Mammuthus lamarmorai

Mammuthus lamarmorai is a species of mammoth which lived during the late Middle and Upper Pleistocene (between 450,000 to perhaps 40,000 years) on the island of Sardinia. M. lamarmorai is a dwarf species, as it is estimated to have reached a shoulder height of only 1.4 m and weighed about 550 kg. This pygmy mammoth has been found mostly in the fine-grained sediments of the western part of the island.

Features

There is a great deal of fossil material known for M. lamarmorai, which includes cranial, dental, and post-cranial findings. So far, no complete skeleton is known. Of the few known molars just only one represents the rearmost tooth. This have 13 cm long and 6.9 cm wide, with at least eleven ridges on the enamel.^[1] A humerus reaches a length of 45 cm.^[2] The few discovered tusk fragments exhibit only a small maximum diameter of 3.5 cm. The length of the femur indicates a shoulder height of 1.4 m. The weight of this dwarf mammoths probably not have been more than 550 kg.^[2] The small size of M. lamarmorai is due to a process of insular dwarfism, which occurred when its original large ancestors reached Sardinia and due to lower food supply and lack of potential predators they reduced their size.^[3][4]

Discovery

Most finds of M. lamarmorai were discovered on the west coast and in the western part of the island of Sardinia, and mainly comprise individual finds, but also belong to associated skeletal elements. The most important fossils are from Funtana Morimenta, a quarry south-southwest of Gonnesa in the valley of Rio Morimenta where it had already been discovered at the end of the 19th century. These fossils embedded in the Funtana-Morimenta lineup, which is composed of aeolian sedimentary formation that is located below a layer of strata dominated by a rock unit of conglomerates (the Tyrrhenian conglomerate). This rock formation is widely spread all over the west coast of Sardinia and is generally attributed to the last interglacial period that bears in northern Alpine region the term Eemian (126000-115000 years ago). The finds include mainly elements of the spine and musculoskeletal system, so among other things, a full foot, nearly complete hand, humerus and ulna, as well as remains of tusks. All discoveries are most likely to belong to a single individual. Other finds are known from San Giovanni di Sinis near Oristano, where a molar tooth was found in also deposited before the Eemian sediments, as well as an additional molar from Campu Giavesu in Sassari, which is, however, significantly larger. Finds from the Upper Pleistocene, which comprise a plurality of teeth are mainly from Tramariglio, near the city of Alghero, and came also from deposited sediments by wind, but above the Tyrrhenian conglomerate.^[4]

Classification

As a mammoth, M. lamarmorai's closest living relative is the modern Asian elephant (Elephas maximus). The occurrence of this mammoth already in the late Middle Pleistocene makes that a descent from the classic woolly mammoth (M. primigenius) rather unlikely, since this latter species first appeared in Europe during the Upper Pleistocene. Rather, it is thought that the steppe mammoth (M. trogontherii), which lived on the continent, is the likely ancestor of M. lamarmorai. The steppe mammoth's molars had only eleven ridges, a feature much more archaic than those of the woolly mammoth, which had twenty six ridges. The Cretan pygmy mammoth (M. creticus) and M. lamarmorai are the only known dwarf mammoths on the islands of the Mediterranean sea, which were otherwise occupied by diminutive members of the genus Palaeoloxodon (also included sometimes in Elephas).^[3][4]

The first description was published in 1883 by Charles Immanuel Forsyth Major, who used the name Elephas lamarmorae. He no published pictures, but saw a clear link to the Southern mammoth (M. meridionalis), which he in turn called Elephas meridionalis due to similarities. The remains were from the quarry Funtana Morimenta and are now kept in the Natural History Museum of Basel, where Major personally studied them. Because of new tooth finds since the mid-20th century, it became clear the close connection to the mammoths, which is why the name Mammuthus lamarmorae prevailed.^[5][6] As a result of adaptation to the International Rules for Zoological Nomenclature, one amendment was made in 2012 for the name, and Mammuthus lamarmorai is currently the valid species name. The species name, lamarmorai, honors to the Sardinian General and naturalist Alberto La Marmora (1789–1863), who had already in 1858 investigated the fossils of Funtana Morimenta.^[4]

Phylogeny

The origin of M. lamarmorai is still relatively unclear – the earliest finds date from the late portion of the Middle Pleistocene, as points their association with the dwarf deer Praemegaceros cazioti, and are thus about 450,000 years old. A colonization of Sardinia through the steppe mammoth should therefore be carried out in the transition from the old to the Middle Pleistocene or early Middle Pleistocene. Probably this happened during the Pleistocene glacial periods in which the global sea level was much lower due to the continental ice sheets and the animals could reach the island by swimming. Whether single mammoth populations Sardinia reached only once, is unclear, maybe the somewhat larger tooth from Campu Giavesu suggests that several migration waves appear to be possible, as is also demonstrated when detecting dwarfed forms of the genus Palaeoloxodon of the Mediterranean islands of Sicily and Malta.^[3]

References