Friday, September 11, 2015

[PaleoMammalogy • 2015] Horopeta umarere • The Earliest Gulp-feeding Mysticetes (Cetacea: Mysticeti) from the Oligocene of New Zealand

Horopeta umarere  Tsai & Fordyce, 2015
Fig. 1 Excavation of Horopeta umarere OU21982.   b, excavation site, Craig Jones with recovered skull block; c, initially prepared skull block, from underside.
photos: R Ewan Fordyce || DOI: 10.1007/s10914-015-9290-0

Horopeta umarere is a new genus and species of extinct baleen whales from the Kokoamu Greensand (early Chattian, Oligocene, in the range 25–27 Ma), Hakataramea Valley, New Zealand. The geological age makes Horopeta umarere one of the earliest named baleen whales. Phylogenetic analysis indicates that Horopeta umarere may be the earliest crown Mysticeti (the sister taxon to Cetotheriidae), or the sister species to the crown Mysticeti; it is clearly not a species of Eomysticetidae. Estimated skull and body length of Horopeta umarere are 1.5-1.6 m and 6.5-7.5 m, respectively. Horopeta umarere shows some features that are linked to gulp feeding as seen in living humpback and rorquals: laterally bowed and robust mandible, D-shaped to teardrop-shaped mandible in cross-section, and posterolaterally deflected triangular coronoid process of the mandible. The sternum of Horopeta umarere is elongate, rod-shaped, and dorsoventrally stout with bilateral anterior and posterior rugose protrusions, indicating the presence of at least two pairs of ribs or costal cartilages. The structure of the skull and mandible are consistent with the use of gulp feeding, but the sternal morphology and rib attachments suggest an early evolutionary stage in gulp feeding employment, where more complex rib attachment may restrict the volume of water and food taken in one gulp compared to living humpback and rorquals. Thus, the morphology of Horopeta umarere has implications for the emergence of gulp feeding in baleen whale evolution as well as the emergence of the crown Mysticeti.

Keywords: Baleen whale, Rorqual, Skull, Fossil, Evolution

Fig. 2 Preserved material of Horopeta umarere OU21982.
Disarticulated rostral elements are interpreted as: i, right premaxilla; ii, right maxilla; iii, left maxilla; iv, left premaxilla; v, left maxilla; vi, left maxilla; vii, right maxilla. Asterisk sign (*) indicates the cross -section of rib shown in Fig. 11. The size of humerus is estimated from an undescribed Oligocene mysticete, ZMT 67.

 Systematic Paleontology
Cetacea Brisson, 1762
Mysticeti Gray, 1864

Incertae familiae
Horopeta umarere, gen. et. sp. nov.
(Figs. 2–13)
Zoobank: http://​zoobank.​org/​References/​43A7AAD3-1E12-4648-A4A2-38C7B605048D 
LSID (Life Science Identifiers) LSID:

Holotype: Horopeta umarere is known only from the holotype (Fig. 2, OU21982, Geology Museum, University of Otago, Dunedin, New Zealand), which preserves a partial skull, including parts of the maxillae and premaxillae, the dorsal braincase (partial parietal and supraoccipital), exoccipitals, and squamosals, as well as the mandibles, both tympanoperiotic complexes, forelimbs (scapulae, radii, and ulnae), all cervical vertebrae, ten thoracic vertebrae, and two possible lumbar vertebrae, 16 identifiable ribs (eight left, eight right), and sternum.

Locality: OU21982 was recovered by R.E. Fordyce, A. Grebneff, and C.M. Jones, 28 January 1988, from the Hakataramea valley, South Canterbury, South Island, New Zealand (Fig. 1). The locality is an active quarry, variously known as Hurstlea Quarry or Haughs’ Quarry or Haka Lime, currently operated by Transport Waimate Limited. The grid reference is I40: 236137; latitude and longitude are 44°39′41″S and 170°39′00″E. New Zealand Fossil Record locality number for OU21982 is I40/f177.
Horizon: OU21982 was recovered by tunneling (the specimen was originally discovered in section in a steep cliff from the middle Kokoamu Greensand, Duntroonian Stage (in the range 25.2-27.3 Ma; Raine et al. 2012), Chattian, late Oligocene. The lithology is a massive bioturbated to slightly bedded, slightly cemented calcareous greensand with sparse macroinvertebrates (pectinid bivalves, brachiopods). The Kokoamu Greensand is 7 to 8 m thick, and above the cetacean horizon grades up over several meters into the overlying Otekaike Limestone. The exact excavation site of OU21982 (Fig. 1) is about 1 m above a diffuse but distinctive brachiopod- and pectinid-rich shellbed, which is a distinctive regional marker for the base of the Duntroonian Stage in the lower to middle of the Kokoamu Greensand.

Etymology: Horopeta means “gulp or swallow” in Maori, alluding to possible gulp feeding habits. Umarere means unusual or different sternum in Maori. Uma- means sternum or chest bone, and rere stands for unusual or different.

The late Oligocene (early Chattian, 25–27 Ma) Horopeta umarere from New Zealand is described. Horopeta umarere adds to the named baleen whales from the poorly documented Oligocene epoch. Morphological combinations (e.g. mandibular and sternal morphologies) of H. umarere imply an early stage of gulp feeding in baleen whale evolution. We interpret H. umarere as representing the currently earliest described crown Mysticeti.

Cheng-Hsiu Tsai and R. Ewan Fordyce. 2015. The Earliest Gulp-feeding Mysticetes (Cetacea: Mysticeti) from the Oligocene of New Zealand. Journal of Mammalian Evolution. doi: 10.1007/s10914-015-9290-0