Asmodochelys leviathan, Smith & Adrian & Kline, 2025

Asmodochelys leviathan sp. nov.

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Etymology: Te species epithet refers to the concept of Leviathan, based in pre-biblical Middle Eastern mythology, in particular a sea monster named Lotan that was defeated by the god Baal. Over time, the term has become more broadly used to refer to any gigantic, powerful entity or large sea monster.

Holotype: HNSMWS-2018.1, a nearly complete carapace, including nuchal, neurals 1–8, suprapygal 1, pygal, costals 1–8, an isolated section of left peripherals 8–10, an isolated partial left portion of the anterior plastron with likely partial epiplastron and hyoplastron, partial right?pubis.

Type locality and horizon: North shore of South Sulphur River, Hunt County, Texas; Neylandville Formation; lower Navarro Group. Exact locality data is on file with Heard Natural Science Museum and Wildlife Sanctuary (HNSMWS) in McKinney, Texas.

Diagnosis

Asmodochelys leviathan sp. nov. is a large-bodied Cretaceous pan-chelonioid that can be diagnosed as a member of Ctenochelyidae based on a prominent single neural keel, the presence of epineural ossifications, and a cordiform carapace ( Baird, 1964; Gentry, 2017, 2018; Gentry et al., 2018, 2019). It can be referred to Asmodochelys based on its thick shell and deep nuchal embayment; lack of nuchal fontanelles (unlike other ctenochelyids; Baird, 1964); horn-like protuberances from the anterodorsal margins of the first peripherals; first epineural positioned at N1/2; relatively short, narrow, and minimally scalloped posterior peripherals ( Gentry et al., 2019).

Asmodochelys leviathan sp. nov. has the following unique combination of traits: broad thick nuchal with deep nuchal embayment including the first peripherals; well-developed anteriorly projecting protuberances on pe1; robust articulations between costal 1 and both peripherals 1 and 2 resulting in costoperipheral fontanelles that begin at costal 3; lack of postnuchal fontanelles; absent preneural; 8 neurals; epineural ossifications at N1/2, N3/4, N5/6, and N7/8; thin, narrow, weakly scalloped posterior peripherals. Its carapace is highly domed, and the anterior carapace is substantially deeper than other ctenochelyid species, most similar to Asmodochelys parhami ( Gentry et al., 2019) . In contrast to all other known ctenochelyids ( Ctenochelys , Peritresius , Prionochelys , and Asmodochelys parhami ) only Asmodochelys leviathan sp. nov. has a robust articulation among the nuchal and first two anterior peripherals, with no evidence of costoperipheral fontanelles in this area ( Baird, 1964; Gentry, 2017, 2018; Gentry et al., 2018, 2019; Matzke, 2007).

Asmodochelys leviathan sp. nov. differs from its congeneric Asmodochelys parhami in its extensive contact between costal 1 and the first two peripherals. Tis arrangement results in free peripherals that are associated with costoperipheral fontanelles beginning at costal 3 in Asmodochelys leviathan sp. nov., whereas in Asmodochelys parhami , these fontanelles extend along the entire length of the carapace, contacting the nuchal, pygal, and all intervening costals. Asmodochelys leviathan sp. nov. has 8 neurals compared to the putative?9 neurals in Asmodochelys parhami . Te positions of the epineurals also differ, falling at N1/2, N3/4, N5/6, and N7/ 8 in Asmodochelys leviathan sp. nov., and at N1/2, N2/3, N4/5, and N6/ 7 in Asmodochelys parhami (Table 2). Posterior peripherals are narrow and weakly scalloped in both species compared to other ctenochelyids, but the condition is amplified in Asmodochelys parhami , which has even narrower and less scalloped peripherals ( Table 3).