Penny Higgins - Storyteller • Artist • Scientist
Combining Science and Joyful Creativity
What’s it about?
The authors observed the decay to two very similar organisms: amphioxus (Branchiostoma), a chordate, and the ammocoete larva (Lampetra), a vertebrate. It was observed that the distinctive characters that distinguish vertebrates from other chordates very quickly decay after death, resulting in both amphioxus and the ammocoete appearing to be merely stem chordates. Continue reading “Why Can’t We Tell If a Chordate Is a Vertebrate in the Fossil Record? – #365papers – 2018 – 35”
What’s it about?
Modern horses have a single obvious hoof on each lef, which is representative of the third digit – equivalent to our middle finger. The fossil record shows that horses evolved from three-toed ancestors, which themselves evolved from four-toed ancestors, which even further back, came from five-toed ancestors.
In modern horses, the remnants of digits 2 and 4 (our index and ring fingers) are evident as tiny splint bones fused to the cannon bone (third metacarpal or metatarsal) of the leg. The authors use study of limbs of adult, full-term fetal, and early fetal horses. They trace the positions of nerves and blood vessels in the legs of horses, as well as consider the articulation between the horse’s toe bones and carpal-metacarpal joints to show that modern horses retain parts of all five of the original toes that their deep ancestors possessed.Continue reading “Horses Have Five Toes on Each Foot – #365papers – 2018 – 33”
Minot, 1890, The Mesoderm and the Coelom of Vertebrates: The American Naturalist, v. 24, p. 877-898.
What’s it about?
At the start of every vertebrate’s life, they are merely a ball of cells. Then a hollow ball (blastula). Then a ball that’s been punched in on one side (gastrula) with a hole (blastopore). At the gastrula stage, the early embryo is composed of two simple layers. On the outside is the ectoderm (sometimes called entoderm), and on the inside is the endoderm.
A third layer, called the mesoderm, arises in vertebrates and later opens to form the body cavity or coelom (pronounced SEA-lome). The coelom is the open space in which our organs essentially hang. Our stomach, intestines, bladder, heart, lungs, liver, pancreas, etc. are not embedded in our body walls, but float and move relatively freely in the coelom, with some connections (mesentaries) to the body wall to keep everything from falling to the bottom. It’s this arrangement that makes things like laparoscopic surgery possible.
Anyway… At the gastrula ‘hollow ball of cells’ stage of an embryo, somehow mesoderm forms between the ectoderm and the endoderm, then divides to form the coelom and the lining thereof.
This paper looks at embryos of many different vertebrates, from sharks to mammals, to explore the origins of the mesoderm and the coelom.Continue reading “Making The Vertebrate Body Cavity – #365papers – 2018 – 33”
What’s it about?
Some late Cretaceous-aged (AKA Maastrichtian) rocks from Romania contain fossilized soils (paleosols), dinosaur bones and teeth, and dinosaur eggshells. The authors use geochemical analysis, specifically stable isotope analysis, from all of these materials to build a fairly complete picture of what the region was like at the time that those dinosaurs were alive. What they found was that the environment was relatively warm and dry, and that the dinosaurs didn’t appear to utilize different parts of the habitat, but instead lived side-by-side.Continue reading “Interpreting Cretaceous Environments from Multiple Sources – #365papers – 2018 – 32”
What’s it about?
The Jehol Biota is a group of fossils that preserve some of the best examples of feathered dinosaurs available. The fossils come from several localities in the Sihetun area of the Liaoning Province of China. The authors here used three cores collected around the region, plus some study of outcrops, to investigate the relative ages and environments of different parts of the Liaoning Basin.Continue reading “Assigning Age and Environment to Fossil-Bearing Cretaceous Rocks – #UREES270 – 2018”
What’s it about?
Sulfur and iron atoms come in different sizes, called isotopes. The relative amounts of these isotopes can tell us a lot. In this paper, isotopes of sulfur are used to recognize active metabolism of microbes that use sulfur in their metabolic processes. These results, combined with results from isotopes of iron, provide evidence not only of the activities of life, but also show that there was some oxygen in the atmosphere at that time, enough to oxygenate shallow water but not deep water of the ocean.Continue reading “How Can We Know When The Earth’s Atmosphere Became Oxygenated? – #365papers – 2018 – 31”
What’s it about?
Sabertoothed mammals are so named because of their massive, elongate canines. A natural question to ask is, how does it get so long? The major ideas are that the teeth grow for a very long time (which would affect how the animals survived before the teeth were fully grown), that they grew very quickly, or some combination.
The author uses isotopes of oxygen from the tooth enamel of some adult sabertooth tigers (Smilodon fatalis) to estimate how long it tooth the tooth to grow. This he compares with known growth rates and timing of development of modern lions and tigers to see how it compares. Continue reading “Sabertooth, Sabertooth, How Do Your Teeth Grow? – #365papers – 2018 – 30”
What’s it about?
Hyenas break bones with their teeth. Mountain lions do not. If a mountain lion tried to break a bone with its teeth, it is likely to break a tooth instead. Evidence for bone breaking in mammal carnivores is seen in the shape of the jaw and the arrangement of jaw musculature. Based on this, it appears that the fossil carnivore Borophagus was also a bone breaker. The authors here discuss evidence from the microstructure of tooth enamel that shows differences between bone crushing and non bone crushing mammals. They compare the structure of the teeth of Borophagus with these differences to show that Borophagus probably was also a bone crushing carnivore.Continue reading “How Do Hyenas Chew Bones Without Shattering Their Own Teeth? – #365papers – 2018 – 29”
What’s it about?
Animals living in the ground leave traces of their burrows and feeding habits. These traces are called ichnofossils, and speak volumes about the environment in which the organisms lived. In this paper, the authors talk about an ichnofossil called Glossifungites, which are U- or tongue-shaped burrows that were later filled with sediment. The authors discuss how Glossifungites, along side two other trace fossils called Thalassinoides and Teredolites, indicate a region that was eroded off during transgression of an ocean (the movement of the shoreline inland, potentially due to sea level rising).Continue reading “Fossilized Burrows Tell an Environmental Tale – #365papers – 2018 – 28”
What’s it about?
The “Tully Monster” (Tullimonstrum gregarium) is a fossil originally described from Carboniferous coal deposits near Mazon Creek, Illinois. It is also known from localities in western New York State, including Taughannock Falls near Ithaca. There has been a lot of discussion about what the Tully Monster is most closely related to (e.g. worms, arthropods, or vertebrates). In 2016, two papers were published that asserted that Tullimonstrum was a vertebrate. The authors here show why that interpretation is in error.Continue reading “Determining What the “Tully Monster” Really Is – #UREES270 – 2018″
Penny Higgins - Storyteller • Artist • Scientist