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

Where, Oh Where Do the Ganglia Go (in Lampreys) – #365papers – 2018 – 50

Modrell, Hockman, Uy, Buckley, Sauka-Spengler, Bronner, and Baker, 2014, A fate-map for cranial sensory ganglia in the sea lamprey: Developmental Biology, v. 385, p. 405-416

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

Squids, and Octopodes, and Nautiluses, Oh My! – #365papers – 2018 – 49

Sanchez, Setiamarga, Tuanapaya, Tongtherm, Winkelmann, Schmidbaur, Umino, Albertin, Allcock, Perales-Raya, Gleadall, Strugnell, Smiakov, and Nabhitabhata, 2018, Genus-level phylogeny of cephalopods using molecular markers: current status and problematic areas: PeerJ v. 6, e4331

What’s it about?

Using DNA sequences, the authors sort out the evolutionary relationships among squids, octopuses, nautiluses, and cuttlefish. 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

We Know Sea Level Rise is Getting Faster – #365papers – 2018 – 48

Nerem, Beckley, Fasullo, Hamlington, Masters, and Mitchum, 2018, Climate-change-driven accelerated sea-level rise detected in the altimeter era: Proceedings of the National Academy of Sciences

What’s it about?

Sea level is rising. In fact, it’s rising faster and faster. Using satellite data, the authors show that this is the case, even when variations from volcanic events and ‘ordinary’ ocean shifts (like El Nino) are taken into account. 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

Footprints Tell a Tale of Everyday Life – #365papers – 2018 – 46

Altamura, Bennett, D’Aout, Gaudzinski-Windheuser, Melis, RAynolds, and Mussi, 2018, Archaeology and ichnology at Gombore II-2, Melka Kunture, Ethiopia: everyday life of a mixed-age hominin group 700,000 years ago: Scientific Reports, v. 8, 2815

What’s it about?

At a 700,000 year old archaeological site, mixed in with the footprints of hippos, birds, and various hoofed mammals are the footprints of people, ranging from adult to toddler. The presence of different ages of humans with evidence of animals and many archaeological specimens tells us that this reflects what everyday life may have looked like for people 700,000 years ago. Continue reading

Sensing Electric Fields: It’s a Vertebrate Thing! – #365papers – 2018 – 45

King, Hu, and Long, 2018, Electroreception in early vertebrates: survey, evidence and new information: Palaeontology, 1-34.

What’s it about?

Electroreception, the ability to detect electric fields such as those generated by other fish swimming nearby, is a common vertebrate ability. It has been argued that bone initially evolved to act as an insulator for electroreceptors to improve their effectiveness. This paper is a review of what the bone evidence for electroreception is, and shows that it appears unlikely that bone evolved first as an insulator in vertebrates. Continue reading

Placoderms, Dentary Bones, and the Origin of the Jaw – #UREES270 – 2018

Zhu, Ahlberg, Pan, Zhu, Qiao, Zhao, Jia, and Lu, 2016, A Silurian maxillate placoderm illuminates jaw evolution: Science, v. 354, p. 334-336.

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