Why is the pack rat not a true rat?

[pippo]

Apparently, the pack rat is not a member of the Rattus genus. It has another, but not able to figure out why. Geez, if it looks like a rat, walks like a rat, squeals like a rat, shouldnt it be a member of the Rattus Genus?

 

(funny, I asked once where does the Norway rat come from......it is not Norway. Guess it actually came from the far east....China??)

[AzurePhoenix]

Species are classified with respect to shared ancestry and degree of relatedness. Old world rats and packrats don't comprise a monophyletic group. All the packrat species within the genus Neotoma are descended from a single shared ancestor.A bit further back along the family tree and you'll find the ancestor that would split into packrats, deermice, and some other new world rodents. Gotta go much deeper into the ancestry before you find the ancestor shared by Neotoma and old world Rattus.

 

Superficial resemblances that arise independently in distinct families are referred to as convergent evolution, and have no influence on classification.

[pippo]

Thanks, Azure. So, not having the tree available in front of me, would you say the rattus is older or newer than the pack rat? Guess that since you referred to rattus as old world, does that imply older?

[AzurePhoenix]

Europe and Asia aren't older than the Americas in any sense, it's just that the Americas were new to the people who discovered and conquered them. Rodents in general seem to have originated in the late Cretaceous or so, across the supercontinent Laurasia, which was a clump of America, Europe and Asia all together. I'm not really all that aware of the intricacies of rodent diversification throughout the eons, but various families would have split and diverged as the continents themselves did, and of course land bridge events throughout the eons may've resulted in back and forth invasions I'd imagine, but I have no idea which of the genera as we classify them can be traced the furthest back.

[Maximus Semprus Veridius]

Lots of niches are the same all around the world. Like eating small to medium mammals is a niche all round the world. Pythons have inhabited everywhere but america and Boas inhabit almost everywhere else (or the other way round, i can't remember). They have independantly evolved very similar adaptations to survive but they only share very primitive (comparivtively) ancestors. The group rat is almost cetainly like the python - boa analogy, meaning their taxanomic rankings are only related further back than is outwardly apparent.

Edited November 17, 2010 by Maximus Semprus Veridius

[pippo]

Makes sense. But azure, you said :

 

Old world rats and packrats don't comprise a monophyletic group.

 

First, I should look up the word monophyletic. I have a rough idea what it might mean, so Biologists decided they are not the same genus for specific reasons (which one could ascertain with some research, of course). It sure seems like splitting hairs, I need to find out why they are split up...I mean, geez, theyre rats for goodness sake. But noooo, someone decided maybe the ugly/distainful Norway Rat is no where near as cute as the pack rat, .....just kidding. But, theres got to be a reason for the split...........Lets see.....hmmmm, wikipedia........

Edited November 23, 2010 by pippo

[CharonY]

It is based on phylogeny. I.e. their relation and common history (and where the diverge). An simple (but somewhat inaccurate) analogy would to declare someone as your cousin because you share a common history (e.g. one of your parent is the brother/sister of one your cousin's parents. It is not based on the fact that both of you may have uncle Willi's nose, for instance (though you may actually have it).

[pippo]

Thanks, Charon.....for some reason, it finally hit me. Yes, now I get it...the idea of common ancestry back in the tree, some place back a few branches away. And not to imply that azure did not explain it well, he did.

 

Now, what are these differences? I looked up some info but couldnt find why pack rate are different regarding their separate genus. I imagine its kinda like a fox vs a wolf. Vulpes vs Canis.

 

Is it their snout? length of their legs? Hoppers vs walkers/crawlers?

Edited November 25, 2010 by pippo

[ewmon]

Geez, if it looks like a rat, walks like a rat, squeals like a rat, shouldnt it be a member of the Rattus Genus?

Well... naming stuff can get a bit flaky. Probably if a rodent looks big, someone might call it a rat, otherwise, it's a mouse, gerbil, hamster, etc. There's a bunch of "pouched rats" (African giant pouched rats, Gambian pouched rats, Emin's pouched rats, etc) that aren't "true rats" but are closer relatives to the mouse than the [true] rat.

 

The same visual mistake might easily apply to some ducks. Some ducks (Aylesbury, Rouen, etc) are large enough to be mistaken for geese if the observer didn't know any better.

[pippo]

Well... naming stuff can get a bit flaky. Probably if a rodent looks big, someone might call it a rat, otherwise, it's a mouse, gerbil, hamster, etc. There's a bunch of "pouched rats" (African giant pouched rats, Gambian pouched rats, Emin's pouched rats, etc) that aren't "true rats" but are closer relatives to the mouse than the [true] rat.

 

The same visual mistake might easily apply to some ducks. Some ducks (Aylesbury, Rouen, etc) are large enough to be mistaken for geese if the observer didn't know any better.

 

Right....good point, ewmon. Hey, just recently, biologists "changed their mond"....LOL, on what genus the skunk belonged to!! Yeah, for eons they categorized it along with other mustelids (mink, weasels, wolverines, badgers, etc etc). Now, they proved the skunk has a different protein produced in, not sure, their genes, whatever. So, hey, tomorrow, maybe they will put out pack rat in with the ugly Norway rat, eh?

[Sisyphus]

Right....good point, ewmon. Hey, just recently, biologists "changed their mond"....LOL, on what genus the skunk belonged to!! Yeah, for eons they categorized it along with other mustelids (mink, weasels, wolverines, badgers, etc etc). Now, they proved the skunk has a different protein produced in, not sure, their genes, whatever. So, hey, tomorrow, maybe they will put out pack rat in with the ugly Norway rat, eh?

 

It's not so much changing the mood as discovering new information that allowed them to correct inaccuracies, mostly based on genetic analysis, which is relatively new and constantly improving. Before genetic analysis, all they had to go on was the fossil record.

 

Originally species were classified according to superficial resemblances. Now they are classified by degree of relatedness. You might look more like your 3rd cousin (or a total stranger) than you do your brother, but you are still more closely related to your brother. Changing from a system of classifying individuals by appearance vs. by family relation would mean a lot of reclassification. (But it wouldn't be totally different, either, since we tend to resemble our close relatives.)

[pippo]

It's not so much changing the mood as discovering new information that allowed them to correct inaccuracies, mostly based on genetic analysis, which is relatively new and constantly improving. Before genetic analysis, all they had to go on was the fossil record.

 

Originally species were classified according to superficial resemblances. Now they are classified by degree of relatedness. You might look more like your 3rd cousin (or a total stranger) than you do your brother, but you are still more closely related to your brother. Changing from a system of classifying individuals by appearance vs. by family relation would mean a lot of reclassification. (But it wouldn't be totally different, either, since we tend to resemble our close relatives.)

 

Thanks, Sisy. But oops....I goofed on the spelling of the word "mind", having typed "mond" instead. You took it as a mispelled "mood", I take it, but no matter....I think your perspective is still valid to your point. Biologists changed their "mind", vs "mood". Again, same thing.

 

Right, thaTS WHAT i MEANT...THAT THEY WILL FIND ADDL INFO TO AUGMENT THEIR CLASsIFICATIONS, IF THE CASE WILL BE SUCH. mAYBE not the rat, but they did it with monerids/fungi/bacteria, and then protozoa. Split them up from the plant kingdom we understood going back to the early 70's. Oh well.

 

Funny how the Norway rat got its name when it never came from that climate, I heard..........the English coined that name to it......

 

Starting another thread on evolution soon........

[richw9090]

Members of the genus Rattus (the true rats) are very different from members of the genus Neotoma (the packrats). Note that in the time of Linnaeus, almost everything which looked vaguely like a rat was put into the genus Rattus, but it has since been broken into several dozen different genera, on the basis of unique shared derived characters (that is, unique at the subfamily level, shared at the generic level).

 

The common ancestor of Rattus and Neotoma is, by definition, equally far back in the past. Both are in the family Muridae, but are placed in different subfamilies (according to the classification I favor, McKenna and Bell, 1997). The differences between the two genera are may be subtle to the layperson, but they are quite distictive to those who study the critters.

 

Rich