Why Can’t We Tell If a Chordate Is a Vertebrate in the Fossil Record? – #365papers – 2018 – 35

Sansom, Gabbott, and Purnell, 2010, Non-random decay of chordate characters causes bias in fossil interpretation: Nature, v. 463, 797-800.

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”

Horses Have Five Toes on Each Foot – #365papers – 2018 – 33

Solounias, Danowitz, Stachtiaris, Khurana, Araim, Sayegh, and Natale, 2018, The evolution and anatomy of the horse manus with an emphasis on digit reduction: Royal Society Open Science, v 5, 171782.

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”

Interpreting Cretaceous Environments from Multiple Sources – #365papers – 2018 – 32

Bojar, Csiki, and Grigorescu, 2010, Stable isotope dirstibution in Maastrichtian vertebrates and paleosols from the Hateg Basin, South Carpathians: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 293, p. 329-342.

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”

Assigning Age and Environment to Fossil-Bearing Cretaceous Rocks – #UREES270 – 2018

Wang, Olsen, Sha, Yao, Liao, Pan, Kinney, Zhang, and Rao, 2016, Stratigraphy, correlation, depositional environments, and cyclicity of the Early Cretaceous Yixian and ?Jurassic-Cretaceous Tuchengzi formations in the Sihetun area (NE China) based on three continuous cores: Palaeogeography, Palaeoclimatology, and Palaeoecology, v. 464, p. 110-133.

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”

How Can We Know When The Earth’s Atmosphere Became Oxygenated? – #365papers – 2018 – 31

Eickmann, Hofmann, Wille, Bui, Wing, and Schoenberg, 2018, Isotopic evidence for oxygenated Mesoarchaean shallow oceans: Nature Geoscience, v. 11, p. 133–138.

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”

Sabertooth, Sabertooth, How Do Your Teeth Grow? – #365papers – 2018 – 30

Feranec, 2004, Isotopic evidence of saber-tooth development, growth rate, and diet from the adult canine of Smilodon fatalis from Rancho La Brea: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 206, p. 303-310.

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”

How Do Hyenas Chew Bones Without Shattering Their Own Teeth? – #365papers – 2018 – 29

Rensberger and Wang, 2005, Microstructural reinforcement in the canine enamel of the hyaenid Crocuta crocuta, the felid Puma concolor, and the Late Miocene canid Borophagus secundus: Journal of Mammalian Evolution, v. 12, p. 379-403.

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”

Fossilized Burrows Tell an Environmental Tale – #365papers – 2018 – 28

King, Gates, Gingras, Zanno, and Pemberton, 2018, Transgressive erosion expressed as a Glossifungites-bearing woodground: An example from the Blackhawk Formation, Utah: Palaios, v. 22, p. 29-35.

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”

Those Tracks Really Were Made by Feet – #365papers – 2018 – 26

Qvarnstrom, Szrek, Ahlberg, and Niedzwiedzki, 2018, Non-marine palaeoenvironment associated to the earliest tetrapod tracks: Scientific Reports, v. 8, 1074.

What’s it about?

Ichnofossils – the tracks and traces left by the activities of organisms – are some of the oldest evidence of life and certain activities in the rock record. Foot prints, specifically those made on land by animals with toes, are the first evidence of tetrapods, the land-dwelling vertebrates.

It had been argued that footprints from Zachelmie (middle Devonian) weren’t good evidence for land-dwelling vertebrates because they were made in ocean sediments. The authors here show that the rocks are actually deposits of ephemeral lakes, showing that the ichnofossils do represent real land-dwelling vertebrates.Continue reading “Those Tracks Really Were Made by Feet – #365papers – 2018 – 26”

Clarifying Medusaceratops – #365papers – 2018 – 25

Chiba, Ryan, Fanti, Loewen, and Evans, 2017, New material and systematic re-evaluation of Medusaceratops lokii (Dinosauria, Ceratopsidae) from the Judith River Formation (Campanian, Montana): Journal of Paleontology, doi: 10.1017/jpa. 2017.62.

What’s it about?

Medusaceratops lokii was named in 2010 by Ryan, Russell, and Hartman. This new paper revises the description of Medusaceratops using some new fossil material.  With the new description, the authors then do a new analysis of the evolutionary position of Medusaceratops.

Why does it matter?

This revision helps explain some of the unexpected characteristics of Medusaceratops by showing that Medusaceratops had been mis-categorized in the first place. In order to understand how evolution occurs, it’s important to have the relationships among animals in the right order.

Why did I read this?

I was kind of tired of geochemistry papers, so dinosaurs seemed like a good idea.