Eschrichtiidae

Eschrichtiidae Temporal range: Miocene–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Cetacea
Suborder:	Mysticeti
Superfamily:	Balaenopteroidea
Family:	Eschrichtiidae Ellerman & Morrison-Scott 1951
Genera
†Archaeschrichtius Bisconti & Varola 2006 †Eschrichtioides Bisconti 2008 Eschrichtius Gray 1864 †Gricetoides Whitmore & Kaltenbach 2008
Synonyms
Rhachianectidae Weber 1904

Eschrichtiidae or the gray whales is a family of baleen whale (suborder Mysticeti) with a single extant species, the gray whale (Eschrichtius robustus). The family, however, also includes three described fossil genera: Archaeschrichtius and Eschrichtioides from the Miocene and Pliocene of Italy respectively,^[1] and Gricetoides from the Pliocene of North Carolina.^[2] The names of the extant genus and the family honours Danish zoologist Daniel Eschricht.^[3]

Taxonomic history

A number of 18th century authors^[4] described the gray whale as Balaena gibbosa, the "whale with six bosses", apparently based on a brief note by Dudley 1725:^[5]

The Scrag Whale is near a kin to the Fin-back, but instead of a Fin upon his Back, the Ridge of the Afterpart of his Back is cragged with half a Dozen Knobs or Nuckles; he is nearest the right Whale in Figure and for Quantity of Oil; his Bone is white, but won't split.^[6]

The gray whale was first described as a distinct species by Lilljeborg 1861 based on a subfossil found in the brackish Baltic Sea, apparently a specimen from the now extinct north Atlantic population. Lilljeborg, however, identified it as "Balaenoptera robusta", a species of rorqual whale.^[7] Gray 1864 realized that the rib and scapula of the specimen was different from those of any known rorquals, and therefore erected a new genus for it, Eschrichtius.^[8] Van Beneden & Gervais 1868 were convinced that the bones described by Lilljeborg could not belong to a living species but that they were similar to fossils that Van Beneden had described from the harbour of Antwerp (most of his named species are now considered nomina dubia) and therefore named the gray whale Plesiocetus robustus, reducing Lilljeborg's and Gray's names to synonyms.^[9]

Scammon 1869 produced one of the earliest descriptions of living Pacific gray whales, and notwithstanding that he was among the whalers who nearly drove them to extinction in the lagoons of the Baja California, they were and still are associated with him and his description of the species.^[10] At this time, however, the extinct Atlantic population was considered a separate species (Eschrischtius robustus) from the living Pacific population (Rhachianectes glaucus).^[11]

Things got increasingly confused as 19th century scientists introduced new species at an alarming rate (e.g. Eschrichtius pusillus, E. expansus, E. priscus, E. mysticetoides), often based on fragmentary specimens, and taxonomists started to use several generic and specific names interchangeably and not always correctly (e.g. Agalephus gobbosus, Balaenoptera robustus, Agalephus gibbosus). Things got even worse in the 1930s when it was finally realised that the extinct Atlantic population was the same species as the extant Pacific population, and the new combination Eschrichtius gibbosus was proposed.^[5]

In his morphological analysis, Bisconti 2008 found that eschrichtiids and Cetotheriidae (Cetotherium, Mixocetus and Metopocetus) form a monophyletic sister group of Balaenopteridae.^[12]

A specimen from the Late Pliocene of northern Italy, named "Cetotherium" gastaldii by Strobel 1875^[13] and renamed "Balaenoptera" gastaldii by Portis 1885, was identified as a basal eschrichtiid by Bisconti 2008 who recombined it to Eschrichtioides gastaldii.^[14][15]

Steeman et al. 2009 found that the gray whale is phylogenetically distinct from rorqual whales and that previous morphological studies were correct in the conclusion that the evolution of gulp feeding was a single event in the rorqual lineage.^[16]

Evolution

Fossils of Eschrichtiidae have been found in all major oceanic basins in the Northern Hemisphere, and the family is believed date back to the Late Miocene.^[14] Today, gray whales are only present in the northern Pacific, but a population was also present in the northern Atlantic before being driven to extinction by European whalers three centuries ago.^[17]

Fossil eschrichtiids from before the Holocene are rare compared to other fossil mysticetes. The only Pleistocene fossil from the Pacific referred to E. eschrichtius is a partial skeleton and an associated skull from California, estimated to be about 200 thousand years old. However, a late Pliocene fossil from Hokkaido, Japan, referred to Eschrichtius sp. is estimated to be 2.6 to 3.9 Mya and a similar unnamed fossil has been reported from California.^[14]

In their description of Archaeschrichtius ruggieroi from the late Miocene of Italy, Bisconti & Varola 2006 argued that eschrichtiids most likely originated in the Mediterranean Basin about 10 million years ago and remained there, either permanently or intermittently, at least until the Early Pliocene (5–3 Mya),^[18] (but see Messinian salinity crisis.)

References

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