Rhizosmilodon
Fiteae pine parts of Rhizosmilodon
- North America, Florida
- Rhizosmilodon fiteae
Rhizosmilodon is a genus of extinct saber-toothed cats ( Machairodontinae ), which so far fiteae only by single lower jaw fragments and parts of the limbs of the type Rhizosmilodon is documented from Florida. The fossils come from a phosphate mine in the Upper Bone Valley Formation at Fort Meade in Florida. They are assigned to the so-called Palmetto fauna or Whidden Creek Local Fauna, who lived in what is now Central Florida about five million years ago.
Rhizosmilodon was like other saber-toothed cats are carnivores, probably actively hunted its prey and killed. It could well be a smaller to medium-sized mammal, the prey spectrum was similar to that of the cougar. The habitat in Central Florida probably consisted of flooding and flood plains with a mosaic of forests with closed canopy, more open woodland and open grass areas.
The first bone of the species were first finds assigned in 1983 to the Americas, the type Megantereon hesperus. 2013 was a revision of the assignment as well as the first scientific description of Rhizosmilodon fiteae as a separate species within the genus also new Rhizosmilodon due to new discoveries.
- 4.1 Fund history and implications for the systematics
- 4.2 Current systematics
- 4.3 naming
Features
The description of Rhizosmilodon fiteae as an independent species was made on the basis of several teeth fragments, also the type remains of several limb bones were assigned to originate from the same locality.
Features of the teeth and teeth fragments
The holotype UF 124634 (UF stands for Florida Museum of Natural History, University of Florida, Gainesville, and names the storage location of the fossils ) is a part of the right mandible with preserved symphysis and the canine (C1 ) and the first molar ( M1); between the alveoli (alveoli ) of the premolars P3 and P4 are present, lacks the teeth themselves. As paratype UF 135626 a fragment of left mandible with preserved premolars P3 and P4 and the molars M1 is selected. Besides these two parts of the mandible type other found the same reference were assigned. This is mainly to some other lower jaw fragments with teeth and partially preserved symphysis and alveoli parts ( UF 22890, UF 223796, UF 212381, UF 272 337 ).
Among the diagnostic characteristics of the type on numerous features of existing teeth and the individual mandible are expressed using the fragments available. So the symphysis of the mandible is almost vertical pronounced and the lower jaw has a slight indentation as an adaptation to the highly elongated canines of the upper jaw. The incisors are small, but not lying. At least the lower canines are large, but much flattened laterally; they have a moderate, rounded perforation. The second Vormahlzahn (P2 ) is missing, P3 is extended but only about two-thirds as large as the last premolar (P4 ), which is enlarged sound like; P3 and P4 are not connected and are not in a line and P4 is not in a direct line with the first molar (M1). Typically, the arrangement of the cusps appear on the crowns of the premolars and molars. So P3 is missing the front tooth cusps and the rear cusp is only slightly formed. Also, the front tooth cusps on P4 is small. The first molar is similarly strong as that of Smilodon.
Features of the limb bones
Besides the described parts of the jaw bone and several parts of the limbs were assigned on the basis of their size the way, even though they were not directly related to the jaw fragments found. It is a complete left femur (UF 133938 ), the lower ( distal ) end of a right femur (UF 65686 ), the distal portion of a left radius ( UF 123836 ), a complete left shin (tibia) (UF 133939 ) and the upper ( proximal ) piece of right tibia (UF 212380 ).
For the first description of Rhizosmilodon fiteae only the two femurs were described in detail. Especially the pronounced extension of the central part of the condyles ( epicondyles ) and the very pronounced just Pectoralgrat, which does not match the typical curved Deltoidgrat the most Panthera species and allows an assignment to the saber-toothed cats are considered typical for this type. Further details of the bone as the bent shaft and the overall robust structure of the bones as well as the structure of the condyles and foramen suggest a kinship proximity to Smilodon. The existence of another, undescribed closely related species besides Rhizosmilodon fiteae from the Fund area to which these bones might belong, is assumed to be unlikely.
Feature reconstruction
Although of Rhizosmilodon fiteae few skeletal constituents are known to have a relatively thorough reconstruction of the entire animal is possible. The paleontologists benefit in this case largely on the species, which are classified into closer relationship, ie primarily known saber-toothed cats, as well as of today living cats of similar size and stature. About a feature comparison many features can as plesiomorphies, ie already in the common ancestral species existing features are provided - including especially the attitude and design of the limbs and the general physique and posture.
On the basis of the existing thigh and shin bones extrapolation to the weight of the cat could be made by the bones were compared with those now living and extinct cats. After this assessment Rhizosmilodon fiteae reached a weight of about 56 to 85 kg, which corresponded to about one living today cougar (Puma concolor ) and jaguar (Panthera onca ). The size also overlaps gracilis with the estimates for the smaller extinct Smilodon.
Characteristics compared with other types
Since Rhizosmilodon fiteae was described as a separate species and genus, had to be adjusted in the original description, the existing and reconstructed features with other potentially closely related species and genera to demonstrate the autonomy and derive a phylogenetic assignment.
The assignment to the Smilodontini, which in addition Rhizosmilodon also the genera Smilodon and Megantereon be made, based on the perforation of the cutting surfaces of the canines, which affects all teeth with representatives of Machairodontini. The vertical position of the teeth and the mandibular P3, P4 and M1 to each other as well as the training of the individual teeth allow the assignment in this relationship. Of the genera Smilodon and Megantereon to Rhizosmilodon but differs by independent features. These are also specific dental features as the concrete moderate and rounded form of the perforation at the lower canine. This is also present in Smilodon gracilis, other types of Smilodon ( Smilodon fatalis, Smilodon popular ) but more pronounced; Megantereon at the perforation is missing, however, and is likely gone lost. The Unterkiefereinbuchtung as an adaptation to the enlarged canines of the upper jaw is compared to Smilodon only slightly pronounced. Other features with significant differences relate to the design of the cusps on the premolars and molars.
Locality and temporal classification
The fossils date back to the first description of a phosphate mine near Fort Meade in Polk County in Central Florida, additional finds from the neighboring regions in Hardee and Hillsborough County. The fossil -bearing strata of this region are assigned to the Upper Bone Valley Formation in Florida, the animals contained the so-called Palmetto fauna and Whidden Creek Local Fauna. This will be chronologically ordered in the late Hemphillium, a period of North American mammal fauna, which overlaps with the early Pliocene, the Zancleum. The fossils contained in this layer are estimated at an age of about five million years.
While most of the fossil remains of vertebrates in the Upper Bone Valley Formation are collected at isolated localities and a targeted search for more fossils is not worthwhile, the mine of the Gardinier Inc. in Fort Meade an exception as since 1989 were thousands in this mine vertebrate fossils in only about 0.8 meters thick layer on a surface of about 2000 square meters, the largest known fossil concentration in the field, are found.
Lifestyle and paleoecology
About the life and ecology of the genus are no data, however, it can be similar to other fossil big cats reconstructed by comparison with extant species. Like other saber-toothed cats will have been a predator that probably actively hunted its prey and also killed Rhizosmilodon. This was according to its size is likely to small to medium-sized mammals that prey spectrum was similar to that of recent cougar (Puma concolor). It is possible that Rhizosmilodon climb trees by its relatively small size and could hide his prey as from larger predators or packs.
The composition of the Palmetto fauna suggests a presence of the species on the seashore. In the fossil layers numerous fossils of marine life such as cartilaginous fishes, bony fishes, turtles and whales are in addition to terrestrial vertebrates contain. The habitat in the Bone Valley in Central Florida probably consisted of wet flood plains and alluvial areas where the vegetation, more open woodland and open grass areas consisted of a mosaic of forest with closed canopy. Overall fossils were identified from 33 different species of mammals in the Whidden Creek Local Fauna, including 11 species of carnivores. It is about 900 fossils, of which about five percent predators. Among the cats are next Rhizosmilodon with Machairodus coloradensis a further saber-toothed cat, Lynx rexroadensis and an unacknowledged member of the genus Pseudaelurus continue dogs ( Borophagus, Carpocyon, Eucyon and Vulpes ), bears ( Agriotherium, Plionarctos ) and small bears, martens and skunks. The remaining mammal fossils are mostly of odd-toed ungulates (approx. 33%), artiodactyls ( about 37%) and whales (about 16 %). Overall, the Palmetta fauna represents one of the most diverse ecosystems in North America this time, and especially the great number of large herbivores is remarkable.
Taxonomy
Fund history and implications for the systematics
The first known fossil of a comparatively small saber-toothed cat from the Palmetto Fauna, a mandible fragment (UF 22890 ), was used in 1983 for the assignment of the find hesperus as Megantereon. The fossil was also assigned as the oldest find of the genus Megantereon world and because of this description was the origin of the genus, which otherwise found mainly in Eurasia and Africa, based in North America.
Megantereon hesperus was described in 1933 by Gazin as Machairodus hesperus basis of a right lower jaw fragment from the Twin Falls County, Idaho, in 1970 and assigned to the genus Megantereon by Schultz and Martin. Through the Fund in Florida, the theory has worked out that the genre has developed in opposition to the hitherto valid Eurasian and African origin in North America and Megantereon hesperus is the oldest representatives of the same. From North America, this thesis has been accepted in accordance with the propagation of the species to Eurasia and Africa about 3.5 million years beginning in the mid- Pliocene Villafranchian which France agrees with the oldest occurrence of the genus in Europe in Les Etouaires. Some later editors took these theses, including about Martinez - Navarro & Palmqvist (1995 ) in a study of the fossils of Megantereon whitei in Spain.
Megantereon hesperus
Megantereon cultridens, Megantereon inexpectatus, Megantereon whitei
Smilodon
Other Machairodontinae
However, the mapping of the North American fossils from Florida to the genus Megantereon led before the description of Rhizosmilodon also confusion and criticism. The paleontologist Alan Turner turned the assignment in question in 1987 and suggested an alternative assignment to a yet unknown species of the widespread genus Dinofelis which is no longer part of the saber-toothed cats today, or to the more primitive genus Paramachairodus ago. Even John -Paul Hodnett favored a classification of the fossils present in the genus Paramachairodus because they resembled the discovery of a Paramachairodus from the Northern Arizona described by him. At the same time he argued with his find also a source of Smilodontini in North America, he then assigned Paramachairodus by the tribe. Wallace & Hulbert 2013 put in their first description of Rhizosmilodon in response to Hodnett, however, very clearly the differences between the Paramachairodus and Rhizosmilodon described by him dar. Webb et al. (2008) also illustrate that the description as Machairodus may not be accurate and show that it must be according to newly found material to a kind in the relationship of Smilodon and Machairodus, however, is different from both. One of the authors, Richard C. Hulbert belonged later to the Erstbeschreibern of Rhizosmilodon.
Current systematics
2013 was a revision of the assignment as well as the first scientific description of Rhizosmilodon fiteae as a separate species within the genus also new Rhizosmilodon on the basis of 1990 found the mandible and other bones that are associated with the type.
Rhizosmilodon
Smilodon
Megantereon
Machairodus
Paramachairodus
Promegantereon
According to the original description the genus Rhizosmilodon is classified based on the existing features at the base of the tribe Smilodontini and there taxon consisting of the genera Smilodon and Megantereon juxtaposed. The system is derived from an analysis of a matrix of characteristics known saber-toothed cats. With an age of about five million years ago are the fossils represent the oldest fossils of the tribe, so Rhizosmilodon lived before the other representatives of Smilodontini.
Specific feature comparisons relate primarily to the expression of individual teeth. Thus, the perforation of the canines was at Rhizosmilodon probably as the first representative of the Smilodontini moderately rounded and pronounced as with the earliest and smallest member of the genus Smilodon, Smilodon gracilis. Within the genus Smilodon fatalis they memorized in Smilodon and popular to a clear and sharp teeth, while she was lost in the genus Megantereon. The Unterkiefereinbuchtung as an adaptation to the enlarged canines of the upper jaw is compared to more primitive species of the taxon as Promegantereon or Paramachaerodus significantly and similarly strong as Machairodus whose enlarged canine teeth were flattened; However, compared to Smilodon and Megantereon with strong and very large upper canines it is only slightly pronounced.
This development would mean that the tribe Smilodontini and the genera originated in North America, where all three species were able to train them and later immigrated from Megantereon to Eurasia and Africa.
Megantereon
Smilodon
Rhizosmilodon
Machairodus
Homotherium
Paramachairodus
Promegantereon
In addition to the authors of the preferred hypothesis, facing a common taxon of Smilodon and Megantereon as sister species after Rhizosmilodon, it is assumed alternatively that Rhizosmilodon and Smilodon form a common taxon and Megantereon opposed to this. For such a hypothesis in particular the training of Unterkiefereinbuchtung and the toothless canines could stand. In this case, the formation of the tribe Smilodontini with Megantereon than most original genus in Eurasia, Africa and a double immigration to North America would be likely.
Naming
The scientific name of the genus Rhizosmilodon based on a composite of the Greek word Rhizo, the, root means' and the already existing generic name Smilodon. In the naming as " root of Smilodon " reflects the set out of the Erstbeschreibern position of the genus at the base of Smilodontini and thus the origin of the well-known genus Smilodon.
The species name Rhizosmilodon fiteae the only previously described species within the genus is derived from the name of the paleontologist Barbara Fite, who donated the paratype from her private collection.