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Source of information on Biology.SE This answer offers an introduction to phylogeny on the case study of dinosaurs and birds. If you are not at ease with the concept of monophyletic group, you should definitely have started with this introduction. This post is somewhat related. Origin of your misunderstanding The question is all about nomenclature (and a ...


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In my view, we simply don't have good enough data to answer this question. The fossil evidence is too sparse prior to the Cambrian and the evidence that we do have suggests that the phyla were already too separated. Meanwhile, the depth of time and the different lifecycles and circumstances of the species involved mean that any "genetic clocks" we might use ...


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As far as I know there is no phylum which appeared after the Cambrian. Every discussion beyond that is close to speculation, as the divergence estimates of different studies vary significantly. You might want to look into one of the resources mentioned below: http://www.timetree.org/index.php http://www.onezoom.org/


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Good question! I had never really though about it, so thank you! Echinodermata have a pentaradial symmetry Echinodermata actually don't have a radial symmetry like jellyfish do. They have a pentaradial symmetry as they systematically have 5 arms. Parsimony Even if Echinodermata were radially symmetric, then it would actually be unlikely that bilateral ...


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A cladogram does not indicate time. That would be a calibrated phylogram. We can tell from the above cladogram that the two synapomorphies "Hair" and "Eggs" with shells are the two most recent, and happened after all the other ones because cladograms do indicate the relative timing of events. However, knowing a bit about mammals, "Hair" is the more recent ...


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There have been some good answers here, but I think some information could be added. Willi Hennig introduced modern phylogenetic systematics, which is sometimes conflicting with traditional taxonomy. Hennig's important insight was that one should only use synapomorphies (shared derived traits) as the evidence for identifying relative recency of common ...


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Why Swordfish (Xiphias gladius), which are very similar to Marlins, do not belong to the same family as Marlin - Istiophoridae? The decision about what we call an order vs a family is very subjective. Someone decided that Istiophoriformes was an order containing the families Xiphiidae and Istiophoridae but someone else could have decided to call ...


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Mammals and reptiles aren't considered amphibians, because amniotes are not hypothesized to descend from Amphibia. That is to say that Amphibia did not evolve into Amniota. They are sister clades (actually Reptiliomorpha in the Tree of Life tree below).


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Some named groups are not monophyletic (see this post for definition if needed). Fishes do not represent a monophyletic group. Groups like "fishes" are completely awful to define but everyone would agree that no, humans are not fish! Now, it is important to understand for many terms, there might have a scientific and a popular definition of the term. For ...


2

As of right now it is still the same, the evidence for sauropodomorpha being a outgroup is not statistically more reliable, this may change, however this will still not have much impact. There are several ways in which dinosauria is defined. The most recent common ancestor of Megalosaurus and Iguanodon is also sometimes used since they were the original ...


1

Many of the problems you are discovering are the basis for phylogenetic classification. Without necessarily answering each of your question specifically, I'll mention some of the basics of phylogenetic classification as compared to traditional Linnean classification: Species are the main "currency". We classify species and species alone. All taxonomic ...


1

Binomial nomenclature does not uniquely define a species unfortunately, there are several duplicates. The Wikispecies directory shows 5 duplicates: each of this is with an organism from kingdom Animalia and another from either Plantae or Fungi. Therefore, you could conclude that binomial nomenclature is a unique identifier within a kingdom.


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The short answer is that cladograms are not compatible with Linnean taxonomy. The longer answer explain how and why. First, there aren't enough ranks in Linnean taxonomy to cover all the cladogram nodes. The "kingdom-phylum-class-order-family..." was originally based on similiarity and not on phylogenetic relationship. For example: the class Reptilia is no ...


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Eyeballing it from http://www.onezoom.org I have this attempt at a breakdown (11 clades): Here, what was preivously 'Fish' (the paraphyletic group of non-tetrapod vertebrates) becomes 5 clades, and 'Reptiles' (the paraphyletic group of non-avian Sauropsids) becomes 3. After doing this it seems the question is equivalent to asking "what is the minimum ...


1

I think the clue is at each step to look for the trait that is shared by most of the remaining taxa. In your example: 9 out of 10 taxa are vertebrae. So you are correct to pick this trait first and outgroup Lancelets. Looking at the remaining 9 taxa: 8 have jaws, and a different set of 8 swim bladders or lungs At this point you can pick one of those traits,...


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It is actually hypothesized that radial symmetry did evolve again, but there are homologies between the echinoderm symmetry and bilateral animals: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2176165/


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-Bacteria 1 is least related to Eukaryote 4 (the furthest branch is always the least related as there common node is furthest away, correct?) In terms of relative relationships, eukaryote 4's least-related relative is Bacteria 1. Bacteria 1's least-related relative is the entire rest of the tree -The most related organisms are Bacteria 2 and 3, and ...


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I provided some edits in my comment -- hope the following clarifies things for you a little bit. To construct a cladogram, two characters are defined. You may be confusing character and character state. It's valid to have a cladogram with a single character (e.g. the single character, "warm-blooded"), but you will need at least two character states to ...


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Two reasonably close relatives of the most recent chimpanzee-human ancestor (CHA) are Sahelanthropus tchadensis and Orrorin tugenensis, but both are poorly attested. One better candidate is Ardipithecus ramidus, which has a fairly-complete skeleton ("Ardi") among other fossils. It's a bit young (4.4 Ma), perhaps, to be a CHA but should be a close relative. ...


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