Leptictidium: Difference between revisions
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==Species== |
==Species== |
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[[Image:Leptictidium auderiense Tobien 1962.JPG|240px|thumb|right|Photograph of the [[Muséum national d'histoire naturelle|MNHN]]'s ''Leptictidium auderiense'', with a full view of the long tail.]] |
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The genus ''Leptictidium'' includes five [[specie]]s: |
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===''Leptictidium auderiense''=== |
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{{main|Leptictidium auderiense}} |
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Described by [[Heinz Tobien]] in [[1962]] based on a series of [[lower jaw]]s 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''.<ref name="WVK-GS"/> It was the smallest species of all and was only sixty centimetres long. Several skeletons have been found at the Messel pit.<ref name="Messel">{{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}}</ref> [[Christian Mathis|Mathis]] remarks the exceptional development of the paraconid (or mesiobucal cusp) of the lower P4 [[premolar]].<ref name="Mathis">{{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 = }}</ref> Its [[premolar]]s and [[molar tooth|molars]] were quite small in comparison to the dentition as a whole. The name of the species refers to the [[Roman Empire|Roman]] settlement of [[Dieburg|Auderia]]. |
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===''Leptictidium ginsburgi''=== |
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{{main|Leptictidium ginsburgi}} |
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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 [[Ludian|Upper Ludian]] strata. The mesostyle typical of the ''Leptictidium'' genus is not developed in this species.<ref name="Mathis"/> The species is dedicated to [[Léonard Ginsburg]], [[France|French]] [[paleontologist]] [[França|francès]] and deputy director of the [[Muséum national d'histoire naturelle]] in [[París]]. |
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==References== |
==References== |
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Revision as of 22:19, 4 June 2008
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Leptictidium ("[[graceful weasels" in latin) is an extinct genus of small prehistoric mammals; together with macropods and humans, they are the only known completely bipedal mammals. They were one of the first branches to split from basal eutherians,[1] appearing in the Lower Eocene, roughly fifty million years ago. Despite the fact that they were widespread throughout Europe, they became extinct roughly thirty-five million years ago leaving no descendants,[2] 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.
Physical characteristics
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 forelegs and large hindlegs, 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.[1]
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,[3] its upper molar teeth were more transverse than those of the North American leptictids and its fourth premolars were molariform.[4] Its C1 canine were incisiviform. Its dentition was quite small in comparison to the size of the mandible and the animal as a whole.[3]
Its size varied between roughly sixty and ninety centimetres in length[5] (more than half of which belonged to the bald tail),[6] and twenty centimetres in height. It weighed a couple of kilograms.[7] This sizes could vary from one specimen to another.
Locomotion
One of the questions about Leptictidium which have not been solved yet is whether it moved by running or by jumping. Because there are very few completely bipedal mammals, it is difficult to find an appropriate animal to compare it with Leptictidium. On one hand, if kangaroos are used as a model, it is probable that Leptictidium ran with its body tilted forward, using its tail as a counterweight.[7] 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.[6] Studies of the bone structure of Leptictidium have yielded contradicting information: on one hand, it seems its leg articulations were too weak too support the shock of repeated jumps, but on the other hand it is obvious that its long feet were not adapted for running, but for jumping.
Kenneth D. Rose did a comparison of 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.[8]
While some paleontologists argue that Leptictidium was obviously a running animal, others reply that what is obvious is that it was cursorial. The fact is that the way this eutherian moved remains a controverted subject.
Behaviour
Leptictidium was 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.[9]
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.[10]
Perfectly preserved fossils of three diferent 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.[9] 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.[3]
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 Paleocene-Eocene Thermal Maximum. It was an episode of quick and intense (of up to 7º C in high latitudes) warming which lasted less than 100,000 years.[11] The Thermal Maximum caused a great extinction which is used to distinguish the Eocene fauna from that of the Paleocene.
The global climate of the Eocene was probablyy the most homogeneous of the Cenozoic; the thermal 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 more warm 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.[12]
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).[13] 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.
Species
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.[3] It was the smallest species of all and was only sixty centimetres long. Several skeletons have been found at the Messel pit.[14] Mathis remarks the exceptional development of the paraconid (or mesiobucal cusp) of the lower P4 premolar.[15] 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.[15] The species is dedicated to Léonard Ginsburg, French paleontologist francès and deputy director of the Muséum national d'histoire naturelle in París.
References
- ^ a b "Leptictidium nasutum n sp., ein Pseudorhyncocyonide aus dem Eozän der "Grube Messel" bei Darmstadt (Mammalia, Proteutheria)". Senckenbergiana lethaea. 66. July 22, 1985.
{{cite journal}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ McKenna, M. C, and S. K. Bell (1997). Classification of Mammals Above the Species Level. Columbia University Press. ISBN 023111012X.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ a b c d "Leptictidium tobieni n sp., ein dritter Pseudorhyncocyonide (Proteutheria, Mammalia) aus dem Eozän von Messel". Cour. Forsch.-Inst. Senckenberg. March 16, 1987.
{{cite journal}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ D. Rose, Kenneth (2006). The Beginning of the Age of Mammals. The Johns Hopkins University Press. Retrieved 20-01-2008.
{{cite book}}: Check date values in:|accessdate=(help); Cite has empty unknown parameter:|chapterurl=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Chaisson, Eric J. (2001). "Leptictidium wildfacts". Animal wildfacts. BBC. Retrieved 30-12-2007.
{{cite web}}: Check date values in:|accessdate=(help); External link in|work= - ^ a b Jehle, Martin (2007). "Insectivore-like mammals: Tiny teeth and their enigmatic owners". Paleocene Mammals. Martin Jehle. Retrieved 30-12-2007.
{{cite web}}: Check date values in:|accessdate=(help); External link in|work= - ^ a b "Leptictidium". Leptictidium bij Kenozoicum.nl. Kenozoicum.nl. 2007. Retrieved 30-12-2007.
{{cite web}}:|first=missing|last=(help); Check date values in:|accessdate=(help); External link in|work= - ^ Rose, Kenneth D. "The postcranial skeleton of early Oligocene Leptictis (Mammalia: Leptictida), with preliminary comparison to Leptictidium from the middle Eocene of Messel".
{{cite journal}}: Cite has empty unknown parameter:|coauthors=(help); Cite journal requires|journal=(help) - ^ a b Haines, Tim (2001). "New Dawn". Walking with Beasts. Londres: BBC Books. Retrieved 30-12-2007.
{{cite book}}: Check date values in:|accessdate=(help); Cite has empty unknown parameters:|chapterurl=and|coauthors=(help) - ^ "Leptictidium". WWB Evidence. ABC. 2001. Retrieved 20-01-2008.
{{cite web}}:|first=missing|last=(help); Check date values in:|accessdate=(help); External link in|work= - ^ http://pubs.giss.nasa.gov/docs/2003/2003_Schmidt_Shindell.pdf
- ^ Stanley, Steven M. (1999). Earth System History. New York: W.H. Freeman and Company.
{{cite book}}: Cite has empty unknown parameter:|coauthors=(help); Text "Data d'accés: 05-04-2008" ignored (help) - ^ Scotese, Christopher (2002). "Paleomap project". Paleomap project. Christopher Scotese. Retrieved 23-01-2008.
{{cite web}}: Check date values in:|accessdate=(help); External link in|work=|work=(help) - ^ "An annotated taxonomic list of the Middle Eocene (MP 11)" (PDF). Cour. Forsch.-Inst. Senckenberg. December 9, 2004.
{{cite journal}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ a b Mathis, C. (1989). "Quelques insectivores primitifs nouveaux de l'Eocène supérieur du sud de la France". Bulletin du Muséum national d'histoire naturelle de Paris. 11: 33–64.
{{cite journal}}: Check date values in:|date=(help); Cite has empty unknown parameter:|coauthors=(help)