The dual origin of turtles to scale

Earlier the large reptile tree recovered a dual origin for soft shell and hard shell turtles. Here (Figs. 1-3) we’ll put the pertinent taxa to scale as animated GIF files. These help demonstrate evolution in a crude sort of way. Unfortunately, this is the best we can do at present with known taxa and published data. More discoveries will fill in the gaps.

Figure 1. Hard shell turtle evolution with Bunostegos, Elginia, Meiolania and Proganochelys.

Figure 1. Hard shell turtle evolution with Bunostegos, Elginia, Meiolania and Proganochelys to scale. Basal hard shell turtles had horns and club tails. The anterior rotation of the forelimbs is a derived trait.

It would be nice to find some Elginia postcrania
A reduction in size and loss of teeth coincided with the appearance of the carapace and plastron in hard shell turtles. Unfortunately, this critical stage is represented at present by a skull-only taxon, Elginia. Basal turtle taxa, like Meiolania, had horns and the limbs remained oriented laterally. A club tail trailed basal turtles. Did that develop earlier? We have not seen the ribs of Bunostegos published yet. One wonders if they were different than those of other pareiasaurs. Probably not if they were unremarkable.

Figure 2. Hard shell turtle evolution featuring Bunostegos, Elgenia, Meiolania and Proganochelys - NOT to scale.

Figure 2. Hard shell turtle evolution featuring Bunostegos, Elgenia, Meiolania and Proganochelys – NOT to scale. Even the palate of Bunostegos is very close to a turtle palate.

The skull of hard shell turtles 
demonstrates the appearance and reduction of knobs/horns along with the elimination of teeth, the reduction and anterior rotation of the naris, reduction of the preorbital region relative to the postorbital region and the gradual appearance of the quadrate in lateral view. The reduction of the horns likewise reduced the dorsal exposure of the post parietals and tabulars. but the supratemporal remained a large element. Unfortunately it  has been traditionally interpreted as a squamosal.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

The evolution of soft shell turtles
also begins with a size reduction from Arganaceras to Sclerosaurus. Thereafter the skull continued to shrink, as the plastron and carapace developed in Odontochelys. Teeth disappeared thereafter, as in Trionyx. Convergent with hard shell turtles the enlargement of jaw muscles in derived turtles included the enlargement of post temporal fenestra anteriorly. embaying the posterior skull. So, not listed yesterday, soft shell turtles converge (or rather developed in parallel) with hard shell turtles, given present data.

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Figure 4. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Small pareiasaurs from China
Since size is an issue in turtle origins, when you find a small pareiasaur, it is worthy of notice. Here (Fig. 5) are two and maybe three humeri from small  pareiasaurs, smaller than Sclerosaurus. None are slenderized nor do they develop spherical proximal articulations as seen in turtles. Apparently they just belong to small or young pareiasaurs.

Figure 5. Small pareiasaur humeri from Benton 2016. Note the scale bars. Some of these are smaller than Sclerosaurus (diagram), yet none are slenderized as in turtles.

Figure 5. Small pareiasaur humeri from Benton 2016. Note the scale bars. Some of these are smaller than Sclerosaurus (diagram), yet none are slenderized as in turtles.

Lee 1993 was correct
in putting pareiasaurs in the ancestry of turtles. That agrees with a large gamut reptile cladogram (subset Fig. 4).

However
Benton (2016) summed up current thinking when he reported, “An unusual aspect of pareiasaurs is that they were identified as an out-group, even the sister group, of turtles by Lee (1993, 1995, 1996, 1997), based on their shared characters of a rigid covering of dermal armour over the entire dorsal region, expanded flattened ribs, a cylindrical scapula blade, great reduction in humeral torsion (to 25°), a greatly developed trochanter major, an offset femoral head, and a reduced cnemial crest of the tibia.

“This was disputed by other morphological phylogenetic analyses (e.g. Rieppel & deBraga, 1996; DeBraga & Rieppel, 1997; Rieppel & Reisz, 1999; Li et al., 2009) that indicated a pairing of turtles and lepidosauromorphs among the diapsids, and by molecular phylogenetic studies of modern reptiles that repeatedly placed turtles among the Diapsida, and the Archosauromorpha in particular (e.g. Hedges & Poling, 1999; Field et al., 2014). New finds of the Triassic proto-turtles Pappochelys and Odontochelys show close links to the Middle Permian Eunotosaurus, and turtles are confirmed as archosauromorphs on the basis of fossil and molecular data, and not related to pareiasaurs (Joyce, 2015; Schoch & Sues, 2015).”

It is interesting to note what Benton does not report…
…a long list of turtle synapomorphies for Pappochelys and or diapsids and or archosauromorphs. He doesn’t because he can’t. A long list of turtle synapomorphies with these clades has not been compiled because it cannot be compiled. Unfortunately, Benton is following the latest literature, not testing it and not seeing the red flags. (Remember Benton was part of the Hone and Benton (2007, 2009) fiasco that attempted to test two origin of pterosaurs hypotheses by eliminating one of them only partly due to self-inflicted typos. The rest was a hatchet job as you can read again here).

Figure 5. Odontochelys pectoral elements reconstructed. Here the acromion process originates along the lower rim of the scapula.

Figure 5. Odontochelys pectoral elements reconstructed. Here the acromion process originates along the lower rim of the scapula. Pelociscus is an extant soft shell turtle. The coracoid of Odontochelys has been cracked at the glenoid. The green area is a hypothetical restoration. The glenoid of the scapula still had a thin veneer of matrix on it when photographed. The ? could be an acromion process. Or it could be a rib. The procoracoid of Sclerosaurus is absent here.

Morphology must trump DNA in prehistoric taxa
In the large reptile tree Pappochelys nests with basal sauropterygians, like Palatodonta, a skull-only basal placodont taxon. Several taxa near this node, including Henodus, Placochelys and Sinosaurosphargis independently developed turtle-like shells. So there was selective pressure to do so in that clade and niche at that time, convergent with extant turtles. No one knows yet why turtle DNA does not nest turtles with lizards more often or why mammal DNA does not nest mammals more closely with archosaurs in concert with the topology of the large reptile tree.

References
Benton MJ 2016. The Chinese pareiasaurs. Zoological Journal of the Linnean Society, doi: 10.1111/zoj.12389

Bunostegos: maybe not so oddly erect in stance after all…

Earlier we nested the knobby-faced pareiasaur, Bunostegos (Sidor et al. 2003, Tsuji et al. 2013, Turner et al. 2015; Fig. 1), with spiky Elginia at the base of all hard-shelled turtles, like Meiolania and Proganochelys. Soft-shelled turtles, like Odontchelys, as you might remember, were derived from a distinct, but closely related pareiasaur clade arising from Arganceras and Sclerosaurus, indicating that living turtles are diphyletic with two clades going back to shell-less ancestors among the smaller pareiasaurs.

Figure 10. The originally published cartoon of Bunostegos with skeletal elements laid on top of it. As you can see, the right humerus was mistakenly illustrated in the right hand position. And this may have led to the error of proposing that this pareiasaur was uniquely erect in gait.

Figure 1. The originally published cartoon of Bunostegos with skeletal elements laid on top of it. As you can see, the right humerus was mistakenly illustrated in the right hand position. And this may have led to the error of proposing that this pareiasaur was uniquely erect in gait. Image from Brown University website (see below)

Bunostegos
was reported (Tsuji et al. 2013) to also have a parasagittal (erect, upright) gait, which is not only odd, but unique for both pareiasaurs and turtles. That put up a red flag. Sorry it took so long to get to. I think I see a mistake here in the humerus identification. Tsuji et al. might have mistaken a left humerus for a right one, based on the cartoon illustration of a complete specimen (Fig. 1). It might have been an easy mistake to make because Tsuji et al. report at least 9 individuals, several sizes, each and all represented by a short list of disarticulated bones.

Figure 1. Here's Proganochelys in dorsal view. Note the humerus. If you look closely you'll see a small depression lateral to the proximal articulation with the shoulder glenoid. And note the larger of the two proximal processes is lateral.

Figure 2. Here’s Proganochelys in dorsal view. Note the humerus. If you look closely you’ll see a small depression lateral to the proximal articulation with the shoulder glenoid. And note the larger of the two proximal processes is lateral here, medial when the elbow is oriented posteriorly as in most other tetrapods.

Let’s start with what we know:
Everyone knows that Proganochelys (Fig. 2) nests as a basal turtle. It is the basalmost turtle in which the elbows were anterior to the shoulders in a normal configuration (in the more basal Meiolania they are primitively lateral). That rotation turns the traditional lateral condyles into medial condyles in practice. I want you to note the slight indentation lateral to the ball-like proximal humerus that fits into the socket-like shoulder glenoid in figure 2. You’ll see that again in Bunostegos (Fig. 3), but much larger.

Meiolania is an even more primitive hard-shell turtle
though this is still not the working hypothesis among traditional paleontologists. Here (Fig. 3) we’ll look at the humerus of Meiolania and other parts (Figs. 4-7) that will match what few bones were recovered from the Bunostegos site.

Figure 3. The left humerus of Bunostegos and the basal turtle Meiolania for comparison, both in dorsal view.. Colors denote homologous areas. That little dip in the medial condyle of Proganochelys (Fig. 2) is much larger here in Bunostegos and small in Meiolania.

Figure 3. The left humerus of Bunostegos and the basal turtle Meiolania for comparison, both in dorsal view.. Colors denote homologous areas. That little dip in the medial condyle of Proganochelys (Fig. 2) is much larger here in Bunostegos and small in Meiolania.

That little dip
in the medial condyle of Proganochelys (Fig. 2) is much larger here (Fig. 3) in Bunostegos and small again in the basal turtle Meiolania. Look again at figure 1 and you’ll see the big basin in Bunostegos was incorrectly flipped in the Brown University illustration.

Figure 3. Pre-turtle pectoral girdle evolution. Here homologous areas are colorized. The acromion process is broken on all specimens of Bunostegos. Pink arrow points anteriorly.

Figure 4. Pre-turtle pectoral girdle evolution. Here homologous areas are colorized. The acromion process is broken on all specimens of Bunostegos. Pink arrow points anteriorly. Note the lowering of the acromion process in Bunostegos. We don’t know how long it was. Also note the narrowing of the scapula. Note the maturation (ontogenetic)  changes to the glenoid in Bunostegos. The more lateral orientation is on the smaller/younger specimens, as in basal turtles.

We’ve been looking for the ancestors of turtles for some time now
And unfortunately these three papers on Bunostegos completely overlooked the possibility of a close relationship to Meiolania and other basal hard-shell turtles. You can see the evolution of the pectoral girdle and other bones provides the most gradual accumulation of derived traits known at present. At present, this blog and ReptileEvolution.com are the only studies that have recovered this heretical relationship.

Figure 5  Once again, and this time to scale, the pectoral girdles of Bunostegos. Note the more lateral orientation of the glenoid in young specimens, as in turtles (Fig. 3).

Figure 5  Once again, and this time to scale, the pectoral girdles of Bunostegos. Note the more lateral orientation of the glenoid in young specimens, as in turtles (Fig. 3).

It is interesting to see
the change in the orientation of the shoulder glenoid in the Bunostegos growth series (Fig. 5). Interestingly, the smaller specimens have more laterally directed glenoids, as in basal turtles (Fig. 4), which are also smaller.

Figure 6. Turtle pelvis evolution. Here are the changes in the pelvis of pre-turtles and basal hard-shelled turtles.

Figure 6. Turtle pelvis evolution. Here are the changes in the pelvis of pre-turtles and basal hard-shelled turtles. We don’t know how long the pubis was in Bunostegos. The ischium is narrower in the last three taxa here. Meiolania has a tall, pareiasaur-like ilium. Bunostegos has a pointed posterior ilium, as in Proganochelys.

The evolution of the turtle pelvis
is best seen in a series of pre-turtle and basal turtle pelves (Fig. 6). The acetabulum in all cases is lateral, but hard-shell turtles develop an acetabular crest that roofs over the joint and altogether form a socket shape for the ball-like femoral head (Fig. 7). This occurs concurrent with the appearance of the carapace and plastron.

Figure 7. Turtle femur evolution. Here the femoral head is interned in Bunostegos and assumes a spherical shape in the turtles, Meiolania and Proganochelys. We know the turtles held the femur horizontally, not parasagittaly.

Figure 7. Turtle femur evolution. Here the femoral head is interned in Bunostegos and assumes a spherical shape in the turtles, Meiolania and Proganochelys. We know the turtles held the femur horizontally, not parasagittaly.Pink arrro points anteriorly in these left femurs.

The evolution of the turtle femur
can be seen in this series of pre-turtle and basal turtle femora (Fig. 7). Note the gradual development of the ball joint on the proximal femur along with the development of the sigmoid (=’S’) shape of the femur. These developments coincide with the appearance of the carapace and plastron.

Figure 9. Even though the femur has an offset and spherical head in this basal turtle, Proganochelys, still it does not indicate a parasagittal gait, but a horizontal, sprawling one.

Figure 8. Even though the femur has an offset and spherical head in this basal turtle, Proganochelys, still it does not indicate a parasagittal gait, but a horizontal, sprawling one.

I was not able to find 
comparable pareiasaur humeri. They are not online and I don’t think anyone has done a large comparative study replete with a rich trove of illustrations yet. Basal turtles are smaller than most pareiasaurs. The hind limbs sprawl more.

I’d like to see
if any osteoderms or turtle-like ribs were found at the Bunostegos site. None have been reported so far. Hopefully this report will spur further studies with an eye toward gathering more pre-turtle data in Bunostegos. At present the many authors don’t know how really special their fossils are. There is a better story here than the false report of parasagittal limbs.

References
Sidor CA, Blackburn DC and Gado B 2003. The vertebrate fauna of the Upper Permian of Niger — II, Preliminary description of a new pareiasaur. Palaeontologica Africana 39: 45–52.
Turner ML, Tsuji LA, Ide O, Sidor CA 2015. The vertebrate fauna of the upper Permian of Niger—IX. The appendicular skeleton of Bunostegos akokanensis (Parareptilia: Pareiasauria). Journal of Vertebrate Paleontology: e994746. doi:10.1080/02724634.2014.994746.
Tsuji LA, Sidor CA, Steyer JSB, Smith RMH, Tabor NJ and Ide O 2013. The vertebrate fauna of the Upper Permian of Niger—VII. Cranial anatomy and relationships of Bunostegos akokanensis (Pareiasauria). Journal of Vertebrate Paleontology 33 (4): 747. doi:10.1080/02724634.2013.739537

Brown University website with news on Bunostegos

wiki/Bunostegos

 

 

Now turtles are diphyletic and finally make sense

Turtle systematics has changed for the better
Flattened softshell turtles are indeed different from domed hardshell turtles. The arose from separate, though closely related, non-shelled ancestors according to the latest data input and recovered from the large reptile tree (subset Fig. 1). The carapace and plastron in each turtle clade arose by convergence, based on present data. Earlier we looked at where other paleontologists have been looking for the ancestors of turtles.

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

I had it wrong earlier
And that’s okay as Science marches on. We build on past successes and mistakes made by both ourselves and others (see below). I saw a Red Flag (= a logical inconsistency, see below) and reexamined my data scores. New understandings popped up, like the absence of a premaxilla in Ocepecephalon and the coincident appearance of a new secondary naris high on the skull dividing the nasal bone (fused at its midline) in two (Figs. 2). That is very weird and may be unique for all tetrapods. A sister, Trionyx, has only a vestige of a premaxilla and no ascending process. So Ocepecephalon simply took it to the next level and completely lost the premaxilla — and perhaps most of the ectopterygoid.

Fig. 2. Ocepecephalon, the siphoning turtle. Originally the long dorsal rostrum bone was considered a premaxilla, but comparisons to sister taxa, like Trionyx, indicate it is an anterior nasal separated from the posterior nasal by a new naris, unlike that of any other turtle or tetrapod.

Fig. 2. Ocepecephalon, the siphoning turtle. Originally the long dorsal rostrum bone was considered a premaxilla, but comparisons to sister taxa, like Trionyx, indicate it is an anterior nasal separated from the posterior nasal by a new naris, unlike that of any other turtle or tetrapod. The naris and jaw opening are one here as the tiny premaxilla found in Trinoxy is completely absent here. The ectopteryogoids appear be broken here, but lacking a connection to the cheek may be yet another autapomorphy. New skull bone identities are labeled here.

This new tree topology for turtles solves the problem
of toothy Odontochelys appearing after the loss of teeth in ancestral taxa, as recovered by the old data with several incorrect scores. And this also solves the problem of soft-shell turtles with dorsally visible orbits, like Odontochelys, Trionyx and Ocepecephalon (Fig. 2), appearing after the orbits had already rotated to the lateral side of the skull in hardshell turtles derived from Elginia, Meiolania and Proganochely.

Figure 3. Dorsal views of bolosaur, diadectid, pareiasaur, turtle and lanthanosuchian skulls. The disappearance of the turtle orbit in lateral view occurs only in hard shell turtles.

Figure 3. Dorsal views of bolosaur, diadectid, pareiasaur, turtle and lanthanosuchian skulls. The disappearance of the turtle orbit in lateral view occurs only in hard shell turtles. Now the gradual accumulation of character traits is even more gradual. 

Correcting mistakes
and seeking new insights are what ReptileEvolution.com and this blog are all about,  whether I made the mistakes or others made the mistakes (usually a combination of the two). On a grander scale, that’s what Science is all about. It also feels good to solve persistent problems.

The .nex file is available on request, as always.

Dorsal views of basal turtle skulls support the cladogram

Earlier
here, here and here we looked at turtle origins — a controversial topic in mainstream paleontology resolved quickly and surely in the large reptile tree, which gives 639 taxa the opportunity to be ancestral to turtles.

Long story short
Toothy Elginia currently nests outside the turtles (only because we don’t have any post-crania) and toothless Meiolania nests as the basalmost turtle (Fig. 1) because it retains supratemporal horns and the elbows still extend laterally, not anteriorly. These taxa are derived from pareiasaurs, which are themselves sisters to diadectids, bolosaurs and proclophonids.

Figure 1. How the large reptile tree lumps and splits the several Diadectes specimens now included here. Note that bolosaurids, including Phonodus, now nest within other Diadectes specimens.

Figure 1. How the large reptile tree lumps and splits the several Diadectes specimens now included here. Note that bolosaurids, including Phonodus, now nest within other Diadectes specimens.

When the skulls of pertinent taxa
are seen in dorsal view (Fig. 2) it is easier to see the reduction of the horns in  pre- and basal turtle skulls. One also gets the impression that when Proganochelys and Odontochelys arrived on the scene in the Late Triassic, they both represent a much earlier radiation of turtles, both horned and not horned. So there are many more basal turtles out there waiting for us to discover them.

Figure 2. Turtles and their ancestors among the pareiasaurs. Note the soft shell turtle clade rotates the orbits until they are visible dorsally. Click to enlarge. Odontochelys is not so primitive as once considered. AND it appears to have redeveloped teeth. Note the reduction of supratemporal horns in basal turtles.

Figure 2. Turtles and their ancestors among the pareiasaurs. Note the soft shell turtle clade rotates the orbits until they are visible dorsally. Click to enlarge. Odontochelys is not so primitive as once considered. AND it appears to have redeveloped teeth. Note the reduction of supratemporal horns in basal turtles.

The Odontochelys tooth problem
Odontochelys is a Late Triassic toothed turtle that originally was considered (Li et al. 2008) a very basal turtle. Not so according to phylogenetic analysis which nests it with soft shell turtles like Trionyx. The odd thing is this soft shell turtle appears to have regrown teeth. More basal and sister taxa do not have teeth (Fig. 3). Odontochelys is also unusual in having nares in the anterior lateral orientation, not completely anterior, as in Trionyx, as in virtually all other turtles, and not dorsal, as in Ocepecephalon, which is also very off for a turtle.

Figure 3. Odontochelys and Trionyx. Note the teeth in ventral view of the Odontochelys skull.

Figure 3. Odontochelys and Trionyx. Note the teeth in ventral view of the Odontochelys skull. Click to enlarge.

The supratemporal problem
This evolutionary sequence demonstrates that the large supratemporal bones of turtles (the supratemporal horns of pre-turtles and Meiolania) have been traditionally mislabeled. This may be part of the problem that workers have had in nesting turtles in prior studies.

The molecule problem
Some researchers have found that turtle DNA is most closely matched to that of living archosaurs: crocs and birds. Everyone knows morphology does not support that nesting. Someone somewhere will figure this out someday.

References
Li C, Wu X-C, Rieppel O, Wang L-T and Zhao L-J 2008. An ancestral turtle from the Late Triassic of southwestern China. Nature 456: 497-501.

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Adding taxa to the Diadectes clade

Adding a few
and distinct Diadectes specimens (no two appear to be conspecific) opens the door to new insights into that corner of the cladogram. Some of the data are from 3D skull images with sutures delineated. Others are from firsthand observation. Some data are from drawings. Berman et al. 1992 made an interesting observation that prior authors illustrated the skull roof of Diadectes in a variety of ways (Fig. 1). The caption does not indicate that all were drawn from the same specimen. I suspect they were not.

Figure 1. How Berman et al. copied the illustrations of prior authors who each figured the skull roof of Diadectes. Perhaps these were several distinct specimens, not just one.

Figure 1. How Berman et al. copied the illustrations of prior authors who each figured the skull roof of Diadectes. Perhaps these were several distinct specimens, not just one. Not sure, at this point, which illustrations represent which specimens.

The Berman et al. phylogenetic analysis
included seven taxa, including two suprageneric taxa, Pelycosauria and Captorhinomorpha. They included only nine characters. The anamniote, Seymouria, was the outgroup. The first clade included Pelycosauria + (Limnoscelis +(Tseajaia and Diadectes). The second clade included Captorhinomorpha + Petrolacosaurus. The large reptile tree includes hundreds more taxa and characters. The pertinent subset is shown here (Fig. 2). It is also clear from the Berman et al. taxon set that they thought they were dealing with a small set of basal reptiles and pre-reptiles. In 2015 it is clear that they did not include the pertinent taxa they should have as some of these taxa are not related to any of the others except distantly.

Figure 2. How the large reptile tree lumps and splits the several Diadectes specimens now included here. Note that bolosaurids, including Phonodus, now nest within other Diadectes specimens.

Figure 2. How the large reptile tree lumps and splits the several Diadectes specimens now included here. Note that bolosaurids, including Phonodus, now nest within other Diadectes specimens.

Now, with current data
it is becoming increasingly clear that both bolosaurids and procolophonids nest within  a fully reptilian Diadectes clade. It is also clear that the genus Diadectes needs to be further split, as Kissel (2010) started to do by renaming Silvadectes and Oradectes from former Diadectes species.

Skeleton of Diadectes. Perhaps unnoticed are the broad dorsal ribs of this taxon, basal to Stephanospondylus, Procolophon and pareiasaurs.

Figure 3. Skeleton of Diadectes (UC 706, UC 1078). Perhaps unnoticed are the broad dorsal ribs of this taxon, basal to Stephanospondylus, Procolophon and pareiasaurs.

Also note
the placement of Stephanospondylus as a proximal sister taxon to the diadectids nesting at the base of the pareiasaurs (including turtles). Turtles are sisters to pareiasaurs and they ARE pareiasaurs because they are derived from pareiasaurs, just as birds are derived from theropod dinosaurs.

Figure 4. Click to enlarge. Stephanospondylus based on parts found in Stappenbeck 1905. Several elements are re-identified here. Note the large costal plates on the ribs, as in Odontochelys. The pubis apparently connected to a ventral plastron, not preserved. The interclavicle was likely incorporated into the plastron.

Figure 4. Click to enlarge. Stephanospondylus based on parts found in Stappenbeck 1905. Several elements are re-identified here. Note the large costal plates on the ribs, as in Odontochelys. The pubis apparently connected to a ventral plastron, not preserved. The interclavicle was likely incorporated into the plastron.

Like everyone who studies prehistoric reptiles
there is a day when you don’t know anything about a taxon and later there is a day when you are making contributions to Science. Those days keep on coming.

References
Berman DS, Sumida SS and Lombard E 1992. Reinterpretation of the Temporal and Occipital Regions in Diadectes and the Relationships of Diadectomorphs. Journal of Vertebrate Paleontology 66(3):481-499.
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Thesis (Graduate Department of Ecology & Evolutionary Biology University of Toronto).

The Phonodus-Bolosaurus-Bashkyroleter connection

This post might be boring.
These are the unpopular, rarely studied plain-looking reptiles that ultimately gave rise to many of the most interesting clades.

Bolosaurids
are rarely studied, rarely included in phylogenetic analyses and little has been published on them. Bolosaurus and Belebey are the classic specimens. Long-legged Eudibamus has been added to this clade by traditional workers (Berman et al. 2000), but the large reptile tree nests it instead with basal diapsids, like long-legged Petrolacosaurus.

The busiest and most difficult corner
of the large reptile tree always seemed to be between Milleretta and Macroleter (Fig. 1).This subset of the tree also includes many previous enigmas here resolved, including  turtles.

Figure 1. A subset of the large reptile tree focusing on the taxa between Milleretta and Lepidosauriformes, perhaps the most difficult corner of the large reptile tree.

Figure 1. A subset of the large reptile tree focusing on the taxa between Milleretta and Lepidosauriformes, perhaps the most difficult corner of the large reptile tree.

Phonodus was originally considered a procolophonid.
(Modesto et al. 2010). Here (Fig. 2) Phonodus nests close to procolophonids, but closer to bolosaurids. As an Early Triassic taxon, Phonodus represents a late surviving member of a Late Pennsylvanian/Earliest Permian radiation that produced Early Permian diadectids and others. Based on its unusual teeth, Phonodus was highly derived.

Figure 1. Phonodus tracing. This turns out to be a basal bolosaurid.

Figure 2. Phonodus tracing. This turns out to be a basal bolosaurid, close to procolophonids. Note the deeply excavated squamosal. The naris was originally overlooked. 

A related taxon
Bashkyroleter (Fig. 3) was originally considered a nyctoleterid parareptile (not a valid clade). Here (Fig. 1) Bashkyroleter is basal to the bolosaur/diadectid/procolophon clade and pareiasaur/turtle clade AND the remainder of the lepidosauromorpha, including the lanthanosuchids proximally. So, it is a key taxon, largely overlooked except for one paper (Müller and Tsuji 2007) on reptile auditory capabilities.

Yes,
this solidification of the large reptile tree involved some topology changes. Science is self correcting. New data brings new insights. One of these new insights involved Bashykyroleter and a previously overlooked connection of the lateral to the naris. (Fig. 2).

Figure 2. Bashkyroleter appears to have a small naris/lacrimal connection.

Figure 3. Bashkyroleter appears to have a small naris/lacrimal connection as shown above. If anyone has a dorsal, occipital  or palatal view of this taxon, please send it along. Another deeply embayed squamosal. 

References
Berman, DS, Reisz RR, Scott D, Henrici AC, Sumida SS and Martens T 2000. Early Permian bipedal reptile. Science 290: 969-972.
Modesto SP, Scott DM, Botha-Brink J and Reisz RR 2010. A new and unusual procolophonid parareptile from the Lower Triassic Katberg Formation of South Africa. Journal of Vertebrate Paleontology 30 (3): 715–723. doi:10.1080/02724631003758003.
Müller J and Tsuji LA 2007. Impedance-Matching Hearing in Paleozoic Reptiles: Evidence of Advanced Sensory Perception at an Early Stage of Amniote Evolution. PLoS ONE 2 (9): e889. doi:10.1371/journal.pone.0000889. PMC 1964539. PMID 17849018

A few more pareiasaurs added to the turtle family tree

Earlier the large reptile tree recovered several turtle ancestors among Sclerosaurus, various pareiasaurs, Stephanospondylus and, more distantly, bolosaurs. Today we’ll add a few more pareiasaurs to see what the updated tree (now 565 taxa) recovers (Fig. 1).

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Figure 1. New cladogram of turtle systematics. Note the separation of soft shell turtles with orbits visible in dorsal view from domed hard shell turtles with laterally oriented orbits here.

Typically
we see small taxa at the origin of major clades. That also happens in stem pareiasaurs (Bolosaurus2.5 cm skull length, Stephanospondylus,11 cm skull length, Fig. 3). Odontochelys (4cm skull length) is a small soft-shelled turtle. Sclerosaurus, the smallest of the pre-turtle candidates (Fig. 3), has a skull length of 8 cm, exclusive of the horns.

Proganochelys and Proterochersis, two Traissic turtles.

Figure 2. Proganochelys and Proterochersis, two Traissic turtles, both of substantial and similar size.

The added pareiasaur taxa
(Fig. 1) clarify the list of more distantly related turtle ancestors. Smaller horned forms without a shell, like Sclerosaurus, ultimately evolved to become shelled turtles with horns, like Meiolania, and then without horns, like Proganochelys. The loss of teeth may have happened at least twice (Fig. 1) and perhaps thrice.

Figure 3. Pareiasaur skulls to scale. Scutosaurus and Bradysaurus are the large ones. Sclerosaurus is the smallest one.

Figure 3. Pareiasaur skulls to scale. Scutosaurus and Bradysaurus are the large ones. Sclerosaurus is the smallest one. Elginia might be a turtle, but is only known from a skull. Click to enlarge. Note the various skull shapes attributed to several genera. This clade needs to be restudied in detail to clear up the confusion here.

The clade of pareiasaurs 
is understudied and, to my eye, currently in need of a good phylogenetic analysis based on every known bone. I am not able to do that with available data on the Internet, but the above cladogram is a good starting point. The latest work on Deltavjatia (Tsuji 2013) does not cover the entire clade, but does show an unusual variety for a single genus (Fig. 3). Perhaps a bit too much lumping here.

Wikipedia reports
“Pareiasaurs appear very suddenly in the fossil record. It is clear that these animals evolved from Nycteroleterids, perhaps a Rhipaeosaur-like form.” The large reptile tree does not confirm that assessment. Rather it finds pareiasaurs evolved from bolosaurs and millerettids. Wikpedia considered nycteroleterids to be procolophonids. They are not related according to the large reptile tree. Macroleter does nest as a sister to Stephanospondylus, which is basal to pareiasaurs + turtles.

Wikipedia also reports
“Some paleontologists have argued that pareiasaurs include the direct ancestors of modern turtles. Pareiasaur skulls have several turtle-like features, and in some species the scutes have developed into bony plates, possibly the precursors of a turtle shell. Jalil and Janvier, in a large analysis of pareiasaur relationships, also found turtles to be close relatives of the “dwarf” pareiasaurs, such as Pumiliopareia. However, the exact relationships of turtles remains controversial, and pareiasaur scutes may not be homologous with the shells of turtles.

From Wikipedia:
Hallucicrania (Lee 1995), The clade Hallucicrania was coined by MSY Lee, for Lanthanosuchidae + (Pareiasauridae + Testudines). Lee’s pareiasaur hypothesis is looking rather less likely following the discovery of Odontochelys, a transitional aquatic turtle with very non-pareiasaur-like teeth and whose half shell matches embryonic development in modern testudines. Recent cladistic analyses reveal that lanthanosuchids to have a much more basal position in the Procolophonomorpha, and that the nearest sister taxon to the pareiasaurs are the rather unexceptional and conventional looking nycteroleterids (Müller & Tsuji 2007, Lyson et al. 2010) the two being united in the clade Pareiasauromorpha (Tsuji et al. 2012).

The large reptile tree notes that these clade members are related to each other, but the clade is not monophyletic.

Pareiasauroidea (Nopcsa, 1928), The clade Pareiasauroidea (as opposed to the superfamily or suborder Pareiasauroidea) was used by Lee 1995 for Pareiasauridae + Sclerosaurus. More recent cladistic studies place Sclerosaurus in the procolophonid subfamily Leptopleuroninae (Cisneros 2006, Sues & Reisz 2008) which means the similarities with pareiasaurs are the result of convergences.

The large reptile tree notes that these taxa are related to each other, but the clade is not monophyletic and recovers Sclerosaurus with pareiasaurs, not procolophonids.

Pareiasauria (Seeley, 1988), If neither Lanthanosuchids or Testudines are included in the clade, the Pareiasauria only contains the monophyletic family Pareiasauridae. It’s a traditional linnaean term.

Correct. But it also contains Sclerosaurus and turtles if you want it to be monophyletic.

References
Lee, M. S. Y. 1993. The origin of the turtle body plan: bridging a famous morphological gap. Science 261: 1716-1720.
Lee MSY 1997. Pareiasaur phylogeny and the origin of turtles. Zoological Journal of the Linnean Society, 120(3): 197-280. doi:10.1111/j.1096-3642.1997.tb01279.x
Jalil N-E and Janvier P 2005. Les pareiasaures (Amniota, Parareptilia) du Permien supérieur du Bassin d’Argana, Maroc. Geodiversitas, 27(1) : 35-132.
deBraga M and Rieppel O 1997. Reptile phylogeny and the interrelationships of turtles. Zoological Journal of the Linnean Society, 120: 281-354.
Tsuji L. 2013. Anatomy, cranial ontogeny and phylogenetic relationships of the pareiasaur Deltavjatia rossicus from the Late Permian of central Russia. Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 104(2):1-42. DOI: 10.1017/S1755691013000492

Another turtle with teeth, Elginia (Newton 1893)

Several years ago
the world of paleontology was delighted to find a turtle with teeth, Odontochelys. Ironically, we’ve known about a turtle with teeth for over 120 years without realizing it.

Adding
the horned turtle, Meiolania (Owen 1882, 1888), to the large reptile tree (still not updated) was the key to realizing that Elginia (Newton 1893), which is known from a skull likewise festooned with spikes and horns, is an unrecognized turtle with teeth. These two represent a clade separate from the main turtle clade, which includes Odontochelys, Proganochelys and Chelonia, the living green sea turtle.

Figure 1. Elginia is a toothed turtle, basal to the giant horned toothless turtle, Meiolania.

Figure 1. Elginia is a toothed turtle, basal to the giant horned toothless turtle, Meiolania.

Elginia was long considered an odd sort of pareiasaur, a close outgroup to the turtles. Evidently, like Clark Kent and Superman, these two have never been tested together in phylogenetic analysis. Same old story retold again.

We’ll look at the details over the next few blog posts.

References
Newton ET 1893. On some new reptiles from the Elgin Sandstone: Philosophical Transactions of the Royal Society of London, series B 184:473-489.
Owen R 1882. Description of some remains of the gigantic land-lizard (Megalania prisca
Owen), from Australia. Part III.Philosophical Transactions of the Royal Society London, series B, 172:547-556.
Owen R 1888. On parts of the skeleton of Meiolania platyceps (Owen). Philosophical Transactions of the Royal Society London, series B, 179: 181-191.

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.

A new face for Sclerosaurus – at the base of the Pareiasauria

Sclerosaurus armatus (Meyer 1859) Middle Triassic ~50 cm in length, was originally considered a procolophonid, then a pareiasaurid, then back and forth again and again, with a complete account in Sues and Reisz (2008) who considered it a procolophonid.

FIgure 1. Sclerosaurus face.

FIgure 1. Sclerosaurus face.

Earlier I reconstructed a lower face for Sclerosaurus, a taxon known from a fossil that has been flattened but still has 3D elements. Unfortunately the top of the snout is missing, but most of the rest of the skull is present in 3D or in impressions. A recent review (what I’ve been doing for the last few months) brought new insight and a higher, more box-like face.

Figure 4. Sclerosaurus reconstructed.

Figure 2. Sclerosaurus reconstructed.

Sclerosaurus is a sister to Elginia, the pareiasaur with really big horns! Sclerosaurus is also a sister to Arganaceras, the basal pareiasaur or pareiasaur cousin with vestigial horns.

Arganaceras

Figure 3. Arganaceras, as originally reconstructed and modified. This taxon nests as a sister to Sclerosaurus and together they nest as the sister to the Pareiasauria. See the reduced horn on the suptratemporal?

Classic pareiasaurs, like Anthodon (Fig. 3), don’t have supratemporal horns, but they do raise the tabular and postparietals to the dorsal plane from the ancestral occipital plane. This is a big reversal since anamniotes also have tabulars and post parietals on the dorsal plane and intervening taxa do not.

Anthodon

Figure 4. Anthodon in various views from Lee (1997).

The outgroup taxon for pareiasaurs is the Early Permian giant millerettidStephanospondylus. The skeleton is poorly known, but no horns were present.

These wide-body omnivores/herbivores had to protect themselves from coeval predators. Turtles did this best. The rest went extinct for one reason or another. But these taxa give us the best picture of the many directions evolution took to solve the basic defense question.

References
Sues H-D and Reisz RR 2008. Anatomy and Phylogenetic Relationships of Sclerosaurus armatus (Amniota: Parareptilia) from the Buntsandstein (Triassic) of Europe. Journal of Vertebrate Paleontology 28(4):1031-1042. doi: 10.1671/0272-4634-28.4.1031 online

Sclerosaurus paleocritti