Osteichthyans, or bony fishes, comprise two categories, each containing over 32,000 living species: Sarcopterygii (lobe-finned fishes and tetrapods) and Actinopterygii (ray-finned fishes). Nevertheless, actinopterygians have an obscure early evolutionary history. The earliest definitive actinopterygian is the Middle Devonian (Eifelian) Cheirolepis, with earlier candidates generally represented by fragments subject to differing phylogenetic interpretations. By contrast, earliest Devonian deposits yield a diversity of lobe-finned fishes and recent discoveries from China extend their origin into the late Silurian.
The Early Devonian (Lochkovian) Xitun Formation of Yunnan, China, provides remarkable fossils to illustrate the evolutionary origins of individual sarcopterygian lineages, but apparently lacks any actinopterygians. Meemannia is the newest--and least understood--member of this fauna. Represented by four isolated skull roofs and a referred jaw, Meemannia presents an intriguing mosaic of characteristics: histology interpreted as a precursor to the "cosmine" of rhipidistian sarcopterygians (lungfishes plus tetrapods) combined with an undivided braincase and skull roof resembling that of actinopterygians. Previous phylogenetic analyses placed Meemannia as the earliest-diverging sarcopterygian, based on histological features.
It lived millions of years ago and was three times as large as the great white shark: the megalodon. So far its extinction has been explained with the onset of an ice age. However, researchers at the University of Zurich have now come to the conclusion that responsibility for the decline of the monster shark lays not with the climate, but with other species.
Is there anyone out there who doesn't know Jaws, the film about the great white shark and the devastation it wreaked? But there have been even bigger and more dangerous sharks in the past: The largest shark in the history of the planet, Carcharocles megalodon, lived between 23 million and 2.6 million years ago, reaching body lengths of up to 18 meters and probably feeding on marine mammals. Then it became extinct. In the past, climate changes have generally been blamed for its disappearance. Now, for the first time, researchers from the University of Zurich have examined the geographical distribution of the megalodon over time and arrived at the following conclusion: The giant shark became extinct because the diversity of its prey decreased and new predators appeared as competitors.
Fishes have adapted a number of different behaviors to move out of the water, but none have been described as being able to walk on land with a tetrapod-like gait. Here we show that the blind cavefish Cryptotora thamicola walks and climbs waterfalls with a salamander-like diagonal-couplets lateral sequence gait and has evolved a robust pelvic girdle that shares morphological features associated with terrestrial vertebrates. In all other fishes, the pelvic bones are suspended in a muscular sling or loosely attached to the pectoral girdle anteriorly. In contrast, the pelvic girdle of Cryptotora is a large, broad puboischiadic plate that is joined to the iliac process of a hypertrophied sacral rib; fusion of these bones in tetrapods creates an acetabulum. The vertebral column in the sacral area has large anterior and posterior zygapophyses, transverse processes, and broad neural spines, all of which are associated with terrestrial organisms. The diagonal-couplet lateral sequence gait was accomplished by rotation of the pectoral and pelvic girdles creating a standing wave of the axial body. These findings are significant because they represent the first example of behavioural and morphological adaptation in an extant fish that converges on the tetrapodal walking behaviour and morphology.
Due to an incomplete fossil record, little is known about lamniform shark life history from the Early Cretaceous of North America. Recent discoveries have shown that during this time, some lamniformes reached gigantic sizes (greater than 6–8 m in total length) not seen in earlier species. Given the importance of life history to understand how organisms reach such sizes, we conducted an ontogenetic analysis on three very large shark vertebrae, representing a single individual from the Lower Cretaceous (Albian) Duck Creek Formation of Texas. Using three different techniques (computed tomography, histological sectioning, and surface texture analysis), we were able to show that this individual was born at a relatively small size and subsequently grew at rapid rate, achieving a total length of over 6.3 m in approximately 18 years; a rate not observed in any other Cretaceous species. Comparison of the different aging techniques yielded complementary results; however, surface texture analysis produced the most complete ontogenetic record for this specimen. More work is needed to determine broad patterns in the life history evolution of giant Early Cretaceous lamniform sharks.
Evolution is usually thought of as occurring over long time periods, but it also can happen quickly. Consider a tiny fish whose transformation after the 1964 Alaskan earthquake was uncovered by University of Oregon scientists and their University of Alaska collaborators.
The fish, seawater-native threespine stickleback, in just decades experienced changes in both their genes and visible external traits such as eyes, shape, color, bone size and body armor when they adapted to survive in fresh water. The earthquake -- 9.2 on the Richter scale and second highest ever recorded -- caused geological uplift that captured marine fish in newly formed freshwater ponds on islands in Prince William Sound and the Gulf of Alaska south of Anchorage.
The findings -- detailed in a paper available online in the Proceedings of the National Academy of Sciences -- are important for understanding the impacts of sudden environmental change on organisms in nature, says UO biologist William Cresko, whose lab led the National Science Foundation-funded research.
Results from a 15-year study of factors affecting population levels of Eastern brook trout in the face of climate change show that high summer air temperatures have a large influence, in particular on the smallest fry and eggs, which are most important to wild trout abundance in streams.
Co-author Ben Letcher, fisheries biologist at the U.S. Geological Survey and adjunct faculty in environmental conservation at the University of Massachusetts Amherst, says, "It took years of sampling four streams and tracking more than 15,000 individual fish, but we feel we can account for about 90 percent of the yearly variation in abundance. The bottom line is that high summer temperatures are bad. That is unfortunate because summer air temperature is expected to increase with climate change and extreme rain is also expected to increase, especially in the spring when vulnerable eggs are hatching and fry are emerging."
"Those two things are heading in the wrong direction for this particular species," he adds. Letcher and his colleagues predict that if climate warming proceeds as projected and the trout don't evolve, in as soon as 15 years these sentinel fish of cold water streams could be gone from the study stream. "If they can evolve, they may at least double their ability to stay in the stream," he notes.
A fast-growing salmon has become the first genetically engineered animal to be approved for human consumption in the United States.
The decision, issued by the US Food and Drug Administration (FDA) on November 19, releases the salmon from two decades of regulatory limbo. The move was met with swift opposition from some environmental and food-safety groups.
But for advocates of the technology, the decision comes as a relief after a long and vexing wait. They say that it could spur the development of other genetically engineered animals. “It opens up the possibility of harnessing this technology,” says Alison Van Eenennaam, an animal geneticist at the University of California, Davis. “The regulatory roadblock had really been disincentivizing the world from using it.”
The genetically modified fish, called ‘AquAdvantage' salmon, were engineered by AquaBounty Technologies of Maynard, Massachusetts, to express higher levels of a growth hormone than wild salmon. The fish grow to full size in 18 months rather than 3 years.
Previously, giant sharks had only been recovered from rock dating back 130 million years, during the age of the dinosaurs. The largest shark that ever lived, commonly called "Megalodon", is much younger, with an oldest occurrence at about 15 million years ago. This means the new fossils from Texas indicate giant sharks go much further back into the fossil record.
After the generous donation of these fossils and careful study with Dr. John Maisey of the American Museum of Natural History in New York, the team was able to estimate how big the entire sharks would have been by comparison with smaller and more complete fossils of closely related sharks. The results were very impressive.
The size range estimated for these two Texas 'supersharks' was between 18 and 26 feet in length (5.5 to 8 meters). The largest of these specimens was 25% bigger than today's largest predatory shark, the Great White. Although not nearly as large as Megalodon, which might have reached up to 67 feet in length (about 20 meters), the fossil sharks from Texas would have been by far the biggest sharks in the sea.
Romer's Gap, the interval following the end-Devonian extinction event, has been described as a post-extinction trough for vertebrates. It is a time roughly equivalent to the Tournaisian stage of the early Carboniferous and has been characterized by a lull in diversity of survivors. Lungfish typified this description. One species was known from one locality. Recently, a diverse collection of lungfish tooth plates, representing seven new forms, was recovered from new Tournaisian vertebrate localities in northern Britain. They display a range of previously unknown morphologies, with tooth shape and wear patterns not seen in other post-Devonian forms. A comparison of tooth ridge number and tooth ridge angle in lungfishes from the Famennian, Tournaisian and Visean reveals marked differences between late Devonian and early Carboniferous taxa. The most common tooth plate shape in the Famennian is absent from our sample of Tournaisian taxa. Two completely new shapes have evolved, one with a relatively low tooth ridge angle, no greater than 40°, in which most of the tooth ridges are essentially parallel, and the other with a much higher tooth ridge angle of up to 180° where the tooth ridges are highly divergent. This high level of morphological diversity over a narrow time period suggests that, following the end-Devonian extinction, gaps in ecospace left by the extinction of major groups of fishes were exploited by a previously unrecorded radiation of lungfishes. Whilst taxonomic diversity of lungfishes declined following the end-Devonian extinction, recovery and diversification among tooth-plated forms was rapid, and morphological disparity among these forms subsequently increased. Contrary to previous assumptions, morphological disparity among lungfish did not decline until much later in the Carboniferous.
The finding reveals that such eye cells have existed for at least 300 million years, and that the ancient fish they were discovered in likely saw in color, according to the study's scientists.
Human vision depends on pigments that absorb light. These pigments lie inside cells known as rods and cones. Cones are sensitive to color and also help perceive fine detail and rapid changes. Rods are more sensitive to light than cones, but are not sensitive to color, and are responsible for peripheral and night vision. Both rods and cones are found in a layer of tissue in the back of the eye known as the retina. [Vision Quiz: What Can Animals See?]
Myllokunmingia may be one of the earliest known creatures with a backbone, and this creature may have possessed a rudimentary cameralike eye, which suggests vision dates back at least 520 million years. However, much remains unknown about the evolution of vision, since the soft tissue of the eye usually decays rapidly after death.
The fossil record of early vertebrates has been influential in elucidating the evolutionary assembly of the gnathostome bodyplan. Understanding of the timing and tempo of vertebrate innovations remains, however, mired in a literal reading of the fossil record. Early jawless vertebrates (ostracoderms) exhibit restriction to shallow-water environments. The distribution of their stratigraphic occurrences therefore reflects not only flux in diversity, but also secular variation in facies representation of the rock record. Using stratigraphic, phylogenetic and palaeoenvironmental data, we assessed the veracity of the fossil records of the jawless relatives of jawed vertebrates (Osteostraci, Galeaspida, Thelodonti, Heterostraci). Non-random models of fossil recovery potential using Palaeozoic sea-level changes were used to calculate confidence intervals of clade origins. These intervals extend the timescale for possible origins into the Upper Ordovician; these estimates ameliorate the long ghost lineages inferred for Osteostraci, Galeaspida and Heterostraci, given their known stratigraphic occurrences and stem–gnathostome phylogeny. Diversity changes through the Silurian and Devonian were found to lie within the expected limits predicted from estimates of fossil record quality indicating that it is geological, rather than biological factors, that are responsible for shifts in diversity. Environmental restriction also appears to belie ostracoderm extinction and demise rather than competition with jawed vertebrates.
Today, ray-finned fish, which belong to the bony fish, are by far the most biodiverse fish group in both salt- and freshwater. Their spectacular variety of forms ranges from eels, tuna, flounders and angler fish all the way to seahorses. With around 1,100 species, the second most biodiverse group is the cartilaginous fish, which are almost exclusively marine and include sharks, rays and chimaeras. Exactly why bony fish managed to prevail in different habitats is the subject of debate: Do they have a better body plan, which is suited to more ecological niches than that of the cartilaginous fish? Or are other factors involved in their successful distribution? Paleontologists from the University of Zurich now reveal that climate catastrophes in the past played a crucial role in the dominance of ray-finned fish today.
Three chondrichthyan radiations are registered in the Famennian of the Ardenne Massif (Belgium). These radiations are already observed in Morocco and in the Carnic Alps, their acme being related with the early expansa transgression. Comparisons of univariate statistical descriptors like Margalef richness and Shannon–Wiener diversity index show variations between both margins of the Paleotethys, variations interpreted in terms of trophic relationships. The Ardenne area, a northern shallow carbonate platform is characterized during the Famennian by endemic shark taxa with durophagous dentition. The southern open deep-sea area, the Variscan Sea, contains large placoderms probably disclosing a negative feedback on “cladodont” chondrichthyans. This supports the hypothesis that the Armorica platelet behaved like a barrier between the central southern Laurussia and northern Gondwana.
The Devil's Hole pupfish Cyprinodon diabolis has iconic status among conservation biologists because it is one of the World's most vulnerable species. Furthermore, C. diabolis is the most widely cited example of a persistent, small, isolated vertebrate population; a chronic exception to the rule that small populations do not persist long in isolation. It is widely asserted that this species has persisted in small numbers (less than 400 adults) for 10 000–20 000 years, but this assertion has never been evaluated. Here, we analyse the time series of count data for this species, and we estimate time to coalescence from microsatellite data to evaluate this hypothesis. We conclude that mean time to extinction is approximately 360–2900 years (median 410–1800), with less than a 2.1% probability of persisting 10 000 years. Median times to coalescence varied from 217 to 2530 years, but all five approximations had wide credible intervals. Our analyses suggest that Devil's Hole pupfish colonized this pool well after the Pleistocene Lakes receded, probably within the last few hundred to few thousand years; this could have occurred through human intervention.
Sharks are one of the most threatened groups of marine animals worldwide, mostly owing to overfishing and habitat degradation/loss. Although these cartilaginous fish have evolved to fill many ecological niches across a wide range of habitats, they have limited capability to rapidly adapt to human-induced changes in their environments. Contrary to global warming, ocean acidification was not considered as a direct climate-related threat to sharks. Here we show, for the first time, that an early ontogenetic acclimation process of a tropical shark (Chiloscyllium punctatum) to the projected scenarios of ocean acidification (ΔpH = 0.5) and warming (+4°C; 30°C) for 2100 elicited significant impairments on juvenile shark condition and survival. The mortality of shark embryos at the present-day thermal scenarios was 0% both at normocapnic and hypercapnic conditions. Yet routine metabolic rates (RMRs) were significantly affected by temperature, pH and embryonic stage. Immediately after hatching, the Fulton condition of juvenile bamboo sharks was significantly different in individuals that experienced future warming and hypercapnia; 30 days after hatching, survival rapidly declined in individuals experiencing both ocean warming and acidification (up to 44%). The RMR of juvenile sharks was also significantly affected by temperature and pH. The impact of low pH on ventilation rates was significant only under the higher thermal scenario. This study highlights the need of experimental-based risk assessments of sharks to climate change. In other words, it is critical to directly assess risk and vulnerability of sharks to ocean acidification and warming, and such effort can ultimately help managers and policy-makers to take proactive measures targeting most endangered species.
About 400 million years ago a group of fish began exploring land and evolved into tetrapods – today's amphibians, reptiles, birds, and mammals. But just how these ancient fish used their fishy bodies and fins in a terrestrial environment and what evolutionary processes were at play remain scientific mysteries.
Researchers at McGill University published in the journal Nature, turned to a living fish, called Polypterus, to help show what might have happened when fish first attempted to walk out of the water. Polypterus is an African fish that can breathe air, 'walk' on land, and looks much like those ancient fishes that evolved into tetrapods. The team of researchers raised juvenile Polypterus on land for nearly a year, with an aim to revealing how these 'terrestrialized' fish looked and moved differently.
"Stressful environmental conditions can often reveal otherwise cryptic anatomical and behavioural variation, a form of developmental plasticity", says Emily Standen, a former McGill post-doctoral student who led the project, now at the University of Ottawa. "We wanted to use this mechanism to see what new anatomies and behaviours we could trigger in these fish and see if they match what we know of the fossil record."
Two incomplete teeth of the chondrichthyan genus Edestus are reported. They were collected fromthe Gray Mesa Formation (Pennsylvanian, late Desmoinesian), Socorro County, New Mexico, in 1996.The better-preserved tooth belongs to Edestus sp. cf. E. heinrichi. The other cannot be identifiedbeyond the generic level. These are the first specimens of the genus known to be reported from NewMexico. The only other specimens known from the Rocky Mountain region are from Colorado. Boththe New Mexico and Colorado collections are from marine limestones. In North America, Edestus ismost common in marine black shales of the Illinois Basin, but to date has not been found in marinegray shales or limestones in the Appalachian Basin. The failure to find Edestus remains in the Appalachian Basin is probably the result of the precise timing and limited extent of marine incursionsinto that region. Edestus might have been less tolerant of restricted marine environments than otherchondrichthyans collected from Pennsylvanian deposits in the Appalachian Basin. The function of thesymphyseal tooth whorls of Edestus is obscure, inasmuch as their convex curvature makes them poorly-adapted to the “scissors” function proposed in some previous studies. Alternatively, it is pro-posed here that Edestus teeth were used to disable prey with a slicing action carried out with a verticalmotion of the head, with jaws fixed relative to each other, and not with a scissors-like action of thejaws moving relative to each other. This hypothesis is supported by the author’s observations of wearand damage on the teeth of the holotype of Edestus newtoni. Helicoprion tooth whorls are similar to those of Edestus in that they contain sharp, serrated tooth crowns along the convex margin of the whorls and extend outside the oral cavity. The whorls might have functioned similarly to the mannerthat is hypothesized for Edestus,that is, to slash prey with a downward motion of the head, with jawsfixed. This proposed similarity in form and function would likely represent convergence
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Stable isotope analysis represents the principal scientific technique used in the reconstruction of ancient human diet. Characterisation of human diet requires that the isotopic baseline is established, i.e. the isotopic signals of consumed food groups. However, cooking may alter the bulk isotopic signal of food groups through the selective loss of macronutrients or biochemical components with different isotopic signals. In this study, we investigate the influence of cooking on the stable isotope values of raw flesh of two fish species (mackerel, with a high fat content, and haddock, having a low fat content) using three potential prehistoric cooking methods. The fish were boiled in a pot, grilled beside an open fire, and steamed in hot sand. Cooking times and temperatures were monitored. Stable isotope ratios (δ13C and δ15N) were measured on multiple fractions (bulk flesh, lipids, lipid-extracted flesh, water-extracted flesh, water-soluble compounds, and fish-bone collagen) before and after cooking. The results show that, for some fractions, cooking modified the composition, but changes in isotopic values relative to raw fish were in general less than 1‰. The results also show that isotopic signals of fish-bone collagen were not significantly altered during cooking, and confirm previous findings that showed significant isotopic offsets between fish-bone collagen and edible fish fractions.
An apparent absence of Silurian fishes more than half-a-metre in length has been viewed as evidence that gnathostomes were restricted in size and diversity prior to the Devonian. Here we describe the largest pre-Devonian vertebrate (Megamastax amblyodus gen. et sp. nov.), a predatory marine osteichthyan from the Silurian Kuanti Formation (late Ludlow, ~423 million years ago) of Yunnan, China, with an estimated length of about 1 meter. The unusual dentition of the new form suggests a durophagous diet which, combined with its large size, indicates a considerable degree of trophic specialisation among early osteichthyans. The lack of large Silurian vertebrates has recently been used as constraint in palaeoatmospheric modelling, with purported lower oxygen levels imposing a physiological size limit. Regardless of the exact causal relationship between oxygen availability and evolutionary success, this finding refutes the assumption that pre-Emsian vertebrates were restricted to small body sizes.
Knowledge of the early evolution of fish largely depends on soft-bodied material from the Lower (Series 2) Cambrian period of South China. Owing to the rarity of some of these forms and a general lack of comparative material from other deposits, interpretations of various features remain controversial, as do their wider relationships amongst post-Cambrian early un-skeletonized jawless vertebrates. Here we redescribe Metaspriggina on the basis of new material from the Burgess Shale and exceptionally preserved material collected near Marble Canyon, British Columbia and three other Cambrian Burgess Shale-type deposits from Laurentia. This primitive fish displays unambiguous vertebrate features: a notochord, a pair of prominent camera-type eyes, paired nasal sacs, possible cranium and arcualia, W-shaped myomeres, and a post-anal tail. A striking feature is the branchial area with an array of bipartite bars. Apart from the anterior-most bar, which appears to be slightly thicker, each is associated with externally located gills, possibly housed in pouches. Phylogenetic analysis places Metaspriggina as a basal vertebrate, apparently close to the Chengjiang taxa Haikouichthys and Myllokunmingia , demonstrating also that this primitive group of fish was cosmopolitan during Lower–Middle Cambrian times (Series 2–3). However, the arrangement of the branchial region in Metaspriggina has wider implications for reconstructing the morphology of the primitive vertebrate. Each bipartite bar is identified as being respectively equivalent to an epibranchial and ceratobranchial. This configuration suggests that a bipartite arrangement is primitive and reinforces the view that the branchial basket of lampreys is probably derived. Other features of Metaspriggina, including the external position of the gills and possible absence of a gill opposite the more robust anterior-most bar, are characteristic of gnathostomes and so may be primitive within vertebrates.
