Another new species of flightless Rail (Aves: Rallidae: Rallus) from Abaco, The Bahamas
Author
Takano, Oona M.
Author
Steadman, David W.
text
Zootaxa
2018
2018-04-11
4407
3
376
382
journal article
30295
10.11646/zootaxa.4407.3.5
6b52aa26-9992-438d-b948-9d4236ff8733
1175-5326
1216608
B33294AD-77AF-4996-A73C-56DD711E5AD0
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
).
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 anterior aspect. 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.
TABLE 1.
Measurements (in mm) of the two species of flightless rails (
Rallus gracilipes
new sp.
,
R. cyanocavi
) from Sawmill Sink, Abaco, The Bahamas, along with mođern R.
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.
| Skeletal Element |
Rallus
|
R. cyanocavi
|
R. longirostris
|
R. elegans
|
R. limicola
|
R. recessus
|
|
gracilipes
|
Abaco |
Floriđa |
Floriđa |
Floriđa |
Bermuđa |
| new sp. |
| U |
U |
M |
F |
M |
F |
M |
F |
U |
|
HUMERUS
|
48.5
|
39.9
|
56.6
|
54.6
|
61.5
|
56.3
|
37.0
|
34.7
|
43.7
|
| length |
1 |
37.5 ̅ 41.8 |
54.4 ̅ 57.4 |
52.1 ̅ 59.0 |
60.3 ̅ 63.0 |
54.7 ̅ 59.7 |
35.0 ̅ 38.1 |
31.9 ̅ 36.4 |
39.7 ̅ 47.4 |
| 7 |
5 |
5 |
5 |
5 |
5 |
5 |
60 |
| miđshaft wiđth |
2.8
|
2.2
|
3.2
|
3.2
|
3.8
|
3.5
|
2.2
|
2.0
|
2.6
|
| 1 |
1.8 ̅ 2.4 |
2.9 ̅ 3.5 |
3.0 ̅ 3.5 |
3.4 ̅ 3.9 |
3.2 ̅ 3.7 |
2.1 ̅ 2.3 |
1.8 ̅ 2.2 |
2.2 ̅ 2.9 |
| 15 |
5 |
5 |
5 |
5 |
5 |
5 |
60 |
| đistal wiđth |
7.0
|
5.6
|
7.5
|
7.3
|
8.7
|
7.8
|
4.9
|
4.6
|
6.1
|
| 1 |
5.3 ̅ 5.9 |
7.3 ̅ 7.8 |
6.9 ̅ 7.9 |
8.4 ̅ 9.0 |
7.5 ̅ 8.1 |
4.6 ̅ 5.0 |
4.3 ̅ 4.8 |
5.6 ̅ 6.7 |
| 8 |
5 |
5 |
5 |
5 |
5 |
5 |
60 |
|
ULNA
|
37.1
|
29.3
|
45.9
|
44.6
|
51.1
|
47.2
|
30.4
|
28.1
|
34.1
|
| length |
1 |
28.1 ̅ 31.0 |
44.0 ̅ 46.9 |
41.9 ̅ 48.8 |
49.9 ̅ 52.0 |
44.6 ̅ 49.9 |
28.9 ̅ 31.7 |
26.0 ̅ 29.9 |
29.3 ̅ 37.3 |
| 6 |
5 |
5 |
5 |
5 |
5 |
5 |
45 |
| miđshaft oblique wiđth |
2.0
|
1.6
|
2.2
|
2.2
|
2.7
|
2.4
|
1.6
|
1.5
|
1.8
|
| 1 |
1.5 ̅ 1.8 |
2.1 ̅ 2.4 |
2.1 ̅ 2.3 |
2.4 ̅ 2.8 |
2.2 ̅ 2.6 |
1.5 ̅ 1.7 |
1.4 ̅ 1.5 |
1.5 ̅ 1.9 |
| 9 |
5 |
5 |
5 |
5 |
5 |
5 |
15 |
| proximal wiđth |
4.7
|
3.7
|
5.0
|
5.0
|
5.9
|
5.2
|
3.4
|
3.0
|
4.2
|
| 1 |
3.6 ̅ 3.8 |
5.0 ̅ 5.3 |
4.8 ̅ 5.5 |
5.7 ̅ 6.1 |
5.0 ̅ 5.5 |
3.1 ̅ 3.5 |
2.9 ̅ 3.1 |
3.6 ̅ 4.5 |
| 4 |
5 |
5 |
5 |
5 |
5 |
5 |
14 |
| đistal đepth |
4.1
|
3.1
|
4.4
|
4.4
|
5.1
|
4.5
|
2.9
|
2.7
|
3.5
|
| 1 |
3.0 ̅ 3.3 |
4.1 ̅ 4.7 |
4.1 ̅ 4.9 |
5.0 ̅ 5.2 |
4.2 ̅ 4.7 |
2.8 ̅ 3.0 |
2.6 ̅ 2.9 |
3.0 ̅ 3.9 |
| 7 |
5 |
5 |
5 |
5 |
5 |
5 |
14 |
|
FEMUR
|
3.7
|
3.1
|
3.6
|
3.5
|
4.2
|
3.8
|
2.5
|
2.4
|
3.6
|
| miđshaft wiđth |
1 |
2.9 ̅ 3.3 |
3.5 ̅ 3.8 |
3.3 ̅ 3.6 |
4.1 ̅ 4.4 |
3.4 ̅ 4.1 |
2.4 ̅ 2.6 |
2.2 ̅ 2.5 |
3.2 ̅ 4.1 |
| 7 |
4 |
5 |
5 |
5 |
5 |
5 |
15 |
|
TIBIOTARSUS
|
65.3
|
61.0
|
78.4
|
75.7
|
89.0
|
81.8
|
54.7
|
50.7
|
66.3
|
| length without cnemial crest |
1 |
58.4 ̅ 62.4 |
74.8 ̅ 80.9 |
71.7 ̅ 82.1 |
87.8 ̅ 90.9 |
78.1 ̅ 87.8 |
53.5 ̅ 56.1 |
48.4 ̅ 52.5 |
58.0 ̅ 71.9 |
| 3 |
5 |
5 |
4 |
5 |
5 |
5 |
30 |
| miđshaft wiđth |
3.6
|
2.9
|
3.5
|
3.5
|
4.0
|
3.7
|
2.4
|
2.2
|
3.4
|
| 1 |
2.6 ̅ 3.2 |
3.3 ̅ 3.7 |
3.1 ̅ 3.8 |
3.6 ̅ 4.3 |
3.5 ̅ 4.0 |
2.2 ̅ 2.6 |
2.1 ̅ 2.4 |
3.2 ̅ 3.6 |
| 11 |
5 |
5 |
4 |
5 |
5 |
5 |
15 |
| đistal wiđth |
6.5
|
6.0
|
6.5
|
6.4
|
7.2
|
6.5
|
4.3
|
4.0
|
6.6
|
| 1 |
5.4 ̅ 6.4 |
6.3 ̅ 6.7 |
6.1 ̅ 6.8 |
6.9 ̅ 7.6 |
6.2 ̅ 6.8 |
3.9 ̅ 4.6 |
3.8 ̅ 4.2 |
6.0 ̅ 7.2 |
| 10 |
5 |
5 |
4 |
5 |
5 |
5 |
30 |
……continued on the next page