Interesting bone evolutions

I wanted to write about the new things that I have been learning this year particularly about bone fusion and its evolution through time. It all stems from the benefits that osteological (bone) fusion can have for a subject. Quite a common usage of increased bone surface area is for muscle attachment. For muscles to be effective, they must latch on to the bones that they act on sufficiently to move them an adequate amount. Muscles themselves can only contract a set amount, approximately 60% of their length. Therefore, decreasing the distance a muscle has to contract to complete a set movement makes the movement far more powerful. This is exemplified in jaw and skull evolution particularly from mammal-like reptiles (MLRs) to modern day mammals. Early mammals began their lives with their lower jaws made up of several bones. What that has developed into is that a single bone (the dentary) now makes up the lower jaw of mammals, joining with the squamosal (lower back bone found on the skull). The additional bones that previously made up the lower jaw in MLRs have now shrunk and manoeuvred themselves to positions where they now are vital components of the inner ear. This has led to increasingly detailed audio information to be taken up by mammal predecessors as more vibrations can be taken up these bones. This is a really interesting topic, and I might go into more detail on this in a later post, but for now this page is a good starting point:
http://evolution.berkeley.edu/evolibrary/article/evograms_05
As for relation to muscles, mammals are part of a group or clade of animals known as synapsids from the prefix "syn-" which relates to fusion, but that's for a later date. What this means is that they have one temporal fenestrae. Deriving from the latin word for "window", these are holes in the skull. Dinosaurs and birds are examples of diapsids, with 2 (di-) temporal fenestrae, and turtles are anapsids, with no fenestrae at all. The inclusion of these fenestrae in the skull structure not only splits up the bones that make up the skull itself, but also the muscles that are related to it. We can see what we might think of as primitive traits in anapsids (no fenestrae) that employ one large set of jaw muscles, known as the adductor mandibulae. Mandibles are the name given to the mouth-parts of spiders and some insects, so that name is reasonably easy to remember. Adduction is the act of muscles pulling bones towards the midline of the body, as opposed to ABduction. Adductors can also be found in the thighs, and is quite a general term. However, with the inclusion of fenestrae, the adductor mandibulae is split into 2 muscles. This is where we start to see why fenestrae are a good idea. Because the previously single muscle group is split into 2 shorter groups, the effectiveness of these muscles is increased as they have to move less of a distance to complete their task. As we said earlier, muscles want to move a shorter distance, so many smaller muscles doing the work of one large muscle is energetically favourable. The whole concept of jaw movement is really interesting, and the more complex it gets, the more it allows for different styles of physical digestion (chewing) and so different lifestyles for the animals involved. Another good page to look at for jaw evolution:
http://www.mhhe.com/biosci/pae/zoology/kardong/instructor/jaws_muscle.pdf
In dinosaurs, we saw what might be the pinnacle of herbivorous eating mechanics in hadrosaurids (a type of duck-billed dinosaur descended from Iguanodon and other iguanodontids). The hadrosaurids developed what is known as kinetic jaw mechanics. First, a quick note about herbivorous eating habits. When digesting plant material, because plant cells have a large amount of a compound called cellulose in them, they are difficult to digest normally because cellulose is a tough material that makes up a plant cell wall, which animal cells don't have (no need to get any more technical yet). Therefore, herbivores want to chew their food as much as possible to break down the material so their digestive juices can do as thorough a job as possible at taking out nutrients from the plants. So, back to kinetic jaw mechanics. This allow hadrosaurids to not only grind their top and bottom layers of teeth forwards and backwards, but also from left to right. This gave a bigger range of motion for the grinding teeth of hadrosaurids so they could squeeze out as much nutrition from the plant matter as possible. This is a really good animation of the motion to visualise what I'm going on about
https://www.youtube.com/watch?v=DZkYcyYdZJU&list=PLBDCC26DA4441F47D
That's all for now, I hope you enjoyed and if you have any questions I'll try to answer. I'm no expert in the field, I just think this information isn't always fully available and appreciated by the public and I want to share my interests so I'll answer as best I can.
Cheers

Fixed gear

During recent weeks, I have become more inclined to look into the possibility of fixed gear cycling. Just to state off the mark, I'm not a self-declared adrenaline junkie looking to flash through every possible red light, flipping of cars and hanging onto trucks just to "get a fix". For those out there who do so, I wouldn't say we share a great deal on the merits of cycling. Much as I love cycling fast and killing it past the river and racing every commuter I have the fortune of coming across, I'm far too accident-prone and indecisive to ensure that every time I get away with my body still in one piece. Nonetheless, the whole business of braking and relying entirely on a couple of small bits of rubber to stop all my momentum has got my thinking, and to be honest quite concerned. Over the summer I decided to finally take a change and have a go at making my own single-speed bike. I have to say, despite my previous assurances of not being a high heartbeat chaser, I am quite enamoured with the whole bike messenger culture. But perhaps not in the way of everyone else. To me, being self-reliant and constantly prepared is something I have always found admirable. Seeing these guys out in all elements with nothing but their shorts, bikes and bags has been something of a revelation to me. That's why, every morning, I make sure to pack my bag with everything I could possibly need for the day ahead. In truth I do have to cut back because the amount of stuff you can find yourself shoving in because you might need it grows exponentially day after day. But that feeling of someone asking you if you've brought any tools that could help them fix up their bike, or just get through a lecture or test, and then pulling an endless stream of handy objects out of your bag to their amazement is something I aspire to. But more on that in another post, I've already started rambling...

I recently read on someone's website about the merits of fixed gear riding. They were talking about the braking aspect of it, and said they would much rather have the option of relying on their own power to stop them rather than cycling under the false-pretences of their brake pads being up the job, no matter the speed they are travelling at. And it's entirely true. I think the vast majority of people don't really think about the amount they rely on their brakes. Stopping an average weight person on a bike travelling at a decent cruising speed is a lot to ask. And fair play to the brakes, they have usually been good, sturdy companions that I can rely on. But then you get the odd days, particularly with a first-project bike, when the brakes turn to mush, and you squeeze the levers to feel absolutely nothing. That's when the panic sets in, and you realise that there is nothing you can do to stop the bike effectively. You relied on something all this time, and this one time it's let you down. That could well be that. In my past experiences of brake failure, they've ranged from bus bouncing to avoiding ladies with prams, neither of which were altogether pleasant experiences. But then, you'll rarely find anyone on the web talking about the merits of fixed gear safety. However they all talk about a totally different "feel of the road". I think this ties in very well with the braking point. When your brakes are spongey, or it's raining and nothing is going right, you have to be self-aware. You are always alert, always spotting when things are going to happen. That's what has changed most about my cycling this year. I'm not going to pretend that I see everything that's happening/going to happen, but certainly I see way more than I ever used to. That's what allows you to take the smart option, and in some cases, to survive. Exposing yourself to that environment allows to take on a totally new view of the road, literally. That's partly why I feel quite comfortable now changing to fixed. Mentally I think I'm prepared for it, just the physical side to go now. I'll update on the transition as I go, and I'll include any gory details for those who love a good saddle-scraper.