Fossil mysticete from the Earthquakes area, Duntroon, North Otago : systematics and geological setting

Author:

Jenkins, Craig M. (Craig Mark)

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Abstract:

OU 22044 is(!lew species of Late Oligocene baleen whale (Mysticeti) from North Otago that represents an early group of toothless mysticetes. Under conventional classifications it would be placed into the family Cetotheriidae, however, due to its possession of some unique characteristics it can not be easily categorised into this group. As viewed traditionally, cetotheres encompass extinct baleen-bearing archaic mysticetes which supposedly include the ancestors of living rorquals. Specimen OU 22044 is from low in the Maerewhenua Member of the Otekaike Limestone near Duntroon in the Waitaki Valley. The skull has a long, narrow, endentulous rostrum with grooves on the ventral . surface of the maxilla which were probably associated with baleen. Long, narrow, parallel nasals indicate an anteriorly placed blowhole. Large temporal fossae separated by a long, narrow intertemporal region indicate massive temporal muscles which encroached little on the relatively delicate frontals. The large, elongate and robust zygomatic processes have a deep furrow along their medial faces. Each mandible is gracile, straight for most of its length, with a low, long, posteriorly positioned coronoid process. The periotic differs dramatically from that of described fossil or extant Mysticeti; it is gracile, with a prominent, laterally compressed anterior process, large anterointernal sulcus, a small and rather smooth body, a large facial canal and broad facial sulcus, a prominent lateral tuberosity, a large pars cochlearis, and a long posterior process characterised by a broad bullar facet. A significant feature of the bulla is the abrupt lip and extensively excavated region on the medial margin of the involucrum.
The long, narrow rostrum, unusual for such an early mysticete, is compatible with rapid "gulp-feeding". Alternatively, rapid snapping may have enabled OU 22044 to quickly catch food without having to engulf large volumes of water. The large temporal fossae and inferred large temporal muscles are perhaps a structural alternative to the more sophisticated jaw muscle origins and fossae seen in rorquals.
At least six other undescribed species of Late Oligocene Mysticeti from North Otago-South Canterbury share a similar periotic, and also bulla, structure with OU 22044, and are probably related closely to it. These species differ from each other in skull size and rostra! structure; they retain a generally archaic cranium and show little variation in the unusual form of the periotic. Overall, the periotic structure amongst these species indicates that they all belong to one short-ranging early clade apparently not related closely to any described family of toothless Mysticeti. A cladistic analysis of OU 22044 and relatives is needed to help delimit the paraphyletic and probably polyphyletic family Cetotheriidae.

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vii, 79 leaves, 5 leaves of plates : ill. (some col.), maps ; 30 cm.

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1993Jenkins

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POLYGON ((170.652432330000124 -44.873964224999952,170.652430549000087 -44.874009201999968,170.652434202000109 -44.874076793999961,170.652725950000104 -44.883175175999952,170.65275826900006 -44.884197606999976,170.617793910000046 -44.883136853999986,170.617843176000065 -44.882462656999962,170.618493393000108 -44.873374186999968,170.61849854400009 -44.873324776999937,170.618499629000098 -44.87329779099997,170.618501255000069 -44.873257311999964,170.618748810000056 -44.859929375999968,170.619003508000105 -44.846263938999982,170.633471384000018 -44.846575105999932,170.653543850000119 -44.847005813999942,170.652433933000111 -44.873923745999946,170.652432330000124 -44.873964224999952))

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http://download.otagogeology.org.nz/temp/Abstracts/1993Jenkins.pdf

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Citation

Jenkins, Craig M. (Craig Mark), “Fossil mysticete from the Earthquakes area, Duntroon, North Otago : systematics and geological setting ,” Otago Geology Theses, accessed May 22, 2024, https://theses.otagogeology.org.nz/items/show/280.

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