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A Silurian placoderm with osteichthyan - Research Paper Example

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A Silurian placoderm with osteichthyan Summary of Article The ancient fossil register of jawed vertebrates (gnathostomes) is typified by four defined groups, which include the Osteichthyes, Placoderm, Acanthodii and Chondrichthyes…
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A Silurian placoderm with osteichthyan
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Download file to see previous pages In this regard, the Chondrichthyes are deficient of the huge cutaneous bones that typify the Osteichthyes. The Chondrichthyes are regarded as the cartilaginous fish while the Osteichthyes are regarded as the bony fish. The mutual opposition of these distinctions and the body structure of the last common ancestor of gnathostomes have continued to be a topic of consensus among scientists (Zhu et al, 2013). In this paper, Zhu and colleagues (2013) identify and delineate a three-multidimensional well-maintained placoderm fish from Silurian of China with combined features of a placoderm-like cutaneous skull roof, shoulder girdle and braincase with osteichthyan-like cutaneous bones of the mandibular and hyoid arches, and a palatoquadrate sharing obtained attributes with crown gnathostomes. This is a thing that had not been seen before. The phylogenetic analysis revealed that the skull roof is level and sturdily curved horizontally. Most of the braincase of the fish was covered with rounded, central and nape plates, winged by corresponding postorbital, peripheral and frontal and subsequent paranuchal plates along the route of the arterial intraorbital and primary lateral line grooves. Additionally, the petite and thin proboscis constitutes a snout, a premedian and premaxillary those seem to be attached mesially. The Dermal cheek comprised the jugal, maxilla and a quadrajugal with a sensory channel pattern. The trunk armour comprised of attributes similar to those of the early arthrodires such as phlyctaeniid. On the other hand, the analysis revealed that the braincase was wide and flattened, replicating that of the ancient arthrodires (Zhu et al, 2013). This review was executed to identify the phylogenetic position of Entelognathus and the effect of its typescripts on gnathostome organic evolution. The evaluation was carried out using a modified version of the data. Entelognathus was placed with arthrodires, crown gnathostomes and ptyctodonts by the severe accord of 117 most frugal trees. The results of the analysis put several acanthodians under the gnathostome and osteichthyan stem clusters. The phonetic resemblances between the chondrichthyans and acanthodians were translated as symplesiomorphies. Zhu et al’s (2003) results portrayed that the resemblances represent synapomorphies of the chondrichthyan entire cluster. The classification of all acanthodians in the chondrichthyan stem cluster indicates that macronery in the preceding mutual ancestor of crown gnathostomes. The results of the analysis also indicated that Chondrichthyes and Osteichthyes had macromeric cutaneous bones and offered a new theoretical account for reviewing crown gnathostome variance. Personal Response This paper clearly brings out a comparison of the four groups of the jawed vertebrate. It makes it clear to me, as a reader, by indicating that two of the groups are still in existent while two are extinct. Additionally, from my observation, similarities and differences between the groups are well articulated through diagrams through the article. The article explains each of the body structures and skeletons before comparing them. For instance, the article shows that Osteichthyans and Placoderms have macromeric cutaneous skeletons dominated by a huge body plates while Chondrichthyans and Acanthodians have micromeric cutaneous skeletons that primarily consist of scales. The article has brought me at ...Download file to see next pagesRead More
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The genus Dunkleosteus is in the order Arthrodita and family of Dinichthyidae. The Gnathostomata became the dominant organisms during the Devonian Period. Their primary difference to other vertebrates is their vertical biting device or the jaws which "consist of an endoskeletal mandibular arch and a wide variety of exoskeletal grasping, crushing, or shearing organs" including the teeth and the jaw bones (Janvier 2).
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