Leptictidium

Taxobox
name = "Leptictidium"
fossil_range = Late Cretaceous - Eocene


image_caption = "Leptictidium auderiense" skeleton at the Muséum national d'histoire naturelle (Paris)
image_width = 200px
regnum = Animalia
phylum = Chordata
classis = Mammalia
subclassis = Theria
ordo = Leptictida
familia = Pseudorhyncocyonidae
genus = "Leptictidium"
subdivision_ranks = Species
subdivision =
*"L. auderiense"
*"L. ginsburgi"
*"L. nasutum"
*"L. sigei"
*"L. tobieni"

"Leptictidium" ("graceful weasel" in Latin) is an extinct genus of small mammals; together with macropods and humans, they are the only known completely bipedal mammals. Comprising five species, they resembled today's elephant shrews. They are especially interesting for their combination of characteristics typical of primitive eutherians with highly specialised adaptations, such as powerful hind legs and a long tail which aided in locomotion. They were omnivorous, their diet a combination of insects, lizards and small mammals. One of the first branches to split from basal eutherians,cite journal | author = Adrian Lister, Gerhard Storch | date = July 22, 1985| title = "Leptictidium nasutum" n sp., ein Pseudorhyncocyonide aus dem Eozän der "Grube Messel" bei Darmstadt (Mammalia, Proteutheria) | journal = Senckenbergiana lethaea | volume = 66 | pages =| url =] they appeared in the Lower Eocene, a time of warm temperatures and high humidity, roughly fifty million years ago. Although they were widespread throughout Europe, they became extinct around thirty-five million years ago with no descendants,cite book | author = McKenna, M. C, and S. K. Bell | year = 1997 | title = Classification of Mammals Above the Species Level | publisher = Columbia University Press | id = ISBN 023111012X] probably due to the fact that they were adapted to live in forest ecosystems and were unable to adapt to the open plains of the Oligocene.

Description

"Leptictidium" is a special animal because of the way its anatomy combines quite primitive elements with elements which prove a high degree of specialisation. It had small fore legs and large hind legs, especially at the distal side (that further from the body). The lateral phalanges of its forelegs (fingers I and V) were very short and weak, finger III was longer and fingers II and IV were roughly equal in size, and slightly shorter than finger III. The tips of the phalanges were elongated and tapered.

The ankles and the iliosacral articulation were quite loosely fixed, while the pelvis had a flexible joint with only one coccygeal vertebra. The anteorbital muscle fenestrae in their crania suggest they probably had a long and mobile snout, similar to that of elephant shrews.

"Leptictidium" had wide diastemata in the antemolar row,cite journal | author = Wighart von Koenigswald, Gerhard Storch | date = March 16, 1987| title = "Leptictidium tobieni" n sp., ein dritter Pseudorhyncocyonide (Proteutheria, Mammalia) aus dem Eozän von Messel | journal = Cour. Forsch.-Inst. Senckenberg | volume = 91 | pages = 107–116, 9 Abb.| url =] its upper molar teeth were more transverse than those of the North American leptictids and its fourth premolars were molariform.cite book | last = D. Rose | first = Kenneth | coauthors = Archibald, J. David | title = The Beginning of the Age of Mammals | url = http://books.google.com/books?id=3bs0D5ix4VAC&printsec=frontcover&dq=leptictidium&hl=es | accessdate = 2008-01-20 | year = 2006 | publisher = The Johns Hopkins University Press | location = | chapter = | chapterurl =] Its C1 canines were incisiviform. Its dentition was quite small in comparison to the size of the mandible and the animal as a whole.

It varied between 60 and 90 cm (24-36 in) in length [cite web | last = Chaisson | first = Eric J. | year = 2001 | url =http://www.bbc.co.uk/nature/wildfacts/factfiles/431.shtml | title = Leptictidium wildfacts | work = [http://www.bbc.co.uk/nature/animals/ Animal wildfacts] | publisher = BBC | accessdate = 2007-12-30] (more than half of which belonged to the bald tail),cite web | last = Jehle | first = Martin | year = 2007 | url = http://www.paleocene-mammals.de/insectivores.htm | title = Insectivore-like mammals: Tiny teeth and their enigmatic owners | work = [http://www.paleocene-mammals.de/insectivores.htm Paleocene Mammals] | publisher = Martin Jehle | accessdate = 2007-12-30] and 20 cm (8 in) in height. It weighed a couple of kilograms. These sizes could vary from one specimen to another.

Locomotion

One of the mysteries about "Leptictidium" is whether it moved by running or by jumping. Because there are very few completely bipedal mammals, it is difficult to find an appropriate living model to compare it with. If the kangaroo are used, it is probable that "Leptictidium" ran with its body tilted forward, using its tail as a counterweight.cite web | last = | first = Kenozoicum | year = 2007 | url = http://www.kenozoicum.nl/database/leptictidium.html | title = Leptictidium | work = [http://www.kenozoicum.nl/database/leptictidium.html Leptictidium bij Kenozoicum.nl] | publisher = Kenozoicum.nl | accessdate = 2007-12-30] On the other hand, elephant shrews combine both types of locomotion; they usually move on four legs, but they can run on two legs to flee from a predator. Studies of the bone structure of "Leptictidium" have yielded contradicting information: its leg articulations appear too weak to have supported the shock of repeated jumps, but its long feet were obviously not adapted for jumping rather than running.

Kenneth D. Rose compared the species "L. nasutum" with the leptictid "Leptictis dakotensis". "L. dakotensis" had a series of traits which show it was a running animal which sometimes moved by jumping. Despite the marked similarities between "Leptictis" and "Leptictidium", there are certain differences in their skeletons which prevent the example of "Leptictis" from being used to determine with certainty the way "Leptictidium" moved: the most important being that, unlike "Leptictis", the tibia and the fibula of "Leptictidium" were not fused together.cite journal | last = Rose | first = Kenneth D. | coauthors = | date =| title = The postcranial skeleton of early Oligocene "Leptictis" (Mammalia: Leptictida), with preliminary comparison to "Leptictidium" from the middle Eocene of Messel | journal = | volume = | pages =| url = ]

While some paleontologists argue that "Leptictidium" was obviously a running animal, others reply that what is obvious is that it was saltatorial. The fact is that the way this eutherian moved remains a controverted subject.

Behaviour

"Leptictidium" was probably a diurnal animal which went out to hunt twice a day, once in the morning and once in the afternoon. One of the first things it did after waking up was grooming intensively. It is believed that it showed a particular habit when it hunted; it cleared paths in the jungle where it lived. Every morning and every afternoon it kept itself busy patrolling these paths, catching any prey it found and clearing them from any object which hindered the way. Keeping these paths clear was of utter importance, as they were the way it used to flee if ever a predator attacked it.cite book | last = Haines | first = Tim | coauthors = | title = Walking with Beasts | url = http://www.amazon.com/WALKING-BEASTS-TIM-HAINES/dp/0563537639/ref=sr_1_2?ie=UTF8&s=books&qid=1199057543&sr=1-2 | accessdate = 2007-12-30 | year = 2001 | publisher = BBC Books | location = Londres | chapter = New Dawn | chapterurl =]

Since "Leptictidium" young were very vulnerable to attacks of predators, it is probable that they were born quite developed and that they became independent when they were still quite young. From the behaviour of today's elephant shrew, the possibility can be suggested that "Leptictidium" young went out to hunt with their mother, and that they learned to distinguish prey by licking their mother's mouth when she had just caught an animal, in order to know the flavour of food. [cite web | last = | first = BBC | year = 2001 | url = http://www.abc.net.au/beasts/evidence/prog1/page5_2.htm | title = Leptictidium | work = [http://www.abc.net.au/beasts/evidence/prog1/page5_2.htm WWB Evidence] | publisher = ABC | accessdate = 2008-01-20]

Perfectly preserved fossils of three different species of "Leptictidium" have been found in the Messel pit in Germany. The marks on their fur have been preserved, as well as their stomach contents, which reveal "Leptictidium" were omnivores which fed on insects, lizards and small mammals. The holotype of "L. tobieni" also had pieces of leaves and notable amounts of sand in its abdomen, but it cannot be determined with certainty if the animal swallowed it.

Habitat

"Leptictidium" lived in the European subtropical forests of the Eocene. From the beginning of this period, the temperature of the planet rose in one of the quickest (in geological terms) and most extreme episodes of global warming in the geological record, termed Palaeocene–Eocene Thermal Maximum. It was an episode of quick and intense (of up to 7°C in high latitudes) warming which lasted less than 100,000 years. [http://pubs.giss.nasa.gov/docs/2003/2003_Schmidt_Shindell.pdf] The Thermal Maximum caused a great extinction which is used to distinguish the Eocene fauna from that of the Palaeocene.

The global climate of the Eocene was probably the most homogeneous of the Cenozoic; the temperature gradient from the equator to the poles was half that of today's, and the deep ocean currents were exceptionally warm. The polar regions were much warmer than today, maybe as warm as the Pacific Northwest nowadays. Temperate forests reached the poles themselves, while rainy tropical climates reached 45º N. The greatest difference was in temperate latitudes; nevertheless, the climate at the tropics was probably similar to today's.cite book | last = Stanley | first = Steven M. | coauthors = | title = Earth System History | url = http://en.wikipedia.org/wiki/Special:BookSources/0716728826 | year = 1999 | publisher = W.H. Freeman and Company| Data d'accés: 05-04-2008 | location = New York | chapter =]

In the Eocene, most of what today is Europe, the Mediterranean and south-west Asia was submerged under the Tethys Sea. Both continents were separated by the Turgai Strait (an epeiric sea).cite web | last = Scotese | first = Christopher | year = 2002 | url = http://www.scotese.com/newpage9.htm | title = Paleomap project | work = [http://www.scotese.com "Paleomap project"] | publisher = Christopher Scotese | accessdate = 2008-01-23] Thanks to high humidity and temperatures, most of the European continent was covered in vegetation.

The region which today is Germany was in a volcanically active zone during the Eocene. It is thought that the Messel pit could have been the old location of a volcanic lake saturated with CO₂. The lake would periodically release the gas it contained, creating a lethal cloud which would asphyxiate any animal in its path. This would explain the great number of non-aquatic species which have been found in the old lake-bed of the Messel pit.

In the lush forests of this region, "Leptictidium" shared its habitat with animals such as "Godinotia", "Pholidocercus", "Palaeotis" or "Propalaeotherium". There were also predators: "Asiatosuchus", "Lesmesodon" or the Messel giant ant. The alpha predator was "Gastornis", a carnivorous bird almost two metres tall.

pecies

The genus "Leptictidium" includes five species:

"Leptictidium auderiense"

Described by Heinz Tobien in 1962 based on a series of lower jaws from the Lutetian faunal stage. Tobien also uncovered a small skeleton he defined as a paratype of the species, but Storch and Lister proved in 1985 that, in fact, the skeleton did not even belong to the genus "Leptictidium". It was the smallest species of all and was only sixty centimetres long. Several skeletons have been found at the Messel pit.cite journal | last = | first = | coauthors = Michael Morlo, Stephan Schaal, Gerald Mayr & Christina Seiffert | date = December 9, 2004| title = An annotated taxonomic list of the Middle Eocene (MP 11) | journal = Cour. Forsch.-Inst. Senckenberg | volume = | pages =| url = http://www.senckenberg.de/files/content/forschung/abteilung/terrzool/ornithologie/morlo_et_al.pdf] Mathis remarks the exceptional development of the paraconid (or mesiobucal cusp) of the lower P4 premolar.cite journal | last = Mathis | first = C. | coauthors = | date = 1989| title = Quelques insectivores primitifs nouveaux de l'Eocène supérieur du sud de la France | journal = Bulletin du Muséum national d'histoire naturelle de Paris | volume = 11 | pages = 33–64| url = ] Its premolars and molars were quite small in comparison to the dentition as a whole. The name of the species refers to the Roman settlement of Auderia.

"Leptictidium ginsburgi"

Described by Christian Mathis in 1989. Fossils have been found in the lagerstätte at Robiac, Le Bretou, Lavergne, La Bouffie, Les Clapiès, Malpérié and Perrière (France), in Upper Ludian strata. The mesostyle typical of the "Leptictidium" genus is not developed in this species. The species is dedicated to Léonard Ginsburg, French paleontologist and deputy director of the Muséum national d'histoire naturelle in París.

"Leptictidium nasutum"

Described by Adrian Lister and Gerhard Storch in 1985. It was a middle-sized species which was seventy-five centimetres long. Several skeletons have been found in the Messel pit, in Lower Lutetian strata. The tail of this species had 42-43 vertebrae, a number surpassed among mammals solely by the Long-tailed Pangolin. Its premolar and molar teeth were quite small in comparison to the dentition as a whole. The name of the species refers to the nose of the animal. The holotype is the complete skeleton of an adult specimen kept in the Forschungsinstitut Senckenberg in Frankfurt am Main.

"Leptictidium sigei"

Described by Christian Mathis in 1989. Fossils have been found in the lagerstätte at Sainte-Néboule, Baby, Sindou and Pécarel (France), and it has a more primitive appearance than "L. nasutum". It is known mainly from isolated teeth. It has a P4 with a much reduced paraconid, as well as very distinct entoconids and hypoconulids on M1 and M2. The species is dedicated to Bernard Sigé, French paleontologist.

"Leptictidium tobieni"

Described by Wighart von Koenigswald and Gerhard Storch in 1987. It was the largest species of all at ninety centimetres long. It is one of the species found in the Messel pit, in Lutetian strata. The species is dedicated to Heinz Tobien, descriptor of the genus "Leptictidium" and promotor of research in the Messel pit during the 1960s. The holotype is a complete and perfectly preserved skeleton of an adult specimen which was uncovered in September 1984 and which can be found at the Hessisches Landesmuseum Darmstadt. There is also a paratype; a non-complete and badly preserved specimen which can be found at the Institut Royal des Sciences Naturelles de Belgique.

It has a relatively robust mandible with a relatively large mesostyle. The molariform premolar teeth are a characteristic of the "Leptictidium" genus as a whole which is very marked in the P4 premolars of "L. tobieni". The well-developed mesostyle and the transversal configuration of the upper molars are other typical traits of this species.

Comparison of the Messel species

By observing the clear morphological differences in the dentition of the three species found in Messel, the possibility can be discarded that either the discovered fossils are specimens of the same species but of different age, or that two of these forms belonged to the same species with a marked sexual dimorphism.

The Messel species developed very quicly a series of characteristical evolutionary traits, common to all of them, which separe them from the lagerstätte of Quercy.

This table compares the size of different specimens of each species found in the Messel pit (sizes in millimetres).

† From the front edge of the orbit. †† Above the "incisura praeangularis".

Evolutionary tendencies

In his work "Quelques insectivores primitifs nouveaux de l'Eocène supérieur du sud de la France" (1989), French paleontologist Christian Mathis studied the evolutionary tendencies of the genus "Leptictidium", based on the comparison of the most primitive and the most recent species. From this observations, Mathis remarks:

*an increase in size;
*a precocious merging of the hypoconulid and the entoconid on M3;
*a slight reduction of the width of the talonid on M3 in comparison to the anterior molars;
*the formation and development of a mesostile on the molariform jugal teeth P4-M3;
*the reduction of the parametastylar and metastylar regions of these same teeth (with some exceptions), in particular with a reduction of the parastylar lobe which rises less in the anterior part of M3 and possibly P4;
*a transverse shortening of the upper molarised teeth, which become more square;
*the development of accessory conuli on the preprotocrista and postprotocrista;
*the development of the postcingulum.

Related species

Together with the genus "Pseudorhyncocyon", the five "Leptictidium" species form the family Pseudorhyncocyonidae, one of the three which form the order Leptictida. These families and genera are: [cite web | last = Haaramo | first = Mikko| year = 2007 | url = http://www.fmnh.helsinki.fi/users/haaramo/ | title = Mikko's Phylogeny Archive | work = [http://www.fmnh.helsinki.fi/users/haaramo/ Mikko's Phylogeny Archive] | publisher = Mikko Haaramo | accessdate = 2007-12-30]

Order Leptictida

*Family Gypsonictopidae (Van Valen, 1967)
**Genus "Gypsonictops" (Simpson, 1924)
*Family Leptictidae (Gill, 1872)
**Genus "Leptictis" (Leidy, 1868)
**Genus "Myrmecoboides" (Gidley, 1915)
**Genus "Ongghonia" (Kellner & McKenna, 1996)
**Genus "Palaeictops" (Matthew, 1899)
**Genus "Prodiacodon" (Matthew, 1929)
**Genus "Xenacodon" (Matthew & Granger, 1921)
*Family Pseudorhyncocyonidae (Sigé, 1974)
**Genus "Leptictidium" (Tobien, 1962)
**Genus "Pseudorhyncocyon" (Filhol, 1892)

Because Leptictida is a paraphyletic group, this list does not take into account the families or genera with an uncertain or disputed affiliation.

In documentaries

A female "Leptictidium" and its young are the main characters in the first episode of the BBC's paleontology series "Walking with Beasts". The episode narrates one day in the life of this animal of the Eocene.

The female "Leptictidium" appears for the first time after the fall of a micrometeorite, when she meets another specimen of the same species just before dawn. She is forced to flee from a "Gastornis", hiding in the nest it has built at the base of a fig tree. Once the sun has risen, the mother goes out to hunt, looking for insects and cold-blooded animals which have not warmed up yet, and she hunts a frog. She reaches the shore of a lake, but she does not approach because an "Ambulocetus" has arrived from the coast. By midday she is forced to return to her nest despite the little success she has had, since it is the time there are more predators in the forest, and she sleeps until the afternoon.

When the hottest hours are over, the female goes out to hunt again. She uses her hindlegs to prepare the paths she will use to escape if a predator pursues her. This time, the young accompany the mother in her hunt. They are able to escape from the attack of a "Gastornis", which ends up killing a "Propalaeotherium". This time, they are successful and are able to feed well.

At nightfall, the "Leptictidium" are some of the few animals which are saved from a cloud of toxic gas, freed by the volcanic lake, thanks to the fact that their nest lay away from the path of the cloud. Instead, the "Ambulocetus" which had attacked them during the day dies asphyxiated by the carbon dioxide, and the following morning the "Leptictidium" pass next to it, knowing it is dead. [cite web | last = BBC | first = | year = 2002 | url = http://www.abc.net.au/beasts/ | title = Walking with Beasts | work = [http://www.abc.net.au/beasts/ "Walking with Beasts" on the ABC's website] | publisher = ABC | accessdate = 2007-12-30]

Bibliography

In English

* cite book
author = Benton, M.
title = Vertebrate Palaeontology
year = 2000
publisher = Oxford: Blackwell Publishers
id = ISBN 0632056142
* cite book
author = Frey, E.; Herkner, B.; Schrenk, F.; Seiffert, C;
title = Reconstructing organismic constructions and the problem of Leptictidium's locomotion
year = 1993
publisher = Darmstadt: Kaupia Darmstädter Beiträge zur Naturgeschichte
id =
* cite book
author = Rose, K.
title = The Beginning of the Age of Mammals
year = 2006
publisher = The Johns Hopkins University Press
id = ISBN 0801884721

In French

* cite book
author = Mathis, C.
title = Quelques insectivores primitifs nouveaux de l'Eocène supérieur du sud de la France
year = 1989
publisher = Paris: Bulletin du Muséum national d'histoire naturelle
id =

In German

* cite book
author = Christian, A.
title = Zur Biomechanik der Fortbewegung von Leptictidium (Mammalia, Proteutheria)
year = 1999
publisher = Frankfurt am Main: Courier Forschungsinstitut Senckenberg
id =
* cite book
author = Maier, W.; Richter, G.; Storch, G.
title = "Leptictidium nasutum" - ein archaisches Säugetier aus Messel mit außergewöhnlichen biologischen Anpassungen
year = 1986
publisher = Frankfurt am Main: Natur und Museum
id =
* cite book
author = Storch, G.
title = "Leptictidium" - ein archaischer Säuger
year = 1987
publisher = Naturwissenschaftliche Rundschau
id =
* cite book
author = Storch, G.; Lister, A.
title = "Leptictidium nasutum" - ein Pseudorhyncocyonide aus dem Eozän der Grube Messel bei Darmstadt (Mammalia, Proteutheria)
year = 1985
publisher = Frankfurt del Main: Senckenbergiana lethaea
id =
* cite book
author = Tobien, H.
title = Insectivoren (Mammalia) aus dem Mitteleozän (Lutetium) von Messel bei Darmstadt
year = 1962
publisher = Wiesbaden: Notizbl. hess. Landesamt. Bodenforsch.
id =
* cite book
author = von Koenigswald; W.; Storch, G.
title = "Leptictidium tobieni" n sp., ein dritter Pseudorhyncocyonide (Proteutheria, Mammalia) aus dem Eozän von Messel
year = 1987
publisher = Frankfurt del Main: Courier Forschungsinstitut Senckenberg
id =
* cite book
author = von Koenigswald, W.; Wuttke, M.
title = Zur Taphonomie eines unvollständigen Skelettes von "Leptictidium nasutum" aus dem Ölschiefer von Messel
year = 1987
publisher = Wiesbaden: Geol. Jb. Hessen
id =

References

External links

* [http://www.bbc.co.uk/nature/wildfacts/factfiles/431.shtml "Leptictidium" at BBC Science & Nature]
* [http://www.kenozoicum.nl/database/leptictidium.html "Leptictidium" at Kenozoicum.nl] nl
* [http://www.abc.net.au/beasts/ "Walking with Beasts" – Australian Broadcasting Corporation]