By David N. Leff
Probably more children -- of all ages -- know the Latin name of one long-extinct animal than of any beast alive today.
Its taxonomic moniker is, of course, Tyrannosaurus rex, which means "terrible lizard" in Greek. That carniverous character trait is amply, if imaginatively, documented in two recent major motion pictures, Jurassic Park and Lost World.
One adult specimen of this horrific species carries the name-tag "MOR 555." That acronym stands for "Museum of the Rockies," which is closely affiliated with Montana State University, in Bozeman.
MOR 555 came to light (literally) in the spring of 1990, when paleontologists excavated its nearly complete fossilized skeleton from the Hell Creek rock formation in McCone County. It was buried under one to 1.5 meters of white sandstone, and looked so perfectly preserved that the scientists wondered if its bones might still harbor traces of protein. If so, such ancient biomass might cast still more light on the biology of dinosaurs in general.
Today's Proceedings of the National Academy of Sciences (PNAS), dated June 10, 1997, reports the discovery of "Heme compounds in dinosaur trabecular [marrow] bone." Simultaneously, the Journal of Vertebrate Paleontology for June 1997 weighs in with "Preservation of biomolecules in cancellous [marrow] bone of Tyrannosaurus rex." Pathologist Jean Starkey, at Montana State, is the senior author of both articles.
The papers' co-senior author is paleontologist Jack Horner. Starkey told BioWorld Today, "Horner has a fairly spectacular eye for looking at things on the ground and saying, 'That's half an inch of dinosaur bone, and the rest of it will follow.'"
MOR 555 roamed what is now Montana's Big Sky badlands country sometime between 67 and 65 million years ago, just as the Age of Dinosaurs was reaching its sudden closure. "Burial was rapid enough," the co-authors wrote in PNAS, "to forestall damage by scavenging and weathering, but not rapid enough to prevent some mineral displacement."
Most of the skeleton itself is being processed at the MOR. Small pieces have been made available to different researchers around the world, but the majority of the bones are in the museum.
The team removed bone segments from one unexposed hind limb, and extracted a reddish-brown supernatant for state-of-the-art imaging and immunological analysis.
Iron Is Iron; Rust Is Rust
It was the rusty color of this substance inside the bone's once spongy, blood-rich interior that gave the investigators a clue what to look for, namely, heme.
Heme is a pigment the same color as rusted iron, and for the same reason. It sits at the center of hemoglobin, the red blood cells that carry oxygen to nourish and energize the body's tissues -- from human to dinosaur. A single atom of iron in the heme molecule turns it red when it picks up its cargo of life-giving oxygen.
After extracting and isolating the reddish-brown residue from T. rex's bone matrix, the co-authors subjected the sample to a battery of imaging techniques, from Raman and resonance Raman spectroscopy to nuclear magnetic and electron spin resonance, plus HPLC (high-pressure liquid chromatography).
Each method in its own way conveyed suggestive evidence of the material's dinosaurian authenticity. However, as stated in PNAS, "The most revealing results were from the immunochemical studies in which a component in the extracts of MOR 555 tissues elicited an immune response in rats specifically against hemoglobin."
Two present-day rats contributed to demonstrating the endogenous proteins in the fossil bone. They were immunized with a total of 0.8 milligrams of whole MOR 555 trabecular extract by four subcutaneous injections over 60 days. The rodents duly produced antibodies that recognized pigeon, turkey and rabbit hemoglobin, whereas their preimmune sera did not.
"That the antisera did not react with snake hemoglobin," the Montanans observed, "shows that the reactivity is specific, and not artifact."
The PNAS paper concluded: "When considered as a whole, the results support the hypothesis that heme prosthetic groups and hemoglobin fragments were preserved in tissues of this Late Cretaceous dinosaur skeleton."
A separate finding, reported in the Journal of Vertebrate Paleontology, determined that the individual immunogenic amino acids contained significant levels of dextro-rotary enantiomers, "suggesting that the source proteins are ancient." Modern essential amino acids are levo-rotary.
Extending this proof-of-principle to identifying taxon-specific epitopes, Starkey proposed, "may provide a means to immunologically classify extinct organisms. Protein fragments yielded by the technique could be digested with specific proteases to yield uniform amino termini, a requirement for amino-acid sequencing."
Besides hemoglobin, the Montana team has since identified amino acids restricted to collagen, Starkey said. "The two protein remains that we've been able to get good evidence for, collagenous and hemoglobins, can provide us with antibody epitopes (sequences) so that we can map the evolution, and see what the dinosaur really was related to."
Which Came First -- Birds Or Dinos?
How closely was it related to birds?
"We were able to do a Western blot," she replied, and explained: "That means residual material from collagen I still had the sequence to react with the antibody that was specific, in this case, against avian, chicken, collagen I.
"This strengthens the impression that birds are related to dinosaurs," Starkey continued, "because every time we do a primary reagent specific for avian species it reacts. We see some cross-reaction with amphibian," she added, "but it tends to be less dominant than with birds. We can't prove which came first, but dinosaurs and birds might have a common ancestor."
The Montana technique may also resolve another still-open question: Were dinosaurs cold-blooded killers or warm-blooded killers?
"The hemoglobins can give you a clue as to that," Starkey pointed out. "This study itself, as far as it goes at the moment, does not. Future work, which is logically due from this, could logically get you that answer."