Did you happen to notice that most of those "quotes" are 30 years old or more?
Here's a tip; if you see a quote of a scientist from a creationist, check the source. It's either a lie or taken out of context or both.
Here's a brief introduction to how evolution occurs, and why we wouldn't expect to see an unbroken continuum of ring species.
First, organisms don't evolve. They stay the same species their entire lives. What evolves is populations. In any given population of organisms, there is going to be a variety of genotypes. That variety will be different in the next generation of the population. Some of that difference will be due to differential reproductive success. In other words, some members of the original population will be more successful at passing their genetic material to the next generation. Some of the difference will be due to mutations from one generation to the next.
Occasionally, populations will split; some portion of the population will go one way and some portion will go another. These two daughter populations can become reproductively isolated from one another. When that happens, they will evolve differently from one another. After enough time has passed, they can become completely different species. Because they are reproductively isolated, there is no intermixing of the genetic material between the two populations. As such, they can evolve in opposite directions (one population produces bigger organisms and the other produces smaller), or they can evolve in completely different ways (one population becomes better at camouflage and the other develops a toxin). In this second instance, there's no reason to expect any kind of intermediate population because there never was a population halfway between the characteristics of the two populations.
This is a very simple description of the process and leaves out a lot of detail, but I think it shows why there's no reason to expect that all organisms will consist of ring species. However, occasionally we do see exactly the kind of thing that you are talking about. We refer to those as
ring species. For more information, click the link that I have created referring to the Wikipedia description of them.
Ridicule is the only weapon which can be used against unintelligible propositions. -- Thomas Jefferson
We see monsters where science shows us windmills. -- Phat
It has always struck me as odd that fundies devote so much time and effort into trying to find a naturalistic explanation for their mythical flood, while looking for magical explanations for things that actually happened. -- Dr. Adequate
...creationists have a great way to detect fraud and it doesn't take 8 or 40 years or even a scientific degree to spot the fraud--'if it disagrees with the bible then it is wrong'.... -- archaeologist