Are Chickens the Closest Living Relative of T. rex? No! And Here’s Where That Rumor Started
Here’s why I admire Dr. Mary Higby Schweitzer: Most women who grew up in the 1960’s like Dr. Schweitzer did, could become nurses. Or secretaries. Or teachers. And that’s about it. Those are all wonderful, important professions, but if a young woman wanted to be something else, she had to single-mindedly swim against the intense current of status quo and societal expectation. Well, Dr. Schweitzer became a paleontologist. Then she made some ground-breaking discoveries and almost singlehandedly created the new discipline of molecular paleontology. And, obviously, she has a Wikipedia page, too.
She grew up in a conservative Catholic family, but as a teenager switched to a fundamentalist church that believed in a literal interpretation of the Bible. This church—and Schweitzer—gave no credence to evolution and believed that the Earth was only 6000 years old.
In the late 1980’s, Schweitzer decided to go back to school to add an education degree to her baccalaureate so she could teach science. She started attending classes at Montana State University. One day she sat in on a lecture by Jack Horner. The lecture piqued her interest and afterward she approached Horner and asked if she could audit his class.
In a 2017 interview in Science, she recalled the conversation. “Hi Jack, I’m Mary. I’m a young Earth creationist. I’m going to show you that you are wrong about evolution.”
“Hi Mary, I’m Jack. I’m an atheist,” Horner replied. But he did allow her to audit his course.
As Horner’s lectures progressed, Schweitzer gradually came to realize the information he was presenting was irrefutable. Evolution was real and the Earth was very old. “He didn’t try to convince me, he just laid out the evidence,” she explained. But, “it cost me a lot: my friends, my church, my husband.” But not her faith. She saw God’s handiwork in the formation of our 4.5-billion-year-old planet and evolution of life on its surface.
Schweitzer also came to realize that her future was in paleontology. She started volunteering in Horner’s lab, and eventually enrolled in a graduate program. Paleontology was changing. With the advent of computers and new techniques, scientists were able to examine dinosaur bones in new ways. For her dissertation, Schweitzer decided to examine the load-bearing bones of large two-legged dinosaurs at a microscopic level. Working with a T. rex femur, she meticulously cut very thin sections—an extremely difficult task with normal bone, and even harder with fossilized bone. Once she could obtain good thin sections, the next challenge was affixing them to microscope slides. Once she accomplished that cumbersome task, she was able to look inside dinosaur bones at a microscopic level. That’s when she saw the blood cells. And that changed the course of her life, her work, and the study of dinosaurs.
What she actually saw were round things that looked just like red blood cells. And they were in exactly the right part of the bone where one would expect to find red blood cells. But that went against everything everybody knew about how fossils formed.
The classic model for how a dinosaur turns into a dinosaur fossil involves these steps: First, the dinosaur dies. Second, the flesh, and all organic matter rots away. Third the minerals of the bone remain and eventually other minerals leach in from the surrounding material. Fossils, the classic model proclaims, are mineral. Red blood cells are organic; thus, they should not exist in fossils.
Jack Horner heard it being bandied about that Schweitzer was seeing blood cells in millions of years old dinosaur bones and summoned her to his office for a discussion. “They are in the right place to be red blood cells. But they can’t be red blood cells. We all know that,” she remembers telling him.
She recalled Horner’s response in a 2006 interview: “Jack said, ‘Prove to me they’re not red blood cells.’ That was what I got my Ph.D. doing.” She remembers that moment in Horner’s office as a turning point in her life. She realized that science can never produce conclusive proof. That’s just how science works. Science cannot and will not ever prove evolution, a non-flat Earth, the Earth’s rotation around the sun, the presence of red blood cells in a dinosaur bone, or anything. It can disprove it or it can support it. And when something is supported over and over in a variety of ways, it eventually becomes generally accepted.
Schweitzer eventually showed that there were fragments of hemoglobin in the dinosaur bone. Hemoglobin is the main protein found in red blood cells. And then she demonstrated the presence of hemoglobin using a different method. And then again, using another method. And again. A total of six different ways. And she showed that there was no hemoglobin present in the sandstone that had surrounded the dinosaur bone. Those analyses became her doctoral work. She earned her PhD in 1995. And in 1997 she published her work in the Proceedings of the National Academy of Science and created a stir. And then she accepted a position at North Carolina State University.
That Mary Higby Schweitzer was able to demonstrate the presence of organic chemicals in millions of years old dinosaur bone was amazing. But the implications of her discovery were even more amazing. In the final paragraph of her 1997 paper, Schweitzer mentioned amino acid sequencing. Proteins are made up of amino acids. While proteins like hemoglobin are shared by a vast array of animals, the hemoglobin in each animal species is different—the order of the amino acids varies. Amino acid sequences are more similar in closely related species and are less similar in distantly related species.
From the very beginning of paleontology, scientists had constructed dinosaur family trees based on the similarity of the appearance of the bones. Now, the possibility of sequencing proteins found in old bones opened up a new door for determining dinosaur relationships. And, in addition, the protein sequences could be compared to today’s living animals, and the grand scheme of how dinosaurs fit with today’s living animals could be determined. The field of molecular paleontology was born.