Douglassciurus

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Douglassciurus
Temporal occurrence
late Eocene ( Chadronian )
37.2 million years
Locations
Systematics
Rodents (Rodentia)
Squirrel relatives (Sciuromorpha)
Squirrel (Sciuridae)
Sciurini
Douglassciurus
Scientific name
Douglassciurus
Emry & Korth , 1996
Art
  • Douglassciurus jeffersoni (Douglass, 1901)

Douglassciurus is a genus of the squirrels (Sciuridae) from the late Paleogene that was extinct in geological times. It is one of the oldest of all known squirrel genera and the oldest species of tree squirrel . It is only documented by thespecies Douglassciurus jeffersoni fossil , which wasfirst described in 1901and which has been recorded in several regions of North America.

features

The skeletal features of the postcranial skeleton of Douglassciurus largely correspond to those of modern tree squirrels of the genus Sciurus , but the sciuromorphic head skeleton and the corresponding muscles are not yet available. Instead, the skull has a protrogomorphic zygomatic arch masseter structure .

The diastema between the incisor teeth and the third premolar is relatively short and corresponds at most to the tooth length of the molars P3 to M3, which is about 10% shorter than that of recent croissants. In addition, a narrow mental foramen is formed on the lower jaw, which is missing in recent species. Other differences relate to the tooth structure and enamel crown of the premolars and molars: The Entoconid the upper molars and Hypoconid the lower molars are formed very large compared to other squirrels and lower molars have a Hypolophid, the other croissants lacking in original Aplodontiidae as Prosciurus occurs. Some of the mentioned tooth features and the few remaining remains of the posterior skull correspond to those of the younger genus Protosciurus . In addition, there is evidence of cranial crests in the area of ​​the apex (temporal crests) similar to those of the genus Cedromus .

Fossil History and Taxonomy

Fossils of the species known today as Douglassciurus jeffersoni were described for the first time in 1901 by Earl Douglass as Sciurus jeffersoni and thus assigned to the squirrels living today . In 1908 the species was assigned to the genus Prosciurus as Prosciurus jeffersoni by Henry Fairfield Osborn and William Diller Matthew , but this genus was later assigned to the Aplodontiidae . 1962 Horace Elmer Wood placed the species in the genus Cedromus , which was rejected by Craig C. Black due to the dentition. He argued that the species should be included in the genus Protosciurus , which was also done by John E. Storer in 1978 when describing new fossils from Saskatchewan. In 1982, Robert J. Emry and William W. Korth described a well-preserved skeleton of the species and, based on the features of the postcranial skeleton, could for the first time safely argue that it was an early tree squirrel. They also classified the species in the genus Protosciurus and in 1996 they described the genus Douglassia with Douglassia jeffersoni as the only species. However, since this genus name was already assigned to a mollusc species , they renamed the genus in 2000 to the name Douglassciurus, which is valid today .

Were named Douglassia and Douglassciurus after the first person to describe the way Earl Douglass.

supporting documents

  1. ↑ a b c d e R.J. Emry, WW Korth: The Chadronian "Sciurus" jeffersoni Douglass, 1901: a new generic name, new material, and its bearing on the early evolution of Sciuridae (Rodentia). Journal of Vertebrate Paleontology 16 (4), 1996; Pp. 775-780. ( JSTOR )
  2. ^ Earl Douglass : Fossil Mammalia of the White River beds of Montana. Transactions of the American Philosophical Society 20, 1901; Pp. 237–279 (first description on p. 252). ( JSTOR )
  3. ↑ a b R.J. Emry, WW Korth: Douglassciurus, new name for Douglassia Emry and Korth, 1996, not Douglassia Bartsch, 1934. Journal of Vertebrate Paleontology 21 (2), 2000; P. 400. doi : 10.1671 / 0272-4634 (2001) 021 [0400: DNNFDE] 2.0.CO; 2

literature

  • Earl Douglass : Fossil Mammalia of the White River beds of Montana. Transactions of the American Philosophical Society 20, 1901; Pp. 237–279 (first description on p. 252). ( JSTOR )
  • Robert J. Emry, William W. Korth: The Chadronian "Sciurus" jeffersoni Douglass, 1901: a new generic name, new material, and its bearing on the early evolution of Sciuridae (Rodentia). Journal of Vertebrate Paleontology 16 (4), 1996; Pp. 775-780.