Parasites, What's this?

What’s this? #10

Do you know what these creepy fellows are?  Bonus points if you know the species and organ they are found on…

Who are they and what are they eating?!

Who are they and what are they eating?!

Advertisements
Standard
Special interest

Bending over backwards to see the past

What killed the dinosaurs? Or more specifically, what killed these dinosaurs?

dinos2

Rearing up with their heads thrown back, mouth open and teeth bared, their final poses seem to bring them to life. But could this body position, called opisthotonic posture (or death pose), give us clues about how and why they died? That’s right, it’s time to play Dino-Detective!

Artist impression of what dinosaurs might have looked like

Opisthotonic death pose is very common in fossils, and so characteristic that you can generally spot it with ease in even the smallest of fossil exhibits. The head and tail are arched over the animal’s back, and the legs are often drawn into rigid-looking positions. But despite being known about and discussed for 150 years, people are still unsure why exactly dinosaurs so frequently adopt this petrified posture.

Many different reasons for the posture have been suggested, ranging from the very plausible to the downright bizarre.  For example, it’s been suggested that the pose it is actually a sleeping posture (does that look relaxed to you?!), or that the animal dived headfirst into mud and got stuck (it probably happened rarely, but is very unlikely in the case of large theropods or Camarasaurus, unless they were particularly stupid).

More comfortable/less horrifying sleeping posture

A more comfortable/less horrifying sleeping posture

Such suggestions are pretty easy to rule out, and aren’t talked about seriously. Rather, the big bone of contention revolves around whether the opisthotonic pose occurred before or after the dinosaur bit the dust.

Many people think that the pose is a post-mortem change, meaning that it happens after death. Different causes have been suggested, from water currents manipulating the body, to rigor mortis, to the ‘pull’ of drying tendons. However, Faux and Padian, writing in 2007 had a different idea. A background in veterinary medicine gave the authors a different perspective – rather than a change after death, perhaps the pose was a clinical sign of underlying pathology. Faux and Padian thought that these dinosaurs were still alive when they assumed the position, and the posture was a symptom of impaired brain function. It’s a symptom that medical professionals and many others will recognise…

Opisthotonos as a symptom of meningitis infection

Opisthotonos as a symptom of meningitis infection

Muscles are pretty trigger happy, and need inhibitory messages from the central nervous system to stop them contracting all the time. A problem in the brain or spinal cord can interfere with this inhibition. When that happens, the muscles all contract at once. Some are stronger than others (usually the extensor muscles) and pull the body into opisthotonic posture by force.

If Faux and Padian are right, it gives us clues about what might have killed these dinosaurs – severe head injuries, infections (e.g. tetanus and meningitis), poisoning, heat stroke, and lack of oxygen (e.g. drowning) can all cause opisthotonus and eventually death.

A dog with tetanus infection, which survived with intense veterinary nursing. Image credit.

A dog with tetanus infection. Without this intense veterinary care she would not have survived. Image credit.

 

Standard
Cases

Cyclops!

The title might give you one eye-dea about today’s topic – yup, we’re talking about cyclopia! Our fun-loving, larger-than-life, mono-ophthalmic monster buddies were first written about by the ancient Greeks, and later adopted by the Romans.

Luckily he has really bad depth perception

Lucky for those guys, he has really bad depth perception

The origins of the cyclops myth has been the subject of much discussion. Some suggest that the Greeks might have stumbled across the fossilised skulls of prehistoric dwarf elephants, and these creatures being extinct and unfamiliar to them, mistaken the schnozz-socket for a single giant eye.

Nasal cavity vs. actual eye hole

Nasal cavity vs. actual eye hole of an elephant skull

Others think that the Greeks had actually seen cyclopes in the flesh. A couple of rare developmental problems can result only one eye: in true cyclopia, only one eye is formed, whereas in synophtalmia, there may be two eyes which fuse.

Cyclopia

Itty bitty cyclops kitty

The Sonic Hedgehog and Pax6 genes are involved in properly dividing the embryonic brain (and extensions from it, such as the eyes) into two separate hemispheres.  There are several things that interfere with this process and so cause cyclopia, including certain drugs, viruses, genetic defects, and radiation. Alkaloid toxins in plants are also a culprit. In fact, ancient Greeks used some of these plants medicinally, and perhaps as a result, did see ‘real’ cyclopes…

Elephants and cyclopes also have another thing in common. Interestingly (or maybe morbidly), some cyclopes develop a tube-like structure instead of a nose, which is called a proboscis because it resembles a tiny trunk.

A cyclopic lamb with a proboscis, or trunk, above its eye

A cyclopic lamb with a proboscis, or trunk, above its eye

 

Standard
What's this?

What’s this? #9 Epitheliocystis

This was a tricky one! Well done to paleomanuel for a superb answer, recognising that this was a magnified picture of fish’s gills.

Normally when we take cross-sections through the gills, we should see thousands of finger-like projections called lamellae. Like the thousands of alveoli in our lungs, the lamellae massively increase the surface area available for gas exchange when water is flowing over them.

The gills form thousands of folds to increase surface area for gas exchange in the water. These gills are relatively normal apart from one affected cell

The gills form thousands of folds to increase surface area for gas exchange in the water. These gills are relatively normal apart from one affected cell.

In this disease, billions of blue-purple staining bacteria (Chlamydia-like species) are replicating within the epithelial cells which line the gills and skin, causing them to balloon out and form cysts. Because of this, the disease caused by these bacteria in the gills is called Epitheliocystis.

The big blue-purple blobs are big colonies of bacteria within the cells lining the gills.

The big blue-purple blobs are big colonies of bacteria within the cells lining the gills.

It is quite a rare cause of disease in wild fish, but occurs more frequently in fish farms because the high stocking densities mean that the bacteria can spread more easily.  Their thickened and damaged gills means that affected fish may die because they are unable to extract oxygen efficiently from the water.  Inflammation of the gills is called branchitis (not to be confused with bronchitis! = the inflammation of the airways in the lungs of mammals, birds, and most reptiles).

Standard
What's this?

What’s this? #8 Spondylosis

What was going on in that strange spine? It’s likely that this poor polar bear had spondylosis (also called spondylosis deformans or ankylosing spondylosis).

He's not letting it ruin his day, though

He’s not letting it ruin his day, though

Spondylosis is the formation of extra bone (osteophytes) between the vertebral bones which make up the spine.  It can look like little projections from the individual vertebrae, or actually form bridges between them.  When joints fuse like this, it is called ankylosis, and is thought to be the body attempting to stabilise the joint (like a bone splint) after damage to the cartilage cushions between the vertebrae.

spondylosis

Projections of bone vs. bridges of bone

Spondylosis is most often seen in dogs, pigs and bulls.  It is particularly important in bulls kept in artificial breeding centres, where repeated mounting of a dummy-cow leads to damage to the lower back.

Your back bone's connected to...uh, all your other back bones (is that how the song goes?)

Your back bone’s connected to…uh, all your other back bones (is that how the song goes?)

In some animals with spondylosis there are no symptoms. However, the bony bridges are more brittle than regular bone, and can sometimes fracture, potentially leading to bleeding and compression of the spinal cord and paralysis.  In most dogs and pigs, spondylosis is often found incidentally and clinical signs can range from nothing to pain and stiffness.

Extra bone around the vertebra. The spinal cord runs through the tunnel at the top of the bone.

Extra bone around the vertebra. The spinal cord runs through the tunnel at the top of the bone (which has been sawn open in this picture).

Standard