Triceratops
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![]() Triceratopsovo okostje
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izumrli (fosil)
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Triceratops je bil rastlinojedi dinozaver iz družine ceratopsov, ki je živel v pozni kredi (pozni Maastricht), pred približno 68 do 65 milijoni let. Živel je na območju, ki je danes Severna Amerika in je bil eden od zadnjih dinozavrov, ki so se pojavili pred velikim izumrtjem. Leta 1893 ga je odkril znani paleontolog Robby Lewis in ga poimenoval po treh rogovih na glavi. "Tri" pomeni število tri, "ceratops" pa rogove (ceras so rogovi, ops pa obraz, ime torej pomeni obraz s tremi rogovi).[1] [2] Z veliko rogato glavo in nekaterimi podobnostmi z današnjimi nosorogi je triceratops eden najbolj prepoznavnih dinozavrov. Čeprav si je delil življenjski prostor z velikimi plenilci, kot je bil tiranozaver, ni jasno, če sta se živali kdaj spopadli na način, ki je prikazan v filmih in slikanicah o dinozavrih.
Čeprav niso do zdaj našli še nobenega popolnega okostja, [3] je triceratops dobro preučen iz mnogih vzorcev, ki so jih po uvedbi redu leta 1887 odkrili. Namen grebena in rogov je dolgo časa navdihoval razprave. Čeprav so jih tradicionalne teorije obravnavale kot sredstvo za obrambo pred plenilci, novejše teorije trdijo, da so se večinoma uporabljali za dvorjenje samicam in za zastraševanje rivalskih samcev. Danes podobno obnašanje vidimo pri jelenih in kozah. [4]
Triceratops je najbolj znana vrsta med ceratopsi, čeprav se glede uvrstitve v red včasih paleontologi ne strinjajo povsem. Sprejeti sta dve vrsti, T. horridus in T. prorsus, še več pa jih je bilo poimenovanih.
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[uredi] Opis
Posamezen triceratops je lahko dosegel okrog 8 metrov dolžive, visok je bil 3 metre in težal okrog 6 ton.[5] Najbolj opazna lastnost je velika lobanja, ena največjih med kopenskimi živalmi. V dolžino je lahko merila več kot 2 m in je predstavljala skoraj tretino dolžine živali. [3] En rog se je nahaja na nosu, nad nosnicami, dva rogova, dolga okrog 1 m, pa nad očmi. Na koncu lobanje se je nahajal koščen greben, ki za razliko od drugih podobnih dinozavrov ni imel odprtin, ampak je bil masiven.
Triceratops je imel čokato in robustno telo s petprstimi prednjimi in štiriprstimi zadnjimi nogami. [6] Čeprav je skoraj zagotovo hodil po vseh štirih, so o položaju nog potekale dolge razprave. Na začetku so mislili, da so sprednje noge podpirale vrat, da bi lažje prenašale težo glave. [4] To se lahko vidi na slikah, ki sta jih izdelala Charles Knight in Rudolph Zallinger. Ichnological evidence in Triceratops trackways, however, and recent reconstructions of skeletons (both physical and digital), seem to show that Triceratops maintained an upright stance during normal locomotion, with the elbows slightly bowed out, in an intermediate state between fully upright and fully sprawling (as in the modern rhinoceros).[7][8] This conclusion does not preclude a sprawling gait for confrontations or feeding.
[uredi] Klasifikacija
Triceratops is the best known genus of the Ceratopsidae, a family of large North American horned dinosaurs. The exact location of Triceratops among the ceratopsians has been debated over the years. Confusion stemmed mainly from the combination of short, solid frills (similar to that of Centrosaurinae), and the long brow horns (more akin to Ceratopsinae, also known as Chasmosaurinae). In the first overview of horned dinosaurs, R. S. Lull hypothesized two lineages, one of Monoclonius and Centrosaurus leading to Triceratops, the other with Ceratops and Torosaurus, making Triceratops a centrosaurine as the group is understood today.[9] Later revisions supported this view, formally describing the first, short-frilled group as Centrosaurinae (including Triceratops), and the second, long-frilled group as Chasmosaurinae.[10][11]
In 1949, C. M. Sternberg was the first to question this and favoured instead that Triceratops was more closely related to Arrhinoceratops and Chasmosaurus based on skull and horn features, making Triceratops a ceratopsine (chasmosaurine of his usage) genus.[12] However, he was largely ignored with John Ostrom,[13] and later David Norman both placing Triceratops within Centrosaurinae.[14]
Subsequent discoveries and analyses upheld Sternberg's view on the position of Triceratops, with Lehman defining both subfamilies in 1990 and diagnosing Triceratops as ceratopsine (chasmosaurine of his usage) on the basis of several morphological features. In fact, it fit well into the ceratopsine subfamily, apart from its one feature of a shortened frill.[15] Further research by Peter Dodson, both a 1990 cladistic analysis[16] and a 1993 study using RFTRA (resistant-fit theta-rho analysis),[17] a morphometric technique which systematically measures similarities in skull shape, reinforce Triceratops' placement in the ceratopsine subfamily.
[uredi] Uporaba v filogenetiki
In phylogenetic taxonomy, the genus has been used as a reference point in the definition of Dinosauria; Dinosaurs have been designated as all descendants of the most recent common ancestor of Triceratops and Neornithes (i.e. modern birds).[18] Furthermore, the bird-hipped dinosaurs, Ornithischia, have been designated as all dinosaurs with a more recent common ancestor to Triceratops than modern birds.[19]
[uredi] Izvor
For many years the origins of Triceratops have been largely obscure. In 1922, the newly discovered Protoceratops was seen as its ancestor by Henry Fairfield Osborn,[20] but many decades passed before additional findings came to light. However, recent years have been fruitful for the discovery of several dinosaurs related to ancestors of Triceratops. Zuniceratops, the earliest known ceratopsian with brow horns, was described in the late 1990s, and Yinlong, the first known Jurassic ceratopsian, in 2005.
These new finds have been vital in illustrating the origins of horned dinosaurs in general, suggesting an Asian origin in the Jurassic, and the appearance of truly horned ceratopsians by the beginning of the late Cretaceous in North America.[6] As Triceratops is increasingly shown to be a member of the long-frilled Ceratopsinae subfamily, a likely ancestor may have resembled Chasmosaurus, which thrived some 5 million years earlier.
[uredi] Odkritje in vrste
Prvi poimenovani primerek, ki se ga danes pripisuje vrsti triceratopsa, par nadočesnih rogov pritrjenih na kos lobanjeje, ki so ga našli blizu Denverja leta 1887.[21] Ta primerek so poslali Othnielu Charlesu Marshu, ki je sprva verjel, da gre za najdbo iz pliocena in na so kosti pripadale vrsti velikega bizona, ki ga je poimenoval Bison alticornis.[22][21] Naslednje leto je iz fosilnih ostankov opisal nov rod, Ceratopse, [23] vendar pa je bil še vedno prepričan, da je bil B. alticornis pliocenski sesalec. Šele po tretjem in podrobnejšem pregledu je ugotovil, da se je motil. Primerek, ki ga je leta 1888 v Wyomingu odkril John Bell Hatcher, je bil najprej opisan kot druga vrsta ceratopsa [24], vendar ga je po premisleku Marsh poimenoval z generičnim imenom triceratops in se sprijaznil s tem, da je bil Bison alticornis druga vrsta iz tega reda. [25] (kasneje je bil tudi ta dodan k triceratopsom [9]). Čvrsta zgradba lobanje je zagotovila, da se je do danes ohranilo veliko fosilnih ostankov, kar je omogočilo, da so znanstveniki lahko preučevali razlike med posameznimi primerki in vrstami. Triceratopsove ostanke so našli še v Montani, Južni Dakoti (poleg Colorada in Wyominga) ter v Kanadskih provincah Saskatchewan in Alberta.
[uredi] Število vrst
Po prvem opisu Triceratopsa, so potem v nekaj desetletjih zbrali različne lobanje, ki so se bolj ali manj razlikovale od prvotnega Triceratopsa, ki ga je Marsh imenoval T. horridus (iz latinščine horridus; "hrapav, naguban", kar je namigovalo na hrapavo teksturo kosti, ki so pripadale temu tipu primerkov, kasneje so ugotovili, da je šlo za starejše živali). This variation is unsurprising, given that Triceratops skulls are large three-dimensional objects, coming from individuals of different ages and both sexes, and which were subjected to different amounts and directions of pressure during fossilization.[4] Discoverers would name these as separate species (listed below), and came up with several phylogenetic schemes for how they were related to each other.
In the first attempt to understand the many species, Lull found two groups, although he did not say how he distinguished them: one composed of T. horridus, T. prorsus, and T. brevicornus; the other of T. elatus and T. calicornis. Two species (T. serratus and T. flabellatus) stood apart from these groups.[9] By 1933, and his revision of the landmark 1907 Hatcher-Marsh-Lull monograph of all known ceratopsians, he retained his two groups and two unaffiliated species, with a third lineage of T. obtusus and T. hatcheri that was characterized by a very small nasal horn.[11] T. horridus-T. prorsus-T. brevicornus was now thought to be the most conservative lineage, with an increase in skull size and a decrease in nasal horn size, and T.-elatus-T. calicornis was defined by large brow horns and small nasal horn.[11] C. M. Sternberg made one modification, adding T. eurycephalus and suggesting that it linked the second and third lineages closer together than they were to the T. horridus lineage.[12] This pattern was followed until the major studies of the 1980s and 1990s.
With time, however, the idea that the differing skulls might be representative of individual variation within one (or two) species gained popularity. In 1986, Ostrom and Wellnhofer published a paper in which they proposed that there was only one species, Triceratops horridus.[26] Part of their rationale was that generally there are only one or two species of any large animal in a region (modern examples being the elephant and the giraffe in modern Africa). To their findings, Lehman added the old Lull-Sternberg lineages combined with maturity and sexual dimorphism, suggesting that the T. horridus-T. prorsus-T. brevicornus lineage was composed of females, the T.calicornis-T.elatus lineage was made up of males, and the T. obtusus-T. hatcheri lineage was of pathologic old males.[15] His reasoning was that males had taller, more erect horns and larger skulls, and females had smaller skulls with shorter, forward-facing horns.

These findings, however, were contested a few years later by Catherine Forster, who reanalysed Triceratops material more comprehensively and concluded that the remains fell into two species, T. horridus and T. prorsus, although the distinctive skull of T. (now tentatively Diceratops) hatcheri differed enough to warrant a separate genus.[27] She found that T. horridus and several other species belonged together, and T. prorsus and T. brevicornus stood alone, and since there were many more specimens in the first group, she suggested that this meant the two groups were two species. It is still possible to interpret this reasoning as describing a single species with sexual dimorphism.[4][28]
[uredi] Priznane vrste
- T. horridus (Marsh, 1889) (izvirno Ceratops) (tipska vrsta)
- T. prorsus (Marsh, 1890)
[uredi] Dvomljive vrste
Naslednje vrste so nomina dubia ("dvomljiva imena"), in so opisane po ostankih, ki so preskromni, da bi jih lahko razlikovali od drugih vrst triceratopsov.
- T. albertensis (C. M. Sternberg, 1949)
- T. alticornis (Marsh, 1887 (originally Bison))
- T. eurycephalus (Schlaikjer, 1935)
- T. galeus (Marsh, 1889)
- T. ingens (Lull, 1915)
- T. maximus (Brown, 1933)
- T. sulcatus (Marsh, 1890)
[uredi] Napačno določeni
- T. brevicornus (Hatcher, 1905) (=T. prorsus)
- T. calicornus (Marsh, 1898) (=T. horridus)
- T. elatus (Marsh, 1891) (=T. horridus)
- T. flabellatus (Marsh, 1889) (=T. horridus)
- T. hatcheri (Lull, 1907) (=Diceratops hatcheri)
- T. mortuarius (Cope, 1874) (nomen dubium; originally Polyonax; =Polyonax mortuarius)
- T. obtusus (Marsh, 1898) (=T. horridus)
- T. serratus (Marsh, 1890) (=T. horridus)
- T. sylvestris (Cope, 1872) (nomen dubium; originally Agathaumas sylvestris)
[uredi] Paleobiologija
Čeprav se triceratopse običajno upodablja kot čredne živali, ni nobenega trdnega dokaza, da so zares živeli v čredah. Za razliko od drugih podobnih vrst, katerih ostanke so našli v skupinah po več deset ali sto živali, so najdbe triceratopsov vedno samo posamične. [4] Vendar pa so ti ostanki zelo pogosti, kot primer, paleontolog Bruce Erickson iz Science Museum of Minnesota je videl 200 primerkov T. prorsusa v Hell Creek Formation v Montani. [29] Podobno je Barnum Brown trdil, da je videl več kot 500 lobanj na polju. [30] Ker so fosilni ostanki triceratopsa tako pogosti, se sklepa, da je bil triceratops ena najbolj dominantnih rastlinojedih vrst pozne krede v današnji Severni Ameriki. leta 1986 je Robert Bakker ocenil, da je predstavljal 5/6 vse velike dinozavrske favne tega obdobja. [31]
Triceratops je bil eden zadnjih ceratopsov, ki so se pojavili pred velikim izumrtjem. Sorodni vrsti tistega časa sta bili Diceratops in Torozaver, daljni sorodnik pa manjši Leptoceratops. Vendar pa so te vrste v fosilnih ostankih redkeje najdene.[4]
[uredi] Prehrana
Triceratops je bil rastlinojed in zaradi nizke glave je glavni del njegove prehrane predstavljala nizka vegetacija. Mogoče je lahko podrl tudi višje rastline. [32][6] Čeljust se je končala z globokim in ozkim kljunom, sklepajo, da je bil kljun boljši za grabljenje in vlečenje kot za grizenje. [33]
Triceratopsovi zobje so bili razporejeni v vrste, imenovane baterije. V vsaki od 36 do 40 vrst je bilo 3 do 5 zob, odvisno od velikosti živali. [6] Tako je imela ena žival med 432 in 800 zob, naenkrat pa jih je uporabljala le nekaj. Menjava zob je potekala vse življenje. [6] They functioned by shearing in a vertical to near-vertical orientation.[6] Velikost in število zob kaže na to, da so jedli velike količine vlaknastih rastlin,[6] morda palm in cycadij[34][35], morda pa praproti, ki so takrat rasle v savanah. [36]
[uredi] Funkcije grebena in rogov
O funkciji triceratopsovih rogov in ovratnika z naborki sta se razvili dve pomembnejši teoriji. Ena je, da so se uporabljali za spopade, druga pa za dvorjenje samicam. Zdaj se smatra, da so bili namenjeni predvsem za slednje. [6]
Pred tem je Lull predlagal, da so bile na naborke pritrjene čeljustne mišice, kar naj bi pomagalo pri žvečenju. [37] Mnogo avtorjev je dolga leta to podpiralo, kasnejše študije pa niso našle nobenih dokazov, da so bile na grebenske kosti pritrjene velike mišice. [38]
Dolgo časa so mislili, da je triceratops uporabljal svoje rogove in naborke na ovratniku za spopade s plenilci, kakršen je bil npr. tiranozaver. Idejo je prvi analiziral C. H. Sternberg leta 1917, 70 let kasneje pa še Robert Bakker.[39][40] Dokazano je, da so tiranozavri plenili triceratopse, saj so našli triceratopsovo medenico z luknjami, ki so jih povzročili tiranozavrovi zobje. Vidijo se tudi sledovi celjenja, kar pomeni, da je bila žival v času napada živa. [41]
V BBC-ejvem dokumentarcu iz leta 2005, The Truth About Killer Dinosaurs, so preizkusili, kako so se triceratopsi branili pred velikimi plenilci, na primer tiranozavri. Da bi ugotovili, če je je lahko napadel tako kot današnji nosorog, so model triceratopsove glave s hitrostjo 24 km/h zaleteli v model tiranozavrove kože. Nadočesna rogova sta kožo predrla, rog nad nosom in kljun pa ne in prednji del lobanje se je zlomil. Sklep je bil, da se triceratops na ta način ni branil, ampak je bolj verjetno počakal in z rogovi ranil napadalca, če se je ta preveč približal.
Poleg uporabe rogov pri spopadih s plenilci slike pogosto prikazujejo tirceratopse, ki se s spuščenimi rogovi borijo med sabo. Čeprav študije kažejo, da je bilo tako obnašanje možno, tako kot pri današnjih rogatih živalih, [42] ni nobenega dokaza, da so triceratopsi to dejansko počeli. Poleg tega, čeprav se razpoke, luknje in podobne poškodbe na lobanjah pogosto pripisujejo poškodbam z rogovi, sodobna študija ni našla nobenega dokaza, da bi udarci z rogovi lahko povzročili take poškodbe (na primer, ni sledi okužbe ali celjenja). Namesto tega študija kot razlog predlaga bolezni kosti. [43]
Velik greben je lahko pomagal tudi pri povečanju telesne površine za lažjo termoregulacijo. [44] Podobna teorija je bila postavljena tudi za plošče stegozavra,[45] čeprav samo ta razlog ne pojasni široke palete različic grebenov, ki jih najdemo pri različnih vrstah ceratopsov. [6] Ta opazka namiguje, da je primarna funkcija zares bila za razkazovanje.
Teorijo o uporabi rebena in rogov za dvorjenje in razkazovanje je prvi predlagal Davitashvili leta 1961 in je v sledečih letih pridobila široko podporo. [46][38][15] Dokaz, da je bil izgled pomemben, ali za dvorjenje ali za drugo družabno obnašanje, je lahko dejstvo, da so se rogati dinozavri jasno razlikovali v svojem okrasju, vsaka vrsta je bila jasno drugačna. Poleg tega jih tudi sodobne rogate živali uporabljajo v podobnih vedenjskih vzorcih. [47] Sodobna študija najmanjše triceratopsove lobanje, ki je potrjeno pripadala mladiču, kaže, da so se greben in rogovi razvili že zelo zgodaj, še pred spolno zrelostjo in so tako imeli pomembno vlogo v vizualni komunikaciji in prepoznavanju vrste na sploh. [48]
[uredi] Upodobitve v popularni kulturi
Zaradi značilnega videza se triceratops pogosto pojavlja v popularni kulturi, med drugim v filmih, računalniških igrah in dokumentarcih. Nastopal je na primer v filmu Jurski park in njegovih nadaljevanjih, pa tudi v dokumentarcih o dinozavrih: Walking with Dinosaurs, The Truth About Killer Dinosaurs in Prehistoric Park. Triceratops je tudi eden od junakov serije risanih filmov Dežela pred časom.
Pojavljanja v videoigrah so v glavnem zasluga filmov Jurski park. Triceratops je tudi uradni državni fosil države Južna Dakota [49] in uradni dinozaver Wyominga.[50]
[uredi] Opombe
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[uredi] Zunanje povezave
- Triceratops, Dino Directory
- Triceratops (ilustracije)
- Triceratops For Kids (za mlajše)
- Smithsonian Exhibit
- Triceratopsova lobanja