Relationships ancestor-descendant

Phytogeny Evolutionary history. The genealogical history of a group of organisms represented by its hypothesized ancestor-descendent relationships. 

The difference between Agassiz s diagram and Romer s diagram is, of course, the influence of Darwin and the desire to recognize ancestor-descendent relationships. Patterson (1977) questions whether Agassiz s depiction of affinity through hierarchies of characters is any more abstract than the ancestor-descendent relationships illustrated by Romer. 

I mention both stratolikelihood and stratocladistics because these are the current developments influencing theoretical paleontological research into phylogeny reconstruction. In many ways, these methods reflect a desire to put stratigraphy, ancestor-descendent relationships and evolutionary models back into phylogeny reconstruction. We must await the reaction of those practicing paleontologists. 

On the basis of morphological similarity and known stratigraphic distribution a case is made for the establishment of a direct ancestor-descendent relationship between Trigonellina pectunculus from the Upper Jurassic (White Jura) of Southern Germany and Praeargyrotheca hexaplicata from the Lower Cretaceous... 

The science of classification is called taxonomy and the organization of life by ancestor-descendent (evolutionary) relationships is called phylogeny. The characterization and comparison of key intracellular molecules has altered prior classification and relationship schemes. 

Myosins are actin-based motors (see Chapter 5). The reason for considering myosin in the context of microtubule motors is that the catalytic domains of myosin and kinesin share structural similarities indicating that both families use a similar mechanism for energy conversion. The structural relationship between these families suggests that both descend from a common ancestor, a primordial nucleotide binding protein (Kull et ah, 1998). 

The phylogeny of bacterial nitrifiers (Teske et ai, 1994) shows that most of them are descendents of a common ancestor that was photosynthetic, rather than descending from a common ancestral nitrifier. Extensive phylogenetic trees depicting the relationships among cultivated nitrifiers, and the relationships of sequences obtained without cultivation from environmental samples, are available in the publications cited in this section and are not reproduced here. 

Placozoa A phylum of simple aquatic animals containing just a single known species, Trichoplaxadhaerens. This has a transparent round flattened body, between 0.2 and 3 mm in diameter, without head, tail, or appendages. It is covered in cilia, which it uses to crawl over surfaces, and it feeds by secreting enzymes from its ventral surface. An adult comprises a few thousand cells of just four types, whose DNA content is the smallest of any anlmaL The evolutionary relationships of placozoans with other animals, especially the sponges ( Porifera), remain speculative. Molecular studies of ribosomal RNA sequences have indicated that the Placozoa maybe secondarily simplified descendants of more complex ancestors and are not closely related to the sponges. 

Tasklets spawned by the same tasklet in the same POP are denoted siblings. Ancestor and descendant denote the nested hierarchical relationships, since spawned tasklets may themselves spawn new tasklets. 

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