Penny Higgins - Storyteller • Artist • Scientist
Combining Science and Joyful Creativity
What’s it about?
The authors look closely at the characteristics that distinguish osteichthians from other jawed fishes. They then review materials from fossil groups of fishes, in particular the Acathodii, and score them for the same characters. The result of their analysis is that they place the Acathodii as basal osteichthians, a sister group to the crown osteichthian groups, the Actinopterygii and the Sarcopterygii.Continue reading “Where Did the Bony Fishes Come From? – #UREES270 – 2018”
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 “Pharyngeal Denticles and the Placoderms – #365papers – 2018 – 58”
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 “What if We’re Wrong About Placoderms? – #365papers – 2018 – 57”
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 “The Value of Fossils from the Margins of Basins – #365papers – 2018 – 53”
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 Do Teeth and Jaws in Placoderms Grow? – #365papers – 2018 – 52”
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 “How Long Have Sharks Been Shark-y? – #UREES270 – 2018”
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 “Whence Come the Teeth of Vertebrates? – #365papers – 2018 – 51”
What’s it about?
Fate-maps show where tissues in an embryo wind up in the adult. It is truly remarkable how cells move around in embryos. I mean, seriously.
In this case, the authors are tracing sensory ganglia, in particular, to branches of the trigeminal nerve: the ophthalmic (or profundal) and the maxillomandibular, which provide sensory functions to parts of the lips and mouth.Continue reading “Where, Oh Where Do the Ganglia Go (in Lampreys) – #365papers – 2018 – 50”
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 “Wait? What Part of the Pharynx Becomes the Jaw? – #UREES270 – 2018”
What’s it about?
Placoderms are among the earliest vertebrates to have full-blown jaws. These jaws are develop from cartilagenous precursors that were once gill arches (or may have supported gills – that’s a whole ‘nuther discussion there). In more advanced bony fishes, like the common fishes we keep as pets, there are dermal bones that overlay these cartilagenous precursors: the dentary on the lower jaw and the maxillae over the upper jaw.
Until recently, it was thought that placoderms lacked these dermal bones. This paper is a description of the second species of placoderm that appears to have dentaries and maxillae.Continue reading “Placoderms, Dentary Bones, and the Origin of the Jaw – #UREES270 – 2018”
Penny Higgins - Storyteller • Artist • Scientist