Piotr Jadwiszczak and Thomas MÃrs (2019)
First partial skeleton of Delphinornis larseni Wiman, 1905, a slender-footed penguin from the Eocene of Antarctic Peninsula.
Palaeontologia Electronica 22.2.32A 1-31.
The oldest fossil record of Antarctic penguins comes from Seymour Island (Antarctic Peninsula) and dates to the Paleocene and Eocene. The Paleocene bones are extremely rare, whereas specimens from the latter epoch are numerous. Despite the recent discoveries of incomplete skeletons assignable to the giant penguins from the Eocene of Antarctic Peninsula, the reliable systematics of their smaller contemporaneous relatives, known from isolated bones, have remained dependent on the tarsometatarsus. Here, new data on the skeleton of Delphinornis larseni, the most abundant among non-giant Eocene penguins, are reported. The specimen, collected from the Submeseta Formation on Seymour Island, comprises the incomplete pelvis and numerous bones from the hind-limb skeleton, including a well-preserved (diagnostic) tarsometatarsus. The acetabular foramen is, like in larger fossil penguins, clearly smaller than the elongated ilioischiadic foramen. The area of the latter opening, not occupied by the connective-tissue sheet, supposedly accounted for one-third of the foramen. We propose that the ischiadic artery was, unlike in present-day penguins, the main blood vessel supplying most of the hind limb. The proximal fovea of the femoral head is uniquely preserved, revealing an osteological aspect of the bone-ligament interface. We surmise that the individual was similar, in terms of body size, to extant Pygoscelis papua, but was characterized by more elongate feet. In our opinion, it was probably a young bird, up to several years old.
Nicolas J. Rawlence, R. Paul Scofield, Matt S. McGlone and Michael Knapp (2019)
History Repeats: Large Scale Synchronous Biological Turnover in Avifauna From the Plio-Pleistocene and Late Holocene of New Zealand.
Frontiers in Ecology and Evolution 7: 158
New Zealand's unique biodiversity is the product of at least 55 million years of geographic isolation, supplemented by persistent transoceanic migration. Palaeontological and genetic evidence suggest most New Zealand avifauna has colonized from Australia. We synthesize evolutionary genetic studies to show a previously unrecognized clustering of divergence times in Australian and New Zealand bird species pairs, across the avian phylogeny at the beginning of the Pleistocene, around 2.5 million years ago. The timing coincides with major climatic and vegetation changes with the initiation of the Plio-Pleistocene glacial cycles. Recent anthropogenic impacts and environmental modifications are replicating in some important ways Pleistocene glacial landscapes, resulting in a new wave of avian ânative invadersâ into New Zealand.
New Zealand has long been regarded as a model system for understanding Southern Hemisphere biogeography and evolution. It is one of the most isolated continental fragments (Zealandia; Mortimer et al., 2017) of the supercontinent Gondwana that was completely severed by ocean around 55 million years ago (Mya) (Roelants and Bossuyt, 2005). It has an excellent fossil record (Worthy and Holdaway, 2002; Worthy et al., 2017), and is home to extant taxa that are known from the old supercontinent (e.g., Giribet and Boyer, 2010; Easton et al., 2017; Wallis and Jorge, 2018).
While its geographic isolation and geological history appears to demand a vicariance explanation for the origin of its biodiversity, there is increasing evidence that New Zealand is rather a âfly paper of the Pacificâ (McGlone, 2005) with a constant flow of immigrant taxa (Flemming, 1962; McDowall, 2008; Gibbs, 2017; Wallis and Jorge, 2018). Many New Zealand plants and animals, once considered ancient, have been shown to be more recent transoceanic immigrants arriving long after the separation of Zealandia from eastern Gondwana (e.g., Knapp et al., 2005; Mitchell et al., 2014). The oceans surrounding the New Zealand archipelago are a permeable barrier (e.g., McCulloch et al., 2017) and, while the focus has been on species mobility, establishment and persistence of immigrants is just as important (Boessenkool et al., 2009; Collins et al., 2014; Rawlence et al., 2015, 2017a; Grosser et al., 2016; Waters and Grosser, 2016; Waters et al., 2017).
Birds are often highly mobile and many are adept at forming breeding populations after crossing ocean barriers (e.g., white eyes Zosterops spp.; Cornetti et al., 2015). Most post-Gondwanan avian immigration to New Zealand is from the closest landmass, Australia (e.g., Scofield et al., 2017; Wallis and Jorge, 2018), which is favorably situated with regard to prevailing winds and ocean currents, although some taxa have their nearest relatives in Asia (e.g., Gibb et al., 2015) or Melanesia (e.g., Boon et al., 2001).
New Zealand has endured more profound geological, topographic, and climatic changes since its separation from eastern Gondwana than any other continental landmass, Antarctica aside (Mortimer et al., 2017). Shortly after the separation of Zealandia, thinning and cooling of its continental crust as rifting ceased resulted in a loss of buoyancy and submergence. No more than 7% of the original Zealandian landmass remained emergent (Mortimer et al., 2017). The portion that was to be the New Zealand archipelago sank; weathering and erosion wore down the original mountainous landmass, and rising sea levels completed a process that culminated in the near-complete marine inundation (up to 80% of New Zealand) during the Oligocene 35â25 Mya (Worthy et al., 2017). Zealandia is therefore best thought of not as a coherent terrestrial entity, but rather as a region of the ocean where diverse geological processes have created a scatter of archipelagos and ephemeral islands (Grandcolas, 2017). While a complete submergence of the New Zealand region has been suggested (Landis et al., 2008), recent geological, palaeontological (e.g., Conran et al., 2014; Scott et al., 2014; Worthy et al., 2017) and genetic research (e.g., Carr et al., 2015; Wallis and Jorge, 2018) strongly favors a small emergent archipelago at that time. Wallis and Jorge (2018) synthesized previous evolutionary genetic studies and found around 75% of 248 New Zealand lineages survived the marine transgression in situ, the majority non-volant terrestrial and freshwater taxa, and trees.
A highly diverse flora and fauna (e.g., Saint Bathans Fauna, Worthy et al., 2017) flourished under the subtropical climate of the early to middle Miocene. The first significant mountain ranges in the South Island arose in the middle Miocene (Nathan et al., 1986). Rapid uplift along the Alpine Fault system (which runs the length of the Southern Alps) began ca. 8 Mya. These rising ranges intercepted the prevailing westerly wind flow, creating rain-shadow climates in the east from the late Miocene onwards (Chamberlain et al., 1999). Climatic change, disruption of the previous low-lying stable landscape and an ever-changing archipelago configuration accelerated biotic turnover with the loss of earlier taxa and a continuing influx of new types (McGlone et al., 2016). An abrupt reorganization of the plate tectonic regime ca. 5 Mya was followed by rapid uplift of erosion-resistant greywacke that began ca. 4 Mya in the far south, and propagated northwards, with tall mountainous relief as late as 1.3 Mya in the northwest of the South Island (Batt and Braun, 1999).
Mountains of the northeastern South Island, the axial ranges of the North Island and the Volcanic Plateau arose later, and in the southern North Island, mountain ranges began to form only about 500, 000 years ago (McGlone et al., 2001). Global cooling from 2.7 Mya initiated the Pleistocene cycles of cold glacials and warm interglacials (Wallis et al., 2016; Craw et al., 2017). Local rain shadow aridification intensified in the southern and eastern regions of New Zealand (Craw et al., 2013). During the Pleistocene glacials the dense evergreen forests that had dominated the archipelago since separation from eastern Gondwana were fragmented into coastal fringes or inland patches on favorable sites from the middle of the North Island southwards, with continuous forest largely confined to northern New Zealand (Newnham et al., 2013). Over most of the archipelago during glacial maxima, shrubland-grassland, and bare ground mosaics prevailed (Newnham et al., 2013).
Human arrival around 750 years ago (Wilmshurst et al., 2008, 2011), during a period of relative climatic stability (Wanner et al., 2008; Allen, 2012; Waters et al., 2017), resulted in the extinction of nearly 50% of the unique avifauna (Tennyson and Martinson, 2007) and widespread destruction of forests (McWethy et al., 2014). Fire induced open shrub and grassland habitats structurally similar to those of the Pleistocene glacials (McGlone, 2009).
Much of the non-endemic indigenous biodiversity of New Zealand is of Australian origin (for example, over 200 plant species are shared between Tasmania and New Zealand; Jordan, 2001) and typical of open habitats, which suggests the Plio-Pleistocene glacials created new opportunities for Australian biota (McGlone et al., 2001; McGlone, 2006; Wood et al., 2017). Here, through a synthesis of molecular dating studies utilizing modern and ancient DNA, we can demonstrate the effect of Plio-Pleistocene environmental changes on the New Zealand avifauna, but also narrow down the timing for the start of the avian influx.