Papasula abbotti nelsoni, Hume, 2023

Hume, Julian P., 2023, A new fossil subspecies of booby (Aves, Sulidae: Papasula) from Mauritius and Rodrigues, Mascarene Islands, with notes on P. abbotti from Assumption Island, Zootaxa 5270 (3), pp. 507-536 : 518-521

publication ID	https://doi.org/ 10.11646/zootaxa.5270.3.5
publication LSID	lsid:zoobank.org:pub:574616B3-9117-45E2-B850-7461E412999E
DOI	https://doi.org/10.5281/zenodo.7863402
persistent identifier	https://treatment.plazi.org/id/03A1C039-E21C-FFCA-FF08-472EFCDAFEF7
treatment provided by	Plazi
scientific name	Papasula abbotti nelsoni
status	subsp. nov.

Treatment

†Mascarene Booby Papasula abbotti nelsoni ssp. nov.

Sula piscator Milne-Edwards, 1873, p.22 , pl. 11, figs. 5, 5a, 5b, 5c.

Sula capensis Milne-Edwards, 1875, p.8 .

Gannet E. Newton & Gadow, 1893, p.282.

Sula abbotti Nelson, 1974 , p.368; Bourne, 1976, p.119; Cheke, 1987, p.31.

Sula (Papasula) abbotti Cheke, 2001, p.73 View in CoL .

Papasula abbotti, Cheke & Hume, 2008, p.47 View in CoL ; Hume, 2013, p.216.

Papasula sp. , Hume, 2017, p.84.

Holotype: Left humerus UMZC 262.AA ( Figs. 4b View FIGURE 4 , 5b View FIGURE 5 )

Measurements: (see Table 2 View TABLE 2 ).

Type Locality: Mare aux Songes, southeast Mauritius (20826051, 200 S; 57841023, 500 E)

Distribution: Mauritius and Rodrigues, Mascarene Islands.

Etymology: Named after British ornithologist Joseph Bryan Nelson (14 March 1932 – 29 June 2015), who first recognised the presence of a Papasula booby on the Mascarenes, and whose ground-breaking studies on sulids and especially Papasula abbotti are still relevant today.

Paratype: Left ulna UMZC 262.AA (almost certainly associated with Holotype), Mare aux Songes, southeast Mauritius ( Figs. 6c, 6f View FIGURE 6 ).

Referred fossil material: All collected from unspecified caves on the Plaine Corail, Rodrigues: coracoid NHMUK PV A9076 (Ld) ( Fig. 2 View FIGURE 2 ); cranial fragment of sternum NHMUK PV A9076 ( Fig. 3 View FIGURE 3 ); humerus (Lp) NHMUK PV A9049 ( Figs. 4a View FIGURE 4 , 5a View FIGURE 5 ); ulna MNHN 6574 (Rd); NHMUK PV A9076 (Rd) ( Fig. 6 View FIGURE 6 ); tarsometatarsus UMZC 995 (R) ( Figs. 7b, 7c View FIGURE 7 ).

Diagnosis: As for genus.

Chronology: No dates are available from bird remains from the 19th century Mare aux Songes (MAS) collections (Basin 0), but 14C dates exist for MAS fossil remains of endemic giant tortoises Cylindraspis ssp., which became extinct c.1730, that were excavated from the same horizon as the Mascarene booby elements ( Hume et al. 2021). The dates range from ca. 1260 to 1830 YBP ( Burleigh & Arnold 1986). On Rodrigues, a partial humerus of the endemic owl Otus murivorus ( Milne-Edwards, 1873) , collected from 60–75 cm below surface in Caverne Dora on the Plain Corail, produced a radiocarbon age of 2850 ± 30 with a calibrated age range of 3060–2870 YBP ( Burney et al. 2015). This suggests very low sedimentation rates in the late Holocene ( Hume 2013; Burney et al. 2015). Although the precise cave from which P. a. nelsoni was collected is unknown, many of the caves on the Plaine Corail have depositional environments similar to that of Caverne Dora ( Hume 2005, 2013).

Description and comparison: Papasula a. nelsoni ssp. nov. differs from Papasula a. abbotti in being larger in all known elements (Appendix 1, Tables 1-4 View TABLE 1 View TABLE 2 ) and by the following diagnostic characters:

Coracoid ( Fig. 2b View FIGURE 2 ; table 1). In mediodorsal view, the proximal end is missing the tuberculum brachiale and facies articularis clavicularis, and sternally is missing the processus lateralis from the lateral point of labrum internum to margo caudolateralis on distal end.

Nevertheless, it differs from P. a. abbotti on the dorsal surface by, impressio lig. acrocoracohumeralis broader and deeper; process on labrum externum larger, more prominent, with extension to distal corner of angulus lateralis more deeply excavated; in ventral aspect, facies articularis sternalis deeper, extending further laterad; in lateral aspect, facies articularis humeralis larger and wider extending further proximally.

Sternum ( Fig. 3 View FIGURE 3 ; table 1). Only a small cranial fragment is preserved that includes two pairs of cranial foramina pneumatici and a single row (right side) of foramina pneumatici that follow the sulcus medianus sterni; it is missing the entire carina sterni and posterior part to processus craniolateralis including all processus costales.

Differs from P. a. abbotti by, in dorsal aspect, tuberculum labri externa with more pronounced ridge on lateral edge; in lateral aspect, labrum interna and tuberculum labri externa larger, with sulcus articularis coracoideus deeper, creating a more pronounced undercutting of labrum interna; in ventral aspect, two cranial foramina pneumatici larger.

Humerus ( Figs. 4a, 4b View FIGURE 4 , 5a, 5b View FIGURE 5 ; table 2). Holotype (UMZC 262.AA), collected on Mauritius, is complete with no erosional damage, whereas the Rodrigues specimen (NHMUK PV A9049) lacks around 66% of the distal end and much of the crista deltopectoralis.

Differs from Papasula a. abbotti by, on caudal surface, tuberculum dorsale larger, more oval, and more rugose on distal surface; tuberculum ventrale larger and more robust, projecting more caudad and extending further mediocaudad; caput humeri more bulbous; incisura capitis more deeply excavated; margo caudalis more clearly defined proximally where it connects laterad to base of tuberculum ventrale; crus ventrale fossa more prominent proximally, especially at base of tuberculum ventrale; crista bicipitalis more convex without rightangled connection to shaft distally; fossa pneumotricipitalis larger, more deeply excavated with medial foramen pneumaticum much larger; sulcus humerotricipitalis more deeply incised, terminating in a sharp angle proximally; sulcus scapulotricipitalis more deeply incised, extending further proximally well beyond proximal level of sulcus humerotricipitalis; processus flexorius blunt, rounded distally, not angular; on cranial surface, sulcus lig. transversus deeply excavated medially, shallower laterally; crista bicipitalis more bulbous, without small distal crista; fossa m. brachialis more excavated; fossa olecrani larger; processus flexorius smaller, directed less medially.

Ulna ( Figs. 6c, 6f View FIGURE 6 ; table 3). Paratype (UMZC 262.AA), collected on Mauritius with holotype, is complete with no erosional damage, whereas the Rodrigues specimen (NHMUK PV A9076)is missing around 85% of the proximal end.

Differs from P. a. abbotti in being longer, overall more robust; shaft less straight, more curved craniocaudally; in dorsal aspect, distal end more expanded; proximal pneumatic foramen larger; in ventral aspect, impressio brachialis more deeply excavated proximally; papillae remigales ventralis more prominent; sulcus intercondylaris deeper; foramen pneumaticum situated above sulcus intercondylaris and undercutting condylus dorsalis larger; presence of second foramen pneumaticum situated proximally on tuberculum carpale (absent in P. a. abbotti ); depressio radialis more deeply excavated; in cranial aspect, cotyla ventralis narrower, more pointed; pneumatic foramen between condylus ventralis ulnaris and tuberculum carpale larger.

Tarsometatarsus ( Figs. 7b, 7c View FIGURE 7 ; table 4). Specimen missing crista medialis hypotarsi and plantar surface of trochlea metatarsi II and IV.

Differs from P. a. abbotti by, in dorsal aspect, sulcus extensorius deeper proximally; incisura intertrochlearis lateralis and incisura intertrochlearis medialis slightly wider; tuberositas m. tibialis cranialis more marked, extending beyond proximal tip of lateral foramina vascularia proximalia; in plantar aspect, crista plantares lateralis more pronounced and lacking small foramen pneumaticum distal to crista lateralis hypotarsi; foramen vasculare distale much larger; wider and deeper sulcus on trochlea metatarsi III;medial surface of trochlea metatarsi IV more excavated, creating a pronounced crista extending proximal to crista plantares medialis; on proximal end, larger, otherwise similar to P. a. abbotti . The specimen figured ( Fig. 8 View FIGURE 8 ) in Milne-Edwards (1873) is the same specimen, but since that drawing’s execution, further damaged has occurred. For example, the crista medialis hypotarsi is now missing.

Differs from P. a. costelloi by, in dorsal aspect, trochlea metatarsi II extends less distally; trochlea metatarsi III with shallower sulcus on dorsal surface; foramen vasculare distale smaller and situated more proximad; in plantar aspect, crista plantares lateralis more pronounced; foramen vasculare distale larger; fossa supratrochlearis more deeply excavated, especially where it connects to foramen vasculare distale medially.

Hypotarsus Larger, otherwise similar to P. a. abbotti .