Wumengosaurus and mesosaurs: how can these two NOT be related?

Figure 1. Wumengosaurus specimens from Wu et al. to scale showing size variety.

Figure 1. Wumengosaurus specimens from Wu et al. scaled to show size variety.

Wumengosaurus, the basal enaliosaur, is known from several sizes (Fig 1). Sometimes that’s not readily apparent when all the images are published at the same size, not to the same scale.

What happens to the skull of Wumengosaurus as it matures (Fig. 2)?

Figure 2. Wumengosaurus in small and large varieties along with Stereosternum and Mesosaurus to scale.

Figure 2. Wumengosaurus in small and large varieties along with Stereosternum and Mesosaurus to scale.

The rostrum doesn’t get relatively longer. The skull becomes relatively smaller.

The relatively small Stereosternum is a sister to Wumengosaurus in the large reptile tree. Their skulls document their similarities, overlooked by Wu et al. (2011) and Jiang et al. (2008). So what if the temporal fenestra disappear in certain (not all) Mesosaurus? That’s just a small number of characters out of a suite of synapomorphies.

References
Jiang D-Y, Rieppel O, Motani R, Hao W-C, Sun Y-I, Schmitz L and Sun Z-Y. 2008. A new middle Triassic eosauropterygian (Reptilia, Sauropterygia) from southwestern China. Journal of Vertebrate Paleontology 28:1055–1062.
Wu X-C, Cheng Y-N, Li C, Zhao L-J and Sato T 2011. New Information onWumengosaurus delicatomandibularis Jiang et al., 2008, (Diapsida: Sauropterygia), with a Revision of the Osteology and Phylogeny of the Taxon. Journal of Vertebrate Paleontology 31(1):70–83.

wiki/Wumengosaurus

The Origin of Rhynchosaurs Revisited

Earlier we looked at the origin of rhynchosaurs. Today, another look.

Figure 1. The best data I have been able to found to document the origin of rhynchosaurs like Scaphonyx and Hyperodapedon. Despite their apparent (from the literature) commonality, there is precious little in the literature about rhynchosaurs.

Figure 1. The best data I have been able to found to document the origin of rhynchosaurs like Scaphonyx and Hyperodapedon, to scale. Despite their apparent (from the literature) commonality, there is precious little in the literature about rhynchosaurs. Lower images from Evans and Jones 2010. I’m a little unsure about the lacrimal on Scaphonyx. Help will be appreciated.

This post was inspired
by learning that Kaikaifilusaurus was conspecific with Priosphenodon (Fig. 1). I was also reviewing the Gauthier et al. (1988) of archosaur traits not shared by lepidosaurs, including the postnarial connection of the nasal and premaxilla. (BTW, Brachyrhinodon and Pleurosaurus (lower right, fig. 1) has this connection while pterosaurs do not.) Here bone colors help tell the story of rhynchosaur origins better than any 1000 words can. The reappearance of the lacrimal, quadratojugal  and socketed teeth are all part of the story. There may also have been a love child produced by the illicit mating of a Priosphenodon with a Mesosuchus. Well, maybe that mystery will be solved when a taxon is found that nests with them.

The reappearance of teeth
on the premaxilla of Mesosuchus documents some sort of legacy genetic code reappearing. So, if this is the case, there was evidently something in the water that permitted the reappearance of several other previously lost traits.

The infilling of the squamosal
on Priosphendon is also an autapomorphy not shared with other rhynchocephalians.

You can look from here to there,
but you won’t find a closer sister taxa among the archosauromorpha that nests more parsimoniously with rhynchosaurs than the rhynchocephalians. If you do, please let me know. In the meantime, the most comprehensive family tree on this subject can be found here.

References
Benton MJ 1983. The Triassic reptile Hyperodapedon from Elgin, functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B, 302, 605-717.
Benton MJ 1990. The Species of Rhynchosaurus, A Rhynchosaur (Reptilia, Diapsida) from the Middle Triassic of England. Philosophical transactions of the Royal Society, London B 328:213-306. online paper
Benton MJ 1985. Classification and phylogeny of diapsid reptiles. Zoological Journal of the Linnean Society 84: 97-164.
Carroll RL 1977. The origin of lizards. In Andrews, Miles and Walker [eds.] Problems of Vertebrate Evolution. Linnean Society Symposium Series 4: 359 -396.
Carroll RL 1988. Vertebrate Paleontology and Evolution. WH Freeman and Company.
Cruickshank ARI 1972. The proterosuchian thecodonts. In Studies in Vertebrate Evolution (ed. Jenkins KA and Kemp TS) 89-119. Edinburgh: Oliver and Boyd.
Dilkes DW 1995. The rhynchosaur Howesia browni from the Lower Triassic of South Africa. Paleontology 38(3):665-685.
Evans S. E. & Jones M. E. H. 2010. The Origin, Early History and Diversification of Lepidosauromorph Reptiles. In Bandyopadhyay S (ed.) New Aspects of Mesozoic Biodiversity,  Lecture Notes in Earth Science 132, 27-44.
GauthierJ, Kluge, AG & Rowe T 1988. The early evolution of the Amniota. pp. 103–155 in Benton, M.J. (ed.), The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds. Oxford: Clarendon Press.
Huxley TH 1869. On Hyperodapedon. Quarterly Journal of the Geological Society, London, 25, 138-152.
Huxley TH 1887. Further observations upon Hyperodapedon gordoni. Quarterly Journal of the Geological Society, London, 43, 675-694.

wiki/Hyperodapedon
wiki/Rhynchosaur

Sometimes the data has to be interpreted…

Yesterday we looked at the reduction of the postorbital and postfrontal in basal cynodonts and their predecessors among the gorgonopsids and theerocephalians. And for those who got there early, a late addition found the missing taxon I was looking for.

Figure 1. Sarctonus data from two different sources -- and they don't quite match.  Here the area at the base of the postorbital is missing, presumed to be squamosal in the lower Bystrow drawing, but never that way in any sister taxa. Upper drawing by Gebauer in two sizes, traced off of mandible and skull, which differ.

Figure 1. Sauroctonus data from two different sources — and they don’t quite match. Here the area at the base of the postorbital is missing — but filled in without being grayed out, presumed to be squamosal in the lower Bystrow drawing, but never that way in any sister taxa. Upper drawing by Gebauer in two sizes, traced off of mandible and skull, which differ in size but at least there is no jugal/squamosal suture shown.  Who knows which is right? Blue color marks typical jugal extent.

Today we’ll look at data that appears great, but a little experience tells you it’s not all there. In Sauroctonus (Fig. 1) it looks like we have a squamosal contributing to the base of the postorbital bar. But sister taxa don’t do that.

Sure, the easy answer is to go visit the specimen
But here I’ve done what I want to do without weeks of planning, a few day’s worth of jetting around, and thousands of dollars in expenses. Does this problem move this taxon up or down the tree a node or two? Doubtful, so why not go with what you’ve got?

Yes, there’s great data and terrible data out there. You have to trust a single source of data, but when given the opportunity to make comparisons, go ahead and test one against the other and their sisters. Sometimes the data is a poor half-a-century-old drawing. Sometimes you take what you can get and make corrections later.

Keep pushing. It will all work out in the end.

References
Bystrow AP 1955. A gorgonopsian from the Upper Permian beds of the Volga. Voprosy Paleont., 2: 7-18.
Gebauer EVI 2007. Phylogeny and Evolution of the Gorgonopsia with a Special Reference to the Skull and Skeleton of GPIT/RE/7113 (‘Aelurognathus?’ parringtoni). PhD Dissertation, Eberhard-Karls University at Tübingen. Online here.

Cynodonts: Where is the postorbital? or is that the postfrontal?

Comparing therapsid skulls shows that basal forms, like the gorgonpsids (Fig. 1) had a postfrontal and postorbital. Derived forms (like Pachygenelus (Fig. 1) had neither. You can see the jugal rise in certain cynodonts, taking over where the postorbital retreated. You can also see either the fusion of the postfrontal and postorbital, or the disappearance of the postorbital (but workers like to label the remaining bone the postorbital even though it is largely a postfrontal). As this all goes into scoring, it’s important to that end.

Figure 1. Several gorgonopsids and cynodonts along with a single therocephalian documenting the disappearance of the postorbital and postfrontal. Pink is the pre parietal, absent in cynodonts. Yellow = prefrontal. Green = postorbital. Blue = jugal.

Figure 1. Several gorgonopsids and cynodonts along with a single therocephalian documenting the disappearance of the postorbital and postfrontal. Pink is the pre parietal, absent in cynodonts. Yellow = prefrontal. Green = postorbital. Blue = jugal.

Not much else today. Just wanted to share this and invite comments. Does anyone know the transitional taxon that might clarify this issue? Likely a basal cynodont, like Charassognathus (Fig. 1). Aelurognathus might have documented something on this subject, but the parts are missing from the fossil. I think we’re looking for a small gorgonopsid or therocephalian to show us, something like Regisaurus (Fig. 1)but more primitive.

All this and more from a PhD study by Gebauer (2007).

Updated the next day, February 16, 2014.

Figure 1. The therocephalian Annatherapsidus documenting a small postfrontal and postorbital documenting a transition at the base of the Cynodontia.

Figure 1. The therocephalian Annatherapsidus documenting a small postfrontal and postorbital on a flat skull identifying this taxon as close to the transition at the base of the Cynodontia. This gives us a better chance that the postorbital fused to the postfrontal.

I just discovered a therocephalian originally named Anna and later renamed Annatherapsidus (Fig. 2) that had a reduced postfrontal and reduced postorbital along with wide temporal fenestra and a rather flat skull, both as in Procynosuchus (Fig.1). This appears to be a transitional taxon, the proximal outgroup to the Cynodontia. And this taxon appears to duplicate the pre-fused shape of the postfrontal/postorbital. 

References
Gebauer EVI 2007. Phylogeny and Evolution of the Gorgonopsia with a Special Reference to the Skull and Skeleton of GPIT/RE/7113 (‘Aelurognathus?’ parringtoni). PhD Dissertation, Eberhard-Karls University at Tübingen. Online here.

Head-first birth in an ichthyosaur – mesosaurs were first with viviparity

Fantastic new fossils
of a head-first live birth in a very basal ichthyosaur, Chaohusaurus (Figs. 1, 2) inspired Motani et al. (2014) to conclude that viviparity in ichthyosaurs (and tetrapods in general, since ichthyosaurs were the last hold out) evolved first on land. They concluded in their abstract, “Therefore, obligate marine amniotes appear to have evolved almost exclusively from viviparous land ancestors. Viviparous land reptiles most likely appeared much earlier than currently thought, at least as early as the recovery phase from the end-Permian mass extinction.” Tail first viviparity is a derived condition in marine reptiles and mammals.

Figure 1. Chaohusaurus embryo at the moment of birth. Nice use of digital coloring here for clarity, even in a perfect fossil like this.

Figure 1. Chaohusaurus embryo at the head-first moment of birth from Motani et al. 2014. Nice use of digital coloring by them for clarity, even in a perfect fossil like this.

Embryo vertebral curling is an issue
Motani et al. report, “The embryos of the sauropterygian Keichousaurus are preserved with their skulls pointing caudally without a clear sign of vertebral curling [7], as in Chaohusaurus. This condition strongly indicates a terrestrial origin of viviparity in Sauropterygia.” and “The presence of curled-up embryos in other Triassic sauropterygians, such as Neusticosaurus and Lariosarus, suggests that the reproductive strategy of these amphibious  marine reptiles may have been variable.” and  “Embryos of the mosasauroid Carsosaurus are preserved curled-up, with their heads inclined cranially. Their tails are positioned more cranially than their respective skulls, making tail-first birth unlikely. They may have been born curled-up, as in some extant lizards that give birth on land.” and  “Hyphalosaurus from the Cretaceous of China is another example of viviparous aquatic reptile, although it lived in freshwater. A case is known where two terminal embryos within the maternal body cavity were straightened while the others still remained curled, most likely in their egg sacs.”

Figure 2. Ichythosaur mothers and embryos from Motani et al. 2014. Red tint added to Chaohusaurus embryo to show connection. Lower derived ichthyosaur is Stenopterygius .

Figure 2. Ichythosaur mothers and embryos from Motani et al. 2014. Red tint added to Chaohusaurus embryo to show connection. Lower derived ichthyosaur is Stenopterygius.

Earlier
Piñeiro et al. (2012)  found curled mesosaur embryos in and out of the body. The large reptile tree found mesosaurs and ichthyosaurs to be closely related and also related to the sauropterygians listed above. So this is about as far back as viviparity originated in that lineage. So Montani et al. (2014) were right. They just needed to know about mesosaurs to  put the cherry on top. Look for viviparity in Wumengosaurus some day. 

References
Piñeiro G, Ferigolo J, Meneghel M and Laurin M 2012. The oldest known amniotic embryos suggest viviparity in mesosaurs, Historical Biology: An International Journal of Paleobiology, DOI:10.1080/08912963.2012.662230
Motani R, Jiang D-Y, Tintori A, Rieppel O and Chen G-B 2014. Terrestrial Origin of Viviparity in Mesozoic Marine Reptiles Indicated by Early Triassic Embryonic Fossils. Plos one. DOI: 10.1371/journal.pone.0088640

Archaeopteryx vs pterosaurs: speciation? or variation? Plus an interclavicle question.

I read this today on Wiki/Archaeopteryx: “Recently, it has been argued that all the specimens belong to the same species, however, significant differences exist among the specimens. In particular, the Munich, Eichstätt, Solnhofen, and Thermopolis specimens differ from the London, Berlin, and Haarlem specimens in being smaller or much larger, having different finger proportions, having more slender snouts lined with forward-pointing teeth, and possible presence of a sternum. These differences are as large as or larger than the differences seen today between adults of different bird species, however, it also is possible that these differences could be explained by different ages of the living birds.”

Figure 1. Archaeopteryx size graphic from Wikipedia.

Figure 1. Archaeopteryx size graphic from Wikipedia created by Matt Martyniuk. Very informative. Size matters!

If that is all that separates one Archaeopteryx from another, it really is time to take another look at pterosaurs.
There are so many Pterodactylus, Pteranodon, Rhamphorhynchus, Germanodactylus, Darwinopterus, etc. etc. etc. that given the same splitting/lumping parameters someone is going to have to come up with a slew of new names.

The problem is, who has the authority?
And if anyone does have the authority, who will recognize, follow and support that authority? That time may have already passed when there were fewer workers setting standards in paleontology. Back in the 1970s the work by Wellnhofer on Solnhofen pterodactyloids (1970) and non-pterodactlyloids (1975) is encyclopedic and widely cited. I’m not sure that someone else in the present day such authority because the professional vacuum that existed then is not present today.

The answer is:
A grad student for his/her PhD dissertation might have no authority, but that doesn’t matter. These least likely candidates are incredibly talented, but largely lacking in experience, which sometimes works to their advantage. And they are always looking for large projects to tackle. This task is enormous and will involve a lifetime of study and restudy. So, maybe the parameters are not narrow enough for a decent thesis.

I suppose lumpers will always fight splitters, and vice versa, like two parents trying to name one child.

>>>>>>>>>

On a side note:
Did early amniotes and their outgroups fuse the coracoid and interclavicle? I am having a difficult time locating coracoids, at the same time that the interclavicle appears to be “amply endowed,” if you know what I mean. Here’s an example in Brouffia: (Fig. 2) and Gephyrostegus (Fig. 3). Please send literature refs if you have them.

Figure 2. Brouffia. Is the coracoid fused to the over robust interclavicle, as it would seem? Lit refs please!

Figure 2. Brouffia. Is the coracoid fused to the over robust interclavicle, as it would seem? Lit refs please!

Figure 3. This Gephyrostegus interclavicle looks suspiciously tripartite. Are coracoids fused here?

Figure 3. This Gephyrostegus interclavicle looks suspiciously tripartite. Are coracoids fused here?

The foot of Archicebus – an early primate

We haven’t looked at mammals or synapsids for awhile.
If you want to check the large reptile tree, they’re still reptiles — just hairier. Todays let’s look at Archicebus (Early Eocene, 55 mya, Ni et al. 2013),  the oldest primate known from a skeleton. Notharctus is 5 million years younger, but more primitive, just as living lemurs are more primitive than modern apes and humans are. Ipso facto, the discovery of Archicebus pushes the origin of lemurs back even further. The younger lemuroid, Smilodectes, had a similar short-snout skull.

Figure 1. Archicebus is close the ancestry of tarsiers and monkeys. It retained a lemur-like foot,

Figure 1. Archicebus is close the ancestry of tarsiers and monkeys. It retained a lemur-like foot, but with distinctly tarsier-like proportions starting to show. Here in a published illustration pedal digit 1 is not illustrated as more robust and the metatarsals are inaccurately similar in length. The size was about that of the smallest living lemur, the pygmy mouse lemur. Moderate size eye sockets are distinct from the giant eye sockets of living nocturnal tarsiers.

My interest in feet
and PILs (parallel interphalangeal lines) goes back a long way (Peters 2000a, 2010, 2011). Pterosaur PILs are instructive, helping flatten or elevate plantigrade and digitigrade pedes. Cats put an interesting twist on PILs due to their retractable claws. Primates do too, because they are adapted to cylindrical substrates (branches), not flat (the ground).

Figure 2. Click to enlarge. The two pedes of Archicebus, bottom sides flipped to match top sides. Toes colorized for reconstruction (Fig. 3).

Figure 2. Click to enlarge. The two pedes of Archicebus, bottom sides flipped to match top sides. Toes colorized for reconstruction (Fig. 3). The talus/astragalus is missing from both pedes.  Note the massive proximal articulation of the big toe.

Nature reports, “By analyzing almost 1,200 morphological aspects of the fossil and comparing them to those of 156 other extant and extinct mammals, the team put the ancient primate near the base of the tarsier family tree.” I haven’t repeated that experiment, buy it looks to me that pedal characters alone would tell the tale Figs. 3,4).

Figure 3. The reconstructed foot of Archicebus alongside that of the basal lemur, Notharctus. Note the gathering of metatarsals 2-4, as in tarsiers.

Figure 3. The reconstructed foot of Archicebus alongside that of the basal lemur, Notharctus. Note the gathering of metatarsals 2-4, as in tarsiers. The missing astragalus/talus sits on top of the calcaneum, a trait first appearing on cynodonts like Probelesodon. I suppose this is an example of modular evolution: first the toes, then the ankle.

Nature reports, “The mammal sports an odd blend of features, with its skull, teeth and limb bones having proportions resembling those of tarsiers, but its heel and foot bones more like anthropoids.” Actually the Archicebus foot is also an “odd blend.” The ankle is short, like that of most other primates (Fig. 3, not just anthropoids). But digit 2 is short and digit 4 is long, like those of tarsiers (Fig. 4). Really it comes down to just these two traits for an accurate nesting of Archicebus. Perhaps an accurate reconstruction would have helped. I took my data (Fig. 1) from online photos of Ni et al. 2014, but I have not seen the paper.

Figure 4. Archicebus pes compared to a living tarsier  pes. Note the elongated proximal tarsals in the tarsier. Archicebus has the elongate digit 3 retained by tarsiers.

Figure 4. Archicebus pes compared to a living tarsier pes. Note the elongated proximal tarsals and shorter metatarsals in the tarsier. Archicebus has the elongate digit 4 and short digit 2 retained by tarsiers. Both of these reconstructions are flattened, which is not the way tarsiers hold their toes (Fig. 5). The lengthening of the ankle makes tarsiers excellent leapers.

PIL continuity
The foot of Archicebus appears to lose the continuity of many PILs (Fig. 4) when laid flat. But that’s not the way tarsiers hold their toes in vivo (Fig. 5). Similarly in the human hand the PILs become more continuous in use, like when you grasp a golf club, hold a baseball bat or make a fist. And, of course, the opposable thumb does not work as part of the lateral four digit sets. It goes its own way.

The elongation of the proximal ankle elements in tarsiers enables them to leap tremendous distances. Archicebus did not have that ability. I suppose Archicebus is an example of modular evolution: first the toes, then the ankle, but, of course, it’s never as simple as that.

Figure 6. The tarsier foot and PILs are shown in action at right angles to the tree cylinder and parallel to the long axis. The use of pads appears to change the way the foot operates, without the strong PILs a grasping or walking foot has.

Figure 5. The tarsier foot and PILs are shown in action at right angles to the tree cylinder and parallel to the long axis. The use of pads appears to change the way the foot operates, without the strong PILs a grasping or walking foot has. The fingers and toes don’t lie flat, but strongly flex at the interphalangeal joints. This messes with PILs that are applied to flat reconstructions (Fig. 3, 4)

Archicebus is well-deserving of its celebrity.
According to Nature, “Because A. achilles sits near the base of the tarsier family tree, scientists say it probably resembles the yet-to-be-discovered creatures that lie at the base of most primate groups — including the anthropoid lineage that ultimately gave rise to humans. “If you retrace primate evolution to its beginning, [A. achilles] is what our ancestors most likely looked like,” says Luo.”

References
Ni X, Gebo DL, Dagosto M, Meng J, Tafforeau P, Flynn JJ, Beard KC 2013. The oldest known primate skeleton and early haplorhine evolution. Nature 498 (7452):60–64.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos, 7: 11-41.
Peters D 2010. In defence of parallel interphalangeal lines. Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605

wiki/Archicebus

Anurognathid eyes: the evidence for a small sclerotic ring

Ever since Bennett 2007, pterosaur workers have been following like sheep to a shepherd and putting a giant sclerotic ring in the antorbital fenestra. That’s a problem. Andres et al. (2010) even reported the confluence of the naris and antorbital fenestra (but to his eye, by placing the sclerotic ring in the antorbital fenestra, there was only one opening ahead of it, the naris). And this he used as a character to unite pterodactyloids with anurognathids in phylogenetic analysis. (I’m not sure it can get any worse than this.)

Figure 1. The flathead anurognathid in visible light (above) and UV (below). Sclerotic rings n pink. Maxillae in blue.

Figure 1. Click to enlarge. The flathead anurognathid in visible light (above) and UV (below). Sclerotic rings n pink. Maxillae in blue. Nasals highlighted in upper left image.

Sclerotic rings are bones formed in the scleral portion of the eyeball. They form a disc around the iris. Then everything rots, they usually fossilize as a ring or the scattered remnants thereof. I have never seen such a ring fossilized standing on edge in a crushed fossil. But this is what you have to believe you get if you follow the Bennett 2007 hypothesis in the flathead anurognathid (Fig. 1, SMNS 81928a & b). Witton, Andres and others bought into this.

When I took a look at that fossil, I found two small sclerotic rings in the back half of the skull (Fig. 1), where they are in all other pterosaurs and anurognathids. What Bennett took to be a giant sclerotic ring on the left is actually the maxilla, convex ventrally. It is difficult to make out the bones of the skull in that fossil, but I have provided a guide here.  Putting the bones back together in a reconstruction seals the deal (Fig. 6). Everything fits and there’s only gradual, not radical, change between sister taxa.

Figure 2. Click to enlarge. Batrachognathus with sclerotic ring impressions highlighted.

Figure 2. Click to enlarge. Batrachognathus with sclerotic ring impressions highlighted. This specimen has the largest eyes known among anurognathids.

In Batrachognathus (click this link to see all bones identified) some of the bones are red/brown. Others are represented by impressions. Such is the case with the sclerotic rings. Here they are larger and more owl-like than in other anurognathids. Nevertheless, a skull reconstruction (Fig. 6) is fairly standard in most aspects.

Figure 3. Click to enlarge. The GLGMV 0002 specimen attributed to Dendrorhynchoides. Sclerotic rings highlighted.

Figure 3. Click to enlarge. The GLGMV 0002 specimen attributed to Dendrorhynchoides. Sclerotic rings highlighted.

The GLGMV 0002 specimen (Fig. 3, Hone and Lü 2010) has two small sclerotic rings at the back of its skull. See the reconstruction (Fig. 6) to make sense of this roadkill.

Figure 4. Click to enlarge. Sclerotic rings on Jeholopterus.

Figure 4. Click to enlarge. Sclerotic rings on Jeholopterus.

Jeholopterus, the vampire pterosaur, also has two small sclerotic rings at the back of its skull. Nothing big filling the front half here.

Figure 5. Click to enlarge. Anurognathus holotype with bones identified. Here the sclerotic ring is not so clear, but the jugal is. And the jugal carries the sclerotic ring.

Figure 5. Click to enlarge. Anurognathus holotype with bones identified. Here the sclerotic ring is not so clear, but the jugal is. And the jugal carries the sclerotic ring. Orange = nasal. Yellow = pmx. Pink = lacrimal. Green = maxilla. Blue = jugal. Digital graphic segregation helps locate and identify elements here. That mass of green is wing membrane.

Ironically, Anurognathus has a very small sclerotic ring over its small jugal. While there is a large antorbital fenestra here, which Bennett and Andres would call the orbit, there is no sclerotic ring in there. It should be very easy to see if present. Trouble is, it’s not present. Observations should be repeatable. Bennett called the flathead pterosaur a juvenile Anurognathus. If they are conspecific, they should have the same bones. So, where is the giant sclerotic ring?

Figure 1. Anurognathid skulls in phylogenetic order.

Figure 6. Anurognathid skulls in phylogenetic order.

The variety in anurognathid skulls is a wonder to behold, but the little monster created by Bennett (20078) stands out as an outlier in this group of skull reconstructions (Fig. 6). Clearly something is wrong here (not duplicated in any other anurognathid).

References
Andres B, Clark JM and Xing X 2010. A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs, Journal of Vertebrate Paleontology 30: (1) 163-187.
Bennett SC 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81(4):376-398.
Hone DWE and Lü J-C 2010. A New Specimen of Dendrorhynchoides (Pterosauria: Anurognathidae) with a Long Tail and the Evolution of the Pterosaurian Tail. Acta Geoscientica Sinica 31 (Supp. 1): 29-30.

On the origins of Dimorphodon and Eudimorphodon

At the base of the Pterosauria
there was one false evolutionary start that gave us Austriadactylus (the Austrian specimen) and Raeticodactylus. Thereafter the clades kicked into full gear with the basal dichotomy, dimorphodontids (which begat anurognathids) and eudimorphodontids (which begat everything else.)

Knowing that a picture tells the story here are the players (Fig. 1):

The origins of Dimorphodon and Eudimorphodon find a common ancestor close to Austriadactylus (the Italian specimen) and prior to that, the basal pterosaur, MPUM 6009. All are Late Triassic except Dimorphodon. The robust skull of eudimorphodontids suggests piscatory (fish eating) while the fragile skulls of dimorphodontids suggests insectivore. The enlarged naris was a legacy from the Italian specimen

The origins of Dimorphodon and Eudimorphodon find a common ancestor close to Austriadactylus (the Italian specimen) and prior to that, the basal pterosaur, MPUM 6009. All are Late Triassic except Dimorphodon. The robust skull of eudimorphodontids suggests piscatory (fish eating) while the fragile skulls of dimorphodontids suggests insectivore. The enlarged naris was a legacy from the Italian specimen

The basic dichotomy of dimorphodontids and eudimorphodontids (Fig. 1) set the pace for the rest of pterosaur evolution. One emphasized the longer, leaner snout of a fish and tetrapod eater while the other had a taller, more fragile and ultimately wider rostrum (in anurognathids) of an insect eater.

You can see (Fig. 1) with such short fore limbs and long hind limbs, with toes under the center of balance at the shoulder glenoid (arm pit) that quadrupedal locomotion was something that would have to be invented in the future of these Triassic clades.

BTW
Yesterday’s note on Atopodentatus garnered about twice as many viewers. Let me know why all the interest because I don’t have a clue.

Atopodentatus and Claudiosaurus compared

Figure 1. Click to enlarge. Atopodentatus and Claudiosaurus (ghosted) and the small one above Atopo's shoulder to scale. Sometimes it just helps to compare sister taxa to see how far, and in what direction, they have come.

Figure 1. Click to enlarge. Atopodentatus and Claudiosaurus (ghosted) and the small one above Atopo’s shoulder to scale. Sometimes it just helps to compare sister taxa to see how far, and in what direction, they have come.

Earlier we looked at the latest Triassic marvel, Atopodentatus unicus. Today there’s a reconstruction (Fig. 1) alongside a more familiar and pleisomorphic Claudiosaurus for comparison.

Atopodentatus was bigger overall with a relatively larger and more robust torso and tail and a weaker shoulder girdle and pelvis, making it a slower swimmer, but more of a tail swimmer. The humerus was larger, but the antebrachium was smaller, so the forelimbs were likely acting as props rather than propulsive organs. The necks was longer and more flexible. Looks like the hands and feet had become paddles.

Those who suggested this was a filter-feeding bottom feeder were probably right on the money.

Look for more transitional taxa between these two in the future.

References
Cheng L, Chen XH,Shang QH and Wu XC 2014. A new marine reptile from the Triassic of China, with a highly specialized feeding adaptation. Naturwissenschaftendoi:10.1007/s00114-014-1148-4.