Rallus gracilipes, Takano & Steadman, 2018

Takano, Oona M. & Steadman, David W., 2018, Another new species of flightless Rail (Aves: Rallidae: Rallus) from Abaco, The Bahamas, Zootaxa 4407 (3), pp. 376-382 : 377-380

Rallus gracilipes , new species

Holotype. UF 420700, complete tarsometatarsus ( Fig. 1 ). Collected through SCUBA diving by Brian Kakuk from the Owl Roost site, Sawmill Sink, Great Abaco Island, Commonwealth of The Bahamas.

Paratypes. UF 420706, complete humerus; UF 241630, complete ulna; UF 420711, partial femur; UF 420698, complete tibiotarsus; all specimens ( Figs. 1 , 2 ) from the type locality.

Referred material. 4 tibiotarsi, 1 tarsometatarsus, 2 pedal phalanges, and 2 cervical vertebrae; UF 420699, 420701–420705, 420708–420710; all specimens from the type locality.

Diagnosis. Rallus gracilipes new species differs from the sympatric and also flightless R. cyanocavi , as well as R. limicola (rare migrant), R. longirostris (resident in estuaries only), and R. elegans (freshwater resident in Florida but not in the Bahamas), as follows. Tarsometatarsus ( Fig. 1 ): 1, fossa parahypotarsalis medialis deeper; 2, shaft narrower (relative to depth or total length) in R. cyanocavi , but stouter than in the three others; 3, acrotarsial surface of shaft less concave than in R. cyanocavi ; 4, foramen vasculare distale located more distally than in all except R. cyanocavi ; 5, in plantar aspect, trochleae metatarsi longer, less splayed laterally. Humerus ( Fig. 2 ): 6, incisura capitalis deeper and more distinctly offset from proximal part of shaft than in all except R. limicola ; 7, proximal one-third of caudal surface of shaft more rounded (less angular) than in all except R. limicola ; 8, fossa musculi brachialis shallower than in R. cyanocavi and R. longirostris but deeper (and narrower) than in R. limicola and R. elegans ; 9, tuberculum supracondylare ventrale deeper; 10, processus flexorius larger and more distally protrudent, resulting in a deeper fossa olecrani. Ulna ( Fig. 2 ): 11, more distinct notch (pit) present between olecranon and cotyla dorsalis in anterior and posterior aspects; 12, in medial aspect, cotyla dorsalis offset more distally from cotyla ventralis; 13, deeper depression beneath cotyla dorsalis in medial aspect; shaft relatively broader in dorsal aspect in all except R. elegans . Femur ( Fig. 1 ): 14, crista supracondylaris medialis more pronounced than in all except R. elegans ; 15, impressio ansae musculo iliofibularis larger and faces more posteriorly than in all except R. elegans . Tibiotarsus ( Fig. 1 ): short relative to the tarsometatarsus ( Table 1).

Geological age. Late Pleistocene.

Measurements. See Table 1.

Etymology. From the Latin gracilis (slender) and pes (foot), meaning slender-footed. Named for the narrow tarsometatarsus of the new species relative to that of other congeneric flightless species ( R. cyanocavi , R. recessus ; Table 1). The name gracilipes is a masculine noun in apposition.

Remarks. Rallus gracilipes new species was a medium-sized to large rail. It may have had longer wings relative to legs than in the extinct, sympatric R. cyanocavi , although this statement is based only on ratios of humeral length to tarsometatarsal length. No carpometacarpus of the new species is available, thus we cannot evaluate the extent of shortening of the distal part of the wing, which typically is a key aspect of flightlessness in rails and other birds ( Livezey 2003). Nevertheless, the humerus of R. gracilipes displays three key features that are found in flightless rather than volant species of rails: a more cranially rotated crista deltopectoralis; a relatively more slender humeral shaft; and a deeper fossa muscularis brachialis ( Kirchman & Steadman 2005, 2006). The tarsometatarsus of R. gracilipes was substantially narrower relative to its length, and longer relative to the tibiotarsus, than in R. cyanocavi (Abaco) or R. recessus ( Bermuda; Table 1).

longirostris , R. elegans , anđ R. limicola from Floriđa, anđ extinct R. recessu s from Bermuđa. All đata from Steađman et al. (2013) except for R. gracilipes (all measurements

newly present herein), R. recessus (6 of 14 measurements newly presenteđ herein; the 8 others from Olson anđ Wingate 2001). F, female; M, male; U, unsexeđ.

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Figures

FIGURE 1. Hindlimb bones of Rallus gracilipes, new species, and the other Bahamian flightless rail, R. cyanocavi. A, B. Femora in posterior aspect.C, D. Tibiotarsi in anterioraspect.E, F. Tarsometatarsi in acrotarsial aspect. G, H.Tarsometatarsi in plantar aspect. R. gracilipes, new species—A. UF 420711; C. UF 420698; E, G. UF 420700 (holotype). R. cyanocavi—B. UF 241521; D. UF 241528; F, H. UF 241600.Arrowed features relate to characters in the diagnosis. Scale bars = 10 mm.

FIGURE 2. Wing bones of Rallus gracilipes, new species and R. cyanocavi. A, B. Humeri in anconal aspect. C, D. Humeri in palmar aspect. E, F. Ulnae in medial aspect.G, H. Ulnae in dorsal aspect. R. gracilipes, new species —A, C. UF 420706; E, G. UF 241630; R. cyanocavi—B, D. UF 241510; F, H. UF 241517. Arrowed features relate to characters in the diagnosis. Scale bars = 10 mm.