It’s Alive! Dr. Bakker Tells us how to make skeletons dance

Bakker Skeleton Mount

A life restoration of the great mammal-like reptile, Placerias, chasing an early dinosaur, Chindesaurus.

Some museums buy fossil-kits, all the bones drilled and filled with pipe fittings so that they click together to make the whole skeletal assembly. It’s quick. But if you have an anatomically sophisticated eye, and you scrutinize the kits, you’ll see serious errors of articulation as well as a general clunkiness.

For our Houston Hall (The Morian Hall of Paleontology), Pete Larson and I and Pete’s co- workers constructed every joint from scratch. We drew up dozens of pages of diagrams for shoulders and elbows, hips and knees, for every skeleton. The dinosaurs are tough but not the biggest challenge.

The Triassic Placerias, last of the big mammal-like reptiles, seemed to be a chimaera , croc-like thighs combined with the forequarters of a duck-bull platypus and the body cavity of a small ox. This barrel-chested beast took three weeks to pose in a believable full-speed run.

Here are the steps we took to capture the live beast:

I). Basic kinesiology.

A). Motion studies of extant species are reviewed to help in determining the limb posture and gait of the extinct species. In the case of Placerias the forelimb is close to that of a platypus and a terrestrial lizard, while the hindlimb is closer to that of a crocodilian and a chameleon.

Bakker Skeleton Mount

Motion studies of an Alligator mississippiensis, left, and a Tupinambis nigropunctata, right, part of the documentation for posing the HMNS Placerias and Smilosuchus.

B). The motion studies are reviewed to determine the range of lateral and vertical movement of the vertebral column, plus torsion in the extinct species. For Placerias the neck and dorsal column is compact but free to twist and flex as much in a Mississippi Alligator.

Bakker Skeleton Mount

Flexibility study of Placerias, top and side view, showing lateral flexibility of vertebral column and twisting, so head rotates down on the right and the pelvis rotates down on the left.

C). Placerias limb joints were like those of lizards and platypuses — motion was not simple flexion-extension in one plane, as occurs in humans, but included rotation in planes at right angles to the flexion-extension. Consequently, detailed diagrams for shoulder, elbow, hip and knee were drawn to guide the mounting process.

Bakker Skeleton Mount

Details of how shoulders and hips, elbows and knees rotate during the restored step cycle in Placerias.

Bakker Skeleton Mount

The movements at the elbow are especially complex — motion studies combined with detailed dissections of elbows of a tegu lizard, shown here, are used as a guide for Placerias.

II). The main limb and axial muscles are restored to determine which motions would be most powerful in locomotion and in combat.

A.) Our library of dissections shows which combination of extant species are most appropriate for restoring the extinct species. For Placerias, forelimb and hindlimb musculature are best reconstructed from the conditions in an echidna (Tachyglossus) or platypus (Ornithorhynchus). The reconstruction was used by the mural artist as he mapped out the body masses for the painting.

Bakker Skeleton Mount

Top and side reconstruction of muscles in Placerias.

B.) The relative strength of the muscles informs our choice of posture and gait. In the case of Placerias, the domination by the forelimb suggests that the animal could dig or climb uneven ground more easily than archosaurian potential predators.

III). Choosing an interactive choreography.

Bakker Skeleton Mount

The Placerias cast being mounted at the BHIGR. Pete Larson on right.

A). A review is carried out for all the species known from the particular habitat and time, and available as skeletons. Placerias occurs in the lower Chinle Formation of Arizona. In the same beds are found three other large tetrapods that are represented by casts: 1). The large terrestrial predator Postosuchus. 2). The very large semi-aquatic predator Smilosuchus. 3). The large terrestrial armored herbivore Desmatosuchus. For the Placerias mount we chose Smilosuchus as the attacker because the body form — long snout, long, low body, long tail — made a dramatic contrast with the rotund compact design of Placerias.

Bakker Skeleton Mount

Final mount of the Placerias cast, viewed from the front.

B). Multiple sketches are generated to test various combinations of poses. The most pleasing pose for the predator-prey dyad was the Smilosuchus lunging from behind the Placerias.

Bakker Skeleton Mount

Antepaenultimate plan for Placerias-Smilosuchus mount.

Summary: The final mounts of a Smilosuchus lunging after a Placerias were not “out of the kit” exhibits. Rather than using pre-fabricated skeletons ready to assemble, we cut apart most of the bone units and studied the range of movements indicated by the joint surfaces and by the attachment sites for major muscles. Analysis of the locomotion adaptations led to choosing posture and gait that are documented by the anatomy in the extinct animal and by study of living species which demonstrate similarities in form and function.

Bakker Skeleton Mount

 

Come see Placerias and more amazing specimens in the Morian Hall of Paleontology at HMNS! Open extended holiday hours (9:00 a.m. – 6:00 p.m.) through January 4!

 

Dispatches From South Dakota: Willie The Dimetrodon [Day 4]

Today’s post is from Michele Whisenhunt, a volunteer on the Museum’s paleontology team. She’ll be sharing photos with us while the team is at the Black Hills Institute, prepping Willie, the Dimetrodon the team discovered. Missed the team’s first dispatches? Day 1, Day 2 and Day 3

All work and no fun makes for a dull paleo preparer, soooo Mary Anderson, Pat Greenfield and I headed out early this beautiful morning for Custer State Park and a 14 mile drive where the buffalo and the pronghorn play. Autumn has hit in the Black Hills but the wildlife was worth the drive not to mention a glorious day. South Dakota is beautiful in so many ways.

Buffalo on the range

Arriving early afternoon for prep work at the BHI our direction turned to beginning the bone cleaning under Dr. Bakker’s direction and the microscope.

Precise fossil cleaning

After experimenting different methods of cleaning, a recipe was found. A vinegar bath gave the desired results.

Willie's leg
Text Goes Here!

Bernt under the magnified visor uncovers and cleans the most compete lower jaw of the Judy block, Trimerorhachis or Panzer Mudpuppy.

Jawbone

Tomorrow will be the beginning of many days prepping thousands of bones to complete Dimetrodon for his 2012 premiere in the new paleo hall.

Dispatches From South Dakota: Willie The Dimetrodon [Day 3]

Today’s post is from Michele Whisenhunt, a volunteer on the Museum’s paleontology team. She’ll be sharing photos with us while the team is at the Black Hills Institute, prepping Willie, the Dimetrodon the team discovered. Missed the team’s first dispatches? Day 1 and Day 2

It’s a beautiful and busy day in the neighborhood of Hill City, South Dakota

When we arrive to the prep lab there is activity everywhere with the Black Hills employees working on our new saber tooth cats, Xenosmilus and Smiledon some of the most fearless to roam. It is interesting to work side by side with the best in their field specializing in the finest fossils and fossil replicas.

Dr. Bakker instructs Mary Anderson, after finding the floating rib, to clean the rib bone and she uncovers a bite mark. Hallelujah, hallelujah! Everyone gathers to see the bite under the microscope.

Uncovered Bite Mark
Uncovered Bite Mark.

Kathy Zoehfeld has uncovered unknown rib in her skull jacket and she will continue working to uncover the pieces of skull.

Bernt Pettersson and Pat Greenfield faithfully work on the Judy Block, a huge Trimerorhachis block, named after the owner Judy, with Bernt uncovering a jaw with skin inside the lower jaw.

Marce Stayer and I are carefully pulling anterior and posterior spines. We’ll keep you posted daily as the work progresses.

Dispatches From South Dakota: Willie The Dimetrodon [Day 2]

Today’s post is from Michele Whisenhunt, a volunteer on the Museum’s paleontology team. She’ll be sharing photos with us while the team is at the Black Hills Institute, prepping Willie, the Dimetrodon the team discovered. Missed the team’s first dispatch from the field? Check it out!

While excavating Willie, the HMNS paleo team also discovered several small pockets of unidentified bones.  They were jacketed and sent along with Willie to the Black Hills Institute. 

Dr. Bakker inspecting Willie
Dr. Bakker inspecting Willie.

Today, volunteers Mary Anderson and Kathy Zoehfeld were each given one of these small presents to open.  Dr. Bakker was fairly sure Kathy’s jacket held a Secodontosaurus jaw.  A Secodontosaurus is a Permian Pelycosaur. He has a fin like Willie, but is smaller in size.  He has a longer snout and a narrower skull than Willie as well.

Kathy carefully started digging into her jacket, unsure exactly where this delicate jaw was located.  Layer by layer she picked away at the rock matrix, finding nothing.  Finally she found the tip of the jaw, then the first few teeth. 

Fossil Prep Work
Kathy doing some fossil prep work in the lab.

Unlike Kathy’s jacket, Mary’s jacket was a complete unknown.  The jacket was labeled “Willie’s feet”, but Dr. Bakker did not remember anyone finding Dimetrodon feet.  Mary started digging…and digging…and digging.  We started joking that the team had made an empty jacket as a joke.  And she kept digging…FINALLY, she found bone!  She called Dr. Bakker over.  He looked at the edge of bone and suddenly burst out OH! OH! I don’t know….She kept exposing more bone and then Dr. Bakker knew…it was not even close to being Willie’s feet—it was a Secodontosaurus vertebrae and neural spine.  A match to Kathy’s animal?  We will have to wait and see.

Willie's Let in a Jacket
One of Willie’s feet?