Beorn leggi

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Beorn leggi
Beorn leggi

Beorn leggi

Temporal occurrence
chalk
Locations
Systematics
Molting animals (Ecdysozoa)
Tardigrade (Tardigrada)
Eutardigrada
Beornidae
Beorn
Beorn leggi
Scientific name
Beornidae
Cooper , 1964
Scientific name
Beorn
Cooper , 1964
Scientific name
Beorn leggi
Cooper , 1964

Beorn leggi is an extinct tardigrade - a species known only from a single specimen preserved in Cretaceous amber from Canada.

In addition to a few other finds from the Cretaceous and Cambrian Periods , Beorn leggi is one of the few indications of the existence of tardigrade in geological history and, thanks to its largely modern appearance, proves that tardigrade has changed only insignificantly from a morphological point of view over at least 65 million years.

The species was first described in 1964 by Kenneth W. Cooper, the type specimen is today in the Museum of Comparative Zoology at Harvard University . The generic name Beorn was chosen by Cooper based on a character of the same name from the children's book The Hobbit by JRR Tolkien , which can appear both in the form of a person and that of a bear. The epithet leggi goes back to the student William M. Legg, who put on a large collection of amber in the summer of 1940, in which the tardigrade specimen was also found. He died in 1953 before he could finish his thesis at Princeton University . Cooper, his friend and scientific mentor, named Beorn leggi after him.

features

Beorn leggi

The only known individual is enclosed in honey-colored amber, the length, width and height of which are given as 7, 6 and 3 millimeters, respectively. The animal itself is 0.3 millimeters long and 0.08 millimeters wide; As with modern tardigrade, the cylindrical body is flattened on the ventral side (ventral).

The outer skin (cuticula) is smooth, on the back somewhat thickened, but not hardened into armor plates (sclerites), so that Beorn leggi is one of the "naked" tardigrade. At right angles to the longitudinal axis of the body (transversely), a total of four furrows run once around the whole body, which superficially divide it into five regions:

  • The first or prostomial region forms the head, on which there are no structures such as thread-like cirri or clavae , which are used in some modern types of sensory perception; eyes cannot be identified either. The area around the mouth is inconspicuous and does not appear to have any wart-like protrusions (papillae).
  • The second region is the first trunk segment, this is also where the first pair of legs is located. On the back there is a short transverse furrow that is slightly shifted backwards compared to the center line of the segment .
  • The third and fourth regions carry the second and third pair of legs. Here, too, there are shorter transverse furrows on the back that run out towards the base of the legs. However, they are shifted forward relative to the center line of the segment .
  • In the fifth region there is a transverse furrow on the abdomen , which ends slightly to the side of the midline of the back.

The length ratio of segments 2 to 5 is given as 1: 1.3: 1.3: 2.

The legs could probably be drawn in telescopically and each have four claws of unequal length and asymmetrically arranged in relation to the median plane of the legs. Other features such as the structure of the stiletto or the pharyngeal muscles cannot be recognized; also the position of the genital opening (gonopore) in relation to the anus, which could have given further clues as to the class of the species, cannot be determined.

Site and habitat

It is not known where the present amber specimen originally comes from; it was part of secondary sedimentary deposits on the shores of Cedar Lake , located not far from the Saskatchewan River outflow and southeast of the city of The Pas in the Canadian province of Manitoba . Accompanying finds suggest that the habitat of Beorn leggi was a swamp-like wetland.

Tribal classification

The affiliation of Beorn leggi to the tardigrade can be considered certain; In addition, the species can even be assigned to one of the three modern classes - the absence of head structures such as cirri and clavae and rear armor suggests a division into the Eutardigrada . Within this class, Beorn leggi is placed in a separate family Beornidae, which must, however, be viewed as a pure form taxon.

Accompanying find

A young animal was found together with Beorn leggi , but it is only very poorly preserved, so that beyond identification as tardigrade it is hardly possible to make any statements about its specific characteristics. Because two structures on or near the head that are difficult to recognize can be interpreted as cirrus and clava, it is sometimes viewed as part of the heterotardigrada ; however, this identification cannot be regarded as secure. There is probably no close connection with Beorn leggi .

literature