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The Kelly and Sears (2011) paper (“Limb specialization in living marsupial and eutherian mammals: constraints on mammalian limb evolution”) aimed to test the argument that the functional requirement of newborn marsupials to crawl to the teat is constraining the evolution of marsupial forelimbs. The paper was based on two core hypotheses: first, that marsupial forelimbs are less specialized than eutherian (placental mammal) forelimbs; and second, that marsupials tend to have more specialized hind limbs whereas eutherians tend to have more specialized forelimbs. The first hypothesis was based on the fact that marsupial forelimbs show a small range of possible forms, are very similar among different functional groups, and are less morphologically different from the average mammal than eutherian forelimbs are. The second hypothesis was based on the fact that marsupial young are born with highly developed forelimbs and shoulders, as they are born premature and need to crawl up to the mother’s teat immediately after birth so they can attach and finish developing. Because specialized morphology is necessary at such an early time in marsupial development, the theory is that it prevents variation in the development of the forelimbs and thus reduces the likelihood that they will evolve and specialize. However, marsupials do not use their hind limbs in this post-birth crawl, which leaves them free to diverge and specialize as they develop. Eutherians, on the other hand, tend to have forelimbs that are more specialized than their hind limbs. The proposed theory for this is that eutherian hind limbs are functionally important to locomotion and this constrains how much their morphology can vary, but the forelimbs are not used for locomotion and this leaves them free to evolve and diversify—the opposite of the pattern of limb specialization seen in marsupials.
An observation notes a fact or occurrence using any of the five senses, whereas an inference explains or interprets the observation. For example, today in lab I picked up a bobcat skull and, while looking at its dentition, observed that it had carnassial teeth. This is just an observation because it involves simply noticing a characteristic of an object. Based on this observation it can be inferred that bobcats are carnivores, as only carnivores have a carnassial complex (although not all carnivores do). This inference explains the observation: carnassial teeth are present in this specific skull because the skull belongs to a carnivore.
Kelly and Sears (2011) “Limb specialization in living marsupial and eutherian mammals: constraints on mammalian limb evolution” aimed to test the argument that the functional requirement of newborn marsupials to crawl to the teat is constraining the evolution of the marsupial forelimb, based on two core hypotheses: first, that marsupial forelimbs are less specialized than eutherian forelimbs; and second, that marsupials tend to have more specialized hind limbs, whereas eutherians follow the opposite pattern and tend to have more specialized forelimbs. The first hypothesis was formulated based on the fact that marsupial forelimbs show a small range of possible forms, are very similar among different functional groups, and are less morphologically different from the average mammal than eutherian forelimbs are. The second hypothesis was based on the fact that marsupial young have highly developed forelimbs and shoulders at birth because they are born premature and need to crawl up to the mother’s teat immediately after birth, where they attach and finish developing. This specialized morphology is necessary at such an early time in their development that the theory is that it prevents variation, and thus reduces the likelihood that marsupial forelimbs will evolve and specialize. The hind legs are not used in this post-birth crawl, which leaves them free to diverge and specialize. Eutherians, on the other hand, tend to have more specialized forelimbs and less specialized hind limbs. The proposed theory is that eutherian hind limbs are functionally important in locomotion, which constrains how much their morphology can vary, but the forelimbs are free to evolve and diversify—the opposite of limb specialization seen in marsupials.
To make the figure, I imported the four pictures into Pages. I clicked on each picture and dragged the corners to resize the pictures so that they each had a width of 3 inches, and also cropped each image to a width of 3 inches. I arranged the pictures in a square by putting the picture of the apple alone in the top left corner, the picture of the subject alone in the top right corner, the picture of the interaction in the bottom left corner, and the apple alone after the interaction in the bottom right corner. I dragged the cursor to select all four pictures at once, right-clicked and selected “Group” to make the four individual pictures into one single image. I inserted a text box in the lower right corner of each photo. In each text box I typed a label for each image: “a.”, “b.”, “c.”, “d.”. Each letter was lowercase and followed by a period, in 15pt Times New Roman font, and had a centered alignment. I arranged the letters such that the picture with the apple alone was “a.”, the picture with the subject alone was “b.”, and the pictures with the interaction and the aftermath of the interaction were “c.” and “d.” respectively. I selected a text box, opened the “Format and Style Options” tab in the upper right corner of the document, then selected “Style”, and from the available options I picked the shape style with the black background and white text. I repeated this for each text box. I moved each label to be flush against the lower right corner of its respective picture, and resized the labels so that they each had a width of 0.60 inches and a height of 0.54 inches. I used the cursor to select the entire image, right-clicked and selected “Group” to integrate the labels into the final image. I went to File, “Export to” and selected “PDF”, setting the image quality to “Best”. I opened the .pdf file that was generated, and used the crop tool in the toolbox to select just the image and crop it. I saved the image—now without the white document background—and the figure was complete.
I took my pictures in the middle room of the Worcester Dining Commons, at a long table on the left side (if facing the sandwich bar) about halfway down the room. I selected an apple from the basket in the Asian room (Oak Room). The apple I selected was small enough to comfortably in the palm of my hand, and was irregularly shaped despite my efforts to pick an apple that was as uniform as possible. I took pictures of the apple with a ruler placed in front of it for scale, then took pictures of the subject who would be eating the apple holding the same ruler. The subject was a friend of mine who agreed to help. I asked the subject to sit facing the windows, so that when taking the pictures my back would be to the light. This was intended to reduce the amount of glare in the pictures and increase visibility of the subject. To document the interspecies interaction, I asked the subject to take a bite out of the apple. I had him facing away from me and towards the tv so that I could take the picture in profile, ensuring that he, the apple, and the interaction between them would be clearly visible. I documented the aftermath of the interaction (the apple with a bite taken out of it) in the same manner as previously, with the ruler placed in front of it for scale, making sure that the bite was clearly visible in the photo.
In the Luo 2007 article “Transformation and diversification in early mammal evolution”, Figure 1 shows that modern carnivores did not descend from Repenomamus. Node 3 in the figure shows that modern carnivores share a common ancestor with Repenomamus, however the Figure also shows that after this common ancestor a diversification event occurred. One of the resulting branches of this diversification was the order eutriconodonta, and Repenomamus was a genus in one of the subgroups of the eutriconodont order. Further separate diversification events lead to groups such as the multituberculates, the spalacotheroids, the stem cladotherians, and the stem boreosphenidans. Modern carnivores share a more common recent ancestor with the stem boreosphenidans than with the eutriconodonts, and the fact that the genus Repenomamus had branched off long before this common ancestor shows that modern carnivores did not descent from Repenomamus.
Molecules encounter strain when their chemical structure experiences some stress which leads to an increase in its internal energy. A strained molecule therefore has a greater amount of internal energy than an unstrained molecule, and only the bonds holding the molecule together prevent the release of this potential energy. Two types of strain are steric strain and torsional strain. Steric strain (also known as Van der Waals strain) occurs when atoms are forced closer together than is allowed by their Van der Waals radii allow. The size of the groups that interact determines the amount of steric strain on the molecule. Torsional strain is dependent on conformation, and occurs when atoms that are separated by three bonds are put in an eclipsed conformation instead of a staggered conformation. This brings the atoms into close proximity and increases their potential energy, which makes the conformation unstable. Torsional strain can resist bond rotation.
Figure 1. Seal- Point coloration In Cat. Cats with seal-point coloration are characterized by a beige colored body; dark brown ears, legs, and tail; and blue eyes. Photo by wapiko☆ available at: https://www.flickr.com/photos/wapiko57/6485554303/in/photolist-aT7akM-oeE5Rz-7Gk6tA-9FjWdg-nRPFr9-icrTAE-9BoHbr-7ca5oc-rbR7a7-eThqYx-roUC7z-a16dos-ahuXf8-8kcQvm-ftStXC-bhSTNx-djzcez-2cYgLsm-cPFfoq-drxap4-nuxVgB-nKbfp3-r2R9M6-r6ud1t-9YtoNu-bsyM7j-2dvnm21-TB7gmW-pUVx5E-a7eijz-ehRHug-dEtDjV-jaE9xb-9jPwYH-g8AtE4-iWEJPL-9BJiXF-BMkFXA-qVYoj6-9pMdEi-e1u5tE-piv3bR-bsiGD5-p2i2j6-agibV3-krcvUD-eDobk7-djzdBB-quyNsV-rRUeFg under CC by 2.0 license