Devonian era animals and plants


This video is called Devonian forest.

From LiveScience:

Devonian Period: Climate, Animals & Plants

By Mary Bagley, Live Science Contributor

February 22, 2014 03:46am ET

The Devonian Period occurred from 416 million to 358 million years ago. It was the fourth period of the Paleozoic Era. It was preceded by the Silurian Period and followed by the Carboniferous Period. It is often known as the “Age of Fishes,” although significant events also happened in the evolution of plants, the first insects and other animals.

Climate and geography

The supercontinent Gondwana occupied most of the Southern Hemisphere, although it began significant northerly drift during the Devonian Period. Eventually, by the later Permian Period, this drift would lead to collision with the equatorial continent known as Euramerica, forming Pangaea.

The mountain building of the Caledonian Orogeny, a collision between Euramerica and the smaller northern continent of Siberia, continued in what would later be Great Britain, the northern Appalachians and the Nordic mountains. Rapid erosion of these mountains contributed large amounts of sediment to lowlands and shallow ocean basins.  Sea levels were high with much of western North America under water. Climate of the continental interior regions was very warm during the Devonian Period and generally quite dry.

Marine life

The Devonian Period was a time of extensive reef building in the shallow water that surrounded each continent and separated Gondwana from Euramerica. Reef ecosystems contained numerous brachiopods, still numerous trilobites, tabulate and horn corals. Placoderms (the armored fishes) underwent wide diversification and became the dominant marine predators. Placoderms had simple jaws but not true teeth.  Instead, their mouths contained bony structures used to crush or shear prey. Some Placoderms were up to 33 feet (10 meters) in length. Cartilaginous fish such as sharks and rays were common by the late Devonian. Devonian strata also contain the first fossil ammonites.

By the mid-Devonian, the fossil record shows evidence that there were two new groups of fish that had true bones, teeth, swim bladders and gills. The Ray-finned fish were the ancestors of most modern fish. Like modern fish, their paired pelvic and pectoral fins were supported by several long thin bones powered by muscles largely within the trunk. The Lobe-finned fish were more common during the Devonian than the Ray fins, but largely died out. (The coelacanth and a few species of lungfish are the only Lobe-finned fishes left today.) Lobe-finned fishes had fleshy pectoral and pelvic fins articulating to the shoulder or pelvis by a single bone (humerus or femur), which was powered by muscles within the fin itself. Some species were capable of breathing air through spiracles in the skull. Lobe-finned fishes are the accepted ancestors of all tetrapods.

Plants

Plants, which had begun colonizing the land during the Silurian Period, continued to make evolutionary progress during the Devonian. Lycophytes, horsetails and ferns grew to large sizes and formed Earth’s first forests.  By the end of the Devonian, progymnosperms such as Archaeopteris were the first successful trees. Archaeopteris could grow up to 98 feet (30 meters) tall with a trunk diameter of more than 3 feet. It had a softwood trunk similar to modern conifers that grew in sequential rings. It did not have true leaves but fern-like structures connected directly to the branches (lacking the stems of true leaves). There is evidence that they were deciduous, as the most common fossils are shed branches. Reproduction was by male and female spores that are accepted as being the precursors to seed-bearing plants. By the end of the Devonian Period, the proliferation of plants increased the oxygen content of the atmosphere considerably, which was important for development of terrestrial animals. At the same time carbon dioxide (CO2), a greenhouse gas, was depleted from earlier levels. This may have contributed to the cooling climate and the extinction event at the end of the Devonian.

Animals

Arthropod fossils are concurrent with the earliest plant fossils of the Silurian. Millipedes, centipedes and arachnids continued to diversify during the Devonian Period. The earliest known insect, Rhyniella praecusor, was a flightless hexapod with antennae and a segmented body. Fossil Rhyniella are between 412 million and 391 million years old.

Early tetrapods probably evolved from lobe-finned fishes able to use their muscular fins to take advantage of the predator-free and food-rich environment of the new wetland ecosystems. The earliest known tetrapod is Tiktaalik rosae. Dated from the mid-Devonian, this fossil creature is considered to be the link between the lobe-finned fishes and early amphibians. Tiktaalik was probably mostly aquatic, “walking” on the bottom of shallow water estuaries. It had a fish-like pelvis, but its hind limbs were larger and stronger than those in front, suggesting it was able to propel itself outside of an aquatic environment.  It had a crocodile-like head, a moveable neck, and nostrils for breathing air.

Mass extinction

The close of the Devonian Period is considered to be the second of the “big five” mass extinction events of Earth’s history. Rather than a single event, it is known to have had at least two prolonged episodes of species depletion and several shorter periods. The Kellwasser Event of the late middle Devonian was largely responsible for the demise of the great coral reefs, the jawless fishes and the trilobites. The Hangeberg Event at the Devonian/Carboniferous Boundary killed the Placoderms and most of the early ammonites. Causes of the extinction are debated but may be related to cooling climate from CO2 depletion caused by the first forests. Although up to 70 percent of invertebrate species died, terrestrial plants and animals were largely unaffected by these extinction events.

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How animals learned to eat plants


Right lateral aspect of the skull of a juvenile specimen of Orobates pabsti. Credit: Dr Amy Henrici, Carnegie Museum, Pittsburgh; Photo permission: Dr Thomas Martens, Stiftung Schloss Friedenstein Gotha, Germany

From the University of Lincoln in England:

Land animals kept fish-like jaws for millions of years

09 May 2013 University of Lincoln

Research has confirmed how early land vertebrates, which evolved from fish, developed weight-bearing limbs and other adaptations long before their feeding systems adjusted to a vegetation-based diet.

Now, for the first time, fossil jaw measurements have demonstrated this gap in evolutionary development.

Scientists from the University of Lincoln (UK), the University of Massachusetts, Amherst, and the University of Oxford (UK), examined the lower jaws of 89 fossils of early tetrapods (four-footed animals) and their fish-like predecessors.

The fossils ranged in age from about 300 to 400 million years old and the team were interested in how the mechanical properties of the jaws of these animals differed through time.

They used 10 biomechanical metrics to describe jaw differences. One of these, called mechanical advantage, measured how much force an animal can transfer to its bite.

Dr Marcello Ruta, from the School of Life Sciences, University of Lincoln, said: “Our study is the first of its kind to address changes in biomechanical properties of the lower jaw across the transition from fish to land vertebrates using a diverse range of extinct species. This work paves the way to in-depth analyses of the rates of evolutionary transformation in other anatomical structures during this major episode in vertebrate history. It also lays the foundations for integrative research that explores themes as diverse as the origin of the first terrestrial food webs, the impact of acquisition of new structures on the diversification of major animal groups, and patterns and processes of functional change.”

So it turns out that just moving into a new environment is not always enough to trigger functional adaptations.

The team discovered that the mechanical properties of tetrapod jaws did not show significant changes in patterns of terrestrial feeding until some 40 to 80 million years after the four-legged creatures initially came out of the water. Until then, tetrapod jaws were still very fish-like, even though their owners had weight-bearing limbs and the ability to walk on land.

In the paper, which has been published in an early online edition of the journal Integrative and Comparative Biology, the authors say the results may be explained by an earlier hypothesis: a shift from gilled to lung breathing in later four-footed animals was necessary before they could adapt their jaw structure to eating plants.

This finding suggests tetrapods may have shown a limited variety of feeding strategies in the early phases of their evolution on land.

Lead author Dr Phil Anderson, from the University of Massachusetts, said: “The basic result was that it took a while for these animals to adapt their jaws for a land-based diet. They stayed essentially fish-like for a long time.”

Dr Matt Friedman, lecturer in palaeobiology at the University of Oxford, said: “The thing that is really interesting is that the diversity of jaw function didn’t really take off until around the origin of amniotes – creatures that lay hard-shelled eggs on land rather than being tied to water for reproduction like fishes and amphibians. It is in amniotes and their closest relatives that we see the first evidence for dedicated herbivory – until that point tetrapods had basically been carnivores. So this means it took at least 50 million years of evolution after the origin of features like limbs, fingers and toes before tetrapods achieved dietary diversity that began to resemble what we see today.”

The statistical methods developed in this work could be used in future studies of more subtle biomechanical patterns in fossil animals that may not be initially clear.

Devonian fossil fish discovery in Pennsylvania


This video from the USA is called Phyllolepis thomsoni, a new fossil species of armored fish.

From Drexel University in the USA:

Dusting for prints from a fossil fish to understand evolutionary change

Pennsylvania highway roadcut yields new species of armored fish from Devonian period

PHILADELPHIA (March 27, 2013) — In 370 million-year-old red sandstone deposits in a highway roadcut, scientists have discovered a new species of armored fish in north central Pennsylvania.

Fossils of armored fishes like this one, a phyllolepid placoderm, are known for the distinctive ornamentation of ridges on their exterior plates. As with many such fossils, scientists often find the remains of these species as impressions in stone, not as three-dimensional versions of their skeletons. Therefore, in the process of studying and describing this fish’s anatomy, scientists took advantage of a technique that may look a lot like it was stolen from crime scene investigators.

In the video … Dr. Ted Daeschler shows the fossil and a rubber cast made by pouring latex into its natural impression in the rock. Once the latex hardened, Daeschler peeled it out and dusted its surface with a fine powder to better show the edges of the bony plates and the shapes of fine ridges on the fish’s bony armor – a lot like dusting for fingerprints to show minute ridges left on a surface. With this clearer view, Daeschler and colleagues were better able to prepare a detailed scientific description of the new species.

This placoderm, named Phyllolepis thomsoni, is one of two new Devonian fish species described by Daeschler in the Bicentennial issue of the Proceedings of the Academy of Natural Sciences of Philadelphia, with different co-authors. The other new species is a lobe-finned fish discovered in northern Canada. This discovery is described at http://drexel.edu/now/news-media/releases/archive/2013/March/Fossil-Species-from-Fish-Eat-Fish-World/.

Honoring A Rich History of Pennsylvania Paleontology

Daeschler, a vice president and associate curator at the Academy of Natural Sciences of Drexel University, and an associate professor in Drexel’s College of Arts and Sciences, and co-author Dr. John A. Long, a leading authority on placoderms from Flinders University in Australia, named the species in honor of Dr. Keith S. Thomson.

Thomson, the Executive Officer of the American Philosophical Society, has been a mentor and colleague to many Devonian fossil researchers, including Daeschler. Thomson has formerly held positions including President and CEO of the Academy of Natural Sciences, Director of the Oxford University Museum, and Dean of the Graduate School of Arts and Sciences at Yale University.

Asked for comment on the discovery named in his honor, Thomson noted his long professional connection with the Devonian fossil beds in Pennsylvania that Daeschler studies:

“The Devonian beds around Renovo PA were worked extensively by my old professor at Harvard, Alfred Sherwood Romer and his associates, in the 1950s. They got some very good material of fishes but gave up on the site as a potential source of the very earliest four-legged vertebrates. In 1965 Romer suggested that I have a go but there had been no major erosion on the sites and therefore nothing much new had become exposed. I moved on to other things, but [in 1993] when Ted asked about possible projects in PA I gave him all the old notebooks, including mine, and off he went. In the intervening period there had been some major roadwork, new exposures were made, and on the Sunday evening of his very first weekend trip Ted came to the house and showed me a part of the shoulder of a tetrapod. Once we had looked at every which way and decided there was no other explanation, he causally reached into his bag and said “in that case, I have another one.” The rest is history — a history of very hard, careful, work, a whole team of collectors, some local, and brilliant discoveries of superb material particularly of fishes of every kind. So I am delighted by the success of this work over the past twenty years and flattered to become associated with it by having a species named after me. (There is a certain symmetry to this as long ago I named one of the species that had been collected by Romer after my wife!)”

Ancient Australian fish discovery


Reconstruction of Edenopteron, photo Melissa Adams

From the Australian National University:

Ancient fish species discovered

FRIDAY, 08 MARCH 2013

Researchers from The Australian National University (ANU) working on the New South Wales south coast have discovered a new species of ancient fish, after unearthing the largest fossilised lobe-finned fish skull ever found in rocks of Devonian age. The descendants of these ancient fish evolved into the first land animals.

Dr Gavin Young from the Research School of Earth Sciences and his research team were excavating the skeleton of an extinct armoured fish from 360 million-year-old rock near Eden, NSW, when the bones they uncovered suggested there was more in the site than met the eye.

“As we lifted out the block, we noticed a very large fang, at least 4 cm long,” said Dr Young. “Armoured fish don’t have teeth, so we knew there must be a much larger predator also preserved at the site.

“We uncovered an almost complete skull and shoulder girdle of an enormous lobe-finned fish, with jaws about 48 cm long.”

Preparing the fossil in the ANU laboratory took several years.

“We used traditional methods of acid etching and casting, but also experimented with the latest surface scanning techniques to reconstruct the bones, and used the ANU high resolution CT scanner to investigate the internal structure of the teeth.

“We compared the shape and structure of the preserved bones with about 100 fossil fish species from elsewhere in the world. It turns out that we have not only found a species new to science, but also a new genus of lobe-finned fish, which we have named Edenopteron after the town of Eden,” said Dr Young.

The species name Edenopteron keithcrooki acknowledges Professor Keith Crook of the former ANU Geology Department, who supervised student geological mapping on the NSW south coast over several decades, when many of the important fossil fish sites were discovered. The new species is described today in the international journal PLOS ONE.

The discovery of this new species has implications for the classification of other Devonian lobe-finned fish, says Dr Young.

“This animal had some unusual features compared to Devonian fish fossils from the Northern Hemisphere, including extra bones in its palate, and strange ornamentation on the scales,” said Dr Young.

“These features were first identified in fish fossils from the well-known Canowindra fossil site in central NSW, and we have now found the strange scales at the Jemalong Range near Forbes, and in similar-aged rocks in Australian Antarctic Territory. The Eden site is only the fourth place in the world where Devonian fish show these unusual features,” explained Dr Young.

When Edenopteron was alive, Australia and Antarctica were joined in the great southern supercontinent of Gondwana.

“It’s pretty clear that we had an endemic lobe-finned fish group in this part of the world, and that has very interesting consequences for hypotheses of where the first land animals evolved,” said Dr Young.

The next step for the research team is to continue excavating the site to see if the body of Edenopteron might be preserved deeper in the rock.

“That would be a massive excavation because it would be 2 to 3m long, but would most definitely be an absolutely spectacular find,” said Dr Young.

This work was completed under an ARC Discovery Grant. The article can be accessed here.

Earliest amphibian moved like a seal


Three-dimensional reconstruction of Ichthyostega from μCT scan data. a, Anterolateral view. b, Dorsal view. c, Lateral view. d, Ventral view. The forelimbs and hindlimbs are shown in their resting pose from which ranges of motion were calculated

From Nature:

Vertebral architecture in the earliest stem tetrapods

Nature, (2013) doi:10.1038/nature11825

Published online 13 January 2013

The construction of the vertebral column has been used as a key anatomical character in defining and diagnosing early tetrapod groups1. Rhachitomous vertebrae2—in which there is a dorsally placed neural arch and spine, an anteroventrally placed intercentrum and paired, posterodorsally placed pleurocentra—have long been considered the ancestral morphology for tetrapods1, 3, 4, 5, 6. Nonetheless, very little is known about vertebral anatomy in the earliest stem tetrapods, because most specimens remain trapped in surrounding matrix, obscuring important anatomical features7, 8, 9.

Here we describe the three-dimensional vertebral architecture of the Late Devonian stem tetrapod Ichthyostega using propagation phase-contrast X-ray synchrotron microtomography. Our scans reveal a diverse array of new morphological, and associated developmental and functional, characteristics, including a possible posterior-to-anterior vertebral ossification sequence and the first evolutionary appearance of ossified sternal elements. One of the most intriguing features relates to the positional relationships between the vertebral elements, with the pleurocentra being unexpectedly sutured or fused to the intercentra that directly succeed them, indicating a ‘reverse’ rhachitomous design10. Comparison of Ichthyostega with two other stem tetrapods, Acanthostega7 and Pederpes8, shows that reverse rhachitomous vertebrae may be the ancestral condition for limbed vertebrates. This study fundamentally revises our current understanding11 of vertebral column evolution in the earliest tetrapods and raises questions about the presumed vertebral architecture of tetrapodomorph fish12, 13 and later, more crownward, tetrapods.

From Nature:

Three-dimensional limb joint mobility in the early tetrapod Ichthyostega

Stephanie E. Pierce, Jennifer A. Clack & John R. Hutchinson

Published online 23 May 2012

The origin of tetrapods and the transition from swimming to walking was a pivotal step in the evolution and diversification of terrestrial vertebrates. During this time, modifications of the limbs—particularly the specialization of joints and the structures that guide their motions—fundamentally changed the ways in which early tetrapods could move1, 2, 3, 4. Nonetheless, little is known about the functional consequences of limb anatomy in early tetrapods and how that anatomy influenced locomotion capabilities at this very critical stage in vertebrate evolution.

Here we present a three-dimensional reconstruction of the iconic Devonian tetrapod Ichthyostega and a quantitative and comparative analysis of limb mobility in this early tetrapod. We show that Ichthyostega could not have employed typical tetrapod locomotory behaviours, such as lateral sequence walking. In particular, it lacked the necessary rotary motions in its limbs to push the body off the ground and move the limbs in an alternating sequence. Given that long-axis rotation was present in the fins of tetrapodomorph fishes5, 6, 7, it seems that either early tetrapods evolved through an initial stage of restricted shoulder8, 9 and hip joint mobility or that Ichthyostega was unique in this respect. We conclude that early tetrapods with the skeletal morphology and limb mobility of Ichthyostega were unlikely to have made some of the recently described Middle Devonian trackways10.

Prehistoric mollusk re-created by computer technology


Protobalanus spinicoronatus

From National Geographic:

Prehistoric “Movie Monster” Mollusk Re-created With 3-D Printer

Creature lived about 390 million years ago.

Ker Than

for National Geographic News

Published September 18, 2012

A spiky, well-armored mollusk that lived in the ocean 390 million years ago has been brought back to life with the help of 3-D printers.

Less than an inch long, the oval-shaped creature—a species of so-called multiplacophoran dubbed Protobalanus spinicoronatus—was previously known from only a few rare and incomplete specimens, which made for inaccurate reconstructions.

“The original reconstruction was made where the plates were arranged in a long row, almost like a long worm with 17 plates down its back,” said study co-author Jakob Vinther, a paleontologist at the University of Texas at Austin.

The latest P. spinicoronatus model is based on the most complete known fossil of a multiplacophoran, discovered in 2001 in northern Ohio. Partially covered in rock, the animal’s shell and spikes had become fragmented as it decayed. …

The new model also reveals that P. spinicoronatus was more heavily armored than other mollusks living at the time, and in fact resembled some modern chitons, which live in shallow, exposed environments where there are a lot of predators—as the team believes was the case for the prehistoric mollusk too.

Multiplacophoran’s hunters would likely have included jawed fish and beaked cephalopods similar to squid and octopuses—both of which had recently evolved.

“It was a really exciting time,” Vinther said, “because there was a lot going on.”

The new mollusk model is detailed in the September 18 issue of the journal Paleontology.

See also here.

September 19, Shenzhen, China – An international research team, led by Institute of Oceanology of Chinese Academy of Sciences and BGI, has completed the sequencing, assembly and analysis of Pacific oyster (Crassostrea gigas) genome—the first mollusk genome to be sequenced—that will help to fill a void in our understanding of the species-rich but poorly explored mollusc family. The study, published online today in Nature, reveals the unique adaptations of oysters to highly stressful environment and the complexity mechanism of shell formation: here.

World’s oldest embryo discovered in 380 million year old fish


This is a video of a Dunkleosteus [big placoderm fish] eating a shark.

From Nature:

The oldest pregnant mum

Devonian fossilized fish contains an embryo.

Carina Dennis

Researchers in Australia have uncovered the oldest record of live birth — viviparity — in any vertebrate (see page 650). The discovery of embryos in fossils of placoderms (ancient, armoured, jawed fish) indicates that vertebrates have been copulating and giving birth to live young for at least 380 million years.

“We’ve discovered the world’s oldest [pregnant] mother,” says palaeontologist John Long at Museum Victoria in Melbourne, Australia, who led the study. Previously, the earliest records of viviparity were from marine reptiles from the Jurassic period that date back to around 180 million years ago, he says.

The fossils are from the Gogo Formation, a one-time coral reef in northwest Australia that is renowned for its remarkably well-preserved fish from the Devonian period, some 380 million years ago. The region is tectonically stable, so specimens have been spared the movements of Earth’s plates that often distort fossils. “Gogo fish are three-dimensional, uncrushed, perfect specimens — as if they died yesterday,” says Long. Soft tissues, including muscle and nerve structures, have been reported in Gogo specimens (K. Trinajstic et al. Biol. Lett. 3, 197–200; 2007).

The researchers identified a single embryo in a new Gogo fish genus, and three embryos in a previously described specimen. “When you find a little fish inside a big fish, you tend to think it was dinner,” Long says. But the researchers concluded that the bones were those of embryos, not ingested remains, because they were not crushed or etched by digestive acids. What nailed it, according to Long, was the identification of an umbilical structure and a putative yolk sac.

Palaeontologists will be excited but not completely surprised by the findings, because many suspected that some placoderms fertilized internally. The males of a sub-group of placoderms, called ptyctodontids, have clasper-like appendages dangling from their pelvic fins — these are reminiscent of the claspers of modern sharks that are used to inseminate females.

See also here.

And here.

Devonian actinopterygian phylogeny and evolution based on a redescription of Stegotrachelus finlayi: here.

Helicoprion was a shark-like fish that arose in the oceans of the late Carboniferous 280 million years ago, and eventually went extinct during the early Triassic some 225 million years ago: here.