Palaeontology has gone from strength to strength in recent years. The astonishing – and astonishingly well-preserved – caches of fossils that have come to light are providing remarkable new insights into the course of evolution, while reconstruction of the Earth's past climate – a crucial context and prerequisite to understanding present climate – is underpinned and constrained by fossil evidence. This kind of work, however, depends utterly on maintaining and improving the systematic knowledge of ‘normal’ fossil assemblages: and this kind of work, being time-consuming and unlikely to attract headlines (or large grants), is increasingly hard to do in these demanding and impatient times. Hence it is welcome to see this major study of graptolites from around the Ordovician–Silurian boundary of Jordan.
It seems at first an unlikely subject to devote so much care and attention to. The graptolites had been hit hard by the end-Ordovician extinction associated with the brief but intense glacial phase of that time, and the general view (that I also used to hold) is of low-diversity faunas of bland and unremarkable normalograptid graptolites, largely resistant to detailed examination. Not so: by the kind of patient and careful study on which he has made his reputation, David Loydell has recognized 42 taxa in this apparently unpromising stuff, three of them new. It gives an altogether different picture of the diversity in this interval – and there are almost certainly more species out there, for there are still unsampled intervals in the stratigraphy. The study is made additionally useful because it acts as a bridge between two major graptolite provinces: the familiar graptolites of the European successions, and the endemic taxa of north Africa, previously biostratigraphically enigmatic.
Following relatively brief sections on the geology and biostratigraphy, the bulk of the work is of systematic taxonomic descriptions, concisely written and effectively illustrated, mostly by simple line drawings (the flattened but thankfully untectonized graptolites are not especially photogenic). There are the kind of surprises here that often turn up when type specimens of long-established and time-worn taxa are re-examined: Charles Lapworth's species normalis, for instance, formerly known as a Climacograptus and now the genotype of Normalograptus, is in reality a third larger in breadth than has been thought for a century. And there are nitpicks, too, of course, the taxonomic assignations that one might individually frown at (the wonderfully biform graptolites here assigned to Neodiplograptus, a genus that I have looked at askance ever since its genotype species, magnus, turned out to have thecae that are as uniform as you please).
No matter: this is a reference work that will continue to be well-thumbed by graptolite workers long after more fashionable scientific papers have faded into obscurity. Ironically, the data within it will be of use both to those extracting petroleum from the ground (the early Silurian transgressive ‘anoxic’ mudrocks are a major oil source rock) and to those pondering the possible effects of this contemporary global experiment (the marked latest Ordovician post-glacial transgression represents one of the most spectacular ice-sheet collapses of all time). A fine demonstration, then, of the diverse uses to be made of the humble graptolite.
