Palaeontologia africana

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Biostratigraphic refinement of tetrapod-bearing beds from the Metangula Graben (Niassa Province, Mozambique). New radiometric dating and the first Lower Triassic tetrapod fossils from Mozambique
(Evolutionary Studies Institute, 2020-12) Aráujo, Ricardo; Macungo, Zanildo; Smith, Roger M H; Tolan, Stephen; Angielczyk, Kenneth D; Crowley, James; Milisse, Dino; Mugabe, João
Numerous fossils of the toothed dicynodont Endothiodon have been collected previously from the Permian K5 formation of the Metangula Graben (Niassa, Mozambique). However, no identifiable vertebrate fossils have been reported from other stratigraphic units in the basin. Here we report likely Triassic tetrapod remains from the base of the Fubué Formation some 700 stratigraphic metres above the dated K5 Formation. We present anatomical comparisons and a phylogenetic analysis that confirm that they have close affinities to the well-known Early Triassic dicynodont therapsid Lystrosaurus. Thus, the Metangula Graben can now join the few regions in the world that preserve terrestrial tetrapod fossils from before and after Permian-Triassic mass extinction event, giving it the potential to provide further insights into the evolution of terrestrial organisms during this major biotic crisis. We present an updated geological section and paleoenvironmental interpretations, as well as the first assessment of the vertebrate taphonomy of the K5, K6, Mount Lilonga, and Fubué Formations. We also report the first radiometric dates for the K5c member of the K5 formation. The K5c has a maximum depositional age of 258.85 ± 0.41 Ma and is thus older than previously thought, falling near the boundary between the Lycosuchus-Eunotosaurus and Tropidostoma-Gorgonops subzones of the Endothiodon Assemblage Zone, rather than being coeval with the Cistecephalus Assemblage Zone.
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.

Palaeontologia africana

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