Mounted specimen on display at Dinosaur Kingdom, in Nakasato, Japan 

Reconstruction by Andrey Atuchin

When: Late Cretaceous (~83 to 70 million years ago)

Where: Mongolia 

What: Saichania was an armored plant eating dinosaur that roamed the deserts of Mongolia in the late Cretaceous. It was about 22 ft (~6 meters) long and heavily built. It was more fearsome looking than most armored dinosaurs as it did not just have flat armor plates on its body, but rather was covered with spikes. These dinosaurs were armored all over, there is even evidence of armored eyelids! This suit of armor would have protected Saichania from predators in the late Mesozoic mongolian desert. Fossils are typically found in deserts and badlands worldwide, but typically these areas were very different environments when the species represented by the fossils were alive. The ancient Gobi Desert was much closer to the harsh modern environment than most. Saichania was well adapted for desert life, with its stocky body and teeth designed for grinding the toughest of the desert plants. 

Saichania falls within Ankylosauridae, a group of armored dinosaurs found almost worldwide. It is one of the last and most derived of the ankylosaurids. One good way to differentiate the deserved ankylosaurids from their armored close relatives is the presence of a tail club. Saichania did not have the most massive club known, but it was still a significant feature. Ankylosaurids were one of the dinosaur groups that made it right up to the end of the Cretaceous period, vanishing with the rest of the non-avian dinosaurs. 


Epidexipteryx hui

…is a small species of paravian dinosaur that lived in middle or late Jurassic Asia. E.hui is known from only one well preserved partial skeleton which had four long feathers on the tail, which were composed of a central rachis and vanes. Epidexipteryx was also covered in smaller body feathers which were composed of parallel barbs. However it lacked wing feathers and could not fly, which indicates that unless E.hui evolved from flying ancestors and lost its wings, its tail feathers were advanced display feathers which might have predated flying.



Images: Nobu Tamura and Fucheng Zhang


Pakasuchus - the cat-like crocodile

When: Middle Cretaceous ~ 105 million years ago

Where: Tanzania, Africa

What: A Notosuchia Crocodylomorpha. Crocodiles today are all aquatic, sprawling, and fairly large (the smallest is about 5ft/1.5 meters long). However, fossil crocodiles occupied many niches and had a wide range of body types not seen in living species. A great example is Pakasuchus. This small and agile croc was completely terrestrial and only about the size of a house cat!  Its dentition was also very different from modern crocs. Living crocodiles are all homodont, all of their teeth are fairly similar cones, but Pakasuchus was heterodont like mammals. Its had not only cone like teeth, but also some teeth well suited for shearing and others for crushing and grinding. 

Pakasuchus and the rest of the notosuchians, most of which are cool enough they will be individual highlighted in future posts, are excellent examples of how the fossil record can show us lost diversity within clades that today are fairly homogenous. Crocodile line archosaurs (the clade containing crocs and dinos) were hit hard by the end Cretaceous extinction, with only modern forms surviving.  Its probable Pakasuchus or animals much like it survived to the end of the Cretaceous, even though we only have a handful of fossils from the mid-Cretaceous. Careful inspection of fossil material for distinctive Pakasuchus teeth needs to happen, and will hopefully increase it’s temporal and geographic range. 

My All Yesterday's List!

Here’s a short list of All Yesterday’s inspired behaviour/features I’d love to see depicted at some point and I’ll certainly draw myself once I get a scanner. (I’m picturing these all the dinosaurs some form of integument, by the way. Quills at least.)

  1. Iguanodon’s thumb spike as a tool for stabbing nuts/fruit and getting to edible parts.
  2. Porcupine-quilled, boar-like Heterodontosaurus bullying some nonspecific coelophysoids off a kill.
  3. Shedding Mosasaurus with some fish picking off skin flakes and eating them.
  4. Woolly Polar Triceratops bull with a broken horn fending off a similarly Woolly Tyrannosaurus
  5. Ophiacodon wrestling like Komodo Dragons.
  6. Humpbacked Spinosaurus basking on a riverside near some similarly basking crocs.
  7. Black and white with a blood-red headed Parasaurolophus male with a huge size advantage over a harem of females bullying some of his mates.
  8. Apatosaurus wading into a lake while some ornithopods ride on his back.
  9. A huge, ugly (think the T.rex from Valley of the T.rex) Eustreptospondylus tearing into some rotten icthyosaur carrion on a beach with some Rhamphorynchus trying to nab a few bites.

Anyone who reblogs should add things they’d like to see! I’m sure somebody (Probably me) will draw it eventually! I’d love to hear what people are thinking of.


Sauria is the crown-group of Diapsida and is subdivided into Lepidosauromorpha and Archosauromorpha, comprising a high percentage of the diversity of living and fossil tetrapods. The split between lepidosauromorphs and archosauromorphs (the crocodile-lizard, or bird-lizard, divergence) is considered one of the key calibration points for molecular analyses of tetrapod phylogeny. Saurians have a very rich Mesozoic and Cenozoic fossil record, but their late Paleozoic (Permian) record is problematic. Several Permian specimens have been referred to Sauria, but the phylogenetic affinity of some of these records remains questionable. We reexamine and review all of these specimens here, providing new data on early saurian evolution including osteohistology, and present a new morphological phylogenetic dataset. We support previous studies that find that no valid Permian record for Lepidosauromorpha, and we also reject some of the previous referrals of Permian specimens to Archosauromorpha. The most informative Permian archosauromorph is Protorosaurus speneri from the middle Late Permian of Western Europe. A historically problematic specimen from the Late Permian of Tanzania is redescribed and reidentified as a new genus and species of basal archosauromorph: Aenigmastropheus parringtoni. The supposed protorosaur Eorasaurus olsonifrom the Late Permian of Russia is recovered among Archosauriformes and may be the oldest known member of the group but the phylogenetic support for this position is low. The assignment of Archosaurus rossicus from the latest Permian of Russia to the archosauromorph clade Proterosuchidae is supported. Our revision suggests a minimum fossil calibration date for the crocodile-lizard split of 254.7 Ma. The occurrences of basal archosauromorphs in the northern (30°N) and southern (55°S) parts of Pangea imply a wider paleobiogeographic distribution for the group during the Late Permian than previously appreciated. Early archosauromorph growth strategies appear to be more diverse than previously suggested based on new data on the osteohistology of Aenigmastropheus.

Marine Reptile Month #25 — Vancleavea

Late Triassic period (228-203 mya)

Vancleavea was an unusual late-surviving “non-archosaurian archosauriform”, which basically means it was about as closely related to the archosauria as it’s possible to get without actually being one. 1.2m long (3ft 11in) and covered in overlapping armored scales, its short limbs, deep tail, and upwards-facing nostrils suggest it was a semi-aquatic swimming animal.

Uniquely among all known tetrapods, it also formed its vertical upper tail fin from a row of highly elongated ostederms.

Color palette used: “Shirley the Medium

The Curious Case of Crurotarsi


Redondasaurus at the Carnegie Museum, by the author

Text ahoy.

As I settle into university life for the first time, I take it upon myself in my free time to become better acquainted with the base of the archosaur tree. If you haven’t noticed the blog’s tag by now, it calls out Archosauria (Cope, 1869) by name, establishing the crown-archosaurs as its focus, and although I make obvious digressions to post about other animals now and again (I am a flighty, easily-distracted individual), this is treated as, more or less, gospel. Unfortunately, this maxim implicitly excludes the more basal archosauriforms and archosauromorphs, who reside along the stem of this tree, and which may well have a fair claim to “archosaurishness” themselves.

But I find myself worrying. This limitation omits a variety of fascinating critters from the Permian, the Triassic, and… otherwise. And on top of this, the boundaries of the “true” archosaurs occasionally blur and shift subtly. Case in point…

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Eukaryota Unikonta Opisthokonta Holozoa Filozoa Animlalia Eumetazoa Bilateria Deuterostomia Chordata Cephaloschordata Craniata Vertebrata Gnathostomata Teleostomi Tetrapoda Reptilioporpha Amniota Reptilia Sauropsida Eureptilia Romeriida Diapsida Neodiapsida Archosauromorpha Archosauriforms Crurotarsi Archosauria Avemetatarsalia Ornithodira Dinosauromorpha Dinosauriforms Dinosauria Eusaurischia Theropoda Neotheropoda Averostra Tetanurae Orionides Avetheropoda Coelurosauria Tyrannoraptora Maniraptoriformes Maniraptora Pennaraptora Paraves/Eumaniraptora Avialae Aves Avebrevicauda Pygostylia Ornithothoraces Euornithes Ornithuromorpha Ornithurae Carinatae Neornithes Neognathae Galloanserae Pangalliformes Galliformes Phasianoidea Phasianidae Phasianinae Gallus gallus domesticus