Aphanapteryx Frauenfeld, 1868a

Hume, Julian Pender, 2019, Systematics, morphology and ecology of rails (Aves: Rallidae) of the Mascarene Islands, with one new species, Zootaxa 4626 (1), pp. 1-107 : 9-12

Genus Aphanapteryx Frauenfeld, 1868a

Aphanapteryx Frauenfeld, 1868a , p.6. Type (by monotypy): Aphanapteryx imperialis Frauenfeld = Apterornis bonasia Sélys- Longchamps.

Etymology: From Greek aphançs = unseen, invisible-wing, privative prefix a, and pteryx = wing.

Revised Diagnosis: Aphanapteryx bonasia ( Fig. 5 ) is distinguished from other Mascarene rallids by the following characters:

Cranium ( Fig. 6 ): largest cranium in Mascarene Rallidae ; in lateral view, cranium dorso-ventrally compressed; small fonticulus orbitocranialis; large foramen n. optici; processus postorbitalis short, bluntly triangular; deep fossa temporalis; os lacrimale wide rostrocaudally and straight extending past os ectethmoidale posteriorly; no foramen in os ectethmoidale; crista nuchalis transversa distinct; crista temporalis indistinct; in dorsal view, frontal narrow, triangular and deeply excavated; in posterior view, crista temporalis extends almost to top of cranium; processus zygomaticus distinct; condylus occipitalis large; foramen magnum large and an inverted heart-shape; in ventral view, tuba audivita communis deep; fossa subcondylaris deeply excavated.

Rostrum ( Fig. 6 ): os premaxillare long and narrow and terminating in a sharp point, and total length nearly 47% longer than cranium length; in dorsal view, os nasale wide, covering narial openings; in lateral view, narial opening reaching 50% the length of the rostrum; foramina neurovascularia, prominent, elongate, running almost to rostral edge of narial opening; os nasale narrow; in ventral view, shallow, indistinct sulcus.

Mandible ( Fig. 6 ): rostrum mandibulae long, length of symphysis approximately 79% of cranium length; in dorsal view, processus mandibulae medialis distinct, triangular; processus retroarticularis long and directed laterad; sulcus on crista intercotylaris deeply excavated; cotyla lateralis distinctly U-shaped; os dentale long, narrow and terminating in a pointed tip; in lateral view, foramina neurovascularia, prominent, deeply set and running almost to a deep sulcus; large fenestra rostralis mandibulae and very small fenestra caudalis mandibulae.

Quadrate: in lateral view, processus orbitalis long, deep and rounded; processus oticus short; processus mandibularis rounded, and strongly directed laterad; fovea quadratojugalaris oval or rounded and deeply excavated; in medial view, condylus pterygoideus deeply incised; in medial aspect, a single foramen pneumaticum rostromediale present and situated anterior to the medial ridge (see Elzanowski & Stidham 2010), which occurs in the same position and with no variation other than size in all Rallidae examined in this paper.

Vertebrae: configuration of vertebrae of Thirioux Aphanapteryx associated skeleton (see details below under Referred fossil material); atlas (1); axis (2); presynsacral (cervical) (3–15); presynsacral (cervicodorsal) (16); notar- ium (presynsacral thoracic vertebrae 17–19); presynsacral (thoracic) (20), plus free caudal (5); pygostyle (1) = (20 + 5 + 1); in Gallinula (20 + 7 + 1); in Fulica (22 + 5 + 1); in Dryolimnas (22 + 6 + 1) and Porphyrio (20 + 7 + 1).

Scapula ( Fig. 7 ): in lateral view, wide; margo dorsalis distinct; facies articularis humeralis shallow; acromion blunt, rounded and directed dorsad; tuberculum coracoideum indistinct.

Coracoid ( Fig. 8 ): comparatively short; shaft wide; in dorsal aspect, cotyla scapularis shallow and indistinct; large oval foramen n. supracoracoidei distal to processus procoracoideus; processus procoracoideus short and weak- ly directed dorsomediad; impressio m. sternocoracoidei deeply excavated.

Sternum ( Fig. 9 ): carina sterni extremely reduced more than in any other Mascarene rallid (See appendix 2, Table 6 ); in dorsal view, processus craniolateralis wide, directed slightly cranially; tuberculum labri externi pronounced; foramen pneumaticum deeply excavated; sulcus medianus sterni not clearly defined; in lateral view, apex carinae directed slightly ventrad; in lateral view, carina sterni extremely reduced.

Humerus ( Fig. 10 ): extremely reduced; shaft strongly curved dorsoventrally; in caudal aspect, tuberculum ventrale pronounced, incisura capitis deeply excavated; fossa pneumotricipitalis extremely shallow; tuberculum dorsale reduced; sulcus humerotricipitalis broad and deep; in cranial view, sulcus transversus shallow; crista bicipitalis, short, weakly square-shaped; crista deltopectoralis long, extending much further distad than crista bicipitalis; fossa m. brachialis deeply excavated; indistinct processus supracondylaris dorsalis.

Radius ( Fig. 11 ): sulcus tendinosa deep extending proximad approximately 25% of total length radius length; facies articularis radiocarpalis deflected ventrally; in ventral aspect, depressio ligamentosa deeply excavated.

Ulna ( Fig. 12 ): short and strongly arched dorsoventrally proximally; in caudal aspect, olecranon indistinct; processus cotylaris dorsalis short; in ventral aspect, impressio brachialis deep.

Carpometacarpus ( Fig. 13 ): in dorsal aspect, processus extensorius short and rounded; os metacarpale majus robust; os metacarpale minus weakly arched creating narrow spatium intermetacarpale.

Phalanges digiti alulae I ( Fig. 13 ): short, equal in length to os metacarpale alulare.

Phalanges digiti proximalis majoris ( Fig. 13 ): short; pina cranialis indistinct.

Pelvis ( Fig. 14 ): extremely wide and robust; in dorsal view, sulcus antitrochantericus extend laterally beyond the ala preacetabularis; distinct, caudally-open canalis iliosynsacralis either side of the crista iliaca dorsalis; distinct foramina intertransversariae; ala postacetabularis ilii wide on lateral edge covering ala ischii; in lateral view, foramen acetabuli larger in size than foramen ilioischiadicum; crista iliaca dorsalis arched; in ventral view, two pronounced processus costales; ala ischii directed ventrad.

Femur ( Fig. 15 ): extremely robust; in cranial view, shaft curved medially and directed caudally at the proximal end; crista trochanteris strongly deflected mediad; linea intermuscularis indistinct; sulcus patellaris deeply excavated; epicondylus lateralis distinct; condylus medialis extends the same distance distally as condylus lateralis; in medial aspect, crista trochanteris extends caudad, offsetting centrally facies articularis acetabularis; shaft strongly arched dorsally; in caudal aspect, impressiones obturatoriae distinct and directed cranially; linea intermuscularis caudalis distinct, forming a ridge; fossa poplitea deeply excavated; tuberculum m. gastrocnemialis lateralis rounded and separated from trochlea fibularis; condylus medialis smaller than condylus lateralis; trochlea fibularis deeply excavated.

Tibiotarsus ( Fig. 15 , 16a ): large and robust, especially at proximal and distal ends; in cranial view, sulcus extensorius deeply excavated, extending proximad; canalis extensorius oval-shaped; pons supratendineus wide and slightly arched, and situated mediad; crista fibularis extends short; crista cnemialis lateralis long; in caudal aspect, crista cnemialis cranialis weakly pronounced; shaft deep; condylus lateralis small, weakly rounded; depressio epicondylaris lateralis shallow.

Fibula : short and robust; in dorsal view, caput fibulae narrow and weakly grooved caudally; tuberculum m. iliofibularis pronounced and excavated cranially.

Tarsometatarsus ( Fig. 15 , 16a, b ): large and robust; in dorsal aspect, trochleae metatarsorum distinctly splayed, especially trochlea. metatarsi II; metatarsi II directed slightly dorsad; retinaculum extensorium tarsometatarsi indistinct; in plantar aspect, foramen vasculare distale deeply excavated; fossa metatarsi I extends proximad; hypotarsi deflected laterad; on proximal end, a monocanaliculate hypotarsus (see Mayr 2016) with crista medialis flexoris digitorum longus; sulcus for tendon of musculus flexor perforatus digiti II and sulcus for tendon of musculus flexor hallucis longus present.

Remarks: Aphanapteryx was a large flightless rail, approximately 35–40 cm in total length, with extremely robust legs and reduced wings and tail. The bill was long, decurved and deep proximally, the plumage was hair-like and dull brownish-red in colouration, with the feathers of the nape elongate; Livezey (2003) estimated a body mass of 1.3 kg in the male and around 1 kg for the female. Size variation between skeletal specimens ( Fig. 16a ) is almost certainly due to marked sexual dimorphism, with the male larger than the female, a common phenomenon in Rallidae ( Olson 1977; Livezey 2003) (see Appendix 2). The bill was reported to be variable in curvature (e.g. Greenway 1958, 1967), but I have examined all known maxillae and found this not to be the case; however, Aphanapteryx exhibited extreme variation in the total length of the rostrum (see Appendix 2, Table 2 ).

Figures

FIGURE 5. An almost complete, associated skeleton of Aphanapteryx bonasia (MI 923) collected by Etienne Thirioux in September 1899 in the Vallée des Prêtres, Moka Range, mid-west Mauritius. Scale bar = 200 mm.

FIGURE 6. Comparison of crania of Mascarene rails, lateral view. A. Aphanapteryx bonasia MU923 u/s; B. Erythromachus leguati NHMUK u/r, u/s. Scale bar = 10mm.

FIGURE 7. Comparison of scapulae (medio-ventral aspect, left side; except B which is lateral aspect, right side) of Mascarene rails with Dryolimnas, A. UMZC 579 Aphanapteryx bonasia u/s, right proximal UMZC 579 u/s; B. NHMUK u/r Erythromachus leguati u/s; C. NHMUK 1882.2.28.2 Dryolimnas cuvieri cuvieri u/s; D. NHMUK S/1989.38.1 D. c. aldabranus ♂; E. NHMUK 1910.4.8.1 D. c. abbotti u/s. Scale bar = 10 mm.

FIGURE 8. Comparison of coracoids (ventral aspect, right side) of Mascarene rails with Dryolimnas, A. FLMR 1081 Aphanapteryx bonasia u/s; B. NHMUK u/r Erythromachus leguati u/s; C. NHMUK 1882.2.28.2 Dryolimnas cuvieri cuvieri u/s; D. NHMUK S/1989.38.1 D. c. aldabranus ♂; E. NHMUK 1910.4.8.1 D. c. abbotti u/s. Scale bar = 10 mm.

FIGURE 9. Comparison of sterna, lateral aspect (left), ventral aspect (right) of Mascarene rails, A. C. UMZC 303BB Aphanapteryx bonasia u/s; B. D. NHMUK u/r Erythromachus leguati u/s. Scale bar = 10 mm.

FIGURE 10. Comparison of humeri (caudal aspect, left side) of Mascarene rails, A. UMZC 579 Aphanapteryx bonasia u/s; B. NHMUK u/r Erythromachus leguati u/s. Scale bar = 10 mm.

FIGURE 11. Comparison of radii (ventral aspect, right side) of Mascarene rails with Dryolimnas, A. UMZC 579.1 Aphanapteryx bonasia u/s; B. NHMUK u/r Erythromachus leguati u/s; C. NHMUK 1882.2.28.2 Dryolimnas cuvieri cuvieri u/s; D. NHMUK S/1989.38.1 D. c. aldabranus ♂; E. NHMUK 1910.4.8.1 D. c. abbotti u/s. Scale bar = 10 mm.

FIGURE 12. Comparison of ulnae (ventral aspect, left side) of Mascarene rails with Dryolimnas, A. MNHN MAD6967 Aphanapteryx bonasia u/s; B. NHMUK u/r Erythromachus leguati u/s; C. NHMUK 1882.2.28.2 Dryolimnas cuvieri cuvieri u/s; D. NHMUK S/1989.38.1 D. c. aldabranus ♂; E. NHMUK 1910.4.8.1 D. c. abbotti u/s. Scale bar = 10 mm.

FIGURE 13. Comparison of carpometacarpi (ventral aspect, right side) of Mascarene rails, A. MI 925 Aphanapteryx bonasia u/s with unique preservation of phalanx digiti alulae I and phalanx proximalis digitis majoris; B. NHMUK u/r Erythromachus leguati u/s. Scale bar = 10 mm.

FIGURE 14. Comparison of pelves (dorsal aspect) of Mascarene rails, A. UMZC 303BB Aphanapteryx bonasia u/s; B. UMZC 303c Erythromachus leguati u/s. Scale bar = 10 mm.

FIGURE 15. Comparison of femora (caudal aspect, right side), tibiotarsi (cranial aspect, right side) and tarsometatarsi (left side, dorsal aspect) of Mascarene rails. A., C., E. UMZC 303B Aphanapteryx bonasia u/s; B., D., F. UMZC 303c Erythromachus leguati u/s. Scale bar = 10 mm.

FIGURE 16a. Sexual dimorphism in the skeleton of Aphanapteryx bonasia: tibiotarsi (UMZC 303B left side, cranial aspect); tarsometatarsi (UMZC 303BB right side, dorsal aspect). Scale bar = 10 mm.