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The gray whale also lacks a dorsal fin, instead bearing 6 to 12 dorsal crenulations ("knuckles"), which are raised bumps on the midline of its rear quarter, leading to the flukes. The tail itself is 3–3.5 m (10–11 ft) across and deeply notched at the center while its edges taper to a point.The two populations of Pacific gray whales (east and west) are morphologically and phylogenically different.This population ranged at least from Southampton, New York, to Jupiter Island, Florida, the latest from 1675.used a genetic approach to estimate pre-whaling abundance based on samples from 42 California gray whales, and reported DNA variability at 10 genetic loci consistent with a population size of 76,000–118,000 individuals, three to five times larger than the average census size as measured through 2007.Small depressions on the upper jaw each contain a lone stiff hair, but are only visible on close inspection.Its head's ventral surface lacks the numerous prominent furrows of the related rorquals, instead bearing two to five shallow furrows on the throat's underside.In January 2011, a gray whale that had been tagged in the western population was tracked as far east as the eastern population range off the coast of British Columbia.
North Atlantic populations were extirpated (perhaps by whaling) on the European coast before AD 500 and on the American coast around the late 17th to early 18th centuries.
Other than DNA structures, differences in proportions of several body parts and body colors including skeletal features, and length ratios of flippers and baleen plates have been confirmed between Eastern and Western populations, and some claims that the original eastern and western groups could have been much more distinct than previously thought, enough to be counted as subspecies.
Since the original Asian and Atlantic populations have become extinct, it is difficult to determine the unique features among whales in these stocks.
The gray whale is the sole living species in the genus Eschrichtius, which in turn is the sole living genus in the family Eschrichtiidae.
This mammal descended from filter-feeding whales that appeared at the beginning of the Oligocene, over 30 million years ago.