Megatherium americanum - skull fragment with teeth

Specimen number: RCSHM/CO 3443 and ENGH: 88202309

Specimen Link: RCSHM/CO 3443

Taxon: Megatherium americanum

Description: Partial cranium with five molariforms preserved on right and left sides. The specimen has been sectioned horizontally on the left side, and vertically on the right side. Two fragments remain and are part of the collections at the Royal College of Surgeons (RCSHM/CO 3443) and Down House, property of English Heritage (ENGH: 88202309). This is a digital reconstruction of both fragments together.

Site: Punta Alta, Argentina

Age: Late Pleistocene to early Holocene (between 126,000 and 8,000 years old)

Collection: Collected on 23rd September 1832 by Charles Darwin

Comments: This specimen was found at Punta Alta, where the majority of the fossil mammal specimens collected by Darwin were found. The site is now buried underneath Puerto Belgrano naval base. On his second day at Punta Alta, whilst searching for fossils, Darwin notes:

Sunday 23rd … I walked on to Punta alta to look after fossils; & to my great joy I found the head of some large animal, imbedded in a soft rock. - It took me nearly 3 hours to get it out: As far as I am able to judge, it is allied to the Rhinoceros. - I did not get it on board till some hours after it was dark.

--Keynes, R. D. 1988. Charles Darwin’s Beagle Diary. Cambridge University Press, Cambridge. Page 107.

After it was sent to the Royal College of Surgeons, this partial skull was sectioned horizontally and vertically. The main section forms part of the collection at the Royal College of Surgeons. The vertical section (showing the teeth on the right side of the skull) now forms part of the collection at Down House (English Heritage), Darwin’s former home. The horizontal section no longer exists. The 3D model is a digital reconstruction of the two existing parts together.

By sectioning the specimen, it was possible to clearly see the number of teeth in the jaw, their shape and structure and to make thin sections of them. It was through doing this that Richard Owen, who described the specimens, was able to determine that M. americanum actually had 5 teeth in its upper jaw, not 4 as had previously been described. He was also able to show that its teeth had no enamel on them, unlike our own teeth and that they were able to form sharp cutting ridges. These blades were formed as a result of the presence of two different types of dentine and cementum. This is now known to be characteristic of sloth teeth. He also determined that the teeth of M. americanum were ever-growing, i.e., the teeth continued to grow throughout the life of the individual and never formed distinct roots. This contrasts with human teeth which cease to grow once the roots have formed.

Upon clearing away the matrix from the palatal and alveolar surface of one of the cranial fragments of the Megatherium in Mr Darwin's collection, I was gratified by the detection of the crown of a fifth molar, corresponding in size and form with the detached tooth, above alluded to: its small size, and its position have doubtless occasioned its being over-looked in the cranium of the great skeleton at Madrid.

--Owen, R. 1838-1840. Part I. Fossil Mammalia. In Darwin, C. R. (ed.), The Zoology of the Voyage of H.M.S. Beagle, under the command of Captain Fitzroy, R.N. during the years 1832-1836. Smith Elder and Co., London. Page 102.

What is Megatherium?

Cite this as

Pip Brewer, Kate Burton, Adrian Lister (2018). Dataset: Darwin's Fossil Mammals. Resource: Megatherium americanum - skull fragment with teeth. Natural History Museum Data Portal (

Retrieved: 05:31 02 Dec 2020 (GMT)

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