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| Fona herzogae |
Abstract
Thescelosaurines are a group of early diverging, ornithischian dinosaurs notable for their conservative bauplans and mosaic of primitive features. Although abundant within the latest Cretaceous ecosystems of North America, their record is poor to absent in earlier assemblages, leaving a large gap in our understanding of their evolution, origins, and ecological roles. Here we report a new small bodied thescelosaurine—Fona herzogae gen. et sp. nov.—from the Mussentuchit Member of the Cedar Mountain Formation, Utah, USA. Fona herzogae is represented by multiple individuals, representing one of the most comprehensive skeletal assemblages of a small bodied, early diverging ornithischian described from North America to date. Phylogenetic analysis recovers Fona as the earliest member of Thescelosaurinae, minimally containing Oryctodromeus, and all three species of Thescelosaurus, revealing the clade was well-established in North America by as early as the Cenomanian, and distinct from, yet continental cohabitants with, their sister clade, Orodrominae. To date, orodromines and thescelosaurines have not been found together within a single North American ecosystem, suggesting different habitat preferences or competitive exclusion. Osteological observations reveal extensive intraspecific variation across cranial and postcranial elements, and a number of anatomical similarities with Oryctodromeus, suggesting a shared semi-fossorial lifestyle.
SYSTEMATIC PALEONTOLOGY
DINOSAURIA Owen (1842).
ORNITHISCHIA Seeley (1887).
NEORNITHISCHIA Cooper, 1985 (sensu Butler et al., 2008).
ORNITHOPODA Marsh, 1881 (sensu Butler et al., 2008).
THESCELOSAURIDAE (Sternberg, 1937).
THESCELOSAURINAE (Sternberg, 1940).
THESCELOSAURINAE indet.
Fona herzogae sp. nov.
Holotype: NCSM 33548, a single partially articulated, nearly complete skeleton.
Occurrence: NCSM 33548 was recovered from the Karmic Orodromine locality (UT-16-07-22-Z1), lower Mussentuchit Member, upper Cedar Mountain Formation, Emery County, Utah, USA (Figure 1). Stratigraphic occurrence is between MAZ1 and Last Chance Sandstone (99.466 + 0.046/−0.053 Ma; Tucker et al., 2023) making it the only locality definitively preserving F. herzogae from the lower Mussentuchit unit to date. Mini Troll (NCPALEOUT16) is the geologically youngest locality, emplaced below MAZ3, with an age of 99.231 + 0.090/−0.052 Ma. FMNH PR 4581 was preserved at the Manolo site (UT130831), (99.411 + 0.056/−0.061 Ma) above MAZ2 in the upper Mussentuchit (Figure 1).
Age data is based on a Bayesian age stratigraphic model (Trayler et al., 2020) of the member originally detailed in Tucker et al. (2023). Materials referable to Fona span the lower to upper Mussentuchit Member of the Cedar Mountain Formation, a range of, at minimum, 235,000 kyr. UT-16-07-22-Z1 and NCPALEOUT16 are located on land administered by the US Bureau of Land Management, respectively; exact locality information is restricted by federal statute and is available to qualified researchers via the NCSM.
DIAGNOSIS: Fona herzogae is a small-bodied, early diverging ornithischian with the following unique combination of characters (autapomorphies are denoted with an asterisk) (Figure 5) *(1) a rostral maxillary fossa located caudal to the first tooth position (unknown in Oryctodromeus and possibly shared by Isaberrysaura and Haya); *(2) an otoccipital that bears a dorsoventrally elongate fossa on the medial surface of the occipital condyle located directly caudal to the medial opening of CN XII; *(3) a rostrocaudally oriented ventral canal on the prootic; *(4) The dorsal margin of the axis neural spine is parallel with the dorsal suture of the centrum, forming an angle of essentially ~0°. *(5) Ischial shaft has bulbous thickening along the dorsal margin directly distal to the obturator process (prominent on both ischia of at least two individuals and weakly present on only the right of another.) (6) base of the prepubic process bears a prominent lateral swelling (possibly present but significantly reduced in Oryctodromeus and Th. neglectus). (7) the caudoventral prong of the jugal's caudal process underlaps a groove along the ventral margin of the quadratojugal (shared by Th. neglectus, likely Changmiania, and possibly at least one specimen of Jeholosaurus [STMN 23–17]). (8) dentary teeth with vertical wear facets on the labial surface that terminate abruptly near the crown base to form a mesiodistally inclined shelf (shared by Oryctodromeus). (9) A low, round tuberosity on the medial side of the scapula located directly opposite to the glenoid ridge (shared with Oryctodromeus and possibly Iani smithi). Standard skeletal measurements of NCSM 33548 are provided in Table 1. Characters 7–9 serve as important synapomorphies that help place Fona within Thescelosaurinae.
Fona n. gen.
Etymology: Fona (/Foat'NAH/) from the Austronesian language Finoʼ CHamoru. The ancestral maga'håga of the CHamoru people is Fo'na whose name can be translated as ‘the origin’. With her brother Pontan, whose name can be translated as ‘a ripe coconut’, they became the first paramount female and male chiefs (the ancestral maga'låhi of the CHamoru people), ancestrally venerated according to CHamoru tradition (Borja-Quichocho-Calvo, 2021; Cruz, 2022). According to oral history and legend, when Pontan's spirit began to perish and die, Fo'na discovers her powers and uses them to craft parts of Pontan's body into the pieces of the universe. His eyes were turned into the sun and moon, his eyebrows became the rainbows, his back the earth, his chest the sky, his blood the ocean, and from his stomach and penis the mountains and the sacred Creation Point stone pillar were born (Duhaylonsod & Cepeda, 2022). Fo'na had such sorrow from the loss of her brother that her tears flowed down his body to form the currents of the sea, and in reverence to her brother's dream, she decided to bring life to the universe, throwing herself into the earth where her body turned to stone. From her fossilized body sprang forth the first people at Fuha Rock, imbued with her good spirit (Cepeda, 2021; Cunningham, 1992; Perez, 2019; Perez, 2021). This ancestral story of the CHamoru people mirrors the life and death of the thescelosaurine dinosaurs at the Mini Troll locality, as there were at least two subadult individuals that may have been male and female, or perhaps siblings. Additionally, their bodies fell into the earth where they too fossilized. This naming, rooted in the story of Pontan's sacrifice and Fo'na's love for her brother, highlights the CHamoru values of inafa'måolek (to make good for all), geftåo (the need for compassion, selflessness, and familial bonds) (Duhaylonsod & Cepeda, 2022), the importance of the equality shared between women and men (Naholowa'a, 2018), and ongoing efforts to decolonize paleontology (Monarrez et al., 2021).
Fona herzogae sp. nov.
Etymology: The specific epithet honors Lisa Herzog (discoverer of the Mini Troll locality) for her unparalleled dedication to the paleontology program at the NCSM and the collection, care, and conservation of fossil specimens worldwide.
CONCLUSION:
Fona herzogae adds to the cryptic diversity of the Mussentuchit Member dinosaur fauna, serving as an important component of this exceptional mid-Cretaceous ecosystem. It would have lived alongside the hadrosauromorph Eolambia caroljonesa (McDonald et al., 2017), the Rhabdadontomorph Iani smithi (Zanno, Gates, et al., 2023), the small-bodied tyrannosaur Moros intrepidus (Zanno, Tucker, et al., 2019), the large-bodied allosaurian Siats meekerorum (Zanno & Makovicky, 2013), an unnamed oviraptorosaur (Zanno, Avrahami, et al., 2019) and neoceratopsian (Zanno, Tucker, et al., 2023), and a collection of other terrestrial vertebrates (Avrahami et al., 2018).
The presence of a distinct thescelosaurine taxon in the Mussentuchit member supports the hypothesis that the ancestors of Thescelosaurus were present in North America as early as the Cenomanian, co-inhabiting the continent with their sister-taxon Orodrominae. To date, members of these clades have not been found together, suggesting different habitat preferences. Shared ecomorphology with, and a close phylogenetic affinity with Oryctodromeus demonstrated here, supports a shared semi-fossorial lifestyle. Some of the extensive intraspecific variation among specimens of Fona is likely attributable to ontogenetic transformations, whereas others may suggest a broad phenotypic range for the taxon or may point to sexual dimorphism.
Haviv M. Avrahami, Peter J. Makovicky, Ryan T. Tucker, Lindsay E. Zanno. 2024. A New semi-fossorial thescelosaurine Dinosaur from the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation, Utah. The Anatomical Record
