Chalicomys jaegeri KAUP , 1832

Rekovets, Leonid, Stefen, Clara & Demeshkant, Vitalii, 2020, Beavers (Castoridae, Rodentia) From The Late Miocene (Mn 9) Locality Grytsiv In Ukraine, Fossil Imprint 76 (1), pp. 165-173 : 166-167

Chalicomys jaegeri KAUP, 1832

Pl. 1, Figs 1–9

1832 Palaeomys castoroides ; Kaup, p. 993, pl. XXVI, figs 1–4.

1832 Chalicomys Jaegeri ; Kaup, p. 995, pl. XXVI, figs 1–6.

1832 Chelodus typus; Kaup, p. 996, pl. XXVI, figs 1, 2.

1948 Castor vidali n. sp.; Crusafont Pairó et al., p. 348, fig. 4, pl. II, figs 1–4.

2009 Palaeomys castoroides KAUP, 1832 ; Rekovets et al., p. 99.

2001 Steneofiber sp. ; Nesin and Nadachowski, p. 112, tab. 1.

2013 Monosaulax sp. ; Nesin, p. 17.

2013 Palaeomys sp. ; Nesin, p. 17.

2013 Palaeomys castoroides ; Rekovets and Nowakowski, p. 160, fig. IA, IB.

M a t e r i a l. Two p4 (NMNHU-P 22/214, 22/215), four Р4 (NMNHU-P 22/211, 22/212, 22/213, 22/216), two M1/2 (NMNHU-P 22/219, 22/220), one М3 (NMNHU-P 22/222).

D e s c r i p t i o n. The right p4 (NMNHU-P 22/214; Pl. 1, Fig. 1a–c) is slightly worn and belongs to a fairly young individual. On the occlusal surface, the paraflexid is slightly longer than the metaflexid, oriented diagonally, and opens mesially and lingually. The mesial opening is represented by a single tiny striid. All flexids are orientated diagonally on the occlusal surface. Para- and metaflexids extend nearly from side to side of the tooth width. The mesostriid ends adjacent and slightly mesial to the short hypoflexid. On the lingual side, striids are well visible: the parastriid is the shortest (2.5 mm), the metastriid is 3.5 mm long, and the mesostriid is the longest (8.5 mm) and extends to almost half of the crown height (Pl. 1, Fig. 1c). On the buccal side, the hypostriid extends to the crown base (Pl. 1, Fig. 1b). There is a thin cement layer in this tooth with a little wear, as the genus Chalicomys is characterized by the appearance of cement in the ontogenesis process ( Lychev 1977). The enamel thickness is almost the same around the entire tooth crown but slightly stronger at the hypo- and the entoconid, and thinner at the protoconid. The enamel surrounding the paraflexid shows some small crenulations. The measurements are presented in Table 1.

Another right p 4 specimen ( NMNHU-P 22 /215; Pl. 1, Fig. 2a–c) is slightly damaged at the mesial side, and the enamel is missing at the protoconid or anterolophid. The tooth is worn and belongs to a relatively young individual. Its paired root is poorly developed. Contrary to all the other examined fourth lower premolars, the parafossettid is closed .

The parafossettid is hook-like on the lingual side and curves towards the hypoflexid. The hypo- and the mesoflexid end adjacent and opposite to each other in about the middle of the tooth length. The mesoflexid is straight linguo-buccally and not curved mesially as in the other p4. The metaflexid starts straight at the lingual side but then curves mesially and extends diagonally on the occlusal surface towards the hypoflexid. The enamel surrounding the para- and the metaflexid show some crenulations. On the lingual side, there are a short metastriid (0.8 mm long) and a longer mesostriid extending about half of the crown height. At the base of the mesostriid, there is an additional stylid (Pl. 1, Fig. 2c). There is cement in the meso- and hypostriid. The hypostriid on the buccal side extends to the crown base (Pl. 1, Fig. 2b). The enamel around the tooth is thin, particularly at the entoconid and the hypoconulid.

The right P4 (NMNHU-P 22/212; Pl. 1, Fig. 5a, b) is strongly worn so the para-, meta-, and mesoflexus are closed. The parafossette is curved or hook-like and is partially parallel to the hypoflexus on the occlusal surface. The hypoflexus extends over more than half of the tooth width; it is diagonally oriented and straight. The mesofossette is strongly curved (convex) and the smaller metafossette fills the distal part of the tooth. It is also slightly curved or hook-like and slightly diagonal linguo-distally. The enamel at the buccal, distal, and linguo-distal sides of the tooth is broken and thin. There are two well-developed roots. The hypostria ends above the crown base; it is very narrow, and filled with some cement.

Another right P 4 specimen ( NMNHU-P 22 /213; Pl. 1, Fig. 6a, b) is broken mesially and bucco-lingually. On the occlusal surface, the hypoflexus, mesoflexus and metaflexus are visible. On the lingual side, the hypostria does not reach the crown base. There are short meso- and metastriae on the lingual side .

The left P4 (NMNHU-P 22/211; Pl. 1, Fig. 7a, b) is associated with a small bone fragment, and shows open para-, hypo-, and mesoflexi and only a closed metafossette. The paraflexus extends slightly less than half of the tooth width and ends adjacent and opposite to the hypoflexus (“face to face”). Where they meet, both flexi show a small extension in mesial direction. The mesoflexus is narrow, strongly curved distally, and extends over the total tooth width nearly to the linguo-distal enamel. The smaller metafossette is nearly straight and occupies the distal part of the tooth.

Another specimen of left P4 (NMNHU-P 22/216; Pl. 1, Fig. 8a, b) shows closed para- and metafossette but open meso- and hypoflexid. The parafossette extends from the buccal side to the hypoflexus less than half of the occlusal surface. It ends mesially to the hypoflexus with an additional enamel fold. The mesoflexus is narrow and curves from the buccal opening to the linguo-distal side of the tooth. The metafossette is small but reaches diagonally from side to side on the occlusal surface. The enamel is thin, but thicker at the proto- and hypocone as well as the mesoflexus. The hypostria does not extend to the crown base.

The left М1/2 is represented by two specimens ( NMNHU-P 22 /219; Pl. 1, Fig. 4; NMNHU-P 22 /220; Pl. 1, Fig. 3). Only the hypoflexus is open, and the hypostria does not extend to the crown base and has some cement. The paraflexus is directly adjacent (or “face to face”) to the hypoflexid which extends over slightly more than half of the occlusal surface. The meso- and metafossette are slightly curved. The enamel on the lingual and distal sides is thin and partially worn. In contrast, it is thick on the mesial side of the tooth. Due to their advanced wear stage, the teeth are relatively low-crowned .

The left M3 (NMNHU-P 22/222; Pl. 1, Fig. 9) is strongly worn and all fossettes still present, here interpreted as hypo-, meso- and metafossette, are closed, and orientated linguobuccally. They appear “on the top of the previous one” on the occlusal surface. The mesofossette is strongly curved, the metafossette is small and oval, and the hypofossette is convex and the longest one. There are three roots.