Spinosaurus the paradigm buster

Figure 1. Spinosaurus from Ibrahim 2014. Yes, the proportions are correct. It's a non bipedal swimming theropod.

Figure 1. Spinosaurus from Ibrahim 2014. Yes, the proportions are correct. It’s a non bipedal swimming theropod. The red bones are known. The gray ones are hypothetical.

Generally I avoid all but the most basal dinosaurs.
However, just a few posts ago we looked at Spinosaurus and Arizonasaurus, two archosauriformes with a similar dorsal sail.  Well, it seems the proportions of Spinosaurus were a little off in the hind leg department. And that makes the new data fascinating.

And POP there goes a paradigm
The Spinosaurus tale has been told by Nat Geo, Science, Nature, and other places. I found the reaction to this heretical pile of facts just as fascinating. There was shock. And there were skeptics! (something I’ve grown accustomed to from the first vampire pterosaur abstract onward).

Skeptics are good. But facts are facts.

From the Abstract
We describe adaptations for a semiaquatic lifestyle in the dinosaur Spinosaurus aegyptiacus. These adaptations include retraction of the fleshy nostrils to a position near the mid-region of the skull and an elongate neck and trunk that shift the center of body mass anterior to the knee joint. Unlike terrestrial theropods, the pelvic girdle is downsized, the hind limbs are short, and all of the limb bones are solid without an open medullary cavity, for buoyancy control in water. The short, robust femur with hypertrophied flexor attachment and the low, flat-bottomed pedal claws are consistent with aquatic foot-propelled locomotion. Surface striations and bone microstructure suggest that the dorsal “sail” may have been enveloped in skin that functioned primarily for display on land and in water.

From the Dinosaur Mailing List
There’s something fishy about the new Spinosaurus
the pelvis and hind limbs are too small.”

Note sure if these questions have been answered
1. Did Spinosaurus knuckle-walk to protect its fore claws? After all, it had to come out of the water, at least to lay its eggs. Perhaps it ventured out only to mud and sand bars as crocs do.
2. Other than display, was the sail used for thermoregulation? Keeping it dry in a hot sun would have allowed it to soak in heat. Wetting it would have cooled the sail by evaporative heat loss.
3. Was the sail used in transportation? If there was a current in the water, the orientation of the sail to the current could have been aligned for minimum impact or at right angles for maximum impact.

When we have missing parts, it is usually okay to fill them in with parts gleaned from sister taxa — until the actual parts become found. Then we have to give up our cherished paradigms and let the facts speak for themselves.

References
Ibrahim N, Sereno PC, Dal Sasso C, Maganuco S, Fabbri M, Martill DM, Zouhri S, Myhrvold N, Iurino DA 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science. doi:10.1126/science.1258750.

History of Spinosaurus with old reconstruction of long hind limbs

Paul Sereno on YouTube

Thadeosaurus renested

Earlier Thadeosaurus (Carroll 1981, Figs. 1-3) nested close to protorosaurs in the large reptile tree (still needs to be updated), as a sister to Tangasaurus at the base of the Enaliosauria. Another look at Currie’s (1984) tracings (Fig. 3), rather than Carroll’s 1981, 1993 reconstruction (Fig. 1), inspired a new reconstruction (Fig. 2) and nested it within the Enaliosauria, on the other side of Tangasaurus, between Adelosaurus and Acerosodontosaurus. So this new nesting shifts Thadeosaurus a few nodes. Thadeosaurus usually nests with tangasaurs. So everyone is in agreement here.

Figure 1. Original reconstruction of Thadeosaurus from Carroll 1981, 1993.

Figure 1. Original reconstruction of Thadeosaurus from Carroll 1981, 1993. I didn’t find the fused scapulocoracoid. All the specimens separated these elements, but they were all subadults to juveniles. The new reconstruction found more variability in the vertebra and a shallower torso. 

At this grade, these basal enaliosaurs show no obvious aquatic adaptations. Rather, Thadeosaurus appears to have been a long-legged sprinter. The skull remains very much like those of basal diapsids. No special features there.

Figure 1. Thadeosaurus reconstructed from bits and pieces over large and small specimens scaled up to the large specimen. Only one of the smallest juveniles preserves any skull bones.

Figure 2. Thadeosaurus reconstructed from bits and pieces over large and small specimens scaled up to the large specimen. Only one of the smallest juveniles preserves any skull bones. Are those sternal plates or posterior coracoids? You have to know the phylogenetic nesting to be sure. 

Sometimes you just have to employ more than one specimen to create a chimaera. In this case, Thadeosaurus was reconstructed from several specimens of various sizes (Fig. 3). Hopefully these are all congeneric and conspecific specimens, as reported by Currie (1984). I didn’t see any red flags here. Nothing about the reconstruction is at odds with Currie’s observations.

Figure 2. The various specimens in various sizes, all to scale attributed to Thadeosaurus. If the largest specimen did not have a bone, it was scaled up from the smaller specimens.

Figure 3. The various specimens in various sizes, all to scale attributed to Thadeosaurus. If the largest specimen did not have a bone, it was scaled up from the smaller specimens.

When genera look so much alike, as basal enaliosaurs do, it is paramount to get the details right. Try to get back to the original material. If not, try to get back to the in situ tracing. If not, use the reconstruction and hope it is accurate.

References
Carroll RL 1981. Plesiosaur ancestors from the Upper Permian of Madagascar. Philosophical Transactions of the Royal Society London B 293: 315-383
Currie PJ 1984. Ontogenetic changes in the eosuchian reptile Thadeosaurus. Journal of Vertebrate Paleontology 4(1 ): 68-84.

wiki/Thadeosaurus

What is Tasmaniosaurus?

Ezcurra 2014 considered the tiny Early Triassic archosauriform Tasmaniosaurus traissicus (Camp and Banks 1978) a tiny proterosuchid, following the original assessment.

Figure 1. The few tiny elements of Tasmaniosaurus reconstructed as a tiny protodinosaur and as a tiny proterosuchid/ erythrosuchid compared to Trialestes, a larger basal protodinosaur. Ezcurra considers the maxilla exposed in medial view, but others think it was exposed in lateral view.

Figure 1. The few tiny elements of Tasmaniosaurus reconstructed as a tiny protodinosaur and as a tiny proterosuchid/ erythrosuchid compared to Trialestes, a larger basal protodinosaur. Ezcurra considers the maxilla exposed in medial view, but others think it was exposed in lateral view. Also check out Pseudhesperouchus and Lewisuchus.

Previous authors thought the maxilla was exposed in lateral view. If so, it has a maxillary fossa. Ezcurra thought the maxilla was exposed in medial view. Proterosuchids do not have a maxillary fossa. If the premaxilla was not downturned, Tasmaniosaurus is anything but a proterosuchid. If the maxilla is exposed in lateral view, Tasmaniosaurus is anything but a proterosuchids=.

Figure 1. Lewisuchus from Romer 1972. Tibia and skull do no match published scale bars. Pelvis and femur are hypothetical. Skull above left per Romer. Below left per Bittencourt et al.

Figure 2. Lewisuchus from Romer 1972. Tibia and skull do no match published scale bars. Pelvis and femur are hypothetical. Skull above left per Romer. Below left per Bittencourt et al.

The convex ventral margin of the maxilla is an archosauriform trait. But how convex is it? What is broken off?

The caudal vertebrae are very long, longer than 3x their width, very un-proterosuchid like. Seven in a row have no neutrals spines.

The interclavicle of Tasmaniosaurus is T-shaped with a very long and slender posterior process. Among archosauriforms, only Euparkeria has a T-shaped interclavicle. Many are I-shaped. In dinosaurs and poposaurs they are poorly ossified to absent.

The femur and tibia/fibula are short and robust, so no possible biped here and the Early Triassic is a little too early for bipeds.

Tasmaniosaurus is tiny. About the size of Youngina and Euparkeria, much smaller than any known proterosuchid or erythrosuchid.

This one needs more work and a decent reconstruction. I don’t see any reconstructions on Google yet. This enigma can be solved.

References
Camp CL, Banks MR 1978. A proterosuchian reptile from the Early Triassic of Tasmania. Alcheringa 2: 143–158.
Ezcurra MD. 2014. The Osteology of the Basal Archosauromorph Tasmaniosaurus triassicus from the Lower Triassic of Tasmania, Australia. PLoS ONE 9(1):e86864. doi:10.1371/journal.pone.0086864

New nesting for Echinerpeton with Secodontosaurus

Figure 1. Just move the mandible forward so the last tooth is anterior to the orbit and Echinerpeton becomes a long snouted pro to-secodontosaur.

Figure 1. Just move the mandible and maxilla forward so the last tooth is anterior to the orbit (as in other pelycosaurs) and Echinerpeton becomes a long snouted proto-secodontosaur. 

Raising my hand to proclaim a nesting error
Earlier (now trashed) I recovered Echinerpeton at the base of the Synapsida and Diapsida, but those elongate dorsal spines seemed odd at that node. Then I noticed that all other pelycosaurs had teeth only in front of the orbit. The skull is largely missing, so there’s no harm in shifting the jaws forward a bit. And suddenly Echinerpeton made more sense.

Echinerpeton intermedium (Reisz 1972), Late Carboniferous, 308 mya. Reisz (1972) tentatively classified Echinerpeton as an ophiacodontid in his initial description, and in 1986 he considered it an indeterminate “pelycosaur“. Benson (2012) could not nest Echinerpeton with certainty, perhaps because he used the wrong outgroups and mistakenly included caseasaurs because he followed tradition without the benefit of a large gamut reptile tree like we have here (Fig. 2).

Figure 1. Secodontosaurus and its ancestors going back to Varanosaurus. Secodontosaurus is the only sphenacodont with a varanopid-like skull.

Figure 1. Secodontosaurus and its ancestors going back to Varanosaurus. Secodontosaurus was the only sphenacodont with a varanopid-like skull. No Echinerpeton has one too.

Here Echinerpeton nests with Secodontosaurus. The snout was long because the last maxillary tooth was in front of the orbit. The maxilla was straight while the dentary was concave dorsally. Both were filled with long teeth.

The dorsal spines were long, but not as long as those of Secodontosaurus.The scapula was small and both the humerus and femur were short and slender. The ankle bones were round elements. Together these point to an aquatic, rather than a terrestrial niche. So Echinerpeton was a crocodile-like sphenacodont pelycosaur.

References
Benson RBJ 2012. Interrelationships of basal synapsids: Cranial and postcranial morphological partitions suggest different topologies. Journal of Systematic Palaeontology: 601-624.
Reisz R 1972. Pelycosaurian reptiles from the Middle Pennsylvanian of North America. Bulletin of the Museum of Comparative Zoology 144 (2): 27–62. online here

 

Teraterpeton shifts toward Diandongosuchus

Recent work with the Diandongosuchus palate opened the door to reviewing the scoring for the enigmatic Teraterpeton (Fig. 1), originally (Sues 2003) considered a relative of Trilophosaurus largely due to its toothless beak and lack of a lateral temporal fenestra. Now Teraterpeton nests as a sister to Diandongosuchus. That clade is a sister clade to parasuchians, which also have dorsal nares. All were derived from the BPI 2871 specimen of Youngina, which shares their long snout.

Diandongosuchus (Li et al. 2012) wasn’t described until nine years after Teraterpeton so Sues (2003) could not have made this connection. Even so, Teraterpeton is so weird, it is no wonder it has remained an enigma for so long. Nesting such enigmas is exactly what the large reptile tree (not updated yet) is for. Earlier Teraterpeton nested with Tropidosuchus in the large reptile tree, not too far off from Diandongosuchus, but a mismatch that needed repairing. And Science marches on.

Figure 1. Diandongosuchus (above) compared to Teraterpeton (below).

Figure 1. Diandongosuchus (above) compared to Teraterpeton (below). Note the similar scapula shapes and the way the posterior dorsal ribs terminate in a line. Both lack the flaring cheeks of parasuchians and Youngina. Teraterpeton, with so few teeth, could well have been a plant eater or anything but a carnivore. Hopefully we’ll find more of this genus someday.

Teraterpeton hrynewichorum (Sues 2003) Late Triassic, ~215 mya, was described as euryapsid (lacking a lateral temporal fenestra) and possibly related to the rhynchocephalian, Trilophosaurus on that basis. Here Teraterpeton is derived from Diandongosuchus, but with a stretched out rostrum and far fewer, smaller teeth. The lateral temporal fenestra has been shortened so much that the lateral temporal fenestra has closed up. So, it’s still a diapsid. Distinct from Diandongosuchus, the skull had a larger antorbital fenestra and a narrower configuration in dorsal view. The teeth had the multiple cusps of a plant eater. The pedal(?) unguals are robust, but note the disparate sizes, distinct from Diandongosuchus.

References
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.
Sues H-D 2003. An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia. Canadian. Journal of Earth Science 40(4): 635-649.

 

Casting a blind eye toward: Scleromochlus

Figure 1. Scleromochlus by Witton 2013, via Benton 1999. Now promoted as a fuzzy pterosaur precursor.

Figure 1. Scleromochlus by Witton 2013, via Benton 1999. Now promoted as a fuzzy pterosaur precursor. Note the quadrate articulating with the surangular and the giant retroarticular process. Lean that quadrate the other way and these problems go away — and suddenly Scleromochlus is a croc! The fossil, found in dorsal and ventral views, does not expose the quadrate, except in one specimen, which is conveniently ignored. Witton gives Scleromochlus one extra cervical than Benton illustrated and a few extra fingers.

We’ve seen this sort of thing before.
Mark Witton is good at cherry-picking his references and keeping his audience in the dark about alternate and more viable realities in paleontology. In a recent blog, M. Witton uncritically takes on the seven specimens of Scleromochlus, first described by Woodward (1907) and later covered by Benton (1999, Fig. 1). He lists the phylogenetic analyses and other papers that posit Scleromochlus as a pterosaur precursor, but not the ones that indicate Scleromochlus was a basal bipedal crocodylomorph, like Terrestrisuchus and Saltoposuchus (Peters 2000, 2002, Fig. 2). These also demonstrate that pterosaurs were something entirely distinct from archosaurs.

From the Witton blog:
“For 100 years Scleromochlus has been implicated as a relative of pterosaurs (e.g. Huene 1914; Padian 1984; Gauthier 1986; Sereno 1991; Bennett 1996; Hone and Benton 2008; Brusatte et al. 2010, Nesbitt 2010) or, at very least, an ornithodiran representing a very early stage of stem-bird evolution (Benton 1999; Hone and Benton 2008).”

And yet Scleromochlus has several traits that rule it out as a pterosaur precursor: 1) flat, wide skull; 2) deep antorbital fossa; 3) broad triangular pterygoids; 4) no sternum; 5) no interclavicle; 6) no elongate coracoid; 9) deep chevrons; 10) diverging pubis and ischium; 11) no laterally increasing fingers 1-4); 12) no pedal digit 5. Click here and here for more info. And click here for the evolution of the pterosaur wing.

All the above traits are shared with basal bipedal crocs. And we already have a long list of taxa that show an increasing number of pterosaurian traits, listed here.

Witton mentions:
*You can’t mention Scleromochlus on the internet without someone pointing out that its status as an ornithodrian has not been tested in analyses containing non-archosaur archosauromorphs. This is true enough, but – at least within the current limits of testing – its ornithodiran status is not controversial, having been recovered in at least six different analyses (e.g. Gauthier 1986; Sereno 1991; Bennett 1996; Hone and Benton 2008; Brusatte et al. 2010) and sharing several unique characteristics with Pterosauria (Padian 1984). Hence, we’re following convention here.”

Again, forgetting Peters 2000 and the large reptile tree at reptileevolution.com.

Basal Crocodylomorpha

Figure 2. Basal Crocodylomorpha, including Gracilisuchus, Saltopus, Scleromochlus and Terrestrisuchus. Here the deep antorbital fenestra, deep chevrons, tiny hands and lack of a fifth toe feel right at home.

After describing the vestigial hand and lack of a fifth toe in Scleromochlus, Witton writes:Scleromochlus hindlimb arthrology betrays a parasagittal posture akin to that of dinosaurs and pterosaurs – the suite of characteristics associated with this is one clue that Scleromochlus is closely related to these clades (Bennett 1996; Benton 1999; Hone and Benton 2008).” Hey, wait a minute Mark! You’re forgetting the bipedal crocs (Fig.2)! And pterosaurs have giant hands and a long fifth toe!

The meat of the blog, it’s raison d’être
After listing the transversely-banded scales on the dorsal surface of the Scleromochlus torso (think croc skin), Witton let’s his imagination out of the barn, “Scleromochlus may have been covered in scales, but it is equally likely that it had fuzz-like filaments in places. There are several reasons for this. Firstly, it belongs within a phylogenetic bracket where filaments are the ancestral condition or, at very least, scales were prone to developing filamentous morphologies. Secondly, virtually all models of archosaur evolution recover Scleromochlus as sister taxon to a fuzzy clade – pterosaurs, so there is good ‘phylogenetic proximity’ for fuzz. Thirdly, insulating integuments are common – if not ubiquitous – in small, active (see below) desert-dwelling animals.” 

Mark, it’s those analyses that expand the inclusion set, that nest Scleromochlus with bipedal basal crocs, you should be keeping an eye on. This is what I don’t understand about paleontologists. Sometimes the obvious (Fig. 2) becomes taboo territory because I’m associated with it.

Leaping pterosaur precursor?
It’s not a stretch to imagine Scleromochlus as a leaping archosaur. But then Witton takes it one step further, “Indeed, the powerful leaping and bounding abilities of early ornithodirans has been tied to the evolution of pterosaur flight (Bennett 1997; Witton 2013).” Unfortunately such hind limb leaping gives the forelimbs nothing to do and no reason to begin flapping. And flapping is key to pterosaurian evolution. Read more on the origin of pterosaur flapping here.

References
Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoolological Journal of the Linnean Society 118: 261–308.
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Padian K. 1984. The Origin of Pterosaurs. Proceedings, Third Symposium on Mesozoic Terrestrial Ecosystems, Tubingen 1984. Online pdf
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Hist Bio 15: 277–301.
Senter P 2003. Taxon Sampling Artifacts and the Phylogenetic Position of Aves. PhD dissertation. Northern Illinois University, 1-279.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. Journal of Vertebrate Paleontology 11 (Supplement) Memoire 2: 1–53.
Woodward AS 1907. On a new dinosaurian reptile (Scleromochlus taylori, gen. et sp. nov.) from the Trias of Lossiemouth, Elgin. Quarterly Journal of the Geological Society 1907 63:140-144.

wiki/Scleromochlus

Solenodonsaurus revealed by DGS

Solenodonsaurus is a crushed fossil basal reptile (Fig. 1). The skull has been difficult to interpret. Previous workers, including Carroll 1970 and Danto et al. 2012 both came up with the same outline, but the details were difficult to ascertain.

Figure 1. Solenodonsaurus interpreted using DGS. That's a 13 cm skull

Figure 1. Solenodonsaurus interpreted using DGS. That’s a 13 cm skull. The pineal opening has been difficult to find because a bony rod (hyoid? parasphenoid process?) sticks up through it. The naris is just beginning to bud off an antorbital fenestra. On the right the layers are segregated, and see how much clarity that brings! And then you can fit the parts together in a reconstruction, then compare that to sister taxa. It’s a longer process than just tracing.

Solenodonsaurus nests with chroniosuchids near the base of the Reptilia. If I made any mistakes, I’ll correct them with valid input.

References
Broili F von 1924. Ein Cotylosaurier aus der oberkarbonischen Gaskohle von Nürschan in Böhmen. Sitzungsberichte der Mathematisch-Naturwissenschaftlichen Abteilung der Bayerischen Akademie der Wissenschaften zu München 1924: 3-11.
Brough MC and Brough J 1967. Studies on early tetrapods. III. The genus Gephyrostegus. Philosophical Transactions of the Royal Society B252: 147-165.
Carroll RL 1970. The ancestry of reptiles. Philosophical Transactions of the Royal Society B257: 267-308.
Danto M, Witzmann F and Müller J 2012. Redescription and phylogenetic relationships
of Solenodonsaurus janenschi Broili, 1924, from the Late Carboniferous of Nyrany, Czech Republic
Laurin M and Reisz 1999. A new study of Solenodonsaurus janenschi, and a reconsideration of amniote origins and stegocephalian evolution. Canadian Journal of Earth Sciences 36:1239-1255.
Pearson HS 1924. Solenodonsaurus (Broili), a seymouriamorph reptile. Annals and Magazine of Natural History 14:338-343.

wiki/Solenodonsaurus