Palaeophysiology of terrestrialisation in the Chelicerata

Selden, Paul A.; Jeram, Andrew J.

doi:10.1017/s0263593300028741

Cited by 56 publications

(50 citation statements)

References 28 publications

(17 reference statements)

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“…28) and vertebrates (7) replaced gills with tracheae and lungs. This transition surely involved primitive lungs or analogous structures (27) that may have been inefficient for sufficient O 2 extraction at levels lower than present. This suboptimality of respiratory structures in air may explain why vertebrates did not become land dwellers before Romer's Gap.…”

Section: Discussionmentioning

confidence: 99%

Confirmation of Romer's Gap as a low oxygen interval constraining the timing of initial arthropod and vertebrate terrestrialization

Ward

Labandeira

Laurin

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

132

104

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The first terrestrialization of species that evolved from previously aquatic taxa was a seminal event in evolutionary history. For vertebrates, one of the most important terrestrialized groups, this event was interrupted by a time interval known as Romer's Gap, for which, until recently, few fossils were known. Here, we argue that geochronologic range data of terrestrial arthropods show a pattern similar to that of vertebrates. Thus, Romer's Gap is real, occupied an interval from 360 million years before present (MYBP) to 345 MYBP, and occurred when environmental conditions were unfavorable for air-breathing, terrestrial animals. These model results suggest that atmospheric oxygen levels were the major driver of successful terrestrialization, and a low-oxygen interval accounts for Romer's Gap. Results also show that terrestrialization among members of arthropod and vertebrate clades occurred in two distinct phases. The first phase was a 65-million-year ( (1) indicates that arthropods, with species interpreted as fully land-based before 400 million years before present (MYBP) (2), preceded vertebrates onto land by tens of millions of years. The first body fossils identified as stegocephalians (limbed vertebrates) are known from strata Ϸ370 MYBP, such that the appearance of the limb with digits, the loss of the opercular apparatus, and the development of other characters that subsequently allowed a terrestrial lifestyle, presumably occurred during the 25-My interval between 385 and 360 MYBP (3, 4). Most of our understanding about these crucial vertebrate events comes from only a few freshwater deposits from Euramerican localities, with outcrops in Greenland producing the most prolific stegocephalian remains. Elginerpeton and Obruchevichthys were first, between 385 and 375 MYBP, followed several million years later by a modest radiation that included Ventastega, Ichythostega, Acanthostega, Tulerpeton, Metaxygnathus, and Hynerpeton. Although most of these taxa possessed limbs (although this is not certain for Elginerpeton and Obruchevichthys), all of these taxa have been interpreted as fully aquatic, rather than terrestrial (5-7). Their respiratory systems are poorly known, but osteology suggests that they were able to derive some amount of O 2 from water instead of being entirely air breathing (8). These stegocephalians disappeared soon thereafter, followed rapidly by rare appearances of limbed vertebrates. This temporal gap has long been called Romer's Gap, and until recently it was unknown whether this hiatus was due to a combination of unfavorable taphonomic conditions and collection failure or whether it represented an interval of intrinsically low diversity and an abundance of limbed vertebrates. Romer's Gap separates occurrences of the earliest (Late Devonian) aquatic stegocephalians from a much larger adaptive radiation that included the first terrestrial vertebrates that commenced during the Visean stage of the Early Carboniferous. Although new collections have partly filled Romer's Gap (9), including the d...

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Section: Discussionmentioning

confidence: 99%

Confirmation of Romer's Gap as a low oxygen interval constraining the timing of initial arthropod and vertebrate terrestrialization

Ward

Labandeira

Laurin

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

132

104

View full text Add to dashboard Cite

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“…The first fossil representatives of animal groups which are wholly terrestrial today do not provide Anderson, 1991). The existence of such pre-terrestrial forms does not of course rule out their coexistence with fully terrestrial relatives, thus, for example, it is likely that the first terrestrial scorpion lineages coexisted with their aquatic relatives for much of late Palaeozoic time (Selden & Jeram, 1989). Aquatic precursors can be suspected when cladograms predict the existence in suspiciously early times of groups presendy wholly terrestrial.…”

Section: Terrestrial Metazoamentioning

confidence: 99%

The development of early terrestrial ecosystems

Edwards

Selden

1992

Botanical Journal of Scotland

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“…The view that basal scorpions were not terrestrial and that terrestrialisation occurred in scorpions independently of other Arachnida (Selden & Jeram 1989) carried the im-plication that the Araneae are not monophyletic (Scholtz & Kamenz 2006). This has been strongly refuted by Scholtz and Kamenz (2006) who argue that booklungs are an apomorphy of Araneae, that the Araneae are monophyletic and that they resulted from a single terrestrialisation event in their common stem lineage.…”

Section: Introductionmentioning

confidence: 99%