SAULI, De Pietri & Worthy & Scofield & Cole & Wood & Mitchell & Cibois & Jansen & Cooper & Feng & Chen & Tennyson & Wragg, 2021

De Pietri, Vanesa L., Worthy, Trevor H., Scofield, R. Paul, Cole, Theresa L., Wood, Jamie R., Mitchell, Kieren J., Cibois, Alice, Jansen, Justin J. F. J., Cooper, Alan J., Feng, Shaohong, Chen, Wanjun, Tennyson, Alan J. D. & Wragg, Graham M., 2021, A new extinct species of Polynesian sandpiper (Charadriiformes: Scolopacidae: Prosobonia) from Henderson Island, Pitcairn Group, and the phylogenetic relationships of Prosobonia, Zoological Journal of the Linnean Society 192, pp. 1045-1070 : 1055-1063

PROSBONIA SAULI SP. NOV. DE PIETRI, WORTHY, SCOFIELD, AND WRAGG

Zoobank registration: urn:lsid:zoobank.org:act:19451CFF-D425-4B8C-B288-B6191390971E

Holotype: The left tarsometatarsus in lot NHMUK S/2001.35.26 ( Fig. 5 AA–DD). It is in near excellent condition, with some minor damage to lateral margin of proximal end. NHMUK S/2001.35.26 also includes a right cranial portion of a scapula, a right radius broken in three parts and a left carpometacarpus missing the os metacarpale minus. These elements do not necessarily represent the same individual as the holotype tarsometatarsus and so are considered as referred material for the new taxon.

Type locality and age: Henderson Island, North Beach (east end), Site # Hen 6 (3 mm), collected from a cave in cliff (12–25 m elevation); Holocene. See Wragg (1995b).

Etymology: The species is named for Edward (Ed) K. Saul, a Cook Island-based ornithologist and conservationist. For the last 30 years Ed has contributed hugely to saving the ‘Kakerori’, Rarotonga Monarch Pomarea dimidiata ( Hartlaub & Finsch, 1871) from extinction.

Diagnosis: Small scolopacid wader, about the size of Prosobonia parvirostris , with bill straight and premaxilla twice wider (mediolaterally) than deep (dorsoventrally) at the level of rostral side narial opening ( Fig. 5A–C); elongated legs, tarsometatarsus ( Fig. 5 AA–D D) with relatively large foramen vasculare distale, prominent plantar projection of the trochlea metatarsi II.

Differential diagnosis: Differs from P. parvirostris in the shape of premaxilla ( Fig. 6A, B), being straighter and proportionally wider, leg bones proportionally longer ( Fig. 6P–U), tuberculum ventrale on humerus rounded instead of flat ( Fig. 6F, H), ulna with impressio brachialis proportionally more elongated ( Fig. 6J, L) and tubercle bordering incisura tendinosa not as pronounced ( Fig. 6K, M), processus extensorius of carpometacarpus more slender and elongated, and proximal and distal synostoses proportionally more elongated ( Fig. 6N, O), tibiotarsus straight not medially concave ( Fig. 6P, Q), tarsometatarsus with sulcus for the tendon for the musculus flexor hallucis longus shallower and more laterally positioned, sulcus for tendon of musculus flexor perforatus digiti 2 deeper and better marked ( Fig. 6V, W), foramen vasculare distale proportionally larger ( Fig. 6R–U), plantar projection of trochlea metatarsi II more prominent ( Fig. 6X, Y) and incisura intertrochlearis lateralis wider ( Fig. 6R–U). Differs from P. cancellata in having proportionally longer legs (assuming P. parvirostris and P. cancellata are similar in leg length, as there is no evidence of the contrary despite the hind toe being presumably shorter in P. cancellata ; Walters, 1993; Jansen & Cibois, 2020). Differs tentatively from P. ellisi in having a straighter bill (see: Walters, 1991). Differs from P. leucoptera in having a mediolaterally wider and dorsoventrally deeper tip of the bill, carpometacarpus with proximodistally more elongated synostosis metacarpalis distalis and only slightly more elongated legs that are possibly not as stout – all three complete tarsometatarsi are at least 2 mm longer than measured for P. leucoptera ( Tables 3, 5; Supporting Information, Table S4).

Material: NHMUK S/2001.35.1 (dR humerus, dR ulna); NHMUK S/2001.35.2 (dR humerus); NMH S/2001.35.4 (left carpometacarpus); NHMUK S/2001.35.6 (2R, 1L phalanx proximalis digiti majoris); NHMUK S/2001.35.7 [dR radius,L humerus missing proximal end, dR ulna, dL carpometacarpus, L tibiotarsus (subadult)]; NHMUK S/2001.35.8 [L tarsometatarsus (subadult)]; NHMUK S/2001.35.9 (cranial portion of sternum, dR tibiotarsus); NHMUK S/2001.35.10 (dR tibiotarsus); NHMUK S/2001.35.11 (dL tarsometatarsus, R phalanx proximalis digiti majoris); NHMUK S/2001.35.12 (L ulna, R carpometacarpus); NHMUK S/2001.35.13 (R scapula, L scapula, cranial portion of sternum, premaxilla, R humerus, R carpometacarpus);

in caudal view. V–X, right tibiotarsus ( NHMUK S/2001.35.21, subadult) in caudal (V), cranial (W) and distal (X) views; Y–Z, right tibiotarsus ( NHMUK S/2001.35.10) in cranial (Y) and medial (Z) views. AA–DD, left tarsometatarsus ( NHMUK S/2001.35.26, holotype) in plantar ( AA), dorsal ( BB), proximal ( CC) and distal ( DD) views. Abbreviations: acr, acromion; cb, crista bicipitalis; cdp, crista deltopectoralis; cdu, condylus dorsalis ulnae; ctd, cotyla dorsalis; ctv, cotyla ventralis; dep, depression; dfp, dorsal fossa pneumotricipitalis; fah, facies articularis humeralis; fmb, fossa musculi brachialis; fvd, foramen vasculare distale; iacd, impressio ansae m. iliofibularis (pars caudalis); pex, processus extensorius; pc, pars cardiaca (sternum); pptII, plantar projection on trochlea metatarsi II; psd, processus supracondylaris dorsalis; pst, pons supratendineus; rid, ridge; sac, sulcus articularis coracoideus; sim, spatium intermetacarpale; sp, sulcus patellaris; spe; spina externa (sternum); st, sulcus tendinosus (ulna); tbc, tuberculum coracoideum; tc, tuberculum carpale; tgl, tuberculum m. gastrocnemialis lateralis; tmt II, trochlea metatarsi II; trel, tuberculum retinaculi m. fibularis lateralis; tub, tubercle delimiting incisura tendinosa (ulna); tub (tst), tuberculum m. scapulotricipitis; tv, tuberculum ventrale. Scale bars equal 0.5 mm except for A–C, which is 0.1 mm. M–N, P–Q, T–U, X–Z, CC–DD not to scale .

NHMUK S/ 2001.35.14 [L humerus missing proximal end, L carpometacarpus missing distal end (subadult)]; NHMUK S/2001.35.15 (cranial portion of sternum, R carpometacarpus, L tarsometatarsus); NHMUK S/ 2001.35.16 (dR tarsometatarsus); NHMUK S/ 2001.35.17 (L carpometacarpus); NHMUK S/2001.35.18 (R femur in two parts, pR tarsometatarsus); NHMUK S/2001.35.19 (dR femur, pR carpometacarpus); NHMUK S/2001.35.20 (dR femur, pL femur, dL humerus, L phalanx proximalis digiti majoris); NHMUK S/2001.35.21 (subadult, likely one individual, L/R humerus, R ulna, L radius, L/R carpometacarpus, L phalanx proximalis digiti majoris, L femur, L/R tibiotarsus, two pedal phalanges); NHMUK S/2001.35.22 (L cranial scapula); NHMUK S/ 2001.35.23 (fragmentary synsacrum); NHMUK S/2001.35.24 (dR tibiotarsus); NHMUK S/2001.35.26 (R cranial scapula, R radius in three parts, L carpometacarpus, L tarsometatarsus).

Measurements (mm): Bill: L as found, 4.7; L from tip to rostral opening of the nares, 3.8; depth at narial opening, 0.8; width from midline to left margin at level of narial opening, 0.9 (i.e. estimated width at narial opening, 1.8). We estimate a 0.3-mm section is missing from the tip of the bill. See Table 5 for summary statistics of multiple elements, and Supporting Information, Table S4 for complete individual specimen measurements.

Description and comparisons

Premaxilla: The right margin of the premaxilla is damaged ( Fig. 5A, B). The premaxilla is flatter and proportionally wider than in P. parvirostris ( Fig. 6A, B), which also has a more decurved tip of the bill. The tip of the bill is straighter in P. leucoptera than in P. parvirostris (see: Zusi & Jehl, 1970) and, in fact, the shape of the premaxilla of P. sauli , at least in lateral view, is similar to that of P. leucoptera , as drawn from an X-ray of its skull by Zusi & Jehl (1970: fig. 5) and confirmed in the radiograph we obtained from RMNH. Measurements for the bill of P. leucoptera , despite the presence of a rhamphotheca in the specimen, would, however, suggest that its bill is more slender mediolaterally than that of P. sauli (width at level of narial opening 0.8 mm vs. an estimated 1.8 mm for P. sauli ) and that it is also dorsoventrally wider (depth 1.9 mm vs. 0.8 mm in P. sauli at the level of the narial opening).

The bill is proportionally shorter in P. parvirostris than in P. leucoptera ; the culmen for the latter was measured at 19.8 mm, which agrees with the value (20.0 mm) provided by Zusi & Jehl (1970), whereas these authors provided 15.5–18.0 mm as the range for the P. parvirostris specimens they measured. The overall length of the bill cannot be assessed for P. sauli .

Scapula: The scapula of P. sauli ( Fig. 5F, G) does not differ from that of P. parvirostris . The acromion is less cranially developed than that of many Scolopacidae , resembling that of Scolopax minor Gmelin, 1789 , Gallinago gallinago ( Linnaeus, 1758) and species of Coenocorypha . In Arenaria interpres ( Linnaeus, 1758) , the acromion is well developed and projects markedly craniodorsally. Unlike in many scolopacids (e.g. Bartramia , Calidris , Limosa and Numenius ), the facies articularis humeralis is round rather than elongated. This is also the case in, for example, Limnodromus scolopaceus , Coenocorypha and species of Scolopax and Gallinago . Similar to Coenocorypha and Scolopax , there is a distinctive notch between the facies articularis humeralis and the tuberculum coracoideum. A pronounced tubercle, presumably the tuberculum m. scapulotricipitis, on the facies lateralis of the corpus scapulae is present in all examined scolopacids.

Sternum: The sternum does not differ between P. sauli and P. parvirostris , being distinctive among scolopacids in that the spina externa is a blunt, knob-like cranial projection with a bifurcated dorsal margin ( Fig. 5D–E). A ventral blade-like margin on the spina externa, as in most scolopacids (exceptions e.g. Coenocorypha , Scolopax and Gallinago ) is absent. A similarly-shaped, bifurcated spina is also present in, for example, Calidris minutilla ( Vieillot, 1819)

tibiotarsus of P. parvirostris in cranial view. R–Y, left tarsometatarsi of P. sauli (R, T, V, X, NHMUK S/2001.35.26, holotype) and P. parvirostris (S, U, W, Y) in dorsal (R, S), plantar (T, U), proximal (V–W) and distal (X–Y) views. Abbreviations: cb, crista bicipitalis; cdp, crista deltopectoralis; cf, crista fibularis; cmp, crista medianoplantaris; ctd, cotyla dorsalis; dfp, dorsal fossa pneumotricipitalis; fhl, sulcus for the tendon of musculus flexor hallucis longus; fpp2, sulcus for the tendon of musculus flexor perforans et perforatus digiti 2; fvd, foramen vasculare distale; iit, incisura intertrochlearis; imb, impressio brachialis; pex, processus extensorius; pptII, plantar projection on trochlea metatarsi II; psd, processus supracondylaris dorsalis; rid, ridge in incisura capitis; smd, synostosis metacarpalis distalis; tlcv, tuberculum lig. collateralis ventralis; tub, tubercle delimiting incisura tendinosa (ulna); tv, tuberculum ventrale (humerus). Dotted lines in B indicate the rostral extent of the narial opening. Scale bars equal 0.5 mm except for A–C, which is 0.1 mm. F–M and V–Y not to scale.

but Prosobonia differs from Arenaria and species of Calidris in that the sulci articulares coracoidei terminate laterally of the rostrum sterni. The cranial margin of the sternum, similar to that of Coenocorypha , is mediolaterally wide, unlike in other scolopacids, in which it is narrower. Rostrally, there is a depression, and a ridge is present toward the apex.

Humerus: The humerus of P. sauli ( Fig. 5J, K) is only slightly more elongated and gracile, proportionally, than that of P. parvirostris ( Fig. 6C, D). Other than in the shape of the tuberculum ventrale, which in proximal view is round in P. sauli and flat in P. parvirostris ( Fig. 6F, H), the proximal end does not differ between the two species. The crista deltopectoralis is short but well developed dorsally (as in most Scolopacidae ). Compared with other scolopacids, the distal extent of the crista deltopectoralis only just surpasses, distally, the level of the crista bicipitalis, as in some species of Calidris (e.g. C. minutilla ) and unlike Arenaria and most other scolopacids. In Prosobonia , the shape of the crista bicipitalis is distinctive among scolopacids in having a rather straight margin connecting the shaft and the tuberculum ventrale ( Fig. 6C, D, F, H) instead of it bulging ventrally. In this aspect it is similar to species of Gallinago [e.g. G. gallinago and G. hardwickii ( Gray, 1831) ]. A dorsal fossa pneumotricipitalis is present in Prosobonia , being shallow and dorsoventrally wide (wider than the ventral fossa pneumotricipitalis) compared to that of all other examined scolopacids. Also contrary to other scolopacids, the ridge in the incisura capitis does not transverse the incisura at a right angle but is oblique. The width of the fossa is related to this ridge meeting the crus dorsale fossae more proximally and ventrally compared to other taxa. This morphology is rather similar to Calidris himantopus ( Bonaparte, 1826) but in P. sauli the ridge in the incisura capitis is more proximally situated.

At the distal end, the shape of the processus supracondylaris dorsalis is the most distinctive feature of Prosobonia . Unlike in all other scolopacids, it points markedly proximally, being wide at its base. It is reduced (shorter) compared to the process in other scolopacids, but it is similar in size to that of Gallinago and Coenocorypha . The depth of the fossa musculi brachialis is comparable to that of other scolopacids.

Ulna: The ulna ( Fig. 5O–Q) is similar in length to that of one specimen of P. parvirostris ( NHMUK Tring; Table 6). The impressio brachialis extends further distally in P. sauli . The shape of the cotyla dorsalis differs slightly between the two species ( Fig. 6J, L): in P. sauli there is, proximally, a straight margin that projects markedly dorsally from the shaft compared to the condition in P. parvirostris . The tubercle that forms the proximal margin of the incisura tendinosa, albeit prominent, is even more dorsally prominent in P. parvirostris ( Fig. 6K, M).

The ulna of species of Prosobonia differs in some features compared to that of most of the examined scolopacids. At the proximal end, the tuberculum lig. collaterallis ventralis ( Fig. 6J, L) is proximodistally short (being more elongated, for example, in Arenaria , Bartramia and Limnodromus ) and it is more ventrally prominent than in species of Calidris and other scolopacids. The tuberculum is also situated far proximally, close to the cotyla ventralis. At the distal end, the condylus dorsalis ulnaris is broad and flares markedly dorsally. The tuberculum carpale ( Fig. 5P) has a distinctive shape among most scolopacids being prominent ventrocranially and sharply offset from the shaft and condylus ventralis ulnaris. The tubercle

bones of Prosobonia sauli (average from Table 5) in comparison to P. parvirostris . Shaft measurements of

the carpometacarpus refer to the os metacarpale majus. Proximal width of the tibiotarsus refers to the articular surface. There were no leg bones for the specimen at NHMUK (Tring)

that borders the incisura tendinosa proximally is more prominent, dorsally, in species of Prosobonia than in the examined scolopacids.

Radius: This element is similar to that of P.parvirostris . The sulcus tendinosus ( Fig. 5M) is better marked than in all other examined scolopacids, showing a distinctly notched distal margin in distal view ( Fig. 5N).

A somewhat similar condition, albeit less pronounced, was found, for example, Tringa glareola Linnaeus, 1758 and Phalaropus lobatus ( Linnaeus, 1758) .

Carpometacarpus: This bone is more elongated with slightly less robust ends than that of P. parvirostris ( Fig. 6N, O). The processus extensorius is slenderer and more elongated in P. sauli (being similar to that of e.g. B. longicauda , Limnodromus scolopaceus ) and the synostosis metacarpalis proximalis and the synostosis metacarpalis distalis are proximodistally longer compared to P. parvirostris . In all the examined specimens, the tuberculum intermetacarpale was less developed than in P. parvirostris (AMNH) . Compared to what is visible from the radiograph of P. leucoptera , this bone appears to be slightly more gracile in the latter, with a proportionally shorter synostosis metacarpalis distalis. However, the proportions in length of the ulna and phalanx proximalis digiti majoris relative to the carpometacarpus are similar in both P. sauli and P. leucoptera . The same relative proportions among these three elements are also maintained in P. parvirostris .

In overall proportions ( Fig.5H,I), the carpometacarpus of the Henderson species is similar to that of Arenaria interpres and Calidris ferruginea ( Pontoppidan, 1763) , being shorter than in many of the other examined scolopacids [e.g. B. longicauda ( Bechstein, 1812) ]. The carpometacarpus of P. parvirostris is indeed relatively shorter than in any other examined scolopacid. Owing to the more (ventro)dorsally positioned os metacarpale minus, the spatium intermetacarpale in species of Prosobonia is wider than in all other examined scolopacids. The phalanx proximalis digiti majoris does not differ between species of Prosobonia and cannot be differentiated from that of most other scolopacids.

Synsacrum: Only a fragment of the synsacrum preserving three (ankylosed) vertebrae cranial and two distal of the vertebra acetabularis (see: Baumel & Witmer, 1993: 91), is known for P. sauli . This fragment cannot be differentiated from P. parvirostris and most other scolopacids.

Femur: Compared to P. parvirostris , the femur is more gracile and elongated in P. sauli ( Fig. 5R–U). The projection of the facies articularis acetabularis is proportionally smaller and more medially protruding in P. sauli . The caudal ridge that borders distally the facies articularis antitrochanterica extends further laterally in P. sauli ; the depression distal to it is larger and more noticeable (as seen on specimen NHMUK S/2001.35.18). In these features, P. parvirostris is more similar to Arenaria and some species of Calidris , differing from the condition in P. sauli . Other than proportional, there are no qualitative differences between the distal ends of species of Prosobonia .

Overall, the proximal end closely resembles that of other scolopacids. The proximal portion of the crista trochanteris is only preserved in an immature individual ( NHMUK S/2001.35.21, Fig. 5R, S) and is similar to that of other scolopacids. The distal end of the only adult individual ( NHMUK S/2001.35.18) is missing its lateral condyle. The distal end ( Fig. 5U) resembles that of Arenaria and species of Calidris , in having a well-marked tuberculum musculi gastrocnemialis lateralis and well-marked cranial and caudal impressiones ansae musculi iliofibularis. Similar to some species of Calidris (e.g. C. ferruginea ), the medial crest that borders the sulcus patellaris is greatly expanded cranially.

Tibiotarsus: As with other leg elements, the tibiotarsus ( Fig. 5V–Z) of P. sauli is more elongated (and gracile) than that of P. parvirostris . The crista fibularis is proportionally longer in P. sauli . The tibiotarsus of P. parvirostris is medially concave, whereas it is straight, as in all other scolopacids, in P. sauli ( Fig. 6P, Q). There are no other significant differences between the two and indeed this bone is overall similar, both in its proximal and distal end, to that of other scolopacids. The pons supratendineus is level with the cranial surface of the medial margin of the bone, and not depressed caudally as in some scolopacids (e.g. B. longicauda ). In all but one specimen, the tuberositas retinaculi extensoris lateralis of P. sauli has the shape of a small, round tubercle and is not as proximodistally elongated as in some scolopacids (e.g. Limosa and Bartramia ), being similar to that of Prosobonia parvirostris ; one specimen ( NHMUK S/2001.35.10) has a slightly more elongated tuberositas. The lateral condyle of Prosobonia is unusual among the examined Scolopacidae in that it is not as inflated or salient cranially and in that it is proportionally much wider, mediolaterally, than the medial condyle, which is more noticeable in distal view ( Fig. 5X).

Tarsometatarsus: The tarsometatarsus is proportionally more elongate than that of P.parvirostris ( Fig. 6R–U). At the proximal end, the hypotarsus varies only slightly between the two species: the sulcus for the tendon of musculus flexor hallucis longus (fhl) is shallower and more laterally positioned in P. sauli , with the crista lateralis flexoris hallucis longus [cl (fhl)] being plantarly shorter than in P. parvirostris ( Fig. 6V, W). The sulcus for the tendon of musculus flexor perforans et perforatus digiti 2 (fpp2), on the other hand, is deeper and better marked in P. sauli ( Fig. 6V). In plantar view, the crista medianoplantaris is more prominent and better defined in P. sauli ( Fig. 6T, U). At the distal end, the foramen vasculare distale is proportionally larger and the plantar projection of the trochlea metatarsi II is more prominent in P. sauli ( Figs 5 DD, 6R–Y). The incisura intertrochlearis lateralis is wider in P. sauli , as the trochlea metatarsi IV is not as closely situated to the trochlea metatarsi III as in P. parvirostris ( Fig. 6R–U).

Within Scolopacidae , the tarsometatarsus of Prosobonia , particularly that of P. parvirostris , is somewhat similar in overall proportions to that of A. interpres , whereas it is more elongated and slender in P. sauli . Compared to most other scolopacids, the shaft is noticeably wider just proximal of the foramen vasculare distale in these species.

At the distal end ( Fig. 5 AA–BB), the trochlea metatarsi II is less plantarly retracted than in nearly all scolopacids, flaring medially instead as in A. interpres (and, for example, B. longicauda ). The trochlea metatarsi IV, however, does not flare laterally, as in A. interpres , being similar to that of other scolopacids. Most scolopacids, however, have a mediolaterally compressed distal end of the tarsometatarsus. In Prosobonia , the sulcus in which the foramen vasculare distale is situated, is mediolaterally broader than in other examined species.

At the proximal end ( Fig. 5 CC), the configuration of the hypotarsus does not depart significantly from that of other scolopacids ( Mayr, 2011), considering the variation across taxa: for example, the canal for the tendon of musculus flexor digitorum longus (fdl) is open in P. parvirostris and the Henderson species, but it is closed in other taxa (e. g. Gallinago , Limnodromus and Numenius ) and in some taxa this canal/sulcus is more centrally situated (e.g. Arenaria ). In P. sauli , there are well-marked sulci for fhl and fp2 (as in Bartramia , Numenius , some species of Calidris ), but there is only one well-marked sulcus in P. parvirostris and many other scolopacids for these tendons (e.g. Arenaria , some species of Calidris ).

OTHER SPECIES OF PROSOBONIA FROM HOLOCENE FOSSIL ACCUMULATIONS

A Polynesian sandpiper was tentatively reported from a cultural site on Tubuai, Austral Islands ( Worthy & Bollt, 2011). The specimen, AM O.72 467, is a left humerus with most of the proximal end missing but preserving the impressio coracobrachialis and the crista deltopectoralis ( Table 3; Fig. 6E). The bone is slightly larger and much stouter than the humerus of P. sauli and P. parvirostris . Despite similarities with Prosobonia that are due to the scolopacid morphology of the bone, it differs from Prosobonia in two key features: the crista deltopectoralis reaches further distally in relation to the crista bicipitalis (in Prosobonia the crista deltopectoralis only just surpasses it distally), and the proximal margin of the processus supracondylaris dorsalis is perpendicular to the shaft instead of pointing proximally, as in species of Prosobonia . Measurements for AM O.72 467 ( Table 3) agree with the Sanderling, Calidris alba ( Pallas, 1764) , as does its overall morphology, and the bone should, therefore, be referred to this species, a regular visitor to the Austral Islands ( Thibault & Cibois, 2017).