Pachyacanthus sp.

Gol’din, Pavel, Haiduc, Bogdan Stelian, Kovalchuk, Oleksandr, Górka, Marcin, Otryazhyi, Pavlo, Brânzilă, Mihai, Păun, Elena Ionela, Barkaszi, Zoltán, Ţibuleac, Paul & Răţoi, Bogdan Gabriel, 2020, The Volhynian (late Middle Miocene) marine fishes and mammals as proxies for the onset of the Eastern Paratethys re-colonisation by vertebrate fauna, Palaeontologia Electronica (a 43) 23 (3), pp. 1-20 : 12

Pachyacanthus sp.

Figure 5G

Material and locality. Thoracic vertebra and a partial rib; Vilkhovets.

Description. The vertebra shows lateral pachyosteosclerotic swelling of the spine distinct for this taxon, and the rib is strongly pachyosteosclerotic. This is the first record for Pachyacanthus in the Fore-Carpathian Basin: before it was only recorded in the Vienna Basin and adjoining areas of the Central Paratethys and at the eastern edge of the Eastern Paratethys (Mangyshlak Peninsula, Kazakhstan) ( Dombrovsky, 1927; Kazár, 2010).

MYSTICETI Flower, 1864

Family CETOTHERIIDAE Brandt, 1872 Cetotheriidae indet.

Figure 5H

Material and localities. Caudal vertebra; Stăuceni, Kolubaivtsi.

Description. The new material from Stăuceni is represented by a caudal vertebra, which is assigned to Cetotheriidae due to its slight pachyosteosclerosis, a specific trait, which is shared only by that lineage during the late Middle Miocene. In dorsal view, the conical short vertebra has two lateral vascular foramina. The vertebra is similar in size to those of Cetotherium riabinini , a 3 m long whale ( Gol’din et al., 2014). The specimen from Kolubaivtsi is a rib fragment, 3 cm wide, with developed pachyostosis and strong osteosclerosis, a distinct feature of the Cetotheriinae from the Eastern Paratethys ( Gol’din and Startsev, 2017), also shared by Otradnocetus , a stem member of Cetotherioidea ( Gol’din, 2018).

Comparison. There is a vertebra reported by Macarovici (1947) from Săveni-Ghireni, and two more vertebrae reported by Macarovici and Zaharia (1967) from Mitoc-Prut, identified by them as Cetotherium priscum : all of the specimens share pachyosteoclerosis and small size, both typical for Cetotheriinae. Also, a similar vertebra was reported by Codrea (2006) from the Volhynian deposits of Ţaga ( Romania) in the Central Paratethys. A small, short pachyosteoclerotic lumbar vertebra of Cetotheriidae indet. also comes from Kaisersteibruch ( Austria), a Badenian-Sarmatian locality in the Central Paratethys ( Kazár, 2006). A small baleen whale from Khonkivtsi reported by Hofstein (1965) (temporarily unavailable for study) could belong to this family based on its extremely small size, short and high vertebrae: the centrum of the longest vertebra, the first caudal one, is 70 mm long, 70 mm wide and 70 mm high. Also, it is different from Ciuciulea davidi ( Gol’din, 2018) and? Parietobalaena sp. from the Central Paratethys ( Gol’din and Radović, 2018) in having short lumbar vertebrae, a derived trait observed in Late Miocene cetotheriids. Meanwhile, its vertebrae are not pachyosteosclerotic, unlike those of the Paratethyan cetotheriines. Thus, it could represent a hitherto unknown dwarf mysticete taxon.

Figures

FIGURE 5. Marine mammals from the Volhynian beds of the Moldavian Platform: A – Phocinae indet. 2, scapula and caudal vertebra, Stăuceni; B – Kentriodon fuchsii, a lumbar vertebra, dorsal and posterior view, Basarabi; C – Kentriodontidae indet. 1 (cf. Imerodelphis thabagarii), lumbar vertebra, dorsal and anterior view, Saur-Mohyla; D – Kentriodontidae indet. 2, caudal vertebra, anterior and lateral view, Stăuceni; E – Kentriodontidae indet. 2, thoracic vertebra, anterior view, Stâncești; F – Kentriodontidae indet. 3, caudal vertebra, anterior and lateral view, Stăuceni; G – Pachyacanthus sp., thoracic vertebra, anterior and lateral view, Vilkhovets; H – Cetotheriidae indet., caudal vertebra, dorsal and lateral view, Stăuceni; I-J –? Mysticeti indet. (“Archaeocetus fockii”), rib fragment, lateral view and cross-section (I), caudal vertebra (J), dorsal and lateral view, Drăgușeni. Scale bars equal 2 cm in A–I and 5 cm in J.