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Neck mobility versus mode of locomotion – in what way did neck length affect swimming performance among Mesozoic plesiosaurs (Reptilia, Sauropterygia)?

Lagerstam Lorien, Clarence LU (2020) In Dissertations in Geology at Lund University GEOR02 20192
Department of Geology
Abstract
Plesiosaurs (Sauropterygia) are a highly successful group of aquatically adapted reptiles that inhabited all of the world’s epicontinental seas and oceans from the Late Triassic through latest Cretaceous; that is, for ap-proximately 135 million years. The debate on plesiosaur locomotion and neck mobility has been ongoing for almost 200 years, and long-necked (plesiosauromorph) forms have generally been portrayed with slender and highly flexi-ble necks. The aim of this study is to: (1) quantitatively and qualitatively examine factors that potentially could determine neck mobility in plesiosaurs and their ancestors; (2) investigate if there is any correlation between neck length and type of locomotion; and (3) integrate these two aspects... (More)
Plesiosaurs (Sauropterygia) are a highly successful group of aquatically adapted reptiles that inhabited all of the world’s epicontinental seas and oceans from the Late Triassic through latest Cretaceous; that is, for ap-proximately 135 million years. The debate on plesiosaur locomotion and neck mobility has been ongoing for almost 200 years, and long-necked (plesiosauromorph) forms have generally been portrayed with slender and highly flexi-ble necks. The aim of this study is to: (1) quantitatively and qualitatively examine factors that potentially could determine neck mobility in plesiosaurs and their ancestors; (2) investigate if there is any correlation between neck length and type of locomotion; and (3) integrate these two aspects into a discussion on how the plesiosaur neck could have affected their swimming performance. The results show that plesiosaurs probably swam with all four flippers (subaqueous flight) in a fashion somewhat similar to that of modern penguins and sea turtles. In addition, short-necked (pliosauromorph) plesiosaurs had relatively larger posterior girdle elements (particularly the coracoid and ischium) and longer hind flippers than long-necked forms, which indicates that neck length imposed functional and/or ecological constraints on the plesiosaur locomotory system. Higher mobility in the middle of the neck is marked by a profound increase in relative vertebral length. This feature evolved convergently in the plesiosaur fam-ilies Microcleididae and Elasmosauridae. The proximal neck region was less mobile, although the distalmost region might have been more rigid than previously assumed if ligaments and other soft tissues are accounted for. Several features of the neck vertebrae, e.g., the zygapophysial angle and dimensions of the neural spines, exhibit a hitherto unappreciated level of morphological variation with potentially interspecific functional implications that should be explored further. This thesis questions the idea of a thin and flexible neck by arguing that a comparatively thicker and stiffer neck would have been more advantageous from a combined locomotory, physical, metabolic and hydro-dynamic perspective. (Less)
Popular Abstract (Swedish)
Svanödlor (plesiosaurier) är en grupp havslevande reptiler som framgångsrikt etablerade sig i marina miljöer från tidig trias fram tills dess att de sista formerna dog ut under sen krittid, d.v.s. under ett tidsspann om ca 135 miljoner år. Vissa svanödlor utvecklade en mycket lång hals som kunde innehålla över 70 halskotor, d.v.s. det största antalet halskotor hos något ryggradsdjur. Debatten om hur plesiosaurierna simmade med en lång och böjlig hals i framänden har pågått nästan 200 år och många hypoteser har presenterats. Syftet med detta arbete är att undersöka dessa frågor utifrån ett integrerat kvalitativt och kvantitativt perspektiv, d.v.s. en kombination av litteraturstudier och mätbara data som beskriver kotkropparnas form samt... (More)
Svanödlor (plesiosaurier) är en grupp havslevande reptiler som framgångsrikt etablerade sig i marina miljöer från tidig trias fram tills dess att de sista formerna dog ut under sen krittid, d.v.s. under ett tidsspann om ca 135 miljoner år. Vissa svanödlor utvecklade en mycket lång hals som kunde innehålla över 70 halskotor, d.v.s. det största antalet halskotor hos något ryggradsdjur. Debatten om hur plesiosaurierna simmade med en lång och böjlig hals i framänden har pågått nästan 200 år och många hypoteser har presenterats. Syftet med detta arbete är att undersöka dessa frågor utifrån ett integrerat kvalitativt och kvantitativt perspektiv, d.v.s. en kombination av litteraturstudier och mätbara data som beskriver kotkropparnas form samt kotutskottens längd, vilka båda spelade en avgörande roll för halsens rörlighet. Resultaten av min studie visar att svanödlor troligtvis simmade på ett sätt som liknar den ’undervattensflykt’ som praktiseras av dagens pingviner och havssköldpaddor, men med skillnaden att plesiosaurierna använda fyra fenor istället för två. Mer korthalsade svanödlor hade generellt annorlunda formade gördelben och de bakre fenorna var längre än hos långhalsade former vilket tyder på att halsens längd på något sätt påverkade simsättet. Låghalsade svanödlor hade i genomsnitt längre halskotor än korthalsade och de längsta halskotorna återfinns i mitten av halsen inom familjerna Elasmosauridae och Microcleididae. Den centrala delen av halsen kan därför ha varit den mest rörliga. Kortare kotor och längre kotutskott in den bakre delen av halsen visar att detta avsnitt med största sannolikhet var mindre rörligt än det främre. Samtidigt uppvisar halskotorna stor morfologisk variation, vilket förmodligen visar på en större skillnad i rörlighet mellan olika svanödlesläkten än vad som tidigare antagits. Slutligen ifrågasätter jag den sedan länge dominerande hypotesen om att svanödlorna hade en tunn och tubliknande hals då en sådan form kraftigt skulle öka energiförlusten, men också minska stabiliteten hos djuren när de simmade. Det är istället mer troligt att hela kroppen var spolformad och att halsen hölls rak när djuren tog sig fram i vattenrymden, i likhet med samtliga nulevande pelagiska ryggradsdjur. (Less)
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author
Lagerstam Lorien, Clarence LU
supervisor
organization
course
GEOR02 20192
year
type
H2 - Master's Degree (Two Years)
subject
keywords
plesiosaur, locomotion, microcleididae, elasmosauridae, hydrodynamic
publication/series
Dissertations in Geology at Lund University
report number
583
language
English
id
9010422
date added to LUP
2020-05-27 09:08:09
date last changed
2020-06-03 12:54:16
@misc{9010422,
  abstract     = {Plesiosaurs (Sauropterygia) are a highly successful group of aquatically adapted reptiles that inhabited all of the world’s epicontinental seas and oceans from the Late Triassic through latest Cretaceous; that is, for ap-proximately 135 million years. The debate on plesiosaur locomotion and neck mobility has been ongoing for almost 200 years, and long-necked (plesiosauromorph) forms have generally been portrayed with slender and highly flexi-ble necks. The aim of this study is to: (1) quantitatively and qualitatively examine factors that potentially could determine neck mobility in plesiosaurs and their ancestors; (2) investigate if there is any correlation between neck length and type of locomotion; and (3) integrate these two aspects into a discussion on how the plesiosaur neck could have affected their swimming performance. The results show that plesiosaurs probably swam with all four flippers (subaqueous flight) in a fashion somewhat similar to that of modern penguins and sea turtles. In addition, short-necked (pliosauromorph) plesiosaurs had relatively larger posterior girdle elements (particularly the coracoid and ischium) and longer hind flippers than long-necked forms, which indicates that neck length imposed functional and/or ecological constraints on the plesiosaur locomotory system. Higher mobility in the middle of the neck is marked by a profound increase in relative vertebral length. This feature evolved convergently in the plesiosaur fam-ilies Microcleididae and Elasmosauridae. The proximal neck region was less mobile, although the distalmost region might have been more rigid than previously assumed if ligaments and other soft tissues are accounted for. Several features of the neck vertebrae, e.g., the zygapophysial angle and dimensions of the neural spines, exhibit a hitherto unappreciated level of morphological variation with potentially interspecific functional implications that should be explored further. This thesis questions the idea of a thin and flexible neck by arguing that a comparatively thicker and stiffer neck would have been more advantageous from a combined locomotory, physical, metabolic and hydro-dynamic perspective.},
  author       = {Lagerstam Lorien, Clarence},
  keyword      = {plesiosaur,locomotion,microcleididae,elasmosauridae,hydrodynamic},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Neck mobility versus mode of locomotion – in what way did neck length affect swimming performance among Mesozoic plesiosaurs (Reptilia, Sauropterygia)?},
  year         = {2020},
}