Romer's gap
Encyclopedia
Romer's Gap is an example of a gap in the fossil
record used in the study of evolution. Such gaps represent a period from which excavators have found no or very few fossils. Romer's gap is named after paleontologist Dr. Alfred Romer
, who first recognised it.
, the early Mississippian (Tournaisian). The gap form a discontinuity between the primitive forests and high diversity of fishes in the "Age of Fishes" - the Devonian
, to a more modern assembly of the Carboniferous. While initial arthropod and vertebrate terrestriality was well under way before the gap, there are remarkably few terrestrial fossils that date from the gap itself.
There has been long debate as to why there are so few fossils from this time period. Some have suggested the problem was of fossilization itself, suggesting that there may have been differences in the geochemistry of the time that did not favour fossil formation. Also, excavators may not have dug in the right places. Recent work on Paleozoic geochemistry has confirmed the biological reality of Romer's Gap in both terrestrial vertebrates and arthropods, and has correlated it with a period of unusually low atmospheric oxygen concentration, which was independently determined from the idiosyncratic geochemistry of rocks formed during Romer's Gap.
Marine vertebrates may have been recovering from a major extinction event during this period , one on par with the that which killed the dinosaurs, although the precise mechanism of the extinction is unclear. Before the event the oceans were dominated by lobe-finned fishes and armored fish called placoderms. After the gap we see modern ray finned fish and shark
s as the dominant forms. The period also saw the demise of the Ichthyostegalia, the early fish-like amphibians.
and Crassigyrinus
. There are a few sites where vertebrate fossils have been found to help fill in the gap, such as the East Kirkton Quarry
, in Bathgate
, Scotland, a long-known fossil site that was revisited by Stanley P. Wood in 1984 and has since been revealing a number of early tetrapods; "literally dozens of tetrapods came rolling out: Balanerpeton
(a temnospondyl), Silvanerpeton
and Eldeceeon
(basal anthracosaurs), all in multiple copies, and one spectacular proto-amniote, Westlothiana
", Paleos Project reports.
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
record used in the study of evolution. Such gaps represent a period from which excavators have found no or very few fossils. Romer's gap is named after paleontologist Dr. Alfred Romer
Alfred Romer
Alfred Sherwood Romer was an American paleontologist and comparative anatomist and a specialist in vertebrate evolution.-Biography:...
, who first recognised it.
Age
Romer's Gap ran from approximately 360 to 345 million years ago, corresponding to the first 15 million years of the CarboniferousCarboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
, the early Mississippian (Tournaisian). The gap form a discontinuity between the primitive forests and high diversity of fishes in the "Age of Fishes" - the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
, to a more modern assembly of the Carboniferous. While initial arthropod and vertebrate terrestriality was well under way before the gap, there are remarkably few terrestrial fossils that date from the gap itself.
Mechanism behind the gap
Marine vertebrates may have been recovering from a major extinction event during this period , one on par with the that which killed the dinosaurs, although the precise mechanism of the extinction is unclear. Before the event the oceans were dominated by lobe-finned fishes and armored fish called placoderms. After the gap we see modern ray finned fish and shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s as the dominant forms. The period also saw the demise of the Ichthyostegalia, the early fish-like amphibians.
Terrestrial gap fauna
The gap has been progressively closed with the discoveries of such early Carboniferous tetrapods as PederpesPederpes
Pederpes is an extinct genus of early Carboniferous tetrapod, dating from the Tournaisian age . Pederpes contains one species, P...
and Crassigyrinus
Crassigyrinus
Crassigyrinus is an extinct genus of carnivorous stem tetrapod from the Early Carboniferous of Scotland and possibly Greer, West Virginia. The type specimen was originally described as Macromerium scoticum and lacked a complete skull...
. There are a few sites where vertebrate fossils have been found to help fill in the gap, such as the East Kirkton Quarry
East Kirkton Quarry
East Kirkton Quarry is a former limestone quarry, now better known as a fossil site known for terrestrial fossils from the fossil-poor "Romer's gap, a 15 million year period at the beginning of the Carboniferous...
, in Bathgate
Bathgate
Bathgate is a town in West Lothian, Scotland, on the M8 motorway west of Livingston. Nearby towns are Blackburn, Armadale, Whitburn, Livingston, and Linlithgow. Edinburgh Airport is away...
, Scotland, a long-known fossil site that was revisited by Stanley P. Wood in 1984 and has since been revealing a number of early tetrapods; "literally dozens of tetrapods came rolling out: Balanerpeton
Balanerpeton
Balanerpeton is an extinct genus of temnospondyl amphibian from the Early Carboniferous period. It reached approximately 50 cm in size .Balanerpeton woodi was discovered by Stanley Wood and is the earliest and most common tetrapod in the East Kirkton Quarry assemblage of terrestrial...
(a temnospondyl), Silvanerpeton
Silvanerpeton
Silvanerpeton is an extinct genus of early reptiliomorph found in the East Kirkton Quarry of West Lothian, Scotland. The find is important, as the quarry represents terrestrial deposits from the Romer's gap, a period poor in fossils where the higher groups labyrinthodonts evolved...
and Eldeceeon
Eldeceeon
Eldeceeon is an extinct genus of reptiliomorph from the Early Carboniferous of Scotland. It is known from two fossil specimens found within the Viséan-age East Kirkton Quarry in West Lothian. The type and only species, E. rolfei, was named in 1994...
(basal anthracosaurs), all in multiple copies, and one spectacular proto-amniote, Westlothiana
Westlothiana
Westlothiana lizziae was a reptile-like amphibian or possibly early reptile that bore a superficial resemblance to modern-day lizards. It lived during the Carboniferous period, about 350 million years ago. The type specimen was discovered in East Kirkton Quarry, Bathgate, Scotland, in 1984, and was...
", Paleos Project reports.