A number of 18th century authors described the gray whale as Balaenagibbosa, the "whale with six bosses", apparently based on a brief note by : The gray whale was first described as a distinct species by 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. 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. 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 and therefore named the gray whale Plesiocetus robustus, reducing Lilljeborg's and Gray's names to synonyms. 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 Peninsula, they were and still are associated with him and his description of the species. At this time, however, the extinct Atlantic population was considered a separate species from the living Pacific population. Things got increasingly confused as 19th century scientists introduced new species at an alarming rate, often based on fragmentary specimens, and taxonomists started to use several generic and specific names interchangeably and not always correctly. 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 combinationEschrichtius gibbosus was proposed. In his morphological analysis, found that eschrichtiids and Cetotheriidae form a monophyletic sister group of Balaenopteridae. A specimen from the Late Pliocene of northern Italy, named "Cetotherium" gastaldii by and renamed "Balaenoptera" gastaldii by, was identified as a basal eschrichtiid by who recombined it to Eschrichtioides gastaldii. found that the gray whale is phylogenetically distinct from rorquals and that previous morphological studies were correct in the conclusion that the evolution of gulp feeding was a single event in the rorqual lineage.
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. 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. 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 and a similar unnamed fossil has been reported from California. In their description of Archaeschrichtius ruggieroi from the late Miocene of Italy, argued that eschrichtiids most likely originated in the Mediterranean Basin about and remained there, either permanently or intermittently, at least until the Early Pliocene,
