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Embryologi och tidig ontogeni hos mesozoiska fisködlor (Ichthyopterygia)

Perneby Molin, Susanna LU (2016) In Examensarbeten i geologi vid Lunds universitet GEOL01 20161
Department of Geology
Abstract
Ichthyosaurs (‘fish lizards’) are a group of marine reptiles that lived during the Mesozoic Era. They are all included in the superorder Ichthyopterygia, which consists of at least 36 genera and 80 species. The earliest ichthyosaurs occur in sediments deposited during the Olenekian in the Early Triassic (about 250 million years ago), and the last forms became extinct during the Cenoman in the Late Cretaceous (about 90 million years ago). Ichthyosaurs are characterized by large eyeballs (up to 25 cm in diameter) and a distinct, elongated snout. Some forms could reach well above 20 meters in length; however, the average length of most ichthyosaurs was around three to four meters. The earliest ichthyosaurs were lizard-like in appearance but... (More)
Ichthyosaurs (‘fish lizards’) are a group of marine reptiles that lived during the Mesozoic Era. They are all included in the superorder Ichthyopterygia, which consists of at least 36 genera and 80 species. The earliest ichthyosaurs occur in sediments deposited during the Olenekian in the Early Triassic (about 250 million years ago), and the last forms became extinct during the Cenoman in the Late Cretaceous (about 90 million years ago). Ichthyosaurs are characterized by large eyeballs (up to 25 cm in diameter) and a distinct, elongated snout. Some forms could reach well above 20 meters in length; however, the average length of most ichthyosaurs was around three to four meters. The earliest ichthyosaurs were lizard-like in appearance but they gradually developed a more fish-shaped body form indicating adjustments to a pelagic life. Ichthyosaurs had two pairs of fins formed by fingerlike bones; these indicate a terrestrial origin. Ichthyosaurs also had lungs instead of gills and thus were forced to swim to the surface to breathe air. Ichthyosaurs gave birth to live young, and there are a number of fossil finds of ichthyosaurs with associated embryos or juvenile individuals. This work describes a putative fossil embryo based on research done on the early ontogenetic development of ichthyosaurs. The potential embryo was found inside the body cavity of an adult individual belonging to the species Stenopterygius quadriscissus from the Early Jurassic of Holzmaden, south-western Germany. The embryo consists of millimeter-sized skeletal remains. The skeletal elements have been examined and photographed and most vertebral centra, a scapula, a clavicle and the teeth compare favorably in both size and appearance with other embryonic Stenopterygius, to suggest that skeletal remains belong to an embryo in an early stage of development. Two bones; i.e., a vertebral centrum and a putative tooth, differ in appearance from the rest of the assemblage, and hence it cannot be excluded that these elements represent stomach contents of the adult specimen. Notably though, all skeletal remains lack any trace of acid etching originating from digestive juices – an indication that the fossil elements indeed represent remains of an embryo rather than stomach contents. Nonetheless, there is a possibility that the ichthyosaur ate just before it died, which potentially could explain the absence of apparent acid etching. (Less)
Abstract (Swedish)
Ichthyosaurierna (fisködlorna) är en grupp marina reptiler som levde under mesozoikum. De är alla inkluderade i överordningen Ichthyopterygia som består av minst 36 släkten och 80 arter. De tidigaste formerna förekommer i sediment avsatta under etagen olenek i äldre trias (dvs. för ca 250 miljoner år sedan), och de sista fisködlorna dog ut under cenoman i slutet av krita, (dvs. för ca 90 miljoner år sedan). Fisködlor kännetecknas bland annat av stora ögon (upp till 25 cm i diameter) och ett nästan spjutspetsformat huvud. Vissa arter kunde bli över 20 meter långa, men medellängden hos de flesta fisködlor låg omkring tre till fyra meter. De tidigaste fisködlorna var ödlelika till utseendet, men efter hand utvecklade de en alltmer fisklik... (More)
Ichthyosaurierna (fisködlorna) är en grupp marina reptiler som levde under mesozoikum. De är alla inkluderade i överordningen Ichthyopterygia som består av minst 36 släkten och 80 arter. De tidigaste formerna förekommer i sediment avsatta under etagen olenek i äldre trias (dvs. för ca 250 miljoner år sedan), och de sista fisködlorna dog ut under cenoman i slutet av krita, (dvs. för ca 90 miljoner år sedan). Fisködlor kännetecknas bland annat av stora ögon (upp till 25 cm i diameter) och ett nästan spjutspetsformat huvud. Vissa arter kunde bli över 20 meter långa, men medellängden hos de flesta fisködlor låg omkring tre till fyra meter. De tidigaste fisködlorna var ödlelika till utseendet, men efter hand utvecklade de en alltmer fisklik kropp, vilket tyder på en anpassning mot en mer marin livsstil. Fisködlorna hade två par fenor uppbyggda av fingerliknande ben, vilket tyder på att de har ett landlevande ursprung. Därav hade de lungor istället för gälar och var således tvungna att simma upp till ytan för att kunna andas. Fisködlorna födde levande ungar, och det finns ett flertal fossila fynd av fisködlor med tillhörande embryon och ungar. I detta arbete beskrivs ett förmodat embryo mot bakgrund av den forskning som gjorts gällande den tidigontogenetiska utvecklingen hos fisködlor. Fyndet hittades inuti kroppshålan i ett fossil av en vuxen individ tillhörande arten Stenopterygius quadriscissus från tidig jura vid byn Holzmaden i sydvästra Tyskland. Det förmodade embryot utgörs av skelettelement i millimeterstorlek. Skelettelementen har undersökts och identifierats. Det mesta tyder på att de fossila benen tillhör ett embryo i ett tidigt utvecklingsstadium. Kotkroppar, gördelben och tänder överensstämmer såväl storleks- som utseendemässigt med andra embryonala Stenopterygius. Liten storlek och endast delvis förbenade kotkroppar tyder på ett tidigt embryonalt stadium. Två av benen: en kotkropp och en förmodad tand, skiljer sig utseendemässigt från de övriga fynden och det går inte att utesluta att dessa element tillhör maginnehållet hos den vuxna fisködlan. Samtliga skelettdelar saknar dock spår av syraetsning från magsyror, vilket brukar ses som en indikation på att fossila element är rester av embryon och inte maginnehåll. Möjligheten finns dock att fisködlan åt precis innan den dog, vilket isåfall skulle kunna förklara frånvaron av syraetsning. (Less)
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author
Perneby Molin, Susanna LU
supervisor
organization
course
GEOL01 20161
year
type
M2 - Bachelor Degree
subject
keywords
fisködlor, embryo, ontogeni, jura, Holzmaden
publication/series
Examensarbeten i geologi vid Lunds universitet
report number
469
language
Swedish
id
8876698
date added to LUP
2016-06-16 11:44:12
date last changed
2016-06-16 11:44:12
@misc{8876698,
  abstract     = {Ichthyosaurs (‘fish lizards’) are a group of marine reptiles that lived during the Mesozoic Era. They are all included in the superorder Ichthyopterygia, which consists of at least 36 genera and 80 species. The earliest ichthyosaurs occur in sediments deposited during the Olenekian in the Early Triassic (about 250 million years ago), and the last forms became extinct during the Cenoman in the Late Cretaceous (about 90 million years ago). Ichthyosaurs are characterized by large eyeballs (up to 25 cm in diameter) and a distinct, elongated snout. Some forms could reach well above 20 meters in length; however, the average length of most ichthyosaurs was around three to four meters. The earliest ichthyosaurs were lizard-like in appearance but they gradually developed a more fish-shaped body form indicating adjustments to a pelagic life. Ichthyosaurs had two pairs of fins formed by fingerlike bones; these indicate a terrestrial origin. Ichthyosaurs also had lungs instead of gills and thus were forced to swim to the surface to breathe air. Ichthyosaurs gave birth to live young, and there are a number of fossil finds of ichthyosaurs with associated embryos or juvenile individuals. This work describes a putative fossil embryo based on research done on the early ontogenetic development of ichthyosaurs. The potential embryo was found inside the body cavity of an adult individual belonging to the species Stenopterygius quadriscissus from the Early Jurassic of Holzmaden, south-western Germany. The embryo consists of millimeter-sized skeletal remains. The skeletal elements have been examined and photographed and most vertebral centra, a scapula, a clavicle and the teeth compare favorably in both size and appearance with other embryonic Stenopterygius, to suggest that skeletal remains belong to an embryo in an early stage of development. Two bones; i.e., a vertebral centrum and a putative tooth, differ in appearance from the rest of the assemblage, and hence it cannot be excluded that these elements represent stomach contents of the adult specimen. Notably though, all skeletal remains lack any trace of acid etching originating from digestive juices – an indication that the fossil elements indeed represent remains of an embryo rather than stomach contents. Nonetheless, there is a possibility that the ichthyosaur ate just before it died, which potentially could explain the absence of apparent acid etching.},
  author       = {Perneby Molin, Susanna},
  keyword      = {fisködlor,embryo,ontogeni,jura,Holzmaden},
  language     = {swe},
  note         = {Student Paper},
  series       = {Examensarbeten i geologi vid Lunds universitet},
  title        = {Embryologi och tidig ontogeni hos mesozoiska fisködlor (Ichthyopterygia)},
  year         = {2016},
}