Ancient Proboscideans – Extinct Elephants and their kindred.

Proboscidea is the order of mammals with trunks, and their more primitive relatives with “proto-trunks”. Today the only living members of this order are in the family Elephantidae, the living Asian, African savannah and forest elephants. These are magnificent megafauna in themselves, treasures of any zoo which has them, butchered for their incisors and occasionally used in human warfare. But there is much more to Proboscidea than the living elephants as this order has a total of around 164 mostly extinct species, which diversified into all sorts of bizarre forms, such as the four tusked deinotheres and the shovel-tusked Platybelodon. These fantastical, mighty beasts are only known to us through the fossil record. It is tempting to compare the largest Proboscideans, to the herbivorous dinosaurs, especially the sauropods, as they fill the niche for large browsing animal. I have no chance of discussing all these species here, but I will mention some of the most outlandish and interesting Proboscideans less familiar to us than elephants and mammoths.

Animals with 3m long teeth don't drop out of the sky, they as an order have a history stretching back into the Paleocene, starting with an apparently humble creature the size of a rabbit. The evolutionary process basically involves a gradual increase in body size, growth of tusks and size of head. The heavy tusked head could not be supported by a long neck, and as their legs were long they could not reach the ground with their mouth to eat and drink. This problem was “solved” by the elongation of the muscular nasal cavity, forming a trunk. These processes were not so smooth and continuous, and the journey had many turns from this path.

A reconstruction of Eritherium.

One of the earliest Proboscidean is Eritherium which lived 60 million years ago, the remains of this creature was first found in phosphate deposits in Morocco in 2012. The Eritherium remains show no sign of a trunk, which is formed by the evolutionary fusion of upper lip and nostril, which would be evident in an enlarged naval cavity. It is a Proboscidean without a proboscis, but probably had a very mobile upper lip, a little like the unrelated tapirs. So what makes this animal a Proboscidean? A number of features which were elaborated in later Proboscideans are present in Eritherium, including enlarged incisors, which would eventually sprout forth to create tusks, and simple lophodont molars (molars with ridges perpendicular to the jaw line). It was 5kg in weight, but this outweighs most other Paleocene mammals, many of which were decided shrew-like. Eritherium was probably somewhat aquatic, like many of the Proboscideans including the swamp dwelling American Mastodon and modern elephants who use their trunks as “snorkels” in order to swim up to 48km offshore. It is likely that the common ancestor of Proboscideans, Sirenians (sea cows) and the extinct Desmostylia were fully aquatic.

A reconstruction of Phiomia

A later group of Proboscideans is Phiomia, a direct relative of modern elephants, which lived between 35 and 25 million years ago. This was a larger animal, 2m high at the shoulder. Remains show evidence of a short rudimentary trunk (based on the larger nasal cavity) and enlarged incisors on the lower and upper jaws, meaning it had two pairs of tusks. Tusks are simply enlarged incisors, about a third of it's length, the pulp cavity, is embedded in the skull. The visible tusk is the ivory made of dentine covered by enamel. After it has shed it's milk tusks a Proboscidean maintains and grows it's tusks throughout it's life. In observed species the male has the longest tusks, as befitting their primary use in fighting, but they are and were also used to strip bark, defend from predators and in species like the woolly mammoth they may have been used to break up ice to find food.

A skull of Deinotherium at the Natural History Museum

The branches of evolutionary tree which did not lead to elephants contain more baroque Proboscideans, including two groups which lived at approximately the same time, Deinotherium and Platybelodon. The skull of Deinotherium is a disturbing thing to bump into in a museum, no doubt horrifying for an ancient person, with no ideas about deep time, to find in the wild. The skull appears to have two horns curved backwards out of it's chin, like a demonic beard presumably used for gouging. If an ancient person who expects all animals to have forward facing eyes like they do, sees the enlarged nasal cavity at the front of the skull, it could be mistaken for the skull of a monster. Indeed, the ancient myths of the Cyclops could be inspired by the discovery of Proboscidean fossils in Greece. Deinotherium itself lost it's upper pair of tusks and maintained the lower tusks (the opposite of modern elephants). As you can tell from a reconstruction of these creatures, the lower tusks hid quite discretely under the trunk which filled the nasal cavity at the front of the animals head, making it look less horrifying. They were quite primitive, lacking the sequential teeth eruption of later Proboscideans.

The skull of Deinotherium is a disturbing thing to bump into in a museum and no doubt horrifying for an ancient person, with no ideas about deep time, to find in the wild. The skull appears to have two horns curved backwards from it chin, like a monstrous beard, used for gouging. Indeed, the ancient myths of the Cyclops could be inspired by the discovery of Proboscidean fossils in Greece, due to the fused external naris resembling an eye socket. Even the name Deinotherium is from the Greek for “terrible beast”. In reality, Deinotherium lost it's upper tusks and maintained it's lower tusks (the opposite of modern elephants), and probably used these curved tusks to scrap bark from tree. The lower tusks would have hid quite discretely under the trunk which extended from the external naris, making it look less horrifying.

A reconstruction of Platybelodon

Platybelodon is in the same family as Gomphotherium and is not a direct ancestor of elephants. It lived about 20 – 8 million years ago and retained all four tusks. The lower tusks flattened out so the each tusk met and formed a sort of “shovel” shape with a deep scoop at the end, which only developed in adulthood. There is speculation about the use of it's tusks. It was originally thought that it they used their “shovel” to scoop through the mud to collect plants; a semi-aquatic lifestyle familiar to Proboscideans. The two lower tusks end with a V-shaped sharpened tip, analysis of the pattern of wear suggests they were used in a scythe-like manner to cut down branches and to strip bark from trees. Palaeontologists removed them from their presumed habitat of lake-side bogs and place them in a more arboreal habitat. The shovel tusks were an adaptation to a crowding niche, as with several genera of Proboscidean in this area at the time, Platybeldon had to specialise to survive.

A reconstruction of Gomphotherium

Another key part of the future elephant physiology was put in place in another of the elephants' direct ancestors, Gomphotherium, living from 20 to 15 million years ago. They retained the four tusks, with the lower tusks being slightly flattened, and show a basic form of sequential tooth development. This is when, due to the stresses caused by eating grasses containing silicon particles, a tooth erupts from behind the existing teeth to replace the one which had eroded at the front. The erupted tooth would be larger than the previous ones, therefore allowing the jaw to continue to grow throughout the animals life. Gomphotherium probably had three teeth in each side of it's jaw, but later species had only one tooth in each side of the jaw. Gomphotherium was a member of the well travelled family Gomphothere, which includes the genera Cuvieronius and Stegomastodon, some species of which travelled as far as South America.

A sketch of American Mastodon Molars, my work

Mastodons were, despite their common confusion with mammoths, very different animals, Mastodons diverged from the line that would lead to elephants after Phiomia, separating them from mammoths by about 20 million years of evolution. The earliest Mastodons were the Losodokodon which lived from 27 to 24 million years ago in East Africa, later radiating throughout Europe, Asia and North America. The most famous Mastodon species is the American Mastodon, whose genus Mammut arrived in North America 11 million years ago. The American Mastodon was around 2.7 metres at the shoulder, small compared to the neighbouring Columbian Mammoth. It was quite stocky with a deep chest and probably quite muscular. It's tusks were up to 2.5 metres long in adult males and curved upwards and slightly outwards, less elaborate than tusks of mammoth. The name Mastodon means “breast tooth”, showing the lumpy nature of their molars. Elephant and mammoth molars are relatively flat and ridged, whereas mastodon molars have rounded cusps, which caused early naturalists to speculate that they were terrifying beasts who caught prey with their tusks. The reason each of these groups have significantly different teeth is because they were used to eat different foods, none of these animal foods. Mastodon teeth were used to crush leaves and twigs in forests, whereas mammoths grazed grassland.

My drawing of a cave painting of a woolly mammoth

The genus believed to be the ancestors of modern elephants and mammoths is Primelephas. These creatures had four tusks, though these were smaller than in Gomphotherium. This is because Primelephus did not need them to shovel though the mud, it had moved to a grassland habitat similar to modern elephants on the savannah or mammoths on the steppe. This genus split into three genera, Loxodonta (African elephants), Elephus (Asian elephants) and Mammuthus (mammoths). Mammuthus belongs to the Elephantidae family, making it as much of an elephant as Loxodonta and Elephus.

Bibliography

www.theguardian.com/science/2012/sep/02/eritherium-azzouzorum-new-to-nature

www.ucmp.berkeley.edu/mammal/mesaxonia/gomphotheriidae.php

www.npr.org/blogs/krulwich/2011/05/20/136436601/a-mouth-i-cant-stop-thinking-about

Understanding proboscidean evolution: a formidable task- Jeheskel Shoshani www.sciencedirect.com/science/article/pii/S0169534798014918

I found the exhibition Mammoths: Ice Age Giants at the Natural History Museum very informative, as well as the book of the same name by Adrian Lister.

This was an entry to Rockwatch's Young Writer 2014 competition. 

Mammoths: Ice Age Giants Exhibition

The preserved body of Lyuba from http://designyoutrust.com/2012/04/baby-mammoth-lyuba-goes-on-display/ originally from Reuters.

On the 3rd August 2014, I visited the Mammoths: Ice Age Giants exhibition at the Natural History Museum, London, which is open until the 7th September 2014. The exhibition was created by the Field Museum, Chicago, and features models of ancient Proboscideans, Pleistocene animals and, the gem of the exhibition, the preserved body of a 35 day old (at death) woolly mammoth, known as Lyuba or Люба, who died around 41,800 years ago on the modern day Yamal Peninsula.  I had read the accompanying book (by Adrian Lister with the same title as the exhibition) beforehand, as research for an essay on extinct Proboscideans, so I went here less for learning new information and more to see, to meet a woolly mammoth, in the flesh. I felt like a pilgrim, visiting the miraculous relics of a saint, in search of enlightenment. I suppose she could be a relic, is a way, for a secular age. A preservation almost as unlikely as the "miraculous" preservation of incorruptible saints, a visitor from an age and a land (in terms of habitat) long gone. I stood in front of her case for a long time. She is remarkable preserved, analogous to ancient Egyptian mummies, but instead of preservation in heat and salt she was preserved in mud and permafrost. She died by suffocation in mud, particles of which were found in her trunk and oesophagus, and you can tell. Her limbs are still in the position she was in when she suffocated, struggling through the mud and her eyes are shut to keep out the mud. It is less a preserved carcass and more of a crime scene, it looks as if she has only recently stopped moving and sunken into the mud. After death, she was rapidly covered in aoxic sediment, so post-mortem decay was negligent. There are some blooms of fungi on the skin; it is signs of the decay which occurred after she weathered out of the permafrost and before refrigerator and preservation by researchers. It is so strange that, around 4,000 years since the very last woolly mammoth died and decayed, mammoths put in "suspended animation" in permafrost still have enough biological material for fungi to grow upon, just as they grow upon a freshly dead elephant. Her trunk is different to that of modern elephants, it had two "fingers" on what would be the top of the nose and the upper lip (?) either side of the nostrils, which are very long and would have been very sensitive, used for the sort of fine motor movements that her feet could never manage. She is hairless, mostly, purely because of the conditions she was buried in, but there is some traces of hair and I saw some on the fold behind her knee. She shrunk after death, down to 50kg when she was found from about 100kg in life due to dehydration; her skin is wrinkled and loose, from one angle you can see her rib cage through the skin. I spent a long time circling her, and I almost felt like crying at the beauty and wonder of it, a visitor from a past age, a lost earth.
As you can see, I got rather too attached to a dead mammoth, but there was the rest of the exhibition to see too. I couldn't take pictures of Lyuba, but here are some pictures of the rest of it. It was very crowded, mostly with families with small children, and became a bit of an Ice Age "selfie safari", but when you could get close to the exhibits it was very good. It did such a good job of highlighting the importance of studying paleontology with a final exhibition on the efforts to prevent the extinction of modern elephants. In mammoths we have a very good model of the extinction which could (is?) facing their proboscidean cousins, the modern elephants. If we had no idea of the past, we can not prepare for and predict the future and this applies in all fields of biology, geography and geology.

The Proboscideans 

This is a model of Moertherium, one of the earliest Proboscideans. It was around the size of a large pig, and was probably largely aquatic, as was some of it's most recent ancestors. Small "tusks" are visible in the upper jaw. 

The fossilized jaw of this blogs name sake, Amebelodon. Amebelodon lived from around 15 to 5 million years ago and had two pairs of enlarged incisors (tusks). The tusks of the lower jaw became flattened and broad, until they nearly touched. These tusks were probably used to "mow" down tough grasses, by moving it's head from side to side like a scythe. 

Left Pygmy Mammoth jaw bone and Right Woolly Mammoth jaw bone. The Pygmy Mammoth is an example of island dwarfism, whereby animals stranded on an island speciate and become smaller, due to a lesser need for scarcer food and lack of predators which they need to be big to defend themselves against. The Pygmy Mammoths evolved after a population of Columbian Mammoths became isolated on the Californian Channel Islands, and was around 1.72m at the shoulder, in contrast to the Columbians at 4.3m at the shoulder. 

A life-sized model of a Pygmy Mammoth, with a mastodon at the front on the background.

A cast of the "Hyde Park Mastodon", an American Mastodon skeleton that was found in New York State and is a 95% complete skeleton. The teeth are clearly visible, which is what the Mastodon ("breast teeth") is named after.

A model of a Columbian Mammoth. Columbian Mammoths occupied some southerly regions of North America, including Mexico and was largely confined to grassland habitats. It existed at the same as the American Mastodon in North America, though as Mastodons probably stuck to swampy habitat they probably did not meet often.

Rest of the museum:

The Skull of a Stegodon, a fairly distant relative of the modern elephants, though due to similarities in habitat they resemble each other, an evolutionary process known as analogy. The tusks grew close to each other, so the trunk would not be able to go between the tusks, but rather hung down on either side of the tusks.

Gomphotherium skull. The Gomphotheriums had four pairs of long tusks, and is one of the earliest examples of sequential tooth development, whereby the cheek teeth of the animal erupt from the back throughout the animal's life to replace those which are worn out. Gomphotherium had a total of three molars in each side of each jaw at one time, and would have had six teeth "pass through" each side in it's lifetime. This became more extreme in mammoths and elephants, who have only one molar in each side of each jaw at one time.

Deinotherium skull, which had only had one pair of lower tusks, and these were probably used to scrap bark which they would have eaten. The trunk would have hung down in front of the lower tusks, and would only be visible when it raised it's trunk.  

Architecture 

The museum was built to house the Natural History Department of the British Museum, so it is laced with all sorts of natural historical details in the architecture. 

A carved ammonite centre, and what looks a bit like an Ediacaran animal, on the right (?), in the bird gallery. 

Carved sea-scorpion in the geology gallery. 

Carved lobed fish on a pillar in the geology gallery.