[Paleontology • 2026] The ontogenetically youngest known pachycephalosaur (Dinosauria: Ornithischia) postcranium

 

juvenile Pachycephalosauria indet. (CMNFV 22039)
Life reconstruction in an environment typical of the upper Maastrichtian Frenchman Formation, Saskatchewan. 

in Moore, Evans, Ryan, Patterson et Mallon, 2026. 

  DOI: doi.org/10.1080/02724634.2026.2616325

Illustration by Kaitlin Lindblad. 

 x.com/Jordan_Mallon

 

ABSTRACT

Pachycephalosaurian dinosaurs are represented in the fossil record primarily by their taphonomically resistant frontoparietal domes that developed fully only at maturity. Consequently, the postcranial record of Pachycephalosauria is poor, particularly for immature forms. Here, we describe the ontogenetically youngest known, and Canada’s second-most complete, pachycephalosaur postcranium, collected from the uppermost Maastrichtian Frenchman Formation, Saskatchewan. Despite its small size (estimated total length ∼90 cm), the skeleton shows several characters diagnostic of Pachycephalosauria, including a double ridge-and-groove articulation on the pre- and postzygapophyses of the dorsal neural arches, a medial flange on the postacetabular process of the ilium, and a highly reduced pubis that contributes only minimally to the acetabular margin. Histological sectioning of the crural bones shows an immature woven bone texture. The absence of cyclical or annual growth indicators suggests that this specimen was less than a year old at the time of death. Phylogenetic analysis recovers the specimen as a member of Pachycephalosaurinae, perhaps related to Prenocephale, but the lack of cranial data for our specimen and the complementary lack of postcranial data for other pachycephalosaurs make this determination tenuous. Spatiotemporal considerations suggest a possible but currently untestable affiliation with Sphaerotholus buchholtzae. The relatively long hindlimbs of the juvenile compared with those of adult pachycephalosaurs indicate probable negative ontogenetic allometry in the hindlimbs.

 Preserved elements (in red) of juvenile Pachycephalosauria indet. (CMNFV 22039).
 The preserved left ischium does not show in this view. Diagram illustrates preserved elements only and does not accurately reflect the proportions of CMNFV 22039.

Skeletal drawing modified after original illustrations of Pachycephalosaurus (postcranium) and “Dracorex” (cranium) by Gregory Paul. Used with permission.

Life reconstruction of CMNFV 22039 in an environment typical of the upper Maastrichtian Frenchman Formation. 

Illustration by Kaitlin Lindblad. Used with permission.

 

Bryan R. S. Moore, David C. Evans, Michael J. Ryan, R. Timothy Patterson and Jordan C. Mallon. 2026. The ontogenetically youngest known pachycephalosaur (Dinosauria: Ornithischia) postcranium. Journal of Vertebrate Paleontology. e2616325. DOI: 10.1080/02724634.2026.2616325 [26 Feb 2026]

 www.tandfonline.com/doi/full/10.1080/02724634.2026.2616325

 x.com/Jordan_Mallon/status/2027031604879835644

[Paleontology • 2026] Xenovenator espinosai • A Thick-Skulled Troodontid Theropod (Maniraptora: Troodontidae) from the Late Cretaceous of Mexico

 

Xenovenator espinosai 

Rivera-Sylva, Aguillón-Martinez, Flores-Ventura, Sánchez-Uribe, Guzman-Gutierrez & Longrich, 2026

DOI: doi.org/10.3390/d18010038

Abstract

Dinosaurs repeatedly evolved adaptations for sexual selection over their 150-million year history, including adaptations for display and intraspecific combat. Adaptations for intraspecific combat have not previously been described in non-avian maniraptorans. We report a troodontid from the Campanian Cerro del Pueblo Formation of Coahuila, Mexico, showing a thickened and domed skull roof. The cranium is domed and bones are extremely thick, a morphology convergent on that of Pachycephalosauridae. Referred specimens show less thickening or doming, suggesting ontogenetic changes or perhaps sexual dimorphism. The holotype shows fusion of the frontal midline suture and tightly interdigitating sutures between skull bones, and a rugose skull roof. The specializations seen here suggest adaptation for intraspecific combat, specifically head-butting as hypothesized for pachycephalosaurids and pachyrhinosaurin ceratopsids. Repeated evolution of elaborate weapons and display features in the Cretaceous suggests that sexual selection became increasingly important in dinosaur evolution during the Cretaceous.

Keywords: Dinosauria; Theropoda; Maniraptora; Troodontidae; Cretaceous; Campanian; Laramidia; sexual selection; intraspecific combat

Saurischia Seeley, 1888 

Theropoda Marsh, 1881  

Avetheropoda Paul, 1988  

Coelurosauria Von Huene 1914  

Maniraptora Gauthier 1986  

Deinonychosauria Colbert and Russell, 1969 

Troodontidae Gilmore, 1924  

Troodontinae van der Reest and Currie, 2017 

Troodontini n. tax.

Xenovenator gen. nov.

Diagnosis. Troodontid characterized by thick frontals, anterior displacement of frontal postorbital processes relative to the parietal suture, broad and transversely arched interfrontal ridge, broad frontal-lacrimal suture.

Etymology. Greek xenos, ‘strange’ + Latin venator, ‘hunter’.

Xenovenator espinosai sp. nov. 

Holotype. CPC 2973, braincase including frontals, parietals, orbitosphenoids, laterosphenoids, exoccipitals, prootics, basisphenoid, basioccipital (Figure 4, Figure 5, Figure 6, Figure 7 and Figure 8).

 

Etymology. The species name honors Luis Espinosa, a pioneer in the study of Mexican dinosaurs and mentor to many generations of paleontologists.

Diagnosis. Xenovenator characterized by the following characters (* = autapomorphy): frontals extensively fused; frontals, parietals, and other cranial bones with strongly interdigitating sutures *; strong doming of frontals *; frontals and parietals massive (up to 12 mm thick) *, thickening well-developed anteriorly and less well-developed in the center of the frontal *; dorsal surface of frontals and parietals rugose and striated *, nasal processes broad between lacrimals *, orbital fossae widely separated ventrally *, frontal with notch and shelf to receive posterior end of lacrimal, parietal forms narrow process inserting between frontals *; triangular parietal table *, anteroventral expansion of the orbitosphenoids and laterosphenoids to enclose braincase ventrally *.

Horizon and Locality. Cerro Del Pueblo Formation, uppermost/latest Campanian (Figure 3), Coahuila, Mexico. CPC 2973 and CPC 3112 are from the La Parrita locality, 54 km west of Saltillo; municipality of General Cepeda, Coahuila, Mexico. CPC 3112 is from the Ejido Trincheras locality, 109 km west of Saltillo, municipality of Parras de la Fuente, Coahuila, Mexico (Figure 2).

 Hector E. Rivera-Sylva, Martha C. Aguillón-Martinez, Jose Flores-Ventura, Ivan E. Sánchez-Uribe, Jose Ruben Guzman-Gutierrez and Nicholas R. Longrich. 2026. A Thick-Skulled Troodontid Theropod from the Late Cretaceous of Mexico. Diversity. 18(1), 38. DOI: doi.org/10.3390/d18010038 [9 January 2026]

 

[Paleontology • 2025] Enigmacursor mollyborthwickae • A neornithischian Dinosaur from the Upper Jurassic Morrison Formation of the western USA

Enigmacursor mollyborthwickae

Maidment & Barrett, 2025

 

DOI: doi.org/10.1098/rsos.242195

Artwork by Bob Nicholls.

Abstract

Although their remains have been known since the 1870s, the small, bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation of the western USA remain poorly known. The historic type specimens are incomplete and poorly preserved and have recently been designated as nomina dubia. Here, we describe a recently collected, partial but three-dimensionally preserved skeleton of a new small-bodied ornithischian from the Morrison Formation of Colorado, USA, that we name Enigmacursor mollyborthwickae gen. et sp. nov. The skeleton includes substantial portions of the axial and appendicular skeleton and, when scored into a phylogenetic analysis, is shown to be a non-cerapodan neornithischian, whose closest relative is Yandusaurus hongheensis from the Late Jurassic of China. The discovery of Enigmacursor enhances the diversity of ornithischian dinosaurs from the Morrison Formation and provides new information on their anatomy. In addition, it demonstrates that there is additional cryptic diversity of small-bodied Morrison Formation ornithischians, suggesting they were a more diverse component of these Late Jurassic ecosystems than was previously realized.

Systematic palaeontology

Dinosauria (Owen 1842)

Ornithischia (Seeley 1888)

Neornithischia (Cooper 1985)

Enigmacursor mollyborthwickae gen. et sp. nov.

Holotype—NHMUK PV R 39000, a partial skeleton that includes three teeth, three cervical, 11 dorsal, two dorsosacral and five caudal vertebrae, 10 dorsal ribs, five chevrons, right sternum, both scapulae, both humeri, both radii, both ulnae, three metacarpals, left ilium, right ischium, right pubis, both femora, both tibiae, both fibulae, right astragalus and both pedes.

Diagnosis—Enigmacursor mollyborthwickae differs from all other ornithischian dinosaurs in possessing the following unique combination of features and one potential autapomorphy (the latter marked with an asterisk): (1) posterior articular facets offset ventrally relative to anterior articular facets on proximal dorsal vertebrae*; (2) absence of a supracetabular crest on the ilium; (3) femoral head separated from the greater trochanter by a trochanteric fossa; (4) apex of anterior trochanter situated level with the ventral margin of the femoral head; (5) absence of a ligament sulcus on the posterior surface of the femoral head; (6) ventral surface of fourth trochanter straight or slightly convex in medial or posterior view; (7) medially directed, hook-like posterior condyle of the proximal end of the tibia.

Etymology—Enigma, meaning a puzzle or mystery, in reference to the convoluted taxonomic history of small-bodied ornithischians from the Morrison Formation; cursor, from the Latin for ‘runner’, in reference to the cursorial morphology of the elongated hind limb and pes. The species name honours Molly Borthwick, whose generous donation allowed the NHMUK to acquire the specimen.

Enigmacursor mollyborthwickae
a) Skeletal reconstruction of with preserved elements shaded.
b) Life reconstruction. Artwork by Bob Nicholls.

Susannah C. R. Maidment and Paul M. Barrett. 2025. Enigmacursor mollyborthwickae, a neornithischian dinosaur from the Upper Jurassic Morrison Formation of the western USA. R. Soc. Open Sci. 12: 242195. DOI: doi.org/10.1098/rsos.242195 [25 June 2025]

https://www.nhm.ac.uk/discover/news/2025/june/new-species-mystery-dinosaur-unveiled-natural-history-museum.html

   

[Paleontology • 2024] Ardetosaurus viator • A New diplodocine Sauropod from the Morrison Formation, Wyoming, USA

 Ardetosaurus viator

van der Linden, Tschopp, Sookias, Wallaard, Holwerda & Schulp, 2024

 DOI: 10.26879/1380 

  Life reconstruction by Ole Zant. x.com/TheBioBob

ABSTRACT

The Morrison Formation of the western United States is well-known for its high diversity of sauropod dinosaurs. The Howe-Stephens Quarry in northern Wyoming is one of several quarries which has yielded several associated to completely articulated dinosaur specimens, among which a semi-articulated diplodocid specimen, MAB011899, which was excavated in 1993. This diplodocid specimen is represented by posterior cervical, dorsal, sacral, and anterior caudal vertebrae, multiple thoracic ribs, two chevrons, a left coracoid, a left ilium, both pubes and ischia, a left femur, a left tibia, and a left fibula. Through comparative anatomy, we interpret this specimen as a new species of diplodocine sauropod, Ardetosaurus viator gen. et sp. nov. Unambiguous autapomorphies include paired accessory laminae in the spinoprezygapophyseal fossae of posterior cervical and anterior dorsal vertebrae, bifurcating anterior centrodiapophyseal laminae in the anterior dorsal vertebrae, fossae present in the centropostzygapophyseal laminae of the second dorsal vertebra, a low vertebral height/centrum length ratio of the posterior dorsal vertebrae and reduced to absent centroprezygapophyseal laminae in the anterior caudal vertebrae. Local autapomorphic features include single centroprezygapophyseal laminae in the posterior cervical vertebrae and a highly elliptical cross-section of the femoral midshaft. Ardetosaurus viator is the first skeletally mature sauropod specimen described from the Howe-Stephens Quarry. This specimen provides insight into serial variation of vertebral laminae and laminar transitions. Finally, the peculiar morphology of the—often not preserved—first chevron is described in detail, and its possible use in studying sexual dimorphism in sauropods is discussed.

Keywords: sauropod; new genus; new species; Morrison Formation; Diplodocinae; Wyoming

  Skeletal reconstruction of  Ardetosaurus viator MAB011899. Skeletal reconstruction indicating preserved bones (white), excavated bones but subsequently lost (light gray) and not preserved (dark gray). Unknown elements are based on other diplodocines.

Scale bar equals 1 m. Reconstruction by Ole Zant.

SYSTEMATIC PALEONTOLOGY

DINOSAURIA Owen, 1842

SAUROPODA Marsh, 1878

EUSAUROPODA Upchurch, 1995

NEOSAUROPODA Bonaparte, 1986

DIPLODOCOIDEA Marsh, 1884

FLAGELLICAUDATA Harris and Dodson, 2004

DIPLODOCIDAE Marsh, 1884

DIPLODOCINAE Marsh, 1884

ARDETOSAURUS gen. nov.

 

Ardetosaurus viator gen. et sp. nov.

 

Holotype. MAB011899: two cervical vertebrae, 10 dorsal vertebrae, sacrum, five caudal vertebrae, eight dorsal ribs, two chevrons, a left coracoid, a left ilium, both pubes, both ischia, a left femur, a left tibia, and a partial left fibula.

Diagnosis. Ardetosaurus viator is diagnosed by the combination of the following autapomorphies: 1) the presence of distinct, paired accessory laminae in the spinoprezygapophyseal fossae (SPRF) in the posterior cervical and anterior dorsal vertebrae, 2) anteroventrally bifurcating anterior centrodiapophyseal laminae (ACDLs) in the anterior dorsal vertebrae, 3) the presence of centropostzygapophyseal lamina fossae (CPOL-f) in the second dorsal vertebra, 4) a vertebral height/centrum length ratio of <2.5 of the posterior dorsal vertebrae, and 5) reduced or absent centroprezygapophyseal laminae (CPRLs) in the anterior-most caudal vertebrae. Ardetosaurus viator differs from all other diplodocines by having unbifurcated CPRLs in the posterior cervical vertebrae and a highly elliptical femoral cross-section. Ardetosaurus viator differs from Amphicoelias Cope, 1878, in lacking the rounded, lateral projections of the neural spine tip and the thin neural spine base in the dorsal vertebrae; from Barosaurus Marsh, 1890, by having tall cervical neural spines, single midline keels, narrower prezygapophyseal rami in the cervical vertebrae, ten dorsal vertebrae, the presence of ...

Etymology. ‘Ardeto’ is an inflection of Latin ārdēre, meaning ‘to burn.’ It refers to the history of some of the elements, which were either fully destroyed in a fire, or still show burn scars from the fire. ‘saurus, ’ Latinized form of the Greek σαῦρος (saúros), meaning lizard or reptile. ‘viator’ is Latin for traveler, referring to the journey of the specimen from the USA, via Switzerland and Germany, to the Netherlands.

Locality and horizon. Ardetosaurus viator comes from the Howe-Stephens Quarry of northern Wyoming, USA. The quarry is dated, based on magnetostratigraphy and correlation with other sections in the Morrison basin (Maidment and Muxworthy, 2019; Maidment, personal communication, 2022) at 150.44 to 149.21 million years old, placing it in the Kimmeridgian Stage of the Upper Jurassic.

 Quarry map of Ardetosaurus viator MAB011899. Excavation map of the Howe-Stephens Quarry, indicating the major finds from 1992-2000. Individual dinosaurs are color coded, and MAB011899 is coded with dark blue, and named ‘Diplodocus Brösmeli’ herein. The red crosses indicate the missing/lost cervical vertebrae. Note the relatively similar color for ‘Brösmeli’ and ‘David’ (SMA 0086), but their significant separation in the quarry.

 Figure is courtesy of the SMA. Quarry sections equal 1 by 0.5 m.

  Life reconstruction of  Ardetosaurus viator MAB011899.

Illustration by Ole Zant.

The skeleton of Brösmeli is on display in the Oertijdmuseum.

  x.com/TheBioBob

Tom T.P. van der Linden, Emanuel Tschopp, Roland B. Sookias, Jonathan J.W. Wallaard, Femke M. Holwerda, and Anne S. Schulp. 2024. A New diplodocine Sauropod from the Morrison Formation, Wyoming, USA. Palaeontologia Electronica. 27(3): a50. DOI: doi.org/10.26879/1380

palaeo-electronica.org/content/2024/5327-new-diplodocine-sauropod

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[Paleontology • 2024] Fona herzogae • A New semi-fossorial thescelosaurine Dinosaur (Neornithischia: Thescelosauridae) from the Cenomanian-age Mussentuchit Member of the Cedar Mountain Formation, Utah

Fona herzogae

Avrahami, Makovicky, Tucker & Zanno, 2024

 

DOI: 10.1002/ar.25505

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

DOI: doi.org/10.1002/ar.25505

https://sciences.ncsu.edu/news/life-underground-suited-new-dinosaur-fine 

[Paleontology • 2024] Eoneophron infernalis • A New oviraptorosaur (Theropoda: Oviraptorosauria: Caenagnathidae) from the end-Maastrichtian Hell Creek Formation of North America

Eoneophron infernalis

Atkins-Weltman, Simon, Woodward, Funston & Snively, 2024

DOI: 10.1371/journal.pone.0294901

Illustration by Zubin Erik Dutta  facebook.com/ZDuttaArt

Abstract

Caenagnathidae is a clade of derived, Late Cretaceous oviraptorosaurian theropods from Asia and North America. Because their remains are rare and often fragmentary, caenagnathid diversity is poorly understood. Anzu wyliei is the only caenagnathid species currently described from the late Maastrichtian Hell Creek Formation of the USA and is also among the largest and most completely preserved North American caenagnathids. Smaller, less complete caenagnathid material has long been known from the Hell Creek Formation, but it is unclear whether these are juvenile representatives of Anzu or if they represent distinct, unnamed taxa. Here, we describe a relatively small caenagnathid hindlimb from the Hell Creek Formation, and conduct osteohistological analysis to assess its maturity. Histological data and morphological differences from Anzu wyliei and other caenagnathids allow us to conclude that this specimen represents a new species of caenagnathid from the Hell Creek Formation, with a smaller adult body size than Anzu. This new taxon is also distinct from other small caenagnathid material previously described from the area, potentially indicating the coexistence of three distinct caenagnathid species in the Hell Creek Formation. These results show that caenagnathid diversity in the Hell Creek ecosystem has been underestimated.

Systematic paleontology

Theropoda Marsh 1878 

Oviraptorosauria Barsbold 1976 

Caenagnathidae Sternberg 1940 

Eoneophron gen. nov. 

Eoneophron infernalis sp. nov.

 

Holotype: CM 96523, partial hindlimb including right femur, right tibia and astragalocalcaneum, a right metatarsal III, and a right metatarsal IV.

Diagnosis: Caenagnathid oviraptorosaur diagnosed by the following combination of traits (autapomorphies are denoted with an asterisk): femoral head directed dorsomedially, rather than perpendicular to the shaft; astragalocalcaneum fused to tibia*, metatarsal III with well-developed posterior cruciate ridges continuous with the distal condyle; distal condyle of metatarsal III transversely wider than anteroposteriorly deep, with medial portion of condyle larger than lateral portion; proximal end of metatarsals III and IV project posteriorly to form proximal protuberance; distal tarsal IV coossified with the proximal end of metatarsal IV at maturity; shaft of metatarsal IV with well-developed oblique longitudinal ridge on anterior surface extending along the distal three-quarters of the shaft*.

Etymology: Genus name derived from the Ancient Greek “eo”–meaning “dawn,” and from the genus name of the Egyptian vulture, Neophron, sometimes referred to as the “pharaoh’s chicken.” The species name derives from Latin for Hell, in reference to the Hell Creek Formation. Together the taxon name equates to “Pharaoh’s dawn chicken from Hell.”

Locality and horizon: Collected from exposures of the upper Maastrichtian Hell Creek Formation, Meade County, South Dakota, United States of America. The specimen was prepared prior to acquisition, but matrix remains adhered to some areas, such as the proximal portion of the tibia and anterodistal region of the femur. These sediments resemble those of typical floodplain deposits such as siltstones with organic material as seen elsewhere in the Hell Creek Formation (KLAW, pers. obs.).

Artist’s depiction of Eoneophron infernalis (top left), MOR 752 (bottom left), and Anzu wyliei (right) in the Hell Creek Formation.

Illustration by Zubin Erik Dutta.

 Kyle L. Atkins-Weltman, D. Jade Simon, Holly N. Woodward, Gregory F. Funston and Eric Snively. 2024. A New oviraptorosaur (Dinosauria: Theropoda) from the end-Maastrichtian Hell Creek Formation of North America. PLoS ONE. 19(1): e0294901. DOI: 10.1371/journal.pone.0294901

 facebook.com/ZDuttaArt/posts/822554889885490

[Paleontology • 2023] Neuroanatomy of the late Cretaceous Thescelosaurus neglectus (Neornithischia: Thescelosauridae) reveals novel ecological specialisations within Dinosauria

Thescelosaurus neglectus

in Button & Zanno, 2023. 

DOI: 10.1038/s41598-023-45658-3

 twitter.com/ExpeditionLive

Artwork: Anthony Hutchings

Abstract

Ornithischian dinosaurs exhibited a diversity of ecologies, locomotory modes, and social structures, making them an ideal clade in which to study the evolution of neuroanatomy and behaviour. Here, we present a 3D digital reconstruction of the endocranial spaces of the latest Cretaceous neornithischian Thescelosaurus neglectus, in order to interpret the neuroanatomy and paleobiology of one of the last surviving non-avian dinosaurs. Results demonstrate that the brain of Thescelosaurus was relatively small compared to most other neornithischians, instead suggesting cognitive capabilities within the range of extant reptiles. Other traits include a narrow hearing range, with limited ability to distinguish high frequencies, paired with unusually well-developed olfactory lobes and anterior semicircular canals, indicating acute olfaction and vestibular sensitivity. This character combination, in conjunction with features of the postcranial anatomy, is consistent with specializations for burrowing behaviours in the clade, as evidenced by trace and skeletal fossil evidence in earlier-diverging thescelosaurids, although whether they reflect ecological adaptations or phylogenetic inheritance in T. neglectus itself is unclear. Nonetheless, our results provide the first evidence of neurological specializations to burrowing identified within Ornithischia, and non-avian dinosaurs more generally, expanding the range of ecological adaptations recognized within this major clade.

 

David J. Button and Lindsay E. Zanno. 2023. Neuroanatomy of the late Cretaceous Thescelosaurus neglectus (Neornithischia: Thescelosauridae) reveals novel ecological specialisations within Dinosauria. Scientific Reports. 13: 19224. DOI: 10.1038/s41598-023-45658-3

 twitter.com/ExpeditionLive/status/1721879200234340466

[Paleontology • 2023] Platytholus clemensi • A New pachycephalosaurid (Ornithischia: Pachycephalosauridae) from the Hell Creek Formation, Garfield County, Montana, U.S.A.

Platytholus clemensi 

Horner, Goodwin & Evans, 2023   

DOI: 10.1080/02724634.2023.2190369  

ABSTRACT

A partial skull of a pachycephalosaurid from the Upper Cretaceous Hell Creek Formation, Montana, is interpreted as a new taxon, Platytholus clemensi gen. et sp. nov. MOR 2915 does not fit into an ontogenetic continuum of known pachycephalosaurids from the Hell Creek Formation, Montana, and contemporaneous sediments from the Western Interior. Comparisons to known ontogimorphs of Sphaerotholus and Pachycephalosaurus preclude including this specimen into an ontogenetic series of either taxon. We hypothesize that MOR 2915 is a new species based on a relatively low, broad dome at this advanced ontogenetic age that is neither round nor oval in dorsal view, distinct but fused lateral cranial elements fully incorporated into the dome without any dorsal lobe differentiation, and individual tab-like tubercle ornamentation dorsolaterally. Phylogenetic analysis posits that Platytholus clemensi is a Prenocephale-grade taxon deeply nested within Pachycephalosaurinae, but it is not a member of Pachycephalosaurini. Platytholus clemensi is intermediate in size between the other contemporaneous pachycephalosaurids in the Hell Creek Formation and suggests a diverse set of taxa-partitioned ecological niches by body size. We confirm a well organized, major internal vascular network using high resolution computed tomography. Foramina present on the orbital roofs indicate these canals penetrated the entire ceiling of the orbits within the frontal and supraorbital bones. Abundant neurovascular canals passing through the dome to the ectocranial surface indicate a keratinous structure of some kind, possibly with a vertical structural framework, was present on the dome. We review the history of the head-butting hypothesis and associated behavioral implications.

An artist's depiction of Platytholus clemensi a newly described species of pachycephalosaur.
The skull is dome-shaped, but UC Berkeley and Chapman University paleontologists believe it was covered with bristles of keratin (purple) that may have been even more elaborate than depicted here. The bony knobs and spikes (yellow) are characteristic of pachycephalosaurs and many other dinosaurs.

Artwork: Jack Horner

 Platytholus clemensi gen. et sp. nov. 

John R. Horner, Mark B. Goodwin and David C. Evans. 2023. A New pachycephalosaurid from the Hell Creek Formation, Garfield County, Montana, U.S.A. Journal of Vertebrate Paleontology. e2190369. DOI: 10.1080/02724634.2023.2190369  

https://phys.org/news/2023-05-newly-species-dome-headed-dinosaur-sported.html

[Paleontology • 2023] Evidence for Heterothermic Endothermy and Reptile-like Eggshell Mineralization in Troodon, A Non-avian Maniraptoran Theropod

Troodon

in Tagliavento, Davies, Bernecker, Staudigel, Dawson, ... et  Fiebig, 2023. 

  DOI: 10.1073/pnas.2213987120

artwork: Alex Boersma

Abstract

The dinosaur–bird transition involved several anatomical, biomechanical, and physiological modifications of the theropod bauplan. Non-avian maniraptoran theropods, such as Troodon, are key to better understand changes in thermophysiology and reproduction occurring during this transition. Here, we applied dual clumped isotope (Δ47 and Δ48) thermometry, a technique that resolves mineralization temperature and other nonthermal information recorded in carbonates, to eggshells from Troodon, modern reptiles, and modern birds. Troodon eggshells show variable temperatures, namely 42 and 29 ± 2 °C, supporting the hypothesis of an endothermic thermophysiology with a heterothermic strategy for this extinct taxon. Dual clumped isotope data also reveal physiological differences in the reproductive systems between Troodon, reptiles, and birds. Troodon and modern reptiles mineralize their eggshells indistinguishable from dual clumped isotope equilibrium, while birds precipitate eggshells characterized by a positive disequilibrium offset in Δ48. Analyses of inorganic calcites suggest that the observed disequilibrium pattern in birds is linked to an amorphous calcium carbonate (ACC) precursor, a carbonate phase known to accelerate eggshell formation in birds. Lack of disequilibrium patterns in reptile and Troodon eggshells implies these vertebrates had not acquired the fast, ACC-based eggshell calcification process characteristic of birds. Observation that Troodon retained a slow reptile-like calcification suggests that it possessed two functional ovaries and was limited in the number of eggs it could produce; thus its large clutches would have been laid by several females. Dual clumped isotope analysis of eggshells of extinct vertebrates sheds light on physiological information otherwise inaccessible in the fossil record.

Several Troodon females laid their eggs in communal nests.

artwork: Alex Boersma/PNAS

 

Significance: The dinosaur–bird transition is among the most fascinating events in evolutionary history, but several biological aspects such as changes in reproductive system, nesting strategy, and body temperature are still poorly understood. Dual clumped isotope thermometry (Δ47 and Δ48) can shed light on these biological aspects in fossils. Our results show that eggshells of modern reptiles and birds differ in their isotopic compositions. Interestingly, analyses of eggshells of Troodon, a non-avian theropod, reveal that it retained a slower, reptile-like mineralization to produce its eggs, despite having already evolved the capacity of changing its body temperature (heterothermic endothermy) like modern birds. Our findings also suggest that Troodon possessed two functional ovaries and that their nests were shared by multiple females.

 

Mattia Tagliavento, Amelia J. Davies, Miguel Bernecker, Philip T. Staudigel, Robin R. Dawson, Martin Dietzel, Katja Götschl, Weifu Guo, Anne S. Schulp, François Therrien, Darla K. Zelenitsky, Axel Gerdes, Wolfgang Müller and Jens Fiebig. 2023. Evidence for Heterothermic Endothermy and Reptile-like Eggshell Mineralization in Troodon, A Non-avian Maniraptoran Theropod. Proceedings of the National Academy of Sciences. 120 (15) e2213987120. DOI: 10.1073/pnas.2213987120

phys.org/news/2023-04-analysis-dinosaur-eggshells-bird-like-troodon.html

[Paleontology • 2022] Zuul crurivastator • Palaeopathological Evidence for Intraspecific Combat in Ankylosaurid Dinosaurs

Zuul crurivastator Arbour & Evans, 2017

in Arbour, Zanno & Evans, 2022. 

DOI: 10.1098/rsbl.2022.0404 

 twitter.com/DavidEvans_ROM 

Abstract

Ankylosaurid dinosaurs were heavily armoured herbivores with tails modified into club-like weapons. These tail clubs have widely been considered defensive adaptations wielded against predatory theropod dinosaurs. Here we argue instead that ankylosaurid tail clubs were sexually selected structures used primarily for intraspecific combat. We found pathological osteoderms (armour plates) in the holotype specimen of Zuul crurivastator, which are localized to the flanks in the hip region rather than distributed randomly across the body, consistent with injuries inflicted by lateral tail-swinging and ritualized combat. We failed to find convincing evidence for predation as a key selective pressure in the evolution of the tail club. High variation in tail club size through time, and delayed ontogenetic growth of the tail club further support the sexual selection hypothesis. There is little doubt that the tail club could have been used in defence when needed, but our results suggest that sexual selection drove the evolution of this impressive weapon. This changes the prevailing view of ankylosaurs, suggesting they were behaviorally complex animals that likely engaged in ritualized combat for social dominance as in other ornithischian dinosaurs and mammals.

Keywords: Dinosauria, Ankylosauria, sexual selection, animal weaponry

 

Victoria M. Arbour, Lindsay E. Zanno and David C. Evans. 2022. Palaeopathological Evidence for Intraspecific Combat in Ankylosaurid Dinosaurs. Biol. Lett. 18: 20220404. DOI: 10.1098/rsbl.2022.0404

  twitter.com/DavidEvans_ROM/status/1600289535128059904