1 Vol.:(0123456789) Scientific Reports | (2023) 13:4459 | https://doi.org/10.1038/s41598-023-30626-8 www.nature.com/scientificreports A new Carboniferous edaphosaurid and the origin of herbivory in mammal forerunners Arjan Mann 1* , Amy C. Henrici 2 , Hans‑Dieter Sues 1 & Stephanie E. Pierce 3 Herbivory evolved independently in several tetrapod lineages during the Late Carboniferous and became more widespread throughout the Permian Period, eventually leading to the basic structure of modern terrestrial ecosystems. Here we report a new taxon of edaphosaurid synapsid based on two fossils recovered from the Moscovian‑age cannel coal of Linton, Ohio, which we interpret as an omnivore–low‑fibre herbivore. Melanedaphodon hovaneci gen. et sp. nov. provides the earliest record of an edaphosaurid to date and is one of the oldest known synapsids. Using high‑resolution X‑ray micro‑computed tomography, we provide a comprehensive description of the new taxon that reveals similarities between Late Carboniferous and early Permian (Cisuralian) members of Edaphosauridae. The presence of large bulbous, cusped, marginal teeth alongside a moderately‑developed palatal battery, distinguishes Melanedaphodon from all other known species of Edaphosauridae and suggests adaptations for processing tough plant material already appeared among the earliest synapsids. Furthermore, we propose that durophagy may have provided an early pathway to exploit plant resources in terrestrial ecosystems. e origin of herbivory in amniotes is intimately linked with the origin of modern terrestrial ecosystem structure and an expansion of niche exploitation 1–3 . Currently, it is thought that the ability to efficiently process plant mate- rial was well-established by the early Permian, with groups including diadectid stem-amniotes, captorhinid and bolosaurid reptiles, as well as caseid and edaphosaurid synapsids being the first tetrapod lineages to adopt this feeding strategy 4,5 . Whereas most early Permian members of the two synapsid clades are interpreted as high-fibre herbivores, such as the iconic large-bodied Cotylorhynchus (Caseidae) and Edaphosaurus (Edaphosauridae), virtually all Late Carboniferous representatives of these synapsid lineages are smaller faunivorous forms that likely preyed on insects or other small animals 6–8 . erefore, there is an apparent lack of transitional Carbon- iferous synapsids with less-specialized dietary preferences such as omnivory and low-fibre herbivory, which would bridge the gap between ancestral carnivores/insectivores and high-fibre herbivores characteristic of the Permian 3,5 (Hotton et al., 1997; Reisz and Sues, 2000). Part of this gap may be explained by the still insufficiently documented Late Carboniferous fossil record of early amniotes, which has recently started to reveal unexpected morphological and ecological diversity (e.g., 9,10 ). Recently, a series of papers 11,12 have used various modelling approaches to address the origins of herbivory in tetrapods, ultimately predicting its appearance during the mid-Carboniferous shortly aſter the origin of amniotes. While quantitative approaches can be powerful, confirmation of the resulting hypotheses can only be established through the discovery of new fossil material. Here we provide such a new record, reporting a new species of edaphosaurid synapsid from the famous Late Carboniferous (Pennsylvanian: Moscovian) fossil locality of Linton, Ohio. e vertebrate-bearing cannel coal from Linton, Ohio, likely represents an abandoned channel or oxbow lake that was an allochthonous deposit of sapropelic plant material 13 . Although this deposit is well known for being particularly rich in fish and amphibian remains 14 , terrestrial faunal components such as amniotes are rarely found (e.g. 9,10,15 ). e new edaphosaurid material is preserved on two blocks of cannel coal that collectively document a good portion of the skull, including the distinctive marginal dentition. Its dentition reveals features indicative of omnivory or low-fibre herbivory, placing this animal among the earliest known tetrapod herbivores and certainly the oldest known synapsid herbivore. is new discovery also offers additional insights into the early evolution of herbivory among tetrapods and their ecosystems, revealing the importance of OPEN 1 Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, MRC 121, P.O. Box 37012, Washington, DC 20013-7012, USA. 2 Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, PA 15213, USA. 3 Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA. * email: MannArjan@si.edu