Flowers from Tzimol Quarry, Chiapas: Evidence of labile merism during the Late Cretaceous

Background: The Cretaceous Terrestrial Revolution represents a key interval in the evolutionary history of major terrestrial groups, including angiosperms. In recent years, the worldwide record of Cretaceous flowers has increased substantially, providing valuable information on the evolution, as well as the ecological and phylogenetic relationships of the early flowering plants; however, reports from low latitudes of North America are still scarce. Questions: Do the flowers from Tzimol, Chiapas, Mexico, support the idea of diversification and differentiation of the angiosperms during the Late Cretaceous? Studied species: Kanalflorum variabilis Study site and dates: Tzimol Quarry (Fm. Angostura), Chiapas, Mexico 2023-2024. Methods: Using light microscopy, we described and identified the fossil flowers by comparing them with extant angiosperms. Furthermore, to explore their potential phylogenetic relationships, we used a morphological matrix which was analyzed through parsimony optimization. Results: Kanalflorus variabilis is proposed as a new extinct genus and species based on bisexual flowers, pedicelled, with an enlarged receptacle, and a reduced calyx, apopetalous corolla with 5-6 concave petals, alternipetalous stamens, basifixed anthers, a nectarial ring disk, and a half-inferior ovary. Its floral structure is similar to eudicots, especially with extant members of the Apiales order, due to the meristic variation of the perianth. Conclusions: Kanalflorus variabilis exhibits a labile meristic pattern, providing evidence of the diversity and morphological complexity of angiosperms during the Late Cretaceous.