#orobates

Result from the Bromacker #Paleostream

It's been a while since we were able to put nearly all animals onto a formation piece!

It was a joy to put this one together because it felt a little like coming home. #Paleostream has a long history with this locality.

I already made this size chart years ago but parts of it were kind of eye balled back then and so I put together a second version

Bromacker Contest Submission #3

DREAMS ON THE HIGH PLATEAU

An ancient four-footed critter stomped around what is now Germany some 280 million to 290 million years ago. One of the earliest creatures to live fully on land, it was pretty good at trekking about, a new study finds. For their study, researchers relied on computer simulations, imitation skeletons and fossil footprints. They even built a walking robot  —the OroBot — to find out how the creature likely moved. The results suggest that efficiently walking upright evolved earlier than researchers once thought.

The scientists started with fossil evidence of Orobates pabsti (Oh-roh-BAY-tees PAB-sty). It was one of the earliest amniotes (AM-nee-oats). And unlike amphibians, which have young that must live in the water, amniotes can live entirely on land. Amniotes first arose some 350 million years ago.

This fossil of Orobates pabsti was discovered nearly 20 years ago at a site in central Germany. It’s been helping researchers deduce how the animal likely walked.

CREDIT:  THOMAS MARTENS/MUSEUM DER NATUR GOTHA

Membranes surrounded their developing young. This allowed amniotes to walk away from a tadpole-type life stage in the water. Reptiles and birds instead surround their embryos with an egg. Most mammal embryos grow inside their mother.

This amniotic membrane was key to allowing early reptiles to leave the water and thrive in drier habitats, says John Nyakatura. He is a paleontologist — someone who studies fossils — at the Humboldt University of Berlin, Germany. He also led the new study.

Learning how early amniotes walked on land could help scientists better understand their evolution from earlier creatures. It also could help explain how amniotes spread globally, Nyakatura says — eventually becoming reptiles, birds and mammals. “Orobates, our focus fossil in this story, is a very close cousin to the last common ancestor of mammals and reptiles,” he explains.

O. pabsti arrived on the scientific scene in 2004. In life, it looked like a large lizard around the size of an iguana. The first fossils showed up at a site in central Germany known as the Bromacher locality. Hundreds of millions of years ago, this site was in a valley between mountains. From time to time, when there was a storm, the valley would flood. Animals strolling through the area left footprints behind in the squishy mud. Sometimes, those animals might die there as well. Eventually buried in mud, they would begin the process of becoming a fossil. O. pabsti is one of the most complete fossils found at this site.  

“These are things preserved from the tip of the nose to the tip of the tails,” notes Stuart Sumida. He is a vertebrate paleontologist, someone who studies only fossils with backbones. Sumida, who works at California State University in San Bernardino, was not involved in the new study. The new fossils “are so well preserved that we can generate [ideas] about how they moved,” he says.

The Bromacher locality doesn’t just have lovely fossil bones. It has fossilized footprints, too. A string of those footprints from the same animal is called a trackway. Scientists were able to link one trackway at the Bromacher locality to the O. pabsti fossil. Those tracks offered more clues to how the animal might have walked.

Scientists figured out that these fossil footprints were made by Orobates pabsti. Footprints and a fossil skeleton helped them figure out how these creatures might have walked.

CREDIT: SEBASTIAN VOIGT/URWELTMUSEUM GEOSKOP THALLICHTENBERG

But there’s more to understanding walking than knowing where an animal put its feet. For instance, they might even build a robot, says Kamilo Melo. He is a bioroboticist — someone who studies robots that imitate living things. He works at École Polytechnique Fédérale de Lausanne in Switzerland. What’s unique about the new study, he says, is that the scientists have combined several of these tactics together. That way, they get the best possible understanding of an ancient creature’s gait.

And, Sumida adds, the German team confirmed something that only the fossil’s original finders suspected: O. pabsti lived its whole life on land — and walking instead of wriggling.

Reanimating a fossil’s source

To gauge how the animal might have moved, the researchers first re-created its skeleton. They used this to find out how far O. pabsti’s arms and legs could move. Explains Melo, they essentially created a puppet. Then the researchers tested the potential range of motion each joint might have. The scientists also used a computer model to find out how the animal’s body would move in response to gravity and the friction from the ground as it walked.

The scientists looked at species still scurrying around today, such as salamanders, skinks, caimans (reptiles related to alligators) and iguanas. They used these animals to imagine ways the ancient animal might have moved. Skinks and salamanders, for example, hold their bodies low. Their limbs sprawl out to the sides as their bellies slither on the ground. Caimens tend have limbs that push their bodies up, holding them higher off the ground.

The scientists then crafted a robot based on what they learned from the fossil, footprint tracks, skeleton, computer model and other species. Called the OroBOT, it demonstrated potential gaits. It matched the footprint trails the scientists had.

Eventually the researchers considered 512 different possible types of movement. They scored each on how much energy they needed, how well the robot balanced and how well the gait matched the tracks without slipping. (The researchers have also put their computer model online; you can try it out.)

The results suggest that O. pabsti had a relatively advanced style of walking. It’s one that researchers thought hadn’t evolved until much later.

The creature would have had a stable, efficient gait — one without a lot of side-to-side, salamander-like wiggles. It also would have held its belly off the ground. This gait likely helped it conserve energy. Melo, Nyakatura and their colleagues describe their findings January 17 in Nature.

Sumida praised the many ways the scientists tested their findings from fossil to computers to a robot. He and others have shown that amniotes from the same area walked in several different ways. Some had limbs that lifted them off the ground like O. pabsti. Others sprawled. At least one animal walked on two legs. “What these studies are showing is that when amniotes first showed up, they were doing lots of things more quickly than we ever realized,” he says.

And these findings are just a start, Nyakatura says. The researchers hope their approach helps scientists better understand how other ancient animals got around. He’s interested in how animals launched into the air, stood up on two legs and even went back into the sea (as did the whales and seals we know today). “We have a whole bag of interesting things to study,” he says.

In 1995, my first year of field work at the Bromacker quarry, Stuart Sumida discovered a fossil that we initially thought was that of the amphibian Seymouria, based on the size and shape of the exposed vertebrae. This tentative identification made sense, because before our collaboration began, Thomas Martens had discovered in the Bromacker a skull of Seymouria, a creature known from localities in the USA. Months later, while I was preparing the specimen, Dave Berman and I realized the fossil wasn’t Seymouria, and that it belonged to the same unnamed animal that Thomas had collected a partial skeleton of before our collaboration began.

Specimen of Orobates pabsti collected in the 1995 field season. We determined that it is a juvenile. Photo by Dave Berman.

In the 1998 field season I discovered a third specimen, which is by far the most spectacular fossil that I have ever discovered. I found it towards the end of the field season when I pried up a piece of rock from the quarry floor. Upon turning over the rock piece, I saw an articulated foot preserved in it. I couldn’t believe my eyes! I knew that at the Bromacker if an articulated foot was found, the rest of the articulated skeleton should be attached to it. The problem was, we didn’t know if I had discovered a front or a hind foot, so we weren’t sure how the specimen was oriented in the quarry and whether it penetrated the nearby rock wall. Dave carefully lifted another piece of rock and thought the bones exposed in it were part of the shoulder girdle. Unfortunately, closer examination revealed that it was a piece of skull roof—another lobotomy—but, lacking x-ray vision, this is how we find fossil bone at the Bromacker. The good news was that the fossil specimen appeared to parallel the quarry wall.

A film crew from the regional MDR television station visited us early on the day of my discovery to interview Dave and Thomas. The discovery was made after they left, so Thomas immediately notified them. They returned and recorded a reenactment of my discovery. The piece of rock I am holding contains the foot. The rest of the fossil lies in the low mound of rocks in front of me. Photo by Dave Berman, 1998.

Dave and Stuart finish plastering the block. The red flag is a north arrow to indicate the orientation of the block in the quarry. Photo by the author, 1998.

Dave, Stuart, Thomas, then-graduate student Richard Kissel (University of Toronto, Mississauga), and I named the animal Orobates pabsti, which is from the Greek “oros,” meaning mountain, and “bates,” meaning walker, in reference to the Bromacker fossil environment being an intermontane basin. “Pabsti” is in honor of Professor Wilhelm Pabst for his pioneering work on the Bromacker fossil trackways.

We determined that Orobates is very closely related to Diadectes, and like Diadectes, was herbivorous. Orobates differs from Diadectes and other diadectomorphs in the group Diadectidae in a number of features, some of which are as follows: spade-shaped cheek teeth that are oriented on the jaw at an angle of 30–40° to the jaw line, rather than being close to 90°; narrower and shorter vertebral spines; 26 vertebrae between the head and hip (Diadectes has 21); proportions and shapes of individual toe bones; and digit (finger or toe) length.

Holotype specimen of Orobates pabsti, the specimen collected in 1998. If a series of specimens exists of a new species, then the specimen that best represents the species is designated as the holotype. If only one specimen is known, it becomes the holotype by default. Photo by Dave Berman.

The Bromacker has long been famous for its exquisitely preserved fossil trackways. Identification of the particular fossil animal that made a given trackway is almost always very difficult, because body fossils often lack completely preserved hands and feet and typically are not found in association with trackways. As a result, trackways are given their own set of names, called ichnotaxa (“ichno” means track or footprint), which are typically referred to major groups of animals instead of individual species. The Bromacker is unique, however, because nearly completely preserved body fossils occur in a rock unit above the trackways, indicating they are very nearly contemporaneous. Five ichnotaxa are known from the Bromacker, and one of them, Ichniotherium, has been attributed to Diadectidae.

A large slab of rock being inspected for trackways shortly after it was unearthed in the commercial rock quarry. The polygonal patterns in the rock are mudcracks. Photo by the author.

Graduate student and trackway expert Sebastian Voigt (now Director at Urweltmuseum GEOSKOP, Burg Lichtenberg, Germany) often visited us at the Bromacker. In 2000, a time when Diadectes was the only known Bromacker diadectid, Sebastian and his advisor Hartmut Haubold (now emeritus at Martin Luther University Halle-Wittenberg, Germany) proposed that Ichniotherium cottae made two track types, designated as A and B, that differed according to the speed at which the trackmakers moved. This contrasted previous studies that proposed three species of Ichniotherium at the Bromacker.

Once the skeletal anatomy of Orobates became known, Sebastian realized that there were two species of Ichniotherium, and they were made by Diadectes and Orobates, respectively. He invited Dave and me to co-author a paper to present this hypothesis. We supplied Sebastian with information about skeletal differences between Diadectes and Orobates, and Sebastian used these data to firmly establish that Diadectes made Ichniotherium cottae (type B) tracks and Orobates was the trackmaker of trackways formerly identified as I.sphaerodactylum (aka I. cottae type A). Even though the makers of the trackways are now known, the ichnotaxon names are still used when referring to the trackways.

Photographs of trackways of Ichniotherium sphaerodactylum made by Orobates pabsti (top) and Ichniotherium cottae made by Diadectes absitus (bottom). Modified from Voigt (2007).

In Diadectes, the fifth digit of the hind foot is relatively shorter than it is in Orobates, which can be seen in the tracks of I. cottae and I. sphaerodactylum, respectively. Furthermore, in I. cottae trackways, the hind foot track overlaps the track of the front foot, whereas in I. sphaerodactylum the hind foot track typically doesn’t overlap the front foot track. This is because Diadectes has less vertebrae between the head and hip (21 vertebrae) than Orobates (26 vertebrae) does.

Front and hind foot track pair of Ichniotherium sphaerodactylum. Track made by the front foot is above the hind foot track. Digits 1–5 indicated. Modified from Voigt, 2007.

Front and hind foot track pair of Ichniotherium cottae. Track made by the front foot is above the hind foot track. Digits 1–5 indicated. Notice that the hind foot track overlaps the front foot track. Drawings are of different specimens than the one photographed. Modified from Voigt, 2007.

A cast of the holotype skeleton of Orobates pabsti is exhibited in the Fossil Frontiers display case in Carnegie Museum of Natural History’s Dinosaurs in Their Time exhibition. Be sure to look for it once the museum re-opens. And stay tuned for my next post, which will feature the amphibian Seymouria sanjuanensis.

For those of you who would like to learn more about Orobates, you can access the abstract here or contact Amy Henrici here. The publication on the track-trackmaker association can be found here.