Biology of the Vertebrates FAQ's

Here we will post many of the questions that we receive from you, and answer them, as they come in. (Please note that your questions will be posted anonymously).

What is the difference between a "vertebrate" and a "vertebra"?

A "vertebrate" is a member of the Vertebrata - the subgroup of craniates containing species with a some form of vertebral column. A "vertebra" is one skeletal unit that makes up said vertebral column.

Regarding cuckolding in bluegill sunfish, what's the difference between sneakers & satellites?

The satellites are just older, larger sneak males on the same alternate developmental track as the smaller sneakers; they still “sneak” copulations while more dominant males are courting, but they manage to do so because they look (in terms of size) and act (in terms of their movements) more like females (recall the female-mimicking behavior shown in the movie), which allows them to get close enough without getting chased away.

When exactly were the Ostracoderms extinct?

The text says that they became extinct in the late Devonian

In blue-headed wrasses, how long does it take for a female to become a male? Do they all eventually turn into terminal phase males?

In the video they said 2 weeks; other sources mention that many of the physiological changes happen over the course of a few days. My sense is that it’s a threshold trait based on size, but also mediated by social interactions - which I perceive to mean that subordinate females (or primary males) may not always have the opportunity to switch sexes. Plus, if the numbers of terminal phase males were too high, then the group spawning initial phase males presumably would have an advantage, so it would pay to remain as a female.

What exactly is a "lek", and what did Dr. Wells mean when he said that "males involved in lek mating systems do not offer up their territories to the females;" how is this different from a typical resource-defense system?

The book calls leks “aggregations of many males [displaying] in a small area.” The male does not provide access to his food/shelter/etc. resources, and typically doesn’t defend any kind of nest or provide parental care. The main distinction here is that in standard resource-defense situations, males defend a nest and/or a female, or may provide parental care. In leks they don’t really defend a territory in the same sense; it’s just a patch of space, in close proximity to similar patches of other males, purely for the purpose of attracting females with the intention of copulating, after which they go about their separate ways (think of a college bar, for instance).

Are the ideas regarding "predator confusion", "predator deterrence," and "enhanced vigilance" associated with Hamilton's "selfish herd theory"?

Not specifically; they are just other explanations for benefits of groups that have been posed by various sources.

On the practice "Tree Quiz" provided on our class website, for question #2, why is the sister group of Archaeognatha Pteryoga, and not Insecta?

Because Archaeognatha and Pteryoga share a MORE RECENT common ancestor (which hypothetically exists at the “node” or point where the branch leading from “Archaeognatha” meets the branch leading from “Pteryoga”) than do Archaeognatha and Insecta (this node occurs further down, toward the base of the tree).

Did the evolution of jaws occur in the Silurian with the Placoderms, or in the Ordovician with the Acanthodians?

The first fossil evidence of jawed placoderms appears in the Silurian, and jawed Acanthodians appear in the Ordivician fossil record, so jaws are presumed to have evolved a bit earlier than the first Acanthodian records (because they didn't just suddenly appear), which would place the evolution of jaws sometime during the Mid-Ordivician (as the text states).

Regarding the practice multiple choice questions, it seems like for #4 the answer B should not have been circled, and in #7 answer A should have...

This is true, and the mistakes have been corrected; be sure to look at the most recent updated version.

Does Dr. Rubega expect us to memorize the specific species of Ornithischians from the last few slides of Thursday's lecture? She did not include any of these names in the lecture or notes that were posted.

I included those specific cases to give some idea of the diversity of ornithischians, to illustrate specific characteristics (e.g., continuous tooth replacement), or to dispel certain mistaken ideas (e.g., all dinosaurs are big). I am much more likely to ask you to remember the nature of the illustration/example than I am to ask you to prove that you learned the name. Thus, this:
“Some ornithischian dinosaurs had hundreds of teeth in use at one time”
is a much more likely question response, that you need to know whether is true or false, than this:
“The dinosaur called Iguanodon had hundreds of teeth in use at one time.”

I am trying to put together a GIANT cladogram that goes all from Chordata to Aves. I am using the images from pages 51, 70, and 198, as well as those from Dr. Rubega's lectures. I am trying to make a more comprehensive cladogram than the one that was given in slide #23, however, if you think this is overkill, then PLEASE let me know.

Making a "grand tree" and plotting synapomorphies and other information from lecture on it is a great way to study. You should start with a tree that shows only major groups, master the major groups, and then draw in smaller branches of the tree as you have the time to. Even if you don't manage to memorize every inch of it, the act of putting it together will help sear the information into your head. Make sure you are using your notes to guide your construction, such that you only include groups we have discussed in lecture.

Since crocodylia arose from crurotarsi, does this mean that all the synapormorphies of crurotarsi are also synapomorphies of all crocodylia?

It means that every crocodylia will HAVE those features, since they are crurotarsans, but a crocodylian synapomorphy is a characteristic which every crocodylian has that is NOT shared by all other crurotarsans --- only other crocodylians.

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