Punctuated equilibria, morphological stasis and the palaeontological documentation of speciation: a biological appraisal of a case history in an African lake

Abstract

The present-day faunas of the great African lakes present some of the world's best examples of 'explosive speciation'. Lakes Victoria and Malawi each probably have several hundred endemic species of cichlid fishes. Much can be inferred about the evolution of these fishes from morphology, behaviour and intra-lacustrine distribution and from the fact that they include taxa ranging from local races, through sibling species, to forms that display extensive differentiation. The time taken to acquire specific distinctness can sometimes be accurately defined, but fossil lineages are unknown. A recent study of a fossil sequence of molluscs in the Turkana basin throws new light on the history of African lake faunas. It also claims to have resolved events during speciation. While critical analysis based on our knowledge of living molluscs in this area fails to substantiate this claim, the fossil molluscs complement information provided by the biology of extant fishes and invertebrates and emphasize the importance of these lakes in the study of evolution in living and extinct populations.

Variation of Shell Shape in the Clonal Snail Melanoides Tuberculata and Its Consequences for the Interpretation of Fossil Series

“…Although these points have already been made in the flurry of critiques that followed Williamson's papers (e.g., Boucot 1982;Mayr 1982;Fryer et al 1983;Kat and Davis 1983), the present study provides some empirical basis to these critiques. Clearly, studying shell shape using multivariate analyses is not sufficient to infer genetic changes in M. tuberculata from the fossil record.…”

“…Moreover, the biology of living relatives of the molluscan lineages studied by Williamson (1981a,b,c) had not been considered (Fryer et al 1983). A central point is the genetic basis of the variation observed in fossils.…”

The oldest fossil cichlids (Teleostei: Perciformes): indication of a 45 million-year-old species flock

“…Fryer et al (1983) pointed out that di¡erent fossil species might be proposed when in fact they are merely two or more morphs of the same species. In cichlids, these morphs are for the most part distinguished by morphological di¡erences in the teeth and jaws that are associated with di¡erent food types or environments (e.g.…”

Punctuated equilibrium, morphological stasis and the palaeontological documentation of speciation: a reply to Fryer, Greenwood and Peake's critique of the Turkana Basin mollusc sequence

“…The current status of these Victoria Bellamyas is therefore that there are four endemic species and two endemic subspecies, all readily recognizable on shell and soft-part morphology, derived in all probability from B. capillata, one distinctive endemic species derived from B. unicolor, and B. unicolor itself. Contrary to the claim of Fryer et al (1983), there is in fact only one form of B. unicolor known from Lake Victoria-the typical form known from much of the African continent. The taxonomy of the modest local endemic radiation of the Victoria Bellamyas has no relevance to the question of morphological variation in the widespread species B. unicolor.…”

“…Schindel, 1982: Although Fryer et al (1983) attempt to show that the modern representatives of at least four of the Turkana Basin lineages (Bellamya unicolor, Cleopatra bulimoides, Pila ouata and Melanoides tuberculata) are highly ecophenotypically variable, their discussion is in each case either unconvincing or erroneous. The discussion of variation in the genus Bellamya in general, and of the species B. unicolor in particular, is inaccurate.…”