Papasula abbotti Olson & Warheit, 1988, p. 10 Type (by monotypy)
Osteological diagnosis and comparison. The following osteological characters in combination characterize the genus Papasula. The fossil specimens are much larger than those of species in most other marine bird genera occurring in the Mascarenes, including those in Oceanitidae, Phaethontidae, Laridae, Stercorariidae, and in all Procellariidae except Macronectes giganteus. Papasula abbotti is smaller than M. giganteus and all species of Diomedeidae. It differs from similar-sized Fregata ariel and F. minor as follows. Coracoid: smaller, more gracile, and processus lateralis much less extensive. Sternum: larger; in lateral view, sulcus articularis coracoideus bordered with a much larger labrum interna and tuberculum labri externa; in dorsal view, foramina pneumatici larger, much more extensive. Humerus: more gracile, much thinner in the shaft and particularly lacks a sharply angular crista deltopectoralis. Ulna: much smaller; cotyla dorsalis larger and directed distad; impressio brachialis much more excavated; papillae remigales much less pronounced. Tarsometatarsus: most notably by much larger size, extremely reduced in length and width in Fregata, and sulcus extensorius much more deeply excavated. The Papasula material described herein is further assigned to Sulidae by the characters identified in Olson & Warheit (1988), Steadman et al. (1988), and van Tets et al. (1988), who also mentioned diagnostic characters of the cranial and other parts of the postcranial skeleton not discussed here.
Coracoid (Fig. 2; table 1)
In Papasula, on dorsal surface, facies articularis humeralis rotated ventrolaterad, with processus procoracoideus directed sharply proximally; cotyla scapulae small; sulcus m. supracoracoidei large and oval, with numerous foramina pneumatici; shaft wide and deep; facies articularis sternalis deep and bordered proximally by a large crista; angulus medialis long projecting proximomedially; processus lateralis strongly square-shaped with prominent distally directed angulus lateralis; labrum externum with a large, pointed process directed dorsally and a distinct proximal edge extending to distal corner of angulus lateralis; in ventral aspect, crista acrocoracoidea to impressio bicipitalis flat, not concave; in medial aspect, facies articularis clavicularis enlarged and convex, directed proximodorsally, with no crista on facies articularis clavicularis; in lateral aspect, facies articularis humeralis large and wide with proximal extension; impressio lig. acrocoracohumeralis broad and deeply excavated; impressio m. sternocoracoidei bordered by a sharp crista dorsally, extending to midline of shaft and creating a deeper, larger proximodorsal surface area.
Coracoids in Masked Booby Sula dactylatra Lesson, 1831 and Red-footed Booby Sula sula (Linnaeus, 1766), in dorsal aspect, overall longer, less robust; processus procoracoideus more pointed, less triangular laterally (extending less laterad in S. sula); sulcus m. supracoracoidei smaller, with smaller and fewer foramina pneumatici; shaft narrower lateromedially and shallower dorsoventrally; facies articularis sternalis deep bordered proximally by a more extensive crista (shorter proximodistally in S. sula); angulus medialis shorter projecting more medially; impressio m. sternocoracoidei less extensive proximally; processus lateralis strongly square-shaped without proximally directed margo caudolateralis (more angular with proximally directed margo caudolateralis in S. sula) and prominent distally directed angulus lateralis; proximally and distally directed corners; pointed process on labrum externum extremely reduced or absent, with a distinct proximal edge extending to distal corner of angulus lateralis; in ventral aspect, crista acrocoracoidea to impressio bicipitalis angled; in medial aspect, facies articularis clavicularis less swollen, not convex and not directed proximodorsally, with a crista on facies articularis clavicularis; angulus medialis deflected to ventral surface due to deeper facies articularis sternalis; in lateral aspect, facies articularis humeralis smaller, narrower, extending less proximally; impressio lig. acrocoracohumeralis laterally compressed and deeper; sharp crista bordering impressio m. sternocoracoidei much shorter, extending to lateral edge of facies articularis sternalis only, and creating a shallower, smaller surface area that extends less proximally.
Coracoids in Northern Gannet Morus bassanus (Linnaeus, 1758), much larger, especially proximally and distally, but shaft proportionally narrower lateromedially and shallower dorsoventrally; in dorsal aspect, sulcus m. supracoracoidei larger, but with proportionately smaller foramina pneumatici; facies articularis sternalis deeper, more extensive laterally, and proximally bordered crista more extensive; angulus medialis rounded; processus lateralis strongly square-shaped without proximally directed margo caudolateralis and prominent distally directed angulus lateralis; pointed crista on labrum externum extremely reduced or absent, with a distinct proximal edge extending to distal corner of angulus lateralis; in ventral aspect, crista acrocoracoidea to impressio bicipitalis angled; in medial aspect, facies articularis clavicularis less swollen and not convex, with a crista on facies articularis clavicularis; angulus medialis strongly deflected to ventral surface due to deeper facies articularis sternalis; in lateral aspect, facies articularis humeralis much larger, more square-shaped proximally; impressio lig. acrocoracohumeralis laterally compressed and shallower; sharp crista bordering impressio m. sternocoracoidei dorsally much shorter, extending to lateral edge of facies articularis sternalis only, creating a shallower, smaller surface area that extends less proximally.
Sternum (Fig. 3; table 1)
Sternum in Papasula, in lateral aspect, rostrum sterni lacks projecting spina interna or spina externa; crista lateralis carinae projects sharply craniad; sulcus articularis coracoideus wide and deep, bordered with a large, oval-shaped labrum interna and a much smaller tuberculum labri externa, less than 50% of the length; in visceral aspect, processus craniolateralis reduced and directed medially dorsally, with tuberculum labri externa extending further laterad than labrum interna; two large, cranial-placed foramen pneumatici present, with a row of smaller foramina that follow each side of the sulcus medianus sterni; in cranial view, sulcus articularis coracoideus compressed midpoint on the rostrum sterni, with the dorsal surface running directly without obstruction to the cranial visceral surface.
Sternum in Sula dactylatra and Sula sula, overall smaller, narrower; in lateral aspect, sulcus articularis coracoideus shallower and narrower, with labrum interna kidney-shaped and tuberculum labri externa narrower but almost the same length (oval-shaped and tuberculum labri externa much smaller, less than 40% of the length in S. sula); in visceral aspect, two foramen pneumatici absent with fewer and smaller foramina following sulcus medianus sterni; in cranial view, sulcus articularis coracoideus more deeply compressed midpoint on rostrum sterni forming a ridge between it and cranial visceral surface.
Sternum in Morus bassanus, slightly narrower; in lateral aspect, sulcus articularis coracoideus deeper, with labrum interna oval-shaped, tuberculum labri externa absent; in visceral aspect, two foramen pneumatici absent but with more numerous, large foramina concentrated cranially and not following sulcus medianus sterni; in cranial view, cranial end deeper; sulcus articularis coracoideus more deeply compressed midpoint on rostrum sterni forming a ridge between it and cranial visceral surface.
Humerus (Figs. 4, 5; table 2)
Humerus in Papasula, long and gracile, almost equal in total length to ulna, with reduced proximal and distal ends; on caudal surface, shaft laterally compressed especially from midshaft to fossa m. brachialis; caput humeri bulbous with a small indentation set slightly ventrad from the midline; incisura capitis rounded, shallow and not reaching proximal edge of margo caudalis; tuberculum ventrale large and prominent connecting to a shortened crus dorsale fossa that terminates with the dorsal edge of incisura capitis; large, open fossa pneumotricipitalis with two foramina pneumatici, medial foramen much larger than lateral; crista deltopectoralis compressed dorsoventrally; crista bicipitalis straight without concavity terminating abruptly with shaft distally; sulcus humerotricipitalis narrow and deeply incised and cutting distinctly ventrodorsally; sulcus scapulotricipitalis narrow and deeply incised cutting proximodistally; fossa olecrani deeply situated; epicondylus ventralis long and narrow, projecting distad to level of condyles; in cranial aspect, sulcus lig. transversus deeply incised, undercutting the caput humeri dorsally; crista bicipitalis bulbous and rugose distally, with a pronounced sulcus n. coracobrachialis that creates a crista between it and impressio coracobrachialis that extends distally beyond crista deltopectoralis; shallow impressio coracobrachialis; crista deltopectoralis terminates distally with a raised rugose crista; fossa m. brachialis deeply incised and directed proximodorsally; two foramina pneumatici situated directly above condylus dorsalis; epicondylus dorsalis indistinct; tuberculum supracondylare ventrale prominent and deflected dorsally and slightly overhangs fossa m. brachialis.
Humerus in Sula dactylatra and S. sula, smaller, distal end comparatively larger; shaft more compressed mediolaterally; on caudal surface, caput humeri larger, more bulbous and base almost connects with margo caudalis distally; pneumatic foramen smaller, situated further proximally (substantially reduced or absent in S. sula); margo caudalis wider, lacking sharp crista; crista bicipitalis with clearly defined, angular contact with shaft; tuberculum ventrale directed more ventrad (more caudad in S. sula); sulcus humerotricipitalis shallower; epicondylus ventralis situated more proximally; in cranial aspect, sulcus lig. transversus deeper (narrower, extending past base of caput humeri in S. sula); crista bicipitalis more bulbous; fossa m. brachialis less extensive proximally and shallower; processus flexorius narrower, on same plane as condylus ventralis and condylus dorsalis.
Humerus in Morus bassanus, overall more robust, especially on proximal and distal ends; on caudal surface, caput humeri smaller, less bulbous; tuberculum ventrale longer, directed more proximally; fossa pneumotricipitalis extremely shallow; crista bicipitalis shorter, less expansive, with slight angular contact with shaft; shaft more compressed mediolaterally; sulcus humerotricipitalis shallower; in cranial aspect, fossa m.brachialis much shallower; sulcus lig. transversus much shallower; crista bicipitalis flatter, less bulbous; fossa m. brachialis shallower, extends less proximally; processus flexorius narrower, on same plane as condylus ventralis and condylus dorsalis.
Ulna (Fig. 6; table 3)
In Papasula, shaft long and gracile with proximal and distal ends caudocranially compressed; in dorsal aspect, olecranon prominent and deflected slightly craniad; cotyla dorsalis weakly excavated with indistinct crista intercotylaris; incisura radialis deeply excavated with large foramen pneumaticum, and extends proximally well beyond cotyla dorsalis; impressio scapulotricipitalis shallow; 19 papillae remigales dorsalis present; incisura tendinosus prominent, especially distally, where it forms a deep sulcus, and extends proximally to top of tuberculum carpale; tuberculum carpale with large pneumatic foramen; in ventral aspect, impressio brachialis shallow and non-pneumatic, with a pronounced crista defining it for its entire length; narrow tuberculum lig. collateralis ventrale extending distally 1/3 the length of impressio brachialis; 19 papillae remigales ventralis present; condylus dorsalis ulnaris long and narrow with pronounced proximal extension; foramen pneumaticum between tuberculum carpale and condylus ventralis ulnaris adjoining sulcus intercondylaris; a second foramen pneumaticum situated craniad on tuberculum carpale; in caudal aspect, condylus ventralis ulnaris sharply hooked and directed craniad.
In S. dactylatra and S. sula, much shorter, comparatively straighter, distal end more reduced; condylus ventralis ulnaris narrower; in ventral aspect, pneumatic foramen between condylus ventralis ulnaris and tuberculum carpale minute or absent; in lateral view, condylus dorsalis ulnaris extends further proximally; in dorsal aspect, tuberculum carpale shorter, extending less medially.
In Morus bassanus shorter, more robust, especially the proximal and distal ends; in dorsal aspect, pneumatic foramen in incisura radialis and between condylus ventralis ulnaris and tuberculum carpale; in ventral aspect, impressio brachialis smaller, less extensive; pneumatic foramen proximal to sulcus intercondylaris minute or absent on tuberculum carpale; in lateral aspect, condylus dorsalis ulnaris less extensive proximally; in dorsal aspect, tuberculum carpale shorter, extending less medially.
Tarsometatarsus (Fig. 7; table 4)
Tarsometatarsus in Papasula, in dorsal aspect, broad, with lateral side of shaft straight in contrast with a concave medial side; eminentia intercotylaris small, pointed and not adjoining lateral edge of shallow cotyla lateralis; cotyla medialis with a small laterally situated crista; sulcus extensorius deeply excavated, extending down shaft to a deeply set foramen vasculare distale; lateral edge thin when viewed dorsoplantarly; two foramina vascularia proximalia, with lateral foramen smaller than medial foramen and situated further proximally; both foramina small and open directly onto plantar side; incisura intertrochlearis medialis much narrower than incisura intertrochlearis lateralis; medial sulcus of trochlea metatarsi III shallow; short, shallow sulcus running proximally from incisura intertrochlearis medialis and terminating at proximal edge of foramen vasculare distale; crista from trochlea metatarsi II to fossa metatarsi I large; trochlea metatarsi II extends further distally than trochlea metatarsi III; in plantar aspect, fossa parahypotarsalis medialis deep, angular and non-pneumatic; crista medianoplantaris prominent, long, running from crista medialis hypotarsi to lateral edge of trochlea metatarsi IV; foramen vasculare distale small; medial sulcus absent on trochlea metatarsi IV; distal surface of shaft and fossa supratrochlearis plantaris rugose; in lateral aspect, proximal margin of trochlea metatarsi IV joins the shaft almost perpendicularly; trochlea metatarsi III protrudes dorsally from plane of shaft; on proximal end, cotyla lateralis smaller than cotyla medialis and divided by a prominent eminentia intercotylaris; crista lateralis hypotarsi and crista medialis hypotarsi separated by a single crista intermedia hypotarsus; crista medialis hypotarsi large and hook-shaped, producing a large sulcus hypotarsus.
Tarsometatarsus in Sula dactylatra, S. sula and Morus bassanus, overall, much narrower and less expanded distally, much longer in M. bassanus; shaft curved more medially, less straight; trochleae less widely spaced; incisura intertrochlearis lateralis much narrower; facies dorsalis less deeply set; three foramina vascularia proximalia present; origin of trochlea metatarsi II situated less proximally, not extending past trochlea metatarsi III; in plantar aspect, sulcus flexorius less rugose; crista plantaris mediana less distinct, shorter, situated less laterad on shaft; foramen vasculare distale smaller and circular, situated less proximally; in plantar aspect, sulcus flexorius less rugose; foramen vasculare distale much larger; cotyla medialis larger than cotyla lateralis; on proximal end, crista lateralis hypotarsi and crista medialis hypotarsi connected to a single crista intermedia hypotarsus; crista medialis hypotarsi square-shaped with large, enclosed sulcus hypotarsus.
Hypotarsus
Hypotarsus in Papasula, in proximal aspect, sulcus for musculus fibularis longus (fbl) shallow; canal for musculus flexor hallucis longus (fhl) open; canal for tendon of musculus flexor digitorum longus (fdl) with an open connection to sulcus for musculus flexor perforans et perforatus (fpp2) and to sulcus for musculus flexor perforatus (fp2). The above-mentioned numerals relate to the number of the trochleae metatarsorum supplied by the tendon. Interestingly, the configuration of the hypotarsus in Papasula is monosulcate; therefore, an apomorphy, as it is bisulcate in Sula and Morus.
Hypotarsus in S. dactylatra and S. sula, in proximal aspect, sulcus for musculus fibularis longus (fbl) deeply excavated; canal for musculus flexor hallucis longus (fhl) and canal for tendon of musculus flexor digitorum longus (fdl) closed, the latter being extremely large; sulcus for musculus flexor perforans et perforatus (fpp2) and sulcus for musculus flexor perforatus (fp2) connected and deeply excavated.
Hypotarsus in M. bassanus, in proximal aspect, sulcus for musculus fibularis longus (fbl) shallow; canal for musculus flexor hallucis longus (fhl) and canal for tendon of musculus flexor digitorum longus (fdl) closed, the latter being small; sulcus for musculus flexor perforans et perforatus (fpp2) and sulcus for musculus flexor perforatus (fp2) connected, but extremely shallow.