Blogs from our Scientific Researchers

Carnegie Museum of Natural History is home to active research and vast scientific collections. Our scientific researchers regularly contribute to the blog at the museum.

June 8, 2020 by carnegiemnh

Is that snow…in June?

Collected on this Day in 1942

cottonwood seeds covering an outdoor trail

It can’t be snow, right? It’s summer! Maybe that is cotton falling from the sky? Well, kind of! It is cottonwood seeds!

Perhaps you’ve seen little cotton-like white particles falling from the sky in early summer, especially around Pennsylvania’s rivers or lakes. It is a common site along the dunes of Presque Isle, for example, and in areas along southwestern PA’s rivers. Aptly named, Eastern cottonwood (Populus deltoides) is a native tree found across the eastern United States that produces seeds that fall from high up in the canopy, attached to cotton-like strands. These fibers act like mini-parachutes and allow the wind to widely distribute the seeds.

This specimen of Eastern cottonwood was collected by Henry T. Skinner on June 8, 1942 on the sand dunes of Presque Isle, Erie. You might notice this specimen is not from the Carnegie Museum herbarium like most of these posts. But instead, this specimen is held at the Morris Arboretum (part of the University of Pennsylvania). Now that museum collections are being digitized, we can search for species of interest, or plants collected from certain places or by certain people, or more…that’s the power of specimen digitization. The Mid-Atlantic Megalopolis Project, funded by the National Science Foundation, is digitizing nearly a million specimens across our region, including Carnegie Museum specimens. This makes our collections all the more powerful, combining all specimens collected in the region and making them accessible to scientists and the public alike.

Find this and more Eastern cottonwood specimens from Presque Isle here.

Check back for more! Botanists at the Carnegie Museum of Natural History share digital specimens from the herbarium on dates they were collected. They are in the midst of a three-year project to digitize nearly 190,000 plant specimens collected in the region, making images and other data publicly available online. This effort is part of the Mid-Atlantic Megalopolis Project (mamdigitization.org), a network of thirteen herbaria spanning the densely populated urban corridor from Washington, D.C. to New York City to achieve a greater understanding of our urban areas, including the unique industrial and environmental history of the greater Pittsburgh region. This project is made possible by the National Science Foundation under grant no. 1801022.

Mason Heberling is Assistant Curator of Botany at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

June 8, 2020 by carnegiemnh

Tulips in June?!

Collected on this Day in 1920

Your tulips may be long gone as spring has faded, but tulip trees are in full force! Although it’s hard to catch a glimpse of them way up in the canopy, tulip tree flowers are just as stunning. Completely unrelated to tulips, Liriodendron tulipifera (called tulip tree, tulip poplar, or sometimes yellow poplar) is named such because its leaves have a distinctive shape reminiscent of tulips.

Found across eastern North America, Tulip trees are one the tallest and fast-growing trees native to Pennsylvania, growing up to nearly 200 feet tall! Tulip trees are relatively shade intolerant and therefore are especially common in young forests (early successional). However, the species can still be found in older forests too. Its tall straight trunks can be impressive, and its wood is widely used by woodworkers, who often refer to it as “poplar.” The tree is not related to true poplars (Populusspecies), which are in the willow family, Salicaceae. Tulip trees are a member of the magnolia family (Magnoliaceae). This beautiful specimen was collected on June 6, 1920 near Trafford, Pennsylvania by Otto Jennings. Jennings was an influential botany curator at the museum for many years.

Find this stunning specimen here.

June 4, 2020 by carnegiemnh

The Bromacker Project Part IV: Diadectes absitus, A Project-Saving Fossil

New to this series? Read The Bromacker Fossil Project Part I, Part II, and Part III.

This post will be the first of a series focusing on notable fossil animals discovered in the Bromacker quarry. I selected Diadectes absitus, a member of the ancient group Diadectomorpha, to present first because, had it not been discovered in the first year of the collaborative field work, the project might not have continued.

Dave Berman and his colleague Stuart Sumida (California State University, San Bernardino) joined Thomas Martens for five weeks of field work in the summer of 1993. They dug a quarry over six feet deep in their search for fossils, while working in a mix of hot and humid or near freezing temperatures, with plenty of rain. It wasn’t until the second-to-last day of the field season that the Diadectes specimen was discovered. By then, as Dave later told me, he was so discouraged by the lack of fossils that he assumed this would be his first and last field season in Germany. I should mention that Stuart had previously uncovered a few small vertebrae, but because the vertebrae resembled an animal described from the Bromacker in 1991, the team was not very excited about the discovery. They couldn’t have been more wrong in their field identification of the vertebrae, however, but more on that in a later post.

The 1993 quarry shortly before discovery of *Diadectes absitus*. Pictured are Stuart Sumida standing in the quarry and Thomas Martens crouched to his right. The *Diadectes* fossil was found in the corner opposite Stuart’s left shoulder, which is out of sight in this image. Photo by Dave Berman, 1993.

The team’s collective attitude changed when Stuart knocked off a chunk of bone-bearing rock from a bench in the quarry corner while shoveling away rock rubble. Careful examination of the fragment revealed part of the top of a roughly five-inch-long skull. We have since joked that Stuart gave it a lobotomy. While collecting the large block of rock containing the remainder of the skull, another piece of rock popped off the the edge of the block adjacent to the quarry wall. This piece had vertebrae in it. The team then realized that only the front portion of the animal was in the block freed from the quarry. The rest of the fossil skeleton remained in the quarry wall. Thomas later excavated the rest of the specimen and shipped it separately to Carnegie Museum of Natural History (CMNH).

You can watch Dave and Stuart excavate the fossil-bearing block by clicking on the video link at the end of this post.

Based on the shape of both the exposed teeth in the broken skull and the exposed vertebrae, Dave and Stuart were able to identify the fossil animal as the genus Diadectes. Thomas had already collected a juvenile skull and other bones of Diadectes before his collaboration with Dave, but the specimen discovered in 1993 was by far the most complete and best preserved.

Skeleton of *Diadectes absitus*. Some of the limb bones are preserved on the underside of the block. Photo provided by Thomas Martens.

Once my preparation of the specimen was completed, which took a little over a year, Dave, Stuart, and Thomas begin their detailed study and description of the fossil. They determined that it represented a new species, which they named Diadectes absitus. “Absitus” is Latin for distant or far, in reference to the species being the first occurrence of Diadectes outside of North America. The generic name Diadectes was coined in 1878 by the famous paleontologist Edward Drinker Cope, and is a combination of the Greek “dia,” meaning crosswise, and “dēktēs,” meaning biter, in reference to its broad teeth. Other species of Diadectes occur in similar-aged rocks in the American southwest, and a few specimens are known from the Tri-State area of Pennsylvania, Ohio, and West Virginia.

Diadectes is a member of the group Diadectomorpha, which has oscillated between being considered a member of Amphibia or Amniota. Amphibians lay their eggs in water, which then hatch into tadpoles that later undergo metamorphosis. Today this group includes frogs, salamanders, and caecilians (limbless, worm-like burrowing amphibians). In contrast, amniotes either lay their eggs on land, like reptiles and birds do today, or the embryo develops sufficiently in the mother for live birth, as in most mammals. Except in rare cases, the type of developmental pathways of fossil animals cannot be determined because they are rarely preserved with their eggs or fetuses. Paleontologists instead study a variety of preserved features to determine group membership. As an example, amphibians typically have four fingers, whereas amniotes generally possess five.

Diadectes and its close relatives were herbivorous, that is, they ate plants. Their spatulate, incisor-like front teeth project forwards and were adapted for cropping vegetation. Longitudinal, parallel striations on their broad cheek teeth suggest that Diadectes could move its lower jaw fore and aft to grind plant matter against its upper jaw teeth, a motion called propalinal.

Skull of *Diadectes absitus* in right lateral (= right side) aspect. Notice the forward-angled front teeth and the bulbous cheek teeth. A black pen was used to mark the boundaries of individual bones in the skull, which aided study of the animal. Modified from photo provided by Thomas Martens.

The presence of an enlarged torso and teeth adapted for grinding tough vegetation are evidence that Diadectes absitus likely consumed a diet of high-fiber plants. Animals that eat high fiber plants, such as cows, have enlarged torsos framed by a rounded rib cage to hold large guts for processing plant cellulose through fermentation by microorganisms.

Diadectes absitus lived at a time when herbivores were just beginning to evolve. One of the oldest known herbivores is the diadectomorph Desmatodon hollandi, which lived about 305 million years ago, whereas Diadectes absitus lived roughly 290 million years ago. We discovered a surprisingly high number of herbivores at the Bromacker.

Teeth of one of the oldest known herbivores, the diadectomorph *Desmatodon hollandi*. This specimen was discovered in Pitcairn, PA by Percy E. Raymund (Assistant Curator, Section of Invertebrate Paleontology) in 1907 and named in honor of Dr. William Holland, the second Director of CMNH. The teeth of Desmatodon are very similar to those of *Diadectes absitus*. Photo by the author, 2018.

A cast of the skeleton of Diadectes absitus is exhibited in the Fossil Frontiers display case in the Dinosaurs in Their Time exhibition. Be sure to look for these once the museum re-opens. And stay tuned for my next post, which features another diadectomorph, Orobates pabsti.

Photograph of a model of *Diadectes absitus* made by the Museum der Natur, Gotha exhibit preparator Peter Mildner. Photo provided by Thomas Martens.

Dave and Stuart excavate the fossil-bearing block (video)

Amy Henrici is Collection Manager in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

Keep Reading

The Bromacker Fossil Project Part V: Orobates pabsti, Pabst’s Mountain Walker

June 1, 2020 by carnegiemnh

What’s So Good About Being a Slug?

When lifestyles or forms evolve multiple times, we often think they must have some benefit. For example, flying creatures evolved at least 4 separate times: birds, bats, insects, and pterosaurs. These 4 separate origins of flight support the idea that there must be an advantage to flying. (You can probably think of some advantages.)

Slugs evolved from snails more than a dozen separate times. By that logic, there must be an advantage to being a slug, but compared to flight, it’s harder to think what the advantage might be. Slugs evolved from snails by reducing the size of the shell and internalizing it (yes, most slugs have an internal shell), and there are likely to be consequences of reducing the shell.

A snail with an external shell large enough for the body to pull back into. *Webbhelix multilineata* from Ann Arbor, Michigan.

Furthermore, in the lineages leading from snails to slugs, an intermediate stage occurs called a semi-slug (not a slug the size of a semi-truck). In contrast to snails that have an external shell large enough to accommodate the body, or slugs in which the shell is completely internal or absent, semi-slugs have an external shell, but the shell is too small to accommodate the animal’s entire body. Many semi-slugs live on our planet today (for example, Vitrinizonites latissimus lives in the Great Smokey Mountains). Curiously, semi-slugs evolved from snails at least 22 times.

A semi-slug whose external shell is too small for the body to fit into. Family Urocyclidae from Mount Kenya

Let’s consider some possible advantages and disadvantages of these body forms: protection from predators, protection from desiccation (drying out), need for calcium, and fitting into tiny hidey holes. As shown in the table, shells protect snails from predators and from drying out, but the snails still need lots of calcium to build shells, and the rigid shell prevents them from squeezing into tiny hidey holes. Snail score: 2 advantages, 2 disadvantages. Slugs, on the other hand, are not protected from predators or drying out, but have less need for calcium and can fit into tiny hidey holes. Slug score: 2 advantages, 2 disadvantages. However, semi-slugs seem to have all disadvantages: no protection from predators or drying out, a need for calcium, and can’t fit into tiny hidey holes. Semi-slug score: 0 advantages, 4 disadvantages.

	Predator protection	Desiccation protection	Need less calcium	Fit in tiny hidey holes
Snail	+	+	–	–
Semi-slug	–	–	–	–
Slug	–	–	+	+

In evolution, every form in a lineage must have at least a limited track record of survival, so how did slugs evolve from snails if they had to go through a life form having so many disadvantages, and how could that evolution have happened so many different times?

A slug with an internal shell (not visible). Ariolimax cf californicus from the Santa Cruz Mountains, California.

Although we don’t know the answer for sure, my studies suggest some possible answers. I examined locations where slugs and semi-slugs evolved from snails. I discovered that many of those events seem to have happened on oceanic islands (40%) and within 35° of the Equator (80%). Islands often have fewer predators and tropical and subtropical islands often have regular moisture inputs (daily rain or fog), so on islands there might be less need of shells or hidey holes for protection from predators or desiccation. I’m not sure what to predict about calcium because many islands are volcanic, with calcium-poor soils, but calcium carbonate would be available from empty seashells washed up on the shore. If calcium were difficult to find, that might favor forms needing less calcium. Evolutionary biologists use the term “relaxed selection” to refer to a situation in which changes to an organism’s environment cause less need to maintain certain forms or behaviors.

It seems likely to me that relaxed selection on tropical islands allowed the evolutionary transition from snails to semi-slugs to slugs by reducing the disadvantages of having, or not having, a shell.

Where better to be sluggish than on a tropical island?

Timothy A. Pearce, PhD, is the head of the mollusks section at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

May 29, 2020 by carnegiemnh

Plants with bladders?

Collected on this Day in 1940

This specimen was collected on May 29, 1940 by Leroy Henry along Pine Creek, north of Wildwood outside of Pittsburgh. Leroy Henry was a mycologist (studied fungi) and botanist who was curator at Carnegie Museum from 1937-1973.

Aptly called “bladdernut” (Staphylea trifolia), this charismatic native understory shrub produces clusters of white flowers in the spring. These dangling flowers develop into striking bladder-like fruit. In each “bladder” pouch are seeds. These fruit often persist through fall and some linger through winter, though the plant is leafless.

Bladdernut has a wide range across eastern North America, and can be found in relatively undisturbed forests in our area, often forming thickets.

Find this specimen here.

Check back for more! Botanists at the Carnegie Museum of Natural History share digital specimens from the herbarium on dates they were collected. They are in the midst of a three- year project to digitize nearly 190,000 plant specimens collected in the region, making images and other data publicly available online. This effort is part of the Mid-Atlantic Megalopolis Project (mamdigitization.org), a network of thirteen herbaria spanning the densely populated urban corridor from Washington, D.C. to New York City to achieve a greater understanding of our urban areas, including the unique industrial and environmental history of the greater Pittsburgh region. This project is made possible by the National Science Foundation under grant no. 1801022.

May 27, 2020 by carnegiemnh

Mesozoic Monthly: Citipati

The month of May that we’re living in is very different from the one we all anticipated at the start of the year. However, society somehow manages to march on. College students are still graduating, moms are still being celebrated, and Mesozoic Monthly continues! Our honoree for the month of May is known to have been a dedicated parent due to several specimens that show adults guarding eggs. Say hello to Citipati osmolskae!

illustration of Citipati, a dinosaur that looks similar to a bird, on a nest of blue eggs

A devoted Citipati parent guarding its nest. Some evidence suggests that the Citipati skeletons found atop nests may have been males (rather than females as was originally thought). Also, recent research indicates that—believe it or not—oviraptorid eggs were blue! Art by ginjaraptor on DeviantArt.

It might not look like it, but Citipati is a theropod, like the more famous dinosaurs Tyrannosaurus, Allosaurus, and Velociraptor. Most theropods were carnivores, sporting skulls with big toothy grins, but not all theropods were ravenous predators! There are several groups of theropods that evolved toothless beaks for specialized diets. One of the stars of Jurassic Park, Gallimimus, was part of a predominantly herbivorous group of beaked theropods called Ornithomimidae. Citipati belongs to another group of beaked theropods called Oviraptoridae. “Oviraptor” means “egg thief,” in reference to an old hypothesis that oviraptorids stole and ate eggs from other dinosaurs’ nests. The discovery of a Citipati skeleton perched in a brooding position atop a nest of eggs was pivotal in changing this idea. We now know that instead of stealing others’ eggs to eat, fossilized oviraptorids preserved near eggs were actually protecting their own eggs! The eggs in an oviraptorid’s nest were arranged in circles with a space in the center for the parent to sit and spread their feathered arms over their incubating young.

Citipati and other oviraptorids are closely related to one of Carnegie Museum of Natural History’s most bizarre dinosaurs, the ‘Chicken from Hell’ Anzu wyliei, shown here on display in the museum’s Dinosaurs in Their Time exhibition.

So, instead of eggs, what would the toothless beak of Citipati have been used to eat? Because most oviraptorid beaks are very deep, like those of modern parrots, most paleontologists infer that these dinosaurs ate mostly plants. However, this doesn’t necessarily mean that meat was off the menu; it would still have been possible for oviraptorids to have eaten small animals, making them omnivores. On top of its thick skull, Citipati possessed a tall, triangular crest that gave its small head a square-shaped profile. This crest was not as impressive as those on some other dinosaurs, but since Citipati grew to ten feet (three meters) long, the animal would still have been quite imposing. I certainly wouldn’t want to get between a Citipati parent and its eggs!

Citipati fossils are found in the modern Gobi Desert of Mongolia, in rocks known as the Djadokhta Formation. The Djadokhta rocks are made of sediments that were deposited late in the Cretaceous Period, preserving details of the ecosystem that existed there roughly 80–75 million years ago. The name Citipati means “funeral pyre lord,” which is fitting due to the hot environment in which this oviraptorid lived. Also, Citipati shares its name with a Buddhist deity that is believed to protect cemeteries from thieves, which is an appropriate parallel considering how the skeleton of this dinosaur was found guarding its fossilized nest.

Although the habitat Citipati lived in was a desert, like the Gobi Desert that is there today, this prehistoric desert was probably not as dry. In the event of rain, water gathered in temporary streams that drained the water to basins and oases. Since desert rain events are by definition few and far between, any animals that did not live near these oases would have needed to have adaptations for going without water for a long period of time. Some of the animals that lived in this unwelcoming environment alongside Citipati included everyone’s favorite small theropod Velociraptor, the hornless ceratopsian Protoceratops, and the tail-club wielding ankylosaur Pinacosaurus.

Lindsay Kastroll is a volunteer and paleontology student working in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum staff, volunteers, and interns are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

Is that snow…in June?

Collected on this Day in 1942

Tulips in June?!

Collected on this Day in 1920

The Bromacker Project Part IV: Diadectes absitus, A Project-Saving Fossil

Dave and Stuart excavate the fossil-bearing block (video)

Keep Reading

What’s So Good About Being a Slug?

Plants with bladders?

Mesozoic Monthly: Citipati

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