Author retracts PNAS paper about alleged Pliocene cheetah fossil that critics said was a fake

A paper about an alleged cheetah fossil from the Pliocene epoch, dogged by questions since its publication in 2008, has been retracted after one of the authors acknowledged it wasn’t what they thought it was.

Here’s the notice for the paper, “A primitive Late Pliocene cheetah, and evolution of the cheetah lineage:“

The undersigned author wishes to note the following: “After further examination, it was determined that the fossil used in the study was a composite specimen from the late Miocene laterite and not from the early Pleistocene loess. The article is hereby retracted.”

The paper, by Per Christiansen, then of the Zoological Museum in Copenhagen, and Ji H. Mazák, of the Shanghai Science and Technology Museum, has been cited 11 times, according to Thomson Scientific’s Web of Knowledge, and purported to show

…a new discovery from the Late Pliocene of China of a new species of primitive cheetah, whose skull shows a unique combination of primitive and derived characters, and demonstrates gradual evolution of the many derived craniodental traits considered characteristic of cheetah lineage, thus shedding new light on the early evolution of the cheetah lineage.

Other scientists have been suspicious of the find, as first reported by Science in 2010. (Thanks to fossil writer extraordinaire Brian Switek for pointing us to all of the background on this case.) Deng Tao, of the Institute of Vertebrate Paleontology and Paleoanthropology, and colleagues raised questions about the skull, noting that some of it was restored in plaster and that many sham fossils were making their way out of China. PNAS, however, would not publish a letter of critique.

Deng tells Retraction Watch:

When I read the proof of this article in the end of 2008, which was sent to me by Rebecca Carroll of National Geographic News, I found that the authors studied a fossil forgery, the sole foundation of the article. Therefore, I immediately wrote to PNAS and indicated that this article should be retracted. On February 5, 2009, I received a response from PNAS. The editor suggested that hard evidence of a forgery would consist of: 1) solid evidence of carving or other deformation to alter morphology; 2) a demonstrable difference in provenance of different pieces of the skull; or 3) construction of morphologically important portions of the skull from extraneous materials. He considered that my comment for this skull lacks the personal examination, so all of my observations can be explained by sloppy preparation, incomplete preservation of the skull, or as characters that differ from my expectations that are based on an a priori hypothesis of relationship or ancestry. As a result, the editor suggested that I must be backed by demonstrated evidence of forgery meeting at least one of the three criteria he outlined.

Mazak declined to give Deng access to the fossil at that time, but in response to the Science story, but he and Christiansen sent a defense to Science in which, notes Deng:

…they first admitted that the occipital area and zygomatic arches of the skull have been heavily restored in plaster, as we have claimed. Unfortunately, they insisted that this does not impinge on A. kurteni’s status as a primitive cheetah. They argued that our questions were without tangible evidence and are not based on personal study of the specimen but on a few images in their study. We had asked for an examination of the skull in person, but Mazák declined our request, and ironically according to Mazák, the senior author of the PNAS paper had composed the paper without having seen the original specimen, only based on the photos of this specimen.

Deng tells Retraction Watch that the retraction validates his concerns. Mazák only gave Deng access to the fossil recently, after Deng invoked the PNAS data access policy:

After the examination, Mazák agreed that the fossil was severely faked and collected from the late Miocene red clay in Guanghe County, instead of the early Pleistocene loess at Longdan in Dongxiang County. In fact, the zygomatic arches of the skull were made from ribs, the incisors were actually premolars from other carnivores, and the posterior part of the skull was simply plastic. As a result, I strongly urged Mazak to retract this article.

Per Christiansen, Mazak’s co-author, did not sign the notice. But the scientist, now at Aalborg University, tells Retraction Watch he hadn’t heard anything about the retraction until we contacted him last week, several days before today’s scheduled PNAS embargo lift:

I was astounded to read your message, because I had no idea about any of this. I know there has been some controversy about this cheetah skull, but frankly, I haven’t followed it very closely. The skull is in China, and I have not had personal access to it; for the initial study, my coauthor analysed the skull and I contributed the data and knowledge about the rest of the felids included. I have, however, for some time pressed my coauthor to take some x-rays of it so that we could put this matter to rest once and for all, but so far this has not happened. I have no idea what has since happened in this case, and the journal has apparently not found it worthwhile to even contact me on the matter. This is certainly a blatant breach of proper conduct.  I will now contact them and make them explain themselves. I must also try and contact my coauthor, but for some reason he has not got back to me in a very long time.

Mazak has not responded to our requests for comment, but we’ll update with anything we learn.

Meanwhile, Switek notes:

As Stone pointed out in his story, there is a major fossil forgery industry in China. National Geographic was misled by “Archaeoraptor,” and now Mazák and Christiansen have been burned by another forgery that made it into a highly-visible publication. This is why geologic data is absolutely essential in descriptions of fossils. We need to know when the fossil was found, where it was found, who found it, and exactly where it sat in the formation it was excavated from. If we don’t demand those details, it’s easy to usher forgeries, black market fossils, and other suspicious specimens into high-profile journals. There’s really no excuse for this. If someone is going to name a new, significant genus or species, journals should demand that researchers provide evidence that the fossil was responsibly collected, prepared, and curated.