Rhodacanthis forfex, James & Olson, 2005

James, Helen F. & Olson, Storrs L., 2005, The diversity and biogeography of koa-finches (Drepanidini: Rhodacanthis), with descriptions of two new species, Zoological Journal of the Linnean Society 144 (4), pp. 527-541 : 531-536

publication ID	https://doi.org/ 10.1111/j.1096-3642.2005.00173.x
persistent identifier	https://treatment.plazi.org/id/03F587EB-FF84-FFE9-1F26-D3DCFB2DFB8D
treatment provided by	Diego
scientific name	Rhodacanthis forfex
status

Treatment

GENUS RHODACANTHIS ROTHSCHILD, 1892 View in CoL

Included species: R. palmeri Rothschild, 1892 ; R. flaviceps Rothschild, 1892 ; R. forfex sp. nov.; R. litotes sp. nov.

Within the Drepanidini , both new species were placed by cladistic analysis in a clade composed of the genera Rhodacanthis and Chloridops and the species Xestospiza conica ( James, 2004: fig. 17). In common with other members of that clade, the new species have sturdy, finch-like bills with pronounced ventral crests of the maxilla that extend about 2/3 of the way to the bill tip ( James, 2004: character 20). The new species resemble Rhodacanthis and Chloridops rather than Xestospiza in having a strongly arched rather than an almost straight dorsal profile of the maxilla, and in lacking a planar dorsal surface of the maxilla ( James, 2004: character 6). They are referable to Rhodacanthis as opposed to Chloridops in having the ventral crests of the maxilla sharp rather than blunt ( James, 2004: character 18), the median fossa of the ventral maxilla relatively wide ( James, 2004: character 17), and in lacking a ventral bulge on the tomial crest of the maxilla (lateral view; James, 2004: character 14). They differ further from Chloridops kona or C. wahi in having the median fossa of the maxilla deeply excavated ( James, 2004; character 16). The mandible of R. litotes (unknown for R. forfex ) differs from that of C. kona or C. wahi by the absence of a median fossa along the dorsal symphysis.

The sharp median crest of the posterior portion of the parasphenoidal rostrum in R. forfex (discussed below) is assumed to be characteristic of Rhodacanthis as a whole, although this skull region is not preserved in any other available specimen of the genus.

RHODACANTHIS FORFEX SP. NOV.

( FIGS 2A–B View Figure 2 , 3A–B View Figure 3 , 4A–B View Figure 4 )

P [sittirostra] (Rhodacanthis) aff. palmeri James et al., 1987: 2353 .

Rhodacanthis aff. palmeri James & Olson, 1991: 44 View in CoL . James, 2004: 249, fig. 17.

Rhodacanthis View in CoL , undescribed species Olson, 1999: 6.

Rhodacanthis sp. Burney et al., 2001: table 2.

Holotype: Nearly complete cranium with disarticulated maxilla, USNM 524870 View Materials ( Figs 2A View Figure 2 , 3A View Figure 3 , 4A View Figure 4 ), collected 07.i.1998 by David Burney and other members of the Kauai Palaeoecology Expedition ( Burney et al., 2001). The maxilla lacks a small piece of the nasals adjacent to the nasofrontal hinge, and the basicranium is badly abraded. The specimen includes a detached piece of the occipital region of the skull about 13 mm in diameter.

Type locality: Island of Kauai : Koloa Quadrangle : Makauwahi Cave (21∞53¢30≤N, 159∞25¢17≤W, near sea level). State Archaeological Site #50-30-10-3097; alternately known as the Mahaulepu cave and sinkhole complex. In the excavation described by Burney et al. (2001), the holotype was collected from Unit IV of the east pit .

Distribution: Kauai: Makauwahi Cave. Maui: Makena Quadrangle: Puu Naio Cave (20∞37¢N, 156∞24¢E, 393 m a.s.l.).

Etymology: from Latin, forfex , a scissors, in reference to the specialized feeding behaviour of members of the genus. Adults of the two species of Rhodacanthis that were observed in life by ornithologists used their sharp maxillary and mandibular tomia (and presumably the crests on the lingual surface of the maxilla) to cut up the green pods of the koa tree ( Acacia koa ), a native legume, in order to consume the pods and seeds ( Perkins, 1893; Munro, 1944).

Measurements of holotype: See Table 1.

Paratypes: Kauai , Makauwahi Cave : Maxilla lacking the fused nasals near the nasofrontal hinge and the left lateral nasal bar, USNM 524871 View Materials . Collected from Unit V of the east pit, 04.ii.1998, by David Burney and other members of the Kauai Palaeoecology Expedition. Maui, Puu Naio Cave: Maxilla lacking the dorsal surface except near the bill tip, and also missing the posterior half of the bone from the right side only, USNM 445792 View Materials , collected 13.ii.1984 by S. L. Olson, H. F. James, D. W. Steadman and C. Walseth ( Figs 2B View Figure 2 , 3B View Figure 3 , 4B View Figure 4 ). The excavation at Puu Naio Cave in 1984 is described by James et al. (1987) .

Measurements of paratypes: See Table 1.

Age of referred specimens: Holocene, based on a series of radiocarbon dates on bone collagen, plant material and coprolites recovered from the cave excavations that produced fossils of the species ( James et al., 1987; James & Burney, 1997; Burney et al., 2001).

Description: The maxilla differs from that of all other species of Rhodacanthis in having a distinct median crest on the dorsal surface ( Fig. 3 View Figure 3 ), and a slightly concave rather than convex profile of the tomial crest (ventral view). The cranium is more robust than other available crania of the genus, with larger zygomatic and postorbital processes, and the scars for attachment of the temporal musculature more sharply delineated and more extensive, rising further onto the dorsal surface of the skull ( Fig. 3 View Figure 3 ). Differs further from R. flaviceps in having a larger skull and maxilla, a deeper median fossa on the ventral surface of the maxilla, and virtually parallel rather than slightly divergent lateral crests of the maxilla. Differs further from R. palmeri in having the maxilla anterior of the nasal cavities deeper ( Figs 1, 2 View Figure 2 ). The maxilla of R. forfex differs from that of R. litotes , the other new species, in the ways mentioned for R. palmeri , and also in being distinctly larger.

Remarks: Because of damage to the modern specimens caused during the skinning process, the holotype of R. forfex is the only osteological specimen of Rhodacanthis in which the posterior portion of the parasphenoidal rostrum is preserved ( Fig. 4 View Figure 4 ), revealing its distinctive sharp-edged median crest. Such a crest does not occur in related drepanidine genera with finch-like bills ( Telespiza , Loxioides , Chloridops and Xestospiza ; see James, 2004), but is found in the cardueline genus Coccothraustes (hawfinches and relatives sensu Howell et al., 1968; James, 2004: character 57, fig. 4) and in an even more extreme state of development in the Maui Parrotbill ( Pseudonestor xanthophrys )( Zusi, 1989), a drepanidine with a parrot-like bill and jaw mechanism. In Pseudonestor and Coccothraustes , the crest is correlated functionally with an expanded origin of M. pterygoideus retractor along the parasphenoidal rostrum and onto the interorbital septum ( Zusi, 1989). The parasphenoidal crest also occurs in parrots, which have a specialized jaw musculature with extensive origin of the pterygoideus muscle on the interorbital septum ( Burton, 1974).

Assuming that the parasphenoidal crest observed in R. forfex also indicates a strengthened and expanded M. pterygoideus retractor, we can speculate that it developed as part of an adaptive complex in the skeletomuscular system of the entire genus Rhodacanthis for feeding on leguminous pods. M. pterygoideus retractor is the only muscle that can depress the maxilla without exerting simultaneous pressure to raise the mandible ( Zusi, 1989). Its expansion in Rhodacanthis might have allowed greater biting force by the maxillary rostrum and greater independence of action by the maxillary vs. mandibular rostra, helping the birds to slice up fibrous pods.

The fossil of an ‘additional Kauai finch’ mentioned by Olson & James (1982: 40), from the Makawehi Dunes of southern Kauai, cannot be referred to R. forfex . That fossil consists only of the caudal part of a mandibular ramus, and its lateral cotyla differs in shape from the distinctive cotyla of Rhodacanthis .

RHODACANTHIS LITOTES SP. NOV.

( FIGS 2F–H View Figure 2 , 3F–H View Figure 3 , 4F–H View Figure 4 , 5B View Figure 5 )

Psittirostra (Rhodacanthis) flaviceps Olson & James, 1982: 39 , 45.

Psittirostra (Rhodacanthis) sp. James, 1987: 225, 228.

P [sittirostra] (Rhodacanthis) aff. flaviceps James et al., 1987: 2353 .

Rhodacanthis aff. flaviceps James, 2004: 249 View in CoL , fig. 17.

Holotype: Complete maxilla, BPBM 158861 View Materials , collected 23.vii.1981 by Aki Sinoto, Patrick C. McCoy et al. ( Figs 2G View Figure 2 , 3G View Figure 3 4G View Figure 4 ).

Type locality: Island of Oahu, Ewa Quadrangle: large sinkhole c. 3.6 km N of Barber’s Point (21∞18¢N, 158∞6¢E, c. 15 m a.s.l.); Bishop Museum archaeological site 50-Oa-B6-22 ( Olson & James, 1982: 27).

Distribution: Oahu: Ulupau Head and Ewa Plain. Maui: all specimens were collected at Puu Naio Cave ( James et al., 1987).

Etymology: From Greek, litotes , a figure of speech in which an idea is affirmed by denying the contrary, an understatement. Once referred to R. flaviceps , the fossils are now recognized as a distinct species because they lack several characters that make R. flaviceps appear to be the more specialized and distinctive of the two.

Measurements of holotype: See Table 1.

Paratypes: Oahu: Maxilla lacking the major parts of the left lateral nasal bar and the fused nasals anterior to the nasofrontal hinge, USNM 445795 View Materials , collected at Ulupau Head, Oahu (James, 1987), 26.iii.1986, by S. Olson and H. James ( Figs 2F View Figure 2 , 3F View Figure 3 , 4F View Figure 4 ). Maui: Maxilla lacking the left lateral nasal bar and part of the cofused nasals anterior of the nasofrontal hinge, USNM 445794 View Materials , collected ii.1984 by S. L. Olson, H. F. James et al. ( Figs 2H View Figure 2 , 3H View Figure 3 , 4H View Figure 4 ). Mandible lacking the posterior part of the left ramus, USNM 445793 View Materials , collected 11.ii.1984 by S. L. Olson, H. F. James et al. ( Fig. 5B View Figure 5 ). The symphyseal part of a mandible with portions of the intermediate parts of the ramus attached, USNM 445796 View Materials , collected 28.iii.1988 by H. F. James .

Measurements of paratypes: See Tables 1 and 2.

Age of referred specimens: Quaternary. The paratype from wetland sediments at Ulupau Head is> 300– 400 kyr old (James, 1987; Hearty et al., 2005). All other specimens are Holocene in age, based on radiocarbon dates on purified collagen from the bones of extinct birds excavated from the same sedimentary deposits as the Rhodacanthis bones ( James et al., 1987; James & Burney, 1997), and from other similar sedimentary deposits on the same local landscape ( Athens et al., 2002).

Description: A species of finch, known from fossils of the maxilla and mandible and similar in most respects to R. palmeri . Smaller than R. palmeri or R. forfex but similar in size to R. flaviceps ( Fig. 1). The maxilla differs from that of R. flaviceps but resembles R. palmeri and R. forfex in having the lateral crests nearly parallel rather than slightly divergent and the median fossa deeper ( Fig. 4 View Figure 4 ). The mandible differs from R. flaviceps but resembles R. palmeri and R. forfex in the slightly recurved rather than nearly straight ventral profile of the mandibular symphysis (lateral view), and in the lateral profile of the tomial crest, which describes a smooth rather than a broken curve ( Fig. 5 View Figure 5 ). In addition to its smaller size, R. litotes differs from R. forfex in the absence of a dorsal median crest on the maxilla and the nearly straight to convex rather than slightly concave lateral profile of the tomial crest of the maxilla (ventral view).

Remarks: As further evidence that the fossil sample from Maui contains two species, the paratypical mandibles occlude very smoothly with the holotypical maxilla of R. litotes , whereas they do not conform at all to the shape of the larger maxilla from Maui referred to R. forfex .

Even though the two fossil maxillae from Oahu are very different in age, they resemble each other closely in morphology and differ from the maxilla of R. litotes from Maui in having a noticeably smaller aperture of the nasal cavity ( Fig. 2F–H View Figure 2 ).