Saturday, 3 March 2012

New Penguins from the Oligocene of New Zealand.

Penguins are thought to have originated in New Zealand and subsequently spread to other parts of the Southern Hemisphere. Certainly both modern and fossil Penguins are at their most diverse in New Zealand. A large number of fossil penguins have been described from New Zealand, although, as is often the case with fossil birds, many of these are fragmentary in nature.

In a paper in the March 2012 edition of the Journal of Vertebrate Paleontology a team of scientists lead by Daniel Ksepka of the Department of Marine, Earth, and Atmospheric Sciences at North Carolina State University describe a new genus of Penguins from the late Oligocene Kokoamu Greensand of North Otago and South Canterbury, South Island, New Zealand. Two species are described within this genus, and a number of previously described, fragmentary penguins from museum collections are referred to it without attempting to classify them to the species level.

The new genus is described as Kairuku, meaning the diver who brings food in Maori. It is divided into two species, named K. waitaki, named for the Waitaki River (which translates as 'river of tears') and K. grebneffi, after Andrew Grebneff, a palaeontologist at the University of Otago who died in 2010.

Skeletal elements from Kairuku waitaki & Kairuku grebneffi. (A & B) Beak tip of K. waitaki in dorsal and lateral views. (C & D) Beak tip of K. grebneffi in dorsal and lateral views. (E & F) Right quadrat of K. waitaki in cranial and caudal view. (G & H) Mandible of K. waitaki in dorsal and lateral view. (I) Right lacrimal of K. waitaki in lateral view. (J) Atlas of K. waitaki in cranial view. (K, L & M) Right coracoid of K. grebneffi in ventral, proximal and dorsal views. (N & O) Left coracoid of K. waitaki in dorsal and ventral views. (P) Omal portion of the scapula of K. grebneffi. (Q) Omal portion of the furcula of K. grebneffi. (R, S & T) Sternum of K. grebneffi in ventral, lateral and dorsal views. (U & V) Sternal trebecula of K. waitaki in ventral and dorsal views. (W) Sternal fragment of K. waitaki in cranial view. Abbreviations: am, tubercle for m. adductor mandibulae externus pars profunda; cl, cotyla lateralis; cm, cotyla medialis; co, capitulum oticum; cq, cotyla quadratojugalis; cr, crest on sternum; cs, cotyla scapularis; csq, capitulum squamosum; dep, depression on processus acrocoracoideus; f, furrow; fas(l/m), facies articularis sternalis (lateral and medial); j, articular facet for jugal; il, incisurae costalis; pl, processus lateralis; po, processus orbitalis; pr, processus retroarticularis; sac, sulcus articularlis coracoideus; tl, trabecula lateralis. From Ksepka et al. (2012).

Both birds were identifies from riverine, rather than marine, sediments suggesting that these early penguins may have been freshwater dwellers. The skeletons are far more complete than many previous fossil penguins, allowing for a more complete model of the living birds to be constructed than has previously been the case.

Reconstruction of Kairuku sp. by Chris Gaskin of the Geology Museum at the University of Otago.

The birds are clearly adapted for the 'underwater swimming' lifestyle of penguins, though the proportions are somewhat different to those of modern species. Previous fossil penguins from New Zealand have been described as 'Giant Penguins' based upon single large bones. Ksepka et al. question the wisdom of this, since the proportions of ancient penguins are not the same as those of modern penguins, individual large bones do not necessarily translate into particularly large birds.

They estimate that in order to be described as a Giant Penguin then a bird would have to be known to be as large as, or larger than, the modern Emperor Penguin (Aptenodytes forsteri). They felt able to estimate a size for only one of the new species, K. grebneffi, at 1.28 m tall. The Emperor Penguin is often described as reaching 1.5 m in height, though Ksepka et al. note that this is at odds with specimens preserved in museums, and recorded by scientists in the field, which range from 83 to 115 cm in height. By these standards K. grebneffi is indeed a Giant Penguin, though this is somewhat less impressive than some previous claims for fossil birds.

The sternum and coracoids of (A) Kairuku grebneffi and (B) The modern Emperor Penguin (Aptenodytes forsteri). From Ksepka et al. (2012).

See also The Penguins of Africa and Birds on Sciency Thoughts YouTube.

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