Dominant group/Paleontology

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This is a photograph of the skeleton of Alligator prenasalis. Credit: Ghedoghedo.

Paleontology is a large subject due to the inclusion of fossils from the rock record, taxonomic classification of these fossils, and the occasional find of residual organic material that sometimes contains genetic material. Like entomology, paleontology has become a home for the entity "dominant group" in the description of phenomena and in theoretical interpretation, explanation, and prediction of effects.

Dominant group[edit]

Examples from primary sources are to be used to prove or disprove each hypothesis. These can be collected per subject or in general.

  • Accident hypothesis: dominant group is an accident of whatever processes are operating.
  • Artifact hypothesis: dominant group may be an artifact of human endeavor or may have preceded humanity.
  • Association hypothesis: dominant group is associated in some way with the original research.
  • Bad group hypothesis: dominant group is the group that engages in discrimination, abuse, punishment, and additional criminal activity against other groups. It often has an unfair advantage and uses it to express monopolistic practices.
  • Control group hypothesis: there is a control group that can be used to study dominant group.
  • Entity hypothesis: dominant group is an entity within each field where a primary author of original research uses the term.
  • Evolution hypothesis: dominant group is a product of evolutionary processes, such groups are the evolutionary process, produce evolutionary processes, or are independent of evolutionary processes.
  • Identifier hypothesis: dominant group is an identifier used by primary source authors of original research to identify an observation in the process of analysis.
  • Importance hypothesis: dominant group signifies original research results that usually need to be explained by theory and interpretation of experiments.
  • Indicator hypothesis: dominant group may be an indicator of something as yet not understood by the primary author of original research.
  • Influence hypothesis: dominant group is included in a primary source article containing original research to indicate influence or an influential phenomenon.
  • Interest hypothesis: dominant group is a theoretical entity used by scholarly authors of primary sources for phenomena of interest.
  • Metadefinition hypothesis: all uses of dominant group by all primary source authors of original research are included in the metadefinition for dominant group.
  • Null hypothesis: there is no significant or special meaning of dominant group in any sentence or figure caption in any refereed journal article.
  • Object hypothesis: dominant group is an object within each field where a primary author of original research uses the term.
  • Obvious hypothesis: the only meaning of dominant group is the one found in Mosby's Medical Dictionary.
  • Original research hypothesis: dominant group is included in a primary source article by the author to indicate that the article contains original research.
  • Primordial hypothesis: dominant group is a primordial concept inherent to humans such that every language or other form of communication no matter how old or whether extinct, on the verge of extinction, or not, has at least a synonym for dominant group.
  • Purpose hypothesis: dominant group is written into articles by authors for a purpose.
  • Regional hypothesis: dominant group, when it occurs, is only a manifestation of the limitations within a region. Variation of those limitations may result in the loss of a dominant group with the eventual appearance of a new one or none at all.
  • Source hypothesis: dominant group is a source within each field where a primary author of original research uses the term.
  • Term hypothesis: dominant group is a significant term that may require a 'rigorous definition' or application and verification of an empirical definition.

Fossils[edit]

This may be an ammonite fossil. Credit: Halvard : from Norway.
Subtaxa within taxa are often distributed unevenly. Credit: Andy Purvis & Andy Hector.{{fairuse}}

Def. "[t]he mineralized remains of an animal or plant" or "[a]ny preserved evidence of ancient life, including shells, imprints, burrows, coprolites, and organically-produced chemicals"[1] is called a fossil.

Derived terms include ichnofossil, index fossil, living fossil, mesofossil, microfossil, and trace fossil.[1]

"At an even smaller scale, genomes provide fossils that indicate great past retroviral diversity12."[2]

"These new phylogenies are pushing back the origins of many groups to long before their earliest known fossils. The palaeontological record indicates a Cambrian explosion of phyla around 540 million years (Myr) ago, but sequences suggest a more gradual series of splits around twice as old23. Likewise, many orders of mammals and birds are now thought to have originated long before the end-Cretaceous extinction24,25, which occurred 65 Myr ago and which was thought previously to have been the signal for their radiation. If the new timescale can be trusted26, these findings present a puzzle and a warning. The puzzle is the absence of fossils. Why have we not found traces of these lineages in their first tens or even hundreds of millions of years? It seems likely that the animals were too small or too rare, with the sudden appearance in the rocks corresponding to an increase in size and rise to ecological dominance27. The warning is that current biodiversity is in a sense greater than we had realized. Major lineages alive today represent more unique evolutionary history than previously suspected — history that would be lost with their extinction."[2]

Per the second image down on the right: "Subtaxa within taxa are often distributed unevenly. Uneven distribution of species among: a, eutherian orders, with rodents being the dominant group; b, rodent families, with murids being dominant; and c, murid genera."[2]

"Although the sampling effect is biological in part — it requires both differences between species and an ecological mechanism making some species more abundant than others — the probabilistic component (more diverse communities have a greater chance of containing a species with particular properties) has made it controversial. Nevertheless, loss of species with key traits, as in the sampling effect, is not restricted to ecological experiments: logging, fishing, trapping and other harvesting of natural resources frequently remove particular organisms, often including dominant species."[2]

Paleontology[edit]

Def. the "[s]tudy of the forms of life existing in prehistoric or geologic times"[3] is called paleontology.

Geology[edit]

"In theory, "dominant group" in geology may have at least two meanings: (1) a dominant group of geology-based objects or (2) a dominant group in some way associated with geology." The fossils and their implications are here. The rocks themselves are in 'dominant group/geology'."[4]

Mass Extinctions[edit]

The numbers (intensity) are marine animal genus extinctions. Credit: Smith609.

"When dominance of particular ecological niches passes from one group of organisms to another, it is rarely because the new dominant group is "superior" to the old and usually because an extinction event eliminates the old dominant group and makes way for the new one.[5][6]"[7]

"The rise of dominant groups such as amphibians, reptiles, mammals and birds occurred by opportunistic expansion into empty ecological niches and the extinction of groups happened due to large shifts in the abiotic environment.[8]"[9]

On page 212 of a 1944 book by Simpson is "[i]n the history of life it is a striking fact that major changes in the taxonomic groups occupying various ecological positions do not, as a rule, result from direct competition of the groups concerned in each case and the survival of the fittest, as most students would assume a priori. On the contrary, the usual sequence is for one dominant group to die out, leaving the zone empty, before the other group becomes abundant."[10] "Simpson noted that major extinctions provide opportunities (space, ecological niches, etc.) for later diversification by the survivors."[11]

Ecological dominance[edit]

Ecological dominance is the degree to which a species is more numerous than its competitors in an ecological community, or makes up more of the biomass.

"The ecological dominance of diatoms under sporadic mixing conditions indicates that their long-term success in the Cenozoic reflects an increase in event scale turbulent energy dissipation in the upper ocean."[12]

"In many paleontological studies, taxonomic diversity" carries with it "[t]he implicit assumption ... that more species in a lineage indicate greater biomass in the lineage as well."[13]

Paleobotany[edit]

With respect to groups of vascular land plant in the Phanerozoic, "[f]ollowing initial invasion of the land, the diversification of each group coincides with a decline in species numbers of the previously dominant group."[14]

“The Mesophytic types begin to appear towards the close of the Palaeozoic period. They come in very gradually, but become more numerous as we pass up through the Permian. It is not until Triassic times that they occupy the position of a dominant group.”[15]

"This is the first such forest reconstruction in Asia for any time interval, it's the first of a peat forest for this time interval and it's the first with Noeggerathiales as a dominant group," Pfefferkorn said.[16]

Holocene[edit]

The Holocene starts at ~11,700 b2k and extends to the present.

Actinopterygii[edit]

"A subclass of the Osteichthyes, the ray-finned fishes (Actinopterygii), have become the dominant group of fishes in the post-Paleozoic and modern world, with some 30,000 living species."[17]

Arthropods[edit]

“No strong or dominant group of flies, like the Tachinide, Dolichopodidse, Syrphidae or Bombyliidae, has ever had in the past a larger average bodily size than is found among their living representatives.”[18][19]

Extant brachiopods[edit]

"The two main extant brachiopod lineages, currently treated as subphyla (Williams et al.1996), comprise one numerically dominant group with a highly mineralised, hinged shell (articulate brachiopods), and one group with valves connected only by soft tissues (inarticulate brachiopods, comprising three lineages: craniids, discinids and lingulids)."[20]

Teleosts[edit]

"The placoderms ... were replaced by the actinopterygians (ray-finned fishes), which ultimately produced the teleosts, the dominant group of modern fish."[21]

Pleistocene[edit]

The Pleistocene dates from 2.588 x 106 to 11,700 b2k.

"Ahl al Oughlam lacks the diversity of murids found in East African sites of this age, but also fully lacks any arvicolid, the dominant group in Europe at that time. Remarkably, this original composition of North African rodent faunas remained virtually unchanged until the end of the Pleistocene ( Jaeger, 1975)."[22]

Pliocene[edit]

The Pliocene ranges from 5.332 x 106 to 2.588 x 106 b2k.

"Primates (particularly cercopithecids) appear to be the most dominant group, followed by artiodactyls and carnivores, respectively. Among the artiodactyls, bovids and suids are dominant."[23]

Miocene[edit]

The Miocene dates from 23.03 x 106 to 5.332 x 106 b2k.

Oligocene[edit]

The Oligocene dates from 33.9 ± 0.1 x 106 to 23.03 x 106 b2k.

"As the Earth began to cool, the tropical plants that had previously been found relatively widespread began to recede towards the equator where it was still warm. The general tropical plants began a transition to more forest like areas. The first grasses also appeared in the late Oligocene. The appearance of these grasses led to to evolution of various herbivore animals. With bodies low to the ground, animals would take advantage of the new grasses that appeared."[24]

Alligators[edit]

"From the late Oligocene until the present, the family Alligatoridae remains the dominant group in North America in terms of both generic diversity and numbers of localities where it is found."[25]

Foraminifera[edit]

"Significantly, the dominant group of planktonic Foraminifera to emerge in the Oligocene were the globigerines, which today are largely restricted to cold-water masses (Cifelli, 1969)."[26]

"Recurrent themes of pre-Cenozoic marine crises suggest that global temperature change also served as a major, and perhaps dominant, agent of extinction in these events: (1) Mass extinctions have frequently been concentrated in the tropics, which seem to have become a refrigerated trap from which there has been no escape; biotas previously occupying high latitudes have shifted equatorward, to replace disappearing tropical biotas. (2) Some crises were not instantaneous but followed protracted and pulsatile temporal patterns, as would be predicted for complex, global climatic crises. (3) Several mass extinctions coincided with recognized intervals of climatic cooling."[26]

Perissodactyls[edit]

"Perissodactyls were the dominant group of large terrestrial browsers right through the Oligocene. However, the rise of grasses in the Miocene (about 20 million years ago) saw a major change: the even-toed ungulates with their more complex stomachs were better able to adapt to a coarse, low-nutrition diet, and soon rose to prominence. Nevertheless, many odd-toed species survived and prospered until the late Pleistocene (about 10,000 years ago) when they faced the pressure of human hunting and habitat change."[27]

Eocene[edit]

The Eocene dates from 55.8 ± 0.2 x 106 to 33.9 ± 0.1 x 106 b2k.

Paleocene[edit]

The Paleocene dates from 65.5 ± 0.3 x 106 to 55.8 ± 0.2 x 106 b2k.

Cretaceous[edit]

"The Cretaceous period is the third and final period in the Mesozoic Era. It began 145.5 million years ago after the Jurassic Period and ended 65.5 million years ago, before the Paleogene Period of the Cenozoic Era."[28]

Ammonoids[edit]

"Desmoceras predominates in the upper Albian–Cenomanian succession regardless of lithofacies, the family Gaudryceratidae is the second-most dominant group in each lithofacies, the abundance of Zelandites decreases offshore, and other groups, including Acanthoceratidae, are uncommon but occur in both inshore and offshore facies."[29]

"The Labeceratidae represent the final evolutionary pulse of the Superfamily Ancylocerataceae which were the dominant group of Valanginian–Aptian heteromorph ammonites."[30]

Bivalves[edit]

This image is Trigonia sp. from the Glen Rose Formation (Cretaceous) near Austin, Texas. Credit: Wilson44691.

"The carbonate successions exposed in the two quarries contain a relatively abundant and diversified bivalve and ammonite fauna, with inoceramid bivalves representing the dominant group."[31]

Enantiornithes[edit]

Longchengornis is an enantiornithine bird from China. Credit: Joerim.

"Euenantiornithes is a superorder of Cretaceous birds. They are considered to contain the more advanced taxa of the Enantiornithes, the dominant group of birds during the late Mesozoic."[32]

Sauropods[edit]

From Saltasaurus, "In the Cretaceous Period, sauropods in North America were no longer the dominant group of herbivorous dinosaurs, with the duck-billed dinosaurs, such as Edmontosaurus becoming the most abundant. However, on other landmasses such as South America and Africa (which were island continents much like modern Australia) sauropods, in particular the titanosaurs continued to be the dominant herbivores."

Tetanurans[edit]

"Shaochilong is the youngest known Laurasian allosauroid suggesting that basal tetanurans not tyrannosaurids, were still the dominant group of large-bodied theropods in Laurasian during the Mid-Cretaceous and that the rise of tyrannosaurids as the dominant group of large terrestrial predators was sudden and confined to the very end of the Cretaceous."[33]

Jurassic[edit]

"The Jurassic Period takes place after the Triassic Period and before the Cretaceous Period. This period is well known for the reign of the dinosaurs of its time and the global tropical landscape."[34]

"The Jurassic is a geologic period and system that extends from about 199.6±0.6 Ma (million years ago) to 145.5±4 Ma; that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period is marked by the major Triassic–Jurassic extinction event. However, the end of the period did not witness any major extinction event."[35]

Ammonite subzone[edit]

"From this time on, perisphinctids spreading north out of the Tethys became the dominant group in the ammonite fauna. A general warming of the climate in Middle Oxfordian time is the most probable cause (see Gygi, 1986)."[36]

Conifers[edit]

"Conifers (Gymnosperms) became the dominant group of plants in mid-Jurassic forests".[37]

Ostracods[edit]

"Notable by their absence, however, are the metacopids and cytherids, while the Cypridacea are the dominant group with 53 % of the total number of specimens."[38]

Saurischians[edit]

"The dominant herbivores of the Jurassic, the sauropodomorph saurischians evolved to larger forms and gave rise to the Neosauropoda".[37]

Triassic[edit]

"Early neopterygian fishes (Fig. 13.9) shared the seas and fresh waters with the chondrosteans through most of the Triassic, Jurassic, and Cretaceous periods but gradually became the dominant group."[39] "They presumably became dominant because of gradual but significant changes in structure that gave them a competitive edge over the chondrosteans. These changes culminated in the subdivision Teleostei, the dominant bony fishes today."[39]

Archosaurs[edit]

"Since its origin in the Late Permian or Early Triassic, the archosaur clade has been a successful and often dominant group".[40]

"The archosaurs became the dominant group during the Triassic period, though it took 30 million years before their diversity was as great as the animals that lived in the Permian."[41]

Hybodonts[edit]

"During Early Mesozoic times, hybodonts were the dominant group of marine selachians, but, when neoselachian and actinopterygian diversity increased in the Middle and Late Jurassic, hybodonts gradually declined in marine habitats."[42]

Permian[edit]

Sauria[edit]

The Tuatara is a living saurian. Credit: Knutschie.

"Sauria is a clade of reptiles that includes all living diapsids, as well as their common ancestor and all its extinct descendants. ... The ancestral saurian was probably a small lizard-like creature living in the Permian Period. This crown group is diagnosed by a number of details in skull and skeleton, and comprises the two important clades Lepidosauromorpha and Archosauromorpha."[43]

Note: crown group is not a relative synonym for dominant group as crown is not a relative synonym for dominant.

"Obviously, other taxa shared the Earth with the reptiles and competed with them for food, but the Sauria were the dominant group."[44]

Carboniferous[edit]

Devonian[edit]

Placoderm radiation[edit]

This is the placoderm Dunkleosteus Skull at the Sam Noble Oklahoma Museum of Natural History. Credit: Mitternacht90.

"The placoderms underwent a spectacular radiation during the Devonian (between 410 and 360 million years ago), but at the end of this period all placoderms—large, small, marine and freshwater—went extinct. They were replaced by the actinopterygians (ray-finned fishes), which ultimately produced the teleosts, the dominant group of modern fish."[8]

Silurian[edit]

Graptolites[edit]

For the Silurian of the Brabant Massif in Belgium, "[m]acrofossils are rare but graptolites provide a good but incomplete coverage."[45] "The facies in the Silurian of the Brabant Massif is always deep neritic ... with no shallow marine sediments observed yet."[45]

"[G]raptolites are nearly the only macrofossils present and until 1969 the sole basis for biostratigraphical dating".[45] "Larvae and prosiculae of graptolites are often encountered in palynological preparations as are rhabdosomes in petrographical thin section".[45]

"Some fossils such as Conularia, Dayia, Cardiola, Orthoceras, Siphocrinites, and some species of Chitinozoa (a.o. Margachitina margaritana, Desmochitina opaca) show the presence of a "less deep" environment at the following levels: upper Aeronian and lower Telychian, lower Wenlock, uppermost Wenlock and a level in the Gorstian. Since in all these levels graptolites are the dominant group of macrofossils, shallow marine conditions are excluded."[45]

Placoderms[edit]

The placoderms surpassed the eurypterids as a large marine predator probably by the early to middle Silurian.

Ordovician[edit]

Rhynchonellides[edit]

Platystrophia ponderosa, Maysvillian (Upper Ordovician) near Madison, Indiana, is now Vinlandostrophia ponderosa (Foerste, 1909). Credit: Wilson44691.

"Although rhynchonellides have never been a dominant group of brachiopods, they are regarded as a successful order because they have first appeared in the early Ordovician, still survive in a wide range of marine environments today, and have left a longer palaeontological record than any other living articulated order, rich enough to allow inferences about their ancestral connections (Williams and Hurst, 1977; Ager, 1987)."[46]

Echinoderms[edit]

"At the beginning of the Middle Ordovician the echinoderms became the dominant group of the benthos in many biotopes of most of the epicontinental seas."[47]

Cambrian[edit]

Brachiopods[edit]

"The Brachiopoda were the dominant group of benthic filter feeding marine invertebrates from the early Cambrian, when they arose over 550 million years ago, until the end of the Permian period."[48]

Mollusks[edit]

"Much of the carbonate mound at Tauwhareparae is fossiliferous and incorporates one dominant group: namely bathymodiolin mussels."[49]

"These methods yielded conservative estimates of numerical dominants through the Phanerozoic because each numerically dominant group received the same score of “1” whether it dominated one shell bed or many shell beds per stratigraphic unit."[50]

Hypotheses[edit]

  1. Dominant groups in paleontology are those that appear most numerous or splendid in the fossil record.
  2. Small monocellular organism probably constituted the most biomass throughout all history.

See also[edit]

References[edit]

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Further reading[edit]

External links[edit]

{{Geology resources}}{{Original research resources}}{{Terminology resources}}