Pharyngeal Denticles and the Placoderms – #365papers – 2018 – 58

Johanson and Smith, 2005, Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms: Biological Reviews, v. 80, p. 303-345

What’s it about?

This paper presents a detailed discussion of tooth development in fishes. In particular, the authors review the state of knowledge of tooth development in placoderms, among the first of the jawed fishes and now extinct. They also make observations about denticles, tooth-like bumps, on the gill arches of many fishes, including jawless forms, and how the development of these relate the development of teeth and external scales in early fishes. With these details, the authors propose a hypothesis for the origins and development of teeth in placoderms and in modern fishes. Continue reading

What if We’re Wrong About Placoderms? – #365papers – 2018 – 57

Zhu, Yu, Ahlberg, Choo, Lu, Qiao, Qu, Zhao, Jia, Blom, and Zhu, 2013, A Silurian placoderm with osteichthyan-like marginal jaw bones: Nature, v. 502, p. 188-193

What’s it about?

I reported on another paper with Zhu as lead author sometime last week. That paper provided evidence that certain dermal bones (the dentary and maxilla), traditionally viewed as synapomorphies for the crown osteichthyes may also be present in placoderms. This is the first paper in which Zhu reported this observation. Continue reading

Plants and Animals Don’t Respond to Climate Change the Same Way – #365papers – 2018 – 54

Wing and Harrington, 2001, Floral response to rapid warming in the earliest Eocene and implications for concurrent faunal change: Paleobiology, v. 27, p. 539-563

What’s it about?

The Paleocene-Eocene boundary is marked by a period of rapid global warming and co-occuring changes in mammals in response to the warming, including the appearance of seemingly dwarfed species and the rise of important mammal groups like the hoofed mammals and primates. The authors here use fossilized pollen from rocks known to bracket the Paleocene-Eocene boundary and discuss the changes in plants during this important episode of climate change. Continue reading

The Value of Fossils from the Margins of Basins – #365papers – 2018 – 53

Muldoon and Gunnell, 2012, Omomyid primates (Tarsiiformes) from the Early Middle Eocene at South Pass, Greater Green River Basin, Wyoming: Journal of Human Evolution, v. 43, p. 479-511

What’s it about?

Much of this paper is a description of a new species of early primate, along with a description of the primate fauna from South Pass, Wyoming, which is on the edge of the Green River Basin. This particular fauna is important because it is on the edge of a geographical basin, so it includes a mixture of animals that prefer flat plains and those that prefer upland areas. Continue reading

How Do Teeth and Jaws in Placoderms Grow? – #365papers – 2018 – 52

Rucklin, Donoghue, Johanson, Trinajstic, Marone, and Stamponi, 2012, Development of teeth and jaws in the earliest jawed vertebrates: Nature, v. 491, p 748-752

What’s it about?

Using tomographic data, the authors tease the different growth stages of the lower jaws of placoderms apart and show that the development of teeth are separate from the development of the jaw bone itself. Continue reading

How Long Have Sharks Been Shark-y? – #UREES270 – 2018

Coates, Finarelli, Sansom, Andreev, Criswell, Tietjen, Rivers, and La Riviere, 2018, An early chondrichthyan and the evolutionary assembly of a shark body plan: Proceedings of the Royal Society B, v. 285, 20172418

What’s it about?

This paper provides a new description of a 385-million-year-old fish called Gladbachus. This fish has characteristics of what we consider sharks and other characteristics that align it with placoderms and bony fishes. With this new description, the authors do a new cladistic analysis that shows what the primitive shark condition looked like and also shows that an enigmatic group called the Acathodii are likely along the same lineage as sharks. Continue reading

Whence Come the Teeth of Vertebrates? – #365papers – 2018 – 51

Smith, 2003, Vertebrate dentitions at the origin of jaws: when and how pattern evolved: Evolution & Development, v. 5, p. 394-413

What’s it about?

Smith presents an argument that all teeth in vertebrates share a common origin, even though they look remarkably different, using evidence from growth lines in fossils, as well as developmental studies of modern fishes to support this. Continue reading

Wait? What Part of the Pharynx Becomes the Jaw? – #UREES270 – 2018

Cerny, Lwigale, Ericsson, Meulemans, Epperlein, and Bronner-Fraser, 2004, Developmental origins and evolution of jaws: new interpretation of “maxillary” and “mandibular”: Developmental Biology, v. 276, p. 225-236

What’s it about?

Historically, it has been thought that the upper part of the first branchial (gill) arch becomes the upper jaw (maxillary) and the lower part of the first arch becomes the lower jaw (mandibular). By tracing neural crest cells in the embryos of axolotls and chickens, the authors show that both the upper and lower jaws develop from the lower part of the first arch, and that the upper part becomes the trabecular cartilage, which is part of the skull. Continue reading

Waves of Extinction Add Up – #365papers – 2018 – 47

Wang and Zhong, 2018, Estimating the number of pulses in a mass extinction: Paleobiology, 1-20

What’s it about?

The problem with the rock record is that it is incomplete. This means that what was really a gradual extinction could look abrupt, or that a large-scale mass extinction can look like it was spread out. The authors of this paper present a method by which it is possible to determine how many pulses or waves of extinction added up to what we consider a mass extinction. Continue reading