Palaeontologia africana

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African chelonians from the Jurassic to the present: phases of development and preliminary catalogue of the fossil record
(Bernard Price Institute for Palaeontological Research, 2000) de Lapparent de Broin, France
The five major phases in the palaeontological history of African chelonians are presented: 1) autochthonous development of the north Gondwanan pleurodires from a Pangean source group; 2) littoral expansion of a member of this group (Bothremydidae), accompanied by the arrival of Laurasian marine turtles; 3) in situ development of pleurodires and the immigration of Eurasian cryptodires (Oligo-Miocene) traversing the Tethys in several waves; 4) great diversification and endemism (Pliocene to Holocene); 5) important faunal reduction due to climatic changes at the end of Holocene times (cooling, aridification); elsewhere, great speciation and arrival during the Present of the last European immigrant in the north. Throughout the period under consideration there were several reductions in taxonomic diversity and emigrations from Africa. A preliminary catalogue of the fossil record of African chelonians is given, presented country by country followed by a taxonomic listing.
Preliminary phylogenetic analysis and stratigraphc congruence of the dicynodont anomodonts (Synapsida: Therapsida)
(Bernard Price Institute for Palaeontological Research, 2001) Angielczyk, Kenneth D
A preliminary phylogenetic analysis of 20 well-known dicynodont taxa was conducted using modern cladistic methods. Many past phylogenetic hypotheses were corroborated, but others conflict with the results of this analysis. Most notably, Diictodon, Robertia, and Pristerodon are reconstructed in more basal positions than previously suggested, whereas Endothiodon and Chelydontops occupy a more crown ward position. These findings are consistent with novel evolutionary scenarios for characters such as the presence of postcanine teeth and anterior palatal ridges. The Relative Completeness Index and Gap Excess Ratio were used to examine the degree of fit between the most parsimonious cladograms of this study and the stratigraphic record of the dicynodonts. Although the results of this analysis suggest that the preferred cladogram is relatively consistent with stratigraphy, the presence of some ghost ranges and ghost lineages imply that the fossil record of dicynodonts is not as complete as is sometimes stated. These findings are important because there is a long tradition of intensive collecting in regions where dicynodont fossils are common; sections of several dicynodont lineages may not be preserved in these areas.
Character state transformations and the fit of phylogenies to the fossil record
(Bernard Price Institute for Palaeontological Research, 2002) Angielczyk, Kenneth D
There is only one true history of life, and the biostratigraphic record and the phylogenetic relationships of organisms provide the most important information regarding this history. Ideally, the historical signal preserved in each of the data sets should be the same, and several methods have been proposed to compare the fit of phylogenies to the fossil record. All of these techniques use stratigraphic data associated with taxa, but our ability to recognize taxa and reconstruct their phylogenetic relationships ultimately is based on patterns of character state distributions that we observe. This raises the question of whether character states can be used to measure the fit of a phylogeny to the fossil record. Here I argue that we can, if the order of appearance of character states is considered. Optimization of character states on a phylogeny results in a predicted order of appearance of character states; derived states must arise after basal states. This order can be compared to that predicted by the fossil record. Although a number of factors can affect the frequency at which derived character states are sampled before basal states in the fossil record, conflicts between the two data sets should be relatively rare. Phylogenies that imply a large number of character state transformations that are inconsistent with the fossil record may need to be reconsidered before the fossil record is criticized.
Makapansgat Limeworks stratigraphy and the singular case of Member X
(Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, 2008-04) Lathan, Alf; Warr, Ginette
Within the infilling sequence of the western Limeworks a newly recognized unit, Member X, lies stratigraphically between the Member 1 massive speleothem and the Member 2 red silts. Member X consists firstly of a subaqueous mammillary layer that is ubiquitous to the whole of the Limeworks. It is succeeded by a series of intercalated clastic sediments and calcite-rich layers that is confined to the area between the Original Ancient Entrance and the Classic Section and which is terminated by a second subaqueous carbonate layer. The evidence suggests that surface sediments were washed into a carbonate-rich pool created by seepage water and, from the presence of several articulated skeletons, the Original Ancient Entrance during this phase appears to have acted as an animal trap. There are a few blocks of Member X to be found in the Limeworks dumps that have been placed in the Member 2 rows but which should be prepared separately. From the evidence of the intercalated carbonate and clastic layers it appears that Member X was deposited slowly at first and then speeded up probably because erosion caused retreat of the entrance. Member X has several unusual features including a unique pseudo-breccia layer of co-deposited calcite-mud formations, deposition of aragonite that increases with height, and calcite-aragonite layers that invert the stratigraphy on overhanging walls and ceilings but not on the floors.

Palaeontologia africana

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