Blue Lake Rhino
Coordinates: 47 ° 33 '59 " N , 119 ° 25' 36" W.
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The Blue Lake Rhino , ( English for "Rhinoceros from the Blue Lake") is an imprint of an extinct rhinoceros that was preserved along with some fossil remains in a basalt lava flow near the city of Coulee City in the central part of the US state of Washington . This impression is dated to an age of around 15 million years and is therefore to be placed in the Middle Miocene . The find is important for two reasons: on the one hand, it is to be classified in the few records of the form of the former soft tissue of an extinct animal; on the other hand, the remains of bones and teeth that have been found are one of the few fossils from volcanic rocks worldwide. The rhinoceros print and individual related bone finds were discovered in 1935.
Site and discovery
The rhinoceros print is located near the village of Coulee City on the Columbia River in Grant County , Washington state . It is embedded in the Columbia plateau basalt , which forms up to 120 m high steep slopes here on the southwest side of Jasper Canyon and thus delimits the Blue Lake as part of the former Grand Coulee river bed . The imprint itself is about 60 m above the water surface in a cave-like opening with an entrance only a few dozen centimeters wide. It was discovered in August 1935 by a group of hikers from Seattle who noticed numerous bones and took a toothed lower jaw with them, which they then handed over to George F. Beck , then a professor at the Central Washington College of Education in Ellensburg , now Central Washington University . Shortly afterwards Beck visited the cavity together with an assistant and documented numerous bony remains, about which he published a first publication in the same year. The finds were later than one Aphelops described -ähnelnden rhino. In the time that followed, several scientists visited the site, including Walter M. Chappell in 1936, but no more intensive investigations could be carried out due to the Second World War . This did not take place until 1948 and 1949, when J. Wyatt Durham visited the rhinoceros print and made an impression.
Geological situation
The rhinoceros imprint is at the base of a roughly 60 cm thick basalt made of pillow lava , which merges into a banky basalt at the top. The pillow lava is somewhat thicker in the area of the rhinoceros imprint, as is the case where other organic objects have been fossilized , such as tree stumps such as a trunk of a walnut tree up to 1.5 m long . The sack-shaped basalts are porous and sometimes even hollow inside. About 230 m south of the location of the rhinoceros imprint, the pillow basalt is only 30 cm thick, so that it can be assumed that the lava flow was somewhat dammed in the area of the inclusions. The entire basalt block is underlain by a 5 to 12 cm thick layer of fine sandy silts , which in turn was sedimented on a heavily perforated basalt.
Originally the basalt was assigned to the Yakima basalt , which is largely exposed on the Columbia and the Yakima River and is assigned to the Miocene to Lower Pliocene . The basalts of the Columbia Plateau basalt were formed by numerous volcanic eruptions that occurred in the geological past in the northwest of today's USA and which flowed out of crevices and cracks rather than originate from real volcanic mountains. Since basalt is made from basic lava with a small amount of silicon dioxide , it is rather thin and can flow at a speed of up to 100 km / h, with a temperature of 900 to 1200 ° C. However, there must have been enough time between the individual eruptions and effusions that a new plant cover with trees several meters high was able to form. The rhinoceros imprint is estimated to be 14 to 16 million years old and therefore belongs to the Middle Miocene. The entrance to the cave-like opening was only created in the Pleistocene , when vast amounts of meltwater from the thawing continental ice sheets eroded into the basalt and thus created the canyons of the Grand Coulee.
Appearance of the imprint and the reconstructed animal
The print has a generally rhino-like shape and is slightly curved. The basalt lacks the shallow depressions that are typical of lava caves , which means that the imprint cannot be classified in this category of cavities in effluent rock. According to the impression, the animal was lying on its left side, but the entire surface of the impression is inclined by about 30 °. The legs are directed slightly outwards, which is typical for living beings in rigor mortis and sometimes form deep holes in the basalt. A pouring out of these depressions showed that the imprints of three toes can be seen on both the front and rear feet, as well as that a thick foot pad was originally formed. The head is long and slightly pointed in front, whereby this protrusion is most likely to be associated with a pointed upper lip. The nose shows some damage because it was stuck between two basalt cushions, but shows the beginnings of two paired horns on the tip of the nose, while no evidence of a horn was found on the forehead. There are transverse dents on the neck that give the impression that the animal had skin folds here, as is known from most of the rhino species still alive today. The entire body of the animal is 168 cm long, the middle of the legs are 112 cm apart. The head and neck extend over 71 cm, so that the head-torso length was about 239 cm.
Fossil remains
Several fossil remains were found within the imprint, possibly more or less the complete skeleton originally existed. Some pieces remained in the cavity, especially from the left front leg, as they were too stuck in the rock and could therefore not be recovered. The bones are porous and silicified , but very hard due to the storage of iron , phosphorus and magnesium as well as other minerals from the surrounding basalt. In addition, they are very small, but can partly be put together to their original shape. An incomplete lower jaw with remains of both halves of the jaw, skull and tooth fragments, parts of the ribs and some carpal bones, including the pea bone, have survived . However, the lower jaw with the ascending joint arch and the complete row of teeth from the second premolar to the last molar is best preserved. The entire row of teeth is 18 cm long. The molars become larger from front to back. The anterior premolar has a length of 1.5, the posterior molar is 3.6 cm. The teeth clearly belong to a rhinoceros, but since they are too badly damaged, no conclusions can be drawn about the exact species or genus , except that the animal is to be placed in a closer relationship to Diceratherium . All finds are now in the Museum of the University of California (Museum number: 40307).
interpretation
The entire print shows the outline of the rhinoceros very well, but it is possibly larger than the original animal because it looks rather bloated. The front foot is well preserved, indicating that it only had three toes, meaning that the animal belongs to the ranks of the more modern rhinos in North America , as the four-toed representatives were already extinct at the end of the Oligocene . The front part of the skull is also well preserved and shows a distinctive, pointed upper lip, which is typical of animals specializing in soft vegetable foods, similar to today's black rhinoceros ( Diceros bicornis ). However, the nasal region is damaged because this part was stuck between two lumps of basalt, so the shape and size of the horns are not known. Due to the size of the imprint, an assignment to Diceratherium , Menoceras or Peraceras is usually made, each of which had paired horns on the nose.
It is assumed that the rhinoceros was already dead when the lava flow caught it and dragged it along; this is indicated on the one hand by the heavily inflated body, as the cast reconstructions made, on the other hand by the position of the splayed legs and the raised head, which is typical of rigor mortis . Pillow lava is created when the lava flow, which is over 900 ° C, enters the water and quickly cools down and becomes rigid. This contact with water and the rapid cooling must take place very quickly, otherwise the organic remains of the rhinoceros would have been burned and the shape of the print would not have been preserved. The same applies to the tree remains found, since wood burns at significantly lower temperatures than that of the basic lava.
meaning
The rhinoceros imprint from Blue Lake is one of the few indications of the soft tissue anatomy of extinct rhinos, which is otherwise only known from mummies from the permafrost or from oil shale and generally passed down from the woolly rhinoceros ( Coelodonta antiquitatis ). In addition, the imprint and bone content is one of the few examples of fossil conservation in rocks of volcanic origin ( igneous rock ), as these are otherwise predominantly only preserved in loose sediments or sedimentary rocks . The marginal evidence of rhinos from volcanic rocks also includes a charred rhinoceros skull from an ignimbrite current southwest of Avanos in central Turkey . This is assigned to today's white rhinoceros ( Ceratotherium simum ) and, with an age of 9.2 million years, represents one of the earliest records of this rhinoceros species. The imprint of Blue Lake was already made by J. Wyatt Durham and Donald E. Savage in 1948, as well how they made a model of the rhinoceros. Both reconstructions can be viewed today at the Burke Museum of Natural History and Culture in Seattle .
Individual evidence
- ^ A b c George F. Beck: Fossil-bearing basalts (more particularly the Yakima basalts of Central Washington). Northwest Science 9 (4), 1935, pp. 4-7
- ^ A b c d e f Walter M. Chappell, J. Wyatt Durham and Donald E. Savage: Mold of a rhinoceros in basalt, Lower Grand Coulee, Washington. Bulletin of the Geological Society of America 62, 1951, pp. 907-918
- ↑ James W. Bingham and Maurice J. Groulier: The Yakima Basalt and Ellensburg Formation of South-Central Washington. Geological Survey Bulletin 1224-G, 1966, pp. 1-15
- ^ Hassan D. Diery and Bates MacKee: Stratigraphy of the Yakima basalt in the type area. Northwest Science 43 (2), 1969, pp. 47-64
- ↑ Donald R. Prothero and Robert M. Schoch: Horns, tusks, and flippers. The evolution of hoofed mammals. Johns Hopkins University Press, Baltimore, 2003, ISBN 0-8018-7135-2 (p. 268)
- ^ A b c d Donald R. Prothero: The evolution of North American rhinoceroses. Cambridge University Press, 2005
- ↑ Kurt Heissig: The American genus Penetrigonias Tanner & Martin, 1976 (Mammalia: Rhinocerotidae) as a stem group elasmothere and ancestor of Menoceras Troxell, 1921. Zitteliana A 52, 2012, pp. 79-95
- ↑ Pierre-Olivier Antoine, Maeva J. Orliac, Gokhan Atici, Inan Ulusoy, Erdal Sen, H. Evren Çubukçu, Ebru Albayrak, Neşe Oyal, Erkan Aydar and Sevket Sen: A Rhinocerotid Skull Cooked-to-Death in a 9.2 Ma- Old Ignimbrite Flow of Turkey. Plos One 7 (11), 2012, pp. 1-12
- ^ Arn Slettebak: Recreating the Blue Lake Rhino Cave. Curator 24 (2), 1981, pp. 89-95