Endotherms are animals such as modern birds and mammals that keep their body temperatures constant. For instance, humans are endotherms and maintain an internal temperature of 37°C, no matter whether the environment is warm or cold. Because dinosaurs were reptiles, and modern reptiles are not endotherms, it was long assumed that dinosaurs were not endotherms. However, dinosaurs differ in many ways from modem reptiles, and there is now considerable evidence that dinosaurs were, in fact, endotherms.
Polar dinosaurs
One reason for believing that dinosaurs were endotherms is that dinosaur fossils have been discovered in polar regions. Only animals that can maintain a temperature well above that of the surrounding environment could be active in such cold climates.
Leg position and movement
There is a connection between endothermy and the position and movement of the legs. The physiology of endothermy allows sustained physical activity, such as running. But running is efficient only if an animal's legs are positioned underneath its body, not at the body's side, as they are for crocodiles and many lizards. The legs of all modern endotherms are underneath the body, and so were the legs of dinosaurs. This strongly suggests that dinosaurs were endotherms.
Haversian canals
There is also a connection between endothermy and bone structure. The bones of endotherms usually include structures called Haversian canals. These canals house nerves and blood vessels that allow the living animal to grow quickly, and rapid body growth is in fact a characteristic of endothermy. The presence of Haversian canals in bone is a strong indicator that the animal is an endotherm, and fossilized bones of dinosaurs are usually dense with Haversian canals.
The reading passage suggests three reasons that support the idea that dinosaurs were endotherms. However, the lecturer insists that those explanations are not convincible.
Firstly, the lecturer states that when dinosaurs were alive, polar regions were warmer than these days, so not endotherms could also live there. In addition, they might have moved to warmer areas or hibernated during unendurable cold seasons. It counterargues the reading passage’s point that dinosaur fossils found in polar regions support that they were endotherms, unlike the modern reptiles.
Secondly, the lecturer mentions that legs positioned underneath a body do not necessarily mean they had used them for running. Their leg positions might have been determined for supporting their large bodies – being larger was beneficial for them. It contradicts the reading passage’s statement that dinosaur’s leg position indicates that they were endotherm.
Thirdly, the lecturer insists that they were not growing quickly all the time, and it is supported by growth rings on their bones. The growth rings are made when the speed of growing is changed, such as fast, slow, fast, and slow. It shows dinosaurs grew slowly during cooler periods, different from endotherms, which can also grow rapidly during cold periods. It disputes the reading passage’s idea that dinosaurs’ Haversian canals imply they were endotherms.
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Attribute Value Ideal
Final score: 23 in 30
Category: Good Excellent
No. of Grammatical Errors: 1 2
No. of Spelling Errors: 6 2
No. of Sentences: 12 12
No. of Words: 212 250
No. of Characters: 1147 1200
No. of Different Words: 132 150
Fourth Root of Number of Words: 3.816 4.2
Average Word Length: 5.41 4.6
Word Length SD: 2.487 2.4
No. of Words greater than 5 chars: 84 80
No. of Words greater than 6 chars: 69 60
No. of Words greater than 7 chars: 44 40
No. of Words greater than 8 chars: 32 20
Use of Passive Voice (%): 0 0
Avg. Sentence Length: 17.667 21.0
Sentence Length SD: 3.923 7.5
Use of Discourse Markers (%): 0.583 0.12
Sentence-Text Coherence: 0.378 0.35
Sentence-Para Coherence: 0.378 0.50
Sentence-Sentence Coherence: 0.088 0.07
Number of Paragraphs: 1 4