Wikipedia:Reference desk/Archives/Science/2020 February 7

= February 7 =

Cetacean dorsal fins
It is well known that land vertebrates' limbs evolved from fins, and in cetaceans they became fins (flippers) again. But what about dorsal fins? Is their fetal development in whales and dolphins controlled by the same genes as in fish? Meaning, when they evolved, did long dormant genes reactivate, or is it a completely new development? If it's not known on a genetical level, are they similar structures anatomically or are there fundamental differences? User38453838 (talk) 07:21, 7 February 2020 (UTC)
 * They seem to be a new development: "There aren’t any bones or cartilage in the dorsal fin and flukes. Instead, they’re made up of dense connective tissue" in https://oceantoday.noaa.gov/killerwhaleanatomy/ 2003:F5:6F06:7900:D570:A85B:2650:24B6 (talk) 11:12, 7 February 2020 (UTC) MPB
 * Note that the gray whale 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. This is known as the dorsal ridge". Alansplodge (talk) 17:40, 7 February 2020 (UTC)