History of Discovery
"Small shellies" in context -590 — – -580 — – -570 — – -560 — – -550 — – -540 — – -530 — – -520 — – -510 — Ediacaran Cambrian ← Small shelly fauna ← Ediacara biota ← Maotianshan shales ← Tommotian age ← Cambrian explosion, if sudden ← Ediacaran shelly fauna Neoproterozoic(last era of the Precambrian)
Palæozoic
(first era of the Phanerozoic)
Axis scale: millions of years ago.
References for dates:
Ediacara biota
Small shelly fauna, but may have been longer
Tommotian age
Cambrian explosion
The term "small shelly fossils" was coined by Samuel Matthews and V.V. Missarzhevsky in 1975. It is quite a misnomer since, as Stefan Bengtson says, "they are not always small, they are commonly not shelly – and the term might equally well apply to Pleistocene periwinkles." Paleontologists have been unable to invent a better term and have vented their frustration in parodies such as "small silly fossils" and "small smellies". The term is often abbreviated to "small shellies" or "SSF".
The great majority of all the morphological features of later shelled organisms appear among the SSFs. No-one has attempted a formal definition of "small shelly fauna", "small shelly fossils" or other similar phrases.
Specimens and sometimes quite rich collections of these fossils were discovered between 1872 and 1967, but no-one drew the conclusion that the Early Cambrian contained a diverse range of animals in addition to the traditionally recognized trilobites, archaeocyathans, etc. In the late 1960s Soviet paleontologists discovered even richer collections of SSFs in beds below and therefore earlier than those containing Cambrian trilobites. Unfortunately the papers that described these discoveries were in Russian, and the 1975 paper by Matthews and Missarzhevsky first brought the SSFs to the serious attention of the non-Russian-reading world.
There was already a vigorous debate about the early evolution of animals. Preston Cloud argued in 1948 and 1968 that the process was "explosive", and in the early 1970s Niles Eldredge and Stephen Jay Gould developed their theory of punctuated equilibrium, which views evolution as long intervals of near-stasis "punctuated" by short periods of rapid change. On the other hand around the same time Wyatt Durham and Martin Glaessner both argued that the animal kingdom had a long Proterozoic history that was hidden by the lack of fossils.
Read more about this topic: Small Shelly Fauna
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