The Z-Letter Archive

As seen by Dr Liz Sheffield from her office window, looking onto the back quad of the Stopford Building at the University of Manchester. One of our resident sparrowhawks with its lunch. Look at that eye! Thanks to Laura for alerting us to the kill, and photocredit goes to Tony Bentley from the Photographics Unit. Let’s hope the sparrowhawks breed again this year.

Having just successfully recruited a PhD student for a project entitled “Building a robot maggot nose”, I was particularly intrigued when I learned of the work of Boston Dynamics, who are developing some astonishing (and scary) robots, in conjunction with the US military. The video below shows Big Dog, described by Boston Dynamics as follows:

“a rough-terrain robot that walks, runs, climbs and carries heavy loads…. BigDog has four legs that are articulated like an animal’s, with compliant elements to absorb shock and recycle energy from one step to the next. BigDog is the size of a large dog or small mule; about 3 feet long, 2.5 feet tall and weighs 240 lbs…. In separate tests BigDog runs at 4 mph, climbs slopes up to 35 degrees, walks across rubble, climbs a muddy hiking trail, walks in snow and water, and carries a 340 lb load. BigDog set a world’s record for legged vehicles by traveling 12.8 miles without stopping or refueling.”

The technology involved is pretty amazing, as is the ability of the robot to mimic quadruped behaviour, and thereby test models of how they move. The parts of the movie where the robot regains its balance when slipping or after being pushed are particularly impressive, and raise the question of whether it’s based on an incredibly sophisticated description of behaviour, or whether the programme that runs Big Dog has learned how to cope with slipping over etc.

If the thing was weaponised it would be doubly scary, which raises the question of the relation between science, technology and warfare. Developments in science, technology (and medicine) are often driven by warfare. Just think of the development of computing, radar, aeronautics, nuclear science and antibiotic treatment during World War 2. Maybe developing robotic dogs to work in the hills of Afghanistan is leading to a new breakthrough in robotics.

One of the biggest questions in paleontology – what colour were the dinosaurs – looks like it might now have an answer. Or rather, we know how we can find out. In an article that has just appeared on the Nature website (abstract free, article requires subscription), a group of scientists from China, Ireland and the UK have examined the microstructure of feathered dinosaurs and birds. As they say in the abstract:

Here we report that melanosomes (colour-bearing organelles) are not only preserved in the pennaceous feathers of early birds, but also in an identical manner in integumentary filaments of non-avian dinosaurs (…) they are often preserved in life position within the structure of partially degraded feathers and filaments.

Then there’s the killer conclusion:

Furthermore, the data here provide empirical evidence for reconstructing the colours and colour patterning of these extinct birds and theropod dinosaurs: for example, the dark-coloured stripes on the tail of the theropod dinosaur  Sinosauropteryx can reasonably be inferred to have exhibited chestnut to reddish-brown tones.

In case you don’t know what Sinosauropteryx looked like, here it is – complete with coloured stripes!

Sinosauropteryx

The details of the paper are complicated (as the details often are), but here’s an example of that Sinosauropteryx tail, complete with electron microcopy of the melanosomes:

a, Optical photograph of the proximal part of the tail. Arrow indicates position of sample removed previously. b, Optical photograph of sample of integumentary filaments; position of SEM sample (inset) indicated by arrow. c, Mouldic phaeomelanosomes within a filament. Scale bars: a, 50 mm; b, main panel, 20 mm, and inset, 1 mm; c, 2 μm.

Of course, these fossils are amazingly well preserved, and its probably unlikely that your average dinosaur fossil will reveal its coloured secrets. But this is an astonishing discovery, which opens a whole new realm for our understanding of dinosaur biology.

If you’re a fish, you don’t want to meet the tentacled snake, Erpeton tentaculatus, as this video shows. If it wasn’t an odd metaphor for an aquatic organism, I’d say it was lightning fast. Blink and you’ll miss it. The video, by Ken Catania from Vanderbilt University, shows the strike in increasingly slow motion. The images are quite beautiful, as long as you aren’t the fish.

Last year, Ken published an article in PNAS (open access) in which he described how the snake apparently both influences and predicts how the fish will turn. This escape response is known as the “C-turn”, and is coded by the “Mauthner neurons”, which we’ve discussed before on the Z-letter. The snake feints like a footballer, causing the fish to respond, then immediately strikes in the opposite direction.As Ken’s abstract puts it: “As a result, fish that were oriented parallel to the long axis of the snake’s head most often turned toward the approaching jaws, sometimes swimming directly into the snake’s mouth.”

Now Ken has just published an article in Journal of Experimental Biology (subscription needed to get past abstract) which explains exactly how the snake manages to detect the fish’s movement. The secret is in those odd tentacles coming out of the front of its head, which you can see in the video. You can see them quite clearly here:

The aquatic snake, is found in SE Asia and can grow to well over 1 metre in length. Since it was first described in 1800, these “tentacles” have been ascribed various functions, including as lures to convince hapless and hungry fish to come closer. Covered in scales as shown in this false colour electron microscope from Ken’s article, the tentacles are in fact mechanoreceptors.

The JEB article shows that the neurons that are found in the tentacles project deep into the snake’s brain, intimately related to the snake’s representation of its visual world. Although snakes will attack video images of fish, showing they do not need mechanical stimulation, they can also successfully feed in the dark, showing they can kill without seeing their prey.

Fig. 2. Innervation of the tentacles by the trigeminal nerve. (A) Tentacle showing dense innervation. (B) Dense network of fine fibers (arrows) that cross the middle of the tentacle. (C) Diagram of the head, brain and selected cranial nerves. Two different subdivisions of the trigeminal nerve (the ophthalmic and a branch of the maxillary) supply roughly equal densities of innervation to the tentacle. V1–3, trigeminal nerve; OB, olfactory bulb; Tel, telencephalon; OT, optic tectum. (D) Dorsal view of the brain showing the olfactory bulb, telencephalon, optic tectum and root of the trigeminal nerve. (E) Ventral view of the brain showing substantial optic nerve (II).

Finally, in a great piece of electrophysiology, Ken and his coworkers recorded from the tentacle neurons to show they responded to mechanical stimulation, and from the snake’s brain to show how both visual and mechanical stimuli overlap.

As shown above, the tentacles are effectively a branch of the trigeminal nerve, which in most vertebrates detects sensation in the face and is involved in eating. In the tentacled snake, the sensory aspects have been developed to an incredibly high level. Two questions remain: first, how is the detected movement transformed into the snake’s ballistic attack and second, what happens if the snake receives contradictory information from its visual and mechanosensory neurons? Which is more important – sight or touch?

JEB magazine article (open access).

Article in Exploration (Vanderbilt magazine – Free)