Morfologia e paleohistologia de dentes Crocodyliformes da Formação Aliança (Bacia do Tucano: Jurássico Superior)

Abstract

Crocodyliforms have a rich evolutionary history, with multiple radiations in marine and terrestrial environments throughout the Mesozoic. The past diversity of the group far exceeds that represented by its modern descendants. In Brazil, the fossil record of Crocodyliforms is abundant during the Cretaceous but considerably scarcer in the Jurassic. As part of this record, isolated teeth were collected in Araci, Bahia, from the Aliança Formation, Tucano Basin (Upper Jurassic). This material represents rare evidence of the group diversification in continental environments of South America during this period, providing an opportunity for paleobiological characterization and taxonomic assessment. This study aimed to investigate these fossils through an integrated approach involving the description of external morphology, morphometry, dental microstructure (paleohistology), and paleoenvironmental context. The analyzed specimens exhibit simple and relatively uniform morphology, with conical teeth, smooth carinae, subtle longitudinal striations, and absence of marked heterodonty. These features are consistent with representatives of basal-diverging Neosuchia, particularly those with homodont dentition and a generalized diet. Histological analyses revealed thin dental enamel and spacing between von Ebner lines as indicative of a relatively efficient dentin deposition rate. The count of these lines suggests a moderate time for tooth formation along with regular functional replacement. These patterns reinforce affinity with Neosuchia and contrast with other specialized groups, such as Notosuchia, whose teeth display thicker enamel and features associated with abrasive diets. The morphological and histological homogeneity among the studied specimens suggests a probable unique taxon, although subtle variations may reflect ontogenetic or anatomic differences along the position in dental arcade. The data indicate that these Crocodyliforms behaved as small-bodied opportunistic predators, with a broad and predominantly carnivorous diet. This study contributes to filling gaps in the South AmericanJurassic record of Crocodyliforms and enhances the understanding of functional dental evolution in Neosuchia, highlighting the presence of generalist forms in continental Gondwanan environments during the Mesozoic.