In 1861, a photographer named Carleton Watkins headed 75 miles into the Yosemite Valley with a team of mules, a mobile darkroom tent, and custom camera. That camera, Stanford University’s Cantor Arts Center explains, produced “mammoth” 18- by 22-inch glass-plate negatives.
One hundred and fifty years ago, the Yosemite Valley was just another stunning natural landscape in the American West. But Carleton Watkins’ work helped convince President Abraham Lincoln and Congress to pass the Yosemite Valley Grant Act. The legislation preserved the land for public use and set a precedent for the American National Park System.
In 2005, researchers came across evidence of the area’s former inhabitants: pterosaurs, a group of flying reptiles that includes the pterodactyl family. Recent excavations of the site have yielded a plethora of fossil specimens of these ancient reptile residents, including the most juvenile of them—their eggs. A team of paleontologists from China and Brazil found that the unearthed bones and fossilized eggs actually represent a previously unknown genus and species of pterosaur. They published their results today in Current Biology.
Before getting into the nitty-gritty details of the discovery, it’s important to note that pterosaurs aren’t dinosaurs. These reptiles share a different evolutionary history to their dino cousins. Thus, unlike dinosaurs, they aren’t directly related to birds either. Pterosaurs dominated the skies during the Cretaceous and Jurassic periods, but pterosaurs and birds are two evolutionary paths that separately reached the skill set of flight.
In the fossil record, pterosaurs are rare commodities: only one or two fossil specimen define each species, and only four eggs have ever been unearthed—all aresmushed or flattened. That makes the Turpan-Hami fossils extremely valuable for analyzing nesting habits. As the researchers write, “sites like the one reported here provide further evidence regarding the behavior and biology of this amazing group of flying reptiles that has no parallel in modern time.”
After the researchers realized they had a huge pterosaur find on their hands, they began systematically excavating the site, and in 2008, they came across their first egg: “I was more excited than surprised,” says Xiaolin Wang, a paleontologist at the Chinese Academy of Sciences in Beijing. With such a fossil-rich site, finding an egg wasn’t out of the realm of possibility.
The team recovered five eggs in total from the site. Microscopic and spectroscopic analysis revealed that the eggs had a thin shell for a top layer, made mostly of calcium carbonate, and underneath that lay a soft, thin membrane. “It is similar to ‘soft’ eggs of some modern snakes; the size and structure are nearly the same,” says Wang.
Beyond cracking the mystery of the eggs, the researchers also wanted to figure out how the Turpan-Hami Basin pterosaurs fit into the larger pterosaur family tree. They had removed fossilized bones from 40 individuals at Turban-Hami, though the entire site could ultimately yield hundreds.
After a closer examination of the bones, they found that these animals had marked differences from other species: a hooked bone at the end of the jaw, wider eye cavities, a well-developed forehead crest, a wrist bone with a protruding spike, and other unique features. Their wingspans ranged from 4 feet to 11 feet, and an evolutionary tree analysis suggested that the individuals belonged to a new genus and species of pterosaur, which the scientists named Hamipterus tianshanensis.
As they unearthed the specimens, the researchers also noticed that some individuals had the same skull (in shape and size) but different head crests: some were large, wrinkled, with a flare at the end of their snout, while others were smaller, smoother, and less protruding. The researchers think they’ve happened upon a sexually dimorphic trait—one that separates the boys from the girls.
Though some modern reptile species do have larger females, the trend in reptiles is big males, small females. So, Wang and his colleagues made the educated guess that, in the case of the pterosaurs, larger crests belong to males and the smaller crests to females.
For creatures like pterosaurs and dinosaurs, figuring out which has male bits and which has female bits can be a window into the lives of these ancient beasts. But as you might expect, sexual dimorphism—though suspected in pterosaurs—can be hard to nail down in fossilized animals. More analysis is needed to say for sure.
In addition, finding the bones and eggs present a picture of gregarious social life and reproduction behaviors that resembles that of modern reptiles. “These pterosaurs nested in the shore of the ancient lake and buried their eggs in the moist sand,” says Wang. The nesting behavior is similar to modern snake species, particularly rat snakes.
Finding in one location evidence of sexual dimorphism and of behaviors that are much more reptile-like than bird-like is quite rare. “This is something of a Holy Grail—a site potentially recording all of these interesting aspects in the same locality,” notes Mark Witton, a paleontologist at the University of Portsmouth who was not affiliated with the study.
“A long-extinct group of flying reptiles may seem unimportant in the big scheme of things, but they’re a component of something we must pay more attention to: our changing biosphere,” Witton added. “Looking at the way species and ecosystems have evolved through Deep Time gives us the only long-term insight into the way the natural world works—how it adapts to adversity, when it blooms and diversifies, and so forth.”
It also shows how populations can be snuffed out—near this lake, the nesting pterosaurs also met their demise. The fossil-containing rock layers at Turpan-Hami are divided by the mud and sand deposits traditionally left by huge storms. These storm layers, called tempestites, form when debris from different sediments mix together in the storm’s deluge. Here’s what the scholars think may have happened: “The storm may have killed live pterosaurs, and transported the dead bodies and eggs for a short distance,” says Wang “And then buried them quickly.”
It must have been horrible way to go for these ancient creatures, but a perfect storm for researchers, who now have a better picture of what life was like when lizards dominated the land and sky.
SMITHSONIAN.COM JUNE 5, 2014 Not long ago, a precious packet of blood traveled more than 7,000 miles by special courier, from America to Australia, to save the life of a newborn. Months before the delivery date, a routine checkup of the mom-to-be had revealed that the fetus suffered from hemolytic disease. Doctors knew that the baby would need a blood transfusion immediately after delivery. The problem was, the baby’s blood type was so rare that there wasn’t a single compatible donor in all of Australia.
A request for compatible blood was sent first to England, where a global database search identified a potential donor in the United States. From there, the request was forwarded to the American Rare Donor Program, directed by Sandra Nance. The ARDP had compatible frozen blood on hand, but Nance knew that a frozen bag might rupture in transit. So her organization reached out to the compatible donor, collected half a liter of fresh blood, and shipped it across the Pacific. When the mother came in to give birth, the blood was waiting. “It was just magic,” Nance says.
You’re probably aware of eight basic blood types: A, AB, B and O, each of which can be “positive” or “negative.” They’re the most important, because a patient who receives ABO +/– incompatible blood very often experiences a dangerous immune reaction. For the sake of simplicity, these are the types that organizations like the Red Cross usually talk about. But this system turns out to be a big oversimplification. Each of these eight types of blood can be subdivided into many distinct varieties. There are millions in all, each classified according to the little markers called antigens that coat the surface of red blood cells.
AB blood contains A and B antigens, while O blood doesn’t contain either; “positive” blood contains the Rhesus D antigen, while “negative” blood lacks it. Patients shouldn’t receive antigens that their own blood lacks—otherwise their immune system may recognize the blood as foreign and develop antibodies to attack it. That’s why medical professionals pay attention to blood types in the first place, and why compatible blood was so important for the baby in Australia. There are in fact hundreds of antigens that fall into 33 recognized antigen systems, many of which can cause dangerous reactions during transfusion. One person’s blood can contain a long list of antigens, which means that a fully specified blood type has to be written out antigen by antigen—for example, O, r”r”, K:–1, Jk(b-). Try fitting that into that little space on your Red Cross card.
Scientists have been discovering unexpected antigens ever since 1939, when two New York doctors transfused type O blood into a young woman at Bellevue Hospital. Type O was considered a “universal” blood type that anyone could receive, yet the woman experienced chills and body pain—clear signs that she was reacting to the blood. After running some lab tests, the doctors confirmed that even type O blood could contain previously unknown antigens. They’d accidentally discovered Rhesus antigens.
Additional kinds of antigens have been discovered every few years since then. Almost everyone has some. More than 99.9 percent of people carry the antigen Vel, for example. For every 2,500 people, there’s one who lacks the Vel antigen who shouldn’t receive blood from the remaining 2,499. (Like many blood types, Vel-negative is tightly linked to ethnicity, so how rare it is depends on what part of the world you’re in.) If a Vel-negative patient develops antibodies to Vel-positive blood, the immune system will attack the incoming cells, which then disintegrate inside the body. For a patient, the effects of such reactions range from mild pain to fever, shock and, in the worst cases, death.
Blood types are considered rare if fewer than 1 in 1,000 people have them. One of the rarest in existence is Rh-null blood, which lack any antigens in the Rh system. “There are nine active donors in the whole community of rare blood donors. Nine.” That’s in the entire world. If your blood is Rh-null, there are probably more people who share your name than your blood type. And if you receive blood that contains Rh antigens, your immune system may attack those cells. In all, around 20 antigen systems have the potential to cause transfusion reactions.
Just to be clear, transfusion patients today don’t have much to worry about. In 2012, there were tens of millions of transfusions in the United States, but only a few dozen transfusion-related deaths were reported to the U.S. Food and Drug Administration. Medical practitioners go to great lengths to make sure that transfused blood is compatible. But curiously enough, they manage to do this without even knowing all the antigens present.
Before a transfusion takes place, lab technicians mix a sample of the patient’s blood with the sample of a donor whose blood type is ABO +/– compatible. If the two samples clump, the blood may be unsafe to transfuse. “The moment you discover that, you do not know why,” Nance explains. Figuring out the precise cause of the problem is like solving a crossword puzzle, she says. “You test many donors that are known types, and you find out, just by process of elimination, what is the contributing factor that makes this incompatible.”
This was the process that helped the newborn in Australia. Lab technicians there had tested the fetal blood and figured out which antigens they needed to avoid. But they still didn’t know where in the world they might find suitable blood. So they sent a rare blood request to the international organization set up for cases just like this: the International Blood Group Reference Laboratory in Bristol, England. The IBGRL consults its database of hundreds of thousands of rare donors worldwide to find compatible blood. For the past 30 years, the process of global blood sharing has been gradually standardized during the biennial congress of the International Society for Blood Transfusion, which took place this week in Seoul, South Korea.
In the past two years, at least 241 packets of rare blood were shipped internationally, according to Nicole Thornton, head of Red Cell Reference at the IBGRL. Many more are shipped within national borders. In 2011, for example, more than 2,000 units of rare blood were shipped within the United States. It’s an impressive feat of coordination.
Even rare donor programs with the resources to identify and ship rare blood are looking to improve. There just aren’t enough rare donors who come in regularly. The American Rare Donor Program has 45,000 rare donors in its database, but 5 percent of transfusion patients still don’t get the blood they need. Coral Olsen, a scientist in charge of regional rare blood banking in South Africa, says that her laboratory often struggles to keep track of registered rare donors. “Because a lot of them are from rural settings, we often can’t get ahold of them. So that’s our challenge, as far as tracing and tracking and maintaining our rare donor base.”
For many countries, an even bigger challenge is simply dealing with resource constraints. National blood laboratories have to maintain a repository of samples if they want to run detailed antigen tests. Olsen says that in developing countries, where starting samples aren’t always available, it’s difficult to even begin classifying and sourcing rare blood. Finally, there’s the high cost of importing rare types, especially for patients who need chronic transfusions. In those cases, medical professionals sometimes have to use blood that’s known to be incompatible, but unlikely to cause severe reactions because of the particular antigens involved.
One day, scientific breakthroughs may make it easier to find compatible blood for anyone. Geneticists are working on testing methods that determine blood types using DNA, without looking at the blood itself. (So far, this process only works with certain antigens.) Nance hopes that one day, every newborn will undergo testing so that blood banks can build a comprehensive database of every rare type, which would immediately point medical professionals to the nearest compatible donor. Biochemists, meanwhile, have been testing chemicals that effectively mask the antigens on red blood cells, seeking to turn them into “stealth” cells that are functionally universal.
Until then, researchers will probably go on discovering antigens one by one. It’s as if the surface of red blood cells started out as a fuzzy picture that scientists have slowly brought into focus, revealing subtle differences that just weren’t visible before. For blood scientists and patients with rare blood types, these differences can be tedious and troublesome. But they’re also a reminder of our remarkable individuality. With hundreds of possible antigens and millions of possible antigen combinations, your blood can be as unique as your fingerprint.