tag:blogger.com,1999:blog-4495945046934115087.post1522775204037119922..comments2023-10-28T09:11:00.756-04:00Comments on Self-designed Student: Centrosaurines vs. ChasmosaurinesAmandahttp://www.blogger.com/profile/01477707480338232435noreply@blogger.comBlogger10125tag:blogger.com,1999:blog-4495945046934115087.post-8692408298196518882008-02-08T10:14:00.000-05:002008-02-08T10:14:00.000-05:00Again I'm late to the game; I feel like such a slo...Again I'm late to the game; I feel like such a slouch. Thanks for clearing up the issue about the supracranial cavity opening, Jerry. Every time I saw that mount I couldn't help thinking that someone had taken a drill to the skull to try to get at the brains of the animal and couldn't seem to find why that hole was there.<BR/><BR/>Thanks for the kind words, too, Amanda. That trip was a lot of fun, and I'm glad I was able to inspire one of your blog posts! I didn't really know about the difference (other than there was a difference) myself until I read Dodson's horned-dinosaurs book, which is a good introduction if you get the time to read it. (Of course a ton of new horned dinosaurs have been added since then so an expanded/updated edition is definitely needed.)<BR/><BR/>And if anyone <I>really</I> wants to confuse themselves about homology/analogy, read some of Cuvier's work and that of other naturalists of his day. He used "analogous" to mean what we mean by "homologous" today, which can be a bit confusing.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-46267611690568353502008-01-31T02:20:00.001-05:002008-01-31T02:20:00.001-05:00This comment has been removed by the author.traumadorhttps://www.blogger.com/profile/00387315561167115253noreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-21027501649316343122008-01-31T02:20:00.000-05:002008-01-31T02:20:00.000-05:00Centrosaur Brinkmani, DPP Pachyrhino (which as you...Centrosaur Brinkmani, DPP Pachyrhino (which as you'll recall I thought was Albertoceratops... having JUST visited the Tyrrell for the first time in over a year I've got that a little straightened out) there is a rumoured new ceratopsian in Texas (according to the technicans at the Tyrrell mind you)...<BR/><BR/>I'll get the definative list from my buddy who claimed this stat as fact, but that's 2 more for sure, and one possible extra.traumadorhttps://www.blogger.com/profile/00387315561167115253noreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-42459694427683075632008-01-30T19:00:00.000-05:002008-01-30T19:00:00.000-05:00Traumador, I'm only aware of Albertaceratops, Kirk...Traumador, I'm only aware of Albertaceratops, Kirkland's new "octoceratops" (still doesn't have a name), a known species of Chasmosaurus getting its own genus (Agujaceratops), and Eotriceratops. Okay, that's a lot, but technically that's only three new animals. Are there more? Am I missing something? I MUST KNOW!Zachhttps://www.blogger.com/profile/08692080707969333711noreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-3123495122245402992008-01-30T18:07:00.000-05:002008-01-30T18:07:00.000-05:00Non-homologous means it is not the same as....in a...<B><I>Non-homologous means it is not the same as.</I></B><BR/><BR/>...in an evolutionary sense, of course. I'm not the same as my car, but that doesn't mean my car and I are nonhomologous, since homology (evolutionary identity) doesn't come into play in such a comparison. (Not correcting Zach, here, since I know that this is what he meant; just putting in a clarification for any other readers that might not be as familiar with the terms "homology" or "homologous" -- you never know; this could be the entry that comes up in some Google search for the term!) Specifically, homologous structures (anatomical, but also behaviors, gene sequences, etc. -- the term applies equally well to genotypic and phenotypic studies) are ones that share an evolutionary ancestry -- homologous structures are those that exist in different taxa because the structure evolved <I>once</I> in a common ancestor of all the organisms that have the structure, and was simply retained (though it can be heavily modified!) in all the descendants of that ancestor.<BR/><BR/>An <I>analogous</I> structure (or gene sequence, behavior, etc.) is, instead, one that arose separately in taxa that don't share a recent common ancestor. It's usually relatively easy to tell whether or not this is true by looking at a broad swath of descendants of an ancestor -- if most of them lack the structure, odds are better that it evolved convergently, but separately (analagously), in the few that have it rather than saying it evolved in a common ancestor but was lost a large number of times. This is because of the "rule" of parsimony -- convergent evolution a few times is a much more simple explanation than loss a large number of times, though the latter is certainly possible.<BR/><BR/>My favorite examples for discussing homology vs. analogy involve things like patellae (knee caps) -- neornithean birds have them and mammals have them, but the taxa that are ancestral to birds and the taxa that are ancestral to mammals lack them. Mammals and birds share a common ancestor, of course (the first amniote), but it's most parsimonious to perceive that the knee cap evolved twice (once in derived birds, once in mammals). It leads nicely to discussions about evolutionary constraints and how they select for particular features in only distantly related organisms -- convergence (analogy) can run rampant!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-44245158786425292342008-01-30T17:52:00.000-05:002008-01-30T17:52:00.000-05:00Too bad you missed the BIG ceratopsian symposium a...Too bad you missed the BIG ceratopsian symposium at the Tyrrell last year (I missed it too *tear*)...<BR/><BR/>There's a ton of new stuff on them in the last few years. They've nearly doubled the number of known ceratopsians in this small window of time.<BR/><BR/>Can't help you on your skull opening question though :(traumadorhttps://www.blogger.com/profile/00387315561167115253noreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-35233545941130692132008-01-30T16:42:00.000-05:002008-01-30T16:42:00.000-05:00Non-homologous means it is not the same as. For ex...Non-homologous means it is not the same as. For example, let's say that bugs suddenly evolved backbones. If the backbones were homologous, that would mean that their spines are in some way related to OURS, but because they evolved the spine independantly, it is NONhomologous.<BR/><BR/>Let's use a dinosaurian example. Ceratopsians, as you probably noticed, have enormous parrot-like beaks. However, the beaks are not homologous to those of actual parrots, or turtles for that matter. The structures evolved independantly.<BR/><BR/>Also, thanks for using me as a reference! I'm glad people still find that old blog useful! I really need to do a ceratopsian post with my own picture...Zachhttps://www.blogger.com/profile/08692080707969333711noreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-71128314507931127472008-01-30T16:40:00.000-05:002008-01-30T16:40:00.000-05:00I'm not sure what you mean by nonhomologous. Is th...<B><I>I'm not sure what you mean by nonhomologous. Is that the same as analogous?</I></B><BR/><BR/>Essentially, yes. It's a bit harsher (in the sense of drawing extra attention to the evolutionary implications) to say "nonhomologous" as opposed to "analogous," but yeah, the two are basically synonyms. But as I like to tell my students, "If <I>everyone</I> knew and used all the technical jargon, then getting a Ph.D. wouldn't be nearly as impressive, now, would it?" ;-DAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-23907428116699023342008-01-30T16:23:00.000-05:002008-01-30T16:23:00.000-05:00Thanks Jerry :)I'm not sure what you mean by nonho...Thanks Jerry :)<BR/><BR/>I'm not sure what you mean by nonhomologous. Is that the same as analogous? Thanks!Amandahttps://www.blogger.com/profile/01477707480338232435noreply@blogger.comtag:blogger.com,1999:blog-4495945046934115087.post-34914357701021444832008-01-30T15:55:00.000-05:002008-01-30T15:55:00.000-05:00Also, you'll notice, in the photo of Chasmosaurus,...<B><I>Also, you'll notice, in the photo of Chasmosaurus, a round opening in the skull slightly above and between the orbital sockets. From what I know, this opening is called the pineal foramen, frontoparietal foramen or postfrontal foramen, though I believe the latter is an out-of-date term. I haven't been able to find much information on this particular part of the skull, nor do I know if it is specific to certain families of Ceratopsians, though I do remember Brian telling me something about it at AMNH.</B></I><BR/><BR/>Actually, what you're seeing in the photo isn't the opening of which you speak, although it's related to it. What you're seeing there is a kind of notch that leads to a compartment called the supracranial cavity. The opening you're referring to (the frontoparietal foramen) is on the floor of this supracranial cavity. The foramen is, apparently, nonhomologous with the parietal foramen (the correct name for what is often called the pineal foramen or pineal "eye"), and its function is unknown. For that matter, I'm not sure if there's a decent explanation for the supracranial cavity, either, but then again, I'm one of those Saurischia snobs*... ;-D <BR/><BR/>*Actually, I like ornithischians just fine -- well, except maybe hadrosaurs -- I've just not had any good opportunity to work on any short of sculpting missing parts for and mounting a bunch of <I>Othnielosaurus</I> juveniles, and mounting an <I>Edmontosaurus</I>, at the Denver Museum.Anonymousnoreply@blogger.com