December 19th on the Cosmic Calendar: The first vertebrates and actual fish appear!
Myllokunmingia is currently the oldest known vertebrate — a 28 x 6mm chordate. It had a distinct head and body, dorsal and ventral fins.
Haikouichthys is considered the first actual fish. Haikouichthys was a craniate, meaning it had an actual skull and backbone (myllokunmingia’s were probably made of cartilage). Haikouichthys was about the same size at 25mm. Fossils show it had between 6 and 9 gills.
This is still the Cambrian explosion!
You may remember Cosmos, the 1980 PBS series by Carl Sagan. Maybe you also recall Sagan’s “Cosmic Calendar” from the series, where in order to put the immensely vast history of the universe into a comprehensible scale, he mapped it onto a calendar year. In other words, if the entire history of the universe were one year, with the big bang in the first second of midnight on January first, and the present day on the last second of December 31st, New Year’s Eve. A project of mine this year has been to note the major events in the Cosmic Calendar, on the real calendar, on this blog!