Junggarsuchus: not a crocodyliform sister, a dino sister

Updated Dec. 22, 2014 with a new tree (Fig. 3), moving the SMNS 12352 specimen between Terrestrisuchus and Gracilisuchus — and that makes the last common ancestor of crocs and dinos Lewisuchus and pulls the Poposauridae into the Archosauria.

Junggarsuchus (Fig. 1, Clark et al. 2004) is known from a Jurassic fossil from China that was purported to be the sphenosuchian closest to the Crocodyliformes (all higher crocs, Fig. 2).

Figure 1. Junggarsuchus colorized. Once thought to be the crocodylomorph closest to crocodylformes, it now nests as a pre-dinosaur.

Figure 1. Junggarsuchus colorized. Once thought to be the crocodylomorph closest to crocodylformes, it now nests as a pre-dinosaur.

Clark et al. (2004, Fig. 2) nested Junggarsuchus between Dibothrosuchus and Protosuchus (Fig. 5) and both basal to the living Alligator.

Figure 2. Crocodylomorph tree according to Clark et al. 2004. Green taxa are crocodylomorphs in the large reptile tree.

Figure 2. Crocodylomorph tree according to Clark et al. 2004. Green taxa are crocodylomorphs in the large reptile tree.

Adding Junggarsuchus to the large reptile tree
When I added Junggarsuchus to the large reptile tree I was not surprised to see it nesting with Pseudhesperosuchus (Figs. 3, 4). The two are more similar to each other than either is to any other tested taxon. Among many other traits, they both share a double mandibular fenestrae, high arching postorbitals, and anterior nares.

Figure 3. Pseudhesperosuchus colorized to show how the maxilla has slipped ventrally. Moving it back in place removes that extra antorbital fenestra that others have noticed.

Figure 3. Pseudhesperosuchus colorized to show how the maxilla has slipped ventrally. Moving it back in place removes that extra antorbital fenestra that others have noticed.

Parrish (1997) and Clark et al. (2000) both illustrated a second antorbital fenestra in Pseudhesperosuchus (Fig. 4). No other sisters have this trait and it disappears when the maxilla is rotated back into place (Fig. 3).

Figure 4. Pseudhesperosuchus by Clark et al. 2000 showing the second antorbital fenestra caused by taphonomic slippage of the maxilla.

Figure 4. Pseudhesperosuchus by Clark et al. 2000 showing the second antorbital fenestra caused by taphonomic slippage of the maxilla.

Adding Caiman (extant croc) to the large reptile tree
When I added Caiman (a living relative of crocodiles and alligators) to the large reptile tree, I expected it to nest with Protosuchus, the conventional sister, as shown above (Fig. 2). Instead Caiman nested with the SMNS 12352 specimen, an anterior skull with anterodorsal nares and a few other traits (like prefrontals that contact each other at the midline) and both of these were sisters to Sphenosuchus (Fig. 5). Shifting Caiman to Protosuchus adds 15 steps.

Figure 1. Ten basal bipedal crocodylomorphs descending from a sister to Decuriasuchus.

Figure 5. Click to enlarge. Ten basal bipedal crocodylomorphs descending from a sister to Decuriasuchus. Here sphenosuchus is basal to living crocs, not Protosuchus.

But wait, there’s more!
Let’s get back to Junggarsuchus and Pseudhesperosuchus. With new data they now nest between basal bipedal crocs and basal bipedal dinosaurs. That new nesting makes more and more sense as sisters begin to look more and more like one another.

Figure 7. Pseudhesperosuchus nests near Trialestes at the base of the Dinosauria.

Figure 6. Pseudhesperosuchus nests near Trialestes at the base of the Dinosauria. Note how closely all sister taxa resemble each other.

Lewisuchus, a tiny basal poposaur
We’ve seen this before: miniaturized taxa at the base of major clades. This time it’s Lewisuchus (Fig. 5) at the base of the Poposauria, basal to Poposaurus and Turfanosuchus. All known poposaurs are larger than Lewisuchus.

Elongate coracoids and proximal carpals. Problem?
Both Junggarsuchus and Pseudhesperosuchus have a narrow (elongate) coracoid, a shape typical of all but the most basal crocs. By contrast, basal dinosaurs have a disc-like coracoid. Unfortunately we don’t know of an in-between coracoid in transitional taxa, Trialestes (Fig. 5) and the PVL specimen. Apparently in dinosaurs the coracoid evolved from a strut to a disc.

In like fashion, Trialestes has the elongate proximal carpals (ulnare and radiale) typical of crocs. Herrerasaurus, a basal dinosaur, does not have elongate proximal carpals. Apparently, as the forelimbs were no longer used for quadrupedal locomotion, the proximal carpals returned to their plesiomorphic state as short discs.

Figure 7. Portion of the large reptile tree showing the ancestry of archosaurs (crocs + dinos) updated with new taxa and new data. Small black squares are miniaturized taxa at the base of several clades.

Figure 7. Portion of the large reptile tree showing the ancestry of archosaurs (crocs + dinos) updated with new taxa and new data. Small black squares are miniaturized taxa at the base of several clades.

It is important
to let the facts recover your conclusions. But if something is untenable, it probably means the tree data is in need of repair, or at least a second look.

References
Bonaparte JF 1969. Dos nuevos “faunas” de reptiles triásicos de Argentina. Gondwana Stratigraphy. Paris: UNESCO. pp. 283–306.
Clark JM et al. 2000. A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs. Journal of Vertebrate Paleontology 20 (4): 683–704.
Clark JM, Xu X, Forster CA and Wang Y 2004. A Middle Jurassic ‘sphenosuchian’ from China and the origin of the crocodilian skull.
Irmis RB, Nesbitt SJ and Sues H-D 2013. Early Crocodylomorpha. Geological Society Special Publications 379:275-302.
Parrish JM 1993. Phylogeny of the crocodylotarsi, with reference to archosaurian and crurotarsian monophyly. Journal of Vertebrate Paleontology 13:287-308.

wiki/Pseudhesperosuchus

wiki/Junggarsuchus

Gracilisuchus colorized

Updated January 14, 2015 with new tracings of the Gracilisuchus skull identifying the postfrontals and the addition of the dinosaur lineage image. 

Until recently
I only had Romer’s version of Gracilisuchus, a basal crocodylomorph. The only problem is no other crocodylomorph has an unfused frontal/postfrontal. Another look at a hi-rez Gracilisuchus (Butler et al. 2014) provided the answer (Fig. 1). Recent phylogenetic analysis places it outside of the croc/dino split. both clades fuse the postfrontal, one to the frontal, the other to the postorbital.

Figure 5. Gracilisuchus skull updated with new colors.

Figure 1. Gracilisuchus skull updated with new colors.

Contra Butler et al. 2014, 
Gracilisuchus nests in the large reptile tree with Scleromochlus and Saltopus, not with Yonghesuchus, yet as in Butler et al. 2014, Gracilisuchus was indeed derived from a sister to Turfanosuchus. (Fig. 2).

Figure 1. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

References
Butler RJ et al. 2014. New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and the biogeography of the archosaur radiation. Evolutionary Bioloty 14:128.
Romer AS 1972. 
The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.

 

Chicken skull colorized

Updated February 05, 2015 with a revised illustration of the chicken skull following further study. See comparisons on the blog post dated 02/05/2015.

Figure 1. Chicken skull (Gallus gallus) with fused and semi-fused skull bones colorized. Postorbital = orange. Squamosal = tan. Lacrimal = brown. Prefrontal = purple. Quadrate = red.

Figure 1. Chicken skull (Gallus gallus) with fused and semi-fused skull bones colorized. Postorbital = orange. Squamosal = tan. Lacrimal = brown. Prefrontal = purple. Quadrate = red.

The chicken (Gallus gallus) was recently added to the large reptile tree. Like most birds several skull bones fuse in adults. Other bones are greatly reduced, losing their old theropod dinosaur appearance. The antorbital fenestra is confluent with the orbit. The  ascending process of the jugal is unossified. Like mammals, birds have a greatly enlarged brain and cranium and that coincides with a reduced quadrate.

This is an example of how DGS (digital graphic segregation) can help illustrate a very common taxon. Earlier mistakes were examples of naiveté as I have avoided studying bird skulls until just recently.

 

 

Basal synapsid occiput wallpaper

If I get started
describing the attached image (Fig. 1), I’ll be here all night. So let’s just let this be today’s wallpaper. Enjoy. Learn about something that rarely gets compared like this. This is evolution in progress…

Figure 1. Basal synapsid occiputs in evolutionary order (left column) with regard to mammal evolution. The data come from various sources. Colorization certainly helps one see the patterns that evolution takes here.

Figure 1. Basal synapsid occiputs in evolutionary order (left column) with regard to mammal evolution. The data come from various sources. Colorization certainly helps one see the patterns that evolution takes here.

This is how I learn.
If I made any errors, please advise with data.

Heleosuchus – the enigma has nested in the Rhynchocephalia

Figure 1. Heleosuchus, a former enigma, nests in the middle of the Rhynchocelphalia, between Planocephalosaurus and Sphenodon.

Figure 1. Heleosuchus, a former enigma, nests in the middle of the Rhynchocelphalia, between Planocephalosaurus and Sphenodon. Here is Heleosuchus in situ and Planocephalosaurus restored to scale. Click to enlarge.

Heleosuchus (Fig. 1) has been an enigma since first described by Owen 1876. Several heavy-hitters in paleontology (Broom 1913, Evans 1984, Carroll 1987) have taken a whack at it without resolving its relations.

According to Wikipedia, “It was originally described as a species of Saurosternon, but was later recognized as a separate taxon by R. Broom. Heleosuchus is suggested as being either an early diapsid reptile, not closely related to other lineages, or as being an aberrant and primitive lepidosauromorph. Heleosuchus shares the hooked fifth metatarsal found in some other diapsids, such as primitive turtles (Odontochelys), lepidosauromorphs, and archosauromorphs, but it also resembles ‘younginiform’-grade diapsids in its gross morphology.  Heleosuchus may also share a thyroid fenestra with these higher diapsid reptiles as well, but the identity of this feature is disputed.”

Based on tracings by Carroll (1987) the large reptile tree (not updated yet) Heleosuchus nested between Planocephalosaurus (Fig. 1) and the clade of Sphenodon and Kallimodon in the middle of the Rhynchocephalia. What was identified as a scapula must be a portion of the interclavicle instead.

However, even Carroll was not sure of the identification of several elements. Unfortunately it appears as though the last time someone published on Heleosuchus was prior to the advent of computer-assisted phylogenetic analysis. Carroll notes, “if a thyroid fenestra is present and the fifth metatarsal is hooked, Heleosuchus would definitely represent a lineage distinct from the younginoids. These features are present in Late Triassic sphenodontids and Jurassic lizards, but they are also present in other groups. In conclusion, the characters that are preserved point to a position near the base of the lepidosauromorph assemblage, possibly close to the younginoids but perhaps representing a distinct lineage.”

What appears to be bothering Carroll is the early appearance of Heleosuchus in the Late Permian of South Africa relative to the lepidosaurs known to him at the time. That early appearance doesn’t bother the large reptile tree, which nests several other Permian contemporaries just as high if not higher in the reptile family tree.

References
Broom R 1913. A revision of the reptiles of the Karroo. Annals of the South African Museum 7: 361–366.
Carroll RL 1987. Heleosuchus: an enigmatic diapsid reptile from the Late Permian or Early Triassic of southern Africa”. Canadian Journal of Earth Sciences24: 664–667.
Evans SE 1984. The anatomy of the Permian reptile Heleosuchus griesbachi. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte, 12: 717-727.
Owen R 1876. Descriptive and illustrated catalogue of the fossil Reptilia of South Africa in the collection of the British Museum. Trustees of the British Museum (Natural History), London, UK.

wiki/Heleosuchus

Adding Homo sapiens to the large reptile tree

Not sure why I didn’t think to do this earlier.
I added Homo sapiens to the large reptile tree (still not updated) and ran a phylogenetic analysis to see where we nest. To no one’s surprise Homo (Fig. 1) nested with the cynodont Procynosuchus among the Therapsida (no other mammals are yet entered).

Figure 1. Homo sapiens alongside sister taxa Australopithecus and Ardipithecus (both in gray).

Figure 1. Homo sapiens alongside sister taxa Australopithecus and Ardipithecus (both in gray). Click to learn more.

Entering characters for Homo and Procynosuchus
was more than enlightening as so many traits were shared between the two. You should try it sometime!

Figure 2. Procynosuchus, a basal cynodont therapsid synapsid sister to humans in the large reptile tree (prior to the addition of advanced cynodonts including mammals).

Figure 2. Procynosuchus, a basal cynodont therapsid synapsid sister to humans in the large reptile tree (prior to the addition of advanced cynodonts including mammals). Click to learn more.

What happens when taxa are excluded? (How deep can we go?)
The contribution of cynodont traits to the story of human evolution was more powerful than I thought. I was surprised at one happened when I took one step further.

Deleting only Procynosuchus
results in Homo nesting results in Homo nesting between Dibamus and Tamaulipasaurus (Fig. 2) two burrowing skinkomorph squamates. My guess is the fusion/loss of so many skull bones, the brevity of the rostrum, the great depth of the coronoid process of the dentary and the complete lack of postcranial characters for the two burrowing taxa are attracting the taxon Homo with similar skull traits.

With the present character and taxon list, these skinkomorphs nest closer to humans than Biarmosuchus and more basal synapsids, like Dimetrodon. They’re just not human enough.

Biarmosuchus, the most basal therapsid.

Figure 3. Biarmosuchus, the most basal therapsid and not a cynodont. Despite nesting as a basal therapsid, its traits do not attract the taxon Homo more than others do. 

You think THAT’S ridiculous. Let’s take the next step…

Figure 2. Tamaulipasaurus nests with Homo sapiens when the basal cynodont, Procynosuchus, is excluded.

Figure 2. Tamaulipasaurus nests with Homo sapiens when the basal cynodont, Procynosuchus, is excluded. The fusion of skull bones, the short rostrum, and the large coronoid process of the dentary are traits shared with humans.

Deleting all the skinkomorph squamates
results in Homo nesting as a turtle/pareiasaur ancestor. Here the short face, anterior nares, tall pelvis and loss of manual and pedal phalanges appear to attract Homo to turtles like Proganochelys.

Proganochelys. Formerly the most primitive turtle.

Figure 2. Proganochelys. Formerly the most primitive turtle. Click to learn more. 

See what happens with taxon exclusion?
Strange bedfellows can result. So many current problems and enigmas in paleontology can be readily settled with a large enough family tree.

In the same light, I challenge paleontologists
to add thalattosaurs to Vancleavea studies… to add fenestrasaurs to pterosaur studies… to add mesosaurs to ichthyosaur studies… and to add millerettids to caseasaur studies. There’s no harm in doing so, and we all might learn something.

 

Restoring Scoloparia as a procolophonid AND as a pareiasaur

Today I have a quandary…
Is Scoloparia a procolophonid or a pareiasaur? I’ve looked at it both ways (Figs. 1, 2). It nests both ways (depending on the restoration), and at least one way is wrong.

This problem highlights more basic problems
found within the Procolophonidae, some of which nest in the large reptile tree (still not updated)  with diadectids (Procolophon and kin, Fig. 1), with pareiasaurs (Sclerosaurus) and the rest nest as pre-Lepidosauriformes (Owenetta and kin). Conventionally procolophonids are considered parareptiles. Cisneros lists Nyctiphruretus as the outgroup and owenettids as basal taxa within the Procolophonidae. The large reptile tree replicated that outgroup only for the owenettids.

Scoloparia glyphanodon (Sues and Baird 1998) is currently represented by several specimens, three of which are figured, colorized and restored here (Figs. 1, 2). All three differ in size. Comparable skulls differ in morphology. This has been attributed to ontogeny.

Figure 1. Scoloparia restored here as a procolophonid together with other procolophonids.

Figure 1. Scoloparia restored here as a procolophonid together with other procolophonids. Click to enlarge. The large YPM mandible is a definite procolophonid. The small 82.1 specimen is a definite procolophonid. The holotype is the big question mark.

Clearly the referred specimens
(the dentary and the small 82.1 specimen) are procolophonids. Only seven blunt and rotated teeth in a mandible that tips down anteriorly along with gigantic orbits mark these taxa as procolophonids. They compare well with other procolorphonids.

Figure 2. Scoloparia restored as a pareiasaur close to Elginia along with several other pareiasaurs for comparison. Sclerosaurus typically nests as a procolophonid, but even with the removal of all skull traits, it nests as a small pareiasaur.

Figure 2. Scoloparia restored as a pareiasaur close to Elginia along with several other pareiasaurs for comparison. Sclerosaurus typically nests as a procolophonid, but even with the removal of all skull traits, it nests as a small pareiasaur. The new restoration reidentifies several bones. Note the convergence with the procolophonids in figure 1.

The problem is in the large holotype
The 83.1 specimen holotype of Scoloparia was preserved without a skull roof or palate, so the nasals, frontals and parietals are restored here.

Originally
the size and morphological differences were attributed to the juvenile status of the smaller specimen. H. Sues wrote to me, “Both specimens have the same peculiar ‘cheek’ teeth, which are unlike those of any other procolophonid.” 

I think what Dr. Sues means is shown below in figure 3. The teeth of the referred specimen attributed to Scoloparia have multiple cusps, unlike most procolophonids, but approaching the serrated morphology of pareiasaurs. The convergences are mounting!! And now you see why this is a quandary!

Figure 4. Teeth compared. Elginia, Scolaparia (referred), Leptopleuron and Diadectes.

Figure 3. Teeth compared. Elginia, Scolaparia (referred), Leptopleuron and Diadectes, a stem procolophonid. Oddly the very procolophonid Scoloparia (referred specimen) does have peculiar teeth for a procolophonid. They are serrated somewhat like those in the pareiasaur, Elginia.

I have asked to see images of the teeth for the Scoloparia holotype. No reply yet.

The mystery of the holotype 
Teeth were not illustrated by Sues and Baird for the holotype 83.1 specimen, who reported the mandible was articulated. The authors described two premaxillary, six maxillary and eight dentary teeth. That low number of teeth point toward a procolophonid ancestry. The upper anterior four teeth are described as incisiform with bluntly conical crowns that are rounded in cross section. The first premaxillary tooth is reported to be much larger than the other teeth. A large medial pmx tooth also points toward a procolophonid ancestry, as we’ve already seen with Colobomycter. In Elginia (Fig. 3)  the many small teeth are slightly constricted at the base and serrated at the crown as in other pareiasaurs.

Figure 4. Elginia colorized in four views. Note the rotation of the tabulars to the dorsal skull.

Figure 4. Elginia colorized in four views. Note the rotation of the tabulars to the dorsal skull. Click to enlarge. Note the many similarities to the pareiasaur-like restoration of Scoloparia. 

Nuchal osteoderms
Sues and Baird noted “nuchal (neck) osteoderms” preserved posterior to the skull in the 83.1 holotype of Scoloparia. Cisneros (2008) reports osteoderms have only been found in Sclerosaurus and Scoloparia. Since Sclerosaurus nests here as a pareiasaur, that means no other procolophonids have osteoderms. Hmmm.

Reversals in the skull roof of pareiasaurs 
In the large reptile tree pareiasaurus are sisters to turtles (all derived from Stephanospondhylus) and bolosaurids, all derived from Milleretta. In Stephanospondylus (Fig 5) a reversal takes place in which the postparietals (or are they tabulars?) rotate to the dorsal surface of the skull and the supratemporals develop small horns. These traits usually appear on pre-amniotes.

Figure 2. Stephanospondylus skull in two views. Note the rotation of the post parietals to the dorsal skull along with the transformation of the supratemporals into small horns.

Figure 5. Stephanospondylus skull in two views. Note the rotation of the post parietals to the dorsal skull along with the transformation of the supratemporals into small horns.

This dorsalization of the tabulars
becomes even more apparent in pareiasaurs (Fig. 2) and Elginia (Fig. 4). If the purported nuchals of Scoloparia are actually large supratemporals, tabulars, and opisthotics, then it’s a pareiasaur. If so, a foramen magnum is also present topped by a supraoccipital and two flanking exoccipitals. What a quandary!

Not quite enough to go on
I am working from a 2D line drawing here (from Sues and Baird 1998), not a photograph. So I await images of the teeth and any other data that may come down the pike. If new data ever comes in, I will let you know. For now, can’t tell if we’re dealing with autapomorphic nuchal osteoderms on a procolophonid or dorsalized tabulars and an occiput on a pareiasaur.

References
Cisneros JC 2008. Phylogenetic relationships of procolophonid parareptiles with remarks on their geological record. Journal of Systematic Palaeontology): 345–366.
Sues HD and Baird D 1998. Procolophonidae (Reptilia: Parareptilia) from the Upper Triassic Wolfville Formation of Nova Scotia, Canada. Journal of Vertebrate Paleontology 18:525-532.

Daemonosaurus has two sister taxa: Haya and Jeholosaurus

Updated February 28, 2015 with a new skull for Daemonosaurus.

Earlier we talked about the Late Triassic saber-toothed dinosaur, Daemonosaurus (Sues et al. 2011, Fig. 1, CM 76821) originally considered a weird basal theropod between Eoraptor and Tawa. That’s due to taxon exclusion. The real sisters of Daemonosaurus were not tested. The authors also mistakenly nested Eoraptor within the Theropoda when it is actually an outgroup, a phytodinosaur closer to Sauropodomorpha, which were only included as a suprageneric taxon, along with Ornithischia. Unfortunately that’s the same suprageneric/taxon exclusion/inclusion problem that happens so often it’s not funny anymore.

Figure 1. Skulls of Daemonosaurus, Haya and Jeholosaurus to scale.

Figure 1. Skulls of Daemonosaurus, Haya and Jeholosaurus to scale nest as sister taxa. And it’s easy to see why. Somewhere in this clade lies the origin of the predentary bone and the retroverted pubis. Long premaxillary teeth and a short rostrum are key traits. Note the infilling of the mandibular fenestra.

Solution: add taxa and avoid suprageneric taxa
In the large reptile tree Daemonosaurus did not nest with theropods, but at the base of the Ornithischia between basal phytodinosaurs like Eoraptor and the basal ornithischian, Pisanosaurus. It’s been three years since that post.

Today Jeholosaurus (Han et al 2012) and Haya (Figs. 1,2), two widely acknowledged basal ornithischians, nest with Daemonosaurus. One look at the three of them together pretty much sums up the rest of this post. Note their chronology. This is a basal clade that lasted through all three periods of the Mesozoic.

That they nest together tells me the post-crania of Daemonosaurus likely had at least a proto-ornithischian pelvis and supports my earlier observation of a proto-predentary.

Figure 1. Haya skull and post-crania.

Figure 1. Haya skull and post-crania. At present this specimen gives us the best approximation of the post-crania of Daemonosaurus, although the neck vertebrate were longer. Note the stub of a fifth toe on the pes.

Fossils of Coelophysis were present on the same block that contained the skull of Daemonosaurus, Wonder if there was a predator/prey relationship? Skull lengths were similar. Overall size was likely similar too.

References
Han F-L, Barrett PM, Butler RJ and Xu X 2012. Postcranial anatomy of Jeholosaurus shangyuanensis (Dinosauria, Ornithischia) from the Lower Cretaceous Yixian Formation of China. Journal of Vertebrate Paleontology 32:1370-1395.
Makovicky PJ, Kilbourne BM, Sadleir RW and Norell MA 2011. A new basal ornithopod (Dinosauria, Ornithischia) from the Late Cretaceous of Mongolia. Journal of Vertebrate Paleontology 31: 626–640.
Sues H-D, Nesbitt SJ, Berman DS and Henrici AC 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society Bpublished online 
Xu, Wang and You, 2000. A primitive ornithopod from the Early Cretaceous Yixian Formation of Liaoning. Vertebrata PalAsiatica 38(4)318-325.

wiki/Daemonosaurus
wiki/Haya
wiki/Jeholosaurus

The Premaxilla of Ticinosuchus (again)

Paleontologists are still mulling over
the origin of aetosaurs. They also keep missing the premaxillae of Ticinosuchus (Fig. 1, PIZ T2817). Long time readers know these two factoids are related.

Figure 1. The premaxillae of Ticinosuchus, a stem aetosaur. Note the sharp triangular shape.

Figure 1. The premaxillae of Ticinosuchus, a stem aetosaur. Note the sharp triangular shape.

As reported several years ago
at reptile evolution.com and an earlier post here from Nov. 2011.

Here (Fig. 1) again, are the short, sharp, triangular premaxillae of Ticinosuchus. This is one of many key traits that nest Ticinosuchus with aetosaurs like these (Fig. 2).

Figure 2. Aetosaur skulls compared to Ticinosuchus, the long-sought outgroup to this clade.

Figure 2. Aetosaur skulls compared to Ticinosuchus, the long-sought outgroup to this clade.

Unfortunately this relationship between Ticinosuchus and aetosaurs continues to be ignored, largely because the the skull bones of Ticinosuchus are in such disarray that workers (Lautenschlager and Desojo 2011, Nesbitt 2011) have not had much success segregating and identifying them. Here (Fig. 1) DGS (digital graphic segregation), comes to the rescue once again.

About Ticinosuchus
Nesbitt (2011) wrote:  “As a result, the phylogenetic position is poorly supported in the few analyses in which it has been included (e.g., Parrish, 1993; Benton, 2004).  I examined the skull region very carefully and have a few comments. Unfortunately, the blocks with skull elements appear to have been reassembled incorrectly.”

Figure 2. Nesbitt (2011) reassembled the in situ skull, but misidentified the premaxilla as a lacrimal.

Figure 2. Nesbitt (2011) reassembled the in situ skull, but misidentified the premaxilla as a possible lacrimal.

Nesbitt has great insight.
Unfortunately Nesbitt (2011) identified one premaxilla as a tentative right lacrimal. Even so, and to his credit, Nesbitt nested Ticinosuchus very close to the aetosaurs, Unfortunately he nested the basal erythrosuchid, Revueltosaurus, at the base of the aetosaurs. Perhaps the misidentified premaxilla is the one key that would have helped Nesbitt nest Ticinosuchus a little closer to aetosaurs. Revueltosaurus does not have a triangular premaxilla. It nests with the very similar but much larger Fugusuchus.

Brusatte et al. 2010
nested parasuchians basal to aetosaurs. Gracilisuchus, Erpetosuchus and crocodylomorpha nested as sister clades, even though they share very few traits with aetosaurs. In Brusatte et al. Ticinosuchus nested with Stagonosuchus (a rauisuchian), Fasolasuchus (a giant rauisuchian known from a maxilla and premaxilla in the skull ) and Arganasuchus (rauisuchian bones recovered include part of the upper jaws, neck vertebrae, and hip bones). Send pdfs of these taxa if you have them and I can comment with more authority, but my guess is that none of these had a triangular premaxilla.

References
Desojo JB and Ezcurra M.D 2011. A reappraisal of the taxonomic status of Aetosauroides(Archosauria, Aetosauria) specimens from the Late Triassic of South America and their proposed synonymy with Stagonolepis. Journal of Vertebrate Paleontology 31(3):596-609. doi:10.1080/02724634.2011.572936
Fraas O 1877. Aetosaurus ferratus Fr. Die gepanzerte Vogel-Echse aus dem Stubensandstein bei Stuttgar. Festshrift zur Feier des vierhundertjährigen Jubiläums der Eberhard-Karls-Universät zu Tübingen, Wurttembergische naturwissenschaftliche jahreshefte 33 (3): 1–22.
Krebs B 1965. Ticinosuchus ferox nov. gen. nov. sp. Ein neuer Pseudosuchier aus der Trias des Monte San Giorgio. Schweizerische Palaontologische Abhandlungen 81:1-140.
Lautenschlager S and Desojo JB 2011. Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus. Paläontologische Zeitschrift Online First DOI: 10.1007/s12542-011-0105-1
Schoch R 2007. Osteology of the small archosaur Aetosaurus from the Upper Triassic of Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlung. 246/1:.1–35. DOI: 10.1127/0077-7749/2007/0246-0001
Walker AD 1961. Triassic reptiles from the Elgin area: StagonolepisDasygnathus and their allies. Philosophical Transactions of the Royal Society B 244:103-204.

wiki/Aetosaurus
wiki/aetosaur
wiki/Stagonolepis
wiki/Ticinosuchus

Restoring Pintosaurus

Pintosaurus (Piñeiro et al. 2004)
was described as a basal procolophonid close to Coletta and Owenetta on the basis of a incomplete skull (Fig. 1). Cisneros (2008) nested Pintosaurus similarly.

Figure 1. Pintosaurus restored from Piñeiro et al. 2004.

Figure 1. Pintosaurus (Late Permian) restored from Piñeiro et al. 2004.

Here (Fig. 1) just a little color and phylogenetic bracketing adds in the missing pieces from the Pintosaurus skull. The upper portions had weathered away, but are here restored.

Distinct from sister taxa,
Pintosaurus had only three teeth in the premaxilla, and it appeared to have a posterolateral process of the premaxilla. The large palatal fangs on the palatine are also unique to this genus. But when Contritosaurus (aka Phaanthosaurus, Fig. 2) is added it shares the trait of three large premaxillary teeth, but the naris is anterior on a transverse premaxilla. This clade has an unusual narial fossa (depression).

Figure 2. Contritosaurus (aka Phaanthosaurus sinus), a sister to Pintosaurus. Note the narial fossa and palatine teeth.

Figure 2. Contritosaurus (aka Phaanthosaurus sinus), a sister to Pintosaurus. Note the narial fossa and palatine teeth.

Like their sister, Coletta (Fig. 3, Gow 2000, Modesto, Damiani and Sues 2002, Early Triassic, GHG 228), these genera likely had upper temporal fenestra. They nest as derived owenettids and stem lepidosauriformes.

Figure 3. Coletta nests with Pintosaurus and Contritosaurus in the large reptile tree. Note the small upper temporal fenestrae, marking this taxon as a stem owenettid.

Figure 3. Coletta nests with Pintosaurus and Contritosaurus in the large reptile tree. Note the small upper temporal fenestrae, marking this taxon as a derived owenettid and a stem lepidosauriform.

These are sisters to the ancestors of the gliding lepidosauriforms, and all lepidosaurs, including Sphenodon, pterosaurs, lizards and snakes.

References
Cisneros JC 2008. “Phylogenetic relationships of procolophonid parareptiles with remarks on their geological record”Journal of Systematic Palaeontology 6:345–366.
Cudinov PK and Vjushkov BP 1956. New data on small cotylosaurus from the Permian and Triassic of the USSR. Doklady Akademii Nauk SSSR 108:547-550.
Gow CE 2000. A new procolophonid (Parareptilia) from the Lystrosaurus Assemblage Zone, Beaufort Group, South Africa. Palaeontologia Africana 36:21–23.
Ivakhnenko MF 1974. New data on Early Triassic procolophonids of the USSR. Paleontological Journal 8:346-351.
Modesto SP, Damiana RJ and Sues H-D 2002. A reappraisal of Coletta seca, a basal procolophonid reptile from the lower Triassic of South Africa. Palaentology 45(5):883-895.
Piñeiro G, Rojas A and Ubilla M 2004. A new procolophonid (Reptilia, Parareptilia) from the Upper Permian of Uruguay. Journal of Vertebrate Paleontology 24:814-821.