27
It is suggested that “forelimbs and skulls became modified in advance of
hind limbs, adapted for supporting the head and front of the body out of the water,
probably in connection with air breathing,” (Clack 2009 ). Prototetrapods and
aquatic tetrapods habituate during Eifelian mostly in humid regions like coastal
lagoon or estuary margin soils (Retallack 2011 ). According to the modern “woodland
hypothesis of tetrapod evolution, limbs and necks were selected for by scavenging
and hunting in shallow-fl ooded woodlands and oxbow lakes during a unique period
in Earth history, after the evolution of fl ood-ponding trees and before effective
terrestrial predator resistance,” (Retallack 2011 ).
Limbed tetrapods originated, probably, between 385 and 380 Ma ago, in the
northern continent of Laurussia (see for review Clack 2002 ; Laurin 2002 ). The
diversity of extant tetrapods is recently reviewed by Benson and co-workers (Benson
et al. 2010 ).
1.2.3.1 Class Amphibia
It is suggested that the common ancestors of modern fi sh, living fossil fi shes and
amphibians, are phylogenetically separated (Wang et al. 2012 ). In general, both
saltwater and freshwater fi sh (including living fossil fi sh) and amphibians are
clustered in different clades. Thus, “the ancestor of living amphibians probably
arose from a type of primordial freshwater fi sh, rather than the coelacanth, lungfi sh,
or modern saltwater fi sh. Modern freshwater fi sh and modern saltwater fi sh were
probably separated from a common ancestor by a single event, caused by crustal
movement,” (Wang et al. 2012 ).
A recent hypothesis about this transition suggests that the diverse assemblages of
marine amphibious fi sh that occur primarily in tropical, high intertidal zone habitats
are analogs of early tetrapods. This suggests that the intertidal zone, not tropical
freshwater lowlands, was the springboard habitat for the Devonian land transition
by vertebrates (Graham and Lee 2004 ). The extant marine amphibious fi sh, which
occur mainly on rocky shores or mudfl ats, have reached the limit of their niche
expansion onto land and remain tied to water by respiratory structures that are less
effi cient in air and more vulnerable to desiccation than lungs.
Indeed, of the 6,500 recognised amphibians, only one species can enter the sea
(Neill 1958 ). However, the early stegocephalians (fossil amphibians whose skullcap
formed a continuous covering and whose trunk was frequently covered with bony
scales) tolerated saltwater, even although they also lived in freshwater (Schultze
1999 ; Niedzwiedzki et al. 2010 ; Laurin and Soler–Gijón 2010 ). Thus, the crab
eating frog, Fejervarya cancrivora – is considered to possess the highest salinity
tolerance among amphibians (Fig. 1.7 ). In this species, 50 % of the larvae survived
in up to 80 % sea water – equivalent to 0.5 % NaCl (see for review Gordon
and Tucker 1968 ). Thus, the skin of “marine amphibians” seems to be a subject of
interest for experts in biological materials science.
1.2 Part I: Biomaterials of Vertebrate Origin. An Overview
It is suggested that “forelimbs and skulls became modified in advance of
hind limbs, adapted for supporting the head and front of the body out of the water,
probably in connection with air breathing,” (Clack 2009 ). Prototetrapods and
aquatic tetrapods habituate during Eifelian mostly in humid regions like coastal
lagoon or estuary margin soils (Retallack 2011 ). According to the modern “woodland
hypothesis of tetrapod evolution, limbs and necks were selected for by scavenging
and hunting in shallow-fl ooded woodlands and oxbow lakes during a unique period
in Earth history, after the evolution of fl ood-ponding trees and before effective
terrestrial predator resistance,” (Retallack 2011 ).
Limbed tetrapods originated, probably, between 385 and 380 Ma ago, in the
northern continent of Laurussia (see for review Clack 2002 ; Laurin 2002 ). The
diversity of extant tetrapods is recently reviewed by Benson and co-workers (Benson
et al. 2010 ).
1.2.3.1 Class Amphibia
It is suggested that the common ancestors of modern fi sh, living fossil fi shes and
amphibians, are phylogenetically separated (Wang et al. 2012 ). In general, both
saltwater and freshwater fi sh (including living fossil fi sh) and amphibians are
clustered in different clades. Thus, “the ancestor of living amphibians probably
arose from a type of primordial freshwater fi sh, rather than the coelacanth, lungfi sh,
or modern saltwater fi sh. Modern freshwater fi sh and modern saltwater fi sh were
probably separated from a common ancestor by a single event, caused by crustal
movement,” (Wang et al. 2012 ).
A recent hypothesis about this transition suggests that the diverse assemblages of
marine amphibious fi sh that occur primarily in tropical, high intertidal zone habitats
are analogs of early tetrapods. This suggests that the intertidal zone, not tropical
freshwater lowlands, was the springboard habitat for the Devonian land transition
by vertebrates (Graham and Lee 2004 ). The extant marine amphibious fi sh, which
occur mainly on rocky shores or mudfl ats, have reached the limit of their niche
expansion onto land and remain tied to water by respiratory structures that are less
effi cient in air and more vulnerable to desiccation than lungs.
Indeed, of the 6,500 recognised amphibians, only one species can enter the sea
(Neill 1958 ). However, the early stegocephalians (fossil amphibians whose skullcap
formed a continuous covering and whose trunk was frequently covered with bony
scales) tolerated saltwater, even although they also lived in freshwater (Schultze
1999 ; Niedzwiedzki et al. 2010 ; Laurin and Soler–Gijón 2010 ). Thus, the crab
eating frog, Fejervarya cancrivora – is considered to possess the highest salinity
tolerance among amphibians (Fig. 1.7 ). In this species, 50 % of the larvae survived
in up to 80 % sea water – equivalent to 0.5 % NaCl (see for review Gordon
and Tucker 1968 ). Thus, the skin of “marine amphibians” seems to be a subject of
interest for experts in biological materials science.
1.2 Part I: Biomaterials of Vertebrate Origin. An Overview