Titanonarke megapterygia Marram̀ & Claeso & Carneval & Kriwe 2018, sp. nov.

† Titanonarke megapterygia sp. nov.

(Fig. 17)

2010 † Titanonarke molini (Jaekel, 1894); Carvalho: 188, figs 3, 5b–c, 8 [pro parte].

Derivation of name. After the Greek words mega ́, meaning ‘large’, and pterygia ́, meaning ‘fins’, referring to the proportionally larger pectoral and pelvic fins compared to those of the type species.

Holotype. MCSNV IG.135576, nearly complete articulated skeleton in a single slab (Fig. 17), 626.2 mm SL.

Type locality and horizon. Monte Postale site, Bolca Konservat-Lagerst¨atte, Italy; early Eocene, late Ypresian, middle Cuisian, SBZ 11, Alveolina dainelli Zone (see Papazzoni et al. 2017).

Diagnosis. † Titanonarke with large subcircular disc of length c. 53% SL and width 56% SL; precaudal tail c. 51% SL; 136 total vertebrae (27 trunk; 74 precaudal, 32 caudal); total tooth row count c. 32 (15 rows in the upper and 17 in the lower jaw); 35 total pectoral radials (12 propterygial, eight mesopterygial and 15 metapterygial); greatly enlarged single-lobed pelvic fins containing c. 19 basipterygial radials; width of pelvic fins c. 61% of disc width; anterior pelvic fin margin length c. 42% disc length; caudal fin with 41 radials (20 dorsal and 21 ventral).

Remarks. Originally, MCSNV 135576 was considered a holomorphic specimen of † T. molini by Carvalho (2010), although that assignment to the type species was tentative. The new species of † Titanonarke differs from the type species † T. molini (Jaekel, 1894) in a combination of morphometric and meristic characters. The differences mostly include those associated with the number of precaudal vertebrae (74 in † T. megapterygia sp. nov. vs. 100–115 in † T. molini). Consequently, the comparably reduced vertebral number in † T. megapterygia sp. nov. (133 in † T. megapterygia sp. nov. vs. 153–155 in † T. molini) results in different body proportions (see also Table 1). † Titanonarke megapterygia sp. nov. also differs from † T. molini by having a greater head length (c. 27 vs. 23% SL), disc length (53 vs. 44% SL), disc width (56 vs. 50%) and shorter tail (51 vs. 58% SL). However, the main difference in body proportions is in the size of the pelvic fins, which have a larger span (34 vs. 26% SL), anterior margin (23 vs. 11% SL) and base length (17 vs. 13% SL) in † T. megapterygia sp. nov. than in † T. molini. Moreover, the caudal fin also is longer in † T. megapterygia sp. nov. (16% SL) than in † T. molini (9% SL), with a higher number of caudal vertebral centra (32 vs. 23–25, respectively). The PCA performed on the entire morphological data set of standardized and log-transformed measurements and counts (Fig. 8) shows a remarkable separation of specimen MCSNV IG.135576 from all others along PC1 (PCA loading values indicate that this axis is mainly related to the variation in tail length, pelvic fin span, and the number of precaudal vertebrae), thereby suggesting that morphometric and meristic data are useful to separate † T. megapterygia sp. nov. from † T. molini.