New Science Bulletin: Sharks--the Past
Scientists use CT scanning technology to compare living and fossil sharks. Over their 450 million-year evolutionary history, sharks have evolved a tremendous diversity of traits, including the ability to detect low-frequency sounds coming from potential prey.
While many of us grew up learning that dinosaurs were physical giants with puny brains, that’s actually not the case, especially for the animals that turn out to be most closely related to birds, such as tyrannosaurs and velociraptors. For the past eight years, Dr. Amy Balanoff has worked to map the big brains of long-dead dinosaurs and find connections to modern birds.
Using an innovative method for peering inside soft-bodied animals, researchers have described a new species of leech and named it after best-selling author Amy Tan.
Chtonobdella tanae, a terrestrial leech from Australia, is the first new species of invertebrate without chitinous or calcified tissues (like a shell or exoskeleton) to be described using computed tomography (CT) scanning. The work was recently published in the journal Zoologica Scripta, and represents a new avenue for studying soft-bodied organisms like worms and jellyfish—especially those like Chtonobdella tanae which, at about 1 centimeter long and 2 millimeters wide, is too small to dissect.
“Historically, to get an idea of what the internal structure of a soft-bodied invertebrate looks like, you have to dissect it by hand or painstakingly section the specimen and then reconstruct it in three dimensions,” said Michael Tessler, lead author on the paper and a student in the comparative biology doctoral program at the Museum's Richard Gilder Graduate School. “CT imaging is not only more precise than physical dissection, but it also doesn’t require us to destroy the specimen we’re studying.”
New research led by scientists at the American Museum of Natural History reveals that the unique way that birds breathe likely first appeared in their dinosaur ancestors. The findings, published recently in the journal PLOS ONE, build upon mountains of recent work exploring the origin of “bird-like” traits such as feathers, wishbones, and flight.
Birds have a highly efficient respiratory system powered by four sets of air sacs that pump air throughout their body. This adaptation allows the air to flow in one direction (as opposed to mammals, like us, who breathe in and out through the same tube) and is vital to birds’ ability to fly high over long distances.
During bird development, finger-like projections from these air sacs invade bone to create networks of internal chambers, a condition called pneumaticity. However, how and why this unique feature evolved in dinosaur ancestors is largely unknown. To directly see these pneumatic chambers in fossils, the researchers used high-resolution computed tomography (CT) scanning, for the first time, on the backbone of a dinosaur closely related to birds, 70-million-year-old Archaeornithomimus.The specimen used in the study was collected on the Museum’s Central Asiatic Expedition to Mongolia in 1923.
“Our work shows that at least part of the avian respiratory system was already in place in Archaeornithomimus, and therefore likely evolved in the common ancestor of birds and Archaeornithomimus over 150 million years ago,” said Aki Watanabe, the paper’s lead author and a student in the comparative biology doctoral program at the Museum’s Richard Gilder Graduate School. What they found was a remarkable network of pneumatic chambers in the vertebrae of the neck and chest, a detail never seen previously.
Museum scientists are getting an up-close look at an extremely rare—and extremely small—shark by taking high-resolution, three-dimensional x-ray scans.
National Oceanic and Atmospheric Administration (NOAA) researchers were trawling in the Gulf of Mexico for a sperm whale feeding study in 2010 when they inadvertently pulled up a tiny, odd-looking shark with a bulbous head and rows of sharp teeth. NOAA researchers subsequently identified the creature as the rare pocket shark (Mollisquama sp.). The specimen is only the second ever collected, 36 years after the first one was found off the coast of Chile.
Named for two small openings above its pectoral fins, the pocket shark is still mostly a mystery, as is the purpose its pockets serve. But instead of dissecting this rare 5.5-inch-long specimen, scientists have turned to non-destructive x-ray techniques: computed tomography (CT) scanning in the Museum’s Microscopy and Imaging Facility and at the European Synchrotron Radiation Facility (ESRF) in France.
“The level of detail we can achieve through x-ray imaging is just incredible,” says John Maisey, a curator in the Museum’s Division of Paleontology who has been working with NOAA researchers and Museum Axelrod Postdoctoral Fellow John Denton to scan the specimen. “It allows you to look at these priceless specimens in a way you couldn’t have 10 or 15 years earlier.”
The CT scans proved especially valuable for counting the vertebrae of the pocket shark, the smallest of which were too small to be picked up using standard x-ray imaging, and for counting the teeth. Many of the specimen’s teeth were missing, but by rotating the image of the jaw and examining its inner surface, researchers were able to count the tiny new teeth coming up to take their place.
The species appears to be closely related to cookie cutter sharks, which feed by taking bites out of the skin of larger animals. And the anatomy of the pocket shark’s jaws and teeth indicate that it inhabits a similar ecological niche.
As for the shark’s mysterious pockets, one working hypothesis is that that they might emit a bioluminescent fluid to either attract mates or to confuse predators. Maisey and Denton are now poring over the extremely high-resolution scans taken at ESRF with Mark Grace, the biologist with NOAA’s Southeast Fisheries Science Center who discovered the specimen, to learn more about their anatomy.
But anything gleaned from the scans will likely remain hypothetical until scientists can observe a pocket shark in action.
“I would love to see a pocket shark alive in its environment,” Grace says. “But the CT scans are the next best thing.”
The latest episode of Shelf Life introduces viewers to foraminifera, microscopic marine organisms known informally as forams.
Although foraminifera are single-celled creatures, they have tiny shells that come in an amazing array of shapes. Forams are usually tiny, about half a millimeter long, but larger specimens can measure up to 20 centimeters—about the length of a guinea pig. (Yes, you read that correctly—a single-celled organism the length of a guinea pig.)
Though there are more than 10,000 recognized species of forams, these organisms can be broken down into two main groups: benthic forams, which live in deep ocean habitats, and planktonic forams, which live in warmer waters closer to the surface.
CT Scan Footage: AMNH/Shaun Mahmood
Three-dimensional scans of two mummified newborn woolly mammoths recovered from the Siberian Arctic are revealing previously inaccessible details about the early development of prehistoric proboscideans. The research, conducted in part by American Museum of Natural History Richard Gilder Graduate School student Zachary T. Calamari, also suggest that both animals died from suffocation after inhaling mud. The findings were published July 8 in a special issue of the Journal of Paleontology.
“These two exquisitely preserved baby mammoths are like two snapshots in time,” said Calamari, who began investigating mammoths as an undergraduate at the University of Michigan working with paleontologist Daniel Fisher. “We can use them to understand how factors like location and age influenced the way mammoths grew into the huge adults that captivate us today.”
