Index fossil

An index fossil is a rare object that is more common than it should be due to occurring from small objects surrounded by empty space. Stabilized index fossils -- i.e., rare still lifes or oscillators found in settled ash -- can be a fairly reliable indicator of the presence of a predecessor bottleneck pattern, sometimes even many thousands of ticks before the index fossil appears.

Examples

• xs37_069bq2s0c4oz359aq54311 is a 37-bit still life that (so far) has reliably taken 6000+ ticks to form from asymmetric 16x16 soups. All of these soups converge to produce a Herschel, beehive, and block, plus the same unnamed small active pattern. The time of appearance of the Herschel can vary considerably, since the Herschel produces two blocks and a ship, and it only matters that these objects are present dozens of ticks later when the active reaction reaches them.

• Lidka is a 29,055-generation methuselah. As of July 8, 2022, Catagolue's combined C1/G1 censuses would have 56,503 methuselahs lasting between 29,000 and 30,000 generations if the number of methuselahs in each grouping of 1,000 generations decayed exponentially. However, as of that day, it has 71,735 (×1.27), which is explained by an abundance of Lidka results. (http://catagolue.hatsya.com/census/b3s23/C1/methuselah)

• There is a 1,376-generation diehard in even fourfold rotational symmetry (C4_4) that consists of four H' (generation 22 of the Herschel without the glider) and four blocks. As of July 8, 2022, the number of diehards in the 1100-1199, 1200-1299, 1300-1399, 1400-1499, and 1500-1599 bins are 20227, 6435, 5593, 6041, and 651 respectively; the huge boost to the 1300-1399 and the 1400-1499 bins can be seen. The reason both bins get boosted is because it often takes time to get to the generation with the canonical H'. (http://catagolue.hatsya.com/census/b3s23/C4_4/messless)

• Omnibus is a 40-cell still life. Its initial configuration of a pi-heptomino and two blinkers can be seen on its page; as it takes a lot of space to form, it requires empty space around it.