Turtle Graveyard locality (Cretaceous of the United States)

Where: Slope County, North Dakota (46.3° N, 104.0° W: paleocoordinates 52.6° N, 77.4° W)

• coordinate based on political unit

• small collection-level geographic resolution

When: Hell Creek Formation (Montana Group), Late/Upper Maastrichtian (70.6 - 66.0 Ma)

• Stratigraphically the quarry is placed in the lower third of the Hell Creek Formation (latest Maastrichtian), approximately 65 m below the Fort Union

•formational contact.

•The site is located in the lower third of the [Hell Creek] formation, approximately 65 m below the formational contact with the Fort Union Formation

• member-level stratigraphic resolution

Environment/lithology: lacustrine - small; sandstone and tabular mudstone

• 2009: The unit in which the fossils are preserved is overlain with a series of sandstone units, a large structureless conglomerate-like unit with clay clasts up to 40 cm in diameter that cuts into the underlying sandstone unit and pinches out to the southeast, and a series of laminated clay units that lie in between sandstone units (Fig. 1). The alternating sequence of high velocity sandstone deposits and zero velocity laminated clay units, as well as the incising channels, indicate an ephemeral paleo-environment, such as a pond or shallow stream, which would periodically flood and dry out (Murphy et al., 2003).

•2011: The depositional setting is interpreted as an oxbow lake in which many turtles aggregated and perished during a drought and where the slightly disarticulated carcasses were later washed together after the onset of rains.

• The fossil-bearing layer varies laterally in thickness from 80–120 cm over a distance of 16 m (Fig. 1). It lies on top of an undulatory, tabular mudstone with scour marks bearing 245degrees southeast. Directly overlying the scoured bed is a structureless layer of rip-up clasts and sand that varies in thickness from 1–12 cm (Fig. 1). The clasts are typically 1 or 2 cm in diameter; however, clasts 3 to 4 cm in diameter are not uncommon. The fossil material, as well as numerous lignified logs, is found in or on top of this layer (Fig. 1). Hollow sandstone moulds up to 10 cm in diameter preserve many of these logs three dimensionally. Branches and turtle shells commonly extend into the overlying unconsolidated sandstone layer. The upper portion of this fining upward unit preserves heterolithic cross-beds dipping approximately 20degrees to the southeast. The bed is 60–70 cm thick in the southeastern part of the quarry and it pinches out into a laminated clay unit on the northwestern portion of the quarry. Discontinuous lag stringers with clay clasts ranging in size from a few mm to 3 cm in diameter are found throughout this portion of the sequence. This layer is overlain with a laminated clay unit, which varies laterally in thickness from 2–18 cm (Fig. 1). The textural and structural data indicate that the entire sequence was the result of deposition from fluvial currents of decreasing energy (Boggs, 2006).

Size class: macrofossils

Collected by Marmarth Research Foundation in 1996-2011

Collection methods: quarrying, surface (in situ),

• MRF, Marmarth Research Foundation, Marmarth, North Dakota, U.S.A.

•This locality is an approximately 125 square meter large quarry, in which a single, fossiliferous layer has been mined by MRF for vertebrate fossil remains over the course of the last 15 years.

Primary reference: W. G. Joyce and T. R. Lyson. 2011. New material of Gilmoremys lancensis nov. comb. (Testudines: Trionychidae) from the Hell Creek Formation and the diagnosis of plastomenid turtles. Journal of Paleontology 5(3):422-459 [R. Benson/R. Benson]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 122903: authorized by Roger Benson, entered by Roger Benson on 07.01.2012, edited by David Nicholson and Evangelos Vlachos

Creative Commons license: CC BY (attribution)

Taxonomic list

• 2011: To date, the quarry has produced more than 100 turtle specimens, mostly baenids, including the skull and shell of Palatobaena cohen Lyson and Joyce 2009a, a skull each of Peckemys brinkman Lyson and Joyce 2009b and Cedrobaena putorius (Gaffney, 1972), and a large series of skulls and shells of an unnamed representative of Eubaena (Lyson and Joyce, 2009a, 2009b).

•2009: The locality, named Turtle Graveyard, has yielded an unsurpassed number of slightly disarticulated baenid turtle specimens including more than 70 shells, 35 skulls, and other postcranial remains partial, disarticulated trionychid turtle skeletons, teeth, and cartilaginous jaw elements from the ray fish Myledaphus, a lone unidentified crocodile dentary, and a few isolated bones from an unidentified theropod

Chondrichthyes
 Rajiformes - Rhinobatidae
Myledaphus sp.2 Cope 1876 guitarfish
cartillaginous jaw elements
Reptilia
 Testudinata - Baenidae
Baenidae indet.1 Cope 1882 turtle
new species
Palatobaena cohen n. sp.2 Lyson and Joyce 2009 turtle
YPM 57498, (holotype) a complete uncrushed skull, mandible, and shell; MRF 257, complete skull and mandible; MRF 259, complete skull; MRF 263, complete skull; MRF 123, shell missing part of carapace
"Peckemys brinkman" = Cedrobaena brinkman3 Lyson and Joyce 2009 turtle
MRF 231 (skull)
Cedrobaena putorius3 Gaffney 1972 turtle
MRF 239 complete skull
 Testudines - Pantrionychidae
Gilmoremys lancensis Gilmore 1916 turtle
MRF 275, nearly complete skull; MRF 277, nearly complete skull; MRF 309, nearly complete skull and anteroposteriorly crushed skull; MRF 758, nearly complete skull (Fig. 6); MRF 759, partial skull, associated jaw and articulated anterior cervical column; MRF 525, nearly complete carapace; MRF 516, a left hyoplastron; MRF 565, a right hyoplastron; MRF 536, a right hyoplastron; MRF 534, a left hypoplastron; MRF 467, a right hypoplastron; MRF 549, a right xiphiplastron; MRF 575, a left xiphiplastron
 Testudines - Trionychidae
Axestemys infernalis1 Joyce et al. 2019 softshell turtle
 Crocodylia -
Crocodylia indet.2 Owen 1842 crocodilian
dentary
 Theropoda -
Theropoda indet.2 Marsh 1881 theropod
'a few isolated bones'