A Mass Extinction?

Suppose that, unknown to us, a taxon originates at time t = 0 and goes

extinct at time t = 100 (in some arbitrary units).

If the fossil record were perfect, then we would expect to find fossil

specimens from t = 0 up to t = 100. However, the fossil record is

incomplete, and very few specimens may be preserved. For instance, we might

find only three specimens at t = 15, 44, and 73. Using the locations of

these finds, can we infer the actual origination and extinction times of

the taxon?

Usually we will have other taxa as well. For a second taxon, say we find

specimens at t = 32, 56, 59, and 93; for taxon 3, say we find specimens at

t = 25, 41, and 87; and so on.

Questions:

1) When did each taxon go extinct?

2) Did all the taxa go extinct at the same time?

3) If so, when is this common extinction time?

4) If we have independent (e.g., geochemical) evidence for an extinction,

does this match the inferred extinction time from the fossil record?

Attached (click here) is a tab-delimited text file with the data. These are

locations of fossil finds for 10 ammonite species at the end of the

Cretaceous Period, near the Cretaceous/Tertiary boundary (when 2/3 of

species living at the time went extinct, including dinosaurs). Ammonites

are relatives of modern squid, octopus, and chambered nautilus.

Each column represents the locations of fossil finds for one taxon. The

units represent locations in meters from a fixed point in the site; for

simplicity, we can assume they represent time. An iridium anomaly

(presumably corresponding to a large meteorite impact) was found at 1160

meters. The data were collected in the mid-80s from a site on Seymour

Island, Antarctica.

Reference: Macellari, C. E. 1986. Late Campanian-Maastrichtian ammonite fauna from

Seymour Island (Antarctic Peninsula). Journal of Paleontology 60

(supplement).

The data were transcribed and provided by Charles Marshall.