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Mark McMenamin | |
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Born | 1957or1958(age 66–67) [1] Oregon, U.S. |
Citizenship | United States |
Alma mater | University of California, Santa Barbara, Ph.D. Stanford University, B.S. |
Known for | Ediacaran fossils; Hypersea theory; Proterozoic supercontinent Rodinia [2] |
Spouse | Dianna L. Schulte McMenamin |
Awards | Presidential Young Investigator Award Sigma Xi National Lecturer 2011 Irish Education 100 Award [2] [3] |
Scientific career | |
Fields | Paleontology, Geology |
Institutions | Mount Holyoke College [2] |
Mark A. S. McMenamin (born c. 1957) is an American paleontologist and professor of geology at Mount Holyoke College. He has contributed to the study of the Cambrian explosion and the Ediacaran biota.
He is the author of several books, most recently Deep Time Analysis (2018) and Dynamic Paleontology (2016). His earlier works include The Garden of Ediacara: Discovering the Earliest Complex Life (1998), one of the only popular accounts of research on the Ediacaran biota, and Science 101: Geology (2007). He is credited with co-naming several geological formations in Mexico, describing several new fossil genera and species, and naming the Precambrian supercontinent Rodinia [4] and the superocean Mirovia. [5] [6] The Cambrian archeocyathid species Markocyathus clementensis was named in his honor in 1989. [7]
McMenamin was born in Oregon, [1] earned his B.S. at Stanford University in 1979 and his PhD at the University of California, Santa Barbara in 1984. [8] In 1980, while at Santa Barbara he met his future wife, Dianna, also a paleontology graduate student, with whom he would co-author several publications. He joined the staff at Mount Holyoke College in 1984. [9] In October 2021, he described a Jurassic-period dinosaur fossil in South Hadley, Massachusetts. [10]
In 1995 McMenamin led a field expedition to Sonora, Mexico, that discovered fossils (550-560 million years old [11] ) which McMenamin argued belonged to a diverse community of early animals and Ediacaran biota. [12] The paper was published in the Proceedings of the National Academy of Sciences of the United States of America where it was reviewed by Ediacaran expert James G. Gehling. In 2011, McMenamin reported the discovery of the oldest known adult animal fossils, Proterozoic chitons from the Clemente Formation, northwestern Sonora, Mexico. [13] [14] [11] However, during earlier report by him, other researchers questioned about its affinity as biogenic fossils, which also predate the majority of Ediacaran biota by at least 50 million years. [15] Further up in this same stratigraphic sequence, McMenamin also discovered and named the early shelly fossil Sinotubulites cienegensis, a fossil that allowed the first confident Proterozoic biostratigraphic correlation between Asia and the Americas. [16] In Lower Cambrian strata higher in the stratigraphic sequence, McMenamin also discovered important stem group brachiopods belonging to the genus Mickwitzia. [17] During a Mount Holyoke College field trip to Death Valley, California, McMenamin and his co-authors found evidence indicating that the Proterozoic shelly fossil Qinella survived the Proterozoic-Cambrian boundary. [18] [14]
In 2012 McMenamin proposed that the enigmatic Cambrian trace fossil Paleodictyon was the nest of an unknown animal, a hypothesis which, if supported, may be the earliest fossil evidence of parental behavior, surpassing previous findings by 200 million years. [19] In his 2019 article 'Cambrian Chordates and Vetulicolians', McMenamin described Shenzianyuloma yunnanense, a new genus and species of Vetulicolia interpreted as bearing myotome cones, a notochord, and gut diverticula in its posterior section. [20]
In an attempt to explain the unprecedented and rapid spread of vegetation over dry land surfaces during the middle Paleozoic, Mark and Dianna McMenamin proposed the Hypersea Theory. [9] Their Hypersea is a geophysiological entity consisting of eukaryotic organisms on land and their symbionts. By means of a process known as hypermarine upwelling, the expansion of Hypersea led to a dramatic increase in global species diversity and a one hundred-fold increase in global biomass. [21] [22] Mark McMenamin's Hypertopia Option has been called one of only two "means by which planetary temperature can be stabilized." [23]
Mark McMenamin has repeatedly criticized conventional Neodarwinian theory as inadequate to the task of explaining the evolutionary process. Joining with Lynn Margulis and the Russian symbiogeneticists, McMenamin has argued that symbiogenesis theory is important as one means of addressing the gap in our understanding of macroevolutionary change in conventional Neodarwinian terms. [24]
In 1996, McMenamin proposed that Phoenician sailors discovered the New World c. 350 BC. [25] The Phoenician state of Carthage minted gold staters in 350 BC bearing a pattern in the reverse exergue of the coins, which McMenamin interpreted as a map of the Mediterranean with the Americas shown to the west across the Atlantic. [25] [26] McMenamin later demonstrated that other (base metal) coins found in America were modern forgeries. [27]
Mark McMenamin and Dianna Schulte McMenamin argued that a formation of multiple ichthyosaur fossils (belonging to the genus Shonisaurus ) placed together at Berlin–Ichthyosaur State Park may represent evidence of a gigantic cephalopod or Triassic kraken that killed the ichthyosaurs and intentionally arranged their bones in the unusual pattern seen at the site. [28] [29]
Opponents have challenged the theory as too far-fetched to be credible. [30] [31] PZ Myers believes that a much simpler explanation is that the rows of vertebral discs may be a result of the ichthyosaurs having fallen to one side or the other after death and rotting in that position, while Ryosuke Motani, a paleontologist at the University of California, Davis, has alternately proposed that the bones may have been moved together by ocean currents because of their circular shape. [32] McMenamin has dismissed both of these concerns as not being in accord with either the sequence of bone placement or the hydrodynamics of the site. [33]
Mark and Dianna McMenamin presented new evidence favoring the existence of the hypothesized Triassic kraken on October 31, 2013 at the Geological Society of America annual meeting in Denver, Colorado. [34] Paleontologist David Fastovsky critiqued McMenamin's argument, saying that the fossil fragment used as evidence was too small to determine its origin and that the argument about currents didn't take into account the lack of knowledge about currents at the time and what would be needed to move the vertebrae. Fastovsky stated that the most likely scenario was one in which, once the tendons and ligaments holding the vertebrae together are gone, the vertebral column "sort of starts to fall over almost like a row of dominoes" with the most likely configuration for that to be the assemblage found. [35] Adolf Seilacher has noted that this ichthyosaur bone arrangement "has never been observed at other localities". [36]
In 2023, McMenamin described a fossil that he interpreted as upper beak rostrum of a large cephalopod and estimated total length of this animal at 28.6 metres (94 ft). Based on the morphology of the fossil, McMenamin rejected previous interpretation of the fossil as part of the hinge of a ramonalinid clam. [37]
Year | Title | Role | Notes |
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2006 | Naked Science--Colliding Continents | Miscellaneous Crew, Himself | National Geographic |
2007 | How the Earth Was Made | Himself | History Channel |
2013 | America Unearthed | Himself | Committee Films TV Documentary |
The Ediacaran is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.
The PaleozoicEra is the first of three geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic and ends 251.9 Ma at the start of the Mesozoic Era. The Paleozoic is subdivided into six geologic periods, Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. Some geological timescales divide the Paleozoic informally into early and late sub-eras: the Early Paleozoic consisting of the Cambrian, Ordovician and Silurian; the Late Paleozoic consisting of the Devonian, Carboniferous and Permian.
Dickinsonia is a genus of extinct organism, most likely an animal, that lived during the late Ediacaran period in what is now Australia, China, Russia, and Ukraine. It is one of the best known members of the Ediacaran biota. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth has been considered consistent with a stem-group bilaterian affinity, though various other affinities have been proposed. It lived during the late Ediacaran. The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal, though these results have been questioned.
Ausia fenestrata is a curious Ediacaran period fossil represented by only one specimen 5 cm long from the Nama Group, a Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. It has similarity to Burykhia from Ediacaran (Vendian) siliciclastic sediments exposed on the Syuzma River of Arkhangelsk Oblast, northwest Russia. This fossil is of the form of an elongate bag-like sandstone cast tapering to a cone on one end. The surface of the fossil is covered with oval depressions ("windows") regularly spaced over the surface in the manner of concentric/parallel rows. The taxonomic identity of Ausia is unresolved.
A trace fossil, also known as an ichnofossil, is a fossil record of biological activity by lifeforms but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or by mineralization. The study of such trace fossils is ichnology - the work of ichnologists.
The Doushantuo Formation is a geological formation in western Hubei, eastern Guizhou, southern Shaanxi, central Jiangxi, and other localities in China. It is known for the fossil Lagerstätten in Zigui in Hubei, Xiuning in Anhui, and Weng'an in Guizhou, as one of the oldest beds to contain minutely preserved microfossils, phosphatic fossils that are so characteristic they have given their name to "Doushantuo type preservation". The formation, whose deposits date back to the Early and Middle Ediacaran, is of particular interest because it covers the poorly understood interval of time between the end of the Cryogenian geological period and the more familiar fauna of the Late Ediacaran Avalon explosion, as well as due to its microfossils' potential utility as biostratigraphical markers. Taken as a whole, the Doushantuo Formation ranges from about 635 Ma at its base to about 551 Ma at its top, with the most fossiliferous layer predating by perhaps five Ma the earliest of the 'classical' Ediacaran faunas from Mistaken Point on the Avalon Peninsula of Newfoundland, and recording conditions up to a good forty to fifty million years before the Cambrian explosion at the beginning of the Phanerozoic.
Treptichnus is the preserved burrow of an animal. As such, it is regarded as the earliest widespread complex trace fossil. Its earliest appearance, around 542 million years ago (mya), which was contemporaneous with the last of the Ediacaran biota, is used to help define the dividing line, considered geologically at 541 mya, between the Ediacaran and Cambrian periods. It is last seen in the fossil record during the Cenomanian.
Vendobionts or Vendozoans (Vendobionta) are a proposed very high-level, extinct clade of benthic organisms that made up of the majority of the organisms that were part of the Ediacaran biota. It is a hypothetical group and at the same time, it would be the oldest of the animals that populated the Earth about 580 million years ago, in the Ediacaran period. They became extinct shortly after the so-called Cambrian explosion, with the introduction of fauna forming groups more recognizably related to modern animals. It is very likely that the whole Ediacaran biota is not a monophyletic clade and not every genus placed in its subtaxa is an animal.
Cephalonega stepanovi is a fossil organism from Ediacaran deposits of the Arkhangelsk Region, Russia. It was described by Mikhail A. Fedonkin in 1976
Swartpuntia is a monospecific genus of erniettomorph from the terminal Ediacaran period, with at least three quilted, leaf-shaped petaloids — probably five or six. The petaloids comprise vertical sheets of tubes filled with sand. Swartpuntia specimens range in length from 12 to 19 cm, and in width from 11.5 to 140 cm. The margin is serrated, with a 1 mm wide groove. A 14 mm wide stem extends down the middle, tapering towards the top, and stopping 25 mm from the tip. The stem has a V-shaped ornamentation on it. The original fossils were found at, and named after, the Swartpunt farm between Aus and Rosh Pinah in Namibia. The generic name comes from Swartpunt, meaning black point in reference to the colour of the rocks. The specific name germsi honours Gerard Germs, who studied the Nama formation of geological beds.
The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.
The end-Ediacaran extinction is a mass extinction believed to have occurred near the end of the Ediacaran period, the final period of the Proterozoic eon. Evidence suggesting that such a mass extinction occurred includes a massive reduction in diversity of acritarchs, the sudden disappearance of the Ediacara biota and calcifying organisms, and the time gap before Cambrian organisms "replaced" them. Some lines of evidence suggests that there may have been two distinct pulses of the extinction event, one occurring 550 million years ago and the other 539 million years ago.
The small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.
The Cambrian explosion is an interval of time beginning approximately 538.8 million years ago in the Cambrian period of the early Paleozoic, when a sudden radiation of complex life occurred and practically all major animal phyla started appearing in the fossil record. It lasted for about 13 to 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification in other groups of organisms as well.
Vendoconularia is a genus of Ediacaran organism consisting of a hexagonal cone, which is thought to have housed a tentaculate organism. Three longitudinal bands are interspersed between the six sides of the cone. The discovery of vendoconulariids in Proterozoic strata of Russia confirmed a 1987 prediction that conulariids constituted part of Ediacaran biota.
Paleontology in Nevada refers to paleontological research occurring within or conducted by people from the U.S. state of Nevada. Nevada has a rich fossil record of plants and animal life spanning the past 650 million years of time. The earliest fossils from the state are from Esmeralda County, and are Late Proterozoic in age and represent stromatolite reefs of cyanobacteria, amongst these reefs were some of the oldest known shells in the fossil record, the Cloudina-fauna. Much of the Proterozoic and Paleozoic fossil story of Nevada is that of a warm, shallow, tropical sea, with a few exceptions towards the Late Paleozoic. As such, many fossils across the state are those of marine animals, such as trilobites, brachiopods, bryozoans, honeycomb corals, archaeocyaths, and horn corals.
The Clemente Formation is a geologic formation composed of 210 m (690 ft) of Ediacaran siltstone, sandstone, quartzite, conglomerate, and minor dolomite. It is exposed in the exposed in the area of Cerro Rajon south of Caborca, northern Sonora, Mexico. It contains an oolitic dolomite marker bed correlated with the Johnnie Oolite in Death Valley, California, and preserves an isotopic record of the Shuram excursion.
The Gamuza Formation is a geologic formation in Mexico. It preserves fossils dating back to the Ediacaran period.
The Papalote Formation is a geologic formation in Mexico. It preserves fossils dating back to the Ediacaran period.
The putative Carthaginian coins must now be removed from the body admissible evidence favoring a pre-Columbian transatlantic crossing. It gives me some chagrin to admit this, as I had earlier come out mildly in support of the authenticity of these coins (McMenamin 1999b, 2000a, 2000b). Weak evidence (involving measurements of die axis; the Arkansas coin has a die axis [33 degrees] differing from the Alabama type coins [12 to 20 degrees]) in support of the authenticity of these coins (McMenamin 2000b) is superseded by the strong evidence in the current work.