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1831: The Iguanodon's "Horn"
1831: The Iguanodon's "Horn"
One of the most memorable paleontological "mistakes" has to be the placement of the Iguanodon's thumb spike initially as a horn. But where did that idea originate from and how did it progress from there?
Although the first illustration of the "horn" was in Gideon Mantell's 1833 book The Geology of the South-East of England (presented below), that is not the first place that the horn was mentioned. In 1831, Mantell wrote an article entitled The Geological Age of Reptiles in which he briefly mentioned that the Iguanodon had a horn. At the time he presented no evidence or background to the story, an oversight he would eventually correct in his 1833 book.
"This creature [the Iguanodon], like some of the recent species of Iguanas, had warts or horns on its snout, and an appendage of this kind has been found of the size and shape of the lesser horn of the rhinoceros!"
Fast forward two years to his The Geology of the South-East of England publication and Mantell provides us with not only details on the discovery of said horn, but also an image of the bone. Since Mantell was the person who initially named Iguanodon back in 1825, it seems apropos for him to further Iguanodon's cultural development. Or, more accurately, Gideon kept himself in the loop, even paying quarry workers to notify him if they find anything of interest.
Gideon attributes the initial discover of the "horn" to his wife, Mary Ann, who is also credited with the initial discovery of the teeth from which the Iguanodon was named. Mary Ann will have to go uncredited though, until Mantell's 1838 publication, The Wonders of Geology. Mantell describes the discovery such that the horn...
"...like the claw-bone, it was discovered imbedded in the conglomerate of Tilgate Forest."
I find it extremely interesting that the horn, eventually to be identified as the thumb spike, was discovered "like the claw-bone" of the Iguanodon. Such was the time that every little piece of bone became a publication, Mantell actually published a brief announcement on the discovery of the claws in 1829, however they contained no mention of the "horn".
Mantell, it seemed, was determined to make the Iguanodon into a giant replica of the modern day iguana. Mantell's description of the horn leads the reader to believe that this horn must have been another indication that the Iguanodon really was just a giant iguana.
"The nature of this extraordinary fossil was for some time undetermined ; and it is to the discrimination of Mr. Pentland, whose high attainments in comparative anatomy are well known, that we are indebted for the suggestion that it probably belonged to a saurian animal. It is well known that some reptiles of that order have bony or horny projections on their foreheads ; and it is not a little curious, that, among the Iguanas, the horned species most prevail. The Iguana cornuta, which is a native of Saint Domingo, resembles the common Iguana in size, colour, and general proportions; on the front of the head, between the eyes and nostrils, are seated four rather large, scaly, tubercles; behind which rises an osseous conical horn, or process, covered by a single scale. That our fossil was such an appendage, there can be no doubt; and its surface bears marks of the impression of an integument by which it was covered, and probably attached to the skull. This fact establishes another remarkable analogy between the Iguanodon, and the animal from which its name is derived."
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| The original illustration of the Iguanodon's "horn" from Mantell's 1833 book, The Geology of the South-East of England |
Even with the discovery of various bits and pieces of the skeleton over the years, from the teeth to the "horn", Mantell was still hesitant to provide anyone with an illustration of the Iguanodon by this point in 1833. That will come in the near future with a discovery that Mantell will be unable to restrain himself from speculating on what the Iguanodon looked like in real life.
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