Mammoth pacificus

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Mammoth pacificus
Skull of mammoth pacificus, holotype specimen

Skull of mammoth pacificus , holotype specimen

Temporal occurrence
Middle to Upper Pleistocene
190,000 to 16,000 years
Locations
Systematics
Tethytheria
Russell animals (Proboscidea)
Elephantimorpha
Mammutids (Mammutidae)
mammoth
Mammoth pacificus
Scientific name
Mammoth pacificus
Dooley Jr. , Scott , Green , Springer , Dooley & Smith , 2019

Mammut pacificus is a species of proboscis from the extinct genus Mammut within the family group of mammoths (Mammutidae; in German sometimes also called "real mastodonts"). It waswidespreadin what is now western North America in the Middle and Upper Pleistocene around 190,000 to 16,000 years ago. The majority of the known fossil finds are from California , a few also come from Idaho . Outwardly, the animals resembled the representatives of the closely related American mastodon . Differences can be seen in the skeleton and tooth structure. Compared to the American mastodon, Mammut pacificus had significantly narrower molars. In addition, no tusks were formedin the lower jaw. Originally the finds from western North America were counted as the American mastodon. The noticeable deviations led to the establishment of a separate species for the western populations in 2019.

features

Lower jaw of mammoth pacificus (holotype)

Mammut pacificus was largely similar to the American mastodon ( Mammut americanum ) in its external appearance and general skeleton structure . The latter was strongly built with an elongated, deep body, the highest point of which was reached at the shoulder girdle and the back line sloped only moderately backwards. The limbs were short and wide and the pelvis was relatively expansive. The skull of the holotype specimen of Mammut pacificus , a fully-grown male, was 100 cm long and 65 cm wide at the area of ​​the eyes. Compared to animals of the same age of the American mastodon, it was characterized as being significantly shorter. The lower jaw was 81.5 cm in length, the joint ends were 54.2 cm apart. In general, the lower jaw was elongated, the symphysis at the front end pointed clearly downward with the upper side, which is a typical characteristic of the genus Mammut . At the posterior molar, the horizontal bone reached a depth of 16.5 cm. Alveoli for the lower tusks were not formed. This is a striking difference to the American mastodon, in which lower jaw tusks were still sometimes found in males.

Skull of mammoth pacificus with a view of the posterior molar
Molars of Mammut pacificus (A – D; I – L; Q and R; U; W; Y; AA; CC; EE; GG; II; KK) and Mammut americanum (E – H; M – P; S and T ; V; X; Z; BB; DD; FF; HH; JJ; LL)

The dentition consisted of the upper tusks and the rear teeth, which in turn consisted of three premolars and three molars per half of the jaw. As in almost all proboscis animals, the upper tusks corresponded to the internal incisors (I1) and were accordingly hypertrophied . They stood at the base of the alveoli at an angle of 5 ° to the upper row of teeth and pointed 20 ° outwards in relation to the midline of the skull. Its course was clearly curved outwards and upwards, so that the tip pointed upwards. On the holotype individual, the right tusk measured 200 cm across the curvature with a maximum diameter at the alveolar exit point of 17.6 cm. The molars changed horizontally , typically for phylloxially more developed proboscis , so that usually only one tooth per half of the jaw was available for chewing. According to this, the teeth could be exchanged five times in the course of the individual development . The tooth pattern was like the American mastodont zygodont with transverse sharp ridges that were divided in the center line by a longitudinal groove. The first two premolars (dP 2 and 3 as well as dp2 and 3) each had two ridges ( bilophodont ), the last premolar (dP4 and dp4) and the first two molars (M1 and 2 as well as m1 and 2) had three ( trilophodont ) . The last molar had four to five ridges in the upper jaw (M3) and always five ridges in the lower jaw (m3) ( tetra- or pentalophodont ). A cingulum, i.e. a low bulge of enamel on the edge of the tooth, was generally weak. A striking difference to the teeth of the American mastodon concerns the general tooth proportions. The last lower molar had an average length-to-width ratio of 2.24, the corresponding upper molar of 1.98. In the latter, the number of ridges in the tetra (1.91) and pentalophodont (2.02) teeth was only slightly influenced . In contrast, the American mastodon had wider teeth, as the ratio of length to width in the third molar in the lower jaw reached an average of 1.91 and in the upper jaw 1.77. The length of the teeth was relatively the same in both species, especially in the lower jaw, where the last molar was about 18.3 cm long. However, the width differed noticeably at 8.2 ( Mammut pacificus ) and 9.7 cm ( Mammut americanum ). In the upper jaw, however, the values ​​are different ( Mammut pacificus length 16.7 cm, width 8.5 cm; Mammut americanum length 17.5 cm, width 9.9 cm), which can be attributed to some very large teeth in the American mastodon. For the two front molars, the difference in length-to-width ratio between the two species was less noticeable.

In the postcranial skeleton there are further deviations between Mammut pacificus and the American mastodon. Strikingly, the sacrum was composed of six fused vertebral bodies, while the American mastodon usually only had five, but the range of variation was relatively high here. The thigh bone appeared shorter and wider than the American mastodon. Two complete femora of Mammut pacificus had lengths of 82 and 96 cm with a width of the lower epiphysis of 22 and 26 cm, respectively. Comparable values ​​were 90 and 95 cm with joint widths of 22 and 24 cm for the American mastodon. The average length of the thigh bone in Mammut pacificus was 92 cm compared to 104 cm in the American mastodon.

Fossil finds

Distribution map of the sites of Mammut pacificus (red circles) and Mammut americanum (blue circles)
Partial skeleton of Mammut pacificus with tusk, molar, femur and various vertebrae

The occurrence of Mammut pacificus was limited to North America , where the species achieved a wide distribution, especially in the western areas. The majority of the finds were recovered in the US state of California , but a few more have also come down to us from southeastern Idaho . Like its close relative, the American mastodon ( Mammut americanum ), the mammoth species was tied to tree-rich landscapes with a predominantly leaf- based diet . Accordingly, barren regions such as the Mojave Desert or the Sonora Desert in the southeast and the high elevations of the Sierra Nevada in the east have acted as barriers to expansion. In some regions, therefore, mammoths have probably been replaced by other trunk forms such as the gomphotheria with Cuvieronius or elephants such as Mammuthus . Mammutid fossil remains are generally rare in Arizona , New Mexico , Nevada and Wyoming , among others . Something similar can be said for the vegetation-poor areas in the south of neighboring Mexico . The distribution limits further north of California are unclear, as only sparse fossil material of the genus Mammut is available from states such as Oregon and Washington , which is also not taxonomically meaningful.

Outstanding fossil remains of Mammut pacificus can be found in the Diamond Valley Lake Local Fauna in Diamond Valley and in Domenigoni Valley in Riverside County in southwest California , among others . Recovered during the construction of Diamond Valley Lake beginning in the mid-1990s, more than 100,000 objects have been found to date, which are distributed over 100 taxa and come from over 2,600 different sites. The collection is one of the most extensive open-land find complexes in southwestern North America. In addition to the exceptionally good fossil conservation, the frequent occurrence of large herbivores and the low proportion of larger predators are particularly noteworthy, which gives the fauna community an undisturbed character. Among the mammals , Mammut pacificus occurs with almost 700 fossil remains of a good 100 individuals, which makes up about a fifth of all identifiable mammal remains. This makes Mammut pacificus the third most common mammal after bison and horses. In addition to individual skull and dentition remains, partial skeletons that belong together could also be documented. The paleontological findings speak for a mosaic landscape of forests and open areas in the immediate vicinity of open waters. Radiocarbon dates classify the Diamond Valley Lake Local Fauna in the Upper Pleistocene (locally stratigraphically rancholabreum ), the absolute ages range from more than 40,000 years to around 15,900 years ago. Furthermore, all mammoth remains from the asphalt pits of Rancho La Brea in the urban area of Los Angeles will be placed in Mammut pacificus . The investigations began here in the second half of the 19th century. Today, the collection of Rancho La Brea, with more than 3 million individual finds of over 650 taxa, is one of the largest find complexes from the Upper Pleistocene in the world and is therefore of extraordinary importance. In contrast to the equally old Diamond Valley Lake Local fauna , however, large predators dominate here compared to the herbivores, which can be attributed to the special find conditions in the asphalt-containing deposits, which at that time acted as natural traps. As a result, the proportion of remains of Mammut pacificus is rather small and consists of fewer than two dozen individuals.

In addition to these two outstanding sites, there are also individual fossil remains from McKittrick in Kern County , from Lakes at Thousand Oaks in Ventura County or from the Bengard Ranch in San Benito County , from where different parts of the lower jaw have been reported. Other locations, such as in Lassen County or Contra Costa County , in turn hid remains of the upper jaw. Some partial skeletons, on the other hand, have been documented from the area around San Diego , for example from the Robertson Ranch or the Wanis View Estate. So far, only isolated teeth from Bingham County have been reported in the state of Idaho . The oldest known finds, however, are so far documented from Murieta in Riverside County and consist of individual jaw fragments. They belong to the late Middle Pleistocene (locally stratigraphically Irvingtonian ), the absolute age is possibly 190,000 to 135,000 years.

Paleobiology

Skeletal reconstruction of mammoth pacificus based on finds from the Simi Valley, California

There are significant differences in height within Mammut pacificus . The finds from Rancho La Brea are on average smaller than most representatives of the American mastodon of eastern North America. The animals from the asphalt pits were reconstructed with a height of 1.82 to 2.44 m, while the American mastodon had a shoulder height of 2.5 to 3.0 m. It was therefore often assumed that the members of the genus Mammut were smaller in western North America than in eastern North America. On the other hand, adult individuals from the Diamond Valley Lake Local Fauna are noticeably larger than those from Rancho la Brea and are in no way inferior to members of the American mastodon living further east. An extremely large individual, colloquially called "Max", brought it to around 3.05 m shoulder height. It is the largest known representative of the genus mammoth in western North America. Another animal, the skeleton of which is around 60% complete, measured around 3 m in the shoulder region.

As with the American mastodon, Mammut pacificus has a certain sexual dimorphism with regard to the tusks. Male animals often have large, upwardly curved tusks, in female animals these are smaller and either straight or also curved upward, but usually always pointing forward. At the point of exit of the tusks from the alveoli , these measure in female individuals of the American mastodon usually less than 36 cm in circumference, in males often over 39 cm. The same is assumed for Mammut pacificus , here female animals have a maximum diameter of the tusks of 7.1 to 7.8 cm, in males they are more than twice as thick. In principle, however, it cannot be ruled out that individuals with smaller tusks also represent young animals. As a result of the larger tusks of male animals, the alveoli are set higher in these, so that there is a certain height difference between the lower edge of the tusk compartment and the row of upper jaw teeth. In female animals, the tusk alveoli are often on the same level as the upper row of molars.

As a rule, a diet of mixed vegetable food with a stronger tendency towards leafy food is assumed for the American mastodon, which is supported by fossil stomach contents and manure residues as well as isotope analyzes and traces of abrasion on the teeth. Mammut pacificus likely followed a similar strategy. Investigations of fossils from the asphalt pits at Rancho La Brea revealed a diet that varied only slightly over time, with nitrogen-fixing taxa being preferred. There are similarities in the isotope values ​​to today's reindeer , which eat large amounts of lichens , especially in barren seasons . The authors of the study conclude that Mammut pacificus may have been alien to Rancho La Brea, which could also explain the low fossil record there.

Systematics

Mammoth pacificus is a kind of the extinct species mammoth within the order of Rüsseltiere (Proboscidea). The genus Mammut is part of the Mammutidae family , which includes relatively original representatives of the proboscis species. Their trilophodontic second molar refers the Mammutidae to the superordinate group of the elephantiformes , which distinguish themselves from the phylogenetically even older proboscis with only two transverse ridges on the first two molars ( bilophodont ). The zygodontic tooth structure is characteristic of the Mammutidae . Paired cusps form rows oriented transversely to the longitudinal axis of the teeth. In most cases, a central furrow divides each groin into two half-ridges; along this central groove, smaller side humps are often formed in each half-ridges. The space between the main and secondary humps is filled with a sharp melt bar, so that a continuous ridge is created. The Mammutidae differ from the Gomphotheriidae , an early line of the Elephantiformes, which appeared almost at the same time. In these, the bumps are either free or the space between the main bumps is filled by smaller side bumps. The resulting occlusal surface pattern is called bunodont . According to molecular genetic studies, the mammoths separated from the gomphotheria and thus from the line of development leading to today's elephants (Elephantidae) in the Upper Oligocene around 24 to 28 million years ago.

In contrast to the diverse gomphotheria, the mammoths are rather poor in shape. At present, there are only around half a dozen different genera. The oldest undoubted representative is Losodokodon from the Upper Oligocene of Africa, the best known mammoth , whose type is the American mastodon ( Mammut americanum ). The exact relationship between Mammut americanum and Mammut pacificus has not yet been clarified. In addition to the different characteristics of the lower tusks, there is a striking difference, above all, in the narrower design of the molars in the latter compared to the former. In addition to the two forms, other mammoth species from North America have been described. These include mammoth raki , of which only a lower jaw fragment from the Palomas Formation in the Sierra County of New Mexico is available. It was scientifically introduced by Childs Frick in 1933 . Another form is Mammut cosoensis . This was created by John R. Schultz in 1938, based on a partial skull and other fragments from the Coso formation in Inyo County in California . A date in the Pliocene is postulated for both representatives . They are characterized by narrow molars. While the lower jaw of Mammut raki differs from Mammut pacificus , the characteristic of Mammut cosoensis is not known. In contrast, based mammoth nevadanus turn on a skull fragment from the Thousand Creek beds of Humboldt County in Nevada and was in 1936 by Chester floor was named. The narrow molars are also striking; the age of the find is given as the Upper Miocene . Assuming a closer, possibly monophyletic connection of the narrow-toothed mammoth species, these could represent an independent line within the genus and thus set themselves apart from the broad-toothed forms such as Mammut americanum .

The scientific first description of mammoth pacificus was in 2019 by a research team led by Alton C. Dooley Jr. published. The publication was preceded by an analysis of the entire population of mammoth finds from western North America. The finds were originally attributed to the American mastodon. As early as the 1990s, however, individual scientists noticed differences to the eastern populations of the American mastodon in terms of body size, which could later be supplemented by tooth morphometric results. The differences that were subsequently determined, which were underpinned by a large collection with remains of 35 individuals of the American mastodon from the Ziegler Reservoir near Snowmass in Colorado , then led to the creation of the new species Mammut pacificus . The holotype is a partial skeleton from the Diamond Valley Lake Local Fauna (specimen number WSC 18743) of a very large individual (nicknamed "Max"), whose exact position was found on the west dam in Diamond Valley near Hemet in Riverside County (locality number 95Q10-16.1 ). The specific epithet pacificus refers to the proximity to the Pacific , since so far all sites of the species are less than 1000 km away from the west coast of North America.

literature

  • Alton C. Dooley Jr, Eric Scott, Jeremy Green, Kathleen B. Springer, Brett S. Dooley, and Gregory James Smith: Mammut pacificus sp. nov., a newly recognized species of mastodon from the Pleistocene of western North America. PeerJ 7, 2019, p. E6614, doi: 10.7717 / peerj.6614

Individual evidence

  1. ↑ Jennifer A. Hodgson, Warren D. Allmon, Peter L. Neste, James M. Sherpa and John J. Chiment: Comparative osteology of late Pleistocene mammoth and mastodon remains from the Watkins Glen Site, Chemung County, New York. In: Warren D. Allmon and Peter L. Nester (Eds.): Mastodon Paleobiology, Taphonomy, and Paleoenvironment in the Late Pleistocene of New York State: Studies on the Hyde Park, Chemung, and North Java Sites. Ithaca: Paleontographica Americana 61, 2008, 301-367
  2. ↑ a b c d e f g h i j Alton C. Dooley Jr, Eric Scott, Jeremy Green, Kathleen B. Springer, Brett S. Dooley and Gregory James Smith: Mammut pacificus sp. nov., a newly recognized species of mastodon from the Pleistocene of western North America. PeerJ 7, 2019, p. E6614, doi: 10.7717 / peerj.6614
  3. ↑ a b Kathleen Springer, Eric Scott, J. Christopher Sagebiel and Lyndon K. Murray: The Diamond Valley Lake Local Fauna: Late Pleistocene vertebrates from inland Southern California. Museum of Northern Arizona Bulletin 65, 2009, pp. 217-236
  4. ↑ Kathleen Springer, Eric Scott, J. Christopher Sagebiel and Lyndon K. Murray: Late Pleistocene large mammal faunal dynamics from inland southern California: The Diamond Valley Lake local fauna. Quaternary International 217, 2010, pp. 256-265
  5. ^ Chester Stock: A Census of the Pleistocene Mammals of Rancho La Brea, Based on the Collections of the Los Angeles Museum. Journal of Mammalogy 10 (4), 1929, pp. 281-289
  6. ^ Leslie F. Marcus: A census of the abundant large Pleistocene mammals from Rancho La Brea. Contributions in Science 38, 1960, pp. 1-11
  7. ^ Daniel C. Fisher: Paleobiology and extinction of proboscideans in the Great Lakes Region of North America. In: G. Haynes (Ed.): The American Megafaunal Extinctions at the End of the Pleistocene. Springer Science + Business Media, 2009, pp. 55-75
  8. ↑ Kathlyn M. Smith and Daniel C. Fisher: Sexual dimorphism of structures showing indeterminate growth: tusks of American mastodons (Mammut americanum). Paleobiology 37 (2), 2011, pp. 175-194
  9. ↑ Katrina E. Gobetz and Steven R. Bozarth: Implications for Late Pleistocene Mastodon Diet from Opal Phytoliths in Tooth Calculus. Quaternary Research 55 (2), 2001, pp. 115-122
  10. ↑ Lee A. Newsom and Matthew C. Mihlbachler: Mastodons (Mammut americanum) Diet Foraging Patterns Based on Analysis of Dung Deposits. In: S. David Webb (Ed.): First Floridians and Last Mastodons: The Page-Ladson Site in the Aucilla River. Springer, 2006, pp. 263-331
  11. ↑ Hilary H. Birks, Bas van Geel, Daniel C. Fisher, Eric C. Grimm, Wim J. Kuijper, Jan van Arkel and Guido BA van Reenen: Evidence for the diet and habitat of two late Pleistocene mastodons from the Midwest, USA . Quaternary Research, 2018, pp. 1–21, doi: 10.1017 / qua.2018.100
  12. ↑ Joan Brenner Coltrain, John M. Harris, Thure E. Cerling, James R. Ehleringer, Maria Denise Dearing, Joy Ward and Julie Allen: Rancho La Brea stable isotope biogeochemistry and its implications for the Palaeoecology of late Pleistocene, coastal southern California . Palaeogeography, Palaeoclimatology, Palaeoecology 205, 2004, pp. 199-219
  13. ↑ Heinz Tobien: The structure of mastodont molars (Proboscidea, mammalian), Part 2: The zygodont and zygobunodont patterns. Mainz Geoscientific Communications 4, 1975, pp. 195–233
  14. ↑ Ursula B. Göhlich: Order Proboscidea. In: Gertrud E. Rössner and Kurt Heissig: The Miocene land mammals of Europe. Munich 1999, pp. 157-168
  15. ↑ Nadin Rohland, Anna-Sapfo Malaspinas, Joshua L. Pollack, Montgomery Slatkin, Paul Matheus and Michael Hofreiter: Proboscidean Mitogenomics: Chronology and Mode of Elephant Evolution Using Mastodon as Outgroup. PLoS Biology 5 (1), 2007, p. E207
  16. ^ D. Tab Rasmussen and Mercedes Gutiérrez: A Mammalian fauna from the Late Oligocene of Northwestern Kenya. Palaeontographica Department A 288 (1-3), 2009, pp. 1-52
  17. ↑ Childs Frick: New remains of trilophodont-tetrabelodont mastodons. American Museum of Natural History Bulletin 59, 1933, pp. 505-652 (p. 630)
  18. ^ Spencer G. Lucas and Gary S. Morgan: The oldest Mammut (Mammalia: Proboscidea) from New Mexico. New Mexico Geology 21 (1), 1999, pp. 10-12
  19. ↑ Robin B. Trayler and Robert G. Dundas: Rancho La Brea Mastodon, are they smaller than Mammut americanum from elsewhere in the United States? Geological Society of America Abstracts with Programs 41 (7), 2009, p. 454
  20. ^ Daniel C. Fisher, Michael D. Cherney, Cody Newton, Adam N. Rountrey, Zachary T. Calamari, Richard K. Stucky, Carol Lucking and Lesley Petrie: Taxonomic overview and tusk growth analyzes of Ziegler Reservoir proboscideans. Quaternary Research 82, 2014, pp. 518-532

Web links

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