Abstract
We describe a new genus and species of pigeon (Columbiformes) from a single coracoid from the St Bathans Fauna of New Zealand (16–19 mya). It is the first columbid species described from pre-Pliocene deposits in Australasia. Two apomorphies identify the fossil as belonging to the ptilinopine group of fruit pigeons, among which it is most similar to Hemiphaga, the large fruit pigeon currently endemic to the New Zealand biogeographic area. This reveals that the Hemiphaga lineage has been in New Zealand since the Early Miocene, which supports recent divergence-date estimates for Hemiphaga and its modern sister taxon (Lopholaimus) based on molecular data.
Resument
Describimos un nuevo género y especie de paloma (Columbiformes) de un único coracoides de la fauna St Bathans de Nueva Zelandia (16–19 millones de años antes del presente). Es la primera especie de paloma descrita de depósitos pre-Pliocénicos en Australasia. Dos apomorfías identifican el fósil como perteneciente al grupo ptilinopino de las palomas fruteras, entre las cuales es más parecida a Hemiphaga, la gran paloma frutera actualmente endémica del área biogeográfica de Nueva Zelandia. Esto revela que el linaje de Hemiphaga ha estado en Nueva Zelandia desde el Mioceno Temprano, lo cual avala estimados recientes de fechas de divergencia para Hemiphaga y su taxón hermano moderno (Lopholaimus) basados en datos moleculares.
THE DIVERSITY OF pigeons (Aves: Columbidae) in Australasia is considerable, with ∼31 indigenous species (including three recently extinct) in 15 genera (Higgins and Davies 1996, Holdaway et al. 2001, Christidis and Boles 2008). In New Zealand, columbids are represented by the single genus Hemiphaga with allopatric species on the Chatham Islands, Norfolk Island, and mainland New Zealand (Turbott 1990, Higgins and Davies 1996, Holdaway et al. 2001, Checklist Committee [O.S.N.Z.] 2010). The fossil history of Hemiphaga is restricted to Late Pleistocene and Holocene deposits in New Zealand (Worthy and Holdaway 2002). The single exception is a distal ulna reported from the Pliocene Whenuataru Tuff in the Chatham Islands by Eagle et al. (2005). It is identical to Hemiphaga chathamensis, and its preservation is very different (no infilled sediment, no wear, no encrusting marine calcareous structures) from that of the other bone described from the same deposit. Its preservation is typical of Holocene bones from other sites on the islands (T. H. Worthy and A. J. D. Tennyson pers. obs.), and it seems likely that this specimen was an unrecognized Holocene intrusion in the Pliocene deposit.
The pre-Quaternary fossil record of columbiforms is meager compared with the fossil records of many birds (Olson 1985, Becker and Brodkorb 1992). There is no Paleogene record of species referable to Columbidae in Europe (Mayr 2005). The putative columbid Microena goodwini from the Early Eocene of England (Harrison and Walker 1977) was relegated to Aves incertae sedis (Mlíkovský 2002). The order Columbiformes is represented, however, by four species in two genera (Archaeoganga and Leptoganga) of sandgrouse (Pteroclidae) from the Late Eocene—Oligocene and Early Miocene of France (Olson 1985, Mlíkovský 2002). Because Columba calcariaMilne-Edwards, 1867–1871, from the Lower Miocene at Saint-Gérand-le-Puy in France, is now also considered a sandgrouse, as Gerandia calcaria (Mlíkovský 2002), there is no pre-Pliocene columbid record in Europe.
Globally, the oldest described pigeons are known from abundant fossils from the Early Miocene (18–19 mya) of Florida (Olson 1985) referred to a modern dove genus, as Columbina prattae, by Becker and Brodkorb (1992). However, Steadman (2008) erected a new genus, Arenicolumba, for this taxon, noting a greater phenetic similarity to the Old World Oena and Turtur than to any New World taxa, but generic comparisons were limited.
Olson (1989) suggested that columbids may have originated in the Southern Hemisphere, but as yet there is little fossil evidence to support this proposal. Pigeons and doves have a fossil record in Australia extending back to the Late Oligocene—Early Miocene, from lacustrine deposits at Lake Palankarinna (Etadunna Formation) and Lake Pinpa (Namba Formation) of central Australia (Vickers-Rich 1991, Boles 2006), but the material is meager and undescribed. Similarly, the New Zealand St Bathans Fauna has revealed a single fossil of a columbid, a distal right ulna of a bird about the size of the Wompoo Fruit-dove (Ptilinopus magnificus; Worthy et al. 2007).
The St Bathans Fauna is derived from sediments deposited in a shallow freshwater lake ∼5,600 km2 in area and is of late Early Miocene age (16–19 mya; Worthy et al. 2007). The faunal-bearing sediments outcrop as the lower Bannockburn Formation of the Manuherikia Group, in Otago, South Island, New Zealand. At the time of deposition, the climate was warm and the surrounding vegetation included casuarinas (Casuarinaceae), Eucalyptus (Myrtaceae), and palms (Arecaceae), in addition to the typical “New Zealand” podocarps (Podocarpaceae), Nothofagus, and araucarias (Araucariaceae) (Pole and Douglas 1998, Pole et al. 2003). This fauna provides the only data on the terrestrial vertebrates that existed in New Zealand during the Tertiary and, so far, has revealed ∼30 avian taxa. The avifauna of the St Bathans Fauna is dominated by anseriforms, with a minimum of eight taxa in five genera, but has a diverse fauna of other birds, including procellariiforms, accipitriforms, gruiforms, a palaelodid, charadriiforms, columbiforms, psittaciforms, apodiforms including both swiftlets and owlet nightjars, and passeriforms including a possible cracticid (Worthy et al. 2007, 2008; T. H. Worthy et al. unpubl. data). Here, we add to this diversity from the St Bathans Fauna and, on the basis of a coracoid, describe the first pre-Quaternary pigeon species from Australasia. We draw phylogenetic inferences of its relationships and discuss its biogeographic implications.
Methods
Several molecular analyses have examined phylogenetic relationships within Columbidae (e.g., Johnson and Clayton 2000, Shapiro et al. 2002), but the most comprehensive is that of Pereira et al. (2007), which used >9,000 base pairs from multiple nuclear and mitochondrial genes from 33 pigeon genera. We used this phylogenetic hypothesis and the distribution of morphological characters to assess the relationship of the fossil described here.
The osteology of the columbid coracoid was the subject of a detailed description (Martin 1904), but this work outlined few intergeneric distinguishing features. More recently, Worthy (2001) detailed coracoid characters useful for generic identification, and these were expanded by Worthy and Wragg (2003, 2008) and by Steadman (2006). Our comparisons were mainly restricted to taxa in the Australasian—Pacific region; because of geographic separation, taxa outside this region were considered unlikely relatives.
AM = Australian Museum, Sydney, Australia;
AMNH = American Museum of Natural History, New York;
CM = Canterbury Museum, Christchurch, New Zealand;
FM = Fiji Museum, Suva, Fiji;
LACM = Natural History Museum, Los Angeles County, California;
MVZ = Museum of Vertebrate Zoology, University of California, Berkeley;
NMNZ = Museum of New Zealand Te Papa Tongarewa, Wellington;
SAM = South Australian Museum, Adelaide, South Australia;
USNM = U.S. National Museum, Smithsonian Institution, Washington, D.C.; and
UWBM = Burke Museum, University of Washington, Seattle.
Anatomical nomenclature.—Names for specific bone landmarks follow Baumel and Witmer (1993). Some common terms are abbreviated: artic. = articularis, m. = musculus, and proc. = processus.
Measurements were made with Tesa dial calipers and rounded to 0.1 mm. The fossil was compared with the following taxa and specimens, with an emphasis on Australasian—Southwest Pacific taxa. All material is from modern skeletons unless stated otherwise; extinct taxa are indicated by a cross. †Bountyphaps obsoleta, MNZ S.44246 (fossil bones). Caloenas nicobarica, SAM B.5056, SAM B.36831, SAM B.51203. Otidiphaps nobilis, USNM 615084. Gallicolumba stairi, NMNZ S.38223 (54 fossil bones, 6 individuals). G. beccarii, AMNH 7718, USNM 615012, UWBM 43037. G. rubescens, MVZ 46017. G. luzonica, MVZ 53804, LACM 89051, LACM 89050. G. rufigula, LACM 106368. G. criniger, LACM 89052. G. jobiensis, AM O.64814, AMNH 6753. Chalcophaps indica, SAM B.31777, SAM B.37059, SAM B.38758. Columba leucomela, SAM B.31352, AM O.58907. C. livia, SAM B.46041, SAM B.46044, SAM B.46046. C. vitiensis, AM O.7921, FM 26. Didunculus strigirostris, AM O.303. Ducula bicolor, AM O.68476, SAM B.23902 (as D. spilorrhoa). D. latrans, FM 28. D. pacifica, AM O.7919. Geopelia cuneata, SAM B.38429. G. striata, SAM B.45091. Geophaps plumifera, SAM B.5094, SAM B.31097. G. scripta, SAM B.49175. G. smithii, SAM B.32611. Goura cristata, SAM B.4997, SAM B.5057, SAM B.11546, SAM B.11551. Hemiphaga novaeseelandiae, AM O.65739. Leucosarcia picata, SAM B. 5090, SAM B.10598. Lopholaimus antarcticus, AM O.65687, AM O.71405. Macropygia amboinensis phasianella, SAM B.38504, SAM B.38757. Ocyphaps lophotes, SAM B. 48075, SAM B.48078, AM B.48939. Phaps chalcoptera, SAM B.46373, SAM B.48297. P. elegans, SAM B.37405, SAM B.47648. Ptilinopus magnificus, SAM B.21929, SAM B.46569. P. magnificus keri, NMNZ OR.27278. P. regina, SAM B.37060. Streptopelia chinensis, SAM B.48177, SAM B.49668.
Systematic Paleontology
Columbiformes Latham, 1790 Columbidae Illiger, 1811
The fossil coracoid is assigned to Columbidae because it has the following combination of features found only in this family: it is elongate with a long shaft region; the proc. acrocoracoideus is large and inflated, with a greater dorsoventral depth than that through the facies artic. humeralis; the cotyla scapularis is rounded and shallow, not a deep cup-like sulcus; the proc. procoracoideus lacks a foramen; and the impressio m. sternocoracoidei contains pneumatic foramina.
Rupephaps, gen. nov
Type species.—Rupephaps taketake, sp. nov.
Diagnosis.—As for species.
Etymology.—Etymology: after Rupe, an honorific term for the Kererū, or New Zealand Pigeon (H. novaeseelandiae) when personified in Maori myths and a name widely used throughout Polynesia for pigeons (Tregear 1891, Best 1942), and phaps (Greek, feminine noun for “wild pigeon”).
Rupephaps taketake, sp. nov
Holotype.—NMNZ S.51259, left coracoid (Fig. 1), collected 12 January 2008 by the University of New South Wales—University of Adelaide, South Australia—CM—NMNZ expedition.
Diagnosis.—A pigeon distinguished from all other taxa by the following unique combination of characters. (1) The facies artic. clavicularis is planar, with a shallow notch at mid-depth, and the ventral lobe extends farther sternally than the dorsal lobe. (2) The ventromedial facies of the proc. acrocoracoideus, or that ventrally of the facies artic. clavicularis, has two pits, interpreted here as the insertion points for ligamentum acrocoraco-claviculare superficiale, the most ventral of which opens via a groove to the ventral facies. (3) The facies artic. clavicularis extends as a rounded lobe medially of the medial margin, rather than being pointed and hooked sternally. And (4) the ridge extending cranially along the medial margin above the angulus medialis does not reach the facies artic. sternalis ventralis, being separated from it and the medial angle by a rounded facies. The latter is an autapomorphy for the species.
Taxonomic remarks.—The fossil shares character 1 with Ptilinopus, Ducula, Lopholaimus, and Hemiphaga: the dorsal and ventral lobes of the facies artic. clavicularis have about even sternal extent and are separated by a marked notch in all other compared taxa, except in Geophaps, in which the facies artic. clavicularis is a medially convex structure without an obvious dorsal lobe. The structure of the pit or pits for the insertion for ligamentum acrocoraco-claviculare superficiale (figure 5.3 in Baumel and Raikow 1993) on the ventromedial tip of the proc. acrocoracoideus (character 2) varies significantly among columbids. The fossil shares with Ducula, Ptilinopus, Hemiphaga, and Lopholaimus the conformation of two distinct pits separated by a ridge, with the ventral-most pit opening to the ventral facies. In many taxa (e.g., Columba, Leucosarcia, Streptopelia, Chalcophaps, Macropygia, Geophaps, Geopelia, and Caloenas), the two pits are merged as a single elongate pit that opens ventrally, whereas in Gallicolumba, Otidiphaps, Bountyphaps, Didunculus, Phaps, Ocyphaps, and Goura a single elongate pit is separated by a ridge from the ventral facies. Both characters 1 and 2 are consistent in allying Rupephaps with Ptilinopus, Ducula, Lopholaimus, and Hemiphaga, to the exclusion of other taxa. These taxa, with the addition of Drepanoptila and Gymnophaps, formed a strongly supported clade (Pereira et al. 2007), termed the “fruit dove group” (Christidis and Boles 2008), for which the name Ptilinopinae Selby, 1835 is available. We consider characters 1 and 2 (as described above for Rupephaps) apomorphies for this clade.
Character 3, where the facies artic. clavicularis is a rounded lobe extending medially of the sulcus m. supracoracoidei margin rather than being pointed and hooked sternally, was observed only in Hemiphaga, Lopholaimus, and Natunaornis. We consider its occurrence in the latter taxon to be non-homologous to the state in Hemiphaga, a convergence that is probably the result of reduction in pectoral structure associated with flightlessness in this large species (Worthy 2001). Hemiphaga and Lopholaimus are strong flyers. Therefore, we suggest that this character is an apomorphy for the well-established Hemiphaga + Lopholaimus + Gymnophaps clade (Goodwin 1967, Pereira et al. 2007). As such, it associates Rupephaps with these large fruit pigeons to the exclusion of other ptilinopines.
Character 4 is an autapomorphy for the fossil taxon; in all other taxa, the crest extends from the ventral sternal facet up the medial margin.
Rupephaps is larger than all species in the genera Ducula and Ptilinopus. It is slightly larger than Lopholaimus (475–600 g) and smaller than Hemiphaga (550–850 g) and so is considerably larger than the well-known Rock Pigeon (Columba livia; ∼300 g; Higgins and Davies 1996).
In Rupephaps taketake, the impressio m. sternocoracoidei extends to the medial margin of the bone and the facies artic. sternalis dorsalis has even breadth over the coracoid width, which distinguishes it from Lopholaimus, in which the impressio m. sternocoracoidei is separated from the medial margin and the dorsal sternal facet is distinctly broader medially. Rupephaps is distinguished from Hemiphaga novaeseelandiae by two features apart from smaller size: a flat lateral facies above the proc. lateralis and the form of the crest above the angulus medialis.
Etymology.—From taketake, Maori for “long established, ancient, original” (Williams 1971), chosen to reflect the longevity of the pigeon lineage in New Zealand. It is pronounced “ta-kay-ta-kay.”
Type locality.—Bed HH1a, a sand and mud cobble layer about 5–10 cm thick with abundant bone and stromatolite fragments, which is overlain by fine sand up to 20 cm thick and is 6.88–7.0 m above the base of the Bannockburn Formation. Home Hills Station, true left side of Manuherikia River, Otago. 44°54′28.6″S, 169°51′29.6″E. New Zealand Fossil Record File Number H41/f88.
Stratigraphy—age—fauna.—Bannockburn Formation, Manuherikia Group, Early Miocene (Altonian); 16–19 mya; St Bathans Fauna.
Measurements of holotype.—Length from angulus medialis to tip of proc. acrocoracoideus = 44.9 mm; length from cotyla scapularis to tip of proc. acrocoracoideus = 13.8 mm; shaft width = 4.1 mm.
Description.—The fossil is stained black and is missing the tip of the proc. procoracoideus, the proc. lateralis, a fragment of the impressio m. sternocoracoidei, and a small section of the medial margin of the shaft above the angulus medialis. It is slightly crushed through the proc. acrocoracoideus in a zone extending from above the facies artic. humeralis to below the facies artic. clavicularis. In addition to the characters described above, the fossil has the following features.
Left coracoids in (A) dorsal, (B) medial, (C) medial ×2, and (D) ventral views of Rupephaps taketake NMNZ S. 51259 (top row) and Hemiphaga novaeseelandiae AM O.65739 (bottom row). Abbreviations: ac = proc. acrocoracoideus, am = angulus medialis, cs = cotyla scapularis, fac = facies artic. clavicularis, fah = facies artic. humeralis, fasv = facies artic. sternalis ventralis, pf = pneumatic foramina, pl = proc. lateralis, pr = proc. procoracoideus, si = impressio m. sternocoracoidei, and ss = sulcus m. supracoracoidei. Scale bar = 1 cm.
The presence and size of pneumatic foramina in the sulcus m. supracoracoidei below the dorsal lobe of the facies artic. clavicularis differ among columbid taxa. The slight crushing through the proc. acrocoracoideus precludes determining whether a small pneumatic foramen was present under the dorsal lobe of the clavicle facet, as seen in Hemiphaga and Lopholaimus, but the area is sufficiently well preserved to exclude the possibility that a large pneumatic fossa as seen in Ptilinopus was present.
The dorsal lobe of the facies artic. clavicularis is rounded and protuberant over the sulcus m. supracoracoidei, but not so much as to be prominent over the cotyla scapularis in lateral view. Therefore, it differs from Gallicolumba, Otidiphaps, Columba, Phaps, Chalcophaps, Goura, Caloenas, Macropygia, Streptopelia, Leucosarcia, Ocyphaps, Geophaps, and Geopelia, in which the dorsal lobe of the facies artic. clavicularis markedly overhangs the cotyla scapularis in lateral view.
The lateral surface distad of the facies artic. humeralis is flattened to slightly convex and without a sulcus in the fossil, as in Ptilinopus, Ducula, Columba, Hemiphaga, Lopholaimus, and some species in the genera Geophaps and Geopelia, whereas a marked sulcus is present in all other compared taxa.
The medial border of the proc. procoracoideus merges with the shaft over a short length, and its cranial margin slopes sternally from the cotyla scapularis, so that although the absolute tip is not preserved, it clearly did not extend toward the proc. acrocoracoideus. A short merging of the proc. procoracoideus with the shaft is shared with most taxa, but Goura, Didunculus, and, to some extent, Caloenas, are distinguished by a very elongate merging of the process to the shaft. In most taxa, the tip of the proc. procoracoideus extends toward the proc. acrocoracoideus and extends craniad to the cotyla scapularis, but the fossil is like Hemiphaga, Lopholaimus, Otidiphaps, and some Gallicolumba species (G. stairi, G. beccarii, G. rubescens, G. leonpascoi, and G. jobiensis, but not G. luzonica, G. criniger, or G. rufigula), in that the tip does not extend cranially past the cotyla scapularis.
In the fossil, the impressio m. sternocoracoidei is well defined but not deep, extends to the medial edge of bone, and has prominent muscular striae, and the main area of pneumatic foramina is located close to the angulus medialis. In Didunculus, Bountyphaps, Goura, Caloenas, Ocyphaps, and Geophaps, the main area of pneumatic foramina is located more centrally in the extremitas sternalis coracoidei. In most taxa, the impression is distinctly separated from the medial margin of the bone above the medial angle, but Ptilinopus, Ducula, Hemiphaga, Streptopelia, Leucosarcia, some Gallicolumba (e.g., G. stairi), Geophaps, and Geopelia are similar to the fossil, in that the impression is confluent with the medial edge of the bone. Ocyphaps and Otidiphaps differ markedly in having a deeper, more extensively pneumatic impression, and in Caloenas, Macropygia, and Geophaps the impression extends farther cranially, into the proximal half of the bone. In the fossil, the impression does not reach the mid-length of the coracoid. The fossil has well-developed sternal articular facets, with the dorsal one wider and of even width across the lateromedial breadth of the coracoid, as in Hemiphaga. In most taxa, Lopholaimus included, the medial part of the facies artic. sternalis dorsalis is distinctly wider than its lateral part.
Although the proc. lateralis is missing, the preserved lateral margin of the impressio m. sternocoracoidei slopes steeply ventrally just above the end of the facies artic. sternalis dorsalis, in a fashion that suggests that a pneumatic foramen was probably present slightly farther laterad of this point, as in most other pigeons but with the notable exception of Didunculus and Gallicolumba jobiensis.
Many of the above features support inclusion of Rupephaps as a member of the ptilinopine clade, and characters 1 and 2 are apomorphies for this clade. Character 3 is shared by Rupephaps, Hemiphaga, and Lopholaimus, exclusive of other taxa. Rupephaps is more similar to Hemiphaga and differs from Lopholaimus by the impressio m. sternocoracoidei extending to the medial margin of the bone and the facies artic. sternalis dorsalis having even breadth over the coracoid width. However, it differs from both in that the crest extending along the medial margin above the angulus medialis does not reach the facies artic. sternalis ventralis. In addition, the lateral margin of the fossil immediately above the missing angulus lateralis is distinctly flattened and is defined dorsally by a crest along the lateral margin of the impressio m. sternocoracoidei and ventrally by a crest leading toward the angulus lateralis. By contrast, this facies is rounded in Hemiphaga and slightly flattened in Lopholaimus.
Discussion
Rupephaps taketake is described on the basis of a single bone, but it is significant as the first fossil columbid to be described from the Australasian region that is older than the Pliocene. At 16–19 mya, it provides the first indication of the evolutionary history for columbids in Australasia, which, with 32 species (Christidis and Boles 2008, Checklist Committee [O.S.N.Z.] 2010), has one of the most diverse columbid faunas globally. Rupephaps taketake is diagnosed as a ptilinopine fruit pigeon by two synapomorphies and is only slightly smaller than the world's largest fruit pigeon, Hemiphaga novaeseelandiae, which at about 550–850 g is about twice the weight of the Rock Pigeon. The fossil is more similar to Hemiphaga than to any other Australasian pigeon, including the extant sister-group species Lopholaimus antarcticus. Rupephaps is distinguished from Hemiphaga by two features of the coracoid, apart from size: a flat lateral facies above the proc. lateralis and the form of the crest above the angulus medialis. The latter is an autapomorphy for the fossil taxon and suggests that the coracoids in Rupephaps had a slightly different relationship with the sternal articulation and associated ligaments attached to the carina sterni. Similarly, the flat lateral side to the coracoid suggests a different relationship to the proc. craniolateralis of the sternum from that in Hemiphaga.
Although our comparative studies were concerned only with the coracoid, it is significant that we have identified two apomorphies to support the monophyly of the clade of Australasian fruit-doves, or Ptilinopinae (Ptilinopus, Drepanoptila, Ducula, Lopholaimus, Gymnophaps, and Hemiphaga): (1) the more sternally elongate ventral lobe of the facies artic. clavicularis; and (2) that the ligament attachment sites on the ventromedial region of the proc. acrocoracoideus form two distinct pits, with one opening via a groove to the ventral facies, rather than a single pit or groove. These taxa form a well-supported clade based on robust and diverse molecular data (Pereira et al. 2007). These apomorphies augment the identification of a characteristic sternal morphology (Boles 1999); however, that character is ambiguous, because a similar state is shared with Treron.
Steadman (2006) described columbids as the most taxonomically diverse family of land birds in the Pacific Ocean region, but until now the antiquity of such radiations in the region has been unknown. Three closely related species in the genus Hemiphaga, all of which inhabit forest, are currently recognized: H. novaeseelandiae from mainland New Zealand and, formerly, the Kermadec Islands; the extinct H. spadicea on Norfolk Island, 1,077 km northwest of Auckland; and H. chathamensis on the Chatham Islands, 769 km east-southeast of Wellington, New Zealand (Checklist Committee [O.S.N.Z.] 2010). The sister-group taxa to Hemiphaga are Lopholaimus of eastern Australian forests and Gymnophaps from subtropical—tropical moist montane forests in Indonesia, Papua New Guinea, and the Solomon Islands (Goodwin 1967, Pereira et al. 2007). Lopholaimus and Hemiphaga are strong fliers and often aggregate in large flocks, which predisposes them to successful dispersal, as evidenced by the recent colonization of Norfolk, Kermadec, and Chatham islands by Hemiphaga.
Our finding that R. taketake occurred on Zealandia (which became modern-day New Zealand) in the Early—Middle Miocene (16–19 mya) and was closely related to both Lopholaimus and Hemiphaga has significant biogeographic implications. It strongly suggests that the Hemiphaga lineage has been present in New Zealand since at least 16 mya. This fits with molecular evidence that suggests that the most recent common ancestor of Hemiphaga and Lopholaimus existed ∼24 mya (19.2–29.6 mya) and a hypothesized dispersal event from Australia ∼24 mya (Pereira et al. 2007).
If the ancestor of Rupephaps colonized Zealandia in the Early Miocene, which would be consistent with the genetic data and the age of the fossil, it would have found a land re-emerging from a maximal submergence during the latest Oligocene—earliest Miocene (Cooper and Millener 1993, Landis et al. 2008) and so increasing in area, geographic complexity, and ecological diversity. Such conditions then probably predisposed Zealandia to colonization by birds. Other colonizing taxa in the Early Miocene probably included a Palaelodus sp. (T. H. Worthy et al. unpubl. data), but other components of the St Bathans Fauna, such as New Zealand wrens (Acanthisittidae; T. H. Worthy et al. unpubl. data) and several waterfowl taxa (Worthy et al. 2007, Worthy and Lee 2008), reveal an avifauna already then quite distinct from that of Australia. Thus, even in the Early Miocene, New Zealand had a composite biota with some long-established taxa and others that are recent arrivals, much like today.
Rupephaps is not, however, the only pigeon taxon in the St Bathans Fauna. The distal ulna NMNZ S.42430 described by Worthy et al. (2007) from Bed HH1a is from a smaller species, and there is a third columbid fossil in the collections from the St Bathans Fauna. NMNZ S.44066 is a pedal phalanx digit I.1, also from Bed HH1a. It is much smaller than that of H. novaeseelandiae and similar in size to that of Ptilinopus magnificus keri (NMNZ OR.27278); thus, it conforms in size with the distal ulna but is not as flattened as in these taxa. These fossils are insufficient, however, to identify an affinity within columbids, but minimally attest to a diversity of at least two pigeon species in the St Bathans Fauna.
Given this diversity among pigeons of the Early Miocene and the long tenure of the Hemiphaga lineage in mainland New Zealand, it is notable that there is no evidence for any modern diversification within the genus. Two observations may explain this apparent anomaly: (1) this lineage has a strong association with forests, especially in warmer regions; and (2) Hemiphaga preferentially eats fruit but otherwise eats leaf material (Clout et al. 1991, Higgins and Davies 1996). Both fruit and leaves would have been a very limited resource in New Zealand during the cold glacial periods, the most drastic effects of which peaked during the last and penultimate glacials (McGlone 1988, Newnham et al. 1999). In those periods, forest was constrained to latitudinal regions <38°S (essentially to the Northland peninsula of the North Island; McGlone 1988) and, given the limited diversity of fruiting trees in the flora, would have provided limited food for pigeons. We have no knowledge of the avian biota during the period between deposition of the St Bathans Fauna and Recent times, but it seems likely that the insular nature of New Zealand combined with the Pleistocene glaciations may have led to the extinction of one or more taxa, leaving just one surviving to the present on mainland New Zealand.
Lastly, Rupephaps provides the first internal fossil-calibration point within the columbid phylogeny, with a minimum age of 16–19 mya for the Lopholaimus—Hemiphaga split. Such calibration points are few in the avian record (Ericson et al. 2006). Because Ptilinopinae is a deeply nested clade within Columbidae, Rupephaps confirms that modern generic diversification had already been attained in Australasia at least by ∼16 mya. The present high diversity of columbids in Australia, most of which are endemic, suggests that a diverse fossil record of pigeons is yet to be revealed there. Undescribed Late Oligocene—Early Miocene columbid fossils are present in the Riversleigh World Heritage Area deposits of northwestern Queensland (T. H. Worthy pers. obs.) and in lacustrine deposits at Lake Palankarinna (Etadunna Formation) and Lake Pinpa (Namba Formation) in central Australia (Vickers-Rich 1991, Boles 2006). Ultimately, we predict that a diverse fauna of Australasian Oligocene—Miocene columbids will be revealed in support of Olson's (1989) hypothesized southern origin for the family.
Acknowledgments
We specifically thank the landowners A. and E. Johnstone, who not only graciously allowed us access to their land but actively contributed to the excavations by working a digger. Further, we benefited greatly from the unstinting efforts of many field assistants in the St Bathans Fauna project, especially M. Archer, J. Wood, J. Nyugen, J. Louys, H. Godthelp, P. Creaser, and the other volunteers for 2008. This work has been supported by Australian Research Council grant DP0770660 for collaborative work by University of New South Wales (UNSW) and New Zealand researchers, and by postdoctoral research support to T.H.W. through the UNSW Strategic Initiative Funding Scheme. T.H.W. thanks W. Boles of the Australian Museum and P. Horton of the South Australian Museum for access to comparative material. We thank J. Parish for images of Otidiphaps.
Literature Cited
Author notes
Associate Editor: G. Mayr
