Those of us who love dinosaurs know that there is something poetic about these animals – the spectacular size of some, their amazing variety, the mysteries of their long life on this planet . We still feel a thrill when we envision the fantastic beasts and we sometimes find ourselves drifting into a reverie in which we imagine the world under their 140 million-year domination. We can almost see, in our mind’s eye, the graceful long-necked sauropods nibbling the trees and shrubs, the stalking bipedal, sharp-toothed theropods tall and small, and the horned, crested, and armored herbivores wandering the landscape.
Our endless willingness to imagine the great beasts, and our persistent desire to learn more about them, is catered to by a growing variety of mass market books that aim to help us understand their biology and the ecosystems in which they lived. One of the best recent additions to this library, by the British paleontologists Darren Naish (author of the popular Tetrapod Zoology blog) and Paul Barrett (of London’s Natural History Museum), stands out for its depth and its wide-ranging look at dinosaurs’ anatomy, behavior, diversity, and evolution.
The book, Dinosaurs: How They Lived and Evolved, starts with a look at some basic biological principles and the history of dinosaur discoveries. Readers are provided a cogent overview of Earth’s geology and climate during the Mesozoic era, the value of cladistics as a tool to make sense of dinosaur variety, and the place of dinosaurs in the larger group of animals known as archosaurs.
Naish and Barrett then move on to a helpful explanation of the relationships among dinosaur species and a detailed look at dinosaur skeletal systems.
This discussion shines for its skillful and picturesque descriptions of the major dinosaur groups. The authors focus not just on the famous Saurischians and Ornithiscians; they take the reader into a just-deep-enough examination of the clades into which these groups are divided.
In the third section of the book Naish and Barrett shift to an examination of scientists’ current understanding of the deeper aspects of dinosaur biology: their diets, their mating habits, the intricacies of their movement, and their social behaviors. This part of the book is a smorgasbord of insights into how fossils, both trace and body, teach us about the structure of an animal’s life.
Next we are presented with a thorough discussion of modern dinosaurs. Here Naish and Barrett not only delve into the ways in which avian anatomy resembles that of their coelurosaur cousins, but also explain the current understanding of feather origins and the genesis of flight.
In the book’s final section Naish and Barrett, after a review of the impact by an asteroid or comet and its consequences for dinosaurs and their world, highlight another possible contributor to the Mesozoic terminus: active volcanoes around the planet.
The authors explain that, notwithstanding the ecological catastrophe that essentially ended their long reign over the planet’s biosphere (an incident known as the K-Pg event), dinosaurs may have been experiencing both climate change and a loss of diversity at the time it occurred. They take pains to emphasize that, contrary to popular myth, some dinosaurs did survive the end of the Cretaceous period. We know them, of course, as the birds.
Gracing the text are numerous photographs, graphs, and computer-generated reconstructions. Naish and Barrett did not, though, include citations to scientific papers or a bibliography.
Dinosaurs: How They Lived and Evolved is ideal for readers that have some basic familiarity with the biological sciences, though detailed knowledge is not required to enjoy the book.
Published by Smithsonian Books and carrying a cover price of $29.95, the book is a worthy and entertaining read for all of us who continue to be fascinated by the dinosaurs.
NOTE: This reviewer obtained a copy of Dinosaurs: How They Lived and Evolved on loan from the Arapahoe Library District. He was not asked by any publisher or author to prepare this review and has not been compensated for it.
Paleontologists have identified an ancestor of modern spiders that lived before the dinosaurs began their long domination of the planet.
The arachnid’s fossil remains were found during the mid-1970s in Europe embedded in an iron-rich mineral, siderite, that is difficult for x-rays to penetrate. Researchers used a synchotron, which emits more powerful x-rays, to identify the organism.
Named Idmonarachne brasieri, the organism was likely a member of a group of arachnids called uraraneids. These animals lacked spinarets, which modern spiders use to spin webs, and instead would have discharged silk in sheets.
“Our new fossil occupies a key position in the evolution of spiders,” Dr. Russell Garwood of the University of Manchester, the lead author of a paper documenting the discovery, said. “It isn’t a true spider, but has given us new information regarding the order in which the bits of the anatomy we associate with spiders appeared as the group evolved.”
Scientists know little of the origin of spiders and the evolutionary path by which such anatomical features as spinarets formed is not well understood.
The paper appears in the March 30 edition of Proceedings of the Royal Society B.
Scientists have found evidence that a ocean-dwelling crocodile about 10 meters long once roamed the area we now know as north Africa.
The beast, which also likely weighed at least three tons, lived about 120-130 million years ago.
Dubbed Machimosaurus rex, the crocodile is the largest known of its kind. A marine reptile, it thrived at a time in Earth’s geologic history when the land now known as north Africa was submerged under an ocean.
Researchers discovered the species in 2014 when a skull measuring almost two meters in length was unearthed in Tunisia. The specimen has teeth that are are shaped like bullets, which the creature may have used to crush the carapaces of marine turtles.
The length of the animal is an estimate, based on the dimensions of similar organisms within the animal’s genus that lived during the Jurassic and Cretaceous periods.
“We have been digging in that area since 2011 because the rocks there are nothing like other places,” Federico Fanti, a paleontologist at the University of Bologna in Italy and lead author of the paper documenting the find, said in a statement. “Globally, good fossils are rare from this age—130 million years ago.”
Fanti and his team later found more of the specimen, including vertebrae, but were not able to remove those parts of the fossil because of ongoing unrest in the country.
The species is part of a larger genus that was first discovered in the nineteenth century. Among M. rex‘s close relatives are crocodilians that roamed Jurassic and Cretaceous period seas that then covered the part of Earth now known as Europe.
M. rex was the largest of the teleosaurids (marine crocodiles) in its genus.
While large, the croc is not the largest known from the planet’s long history of life. At least several species of freshwater crocodile that lived during the time of the dinosaurs, Sarcosuchus imperator and those in the genus Deinosuchus, were more imposing than M. rex.
S. imperator was about two meters longer than M. rex, while some Deinosuchus species may have been only slightly longer than M. rex.
The paper documenting the discovery of M. rex was published online in the Jan. 10, 2016 edition of Cretaceous Research.
This photograph shows the locations of two embryos and one neonate, along with the female ichthyosaur, documented in a new study that indicates marine reptile viviparity may have evolved on land. Image courtesy Ryosuke Motani.
Scientists have discovered a fossil that preserves an infant prehistoric marine reptile in the process of being born, a find that indicates live birth may have first evolved among land-dwelling organisms.
The specimen dates to about 248 million years ago, during the early Triassic period, and is of a female ichthyosaur, along with two embryos and one neonatal individual.
One of the embryos was still inside its mother when death came, another was partially outside the adult individual’s pelvis, and a third was entirely outside its mother.
The position of the embryo that is half-way out of its mother’s body indicates that head-first birth occurred among ichthyosaurs. If so, then the birth may have occurred on land and not in the water, as has generally been presumed by scientists to be likely in the case of early Mesozoic animals.
Viviparity, as live birth of infants is known, has independently evolved across a wide variety of organisms. It is known in fishes, amphibians, reptiles, and mammals and, even among ichthyosaurs, the phenomenon has been observed in fossils dating from the middle Triassic period to the Cretaceous period.
Mosasaurs and plesiosaurs are other Mesozoic era marine organisms that were viviparous. Those reptiles lived during the Cretaceous period.
The fossil preserved individuals of the genus Chaohusaurus would have plied seas near present-day Chaohu and Yuanan, China. The adult specimen was about 100 centimeters long, while the embryos and neonate were about 18 centimeters long.
A paper documenting the fossil discovery appears in the Feb. 14, 2014 edition of PLOS One.
The fossils documented in it are at the Anhui Geological Museum in Hefei City, China.
Paleontologists recently announced their conclusion that a huge predatory carcharodontosaurid roamed land in what is now western North America during the late Cretaceous period, forcing tyrannosaurs – the family of dinosaurs that included Tyrannosaurus rex – to be lesser predators on the prehistoric food chain.
The newly-discovered animal, dubbed Siats meekerorum, lived alongside tyrannosaurids and competed with them for food. It is the third-largest carnivore ever found on the continent.
“It’s been 63 years since a predator of this size has been named from North America,” Lindsay Zanno, a North Carolina State University paleontologist who is the lead author of the paper describing the dinosaur. “You can’t imagine how thrilled we were to see the bones of this behemoth poking out of the hillside.”
The last carcharodontosaurid discovered in North America was found in 1950. Called Acrocanthosaurus, that 40 foot-long dinosaur lived at least 10 million years earlier than Siats meekerorum.
The animal discovered by Zanno and her colleague Peter Makovicky, a paleontologist at Chicago’s Field Museum, would have been about 30 feet long and weighed about four tons.
Its discovery may be the missing piece to a puzzle that has gone unanswered by science for many years: What was the top predator between the time that Acrocanthosaurus went extinct and Tyrannosaurus rex rose to the top of the food chain during the late Cretaceous period?
“The huge size difference certainly suggests that tyrannosaurs were held in check by carcharodontosaurs, and only evolved into enormous apex predators after the carcharodontosaurs disappeared,” Makovicky said.
Zanno and Makovicky found the fossils that were later determined to be those of Siats in Utah’s Cedar Mountain Formation in 2008.
Siats meekerorum is named to honor a family that has supported the research efforts of Field Museum paleontologists.
Artist’s conception of Siats meekerorum by Jorge Gonzales, courtesy North Carolina State University.
Found in the northwest province of Xinjiang, the fossil deposit contains the remains of as many as 1,800 turtles.
The fossils were found in April 2008 in China’s Turpan Basin. The region, which is likely China’s hottest and driest, lies below sea level.
“The area is absolutely desolate with almost no green, but a series of oases are nearby that used to serve as stopping posts along the silk road,” Dr. Walter G. Joyce, a paleontologist affiliated with Germany’s University of Tubingen and Yale University, said in an email response to questions.
The fossils are concentrated within an area of less than a hectare in size. A hectare is equal to 10,000 square meters.
“Some of the shells were stacked up on top of one another in the rock,” Joyce said.
A paleontology graduate student working with Wings on a prospecting expedition unexpectedly found the turtle remains.
“Given that the mesa is rather narrow, a colleague decided to check out the other side and was surprised to see turtles litter the surface,” Joyce said.
Researchers removed a half-meter square block of the rock containing a high concentration of the fossils for study off-site. They photographed the individual fossils contained in it and, from the number of individual remains found, determined that the density of specimens within the bone bed is equal to about 36 per square meter.
Joyce explained that a second area of the bone bed has a lower concentration of fossils and that the team estimated the number of individuals in that section by counting the number of shell pieces found in that area.
“What we got at the end is a conservative estimate,” he said. “It is very likely that many more turtles died at the site!”
Joyce added that the specimens are likely to increase the number of known Jurassic turtle individuals by at least two-fold.
During the Jurassic period, which ended about 145 million years ago, the area of Xingjiang in which the fossils were discovered was verdant, with many lakes and rivers.
Scientists are able to infer the climactic conditions of the area tens of millions of decades ago by closing examining the sediments that surround the fossils. The distinctive red sediments in the particular geologic formation in which the fossils were found indicates that, at the time they were laid down, the climate in the area was seasonally arid.
Joyce clarified that the “characteristic assemblage of plant and animal fossils” and “such rarities as the turtle mass grave we found” also give researchers enough information to support that conclusion.
The rock layer that holds the fossils, called the Qigu Formation, includes the remains of freshwater mollusks, which indicates the area was periodically subjected to river flows or under a lake.
The fossils are not scattered throughout the thickness of the Qigu Formation. According to the paper describing the discovery, the depth of the bone bed does not exceed 20 centimeters.
Wings and Joyce, together with their colleagues, therefore concluded that the turtles likely gathered in a dry lake bed to await rain. When the rain fell, it produced a flood that moved the turtles into one place, where sediment buried them.
“We know from modern semi-tropical areas, regions with dry and wet seasons, that aquatic turtles will accumulate in retreating rivers and ponds as droughts progress and often die when these water dry out completely,” Joyce said. “This is particularly typical for Australia, but also seen in parts of Africa, South America, and even Florida.”
The turtles may belong to a previously unknown species.
“We presume we found a new species, but we are not sure yet,” Joyce said.
The fossils date to the middle Jurassic, about 164 million years ago. The oldest known turtle species dates to about 220 million years ago. Turtles have existed on Earth for a period longer than snakes, lizards, or crocodiles.
Joyce said that the find is likely to help paleontologists gain a greater understanding of Mesozoic turtle diversity.
“We know from living organisms that individuals of some species look very similar, whereas individuals of other species show a lot of variation,” he said. “As a paleontologist, it is therefore always difficult to assess if your fossil looks different from others because it is a new species, or because it is part of an already known, but variable species. With data from the new site we will finally be able to more rigorously assess patterns of diversity of turtles in the Jurassic of Asia.”
Wings and Joyce, together with other scientists, conducted further examination of the specimens and surrounding rock layer on-site in April 2009 and October 2011. Their research was published in the Oct. 21 edition of Naturwissenschaften.
Journal reference: Oliver Wings, Márton Rabi, Jörg W. Schneider, Leonie Schwermann, Ge Sun, Chang-Fu Zhou, Walter G. Joyce. An enormous Jurassic turtle bone bed from the Turpan Basin of Xinjiang, China. Naturwissenschaften, 2012. DOI: 10.1007/s00114-012-0974-5.