New bioerosion traces in rhynchosaur bones from the Upper Triassic of Brazil and the oldest occurrence of the ichnogenera Osteocallis and Amphifaoichnus Author Cunha, Lucca S. Author Dentzien-Dias, Paula Author Francischini, Heitor text Acta Palaeontologica Polonica 2024 2024-01-30 69 1 1 21 http://dx.doi.org/10.4202/app.01093.2023 journal article 10.4202/app.01093.2023 1732-2421 10981169 Osteocallis mandibulus Roberts et al., 2007 Figs. 4A, B , 5A, B, E . Diagnosis .—Shallow, meandering trail of arcuate grooves (apparently paired) bored into external (cortical) bone surfaces. Occurs as single trails or network of randomly overlapping trails. Material .—UFRGS-PV-1581- T #2, #5 ( Fig. 6C ), #8, #19, and #23 ( Fig. 4B ) present single trails. UFRGS-PV-1581- T #3 ( Fig. 4A ) and UFRGS-PV-1581- T #18 present two trails without overlapping. UFRGS-PV-1581- T #1 presents two overlapping trails and UFRGS-PV-1581- T #14 ( Fig. 5A, B, E ) presents three trails without overlapping. All of these bone fragments are referred to Hyperodapedon mariensis from Buriol Site, São João do Polêsine municipality, Rio Grande do Sul State , Brazil ; Base of the Candelária Sequence (vertebrate remains associated to the lower subunit of the Hyperodapedon AZ ), SMS, Paraná Basin; middle Carnian (lower Upper Triassic). Description .—All 14 trails formed by successive mainly arcuate and apparently paired grooves on the bone surface ( Figs. 4 , 5A, B, E , 6C ). In some cases, the grooves overlap, forming long arcuate grooves or crossing each other. Most of the trails present some degree of meandering. Trail length is 1.1–21.5 mm and the width is 0.1–4.4 mm . Remarks .—The grooves that compose the trails are not always arcuate, with some trails also presenting straight grooves. Osteocallis leonardii ( Collareta et al. 2023 ) presents both straight and arcuate grooves as well, but in opposition to the materials referred herein to O. mandibulus , the grooves are predominantly straight. In some of the trails it is difficult to ascertain if the grooves are indeed paired, especially when their overlapping results in long arcuate grooves. This makes the precise measurement of individual grooves nearly impossible. UFRGS-PV-1581- T #14 was found covered by a thin layer of iron oxide that served as a natural cast, allowing for the observation of the traces in a positive relief ( Fig. 5A, B ). Trails on UFRGS-PV-1581- T #5, #11, #14, and #23 are associated to clusters of grooves ( Figs. 4B, D , 5A, B , 6C ). In UFRGS-PV-1581- T #14 a cluster is overlapping one of the trails. The only association of trails with other borings occurs in UFRGS-PV-1581- T #3 ( Fig. 4A 1 ).