Caloenas undetermined

CALOENAS SP. INDET .

( FIG. 3)

Material: Ofu: Of1.05.12.06, dL sR tmt; Of1.05.12.06, pL tib; Of1.05.12.07, pL rad; Of1.05.12.07, two sternal ends L cor; Of1.05.12.08, d+sL tmt; Of1.05.12.08, ant stern; Of1.05.12.08, p+sR tib; Of1.05.12.09, dL tmt; Of1.05.12.09, pL cmc; Of1.05.12.10, dR hum; Of1.05.12.10, dR ulna, pR rad; Of1.05.20.06, L ulna; Of1.05.20.07, s+dR tmt; Of1.05.20.07, pRsL cmc; Of1.05.20.09, dR ulna; Of1.05.20.10, cran pt L cor; Of1.05.21.08, pLdL rad; Of1.05.22.04, cran pt L cor; Of1.05.22.05, dR ulna; Of1.05.22.05, pL tmt; Of1.05.22.06, dL rad; Of1.05.22.07, dLsR tib; Of1.05.22.07, dL ulna; Of1.05.22.07, one sternal pt L cor; Of1.05.22.08, cran and sternal pts L cor; Of1.05.22.08, sLsR tmt; Of1.05.22.08, sR tib; Of1.05.22.08, dRsL ulna; Of1.05.22.09, pRpL tmt; Of1.05.22.09, cran and sternal pts R cor; Of1.05.22.09, R scap; Of1.05.22.09, pR rad; Of1.05.22.09, pR fem; Of1.05.22.10, dL hum; NISP = 44, MNI = 4. Vuna: Pa1.04.21.09, dL cmc; NISP = 1, MNI = 1.

Remarks: All but one specimen was from the Lapita component.

Description and comparisons

Coracoid ( Fig. 3I, J, L): On the processus acrocoracoideus, tuberculum A is considered distinct from the brachial tuberosity, following Worthy (2012), because it marks the insertion of the plica synovialis coracoidea. The brachial tuberosity, as defined by Baumel & Witmer (1993), marks the insertion of the impressio ligamentum acrocoraco-acromion, and thus lies ventromedial to tuberculum A and forms the dorsal part of the facies clavicularis. The morphology and degree of separation of tuberculumA from the impressio ligamentum acrocoraco-acromion distinguishes many columbid genera ( Worthy, 2012). In Caloenas and in the Tongan fossils, e.g. Of1.05.22.09f, tuberculum A is distinctly separated from the impressio ligamentum acrocoraco-acromion by a groove and is globose.

In addition to the above diagnostic characters, the sulcus supracoracoideus is pneumatic under the facies clavicularis, but the precise location and size of foramina vary, as they do in C. nicobarica . Associated with this feature is an elongate groove located adjacent to the facies humeralis that undercuts tuberculum A. This groove is also present in Didunculus , wherein it was identified as an autapomorphy ( Worthy et al., 2015). In three of the four available specimens of the Tongan species of Caloenas , this groove is apneumatic, but in Of1.05.22.09f it opens via a pneumatic foramen into the acrocoracoideum. The processus acrocoracoideus, as seen in dorsal view, markedly overhangs the medial shaft margin, and the area for the insertion for ligamentum acrocoraco-procoracoideum is slightly hooked sternally. The processus procoracoideus has an elongate origin on the shaft, but it extends abruptly out from the shaft in its omal half, as in C. nicobarica ; the sternal end of the origin of the procoracoid is marked by a swollen ligamental attachment site. The only columbids with coracoids somewhat similar to those of Caloenas are Goura and Didunculus . However, both differ by having the procoracoid tapering evenly (vs. angular) towards the sternal end. Additionally, in Goura , it extends relatively further sternally along the shaft and has a more robust, elevated ligament attachment at its sternal end.

Sternally, in Caloenas , Goura and the Tongan fossils, the angulus medialis and the corpus medial to the impressio m. sternocoracoidei are both distinctively inflated or thickened dorsoventrally, resulting in a wide separation of the impressio from the medial margin. Associated with this, the facies articularis sternalis dorsalis is more robust and omalsternally broad in comparison to other columbids. As a result, the impressio m. sternocoracoidei is constricted to about half of the available width and is pneumatic, with foramina in the deeper medial corner. However, coracoids of species of Caloenas are further distinguished from those of Goura by having a relatively larger impressio m. sternocoracoidei, which originates omally at a distinct ligamental attachment site located closer to the cotyla scapularis than the mid-point between the cotyla and the sternal end. In contrast, in Goura , the omal end of the impressio m. sternocoracoidei is well sternad of the halfway point between the cotyla and the sternal margin.

Coracoids of both C. nicobarica and the Tongan fossils have a small pneumatic region laterally, level with the end of the facies articularis sternalis dorsalis. Also, in both, the angulus medialis is not acute, but it is marked by a flattened facet (facies angulus medialis) on the medial margin aligned roughly at right angles to the sternal facet. Yet in articulation with the sternum, the coracoids in C. nicobarica are separated and diverge omally; therefore, this facet is not articular in nature. A sharp crista medialis extends from the angulus medialis along the ventral margin of the facies angulus medialis to the dorsal shaft facies. In all these features, coracoids of the Tongan bird are similar to those of C. nicobarica . However, in the Tongan bird the facies angulus medialis extends omally to a point level with the omal side of the facies articularis sternalis dorsalis (e.g. Of1.05.12.07), but in C. nicobarica it is relatively shorter, extending to only about a third of the height of the dorsal facet. The Tongan bones differ from the holotype of C. canacorum by the facies articularis sternalis dorsalis being about twice as broad omal–sternally, and so extending omally about as far as the facies angulus medialis does. In the holotype of C. canacorum , the facies angulus medialis extends omally twice as far as the breadth of the facies articularis sternalis dorsalis.

For measurements, see Table 3. The few Tongan coracoids are substantially larger than those of C. nicobarica , but are perhaps slightly smaller than those of C. canacorum .

Scapulae: Scapulae of C. nicobarica are pneumatic on the proximolateral side of the acromion and via a small fossa dorsally, adjacent to the facies articularis humeralis; the dorsoventral height of the facies articularis humeralis is greater than its craniocaudal length; the tuberculum coracoideum is slightly prominent cranially and has a small facet medially. The Tongan specimen Of1.05.22.09 displays all these features and differs only in its larger size. Species of Ducula , including the large form from the Tongan assemblage below, differ in lacking pneumatism in both regions of the scapula, and the facies articularis humeralis is of equal length and height. In species of Ducula , the lateral facies dorsal to the humeral facet is laterodorsally expanded into a buttress for the acromion, whereas in the fossil referred to Caloenas , a broad, shallow groove separates the articular facies from the lateral expansion of the acromion. The measurements are: maximum dorsoventral height cranially 13.6 mm; height facies articularis humeralis 6.2 mm; length facies articularis humeralis 5.2 mm.

Humerus ( Fig. 3E, F): The distal humerus of Caloenas differs markedly from that of Goura in the relatively proximal placement of the insertion of the dorsal branch of m. extensor carpi radialis (not ligamentum collaterale dorsi of Balouet & Olson, 1989), level with the proximal margin of fossa brachialis, whereas the ventral branch inserts more distally, immediately proximal to condylus dorsalis, midway between the fossa brachialis and the dorsal margin. In Goura , both dorsal and ventral branches insert distally, level with the condylus dorsalis. The Tongan specimens (Of1.05.12.10, dR hum; Of1.05.22.10, dL hum) conform with Caloenas in these features, which are also evident in C. canacorum (see Balouet & Olson, 1989: fig. 6). The Tongan bones have a deep, well-defined fossa brachialis, a facet on tuberculum supracondylare ventrale that is as wide as it is long and well projected cranially, and narrowly separated (less than facet width) from condylus dorsalis. The insertion of the dorsal branch of m. extensor carpi radialis does not form a processus supracondylaris dorsalis, merely a slight elongate rugosity, and the epicondylaris dorsalis is large and prominent. The processus flexorius is little projected distally. Although breakage precludes measurements of the distal width, as far as comparisons with the image shown by Balouet & Olson (1989: fig. 7) allow, the Tongan bones are the same.

The Tongan humerus (distal width 18.3 mm, depth dorsal condyle 11.7 mm) is much larger than those of C. nicobarica (DW, mean 13.1 mm, range 12.5–13.4 mm, N = 21; depth of dorsal condyle, mean 8.8 (8.2–9.5) mm, N = 21; Balouet & Olson, 1989), but similar to that of C. canacorum (distal width 18.6 mm; depth of dorsal condyle 11.5 mm; Balouet & Olson, 1989)

Ulna : In fossils attributed to Caloenas , the entire rim of the condylus dorsalis ulnaris overhangs the adjacent caudodorsal facies. There are two strongly marked ligament insertion scars immediately caudal to the incisura tendinosa. The condylus ventralis is prominent ventrally and pointed, and a sharp crest extends from the depressio radialis along the ventrocranial margin towards the tip of the tuberculum carpale. In Ducula species, the rim of the condylus dorsalis ulnaris overhangs the caudal facies near the incisura tendinosa, but from its mid-depth to its proximal end the rim does not overhang the adjacent facies. The insertion points for ligaments beside the incisura tendinosus are more weakly marked in the species of Ducula , including the large species described below. In species of Ducula , the condylus ventralis is not prominent ventrally, and instead has a flattened ventral facies, although it is broadly rounded distally.

reconstructed tarsometatarsus from A, B (mirrored) and C, sized to fit. E, distal right humerus Of1.05.12.10 in cranial view. F, distal left humerus Of1.05.22.10 in cranial view. G, proximal right femur Of1.05.22.09 in cranial (G 1) and caudal (G 2) views. H, distal left tibiotarsus Of1.05.22.07 in cranial view. I, cranial part of right coracoid Of1.05.22.09 in dorsolateral view. J, cranial part of left coracoid Of1.05.20.10 in dorsal view. K, proximal left carpometacarpus Of1.05.12.09 in ventral view. L, sternal part of left coracoid Of1.05.12.07 in dorsal view. Scale bars: 10 mm. Abbreviations: diecr, insertion of the dorsal branch of m. extensor carpi radialis; dtRET, the distal attachment point for the retinaculum extensorium tibiotarsi; ilap, insertion for the ligamentum acrocoraco-procoracoideum; ire, impressiones retinaculi extensorii; proc., processus; ptRET, the medial tuberosity for the proximal attachment of the retinaculum extensorium tibiotarsi; tub. A, tuberculum A; tub. m., tuberositas musculus; viecr, insertion of the ventral branch of m. extensor carpi radialis.

Caloenas nicobarica View in CoL : SAM B.5056, SAM B36831 and SAM B.51203; data from Balouet & Olson (1989), N = 21. Caloenas canacorum values (holotype, paratype); values of medial length and shaft width are those given by Balouet & Olson (1989) in text under ‘Measurements of holotype /paratype’, which data differ from those in their table 6.

*Length here is the greatest length because the medial length was not provided, but medial length is slightly (95 and 96%) smaller than the total length in the two type specimens for C. canacorum ; therefore, medial length might be inferred as 43.9 (41.3–46.8).

There is no crest along the ventrocranial margin leading to the tuberculum carpale.

For measurements, see Table 4. The Tongan bones are larger than those of C. nicobarica .

Carpometacarpus ( Fig. 3K): Carpometacarpi of C. nicobarica are characterized by the cranial projection of the processus extensorius being about equal to the craniocaudal width of trochlea carpalis and having a rugose tip that projects strongly proximally. The ventral rim of the trochlea carpalis, as seen in ventral aspect, ends well proximal to the level of the distal side of processus alularis and is slightly longer than the dorsal rim. The dorsal rim (proximal aspect) extends in a caudal direction slightly less than the ventral rim of the trochlea carpalis, leading to a deep, dorsally open notch enclosed caudally by os metacarpale minus where it joins to the dorsal rim and os metacarpale majus at the proximal synostosis. Specimen Of1.05.20.07 shares these features, although the dorsal and ventral rims of the trochlea carpalis (proximal aspect) have about equal caudal extent and the dorsal rim is relatively longer than in C. nicobarica , creating a deeper notch between it and the synostosis of the minor metacarpal. Carpometacarpi of species of Ducula , including the similar-sized, large undescribed species from this assemblage, differ markedly, with a more elongate ventral rim of the trochlea carpalis that extends distally to a point level with the processus alularis, and the dorsal rim of trochlear carpalis is markedly less projecting caudally than the ventral rim.

For measurements, see Table 4. For Of1.05.20.07, the ventrodorsal depth of trochlea carpalis is 7.1 mm. Femora ( Fig. 3G): Femora of C. nicobarica are characterized by several characters: the trochanter projects proximally of the facies articularis antitrochanterica and cranially adjacent to this facies is penetrated by pneumatic foramina. The scar for m. iliotrochantericus medius is midway between that for m. iliotrochantericus caudalis (proximally) and m. iliotrochantericus cranialis (distally) and is adjacent to, but cranial of, the scar for m. ischiofemoralis. In Ducula goliath (Gray, 1859) and Ducula galeata (Bonaparte, 1855) , the trochanter is relatively longer and extends well distad of the level of the scar for m. ischiofemoralis.

One proximal R femur (Of1-05-22-09) is identified as being from a species of Caloenas . It has a relatively short trochanter, much shorter than the proximal width of the femur, whereas these values are approximately equal in Ducula . It is larger than the specimens attributed to the undescribed species of Ducula from Tonga, but is less robust, with a thinner shaft. Although the proximodorsal crest of the trochanter is eroded, the medial rim of a large pneumatic foramen is preserved, and the proximal projection over the facies articularis antitrochanterica is marked, more so than all the specimens of the sympatric large species of Ducula from this assemblage. The linea intermuscularis cranialis does not lie on the most cranial part of the shaft, being offset medially and joining to the trochanter on its medial side, whereas in species of Ducula , it passes along the cranial-most margin and links to the distal end of the trochanter. Proximally, the caudal facies is linked to the lateral facies by an even curve, especially in the region between

Abbreviations: cmc L, length of carpometacarpi on os metacarpale majus; cmc PW, proximal width of carpometacarpus; Ulna DWmax, maximum distal width; Ulna SW , least width immediately proximal to condylus dorsalis in ventral aspect; Ulna Wdc , width of condylus dorsalis.

the impressio obturatoriae caudalis to a point more distally and level with the scar for m. ischiofemoralis. In species of Ducula , this caudolateral junction is rather more angular, and this is made more so by a larger, more prominent impressio obturatoriae caudalis, which has the effect of laterally enclosing a shallow, flat-bottomed sulcus that lies distally adjacent to the facies articularis antitrochanterica. Laterally, the three scars for m. iliotrochantericus caudalis, medius and cranialis are evenly spaced. That for m. ischiofemoralis spans the interval between that for m. iliotrochantericus medius et cranialis, and its distal margin is level with the distal end of the trochanter. In Du. galeata , Du. goliath and the large Tongan species described below, the trochanter passes well distal to the scar for m. ischiofemoralis. The large Tongan species of Ducula differs further, with the scar for m. ischiofemoralis lying immediately caudal to that for m. iliotrochantericus medius and proximally adjacent to that for m. iliotrochantericus cranialis. Caudally, the shaft bears two linea intermuscularis, one laterally, which extends distally from the impressio m. ischiofemoralis in an arc onto the caudal surface and distally along the caudolateral surface, past the distinct scar for the insertion of m. caudofemoralis, to end immediately past the point of least shaft width. The medial linea is more robust and extends from the broken distal end up past original mid-length to the medial side of the scar for the insertion of m. caudofemoralis, and thus remains well separated from the lateral linea. In the large Tongan species of Ducula , the lateral linea is more prominent and extends further distally and at mid-length is closely applied to the medial linea.

Measurements: Of1-05-22-09, preserved length missing about the distal third, 44.6 mm; craniocaudal depth of trochanter 11.2 mm; proximal width as preserved (but damage to proximal side of caput means this is a minimum) 14.1 mm; craniocaudal depth caput 5.9 mm; least shaft width 6.6 mm.

Tibiotarsus ( Fig. 3H): In addition to the diagnostic features listed above, tibiotarsi of the Tongan bird display the following features: the distal margin of pons supratendineus is aligned across the shaft; the condyles diverge cranially; and the sulcus for m. fibularis is mainly on the cranial facies.

Those of ptilinopine pigeons and species of Columba and Patagioenas differ greatly, with the ptRET being positioned far more proximally, and the sulcus extensorius being bounded by a sharp crest laterally. Distal width is also wider in these taxa, being equal to or greater than craniocaudal depth of condylus medialis, and the condyles do not diverge cranially. In Didunculus , the distal margin of the pons is aligned proximomedially across the shaft, the dtRET is proximodistally elongate, the sulcus for m. fibularis is on the lateral facies, with the mtRMF widely separated from the dtRET by a shallow sulcus, and there is a large foramen immediately proximal to condylus lateralis on the cranial facies ( Worthy & Wragg, 2003, 2008). In species of Gallicolumba and Alopecoenas , tibiotarsi are smaller, with a narrower incisura intercondylaris and a more prominent and elongate mtRMF.

The Tongan tibiotarsi are similar to those of Caloenas and Goura , but those of Goura are larger and otherwise differ by the distal margin of the pons being aligned proximomedially. The epicondylaris medialis forms a prominent tubercle (tubercle absent in Caloenas ), and the condylus lateralis slopes gradually to the shaft cranioproximally (right angles in Caloenas ). In both, the dtRET is round, but in Caloenas the mtRMF abuts the dtRET and extends proximally as an elongate rugose scar to a point proximad of the pons. In contrast, in Goura the mtRMF is separated proximally from the dtRET and forms a low crista extending proximally and parallel to the sulcus extensorius. The ltRMF in Caloenas is a laterally prominent crista in cranial view, making the shaft profile convex, and in lateral view is seen proximocaudally to traverse the shaft to about mid-depth at a shallow angle. In contrast, in Goura the ltRMF is barely perceptible in cranial view and traverses the shaft at a steeper, 45° angle. Lastly, in Goura the foramen proximal to the condylus lateralis is smaller than in Caloenas .

Generally, the Tongan bones are similar to C. nicobarica , but differ as follows: they are larger; the ptRET is relatively closer to the condylus medialis [it is 4.0 mm from the condylus medialis, whose proximodistal height is 7.5 mm, giving a separation of 53% of condyle height, compared with 94% (SAM B.51203) and 90% (SAM B.36831) in C. nicobarica ]; the shaft facies between the tuberculi retinaculi m. fibularis is cranially directed (not craniolaterally directed); and the foramen proximocranial to the condylus lateralis is smaller.

For measurements, see Table 5.

Tarsometatarsus ( Fig. 3A–D): In addition to the diagnostic character list above, the Tongan bones have the following features: impressiones retinaculi extensorii on anterior facies, with medial one longest and adjacent to foramen vascularia proximalia medialis; fossa infracotylaris dorsalis small, narrows proximally to foramina; medial foramen vascularia proximalia slightly proximad of lateral one and slightly larger, with both set deep in the sulcus extensorius; tuberositas m. tibialis cranialis located immediately distal to medial foramen and partly straddles floor of the sulcus extensorius and medial wall of sulcus; fossa parahypotarsalis medialis broad, wider than half shaft width; sulcus extensorius bounded by lower ridge medially than laterally, extends to about mid-length where open to medial side; foramen vasculare distale connected via canalis interosseus distalis to both the incisura intertrochlearis lateralis and the plantar surface (some individuals, e.g. Of1.05.12.09e) have the plantar foramen and the intertrochlear foramen merged as an open groove plantarly).

The proportions of the tarsometatarsus are similar to those of Alopecoenas , Caloenas , Didunculus , Gallicolumba , Goura , Natunaornis , Pezophaps and Raphus : the tarsometatarsus of Otidiphaps is more elongate; those of all ptilinopine and phabine pigeons and of species of Columba and Patagioenas are much shorter relative to proximal width. Ptilinopine pigeons ( Ducula , Ptilinopus and relatives) differ further, with a greatly enlarged foramen vascularia proximalia medialis. Natunaornis from Fiji is much larger; ridges of equal height bound the sulcus extensorius laterally and medially, and the foramina vascularia proximalia are relatively larger, although both medial and lateral ones are similar in size. Raphus , apart from being much larger, differs in having a shallow fossa infracotylaris dorsalis, a prominent tuberositas m. tibialis cranialis and a shallow fossa parahypotarsalis medialis. Pezophaps , also much larger and from the Mascarenes, has a deep fossa infracotylaris dorsalis, but differs by having a relatively narrower fossa parahypotarsalis medialis. In Alopecoenas and Gallicolumba , the trochlea metatarsi IV extends level with or distad to trochlea metatarsi II, and trochlea metatarsi IV is deeply notched distoplantarly. In Didunculus , the foramina vascularia proximalia have greater separation, the lateral one is more proximally located, the anterior facies adjacent to the sulcus extensorius has a broad shallow sulcus passing laterad of the prominent tuberositas m. tibialis cranialis, the shaft is more elongate, and trochlea metatarsi IV extends distad to trochlea metatarsi II ( Worthy, 2001; Worthy & Wragg, 2005; Wragg & Worthy, 2006; Worthy et al., 2015). The tarsometatarsus of Microgoura meeki Rothschild, 1904 is much more elongate ( Worthy, 2001). The tarsometatarsus of Goura is much larger, more elongate, and the sulcus extensorius extends to mid-length.

In Goura , the dorsal crista lateralis extends to the fossa infratrochlearis and thus defines the sulcus extensorius laterally and extends distally beyond

Abbreviations: CLch, craniocaudal height condylus lateralis; CMch, craniocaudal height of condylus medialis; DW, maximum distal width including the plantar flange on trochlea metatarsi II; PW, maximum proximal width across articular surface; SW, minimum shaft width; TL, total length.

the metatarsal facet. In lateral view, this crista is straight and proximally prominent, resulting in the dorsal facies at mid-length being flat. In contrast, in Caloenas , this crista is weak and does not extend proximal to the tuberositas m. tibialis cranialis, and the middle third of the shaft length is notably convex and prominent cranial to this crista. Proximally, on the hypotarsus, the sulcus for fpp2 (tendon of m. flexor perforans et perforatus digiti 2) is shallow in Goura and nearly enclosed, forming a canal, in Caloenas . The impressiones retinaculi extensorii are poorly marked in Goura , but form prominent crista in Caloenas , the medial one especially so, and it is elongate, extending down to the medial vascular foramen.

The Tongan bones are similar to C. nicobarica , which differs by smaller size ( Table 6). Both the Tongan fossils and C. nicobarica display variation in size of the foramina vascularia proximalia, but this was more extreme in SAM B51203 where the lateral foramen vasculare proximalia is closed.

For measurements, see Table 6.

Remarks: A large species of Caloenas existed in Tonga, as evidenced by the bones reported above. It is similar to C. nicobarica in most features, but is rather larger. The preserved bones reveal that this pigeon could fly as well as the extant Nicobar pigeon, and its lightly built leg bones support an inferred primary arboreal habit. The described bones of C. canacorum from New Caledonia allow the effective comparison of it and the Tongan species only using the coracoid and the distal humerus. Insofar as comparisons from images and descriptions by Balouet & Olson (1989) allow, the Tongan bones are about the same size as those of C. canacorum and differ only in the coracoid, perhaps having a slightly narrower shaft yet mediolaterally wider and, omal-sternally, a much broader facies articularis sternalis dorsalis. This evidence and the wide geographical separation of the populations make it likely that the Tongan bones represent a distinct species, but further remains, especially of tibiotarsi and tarsometatarsi from C. canacorum , are needed to define that species better and allow these extinct Tongan populations to be distinguished.