Origin and Evolution of Tetrapods and Fossils - Term Paper Example

Affiliation: Fossils and their Interpretation Essay - Eusthenopteron Eusthenopteron is the genus of the prehistoric sarcopterygian. The same genus was oftenly called the lobe-finned fishes, which has managed to attain the iconic status due to its close relationship to the tetrapods. The early definition of this type of animal shows that it emerged from water onto the land, but some contradiction arises in the essence that some paleontologists are agreeing widely that this animal was strictly aquatic. This genus (Eusthenopteron) receives the acknowledgement from other several species that were existing during the time of Late Devonian period, which is about 385 million years ago. Several paleontologists have managed to collect close to 2000 Eusthenopteron specimens, which have been effective at providing room for the detailed study of this species. Basing on the anatomy, Eusthenopteron shares several unique features that are common with some earliest known tetrapods. The largest individual was capable of growing up to 1.8 meters in length, while is also shares the similar pattern of the skull roofing bones with other forms, such as Ichthyostaga and Acanthostega. Eusthenopteron like any other tetrapodomorph fisheries had internal nostrils, which are only found in the land animals. From this fossil, one can develop a thesis that all creatures developed from a transition of other creatures. The image of this fossil is as shown below; Figure: Eusthenopteron foordi. University Museum of Zoology Cambridge specimen GN. 786. Scale bar is 10 millimeters. Photograph by JAC Pathologists Jennifer A. Clack (2002) believes that Eusthenopteron showed some characteristics of crawling across the dry landscape with the help of its fore fins while moving around. This fossil also shows that it had labyrinthodont teeth, which are characterized by the infolded enamel, which also characterizes the rest of earliest known tetrapods as well. Similar to any other fish species, Eusthenopteron posses a two-part cranium, which hinged at the mid-length along the intracranial joint. Then the notoriety of this fossil comes from the common pattern of its fins, which bears some distinct humerus, ulna, and the radius, the femur, tibia and fibula. The appendicular long bones of this fossil shows that it had some epiphyseal growth plates that were essential at allowing substancial longitudinal growth through the endochondral ossification, as similar to the case of tetrapod long bones. The genus has six appendicular bones that also occur in tetrapods and are thus a synapomorphy of the large clade of sarcopterygians, which is also possibly the subclass Tetrapodomorpha. This genus also lacks some superficial odontodes on its elasmoid scales, which are composed of the dentine and enamel. The lack of such similarities implies that there is a synapornorphy with more crownward tetrapodomorphs. The genus Eusthenopteron also differs from the later Carboniferous tetrapods basing on the apparent absence of some recognized larval stage and the definitive metamorphosis. But on the even smallest known specimens of the Eusthenopteron foordi, when it attains a length of 29mm, the lepidotrichia is able to cover all the fins, which on the contrary do not happen with after metamorphosis occurs in the genera like Polyodon. This has the implication of stating that Eusthenopteron developed directly, with its hatching already managing to attain the general body of the adult species. This therefore implies that Palaeospondylus gunni might not have been the larva of Eusthenopteron. The author responds to these claims about Eusthenopteron with some sort of analysis. There are emerging issues that now, nearly 20 years of which this subject has undergone a renaissance; there is much enriched fossil record to draw implications from. However, much of this recent work is yet to reflect on the popularity of the accounts on this subject. There is some assumption that Devonian tetrapods and the respective close fish relatives originate from the worldwide localities, and though the process is still rare. The new cast of characters is able to provide people with some information on which to base their ideas from. For instance, the sequences under which tetrapod characters are obtained, then the sorts of environment that they lived on, and the timing of some events that are leading to the origin of these tetrapods are all becoming approachable means with the use of fossil records. More so, some questions are becoming much easier to answer through the use of developmental and genetic studies of the modern animals. The first story that develops while assimilating the understanding of the new story about the origin of Eusthenopteron is basing on phylogeny, which states on the manner of which the animals in question are relating to each other. Coming up with an understanding of this evolutionary relationship provides room for some testable hypothesis, which helps in understanding the order under which tetrapod-like characters were able to appear. This can thus suggest some hypothesis on how or for what reasons these characters were able to rise. The emerging issues now implies that there is now a good form of consensus in the paleontological community basing on the relationship of texa that represents transitions, though such claims will always remain provisional. Tetrapods as the group belong to the lobe-finned vertebrate, of which who’s only other modern representatives evident in coelacanth and the lungfishes. All of this had a common ancestor in the Early Devonian period, implying that despite their relation, they are also specialized in their own way. The most recent evidence implies that lungfishes are the most related to the Eusthenopteron subclass, despite the early conception that stated coelacanth as the iconic “tetrapod ancestor”. The lobe-fins are quite distinct from ray-fined fisheries, which is the group of which almost all fish belong. An individual breakdown on these concepts and theories shows that Eusthenopteron is basically a tetrapodomorph that originates from the early stages of the Late Devonian. It is a fact that Eusthenopteron belongs to the tristichopterids family, although it is only still a primitive member. This implies that it is necessary to check on whether some cited features were present in the more primitive members, or whether it was just an evolution from the works of transitions. It is an assumption that Eusthenopteron grew up to a meter long. This is based on the fact that its fin skeleton has some substantial humerus, radius, and the ulna, as well as having some skeletal elements, which have been able to provide the baseline of which the limb evolved. This has been known since the early periods of twentieth century, when combination of research and theories provided some basis of understanding in the many transformation scenarios. In conclusion, it is important to evaluate the thesis, which states that “all creatures developed from a transition of other creatures”. This is important basing on the fact that the recent discovery of fossils shows some common resemblance to other creatures of the past. For instance, the recent part of the skull of the fossil fish shows similarities with the deposits available as Eusthenopteron. Although this is only known as the partial skull roof, large proportions of it seem to be more of tetrapod than just of any other fish. Thus, it is subject for developing an understanding that fossils are only transitions from other creatures. Works Cited Clack, J. A. Gaining ground: the origin and early evolution of tetrapods. Bloomington: Indiana University Press; 2002 p. 369 Read More