Osteocallis mandibulus Roberts et al., 2007

Cunha, Lucca S., Dentzien-Dias, Paula & Francischini, Heitor, 2024, New bioerosion traces in rhynchosaur bones from the Upper Triassic of Brazil and the oldest occurrence of the ichnogenera Osteocallis and Amphifaoichnus, Acta Palaeontologica Polonica 69 (1), pp. 1-21 : 7

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 ).

Figures

Fig.4.Feeding traces of Osteocallis on bone fragments of the rhynchosaurid archosauromorph Hyperodapedon mariensis (Tupi Caldas, 1933) from Buriol Site, Brazil, Hyperodapedon AZ, Carnian. A. UFRGS-PV-1581 #3; A1, Osteocallis mandibulus Roberts et al., 2007, associated to arthropod bioerosion trace fossil Amphifaoichnus isp.; A2, details of one of the trails. B. UFRGS-PV-1581 #23; B1, Osteocallis mandibulus associated to a cluster of grooves in crescent shape; B2, schematic drawing highlighting the grooves. C. UFRGS-PV-1581-T #12 showing two overlapping Osteocallis infestans Paes Neto et al., 2016. D. UFRGS-PV-1581-T #11 showing Osteocallis isp. (arrow) associated to a cluster of larger grooves.

Fig. 5. A suite of traces in the rhynchosaurid archosauromorph Hyperodapedon mariensis (Tupi Caldas, 1933), UFRGS-PV-1581-T #14, bone fragment from Buriol Site,Brazil, HyperodapedonAZ,Carnian.A.Two feeding traces of Osteocallis mandibulus Roberts et al., 2007,overlapped by a cluster of larger grooves. B. Natural cast formed by a cover of iron oxide showing the grooves in positive relief. Image mirrored to facilitate comparison. C, D. Clusters of grooves on different surfaces of the same bone fragment. E. Small Osteocallis mandibulus close to the trails shown in A and B.

Fig. 6. Clusters of grooves on bone fragments of the rhynchosaurid archosauromorph Hyperodapedon mariensis (Tupi Caldas, 1933) from Buriol Site, Brazil, Hyperodapedon AZ, Carnian. A. UFRGS-PV-1581-T #20, arcuate and paired grooves, similar to feeding traces of Osteocallis mandibulus Roberts et al., 2007, but without forming a trail. B. UFRGS-PV-1581-T #22, densely concentrated grooves, giving the bone surface an etched appearence. C. UFRGS-PV-1581-T #5, straight and arcuate grooves closely associated to an incipient Osteocallis mandibulus (arrow). D. UFRGS-PV-1581-T #26, straight and arcuate grooves and some isolated grooves. E. UFRGS-PV-1581-T #6, dentary fragment; E1, two clusters of grooves; E2, schematic drawing. F. UFRGS-PV-1581-T #17; F1, subparallel grooves; F2, subparallel grooves associated to a subcircular cluster of grooves (arrow).

Fig. 1. Geological and geographic context. A. Location of the Paraná Basin in Brazil. B. Limits of the Triassic rocks of Rosário do Sul Group and the Triassic rocks of Paraná Basin in Rio Grande do Sul state. C. Location of the Buriol Site, locality of UFRGS-PV-1581-T, and nearby Predebon and Janner sites. D. Chrono-, lito-, and biostratigraphy of southern Brazilian Triassic (modified from Schultz et al. 2020).Arrow indicates stratigraphical position of UFRGS-PV-1581-T; * refers to absolute ages from Langer et al. (2018); ** refers to absolute ages from Philipp et al. (2018).