User talk:ScienceApe

From Wikipedia, the free encyclopedia

Hi ScienceApe! Under modern classification (called phylogenetic nomenclature), a group is defined by its shared evolutionary ancestor and includes all descendants of that ancestor. If a group contains some descendants of that ancestor but not others, it is called paraphyletic and not considered valid by most modern researchers. The group Reptilia is defined as the common ancestor of all modern reptiles (lizards, turtles, snakes, crocs, etc.) and all its descendants. Birds evolved from reptiles (specifically dinosaurs), so birds are among those descendants. Therefore, birds are a type of reptile. If birds are considered separate from reptiles even though they evolved from them, "reptile" becomes a paraphyletic group. Similarly, mammals are a type of synapsid. Synapsids and mammals are not reptiles, however, because they did not evolve from the common ancestor of modern reptiles and birds, but from the common ancestor of all amniotes. Dinoguy2 (talk) 02:09, 3 June 2008 (UTC)

The way reptile is defined in modern classification is based on the ancestor of all kinds of reptiles alive today. The ancestor of all these was actually more advanced than the things mammals evolved from. So technically, mammals did not evolve from reptiles, their ancestor was more "amphibian" like. So the term mammal-like reptile is technically wrong. In fact, skin impressions from early Synapsids (the actual ancestors of mammals) show that they had scaly skin--but not similar to reptile scales--rather their scales were the same as the ones found in primitive tetrapods ("amphibians") like Ichthyostega, and are similar to fish scales! The sclaes of lizards, snakes, crocs, and birds evolved later, in true reptiles. Dinoguy2 (talk) 23:32, 3 June 2008 (UTC)

Well, hopefully not to make things even more confusing, but for similar reasons, reptiles and mammals are not amphibians. Just like Reptilia now refers only to the group composed of living types of reptile, Amphibia is defined as the group of living amphibians (frogs and salamanders, etc.) and their common ancestor, and all its descendants. This includes things like Eryops, but not other things traditionally thought of as amphibians like Ichthyostega]] or Diadectes. A better name for this whole group is tetrapods. So, to simplify, it goes like this: Tetrapods evolved from things like Tiktaalik. Amphibians (frogs, salamanders) evolved from some of these early tetrapods. Later, reptiles and synapsids evolved from a different set of tetrapods. Much later, birdsevolved from other reptiles and mammals evolved from other synapsids. Mammals are therefore synapsids and tetrapods, but not amphibians or reptiles. Ambibians and reptiles are other kinds of tetrapods. Birds are another type of reptile, and also tetrapods.

However, many people still use "amphibian" in a general sense, to mean any frog or salamander-like tetrapod that needs to reproduce in the water. In that sense, yes, mammals and reptiles evolved from amphibians, just as "amphibians" evolved from "fish" (another informal term for a broad type of animal). Dinoguy2 (talk) 02:18, 4 June 2008 (UTC)

[edit] Wikipedia:WikiProject Dinosaurs

Hi ScienceApe, I saw you just added yourself to the participants list. Welcome to the team! :) Firsfron of Ronchester 03:51, 3 June 2008 (UTC)

[edit] Largest dinosaurs

Hey SA. As you can see in the image, the weight estimates for Bruhathkayosaurus are either ridiculously over-inflated or the weight estimates for Amphicoelias leaned towards the conservative end of the spectrum, and it probably weighed more than Carpenter was willing to speculate. Or both, which is most likely. Remember that diplodocids also tend to be much slimmer and more lightly built than titanosaurs, so even if a diplococid appears larger in profile than a titanosaur, the titanosaur can still weigh the same amount or more. Still, I have serious doubts that Bruhathkayosaurus is nearly as large as the estimates say. Amphi estimates are based on one detailed drawing of a member of a well-known group. Bruha is based on one extremely poor drawing of a member of a poorly known group. To simplify, as you can see the Bruha in the chart is 34 long, matching the length estimate. For a 34m animal to weigh 140 tons, it would have to be incredibly fat ;) Dinoguy2 (talk) 02:35, 6 June 2008 (UTC)

Gigantoraptor didn't actually preserve any evidence of feathers--it's assumed to have feathers based on its relationship to known feathered dinosaurs. Some larger dinosaurs are also thought to have feathers based on relationships, including Therizinosaurus, which was larger. It's possible that T .rex had feathers, it would have been the largest feathered dinosaur in that case. The largest dinosaur found with direct evidence of feathers is either Beipiaosaurus. Sinocalliopteryx was a bit longer but lighter. Dinoguy2 (talk) 22:06, 10 June 2008 (UTC)