specimens;and Tracy Hall of Georgia Highlands College, for assistance in preparingcomposite figures. We also thank reviewers Pauolo Souto, Adrian Hunt,and others, for critical comments which helped us greatly improve themanuscript.FIGURE 7. Cross-sectional view of smaller coprolite, CSUK-09-04-16,similar in size and morphology to the specimens in Figure 6C. The specimenis embedded in epoxy and polished, showing microcrystalline apatitecomposition with numerous ~ 1 mm diameter voids. Scale bar for this figureis 1 mm.213REFERENCESCase, G.R. and D.R. Schwimmer, 1988, Late Cretaceous fish from theBlufftown Formation (Campanian) in western Georgia: Journal of Pale-ontology, v. 62, p. 290-301.Chin, K., 2002, Analyses of coprolites produced by carnivorous vertebrates:Paleontological Society Papers, v. 8, p. 43-49.Fisher, D.C., 1981, Crocodilian scatology, microvertebrate concentrations,and enamel-less teeth: Paleobiology, v. 7, p. 262-275.Frazier, W.J. and Schwimmer, D.R., 1987, Regional stratigraphy of NorthAmerica: Plenum Publishing, New York, 719 p.Hendry, J.P., Pearson, M.J., Trewin, N.H., and Fallick, A.E., 2006, Jurassicseptaria concretions from NW Scotland record interdependent bacte-rial, physical and chemical processes of marine mudrock diagenesis:Sedimentology, v. 53, p. 537 – 565.McBride, E.F., Picard, M.D., and Milliken, K.L., 2003, Calcite-cementedconcretions in Cretaceous sandstone, Wyoming and Utah, USA.: Journalof Sedimentary Research, v. 73, p. 462-483.Reinhardt, J. and Donovan, A.A., 1986, Stratigraphy and sedimentology ofCretaceous continental and nearshore environments in the eastern GulfCoastal Plain; in Reinhardt J., ed., Stratigraphy and sedimentology ofcontinental, nearshore and marine Cretaceous sediments of the EasternGulf Coastal Plain: Society of Economic Geologists and Paleontologists,Annual Meeting Field Trip Guidebook, v. 3, p. 3-10.Sawyer, G.T., 1981, A study of crocodylian coprolites from WannaganCreek Quarry (Paleocene—North Dakota): Scientific Publications ofthe Science Museum of Minnesota, New Series, v. 5, p. 1-29Schwimmer, D.R., 1986, Late Cretaceous fossils from the Blufftown For-mation (Campanian) in Georgia: The Mosasaur, v. 3, p. 109-123.Schwimmer, D.R., 2002, King of the crocodylians, the paleobiology ofDeinosuchus: Indiana University Press, 221 p.Schwimmer, D.R., Stewart, J.D., and Williams, G.D., 1994, Giant fossilcoelacanths of the Late Cretaceous in the eastern United States: Geol-ogy, v. 22, p. 503-506.Schwimmer, D. R., Stewart, J.D., and Williams, G.D., 1997, Xiphactinusvetus and the distribution of Xiphactinus species in the eastern UnitedStates: Journal of Vertebrate Paleontology, v. 17, p. 610-615.Schwimmer, D.R. and G.D. Williams, 1996, New specimens of Deinosuchusrugosus, and further evidence of chelonivory by Late Cretaceous eusuchiancrocodiles: Journal of Vertebrate Paleontology, v. 16, supplement to no.3, p. 64A.Schwimmer, D.R., Williams, G.D., Dobie, J.L., and Seisser, W.G., 1993,Late Cretaceous dinosaurs from the Blufftown Formation in westernGeorgia and eastern Alabama: Journal of Paleontology, v. 67, p. 288-296.Thulborn, R.A., 1991, Morphology, preservation and palaeobiological sig-nificance of dinosaur coprolites: Palaeogeography, Palaeoclimatology,Palaeoecology, v. 83, p. 341-366.Weeks, L.G., 1953, Environment and mode of origin and facies relation-ships of carbonate concretions in shales: Journal of Sedimentary Petrol-ogy, v. 23, p. 162-173.214Chinese alligator. Photo by Jesper Milàn.

Coprolites of Deinosuchus and other crocodylians from the Upper Cretaceous of western Georgia, USA

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Coprolites of Deinosuchus and other crocodylians from the Upper Cretaceous of western Georgia, USA

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