Finally back for some discussion of saber-tooth cats, nimravids, and barbourofelids. There are two complementary articles that appeared almost simultaneously regarding the shape of the saber-tooth skull. Skull shape was examined by mapping various landmarks on different species’ skulls and measuring the change in position of these landmarks compared to average values.
Ends up that my thesis revisions ate my brain too. That’s all finished now, but I’m leaving on vacation and am just out of time for writing! However, I will post on the saber-tooth papers on the 26th or 27th after I come back from vacation.
Who would have thought getting a Ph.D. would be so distracting? After dropping off the face of the earth, I wrote my thesis and successfully defended last Friday. I still have things to wrap up (revisions!) but will then take a couple weeks off before beginning a post-doc. I hope I can say that I’m back now, but probably will not be able to return to my previous posting rate for a while—perhaps I can incorporate some of the reading I’ll do getting up to speed for my post-doc into blog posts.
Yesterday I checked up on some of the paleontology journals that have had new issues come out in the past couple months and was elated to find not zero, as usual, or even one or two, but three papers on saber-toothed predators! I will be writing a post about these, and rounding up links to discussions on other blogs.
I’ve been incredibly idle here, so I wanted to give an update. I’ve been working extensively on writing my thesis for the past couple weeks. It’s going pretty well, I hope to have the first complete draft done by the end of next week. I don’t think I need to be in such a rush, but I want to have it hammered out well before my defense. Perhaps then I will be able to post more here. At the moment I’m trying to keep my evenings clear, but after writing all day I don’t have any energy for reading and writing even more!
This has also coincided with a dearth of really interesting papers, although I haven’t really had time to do much more than skim the abstracts. However, this week produced some interesting papers that I’ve set aside for possible later coverage here, unless something even cooler comes up!
I’ve been much delayed, since I am starting to work seriously on my dissertation. This sucks up an amazing amount of brainpower. Initially I was planning on delaying this post another day, but have now been fortified with a BLT (heavy on the bacon) and am ready to tackle the topic. It is one that interests me because it combines two fascinating topics, malaria and sex ratios.
Just a quick round-up of some links. On the same day I wrote about Gerobatrachus hottoni PZ Myers at Pharyngula also posted regarding the transitional amphibian, including a beautiful photograph of the fossil. I also logged in a few days ago to find to my surprise that my recent post on the non-necessity for mice of some genes that are required in humans was included in the Gene Genie blog carnival. This blog carnival covers human genetics, usually focusing on the field of medicine. Medicine is another interest of mine (I skim New England Journal of Medicine and The Lancet weekly), but since this blog is focusing on evolutionary biology I haven’t covered medicine much here, and it hadn’t occurred to me that post would meet inclusion in Gene Genie! You can read the current Gene Genie at Highlight Health. I also read the medicine-themed blogs Denialism and Respectful Insolence, so check those out if medicine interests you.
I checked in on Nature earlier, since a new issue comes out tomorrow, and find that there’s an article combining two favorite topics of mine—malaria and sex ratios. I can only read the abstract from home, so I hope the suspense doesn’t keep me up too late. I anticipate that paper will show up on my blog shortly.
A PAPER PUBLISHED recently in Nature details the discovery of a common ancestor of salamanders and frogs, Gerobatrachus hottoni, by Anderson and coworkers. This creature had a salamander-like build, but has a broadened skull like frogs. A variety of traits were studied to determine this organism’s relationships, such as the teeth, various skull bones, presacral spine, and otic notch. Its position in the early Permian places the frog/salamander divergence in the Middle Permian, about 270-260 million years ago. Of course this find is interesting, but I was perhaps more interested by the phylogenetic tree that they composed including this new species.
ANIMAL MODELS are widely used in medical research, sometimes in testing new drugs for safety before human trials, other times as model systems for human diseases. Like all mammals, humans and mice share most of their genes, and maintain high sequence similarity. These factors suggest that many of these genes should share the same role. A new study in Proceedings of that National Academy of Sciences examines this hypothesis.
I HAD PLANNED on covering the article on the platypus genome that came out in Nature last week, but since then this paper has been discussed in detail on Pharyngula and Adaptive Complexity and I think further discussion would be moot. I did notice while reading the paper that the unfortunate description of certain platypus genes as “reptilian” cropped up frequently. Although the authors noted that the sauropsids and synapsids are amniotes, they never mentioned that platypus genes shared with reptiles are actually basal amniote genes. Although their phylogenetic tree shows synapsids and sauropsids clearly diverging from a common amniote ancestor, they do not seem to realize referring to these ancestral amniote genes as “reptilian” suggests evolution of the platypus (and thus all synapsids) from reptiles instead of from a non-reptilian amniote.
However, today I want to talk about the platypus’ sex chromosomes. Platypuses, like the therians, have genetic sex determination. They have an XX/XY system in which males (XY) are the heterogametic sex. Many reptiles have environmental sex determination, with sex determined by factors such as incubation temperature during embryonic development. However, some reptiles and all birds have a ZW/ZZ sex determination system, with females (ZW) as the heterogametic sex.
LET’S SUPPOSE that we are interested in studying the evolution of the squamates, the snakes and lizards. We know that if we track down the evolutionary tree of the squamates we find that they are lepidosauromorphs, and a sister group to the archosauromorphs. Ah-hah! The archosauromorphs diverged before the evolution of the lizards, so living archosauromorphs must preserve ancestral traits, we think. So we go forth and find an archosauromorph and sequence its genome. There are multiple species from which to choose, but we grab the closest one—the European starling. Since this is an archosauromorph and early diverging compared to the snakes and lizards that must mean that it is “primitive”.
Does this seem odd to you?