2018 in Stem-Mammals

It’s that time of year again, when everyone does some kind of “year in review” post. I figured I might as well do one for non-mammalian synapsids, a subject which I find interesting that often gets overlooked in favor of dinosaurs.

One of the year’s most remarkable stem-mammal discoveries is the new varanopid Ascendonanus, from the early Permian of Germany. Ascendonanus is the earliest known arboreal animal and is known from numerous specimens with well-preserved soft tissue, showing that varanopids were scaly (Spindler et al. 2018). However, a restudy of the early diapsid Orovenator has led to the discovery that varanopids may be diapsids, not synapsids (Ford and Benson 2018).

The late Permian of Russia has two new predators. Nochnitsa is the most basal gorgonopsian known, and one of the smallest (Kammerer and Masyutin 2018a). The real apex predator of its ecosystem was the much larger Gorynychus, a therocephalian (Kammerer and Masyutin 2018b).

A specimen of the tritylodontid cynodont Kayentatherium was found alongside a clutch of 38 babies, showing that unlike mammals, non-mammaliaform cynodonts were still r-strategists that didn’t invest heavily in parental care (Hoffman and Rowe 2018).

At nearly ten tonnes, Lisowicia, a new dicynodont from the Late Triassic of Poland, is the largest known non-mammalian synapsid and is neck-and-neck with contemporary early sauropods such as Lessemsaurus for being the largest known Triassic land animal (Sulej and Niedźwiezki 2018).

Dicynodonts weren’t just equaling the size of sauropodomorphs, they were living alongside them. A new dicynodont, Pentasaurus, has been discovered in the Lower Elliot Formation, making it a contemporary of early sauropodomorphs such as Melanorosaurus, Blikanasaurus, and “Thotobolosaurus,” and one of the few Late Triassic dicynodonts (Kammerer 2018).

A new edaphosaurid, Gordodon, is the fifth confirmed genus of this group of sail-backed herbivores. It had an unusually long neck for an early synapsid and an almost rodent-like tooth arrangement of incisor-like front teeth and molar-like back teeth, unique among such early land animals (Lucas et al. 2018).

Other discoveries include a new burnetiamorph, Leucocephalus, a new traversodontid cynodont, Siriusgnathus, and another varanopid, Microvaranops.

Best of the year:

  • Best Name: Gorynychus: A name with a double meaning, as an allusion to the dragon of Russian folklore, Zmey Gorynych, and a combination of the English word “gory” with the Greek word “onychus,” meaning “claw.”
  • Weirdest: Ascendonanus, narrowly beating out Gordodon.
  • Awesomest: Lisowicia.
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Revival

Around a year ago, I started this blog to post observations I had on phylogenetics. I never really followed up on that. Life finds a way to get in your way. But here I am now, trying to revive this blog.

I’ve been following paleontology online for years, usually as more of a lurker than a content producer. I sporadically tweet, use Tumblr, and post drawings on DeviantArt, but have never really been as active as I would like. With the doomsayers foreseeing Tumblr’s demise, I figure now is as good of a time as ever to start blogging more actively here.

This time around, I probably won’t stick to any particular theme. I hope to post miscellaneous thoughts paleontological every few weeks, depending on what catches my interest. I guess we’ll just see where this takes me.

The Therapsid Problem

Today I want to talk about one of the more unappreciated areas of phylogenetic uncertainty. Most of the time, you’ll see therapsid phylogeny depicted as a pectinate arrangement of Biarmosuchia, Dinocephalia, Anomodontia, Gorgonopsia, and Therocephalia as successively closer to Cynodontia.

synapsidconsense

This is the phylogeny shown in review papers such as Rubidge and Sidor (2001) and repeated in textbooks such as Kemp (2005) and Benton (2005). Wikipedia uses it. More recently, it has become common to depict it as ambiguous whether anomodonts or gorgonopsians are closer to cynodonts, as in Angielczyk (2009) and this TetZoo article, but the tree remains otherwise the same.

But if you look at the phylogenies in the literature, what do you see?

synapsidphylos

Phylogenies summarized from: A. Cisneros et al. 2015 B. Amson and Laurin 2011. C. Kammerer and Smith 2017. D. Huttenlocker and Sidor 2016.

You see a lot of different topologies, but nothing that matches the traditional arrangement perfectly. In fact, I can’t think of a single paper from the last several years which matches the “consensus” view of therapsid phylogeny—the only one I figured that gets close has anomodonts closer to cynodonts than gorgonopsians, which at least is acknowledged as a possibility in some more recent cladograms. Now, to be fair, some of these cladograms (C and D) are taken from outgroups of phylogenetic analyses that were primarily focused on the internal relationships of one specific group, and might not have had the data to accurately resolve the relationships outside of the group focused on. However, the overall variety in therapsid phylogenies is still interesting. Why is there this lack of consensus?

I’m not sure, and one of my goals going forward with this blog will be to look into just what’s going on here. More as this story develops.

Amson E., Laurin M. 2011. On the Affinities of Tetraceratops insignis , an Early Permian Synapsid. Acta Palaeontologica Polonica 56:301–312. DOI: 10.4202/app.2010.0063.

Angielczyk KD. 2009. Dimetrodon Is Not a Dinosaur: Using Tree Thinking to Understand the Ancient Relatives of Mammals and their Evolution. Evolution: Education and Outreach 2:257–271. DOI: 10.1007/s12052-009-0117-4.

Benton MJ. 2005. Vertebrate palaeontology. Malden, MA: Blackwell Science.

Cisneros JC., Abdala F., Jashashvili T., de Oliveira Bueno A., Dentzien-Dias P. 2015. Tiarajudens eccentricus and Anomocephalus africanus , two bizarre anomodonts (Synapsida, Therapsida) with dental occlusion from the Permian of Gondwana. Royal Society Open Science 2:150090. DOI: 10.1098/rsos.150090.

Huttenlocker AK., Sidor CA. 2016. The first karenitid (Therapsida, Therocephalia) from the upper Permian of Gondwana and the biogeography of Permo-Triassic therocephalians. Journal of Vertebrate Paleontology 36:e1111897. DOI: 10.1080/02724634.2016.1111897.

Kammerer CF., Smith RMH. 2017. An early geikiid dicynodont from the Tropidostoma Assemblage Zone (late Permian) of South Africa. PeerJ 5:e2913. DOI: 10.7717/peerj.2913.

Kemp TS. 2005. The origin and evolution of mammals. Oxford ; New York: Oxford University Press.

Rubidge BS., Sidor CA. 2001. Evolutionary patterns among Permo-Triassic therapsids. Annual Review of Ecology and Systematics 32:449–480.

An Introduction

I think phylogenetics is cool.

Reading phylogeny papers and investigating paleontological phylogenetic analyses are some of my favorite hobbies. I was talking with one of my friends the other day about some of the phylogenetic stuff I was doing, and they told me “you should start a blog,” so here I am!

I’m interested in a lot of different groups of animals phylogenetically, but some of my favorites to study are titanosaurs, Triassic reptiles, and basal therapsids. I’d say theropods, too, but frankly I think the professionals have those covered.

While I did major in biology, I’m not a professional scientist or a grad student. I think I know a lot about phylogenetics, though, and hope I’ll have something meaningful to say.

You can probably expect to see me review published phylogenetic analyses and attempt to code taxa into datasets that they haven’t been before. Maybe I’ll find interesting results along the way.