Paleontology’s Most Famous Missing Links

Now that "Ida" is a star, a look at some other famously transitional stars of the fossil record

The phrase "missing link" first appeared in print only four years after the publication of The Origin of the Species. By the end of that year, legendary paleontologist Richard Owen published a description of the fossil Archaeopteryx, the first specimen to carry that moniker. And with that, the concept of a "missing link" embedded itself in the popular imagination.

With missing links again thrust hastily and breathlessly into the spotlight again with the History Channel's hyped-through-the-roof unveiling of Ida, "the most important find in 47 million years," a look at missing links throughout history may help put things in perspective.

Of course, anyone with even a rudimentary understanding of evolution knows that there's no such scientific concept as a missing link, that the gradual nature of evolution renders all species "intermediates" between past and future forms, and that filling in the gaps between distinct groups is the paleontological equivalent of Zeno's paradox. That has not, however, stopped almost 150 years of hype around the spectacular fossils whose chimerical appearance seems to embody the very concept of evolution.

So, in the spirit of the description of Darwinius masillae, have a look at some of the exquisite fossils that have served as prima facie evidence for the process of evolution. See it here.

The London Archaeopteryx
Called "arguably the best-known fossil anywhere" by Richard Fortney in his book Life, and mentioned in the forth edition of the Origin of Species, Archaeopteryx lithographica provided Darwin with the evidence he needed to convince some of his most skeptical opponents that evolution has, does, and will continue to occur. The original "missing link", Archaeopteryx has the skeleton of a small dinosaur, but unmistakable feathers, linking it to birds.courtesy of Wikimedia commons
Owen’s "Hyracotherium" and Marsh’s “Eohippus”
Although Richard Owen (the same paleontologist who described- as in, scientifically documented- Archaeopteryx), first discovered fossilized teeth and bones from this animal in England in 1841, it wasn't until Othniel Marsh discovered a full skeleton in 1878 that anyone realized what it was. Hyracotherium represents the first in an evolutionary line that would eventually culminate in the modern horse.Courtesy of Jeff Kubina, via Wikimedia commons
The Taung Child
When Raymond Dart published his description of this Australopithecus fossil in 1924, he claimed that it was the earliest form of human every discovered. Unfortunately, it would be another decade before anyone else believed him. Dart didn't quit though; he found additional early hominid specimens throughout the 1930s and 1940s. Although he was not appreciated by his peers in his own time, Roger Lewin's book the Principles of Human Evolution claims that Dart's work resulted in the founding of modern paleoanthropolgy.Courtesy of Luna04, via Wikimedia commons
Sphencomyrma Freyi in Amber
When amateur collector Edmund Frey found a bit of amber in Cliffwood, NJ, he had no idea he had stumbled on one of the great missing links in fossil history. Eventually described in a 1967 paper and named Sphencomyrma freyi after the man who discovered it, this amber-encased insect has features of both wasps and ants, and serves as the clearest evidence that ants and wasps evolved from a common ancestor.Courtesy of Frank M. Carpenter, Museum of Comparative Zoology, Harvard University, Cambridge, Mass.
Lucy
Undoubtedly one of the most famous fossils of all time, "Lucy" is an Australopithecus afarensis who was discovered by Donald Johanson in 1974. Named after the Beatles song "Lucy in the Sky with Diamonds", this specimen is the most complete pre-_Homo hominid fossil ever found.courtesy of 120, via Wikimedia Commons
The Smithsonian Pikaia-Type Specimen
While this specimen was discovered in 1911, it wasn't until 1979 that it's true value was understood. Originally thought to be nothing more than a worm, subsequent re-examination determined that Pikaia actually represents the earliest member of the phylum Chordata, which includes all vertebrates. In his book Wonderful Life, Stephen Gould said of Pikaia, "Pikaia is the missing and final link in our story of contingency- the direct connection between [the Burgess Shale] and eventual human evolution."Courtesy of Wikimedia commons
Ambulocetus-Type Specimen
Discovered in Pakistan, Ambulocetus is, simply, a whale with legs. Hell, it's name even means "walking whale." However, Ambulocetus is not special because of what it taught the scientific world, but instead it's because it was found recently. Scientists have known for decades that whales evolved from a hippopotamus-like ancestor, but it wasn't until 1996 that an intermediary form as clear as Ambulocetus was discovered.Courtesy of Thesupermat, via Wikimedia Commons
Tiktaalik
The most recently discovered of our fossils, Tiktaalik is half fish, half lizard, and all missing link. First described in 2006, this specimen has forelimbs that resemble land animals, but a decidedly fish-like tail. The fossil has appeared on the cover of The New York Times and on the Colbert Report, creating a news blitz that was itself a missing link between the simple publicizing of the "Lucy" discovery and the all out media circus around "Ida" the Darwinius.Courtesy of the National Science Foundation