Is Nyasasaurus the oldest dinosaur?

Nesbitt et al. (2014) report, “Here, we describe Nyasasaurus parringtoni gen. et sp. nov., which is identified as either the earliest known member of, or the sister–taxon to, Dinosauria. Nyasasaurus possesses a unique combination of dinosaur character states and an elevated growth rate similar to that of definitive early dinosaurs.”

Nesbitt et al. (2012) did not provide a reconstruction. The specimen is only known from a few Middle Triassic (Anisian) vertebrae and a proximal humerus. Here (Fig. 1) is a reconstruction that seems to fit pretty well based on the holotype and referred specimens of Nyasasaurus placed onto the bauplan of a large and slightly larger (for the cervicals) specimen of Turfanosuchus, a basal archosaur at the base of the Poposauridae (now nesting basal to archosaurs in the large reptile tree). This was, what you might call, an early ‘false start’ mimicking the actual rise of the Dinosauria.

Figure 1. Click to enlarge. Nyasasaurus bones placed on an enlargement of Turfanosuchus, a middle Triassic basal archosaur, not a dinosaur. Dinos and crocs all started out as tiny bipeds.

Figure 1. Click to enlarge. Nyasasaurus bones placed on an enlargement of Turfanosuchus, a big. middle Triassic basal archosaur, not a dinosaur. Dinos and crocs all started out as tiny bipeds, also derived from Turfanosuchus, but smaller.

Nesbitt et al. ran their analysis and found Nyasasaurus to nest between 1) Lewisuchus and dinosaurs; 2) basal to Ornithischia; or 3) as the sister to Dilophosaurus, a Jurassic dinosaur. I didn’t run an analysis as my characters would not resolve relationships based on so few parts.

The large reptile tree finds two small specimens, Trialestes and an unnamed specimen incorrectly referred by Lecuona and Desojo (2011) to Gracilisuchus (PVL 1259) at the base of the Dinosauria. The latter is as old as Nyasasaurus, fulfilling chronological predictions.

Nesbitt et al. note a ventrally elongate deltopectoral crest on the humerus, but that assumes a short humerus. The crest is not so elongate if the humerus is a little longer.

Nesbitt et al. note three sacral vertebrae, but basal dinos don’t have three sacrals, only two. Turfanosuchus also has only two, but look at the size difference! Poposaurus, a sister taxon, has five sacrals. So Nyasasaurus is something else. Nesbitt et al. note hyposphene–hypantrum intervertebral articulations in the pre sacral vertebrae. Sorry, not much about that in Turfanosuchus data. In Turfanosuchus, as in Nyasaurus, the cervical vertebrae are laterally concave.

References
Lecuona A and Desojo, JB 2011. Hind limb osteology of Gracilisuchus stipanicicorum (Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 102 (2): 105–128.
Nesbitt SJ, Barrett PM, Werning S, Sidor CA and Charig AJ (posthumously) 2012. The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania. Biology Letters 9: 20120949.

 

 

Poposaurs – Topology Shift

Yes, I was wrong. And it’s time to man-up.
Earlier, based on available data, the large reptile tree nested poposaurids with phytodinosaurs and attributed the appearance and growth of the calcaneal tuber in certain poposaurs to convergence with the Crocodylomorpha. So the earlier data recovered poposaurs as dinosaurs with an odd ankle, not crocs with a “massive convergence” with dinosaurs, which is still the widespread hypothesis (see Nesbitt 2011 and others).

That seemed to make sense — except some poposaurs, like Lotosaurus and Asilisaurus (Fig. 1), appeared a little too early in the Triassic. They seemed to be anachronistic, and that can be a red flag.

So going back to the phylogenetic analysis,
I reexamined certain specimens, discovered a few items not originally presented (I trusted original tracings instead of making my own from in situ photos) and I found several bad scores. The newly recovered tree finds poposaurids derived from Turfanosuchus, a taxon that earlier stood alone at the base of the Archosauria (basal to crocs and dinos). Now things seem to make more sense, phylogenetically, chronologically (Fig.1) and morphologically. See if you agree…

Figure 1. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

Figure 1. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos. Among these, only Silesaurus and Asilisaurus lost the calcaneal tuber.

Figure 2. The Euarchosauriformes featuring a new nesting for the Poposauridae.

Figure 2. The Euarchosauriformes featuring a new nesting for the Poposauridae.

Now the odd thing is: 
Poposaurs appear to provide a sort of preview to what would eventually evolve in the Dinosauria itself, likely filling similar niches in earlier strata.

Turfanosuchus and Poposaurus (Fig. 1) were convergent with theropods. The larger Asilisaurus was convergent with sauropodomorphs. The remainder were convergent with various ornithischians, even down to the toothless predentary they shared by convergence. Lotosaurus was a stegosaur mimic. Shuvosaurus was a Dryosaurus mimic. Silesaurus was a Camptosaurus mimic, down to losing the calcaneal tuber. Sacisaurus was a little Agilisaurus mimic. Effigia was still the oddball with those vestigial hands and back-sloped braincase.

So poposaurids are not dinosaurs. They are also not basal to rauisuchidae (contra Nesbitt 2011), but were derived from basal rauisuchia like Decuriasuchus and Vjushkovia. They are the most basal archosaurs. Basal poposaurs were the last common ancestors of crocs and birds. From their basalmost taxon, a sister to little Turfanosuchus, both tiny basal bipedal crocs and tiny bipedal basal dinos evolved.

Size
Poposaurs, in the form of Nyasasaurus, Asilisaurus and Lotosaurus (Fig. 1), were the first archosaurs to evolve substantial size in the Middle Triassic. Crocs and dinos remained small until the late Triassic (mid-Triassic for the basal Herrerasaurus) when they had their great radiation and poposaurs began to fade. This is an unrecognized faunal turnover.

Discovering and correcting errors is what scientists do. 
And I was happy that these new insights appeared.

What took so long?
Inattention to red flags. We should all look more closely at problems. They lead to new insights.

M.M. I hope this helps the cause. And yes, I have made and will make changes to earlier posts on this subject.

References
Brusatte SL, Benton MJ, Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Irmis RB, Nesbitt SJ, Padian K, Smith ND, Turner AH, Woody D and Downs A 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science 317 (5836): 358–361. doi:10.1126/science.1143325. PMID 17641198.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Nesbitt SJ, Irmis RB, Parker WG, Smith ND, Turner AH and Rowe T 2009. Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29 (2): 498–516. doi:10.1671/039.029.0218

MCSNB 3496 reconstructed

And one more Triassic pterosaur first reported by Wild (1978) and reviewed by Dalla Vecchia (2003), MCSNB 3496 (Fig. 1). So few parts are known that it would be very difficult to accurately nest this one. The fused pubis/ischium is like Dimorphodon. So is the inturned femoral head. The wing phalanges appear to be very gracile, but perhaps they are only partly exposed or misidentified.

MCSNB 3496 in situ and reconstructed from the very few parts here.

Figure 1. MCSNB 3496 in situ and reconstructed from the very few parts here.

Earlier we looked at other Triassic bits and pieces herehere and here.

References
Dalla Vecchia FM 2003. A review of the Triassic pterosaur record. Riv. Mus. civ. Sc. Nat. “E. Caffi” Bergamo 22:13-29.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

MFSN 19864 compared

MFSN 19864 is a Triassic pterosaur tail. Well… I imagine it’s a pterosaur tail. We don’t know the rest of this specimen. Compared to another basal pterosaur, MPUM 6009, MFSN 19864 is longer and more robust with what appears to be a tiny vane at the tail tip (Fig.1).

Figure 1. MFSN 19864 compared to MPUM 6009 another pterosaur with an attenuated tail without ossified reinforcements.

Figure 1. Click to enlarge. MFSN 19864 compared to MPUM 6009 another pterosaur with an attenuated tail without ossified reinforcements.

Dalla Vecchia (2003) noted that this tail had no ossified reinforcing “bundles” of pre- and post-zygopophyses, although such “bundles” were probably present and unossified. This appears to have been a larger pterosaur based on the size of the proximal caudals.

Earlier we looked at other Triassic bits and pieces herehere and here.

References
Dalla Vecchia FM 2003. A review of the Triassic pterosaur record. Riv. Mus. civ. Sc. Nat. “E. Caffi” Bergamo 22:13-29.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

MCSNB 2887 reconstructed

Another of Wild’s (1978) Triassic pterosaurs featured by Dalla Vecchia (2003) is MCSNB 2887. Here it is in situ and reconstructed (Fig.1) as a Triassic basal dimorphodontid. It nests with Preondactylus.

Figure 1. MCSNB 2887 in situ and reconstructed as a basal dimorphodontid/basal anurognathid.

Figure 1. MCSNB 2887 in situ and reconstructed as a basal dimorphodontid/basal anurognathid. It nests with Preondactylus.

Earlier we looked at other Triassic bits and pieces herehere and here.

References
Dalla Vecchia FM 2003. A review of the Triassic pterosaur record. Riv. Mus. civ. Sc. Nat. “E. Caffi” Bergamo 22:13-29.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

MCSNB 2886 reconstructed

MCSNB 2886 is another roadkill partial pterosaur from the Triassic (Wild 1978, Dalla Vecchia 2003). Here it is (Fig. 1) and here it is reconstructed (Fig. 2) as a basal dimorphodontid, probably close to Peteinosaurus.

Figure 1. MCSNB 2886 a Triassic pterosaur in situ

Figure 1. MCSNB 2886 a Triassic pterosaur in situ

Figure 2. MCSNB 2886 reconstructed as a basal dimorphodontid.

Figure 2. MCSNB 2886 reconstructed as a basal dimorphodontid close to Peteinosaurus.

Earlier we looked at other Triassic bits and pieces here and here.

References
Dalla Vecchia FM 2003. A review of the Triassic pterosaur record. Riv. Mus. civ. Sc. Nat. “E. Caffi” Bergamo 22:13-29.
Wild R 1978. Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien. Bolletino della Societa Paleontologica Italiana 17(2): 176–256.

The manus of Poposaurus revised — again

 

Revised April 23, 2014 based on further study. 

 Figure 1. Poposaurus manus as originally restored and with digit 1 switched to 5.


Figure 1. Poposaurus manus as originally restored and with digit 1 switched to 5. Note the resemblance to dinosaur and basal croc hands in this basal archosaur.

The manus of basal archosaurs is very rare.
What few clues we have indicate that metatarsals 1-3 aligned distally and digit 5 is a vestige. Revising the manus of Poposaurus to that pattern is demonstrated here (Fig. 1).

References
Gauthier JA, Nesbitt SJ, Schachner ER, Bever GS and Joyce WG 2011. The bipedal stem crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion. Bulletin of the Peabody Museum of Natural History 52:107-126.
Mehl MG 1915. Poposaurus gracilis, a new reptile from the Triassic of Wyoming. Journal of Geology 23:516–522.

wiki/Poposaurus

MPUM 7039: a pterosaur sternal complex?

Figure 1. MPUM 7039, an isolated Triassic pterosaur sternal complex with parts colorized. The shape is very much like that of Eudimorphodon.

Figure 1. MPUM 7039, an isolated Triassic pterosaur sternal complex with parts colorized. The shape is very much like that of Eudimorphodon (MCSNB 2888) and would have belonged to a powerful flapping flyer with large chest muscles anchored here. This is about 3x life-size at the 72dpi of your monitor screen.

Yes!
MPUM 7039, identified by Dalla Vecchi 2003 as a “relatively large, incomplete and isolated sternal plate “prudently consider it as cf. Eudimorphodon” is indeed that.

Of course, as well all know, a sternal complex includes the interclavicle and clavicles along with the sternal plate, here (Fig. 1) colorized for easy identification. Let’s keep calling this a sternal complex because it’s not just a sternum and sometimes the sternal portion is the smallest part.

This post is part of a Triassic series that follows an earlier one on a gastric pellet containing a pterosaur.

References
Dalla Vecchia FM 2003. A review of the Triassic pterosaur record. Riv. Mus. civ. Sc. Nat. “E. Caffi” Bergamo 22:13-29.

New Mexican Pterosaur Tracks?

Figure 1. I'd like to see 4 toes if this is indeed a pterosaur track. Here three toes points toward a theropod.

Figure 1. I’d like to see 4 toes if this is indeed a pterosaur track. Here three toes suggest a theropod.

Recent announcement of 110 million-year-old pterosaur tracks by Raul Frank Gio Argáez, researcher at the Institute of Marine Sciences and Limnolog , National Autonomous University of Mexico (UNAM ) made the news here.

Unfortunately all pterosaur tracks that I am aware of have four toes.

Here (Fig. 1) the fourth toe appears to be missing, suggesting a misidentification. Looks more like a theropod track. If anyone can see the fourth toe, please let me know.

The Triassic Pterosaur Gastric Pellet – Reconstructed

This is the first in a series of Triassic pterosaur enigmas.

Figure 1 From Dalla Vecchia et al. 1983. Original identification of the pterosaur pellet elements. Scale bar = 1 cm.

Figure 1 From Dalla Vecchia et al. 1983. Original identification of the pterosaur pellet elements. Scale bar = 1 cm. Slightly distorted to match the published photograph. cV= caudal vertebra. Cv = cervical vertebra.

An odd jumble of Triassic bones was identified by Dalla Vecchia, Muscio and Wild (1983) as the remains of Preondactylus (Fig. 2), one of the few Triassic pterosaurs known at that time, in a gastric pellet (aka: vomited bones). The problem is, if you put the bones, as originally identified, on a reconstruction of Preondactylus, you’ll find a few matches and several mismatches (Fig. 1).

Figure 1. The major bones of the Triassic gastric pellet placed upon the skeleton of Preondactylus, a contemporary pterosaur. Note the several mismatches.

Figure 2. The major bones of the Triassic gastric pellet placed upon the skeleton of Preondactylus, a contemporary pterosaur. Note the several mismatches.

Generally the wing finger elements are too gracile and so is the femur. The dorsals are a bit too long and metacarpal 4, the base of the wing, is not quite large enough.

Putting the originally traced bones together in a different, yet still Triassic way, yields a pre- or proto-pterosaur with some resemblance to Longisquama. Now the more gracile and possibly much shorter wings make some sort of sense, because this was not a flyer, but a running flapper and a glider at best. Of course, in this case, I was able to draw the imagined parts “to fit.”

Freddy Mercury put it best, “Is this the real life? Is this just fantasy?”

Figure 2. With so few bones, and so few of those complete, you can rebuild the gastric pellet into a pre- or proto- pterosaur, something like Longisquama.

Figure 3. With so few bones, and so few of those complete, you can rebuild the gastric pellet bone tracings of Dalla Vecchia et al. into a pre- or proto- pterosaur, something like Longisquama. Now the femur becomes a distal humerus. What was a metatarsal becomes a metacarpal similar in size and thickness to metacarpal 4. The large dorsals are a good fit as Longisquama had a long torso. Minimizing the amount of bone lost from each of the wing/finger phalanges yields a much shorter wing, like Longisquama. Black wiry shapes are completely imagined, as is most of the rest of this restoration. The actual animal shape may never be adequately known.

Wouldn’t it be exciting if the gastric pellet, now known for over 30 years, turned out to be an example of a transitional/basal taxon? Odd that only segments of all four wing phalanges would be preserved.

After producing these images I learned the pellet is under study once again. Hopefully those studies will help resolve this mystery.

When I ran the published images through DGS I was able to identify many other bones and create another much more complete reconstruction that also made sense. It was standard basal pterosaur. But then, the data I was using was poor at best.

Given the mishmash of the in situ fossil, the poor quality of my data and the detailed new study of the gastric pellet specimen to come, I hesitate putting it out early. I will say that the originally identified ‘palatine’ and ‘pterygoid’ are probably the first two dorsal ribs, which were more robust than the others, as in other pterosaurs. And several more ribs are present, which were generally overlooked in the original tracing (Fig. 1).

References
Dalla Vecchia FM, Muscio G and Wild R 1983. Pterosaur remains in a gastric pellet from the Upper Triassic (Norian) of Rio Seazza Valley (Udine, Italy). Gortania – Atti Museo Friul. Storia Naturale 10(88):121-132.