''Eschrichtius akishimaensis'', described in 2017, is one of two species, with the modern day

gray whale The gray whale (''Eschrichtius robustus''), also known as the grey whale,Britannica Micro.: v. IV, p. 693. is a baleen whale that migrates between feeding and breeding grounds yearly. It reaches a length of , a weight of up to and lives between ...

, of the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

'' Eschrichtius'', and is the first and only fossil species of the genus, dating to around 1.77–1.95

million years ago Million years ago, abbreviated as Mya, Myr (megayear) or Ma (megaannum), is a unit of time equal to (i.e. years), or approximately 31.6 teraseconds. Usage Myr is in common use in fields such as Earth science and cosmology. Myr is also used w ...

(mya) in the

Early Pleistocene The Early Pleistocene is an unofficial epoch (geology), sub-epoch in the international geologic timescale in chronostratigraphy, representing the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently esti ...

History of discovery

The bones were first found in 1961 by a father and son, Masato and Yoshio Tajima, in a riverbed in Akishima, Tokyo, lending it the nickname of the Akishima whale. It was prepared by locals, under the mentorship of Hiroshi Ozaki, and subsequently put into storage at the

National Museum of Nature and Science The is in the northeast corner of Ueno Park in Tokyo. The museum has exhibitions on pre-Meiji period, Meiji science in Japan. It is the venue of the taxidermied bodies of the legendary dogs Hachikō and Taro and Jiro. A life-size blue whale mod ...

until it was transferred to

Gunma Museum of Natural History is a museum of the natural sciences in Tomioka, Gunma, Tomioka, Gunma Prefecture, Japan. History The museum first opened in 1978 under its old Japanese name, after repairs to the former . In 1996, the old museum closed, and its collection was tra ...

to be studied. The discovery generated local enthusiasm in the city, having both a ''Kujira matsuri'' (whale festival) and a ''Kujira Park'' (Whale Park) in its honor, and plans for a life-size replica skeleton in a new educational facility to open March 2020. Prior to its formal description, ''E. akishimaensis'' was referred to as "Japonocetus" ''akishimensis'', though the name was never used in any way that fulfils the

International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted Convention (norm), convention in zoology that rules the formal scientific name, scientific naming of organisms treated as animals. It is also informally known as the I ...

's requirements for species description. The

species name In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...

of ''Eschrichtius akishimaensis'' derives from Akishima, Tokyo, where the holotype was discovered.

Description

The only specimen of ''Eschrichtius akishimaensis'' consists of a skull, seven neck vertebrae, thirteen

thoracic vertebra In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...

e, eight

lumbar vertebra The lumbar vertebrae are located between the thoracic vertebrae and pelvis. They form the lower part of the back in humans, and the tail end of the back in quadrupeds. In humans, there are five lumbar vertebrae. The term is used to describe the ...

e, twelve tail vertebrae,

chevrons Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * '' Eulithis testata'', a moth * Chevron (geology), a fold in rock la ...

rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...

s, and arm bones, and has a total length of about . ''E. akishimaensis'' can be distinguished from '' E. robustus'' based on a number of characteristics. The posterior border of the

nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery * ...

is squared off, the ascending process of the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

is dorsolateral and narrower compared to that of the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

, and the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestra ...

concavity is deep and large.

References

Fossil taxa described in 2017 Pleistocene mammals of Asia Eschrichtiidae Pleistocene cetaceans {{Paleo-whale-stub