Machichnus inrosus, Yanenko & Kovalchuk, 2023

Yanenko, V. & Kovalchuk, О., 2023, Late Miocene Turtles Of Grytsiv (Western Ukraine) With Rodent Gnaw Marks On The Carapace Surface, Zoodiversity 57 (4), pp. 311-322 : 315-316

Machichnus Mikuláš, Kadlecová, Fejfar & Dvořák, 2006 Machichnus inrosus , isp. n.

Holotype. NMNHU-P AR 407 , a series of scratches on the upper right margin of the turtle shell fragment ( FIg. 3 ).

Etymology. The ichnospecies name has Latin derivation (‘in’ means not enough, and ‘rosus’ means gnawen) and displays that a relatively small area of the turtle shell is affected by traces of gnawing or rasping.

Diagnosis. Machichnus consisting of narrow, subparallel grooves with a double longitudinal striation exposed on a small area of the substrate.

Description. There is a series of about 20 elongated shallow grooves on the surface of the nuchal of the Testudo chernovi carapace. The striae are uniform in shape, and they cover 10–12 % of the affected substrate. They are slightly arcuate in cross-section and bear two thin parallel furrows, one of which is located in the centre, and the other is shifted to the periphery. These furrows are traces of the longitudinal ridges on the lower incisors of a rodent, with which it gnawed (rasped) the turtle shell. The width of the striae is 1 mm, and the length of individual scratches reaches 8 mm.

Comparison. The new ichnospecies is similar in shape to those of the ichnogenus Machichnus Mikuláš et al., 2006 from the Early Miocene of the Czech Republic, although it differs from Machichnus regularis in having a greater length of scratches, while the width of individual striae is at the upper limit of values for the latter. On the contrary, Machichnus multilineatus is characterised by wider striae and longer traces. The area affected with scratches in Machichnus inrosus is much smaller than that in Early Miocene ichnospecies from the Czech Republic. Machichnus bohemicus Mikuláš et al. (2006) resembles M. inrosus in the length of traces but differs from the latter in the character of scratches and smaller width of individual striae. Other members of Machichnus — from the Late Cretaceous of England ( Chumakov et al., 2013), Neogene of the Atlantic Coastal Plain, USA ( Lindholm et al., 2023) and the Late Pleistocene–Early Holocene of Brazil (de Araújo-Júnior et al., 2017) — substantially differ from M. inrosus in morphology and shape.

Figures

Fig. 3. The nuchal plate of Testudo chernovi NMNHU-P AR 407 from Grytsiv with gnaw marks (A); B–C — Machichnus inrosus isp. n., enlarged affected area (B) and a set of individual striae (C); D — combined SEM image of the mandible of Anomalomys grytsivensis Nesin & Kovalchuk, 2021 (NMNHU-P 22/2703) showing the labial surface of the lower incisor with longitudinal ridges.