doi:10.5474/geologija.1995.001Školjke so na področju južne Slovenije, v pretežno mirnem okolju zaprtega šelfa sestavljale podmorske trate ali biostrome. Njihove lupine le malokje najdemo v življenjskem položaju. Horizont s školjkami (»litiotidni horizont«) v južni Sloveniji uvrščamo v pliensbachij (domerij). Debel je do 75 metrov in se skoraj ne izklinja. V njem so posamezne lumakele školjk debele od nekaj centimetrov do 10 metrov in so vezane skoraj le na plasti temnega, mikritnega, ponekod lapornatega apnenca in bituminoznega dolomita. Biodiverziteta v njih je zelo nizka. Vmesne plasti brez školjk najpogosteje sestavljata oolitni in biosparitni apnenec. V našem prispevku so opisana posamezna nahajališča iz različnih predelov karbonatne platforme. Podane so paleogeografske in paleoekološke razmere, ki so pogojevale obstoj značilne školjčne favne.
In this contribution the ontogenetic development of dentition in the cave bear {Ursus spelaeus Rosenmüller & Heinroth) is described up to the age of about four years, when the animals became adult and the formation of their teeth was complet ed. The process of tooth growth and the replacement of deciduous teeth by perma nent dentition took place in a similar way as with the present-day brown bear {Ursus arctos Linné). The teeth eruption sequence is the same in both species.The specimens of cave bear jawbones that served for this study were collected from the well-known Palaeolithic site Divje babe I (W Slovenia). Individual age estimations of these jawbones were made on the supposition that a certain ontoge netic stage in the development of cave bear dentition corresponds to an approxi mately equal age of an individual as with the brown bear. The growth of the jaw, however, was essentially faster in cubs of the cave bear We also presume that the secondary sex dimorphism in cave bears with males having larger jawbones than females was already expressed in the first year of life.With regard to some indices, especially after noting the obvious discordance between the expected and actually observed mortality profile, we should also con sider another possibility; that ontogenetic development in the cave bear was signifi cantly slower than in present-day bears. However, this alternative does not seem very probable, because a proper ontogenetic development has its functional impor tance. A long time iag in the eruption of permanent molars would mean a certain disadvantage to the species. Kratka vsebinaV prispevku je opisan ontogenetski razvoj zobovja jamskega medveda {Ursus spelaeus Rosenmüller & Heinroth) vse do starosti približno štirih let, ko so živali odrastle, njihovi zobje pa so bili dokončno formirani. Proces rasti zob in zamenjave mlečnega zobovja s stalnim je pri jamskem medvedu potekal na podoben način kot
Izvleček UDK 902.035:569.74(497.4) Irena Debeljak: Struktura fosilne populacije in umrljivost jam skega medveda iz Mokriške jame (severna Slovenija): Struktura fosilne populacije jamskega medveda iz Mokriške jame je bila proučena z namenom, da bi dobili nove podatke o vedenju in umrljivosti te izumrle vrste. Starost ob smrti je bila ocenjena za 128 različni� osebkov, in sicer na podlagi analize cementni� prirastnic, formiranosti korenine in obrabe krone levi� M 1 zob. Po frekvenčni distribuciji primerkov v enolet-ni� intervali� la�ko ocenimo trend umrljivosti v različni� življenjski� obdobji� in ji� interpretiramo glede na podatke o današnji� medvedi�. V prvotni mrtvi združbi so po vsej verjetnosti prevladovali mladiči. Izjemno kr�ki molarji manj kot 6 mesecev stari� živali se niso fosilno o�ranili. Enoletniki so najbolj številčno zastopana starostna skupina v fosilni populaciji iz Mokriške jame. Umrljivost je drastično upadla, potem ko so jamski medvedi preživeli svojo prvo �ibernacijo v drugi zimi. Najnižja stopnja umrljivosti je bila ugotovljena za starostno obdobje 9-15 let, ko so bili jamski medvedi očitno na vr�uncu moči. Z analizo cementa ugotovljena najstarejša starost znaša okoli 30 let, kar kaže, da je bila najdaljša življenjska doba podobna kot pri današnji� medvedi�. Analiza zobni� tkiv je pokazala, da je bila umrljivost v jami sezonsko omejena-večina živali je poginila pozimi in zgodaj spomladi. Spolna struktura je bila raziskana na vzorcu 750 podočnikov. Izrazito večji delež samcev v skupini starejši� mladičev in napol odras-li� živali bi la�ko razložili z dejstvom, da je tudi pri današnji� medvedi� obdobje osamosvajanja bolj kritično za samce. Pri mlajši� odrasli� in zreli� odrasli� živali� je bila umrljivost verjetno večja pri samica�. Spolna struktura odrasli� medvedov, še posebej starejši� živali, kaže, da so Mokriško jamo kot zimski brlog večinoma zasedali samotarski samci.
Lithiotid bivalves are a characteristic faunal element of the shallow marine fades of Lower Jurassic beds in southern Slovenia. The horizon containing Middle Liassic bivalves, which is up to 75 m thick, is called the "lithiotid horizon" and is attributed to the Pliensbachian or Domerian.In Slovenia the name lithiotid bivalves represents three morphologically similar genera or species of sessile monomyarian dysodont bivalves: Lithiotis problematica, Cochlearites loppianus and Lithiopema scutata, which are systematically examined in this paper The term lithiotid bivalves does not have any taxonomic significance, since they are now classified in different families. The order is Pterioida.Lithiotid bivalves lived in an upright position on soft lagoonal bottoms in a tight aggregate of individuals crowded together which mutually supported one another and simultaneously competed for living space and light. The sedimentation of calcareous mud was fairly rapid, thus throughout their lives they grew constantly in a subvertical direction so that the small soft body space at the ventral end remained above the level of the surrounding substratum. Lithiotid bivalves had peculiar, variable shells adapted to the specific environment. They are very large, flat and distinctly dorso-ventrally elongated. Their inner surface is tripartite; in the middle is the central area, and at the sides there are feather-like areas. The mechanism of opening and closing their valves has not yet been fully explained. Kratka vsebinaLitiotidne školjke so značilen favnistični element plitvomorskega razvoja spodnjejurskih plasti južne Slovenije. Do 75 metrov debeli horizont s srednjeliasnimi doi:10.5474/geologija.1997.001 školjkami imenujemo "litiotidni horizont" in ga uvrščamo v pliensbachij oz. domeri] • Pod imenom litiotidne školjke v Sloveniji združujemo tri morfološko podobne rodove oziroma vrste sesilnih, monomiarnih, disodontnih školjk: Lithiotis problematica, Cochlearites loppianus in Lithiopema scutata, ki so sistematično obdelane v tem prispevku. Izraz litiotidne školjke nima taksonomskega pomena, saj jih danes uvrščamo v različne družine. Spadajo v red Pterioida.Litiotidne školjke so v pokončnem položaju živele na mehkem lagunskem dnu, v tesni združbi skupaj nagnetenih osebkov, ki so se med seboj podpirali in hkrati tekmovali za življenjski prostor Sedimentacija karbonatnega blata je bila precej hitra, zato so litiotidne školjke vse življenje enakomerno rastle v navpični smeri, tako da je njihov bivalni del na ventralnem koncu ostajal nad nivojem obdajajočega substrata. Litiotidne školjke so imele nenavadne, variabilne, specifičnemu okolju prilagojene lupine. So zelo velike, sploščene in izrazito razpotegnjene v višino. Njihova notranja površina je tridelna; v sredini je glavno oz. osrednje polje, ob straneh pa peresasti polji. Mehanizem odpiranja in zapiranja njihovih lupin še danes ni docela pojasnjen.
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