Xylotitanium

Xylotitanium
Temporal occurrence
Middle Eocene
45.4 to 42.9 million years
Locations
North America (Oregon)
Systematics
Higher mammals (Eutheria) Laurasiatheria Unpaired ungulate (Perissodactyla) Hippomorpha Brontotheriidae Xylotitanium
Scientific name
Xylotitanium
Mihlbachler & Samuels , 2016

Xylotitan is an extinct genus of the Brontotherien , a non-existent group of odd- toed ungulates that is possiblycloser tothe Equidae . The genus was proven in the Clarno Formation in the US state of Oregon , which forms part of a very fossil-rich region. The previously known find material consists of individual bits of dentition and isolated teeth. It has an absolute age of around 44 million years and thus dates to the Middle Eocene . The remains belong to a small representative of the Brontotherien. Its most noticeable feature, in addition to its small size, was that the nose was only slightly indented and therefore short. In the other characteristics, the animals resembled other members of the group. On the basis of the paleontological findings of the Clarno Formation,a very dense subtropical forest can be reconstructedfor the living environment of xylotitan . It is assumed that the small size of the animals is an adaptation to this habitat . The genus was scientifically introduced in 2016.

features

Xylotitan is a representative of the Brontotherien, the evidence of which is based on individual dentition fragments and isolated teeth. Based on the size of the teeth, a small member of the group can be inferred, whose body weight is reconstructed at around 430 kg. Few fragments of the skull are available for diagnostic features. The short interior of the nose, which ended almost vertically approximately above the first premolar , was striking . This makes it comparatively short as in Sthenodectes , Wickia or Metatelmatherium and not drawn back as long as, for example, in Metarhinus or Telmatherium . The shape of the nasal cavity also suggests a high and short rostrum . The infraorbital foramen opened above the fourth premolar. Since this is always just in front of the orbit in Brontotheria, a position of the eye socket with the anterior margin at the level of the first molar can be assumed for xylotitan . This would be comparable to Wickia or Metatelmatherium , but shifted significantly further forward than with Mesatirhinus and Metarhinus . On the lower jaw, the front edge of the symphysis , which connects the two halves of the jaw, protruded at an angle of 45 °. The posterior end of the symphysis was located between the second and third premolars.

The rear teeth are largely covered by the dentition. An upper incisor and several canines are isolated. The former had a rather conical shape and was reminiscent of a canine, the latter were large. Nothing is known about their exact position in the dentition, but an upper jaw fragment indicates a diastema in front of the premolars, so that the upper canine was isolated from the posterior dentition. In the lower row of teeth there were three front teeth and one canine tooth per half of the jaw, but only the alveoli have survived. The anterior dentition was therefore unreduced compared to some late Brontotheria. As in numerous Brontotheria, the incisors formed a clear arch, behind which the canine was directly attached. There was a short diastema around 1 cm in length to the posterior dentition. Another, only half as long, separated the first from the second premolar in the lower jaw. A corresponding tooth gap was missing in the upper jaw, but occasionally occurred in other Brontotherias, albeit in variable degrees. The first premolar in each case was relatively small and of simple construction with a single point. The other premolars had a rather elongated to rectangular shape and increased in size and molarization towards the rear. However, none of the premolars resembled the molars completely. The molars show hardly any diagnostic features, so they differ little from those of the other Brontotheria with the exception of the earliest representatives. Compared to similarly large forms such as pygmy titanium and microtitanium , however, they were relatively smaller. A typical W-shaped ectoloph was found on the upper molars on the cheek side of the chewing surfaces, a shear bar between two main cusps of a tooth, which was fully developed and thus advocates a position within the developed Brontotheria for xylotitanium . On the tongue side, the ectoloph had only a thin layer of tooth enamel . There was only a narrow cingulum on the front side of the tooth, a low bulge of tooth enamel that did not continue on the inside of the tooth. In early Brontotheria, the anterior cingulum was much thicker. The lower molars had the double-crescent-shaped outline typical of Brontotheria. The row of premolars was about 6.6 cm in length in the upper jaw and 6.7 cm in the lower jaw. A complete back row of teeth of a lower jaw measured from the first premolar to the last molar was 16.1 cm in length. The largest tooth in the dentition was the last molar. It was around 3.3 cm long and 3.4 cm wide at the top, the corresponding dimensions at the bottom were 4.3 and 1.8 cm. The extremely small first premolar, on the other hand, was only about 1 cm long and wide.

Fossil finds

The previously known fossil finds of xylotitanium came to light in the Clarno Formation in the John Day Basin in the US state of Oregon . The John Day Basin is part of an extremely fossil-rich region that has been explored for more than 150 years. The finds there are spread over hundreds of different locations with a time range from the Middle Eocene to the Upper Miocene . While the more recent fossil sites of the Oligocene and Miocene - geologically counted as part of the John Day Formation - stand out due to their richness with a high diversity of vertebrates , those of the Eocene and thus the Clarno Formation are comparatively poor. Mammals of this time have only been observed in two places, the stratigraphically older Clarno Nut beds and the geologically somewhat younger Hancock Mammal Quarry . Both are close together within the boundaries of the John Day Fossil Beds National Monument . The latter hid among others besides the known Clarno Rhinos of the genus Teletaceras the remains of Eubrontotherium , another representative of the Brontotherien from the former was Xylotitan reported. The Clarno Nut beds take up only about 10 m within the 1800 m thick series of deposits of the Clarno Formation. You are outcropping an acre on the west side of Hancock Canyon in Wheeler County, Oregon. They mainly consist of well-formed siltstones and sandstones as well as conglomerates , between which individual layers of volcanic tuff are interposed . Radiometric dating gives the deposits an age of around 44 million years, which corresponds to the Middle Eocene (locally stratigraphically called Uintum ).

The vertebrate fossil records within the Clarno Nut beds are very rare and highly fragmented. So far, remains of crocodiles and turtles as well as individual mammals have been detected , including various odd- toed ungulates such as Orohippus (an early member of the horses ) or Hyrachyus (a relative of the tapir - rhinoceros line) and representatives of the predatory Oxyaenodonta . It is the oldest mammalian fauna in the Pacific Northwest. Xylotitan is represented by individual upper and lower jaw fragments and isolated teeth. So far, around 30 objects have been assigned to the genus, which is the most extensive material of all vertebrate forms of the Clarno Nut beds . Compared to the rather sparse fauna finds, the remains of the flora of the Clarno Nut beds are among the most extensive in the world. They go back to a broad-leaved, subtropical forest in which warmth-loving plants such as cycads or palm and banana plants existed mixed with plants in temperate zones such as walnut , birch and elm plants (the name Clarno Nut beds goes back to the numerous fossilized walnuts found and was first used in the 1940s). Comparable landscapes can be found today in southeastern North America or in Central America , the plants found reveal not only relationships with today's Central America but also those with Southeast Asia . The forests of the Clarno Nut beds must have been very dense, as 40% of the fossil flora consists of tendrils and climbing plants such as lianas . On the basis of the paleobotanical remains, an annual average temperature of around 17 ° C with a range of 14 to 21 ° C can be assumed, the annual precipitation was probably around 3000 mm.

Paleobiology

With a presumed body weight of around 430 kg, xylotitan is one of the smaller representatives of the Brontotheria. Only early forms such as Eotitanops were significantly smaller at around 140 kg. The largest members of the group such as Megacerops and Embolotherium , on the other hand, reached gigantic proportions with over 3000 kg (estimates range up to 8500 kg). The closest relatives of xylotitan , namely Wickia and Metatelmatherium , weighed around 1640 to 2140 kg. This means that xylotitan joins other forms of Brontotheria such as pygmaetitan , microtitan and nanotitanops , in which a secondary dwarfing has been proven. The predominant part of the small- stature developed Brontotheria is documented in today's Eurasia, whereas with xylotitan a first such proof is also available from North America. It is possible that the small body size of xylotitan is an adaptation to a life in the extremely dense subtropical forests, as they are reconstructed for the Clarno Nut beds of the Clarno Formation . The size of the animals is comparable to today's tapirs , which inhabit a similar habitat. Therefore it can be assumed that xylotitan had a comparable ecological claim as the recent tapirs.

Systematics

Internal systematics of the Brontotheriinae according to Mihlbachler and Samuels 2016   Brontotheriinae    Bunobrontops      Mesatirhinus      Acrotitan      Desmatotitan      Dolichorhinus      Sphenocoelus      Microtitan      Fossendorhinus      Metarhinus      Sthenodectes      Telmatherium      Xylotitanium      Wickia      Metatelmatherium      Qufutitan      Epimanteoceras      Nanotitanops      Brontotheriina

Xylotitan is a genus within the extinct family of the Brontotheriidae (originally Titanotheriidae) and the order of the odd ungulate . The family can be viewed as a distant kinship of today's horses in terms of the design of the teeth . Their representatives were very diverse and lived mainly in the Eocene in North America and Eurasia . The late forms such as Megacerops and Embolotherium were characterized by an enormous physique and by bony horns on the nose. The family relationships within the Brontotherien have not been completely clarified, as the various forms show relationships to one another across the individual continents of their distribution at that time. A study from 2008, presented by Matthew C. Mihlbachler , suggested that all representatives with more modern tooth characteristics, whether horn-bearing or not, be assigned to the subfamily of the Brontotheriinae . Within this are the horn-bearing forms in the tribe of the Brontotheriini . According to phylogenetic studies, the genus Xylotitan has closer ties to Wickia and Metatelmatherium . Both forms are also known from northern America. The exact relationships between the three genera are not clear, so that no exact sister form to xylotitan can currently be determined. Both Wickia and Metatelmatherium are referred together with Telmatherium to the sub-tribus of Telmatheriina , whose common feature is only slight bony nasal bulges. Opposite this sub- tribus are the Brontotheriina with clear cone-like or battering ram-like horns, which include terminal forms such as Megacerops and Embolotherium .

In a 1996 revision of the fauna of the Clarno Nut beds of the Clarno Formation , the remains of the Brontotherien were assigned to the genus Telmatherium . In 2013, however, Matthew C. Mihlbachler and Joshua X. Samuels noted that these probably represent a new, small-stature genus. A good three years later, Mihlbachler and Samuels published the first scientific description of xylotitan based on the material from the Clarno Nut beds . They identified a left, partially preserved upper jaw as the holotype , to which the four premolars are still attached (specimen number UCMP 121825). The generic name is derived from the Greek words ξύλο ( xylo ) for "wood" and τιτάν ( titan ) for "titanium" or "giant". The former refers to the numerous fossilized woods of the Clarno Nut beds and the palaeoenvironment of that time reconstructed from them, the latter refers to the legendary giant family of the titans in Greek mythology and is a component of the name often used in Brontotherien. Mihlbachler and Samuels X. named cenosus as the only species so far . The specific epithet is of Latin origin ( caenōsus ) and means something like "boggy". It alludes to the numerous volcanic mud flows within the Clarno Nut beds .

literature

• Matthew C. Mihlbachler and Joshua X. Samuels: A small-bodied species of Brontotheriidae from the middle Eocene Nut Beds of the Clarno Formation, John Day Basin, Oregon. Journal of Paleontology 90 (6), 2016, pp. 1233-1244 doi: 10.1017 / jpa.2016.61

Individual evidence

1. ↑ ^{a b c d e f g h i} Matthew C. Mihlbachler and Joshua X. Samuels: A small-bodied species of Brontotheriidae from the middle Eocene Nut Beds of the Clarno Formation, John Day Basin, Oregon. Journal of Paleontology 90 (6), 2016, pp. 1233-1244 doi: 10.1017 / jpa.2016.61
2. ^ ^{A b} Steven R. Manchester: Fruits and seeds of the middle Eocene Nut Beds flora, Clarno Formation, Oregon. Palaeontographica Americana 58, 1994, pp. 1-205
3. ↑ ^{a b c} C. Bruce Hanson: Stratigraphy and vertebrate faunas of the Bridgerian-Duchesnean Clarno Formation, north-central Oregon. In: Donald R. Prothero and Robert J. Emry (Eds.): The Terrestrial Eocene – Oligocene Transition in North America. Cambridge University Press, 1996, pp. 206-239
4. ↑ EA Bestland, PE Hammond, DLS Blackwell, MA Kay, GJ Retallack and J. Stimac: Geologic framework of the Clarno Unit, John Day Fossil Beds National Monument: Central Oregon. Oregon Geology 61, 1999, pp. 3-19
5. ^ EA Wheeler and SR Manchester: Woods of the Middle Eocene Nut Beds Flora, Clarno Formation, Oregon, USA. International Association of Wood Anatomists Journal Supplement 3, 2002, pp. 1-188
6. ↑ Richard M. Dill Hoff, Thomas A. Dill Hoff, Regan E. Dunn, Jeffrey A. Myers and Caroline AE Strömberg: Cenozoic paleobotany of the John Day Basin, Central Oregon. In: JE O'Connor, RJ Dorsey and IP Madin (Eds.): Volcanoes To Vineyards: Geologic Field Trips Through The Dynamic Landscape Of The Pacific Northwest. Geological Society of America Field Guide 15, 2009, pp. 135-164
7. ^ ^{A b} Matthew C. Mihlbachler and Joshua X. Samuels: Little titans of the Eocene: Cope's rule or sampling artifacts? Journal of Vertebrate Paleontology 33 (suppl.), 2013, p. 176
8. ^ Matthew C. Mihlbachler: Species taxonomy, phylogeny, and biogeography of the Brontotheriidae (Mammalia: Perissodactyla). Bulletin of the American Museum of Natural History 311, 2008, ISSN 0003-0090, pp. 1-475