So, only four days late putting this up. I’ll save the things happening this week for Fridays post, but fear not! Plenty occurred in the paleontological world last week. Some of it’s even non-Mesozoic (gasp!).
The last hurrah of the ichthyosaurs. This group of iconic Mesozoic marine reptiles, who recently starred in TOTW, didn’t quite make it all the way to the K/T party, and went extinct during the late Cretaceous. Traditionally the group has been seen as going out on a bit of a whimper after a lengthy decline from the Jurassic. New work on European ichthyosaurs by Fischer et al has shown that this picture isn’t necessarily correct, with ichthyosaurs showing a pretty stable diversity throughout their existence, at least in Europe.
Stem tetrapods can breathe easy with the news that Polypterus, a basal ray-finned fish, breathes air through its spiracles. These large paired openings on its had have previously been argued to have a use in air breathing, but Graham et al have for the first time demonstrated this to actually be the case. Stem tetrapods (the lineage of fish leading up to terrestrial vertebrates, including our friend Tiktaalik) possessed spiracles which have been linked to the transition to air breathing, and this work supports this argument.
Giant Silesaurids! Silesaurids are a group of Triassic archosaurs thought to be somewhere near the base of the dinosaur lineage, and so are important to understanding early dinosaur evolution. Previously silesaurids have all been fairly small animals, particularly when compared to their later dinosaurian brethren. Barrett et al have, however, described the femur of an unprecedentedly large silesaurid from Tanzania. This specimen, with the catchy name NHMUK R16303, shows that silesaurids gained bigger sizes than previously thought, bigger than some early dinosaurs, with implications for ideas of why and how dinosaurs were so successful.
An ancient seabird has been described from the Palaeocene of New Zealand by Mayr and Scofield, and unlike everything else described from this locality it isn’t a penguin! While I love penguins as much as the next man, this fleshes out the picture of the avian fauna of this area shortly after the K/T extinction. It also continues to expand the picture of the diversity of birds in the Palaeocene, showing that the dinosaurs were still doing pretty well. Extinct indeed.
Fish fingers. For a long time, scientists have been trying to reconcile the digits of tetrapods with fishes’ fins. These two structures that are superficially similar, but frustratingly different in layout. While fossil data has been building up a picture of this transition, ‘evo-devo’ studies have also been providing valuable information. One such recent study, by Woltering et al, suggests that the digits of tetrapods aren’t in fact homologous (ie. evolutionarily the same) to the fin radials in a fishes’fin. This is based upon the expression of Hox genes (genes that dictate the layout of a developing organ) in zebrafish and mice. When Hox genes from the fish were expressed in developing mice, they only affected development in the proximal parts (ie. arm) of the limb, suggesting fish don’t use the ‘digit-causing’ part of their genetic toolkit. This in turn suggests the two structures are not homologous.
- Fischer et al (2014) High diversity in Cretaceous icthyosaurs from Europe prior to their extinction. PLOS One
- Graham et al (2014) Spiracular air breathing in polypterid fishes and its implications for aerial respiration in stem tetrapods. Nature communications.
- Barrett, Nesbitt and Peecook (2014) A large-bodied silesaurid from the Lifua Member of the Manda beds (Middle Triassic) of Tanzania and its implications for body-size in Dinosauromorpha. Gondwana Research.
- Mayr and Scofield (2014) First diagnosable non-sphenisciform bird from the Early Paleocene of New Zealand. Journal of the Royal Society of New Zealand.
- Woltering et al (2014) Conservation and divergence of regulatory strategies at Hox loci and the origin of tetrapod digits. PLOS Biology.