Natural Wonders: Treasures of the TMM

TMM2415-1, SiO₂
Found in Rio Grande do Sul, Brazil

This enormous amethyst geode weighs about 250 pounds. A geode is a hollow globular rock that is lined with inward-facing crystals. Geodes form over time as water seeps into cavities within rocks and leaves behind different minerals. These minerals can form large, distinct crystals as seen in this amethyst quartz geode. Can you spot another mineral, white calcite, inside this geode?

This wonderful specimen has a rich purple amethyst color. Amethysts are the most valuable variety of quartz, and were one of the first gemstones used by people around the world. The Greeks believed that drinking wine from an amethyst cup would prevent intoxication. Royalty has also favored the purple gemstone, and at one time amethysts were reserved for royalty alone. Amethysts are found in the British Crown jewels.

B345, Al₂[F/OH₂/SiO₄]
Weighs 1778 carats (heavier than a full can of soda)
Found in Dawson Mine, Minas Gerais, Brazil

Topaz has fascinated human cultures for hundreds of years. It occurs in many colors, not just blue, and is used in jewelry because of its hardness and beauty. The intense blue color of this topaz specimen is probably natural. Today topaz is often irradiated to create artificial blue colors for jewelry. Many times it also has inclusions, or imperfections, inside the gem. Look closely at this specimen, and you’ll see clear through to the other side. It is very rare to find a large topaz like this one so clear, and with natural blue color. Blue topaz is also found in Mason County and is the state gemstone of Texas.

B371, SiO₂
Found in the Irai District, Rio Grande Do Sul, Brazil

Citrine is quartz with a lemon yellow color. In natural citrine this color is produced by iron. But natural citrine is rare, so amethyst quartz is often heated or irradiated to change its purple color. The dark yellow to red brown color of this specimen formed when it was heated to more than 1000 degrees Fahrenheit.

Aluminum silicate - Al2SiO5, NPL 3098
From Taquaral, Minas Gerais, Brazil

The fine blue blades of this kyanite specimen are unusual because of their size and color. They are often embedded in quartz as they are here, and can easily break away. Most of the crystals in this specimen are fully formed or terminated which is unusual for kyanite. These superb crystals can measure almost six inches (145 mm) long. They represent the finest kyanite available today.

Kyanite is typically formed during metamorphism when rocks are subjected to increasing pressure and temperature. Kyanite is a polymorph; it has the same chemical makeup as two other minerals, sillimanite and andalusite. They all have the same chemical formula, but each has its own distinct crystal structure and physical properties. Kyanite and the other two polymorphs are each stable at a different temperature and pressure. By studying where each of these polymorphs is formed, scientists can discover much about the geologic history of the rocks containing these minerals.

Look for this beautiful mineral specimen in the SILICATES display case.

Coilopoceras eaglefordensis, BEG35442
Lived around 90 million years ago
Found at Chispa Summit, Jeff Davis County, Texas

Ammonites are an extinct group of predators from Mesozoic seas. The ammonite's closest living relative is the squid, but ammonites look most like the present-day Nautilus, to the right. Each animal lived in a large chamber inside a shell, and created a spiral of chambers as it grew larger. Look at the cut shell of the Nautilus, and you can see that the walls of each chamber connect with the outer shell. These connections are called sutures, and the shape of the lines is called the suture pattern.

This ammonite fossil has been painted to reveal the suture patterns. Each ammonite species has a different suture pattern, so scientists often highlight the patterns to make them easier to study. Look closely at the top right corner of this specimen. There are peg-like indentations on both sides of the fossil— most likely teeth marks from the forceful bite of mosasaur! Ammonites grew to very large sizes and would have made a good meal for the enormous mosasaur.

Placenticeras meeki, TMM 2415-3
Lived about 71 million years ago
Found in Southern Alberta, Canada

This large ammonite is a different genus and species than the one to the left. It is very special to the museum because its shell has been preserved in an unusual way. All ammonites created their shells by secreting layers of a mineral called aragonite. In life these layers were shiny and iridescent, and the inside of the shells looked like some present-day mollusk shells. But it is very rare to find the aragonitic layers preserved in a fossil, and ammonites like this one are valued as gemstones. When aragonitic ammonites are cut and made into jewelry, the stones are called ammolite.

The iridescent colors of this specimen are mostly fiery reds and hints of green. Keep your eye on the fossil as you slowly move from side to side. Does the color change?

These ammonites are now on permanent exhibit in the Hall of Geology and Paleontology.

Canis dirus, TMM 31021-1
Lived from 40,000 to 10,000 years ago
Found in Rancho La Brea tar pits, Los Angeles County, California

The dire wolf Canis dirus lived from 40,000 to 10,000 years ago, ranging from Canada through the Americas to Venezuela, Bolivia, and Peru. This fossil is from the famous “La Brea Tar Pits” at Rancho La Brea, in Los Angeles. More than 2,000 dire wolves have been found preserved in the asphalt deposits of the tar pits. The wolves came to the pits to prey on trapped animals, but often became trapped themselves. They died a slow death in the tar pits, and then became food for other scavengers. That's one reason why most of the fossil dire wolf skeletons found at the tar pits are not complete. Even TMM 31021-1 is a composite, meaning the bones are from more than one individual.

Dire wolves were about the size of modern day gray wolves (Canis lupus), but were more massive in build, with a large broad skull. The teeth and jaws of dire wolves were capable of cracking bone! But life was not always easy for these large predators. Look just above the left eye of this specimen. There is a healed injury to its skull that was probably from the powerful kick of a hoofed prey animal. Many dire wolves recovered from the tar pits show evidence of injuries from the hooves or horns of large mammals such as bison.

The dire wolf is now on permanent exhibit in the Hall of Geology and Paleontology.

NPL 14795
Found in the Erfoud region of Morocco

This intriguing limestone slab was extracted from Middle-Upper Ordovician (about 450 million years old) rocks in the Anti-Atlas part of the Atlas Mountains of Morocco. This slab was once part of an ancient sea floor that was uplifted and incorporated into mountains about 80 million years ago, long after the sea floor turned into thick layers of rock.

The fossils preserved in this slab include early echinoderms (spiny-skinned marine invertebrate animals) known as eocrinoids and ophiuroids (brittle stars). The brittle stars are clearly recognizable, with their five prehensile arms and compact central body. They look very similar to living species of brittle stars, most of which live in reef, shallow near shore and deeper water environments, and feed on small organisms suspended in the water.

Eocrinoids are more unusual, with long thin tapering stems and clusters of arm-like appendages at the opposite end. These animals are probably the eocrinoid Ascocystites, a suspension feeder that would have extracted food directly from the water column, filtering out micro-organisms with the help of those appendages.

Despite the name, eocrinoids were unrelated to crinoids (sea lilies) and differ in several morphological features from ancient and modern crinoids. However, like many fossil crinoids, their elongated stem allowed for attachment to hard substrates and the possibility of raising themselves higher off the sea floor.

There appear to be several larger individuals along with a number of much smaller ones. Those smaller animals may be juveniles of the larger form or a different species. Do you notice how the smaller individuals often seem to be in close contact with the brittle stars? We are left to wonder whether the brittle stars were feeding on the smaller eocrinoids.

This beautiful slab is now on permanent exhibit in the Hall of Geology and Paleontology.

Homotherium serum
TMM 933-3235, TMM 933-3497
Lived around 20,000 years ago
Found in Friesenhahn Cave, Bexar County, Texas

The scimitar-toothed cat Homotherium serum lived in Texas around 20,000 years ago but ranged widely in North America for almost 2 million years. These rare fossils are the complete skeletons of juvenile scimitar-toothed cats, or young kittens. The earth was not disturbed after the kittens died, so the fossils are well preserved. By studying the bones of these kittens scientists can learn about the growth and behavior of all saber-toothed cats. TMM 933-3235 is the larger kitten, and lived to be about four months old. TMM 933-3497 was about 2-3 months old when it died. The kittens would have grown to the size of an African lion, about 6 feet long and weighing around 300 pounds. But unlike lions these cats had longer front legs, and could easily run and leap upon prey. In fact, scimitar-toothed cats killed animals like young mammoths— larger than themselves— and dragged them into the cave. The cats used Friesenhahn Cave as a den, and more than 300 teeth from juvenile mammoths have been found there.

A Texas Memorial Museum field party including Glen Evans, Grayson Meade, Charles Mear, John White, Carl Moore, and Kenneth Rochat excavated at Friesenhahn Cave during the summers of 1949 and 1951. The group discovered the kittens and other fossils, including an adult scimitar-toothed cat.

The kittens are now on permanent exhibit with an adult cat in the Hall of Geology and Paleontology.

Archaeocidaris sp.; Delocrinus sp.
1967TX100
Lived around 300 million years ago
Found at the Lake Brownwood spillway, Brown County, Texas

This rare fossil slab is overflowing with sea urchin specimens. Even the spines are preserved, because the mud around them was not disturbed after death. We do not know how these animals died, although it was probably not due to force. Changes in temperature or salinity of the ocean water could have caused their death.

By studying the animals here and how they are grouped together, scientists can learn about all modern day sea urchins. The slab shows that sea urchins were already aggregating, or living in groups, around 300 million years ago. Today sea urchins group together to feed and to breed.

Look closely and you’ll also see a ring shape with flattened plates beside a long, thin stalk. The stalked sea lily Delocrinus was very common during the Paleozoic but now lives only in ocean water more than 100 meters (328 feet) deep.

The sea urchins and sea lily are now on permanent exhibit in the Hall of Geology and Paleontology.

Crateraster mccarteri (originally Austinaster mccarteri)
TMM BEG 34041
Late Cretaceous (about 85 million years ago)
Travis County, Texas

These sea stars (starfish) were found in Bouldin Creek, here in Travis County. This is one of two pieces that were cut out of a 1200-pound slab. The smaller piece was first exhibited in 1936, and the sea stars have been gems of the university's collections ever since. They were featured in the 1986 exhibit, "Treasures of the Texas Memorial Museum," which celebrated the Museum's 50th birthday.

Sea stars are invertebrates that can be found in oceans all over the world. They live in a wide range of marine environments, and they vary greatly in size and shape. In fact, there are about 1800 different species of sea stars alive today, and hundreds more are known from the fossil record.

The specimens are embedded in a limestone known as the "Austin Chalk." This layer of rock was formed from the settling of fine layers of sediment during the late Cretaceous, about 85 million years ago.

Surprise! Did you know that, occasionally, a "five-legged" starfish is born with only four legs? Variation like this occurs in all natural populations. However, it's very rare that enough individuals are fossilized together for us to see this variation in fossils.

The sea stars are now on permanent exhibit in the Hall of Geology and Paleontology.

Quetzalcoatlus northropi, TMM 41450-3

Soaring through the Great Hall of Texas Memorial Museum is the reconstructed skeleton of one of the the largest flying creatures ever discovered. Fossil remains of this giant pterosaur were found in 1971 by Douglas Lawson, a graduate student working with the Texas Memorial Museum's Dr. Wann Langston, Jr. Quetzalcoatlus lived in what is now Big Bend National Park, in West Texas, about 65 million years ago, during the late Cretaceous Period. Its wingspan is estimated to have been 36 feet.

Pterosaurs (pronounced "TARE-uh-soars") were flying reptiles, and they were not close relatives of either birds or bats. When Lawson first found bone fragments from this animal, he was not sure what they were. He and Langston examined the fragments and realized that the bone's shape and hollow structure could only be those of a pterosaur. Quetzalcoatlus is one of the most famous finds in the history of paleontology. Its discovery was reported in journals, newspapers, and radio and television broadcasts all over the world. Later, it became famous again, when CalTech's Paul MacCready built a flying model of the creature in the mid-1980s.

TMM 41436-1
Lived about 65 million years ago
Found in Big Bend National Park, Brewster County, Texas

This fossil is the upper jaw of the dinosaur Tyrannosaurus. The University of Texas at Austin graduate student, Doug Lawson, found this specimen in Big Bend National Park in 1970. Most Tyrannosaurus fossils are found in the foothills of the central and northern Rocky Mountains, so this find is special to scientists. It shows us that Tyrannosaurus once ranged as far south as present-day West Texas.

This Tyrannosaurus was relatively small, and had grown to only about thirty feet long when it died. You can see many of the tooth roots on this fossil because part of the outer jaw is broken away. Can you see how deeply the roots fitted into the jaw? Tyrannosaurid teeth were very thick, and had deep roots that anchored the teeth during powerful biting. Scientists believe that the strength of tyrannosaurid teeth evolved to deal with more dangerous prey like Torosaurus.

The Tyrannosaurus jaw is now on permanent exhibit in the Hall of Geology and Paleontology.