Summarize the points made in the lecture, being sure to explain how they challenge the specific theories presented in the reading passage.
Certainly, there are different assumptions, and doubts about how agnostids may have lived 450 million years ago. Basically, agnostids were a group of marine animals that had similarity in some aspects to modern-day insects. The reason why paleontologists cannot be sure about how agnostids behaved or what they ate is that their fossil does not give paleontologists precise information. As a result, there are three theories among other theories that have been discussed in the passage. Although, these theories are rejected by the represented points in the lecture. Here we go to analyze these points: The first theory that has been mentioned in the passage is called "Free-Swimming Predators." This theory explains; the agnostids were predators that hunted smaller animals, or organisms that were prey to them. In the opposite viewpoint, the lecturer explains due to their small eyes and inadequate vision, and having no special sensory organs, they could not be a predator. The second theory is called "seafloor Dwellers." This theory describes; the agnostids may have dwelled on the seafloor, and living by scavenging dead organisms or by grazing on bacteria. The lecturer rejects this theory too. The reason is that seafloor animals were slow and localized. On the other hand, the agnostids were fast animals, and they had different habitats. In the third theory, the agnostids have been supposed as parasites. This theory creates the possibility that the agnostids were parasites, which living on and feeding off larger organisms such as; primitive fish or larger arthropods. However, the lecturer disagrees with this theory. Since parasites are not large in population, and if they are then they cause to death of the host body. So this theory cannot be correct. In conclusion, there are various theories about how agnostids may have lived, but there is not enough data to be sure of that. Consequently, there should be more investigations on this subject.
Submitted by Javad on