Sunday, December 15, 2019

[PaleoOrnithology • 2019] Kupoupou stilwelli • Chatham Island Paleocene Fossils provide insight into the Palaeobiology, Evolution, and Diversity of early Penguins (Aves, Sphenisciformes)

Kupoupou stilwelli
Blokland, Reid, Worthy, Scofield, 2019.

 DOI: 10.26879/1009

Numerous skeletal remains recovered in situ from the late early to middle Paleocene Takatika Grit of Chatham Island, New Zealand, are among the oldest known fossils attributed to the penguin clade (Aves, Sphenisciformes). They represent a new medium-sized taxon, for which we erect a new genus and species, and a second, notably larger form. These new penguins are analysed in a parsimony and Bayesian framework using an updated and revised phylogenetic matrix, based on morphological and molecular characters, and interpreted as among the most basal of known sphenisciforms, closely related to Waimanu. While sharing numerous characteristics with the earliest wing-propelled divers, the novel taxon records the oldest occurrence of the characteristic penguin tarsometatarsus morphology. These ancient Chatham Island representatives add to a growing number and increased morphological diversity of Paleocene penguins in the New Zealand region, suggesting an origin for the group there. With their addition to other Paleocene penguins, these taxa reveal that sphenisciforms rapidly diversified as non-volant piscivores in the southern oceans following the end-Cretaceous mass extinction. They also provide further evidence for the hypothesis that their origin predates the Paleocene. This implies that stem Sphenisciformes and their sister group, the Procellariiformes, both originated in, and so may be expected to occur in, the Late Cretaceous.

Keywords: new genus; new species; palaeontology; New Zealand; phylogenetics; waterbirds

Class AVES Linnaeus, 1758
Order SPHENISCIFORMES Sharpe, 1891

Genus KUPOUPOU gen. nov.
Type species. Kupoupou stilwelli, sp. nov.

 Etymology. From Te Re Moriori, the native language of Chatham Island, in recognition of where the fossils were recovered. “Kupoupou” meaning “diving bird”. The gender is nominated as neuter.

Diagnosis. Kupoupou, n. gen. is referred to Sphenisciformes because it shares the synapomorphy of having flattened long bones of the forewing/flipper. Kupoupou, n. gen. is characterised by the combination of the following osteological apomorphies: a bifurcated processus transversus of the axis with a dorsally protruding torus dorsalis; the processus acrocoracoideus has a rounded and protruding omal crista acrocoracoidea of the coracoid, the insertion for ligamenti acrocoraco-procoracoidale on the facies articularis clavicularis is weakly hooked with a rounded facies apicalis, a weakly defined tuberculum for the insertion of plica synovialis coracoidea, joined by a low ridge to the impressio ligamenti acrocoraco-acromiale, the latter of which is separated by the impressio ligamenti acrocoraco-procoracoidale by a groove; a well-defined labrum internum of the coracoid that is compressed in the sternal-omal direction; the distal margin of the crista bicipitalis on the humerus is nearly perpendicular to the long axis of the shaft; the distal caudal border of the olecranon of the ulna is distinctly angled, with a marked bony caudal protuberance; a dorsocaudally situated sub-triangular insertion scar for the musculus supinator on the proximal radius; a distinct caudally projecting tuberculum aponeurosis ventralis from the ventral caudal margin of the distal radius and an associated prominent ulnar depression; a proximally directed process on the phalanx III-1; a marked laterally protruding epicondylus lateralis on the femur; the sulcus for the tendon to the muscle flexor hallucis longus is bounded by medial and lateral hypotarsal crests of distinct subequal plantar projection on the tarsometatarsus; a strongly plantar projecting flange on the lateral rim of trochlea metatarsi IV.

Kupoupou stilwelli sp. nov.
Etymology. The type species “stilwelli” honours palaeontologist Jeffrey D. Stilwell, who led and organised the parties to recover the holotype and the only known referred specimens.

Holotype. NMNZ S.47312; associated left tarsometatarsus, left radius, and caudal vertebra.

Type locality, horizon, and age. Maunganui Beach, east of Tahatika Creek, north western Chatham Island, near 43°45’10.1”S, 176°40’46.8”W; New Zealand. The fossils come from a narrow greensand layer in outcrop on the wave platform that overlies the Upper nodular-phosphate and bone package horizon (NPB, Figure 1.3), Takatika Grit (late early-middle Paleocene, 62.5-60 Ma) (Consoli et al., 2009; Consoli and Stilwell, 2009; Hollis et al., 2017).


Kupoupou stilwelli n. gen. et sp.

 Kupoupou stilwelli n. gen. et sp. is a medium-sized sphenisciform (relative to all known fossil and extant penguins), likely slightly smaller than a modern adult Aptenodytes patagonicus. The referred specimens are assigned to Kupoupou stilwelli n. gen. et sp. based on similarity of overlapping skeletal elements (Figure A4), size, and their origin in the same horizon of the same bed in the Takatika Grit. The dimensions of the forewing elements reveal that Kupoupou stilwelli n. gen. et sp. was likely smaller than both Muriwaimanu tuatahi and Sequiwaimanu rosieae. Its humeri and coracoids show that it was smaller than the larger Chatham Island form described later in the text (Figure 3).

New Zealand stem penguins of broadly comparable age examined directly included Waimanu manneringi, Muriwaimanu tuatahi, ?Crossvallia waiparensis, and Sequiwaimanu rosieae. Additionally, other similarly aged taxa including the giant Waipara Greensand penguin, Kumimanu biceaeKaiika maxwelli, and Crossvallia unienwillia, were compared from relevant literature (Tambussi et al., 2005; Fordyce and Thomas, 2011; Jadwiszczak et al., 2013; Mayr et al., 2017a, 2017b, 2019).

Jacob C. Blokland, Catherine M. Reid, Trevor H. Worthy, Alan J.D. Tennyson, Julia A. Clarke, and R. Paul Scofield. 2019.  Chatham Island Paleocene Fossils provide insight into the Palaeobiology, Evolution, and Diversity of early Penguins (Aves, Sphenisciformes). Palaeontologia Electronica. 22.3.78; 1-92. DOI: 10.26879/1009