Meet Odontochelys semitestacea.
This little creature spends its days splashing in Late Triassic swamps with a host of other reptiles.
Under the surface lies its best defense against attack: a hard shell on its belly.
Odontochelys is an early ancestor of the turtle.
Its half-shelled body illustrates an important point about the modern turtle: it actually has two shells that develop totally separately while the turtle is still an embryo.
Both are extensions of the animal’s skeleton, and together they are made of almost 60 bones.
Like other embryos, turtle embryos are made of undifferentiated cells that become specific cell types, and then organs and tissues, through gene activity and communication between cells.
At first, turtle embryos look very similar to those of other reptiles, birds, and mammals, except for a bulge of cells called the carapacial ridge.
The ridge expands around the body between the neck and lower back, creating a disc shape.
It guides the formation of the upper part of the turtle’s shell, called the carapace, likely by attracting the cells that will become ribs.
Instead of curving downwards to make a regular rib cage, the ribs move outwards towards the carapacial ridge.
They then secrete a signaling protein that converts surrounding cells into bone-forming cells.
These fifty bones grow until they meet and connect with sutures.
A ring of bone solidifies the carapace’s edges.
The outer layer of skin cells produces the scales, known as scutes, that cover the carapace.
The development of the bottom half of the shell, the plastron, is driven by neural crest cells, which can produce a variety of different cell types including neurons, cartilage and bone.
A thick shield of these cells spreads across the belly, coming together in regions that produce nine plate-like bones.
Eventually, these connect to the carapace by sutures.
A turtle’s shell has obvious advantages for guarding against predators, but the rigid casing also presents some challenges.
As the turtle grows, the sutures between the bones of the carapace and plastron spread.
Most mammals and reptiles rely on a flexible rib cage that expands to allow them to breathe, but turtles use abdominal muscles attached to the shell instead: one to breathe in, and one to breathe out.
So how did the shell evolve?
Though there are still gaps in the fossil record, the first step seems to have been a thickening of the ribs.
The oldest known turtle ancestor, a creature called Eunotosaurus africanus, lived 260 million years ago and looked almost nothing like a modern turtle, but it had a set of broad, flat ribs that anchored the muscles of its powerful forearms.
Eunotosaurus was likely a burrowing creature, digging homes for itself in what’s now southern Africa.
Odontochelys semitestacea illustrates another, later step in turtle evolution, with thick ribs like Eunotosaurus plus a belly plate for protection.
Our first fossil evidence of the full shell characteristic of modern turtles is about 210 million years old, and belongs to a species called Proganochelys quenstedti, whose ribs had fused.
Proganochelys could move between water and land.
Unlike modern turtles, it couldn’t retract its head into its shell, but had defensive spines on its neck.
Modern turtle shells are almost as diverse as the turtles themselves.
Sea turtles have flatter, lighter shells for streamlined gliding through the water.
Land-dwelling tortoises, meanwhile, have domed shells that can slip free of predators’ jaws and help them turn right-side up if they fall on their backs.
Leatherback and softshell turtles have shells without the ring of bone around the edge of the carapace or the tough scutes covering it, making it easier for them to squeeze into tight spaces.
What's that sound?
Depending on whom you ask, the crackle of popping joints is either the sound of sweet relief or the noxious tones of a stomach-turning habit.
Really, though.
What's that sound?
I mean, why does bending your joints in a certain way make them pop like that?
Scientists have offered several explanations, including rapidly stretching ligaments, and in severe cases, actual bones grinding against each other.
But the most common explanation for why your stretched-out joints sound like bubbles popping is that, well, there are bubbles in there.
The joints in your fingers are the easiest ones to crack, but many people also crack the joints between vertebrae in their neck and back, and even their hips, wrists, shoulders and so on.
All these joints are synovial joints, and they're the most flexible ones in your body.
The space between the two bones is filled with a viscous liquid, synovial fluid, which contains long, lubricating molecules, like hyaluronic acid and lubricin.
Synovial fluid is more or less the texture of egg yolk and its primary purpose is to cushion the bones and help them glide past each other.
It also contains phagocytic cells that help clean up any bone or cartilage debris that ends up in the joint.
But the reason it's important for knuckle cracking is that, like other fluids in your body, it contains lots of dissolved gas molecules.
Knuckle-crackers know that to get that satisfying pop, you stretch the joint farther than it normally goes by bending your fingers backwards, for example.
When you do that, the bones move away from each other.
The space between bones gets bigger, but the amount of synovial fluid stays constant.
That creates a low-pressure zone that pulls dissolved gases out of the synovial fluid, just like the carbon dioxide that fizzes out of soda when you twist open the cap.
Inside the joint, the escaping gases form a bubble with a pop.
But the bubble doesn't last long.
The surrounding fluid presses on it until it finally collapses.
The bubble's gases scatter throughout the synovial cavity and slowly dissolve back into the fluid over the course of about twenty minutes, which is why it can take a while before you can pop the same joint again.
Some scientists think there may actually be two pops.
One when the bubble forms, and another when it bursts.
Popping a joint temporarily enlarges it, which may be why dedicated knuckle-, neck- and back-crackers say the habit makes their joints feel looser and more flexible.
But you may have heard from a concerned relative or annoyed officemate that cracking your joints will give you arthritis.
A doctor named Donald Unger heard this, too.
So, determined to disprove his mother's warnings, he cracked the knuckles of his left hand repeatedly for 50 years, while the right-hand knuckles went unpopped.
36,500 cracks later, both hands were arthritis-free.
For this selfless act of devotion to science, Dr. Unger received an Ig Nobel Prize, a parody of the Nobel Prize that recognizes wacky, but weirdly fascinating, scientific accomplishments.
Unger wrote that his results should prompt investigation into other parental beliefs, like the importance of eating spinach.
The jury's still out on that one.
As for knuckle-cracking, one study suggests that all that joint stretching and bubble bursting can cause your hands to swell and weaken your grip.
But the biggest proven danger seems to be annoying those around you.
Like every passionate software engineer out there, I closely follow technology companies in Silicon Valley, pretty much the same way soccer fans follow their teams in Europe.
I read articles on tech blogs and listen to podcasts on my phone.
But after I finish the article, lock my phone and unplug the headphones, I'm back in sub-Saharan Africa, where the landscape is not quite the same.
We have long and frequent power outages, low penetration of computers, slow internet connections and a lot of patients visiting understaffed hospitals.
Since the HIV epidemic, hospitals have been struggling to manage regular HIV treatment records for increasing volumes of patients.
For such environments, importing technology systems developed elsewhere has not worked, but in 2006, I joined Baobab Health, a team that uses locally based engineers to develop suitable interventions that are addressing health care challenges in Malawi.
We designed an electronic health record system that is used by health care workers while seeing patients.
And in the process we realized that we not only had to design the software, we had to implement the infrastructure as well.
We don't have enough medical staff to comprehensively examine every patient, so we embedded clinical guidelines within the software to guide nurses and clerks who assist with handling some of the workload.
Everyone has a birthday, but not everyone knows their birthday, so we wrote algorithms to handle estimated birthdates as complete dates.
How do we follow up patients living in slums with no street and house numbers?
We used landmarks to approximate their physical addresses.
Malawi had no IDs to uniquely identify patients, so we had to implement unique patient IDs to link patient records across clinics.
The IDs are printed as barcodes on labels that are stuck on personal health booklets kept by each patient.
With this barcoded ID, a simple scan with a barcode reader quickly pulls up the patient's records.
No need to rewrite their personal details on paper registers at every visit.
And suddenly, queues became shorter.
This meant patients, typically mothers with little children on their backs, had to spend less time waiting to be assisted.
And if they lose their booklets, their records can still be pulled by searching with their names.
Now, the way we pronounce and spell names varies tremendously.
We freely mix R's and L's, English and vernacular versions of their names.
Even soundex, a standard method for grouping words by how similar they sound, was not good enough.
So we had to modify it to help us link and match existing records.
Before the iPhone, software engineers developed for personal computers, but from our experience, we knew our power system is not reliable enough for personal computers.
So we repurposed touch screen point-of-sale terminals that are meant for retail shops to become clinical workstations.
At the time, we imported internet appliances called i-Openers that were manufactured during the dot-com era by a failed US company.
We modified their screens to add touch sensors and their power system to run from rechargeable batteries.
When we started, we didn't find a reliable network to transmit data, especially from rural hospitals.
So we built our own towers, created a wireless network and linked clinics in Lilongwe, Malawi's capital.
(Applause) With a team of engineers working within a hospital campus, we observed health care workers use the system and iteratively build an information system that is now managing HIV records in all major public hospitals in Malawi.
These are hospitals serving over 2,000 HIV patients, each clinic.
Now, health care workers who used to spend days to tally and prepare quarterly reports are producing the same reports within minutes, and health care experts from all over the world are now coming to Malawi to learn how we did it.
(Applause) It is inspiring and fun to follow technology trends across the globe, but to make them work in low-resourced environments like public hospitals in sub-Saharan Africa, we have had to become jacks-of-all-trades and build whole systems, including the infrastructure, from the ground up.
Thank you.
(Applause)