#spec-dinovember

[derived-centrosaur]

Spec-Dinovember Day 21: Sea Cow, a herbivorous marine vertebrate from the Mesozoic

Ceratopsids were geographically limited to only Laramidia but becoming locally abundant there. A single centrosaurine is known from beyond that continent, Sinoceratops zhuchengensis, which had managed to cross Beringia and settle within China. A single chasmosaurine managed to cross into Asia as well, though it came by another route. Bathyceratops vitulus is a marine animal found in the algal forests around Japan. At 4 meters long and 2000kg they are of average size for a ceratopsid. Their proportions however are anything but average: their limbs are short and stocky, while the body and neck have elongated. The tail and frill are exceptionally short and the eyes and antorbital buttress have been elevated. The narial window has become rostrocaudally shortened and dorsally heightened. Unlike most other tetrapods their nostrils have migrated away from the front of the narial window and instead are located at the dorsal peak of it. All are adaptations to their life of bottom walking and punting to the surface. They feed upon the kelp-like algae that grows near the shore and occasionally snack upon mollusks or echinoderms. While their legs are short they are still quite capable of walking ashore, though this primarily only done to sleep and nest. They are social creatures and are rarely seen alone, usually foraging in pods of 2 to 20. Pods belong to larger colonies of hundreds of individuals that will gather upon communal beaches or rocks to sleep and socialize. The ancestor of B. vitulus likely became aquatic in Western Laramidia and from there followed the coast until it reached its current range. The majority of the species is found around Japan with a discontinuous second population around what will become the Kamchatka peninsula. A second species, B. vagrans, is found in the red algae forests around the Meiji and Detroit volcanic islands, though how they crossed so much open ocean to get there remains a mystery.

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It had to be a ceratopsid. 1) they're my favorites. 2) Cows of the Cretaceous? more like Sea Cows of the Cretaceous. 3) there's an argument to be made that whichever chasmosaurine CMN 8547 belongs to was already adapting towards a hippo-like lifestyle (potentially). So a desmostylian-style Chasmosaurus? Sure! that sounds fun!!

[lolpyi]

Spec-Dinovember Day 3 - Fan favorite, a member of an obscure group filling the niche of a much more popular dinosaur.

Now I wouldn't call Miragaia very obscure but I have been planning to draw something like this for a while. Finally seeing Miragaia live its sauropod dreams simply makes me happy, no further thought put into the prompt for the day.

[theenatiornithebandwagon]

Spec-Dinovember

@blue-jayed-dillophosaurus, this goes here too! You can participate here as well

(Also 4 or 5 of these are mine. I created my own 30 day prompt list to submit, and uh… apparently they were picked randomly… as in my things got in there through sheer sample size!)

[derived-centrosaur]

Spec-Dinovember Round-Up

Days 1-10:

Short King Dovahkiin Fan Favorite

Wildest Dream Deep One

Only a Mother Could Love Cliffhanger Floor is lava

Double-Crested Kingdom Behemoth

[derived-centrosaur]

Spec-Dinovember Day 4: Your Wildest Dream, a wild speculative behavior that left no fossil trace

Nearly every extant horned animal keeps their horns for their entire life. Deer grow and shed their antlers every year, though antlers are developmentally and structurally very different from horns. But, there is a singular outlier, the Pronghorn! Pronghorn have horns with deciduous sheathes, and moreover the bony core of the horn has similar texture to those of regular horns. So maybe, just maybe, some ceratopsians bore similarly deciduous sheathes!

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This isn't a behavior per se, but I think it's a pretty wild speculation so I ran with it! I couldn't find much on how pronghorns grow their sheathes (how do they grow the prong?) except for sources more concerned with hunting. Though one of these informed me that the distal curve grows for ~8 weeks, then the straight proximal portion grows for another ~12 weeks. So, I stacked the outline of the horncore 20 times to get the shape of the full sheathe. Also the roughened area anterior to the orbit and below the horncore lined-up nicely for a justifiable place to grow the 'prong' from. In some centrosaurines this area has correlates for a single large scale, though it seems centrosaurines and chasmosaurines may have differed in facial integument, and some ceratopsids lack this rough area entirely so... plenty of space to play around with weird structures! I don't think this is a likely reconstruction, but there is a *very* slim chance it is possible, and that's pretty fun!

[derived-centrosaur]

Spec-Dinovember Day 22: Parody, an incorrect/outdated reconstruction that turns out to be a real creature

The first fossils of Therizinosaurus to be found were the fragmentary remains of three massive claws. Uncertain of what kind of creature they belonged to, they were tentatively hypothesized to be from a large turtle-like reptile. Many further excavations revealed the therizinosaurs and segnosaurs to be the same animals, and that they were very odd theropod dinosaurs. However, a continent away and across the Tethys there would yet be a giant scythe-clawed turtle. Austrochitra maleevii is the largest member of the trionychidae family and one of the largest turtles, matching Archelon in dimensions but falling short in mass. Like the other giant turtles it is marine in habit, natively found within the shallow Eromanga Sea which covers much of Australia in the mid-Cretaceous. They are carnivorous and will attempt to eat just about anything they can catch. Much like their relatives they often wait buried in the seabed for prey to come close. also like their relatives they are capable of gas exchange via the vascularized oral tissue. They are rather swift swimmers if the need arises, occasionally pursuing prey for short bursts if their initial ambush misses. The large claws aid them in digging and tossing sand and mud over themselves when they hide, and in fending off potential predators or rivals. Their range is quite limited as their hunting method requires a loose sediment floor and comparatively shallow water depth. Occasional vagrants can be found out around the coasts of greater Australia, but no permanent populations have been able to establish themselves outside the Eromanga Sea.

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Not a dinosaur this time, but tangentially relevant. I dunno why, but it just felt like it had to be a softshell, and like the family is already named for having 3 claws so... it kinda fits. Australia is a long ways from the original Therizinosaurus locality, but I couldn't just plop this thing back into the Nemegt fauna with how well sampled it is. So I done what I've been doing for all these and trying to think of times and places that are poorly represented. The inland sea has produced the most Mesozoic fossils from anywhere in Australia, but that's just how scrappy most of the fossils of that time are there, so I went with it. Plus I've always just kinda had a soft spot for the dinosaurs of Down-Under ever since seeing the original Walking With Dinosaurs and reading Dinosaurs of Darkness (mine's a 1st edition hardcover, but it appears this 2nd edition has a few new chapters at the end, cool!). Also I don't know anything about turtles, so turtle experts how'd I do?

[derived-centrosaur]

Spec-Dinovember Day 17: Rexy and Blue, tyrannosaurs and maniraptorans swap niches

The earliest stages of the Cretaceous were a time of transition. The conifer and cycad plant communities of the past were being replaced by newly evolved angiosperms. With the change in plants came a change in herbivores and with that too a change in carnivores. Across Laurasia sauropods were disappearing, stegosaurs were supplanted by ankylosaurs, and the old guard of ceratosaurs, carnosaurs, and megalosaurs were being replaced by new clades of coelurosaurs. Much as in the Early and Middle Jurassic, this reshuffling of niches allowed for brief but interesting role reversals. During the Hauterivian stage in central Siberia the small carnivore guild is populated by coelurosaurs and a few odd ceratosaurs. Among this first group are members of the Proceratosauridae, tiny Tyrannosaurs, who primarily prey upon the many local mammals and the occasional early ceratopsian. The apex predator niche is occupied by a gigantic Eudromaeosaur. At just over a ton in mass, it is large enough to prey upon even the relict stegosaurs of the area.

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Utahraptor is really odd in that not only is it the largest dromaeosaur, but its also one of the earliest to show up in the fossil record. It's found in the Yellow Cat member of the Cedar Mountain Formation, with essentially only an unconformity and/or the Buckhorn conglomerate separating it from the Jurassic Morrison Formation. Larger carnosaurs don't appear until further up the strat-column in the Ruby Ranch and Mussentuchit Members. This pattern looks like a local extinction of the Jurassic dinosaurs, and then the dromaeosaurs capitalize and quickly fill the large carnivore niche before being outcompeted by a bigger predator that survived somewhere else. So my starting point for this prompt was to take this pattern and put it somewhere that has Early Cretaceous proceratosaurid tyrannosaurs. Most of that clade is Jurassic aged, though Dilong and Yutyrannus are from the Barremian stage. I went with a Siberian location because Kileskus is Siberian (though from the wrong time frame) and there's fragmentary evidence of possible stegosaurs persisting in paleoarctic latitudes there in the middle Cretaceous. So I split the time difference and put all the taxa there. Plus there was probably a period of glaciation during the Hauterivian stage, so this would've been a chilly place and that's neat.

[derived-centrosaur]

Spec-Dinovember Day 8: The Floor is Lava, a pterosaur with reduced or absent legs

Marevagus prognathops is a highly specialized nyctosaurid that can be found across the Pacific during the Late Creatceous. From Zealandia to Laramidia they use dynamic soaring to cross thousands of miles of open ocean, often riding the wind gradients ahead of storm clouds. Like other nyctosaurs they lack any fingers save for the wing finger, and these along with the entire wing are long and narrow to best fit their preferred flight style. Other nyctosaurs have proportionally small legs, which when paired with their long arms, makes them a bit cumbersome on the ground. Marevagus are extreme long-range specialists, only landing on solid ground to breed and nest, and as such have taken this to the extreme. Their legs are no more than thin bony rods, used mainly to expand and contract their enlarged uropatagium for fine flight maneuvering. They are able to move about if grounded, but they don't move their legs independently, instead both of the legs and the body move altogether, giving them an odd tripod-like gait. They are quite adept at water launching, though this is energy-intensive so they commonly only land on the surface when the wind has calmed and they are waiting for a renewed gust to ride upon. They also hunt upon the wing. Unlike other marine pterosaurs who hunt by diving, dipping, or surface-seizing, Marevagus are the only pterosaurs to engage in surface-skimming. Their lengthened lower jaw is laterally compressed along much of its length to reduce drag. Their jaw-joint and closing muscles, as well as their neck muscles, are all heavily built and beefy to resist the drag experienced when the lower jaw is submerged. The corners of the mouth and beak as well as the tongue are covered in keratinous papillae and serrations that they use to hold fish that have already been caught letting them maximize the amount of time they are skimming when they encounter a school of fish. The main breeding ground for these pterosaurs is upon the Meiji and Detroit volcanic islands, at the head of what will one day become the Hawaiian-Emperor seamount chain.

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I knew what I wanted to do for this prompt from the moment I read it. A legless pterosaur is either spending all its time flying or it's become a Dougal Dixon level creature. Fortunately there are plenty of birds today that spend so much time in flight that their legs have atrophied to the point they can't properly walk: Hummingbirds, swifts, and just about any Procellariiforme that isn't an albatross or giant petrel. Nyctosaurids were the chosen group of pterosaur because they show evidence of a locking mechanism in their wings which when paired with their lack of fingers (the only pterosaurs to do that) they seem to have been the Cretaceous equivalent of petrels and albatrosses. Cool, let's take that to the natural extreme! Also pterosaurs are often shown skim-feeding, but this would 100% rip the jaw off any known pterosaur. The only birds that skim, the genus Rynchops, have very weird beaks, skulls, and eyes in order to feed that way, and no known pterosaur has anything in common with these birds that would even hint at skimming being possible. So naturally that's what I had to have this one do, and it also lets it hunt without landing so even more incentive to ditch the legs. And I figured the fish-storing beak thing of puffins and razorbills would fit here too. Finally, I had a look at the Emperor seamounts to see if any had appeared in the Mesozoic, only the earliest ones seem to have been active by the Late Cretaceous. I wanted to incorporate some volcanic island so that even when the pterosaur lands the floor will still be 'lava'