Erythromachus Milne-Edwards, 1874

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 : 32-33

Genus Erythromachus Milne-Edwards, 1874

Erythromachus Milne-Edwards 1874, p.6 , pls.11–12. Type by monotypy: E. leguati Milne-Edwards

Etymology: From Greek eruthros = red, and makhç = battle, combat, in reference to the rail’s aggression shown towards red cloth.

Revised Diagnosis: Erythromachus differs from other Mascarene genera by the following characters:

Cranium ( Fig. 6 , 22 ): cranium medium-sized; in lateral view, dorso-ventrally compressed; small fonticuli orbitocraniales; large foramen n. optici; processus postorbitalis short and triangular; fossae temporales shallow.

Rostrum ( Fig. 6 , 22 ): os premaxillare long, os nasale narrow, and total length nearly 60% longer than cranium length; in lateral view, shallow; narial opening extremely long, extending for 66% the length of the rostrum; foramina neurovascularia present, not extending to rostral edge of narial opening; os nasale narrow; in ventral view, deep, wide sulcus.

Mandible ( Fig. 6 ): rostrum mandibulae long and narrow terminating in a sharp point, length symphysis approximately 65% of cranium length; in dorsal view, processus mandibulae medialis indistinct; processus retroarticularis small; sulcus on crista intercotylaris deeply excavated; cotyla lateralis weakly U-shaped; os dentale long, narrow and terminating in a pointed tip; large foramina neurovascularia, deeply set and running almost to a deep sulcus situated in centre of mandible.

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

Coracoid ( Fig. 8 ): short but shaft wide; in dorsal aspect, cotyla scapularis deep, oval-shaped; large foramen n. supracoracoidei sternal to processus procoracoideus; impressio m. sternocoracoidei deeply excavated.

Sternum ( Fig. 9 ): small; processus craniolateralis narrow, directed laterad; in dorsal aspect; tuberculum labri externi indistinct; foramen pneumaticum on midline shallow; in ventral view; spina externa variable, reduced or more distinct and square-shaped; in lateral view, carina sterni extremely reduced; apex carinae directed ventrad.

Humerus ( Fig. 10 ): extremely reduced, shaft curved dorsoventrally; in caudal aspect, incisura capitis deeply excavated; fossa pneumotricipitalis shallow; in cranial view, crista bicipitalis, short, square-shaped; fossa m. brachialis shallowly excavated.

Radius ( Fig. 11 ): short; sulcus tendinosa deep extending proximad approximately ¼ of total length radius length; facies articularis radiocarpalis deflected ventrally; in ventral aspect, depressio ligamentosa deeply excavated.

Ulna ( Fig. 12 , 22 ): short and strongly arched dorso-ventrally proximally; tuberculum ligamentosa collateralis prominent; in caudal aspect, olecranon indistinct; processus cotylaris dorsalis short.

Carpometacarpus ( Fig. 22 ): in dorsal aspect, processus extensorius short and rounded; os metacarpale majus robust; os metacarpale minus weakly arched creating narrow spatium intermetacarpale; proximal synostosis long.

Pelvis ( Fig. 14 , 22 ): in dorsal view, ala preacetabularis weakly expanded laterally; in lateral view, foramen ilioischiadicum is equal or slightly larger than foramen acetabuli; canalis iliosynsacralis extend to distal edge of foramen ilioischiadicum.

Femur ( Fig. 15 , 22 ): extremely robust; in cranial view, shaft curved medially and directed caudally at the proximal end; crista trochanteris strongly deflected mediad; in medial aspect, shaft strongly arched dorsally; in caudal aspect, condylus medialis larger than condylus lateralis.

Tibiotarsus ( Fig. 15 , 22 ): short, but robust; sulcus extensorius shallow and restricted proximally; canalis extensorius circular, less oval; pons supratendineus arched.

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

Tarsometatarsus ( Fig. 15 ): short, but extremely robust; in dorsal aspect, trochleae metatarsorum distinctly splayed, especially trochlea metatarsi II; metatarsi II directed slightly dorsad; presence of an ossified bridge connecting retinaculi extensorii individually variable; in plantar aspect, crista medialis hypotarsi central, not deflected laterally; in plantar aspect, surface area of foramen vasculare distale shallowly excavated; fossa metatarsi I extends proximad; hypotarsi deflected laterad; on proximal end, crista medialis flexoris digitorum longus present; sulci for tendon of musculus flexor perforatus digiti II and musculus flexor hallucis longus present.

Remarks: Milne-Edwards (1874), when describing Erythromachus , possessed both the original accounts and the first subfossil remains then recently discovered in caves on the Plaine Corail, Rodrigues ( Fig. 4 ). These, along with elements of Rodrigues Night Heron Nycticorax megacephalus ( Milne-Edwards, 1874) , Rodrigues Turtle Dove Nesoenas rodericanus ( Milne-Edwards, 1874) and Rodrigues Parrot Necropsittacus rodricanus ( Milne-Edwards, 1867a), were sent to Milne-Edwards in Paris by Edward Newton, brother of Alfred Newton, professor at the UMZC ( Milne-Edwards 1869b; A. Newton 1875b; Hume 2007, 2011a, 2014a, b) (data taken from labels). From these he determined that a flightless rail, related to Aphanapteryx on Mauritius, had once occurred on Rodrigues, and proposed a new genus, Erythromachus . As better material became available it was later referred to Aphanapteryx by Günther & Newton (1879); however, Piveteau (1945) noted that distinct differences in the cranium justified the generic separation of Erythromachus , which was an assignation followed by Olson (1977), Mourer-Chauviré et al. (1999) and others, and applied here. As recently shown in the endemic scops owls of Mauritius and Rodrigues ( Louchart et al. 2018), there is precedent for differing evolutionary pathways for the two endemic genera of rails.

Figures

FIGURE 4. Detail of Rodrigues, showing the place names mentioned in the text (adapted from Cheke & Hume 2008).

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 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 22. Associated partial skeleton of NHMUK u/r Erythromachus leguati collected in Caverne Poule Rouge. Clockwise from top; cranium and rostrum; pelvis, right and left femur; right and left tibiotarsus, right carpometacarpus, left ulna. Scale bar = 10 mm.