The evolution of feathers in about 3 and a half minutes

By Carl Zimmer:

[Hat tip to Brian Switek.]

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Recent critter encounters

As I continue to try and adapt to having a significantly longer commute to work, settle into our rental house, and generally try to get my crap together, here are some pictures of some critters I’ve encountered over the last few months.

First a mollusk:

I discovered this rather large (approx. 10cm) slug making its way across my front walk. Not sure about my ID but I’d say it was possibly a Limacus flavus, which would make this an introduced ALIEN SLUG! [Scream!]

Limacus

Secondly a couple different arthropods, one terrestrial and the other aquatic:

This dangerous little bugger was hitchhiking in a load of horse manure that my mother was unloading from the back of her pickup truck. A centipede, probably a Scolopendra polymorpha. After I told my mother that I wasn’t interested in adopting it she ended up feeding it to her chickens, which was probably a little spicier than their usual fare.

centi-sm

OK, there is a bit of a set up to our next crawly, or rather swimy critter. I was on my way to work one morning and while driving by a vacant lot around the corner from my house, I noticed three adults standing around a large puddle in middle of the lot that was left over from some recent rain. My brain noted that this was an unusual thing to see, so I slowed down a bit and saw that a couple of them were holding small fishnets, of the sort that an aquarist might keep handy. Quickly running through the possibilities of what three adults with fishnets standing around a small ephemeral body of water in a generally arid environment might be up to and my brain instantly hit upon what seemed to be the only logical conclusion…BIOLOGISTS!

Unfortunately I was already a little late for work and couldn’t stop and talk to them, however I immediately vowed to myself that I would visit the puddle ASAP to see what might have drawn a trio of probable biologists to this vacant lot. So on my way home from work I stopped at the lot and checked out the puddle.

At first I didn’t see anything but once my eyes adjusted to what I was looking at I noted some small (maybe 2cm) things swimming fairly vigorously around the puddle. At first I thought that they might be fish, perhaps Gambusia which are often stocked in our local waterways to control mosquitoes. This wasn’t totally crazy as there is a catchment basin immediately adjacent to the lot and I thought that, while it was unlikely, it might be possible for some Gambusia to have somehow made it into this puddle.  However given that this was a very ephemeral body of water and that Gambusia would be considered “junk fish” by an ichthyologist I quickly dismissed this idea.

Looking a bit closer at the tiny swimming creatures I realized what their true nature was and why thy might be of interest to biologists became much less of a mystery. They were fairy shrimp, possibly of the Family Streptocephalidae, some members of which are very endangered. In this case possibly Streptocephalus woottoni A.K.A. the “Riverside fairy shrimp“, though this puddle was a little shallow (under 30mm) for the normal bodies of water that S. woottoni are supposed to inhabit.

Anyway, after seeing that they were indeed fairy shrimp I rushed home and got one of my critter keepers (a small plastic aquarium) and fashioned a small, pitiful, net out of a coat-hanger and one of my wife’s old nylon stockings. Pitiful as my jury-rigged net was, it allowed me to catch a few of the shrimp.

Fear not for the shrimp though, after I photographed them (which isn’t an easy thing!) I returned them to their puddle which remained habitable for three or four days longer.

Shrimp1

Shrimp3

Last but not least a couple different chordates, in this case both mammals:

While driving through a local rural area (Reche Canyon) my wife and I spotted a herd of feral burros (Equus africanus asinus) that we had heard (get it?) lived in the area. I wasn’t able to get too close to them and only had my cell phone camera so these are not the best pictures. However if you look carefully at the second picture below you’ll get a glimpse of some “hot donkey action” going down (brown chicken, brown cow!).

Apparently there is something of a mystery involving these burros lately. It seems that several of the newborns have gone missing and it becoming a concern for the locals who watch over them.

ass_2

ass_1

Finally a rough pair of middle aged male apes (H. sapiens). Yours truly with Dr. Sean B. Carroll Professor of Molecular Biology, Genetics, and Medical Genetics at the University of Wisconsin–Madison at U.C. Riverside on 2-11-2013. Dr. Carroll had just given a very entertaining talk: Remarkable Creatures: Epic Adventures in the Search for the Origins of Species about the adventures and scientific contributions of Alfred Russel Wallace, Charles Darwin and Henry Walter Bates in honor of Darwin Day 2013 (Photo and my shirt by Lani Britain, a.k.a. Mom).

OK, so this wasn’t a scathing dissection of creationist silliness, but it was something…

Zebras: Nature’s Ultimate Prey

In a related story:

God Admits Humans Not Most Impressive Creation

Loves me some The Onion

I started early with this paleo stuff

I finally had a chance this weekend to pick through some of my mother’s family photo collection and found a few pictures of myself that are prophetic about what my lifelong interests would be. They are from one of the family camping trips we took, traveling all over the American Southwest. During this trip, circa 1975, we went to Dinosaur National Monument in Utah/Colorado.

First is a picture of me (10 years old) with the famous Stegosaurus statue that greets visitors outside the Quarry Exhibit Hall. You can tell by the look on my face that I was having a terrible time.

Now admittedly the color they had originally painted this statue (a brownish green scheme) was a little dull, though we have no way of knowing what color Stegosaurus actually was. But the current paint job on the statue seems a little bizarre to me.

And here we have a shot of me inside the Quarry Exhibit Hall, being much more serious in the presence of the astonishing number of dinosaur fossils exposed in the Carnegie Dinosaur Quarry.

Ah, memories…

“Gill slits” by any other name…

Charles Darwin once said that he thought the evidence from the comparative anatomy of embryos was “by far the strongest single class of facts” in favor of common descent (Darwin, 1860) and while it has since been eclipsed by genetics, it remains one of most compelling subsets of evidence for evolution. And perhaps the single most striking detail in the comparative embryology of vertebrates, are the structures colloquially known as “gill slits”.  

Embryonic “gill slits” or “branchial clefts” (branchia is Greek for gill) or more properly pharyngeal clefts (grooves, folds, etc.) are part of what is called the “pharyngeal apparatus” found in front (ventral) and sides (lateral) of the head/neck region of all vertebrates in the “pharyngula stage” of development. In “fish”, and the larva of amphibians, these develop into respiratory organs used to extract oxygen from water while in amniotes (“reptiles”, birds and mammals) they are modified into other structures.

Before I go on, a brief digression about “fish”. Throughout this article I will often use “fish” in the generic sense; but it should be noted that the term as it is commonly used—to refer to any vertebrate that swims in the water, has fins and gills—is not a valid scientific classification. This is because the three main types of animals commonly called “fish” —the Chondrichthyes (sharks, rays, skates and chimaeras), the Actinopterygii (ray fined fish, which constitutes the majority of living fishes), and the Sarcopterygii (lobe fined fish, the group from which four legged land animals, i.e. tetrapods, evolved)—are not a monophyletic group. That is they are not very closely related to each other despite some of their outward similarities (like gills). For example the living Sarcopterygii, lung fish and coelacanths share a more recent common ancestor with us (and all tetrapods) than with the other “fishes”.

OK, so the “pharyngeal apparatus” consists of a series of paired pharyngeal arches and fissures which develop on the exterior with a corresponding set of pharyngeal pouches on the inside of the throat, separated from the external fissures by a thin membrane (more on the details in a moment). And in fact the possession of these structures at some point in development, along with a hollow dorsal nerve cord, a notochord and a post anal tail, are the defining characteristics of the phylum chordata to which we and all other vertebrates belong.

Copyright © 1999 McGraw-Hill Companies, Inc.

Please note that the above illustration is diagrammatic and not intended to be photographically accurate (I have to say that lest I be accused by creationists of conveying a fraud). Below are actual photographs of both a skate embryo and a human embryo for comparison. Also note: the gill structures in the embryos of Elasmobranch fishes—the subdivision of Chondrichthyes which contains sharks, rays and skates—are much less derived than in other “fishes” and therefore generally more similar to those of amniote embryos than the corresponding structures in the bony “fishes” (which are significantly modified).

(Gillis et al 2009, p.5721)

The first of the arches, the mandibular arch, forms the jaw in all jawed vertebrates (Gnathostomes). Most vertebrates develop a total of six arches but the full complement is usually only retained into adulthood by hexanchiform sharks. Hexanchiformes are very plesiomorphic which means that they are more like earlier types of sharks.  Some species of hexanchiformes even develop a seventh arch. Likewise the extant jaw-less vertebrate, the lamprey, also have seven gill openings.

Read on»

A lizardy day

The weather was nice today (Sunday 4-22-12); sunny but not too hot, so I spent a couple hours over at my parents’ house today wandering around the yard looking for critters like I used to do when I was kid. Only this time I was armed with a camera instead of a jar or coffee can, intending to capture images rather than bodies. My target was the host of lizards that have taken up residence in my parents’ yard; specifically Western fence lizards (Sceloporus occidentalis).

When I  was a kid used to find all sorts of invertebrates, miscellaneous insects (of course), solifugids (“sun” or “wind scorpions”) and one time I even found a tarantula (probably a Aphonopelma; I damn near stepped on it while running through the back yard).

As for vertebrates I often found Slender salamanders (Batrachoseps) and the feisty Southern alligator lizard (Elgaria) but never any fence lizards. To find them I had to hike three quarters of a mile or so to an undeveloped area dominated by a rocky hill (a modest pluton locally known to us a “Lionshead”) where they were fairly abundant amongst boulders of decomposing granite.

This is not the case anymore.

I had noticed on previous visits that the fence lizards were around my parents’ yard but today I realized that the place was absolutely crawling with them. I have no idea what has changed in the environment that has led to an expansion of their range, from the hills and undeveloped areas to the middle of the suburbs, but personally I’m glad of it.

At first they played a little hard to get. It was already afternoon and while it wasn’t really hot it was warm so their metabolizes were no doubt running at nearly at mammalian levels. So they would dash for cover before I got too close.

This little one was hiding behind some old window screens at the back of the garage. It had a larger companion who was missing part of its tail, however I couldn’t get a picture of it. Read on»