the date of description of a genus is an unreliable source. Similarly, a number of records
are based on specifically indeterminate material and commonly do not have an
accompanying date. In addition, dates of description are occasionally omitted. For major
taxa where such indeterminate records exceed five per cent of the total, both the total
number of records and the number of ‘unknowns’ are given in the relevant figure (e.g.
echinoderms in Figure 5.7c). Where two dates are given, the first is the date of
description of the species and I have assumed that the second (later) date is the date of
discovery of an earlier stratigraphic occurrence of the species. Occasionally, however, the
later date is for a compendium of stratigraphic occurrences and may not reflect an
extension of range. To be on the conservative side, I have consistently taken the later date
as the time of discovery of the earliest occurrence of the fossil species. Where only one
date is given, I have assumed that this is the date of discovery of the earliest occurrence of
the species with one exception. A few records are of species described by Linné (1758). I
have assumed here that these are Recent species discovered later as Pleistocene or
Pliocene fossils. Subject to these caveats, Benton (1993) provides an invaluable source of
data for most major taxonomic groups, with only a small proportion of ‘doubtful’
records.
ResultsResults are shown in Figure 5.7A–D and are based on the relevant chapters in Benton
(1993). The key points to look for are where the curves start and how steeply they rise
towards the present day. In general, curves to the left of the ‘effort’ curve represent a
‘good’ record, those to the right a ‘poor’ record (e.g. conodonts, Figure 5.7D). Equally,
the more concave a curve is, or the steeper the slope of the most recent portion, the
‘worse’ the fossil record. The sponges and to a lesser extent the cnidarians, show
interesting subdivisions. Sponges plus stromatoporoids have an apparently good record,
whereas archaeocyathids have a significantly worse record. It is perhaps significant that
both ‘problematica’ and ‘miscellanea’ have curves closest to the effort curve, suggesting
that these enigmatic fossils are discovered in exact proportion to the effort expended in
looking for fossils in general.
The bivalves and teleost fish have curves that begin before 1775, the non-ostracod
Crustacea, Zoantharia, and ‘other cnidarians’ have curves that begin before 1800.
However, most groups (24 out of 35 total) have curves that start between 1800 and
- The archaeocyathid curve starts between 1900 and 1925, whereas that of
conodonts not until between 1925 and 1950. To some extent this may reflect the
relatively recent change from element-based conodont taxa to apparatus-based taxa.
However, this cannot be the entire explanation, since newly recognized apparatus-based
taxa will still take the oldest available name for any element in the apparatus, in the same
way that the conodont animal, first recognized in 1983 (Briggs et al. 1983), was
tentatively referred to a species described in 1969.
The conodonts are an example of a somewhat unexpected result that stratigraphically
important groups appear to have relatively poor records. Only the foraminifera and
nautiloids have curves that start before 1825, ammonites and trilobites start before 1850,
ostracods and graptolites before 1875 and conodonts not until after 1925. Of the
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