No longer an enigma: Kudnu mackinlayi

I live for discoveries like this one,
which started as a Facebook post of the tiny specimen. This is what the LRT (Fig. 3) was built for.

Benton 1985 wrote:
“Bartholomai (1979) has described Kudnu [QMF8181], a partial snout from the early Triassic of Australia, as a paliguanid. The exact relationships of these forms to each other, and to other early ‘lizard-like’ forms are unclear (Carroll, 1975a, b, 1977; Currie, 1981c: 163-164; Estes, 1983: 12-15). Indeed, the group cannot be defined by any apomorphy, and the genera must be considered separately. As far as can be determined, all of these genera are lepidosauromorphs. Kudnu lacks the lepidosaur character X4 and the squamate character Y 1, but none of the others may be determined. Blomosaurus and Kudnu are classified here as Lepidosauromorpha, incertae sedis.”

Figure 1. Kudnu colorized using DGS and slight restored postcranially, shown 10x natural size at a 72 dpi standard screen resolution. Here’s a taxon basal to Stephanospondylus, pareiasaurs and turtles. Prior workers excluded Stephanospondylus from their studies.

Contrad 2008 wrote:
“Other authors have followed this opinion and have described new ‘‘paliguanids’’, including Blomosaurus (Tatarinov, 1978) and Kudnu (Bartholomai, 1979). Even so, ‘‘Paliguanidae’’is widely regarded as a paraphyletic taxon and, unfortunately, the preservation of specimens constituting the known ‘‘paliguanid’’ genera (including Paliguana, Palaeagama, and Saurosternon) makes it impossible to characterize them except through plesiomorphy (Benton, 1985; Gauthier et al., 1988a; Rieppel, 1994). Thus, their position within Lepidosauromorpha is currently impossible to ascertain with any kind of precision.”

Evans and Jones 2010 wrote:
“Kudnu (Australia, Bartholomai, 1979) and Blomosaurus (Russia, Tatarinov, 1978) are too poorly preserved to interpret with confidence but are probably also procolophonian.”

Figure 2.  Stephanospondylus was considered a type of diadectid, but it nests with turtles and pareiasaurs, all derived from millerettids,.. next to diadectids.

All that being said,
what does the LRT recover? In the large reptile tree (LRT, 1583 taxa, subset Fig. 3) Kudnu nests basal to Stephanospondylus (Fig. 2), a late survivor from deep in the lineage of pareiasaurs + turtles, not far from bolosaurids + diadectids + procolophonids. These clades are derived from Milleretta (Fig. 2) which was  2 to 3x larger.

Due to its small size,
Kudnu can be considered phylogenetically miniaturized, the kind of taxon we often find at the base of many major reptile clades.

Sadly, earlier workers (see above)
were looking at the wrong candidates for sister taxa, excluding the right taxa. This is a problem that is minimized by the LRT due to its large number of taxa over a wide gamut.

Figure 2. Carbonodraco enters the LRT alongside another recent addition, Kudnu, at the base of the pareiasaurs + turtles.Figure 1. Carbonodraco enters the LRT alongside another recent addition, Kudnu, at the base of the pareiasaurs + turtles.

Once again,
you don’t need to see the fossil firsthand in a case like this. What you need is a wide gamut phylogenetic analysis like the LRT, to figure out how an enigma like Kudnu  nests with other reptiles.

If
Kudnu was earlier associated with Stephanospondylus, let me know and I will publish the citation. Otherwise, this is a novel hypothesis of interrelationships that inserts Kudnu without disturbing the rest of the LRT tree topology.

---

References
Bartholomai A 1979. New lizard-like reptiles from the Early Triassic of Queensland. Alcheringa: An Australasian Journal of Palaeontology 3:225–234.
Benton MJ 1985. Classification and phylogeny of the diapsid reptiles. Zoological Journal of the Linnean Society 84:97–164.
Conrad JL 2008. Phylogeny and systematics of Squamata (Reptilia) based on morphology.  Bulletin of the American Museum of Natural History 310: 182pp.
Evans SE and Jones MEH 2010. Chapter 2 The Origin, Early History and Diversification of Lepidosauromorph Reptiles in Bandyopadhyay S (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7_2 Springer-Verlag Berlin Heidelberg 2010

Sphodrosaurus: here identified as a stem soft shell turtle

Known for decades as an enigma,
Sphodrosaurus pennsylvanicus nests here more primitive than Odontochelys and sheds light on the pareiasaur-to-soft shell turtle transition.

FIgure 1. Partial reconstruction of Sphodrosaurus based on tracings in figure 2. This turtle is more basal than Odontochelys. Lots of loose parts here and no attempt was made to reassemble the manus or pes.

Colbert 1960
described Sphodrosaurus pennsylvanicus (Fig. 1) as, “A new Triassic procolophonid from Pennsylvania” based on North Museum No. 2321, a natural mold in ventral view of a partial skeleton (Fig. 2) resembling Hypsognathus and located less than a mile from the skull of this genus. In the large reptile tree (LRT, 1308 taxa; subset Fig. 3) Sphodrosaurus nests between the tiny pareiasaur Sclerosaurus (Fig. 4) and the basal soft-shell turtle (known only from skull material) Arganaceras.

Based on the appearance of a shape in the mudstone
beneath the ribs (in ventral view, thus dorsal in life), Sphodrosaurus appears to be (by observation and phylogenetic bracketing) the first taxon to have some sort of soft carapace without developing any sort of expanded ribs or any sort of plastron. Thus it informs on the likely appearance of the currently missing post-crania of Arganaceras. Some loose gastralia-like ossifications (in cyan) are apparent. These are plastron precursors (again, based on phylogenetic bracketing). These inform on a previously unknown genesis for the plastron in soft shell turtles. Sclerosaurus lacks them. Odontochelys has massive plastron elements.

Figure 2. Sphodrosaurus in situ, ventral view, with colors added to bones and possible soft carapace impression overlooked originally. Colbert  1960 tracing also shown here.

Traditionally
Sclerosaurus nests with procolophonids, but that nesting is based on taxon exclusion. Sphodrosaurus is very similar to Sclerosaurus, but a little more derived toward the soft shell turtles.

Figure 3. Sphodrosaurus nests with other soft-shell turtles arising from pareiasaurs without invoking the carapace.

Sphodrosaurus pennsylvanicus (Colbert 1960; North Museum No. 2321; Newark Supergroup, latest Carnian, Late Triassic). Distinct from Sclerosaurus, the femur is longer, the coracoid is smaller. The antebrachium is longer. As in Trionyx, pedal digit 5 is gracile. The specimen was found in mudstones. Note the wide, flat torso, the tall, slender scapula, sigmoidal femur and long-clawed toes… all turtle traits.

Colbert reported,
“The skull seems to have been unusually large in comparison to the size of the postcranial skeleton. The posterior portion of the skull is produced back into a “frill,” as is common in the advanced procolophonids, this frill covering about five cervical vertebrae. There are 25 presacral vertebrae, to which are articulated widely spreading holocephalous ribs. The scapula is rather slender, the ilium seemingly deep. The pubis and ischium are platelike bones, the former being proximally constricted and distally expanded. The hind limbs are large, the extended limb being approximately equal in length to the total length of the presacral series of vertebrae. In total length and in each of its component sections the linear dimensions in the hind limb are about double those in the fore limb. The metatarsals are rather slender, and long. The ungual phalanges of the pes are large, pointed claws.”

Figure 4. Sclerosaurus reconstructed.

Colbert continues,
“Perhaps the most striking differences between this form and the established genera of procolophonids are in the great length and robust size of the hind limb in the Pennsylvania specimen, and the long, sharp claws of the pes. Such characters might lead one to doubt the true procolophonid relationships of Sphodrosaurus, but other characters, such as size, the obviously large skull, the extension of the back of the skull in a sort of frill over the cervical region, the evidently broad vertebral neural arches (as indicated by the separation of the heads of the ribs), and the holocephalous, flaring ribs, are all characters that point to procolophonid affinities for Sphodrosaurus.”

The following paper
was discovered after the reconstruction and phylogenetic analysis were made:

Sues, Baird and Olsen 1993 reexamined Sphodrosaurus
and determined that the specimen was not a procolophonid, but some sort of diapsid or neodiapsid. They note, Baird (1986) suggested rhynchosaurine affinities. They also note “This combination of characters has not been found in any other known diapsid.” 

The authors note
the preservation of the posterior mandibles, rather than a set of dorsal skull bones as Colbert reported. They failed to see the detached retroarticular process. The cervicals and anterior dorsals have a ventral ridge. So do soft-shell turtles, but the authors did not make that connection. What they identify as extremely long cervicals parallel to the spine and apparently coosified are interpreted here as clavicles. They remarked on the “great width of the trunk region,” as in pareiasaurs and turtles, but the authors did not make that connection. They note the scapula has a “slender  blade”, as do turtles, but the authors did not make that connection. They note the femur is sigmoidal, as in turtles, but the authors did not make that connection.

The authors conclude,
“The mode of preservation of the holotype and only known specimen of Sphodorsaurus pennsylvanicus leaves very few anatomical features for assessing its phylogenetic position.” This is true, but phylogenetic analysis over a wide gamut of potential candidates leaves no doubt in the LRT about where this specimen nests, based on the characters that are visible. There is no mention of pareiasaurs or turtles in the Sues, Baird, Olsen 1993 paper.

As in many enigma taxa studied here,
the solution to their nesting problem appears whenever the enigma taxon is permitted to be tested against a wide gamut of taxa. This minimizes initial bias and lets the software do what it was intended to do… keep human preconceptions from interfering in a cold-blooded scientific process.

Added later the same afternoon
Rice et al. 2016 report: “We show that plastron development begins at developmental stage 15 when osteochondrogenic mesenchyme forms condensates for each plastron bone at the lateral edges of the ventral mesenchyme.” In this way ontogenesis recapitulates the phylogenesis demonstrated by Sphodrosaurus.

References
Colbert EH 1960. A new Triassic procolophonid from Pennsylvania. American Museum Novitates 2022:1–19.
Rice R, Kallonen A, Cebra-Thomas J and Gilbert SF 2016. Development of the turtle plastron, the order-defining skeletal structure. PNAS 113 (19):5317–5322.
Sues H-D, Baird D and Olsen PE 1993. Redescription of Sphodrosaurus pennsylvanicus Colbert, 1960 (Reptilia) and a Reassessment of its Affinities. Annals of Carnegie Museum 62(3):245-253

wiki/Arganaceras
wiki/Sclerosaurus
http://reptileevolution.com/arganaceras.htm

North Museum of Nature and Science
Franklin and Marshall College
400 College Avenue
Lancaster, PA 17603
717.358.3941

Turtles as Hopeful Monsters – Future book and past essay by O. Rieppel

Figure 1. Turtles as Hopeful Monsters by O. Rieppel, a book due to be published in 2017. The cover pictures Odontochelys, the earliest known soft shell turtle. The 2001 summary with the same title by O. Rieppel is the subject of the present blogpost.

Summary of this blogpost:
Without a large gamut phylogenetic analysis, such as the large reptile tree, that recovers two turtle clades derived from two phylogenetically reduced pareiasaur clades, any discussion of the origin of turtles is handicapped and will suffer from a surfeit of guesswork and error due to taxon exclusion. Sclerosaurus, Meiolania and Elginia are rarely considered in such studies, but are key to understanding turtle origins. Thankfully we have excellent embryological studies that more or less recapitulate phylogeny.

Dr. Rieppel has long been an advocate of a diapsid/placodont ancestry for turtles, and has applied molecule evidence to link turtles with archosaurs. He was part of the Odontochelys (Fig.1 ) team.

The hopeful monsters hypothesis is a biological theory which suggests that major evolutionary transformations have occurred in large leaps between species due to macro mutations. The LRT does not support major evolutionary transformations. All transitional taxa greatly resemble their nested sisters and microevolution is the only factor at play here.

From the Rieppel summary:
“A recently published study on the development of the turtle shell highlights the important role that development plays in the origin of evolutionary novelties.”

“Early theories attempted to explain the evolution of the turtle shell in the context of a step-wise, hence gradual process of transformation. The distant ancestor of turtles was hypothesized to have had a body loosely covered by osteoderms. Within the evolutionary lineage leading to turtles, the number of osteoderms would have gradually increased, until the bony plates would eventually have provided a complete covering of the trunk, thus forming an epitheca. Thecal ossifications would have developed below the epi- theca at later stages in the evolution of the turtle body plan, while epithecal ossifications would subsequently be lost at even more advanced stages of turtle evolution. This theory met with various difficulties, however, such as the fact that the earliest fossil turtle (Proganochelys) from the Upper Triassic of Europe (215 Mio years) has a complete theca. Furthermore, epithecal ossifications appear later than ossifications of the theca in development and, in modern turtles, epithecal ossifications tend to form in evolutionarily relatively advanced forms only.

“Turtles are unique among tetrapods, however, in that the shoulder blade (scapula) lies inside the rib cage (Fig. 3). The reason for this inverse relationship of the scapula is the close association of the ribs with the costal plates of the theca. The scapula of turtles comes to lie inside the rib cage because of a deflection of rib growth to a more superficial position. Recent developmental work has identified inductive interaction generated by the carapacial ridge as probable cause of this deflection of rib growth.

“A recent theory proposed the evolution of turtles from Paleozoic Pareiasaurs by a process of “correlated progression”. Correlated key elements of this progressive transformation are an increase in the number of osteoderms until they form a closed dorsal shield (carapace), the broadening of the ribs below this dorsal hield, the shortening of the trunk, the immobilization of the dorsal vertebral column and a backwards shift of the pectoral girdle.”

In the phylogenetic analysis provided by the LRT
turtles have two parallel origins, both from pareiasaurs: One for the domed, hard-shell clade (Bunostegos > Elginia > Meiolania) and one for the flattened soft-shell clade (Sclerosaurus > Odontochelys > Trionyx). In both these cases it appears that the tall scapula extended to either side of the narrow, cervical-like dorsal ribs. Then the anterior dorsal ribs rotated anteriorly over the tall scapulae, paralleling the rotation of the elbow anteriorly. You’ll note that turtles have more cervicals and fewer dorsals than pareiasaurs. The posterior cervicals in turtles appear to be the former dorsals of pareiasaurs. So, the pectoral girdle did not shift, but the posterior cervicals and anterior dorsals transformed around them. And this occurred during phylogenetic miniaturization.

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

Distinct from other reptiles
turtles do not have lateral movement in the torso with precursors in the short-torsoed, heavily ribbed pareiasaurs. “This repositioning of the vertebrae relative to the primary body segments is achieved by resegmentation of the somites. Each somite splits in half, and the posterior part of one somite recombines with the anterior part of the succeeding somite to form a vertebra,” reports Rieppel.

Figure 1. Hard shell turtle evolution with Bunostegos, Elginia, Meiolania and Proganochelys. The narrow and tall scapulae of pareiasaurs are carried forward in their descendant turtles during phylogenetic miniaturization. 

More from Dr. Rieppel
“As a turtle embryo grows and develops, the contours of the future carapace are soon mapped out by an accelerated growth and a thickening of the skin on its back.”

“The ribs of turtles are unique among vertebrates in that they chondrify within the deep layers of the thickened dermis of the carapacial disk.”

It has been known for over 100 years that in turtles, the neural arches of the dorsal vertebrae shift forward by half a segment, carrying the ribs with them, again a unique condition in amniotes.”

Embryological studies
(Ruckes 1929) indicate, “the scapula of turtles comes to lie inside the rib cage because of a deflection of rib growth to a more superficial position. The ribs come to lie lateral to the no longer functional intervertebral joints. The functional reason for this anterior shift of the neural arches is not clear, other than that it may contribute to the mechanical strength of the carapace, as the neural plates come to alternate with the costal plates. Neural and costal plates are endoskeletal components of the turtle carapace, and cannot be derived from a hypothetical ancestral condition by fusion of exoskeletal osteoderms. All other parts of the turtle carapace are exoskeletal.” Rieppel reports, “The turtle body plan is evidently highly derived, indeed unique among tetrapods.”

I’m going to say ‘not true’ here…
Several turtle-like forms developed among placodonts and the two turtle clades developed independently in parallel. Glyptodon had a turtle-like carapace, but no plastron. Even Minimi, the phytodinosaur, developed a club tail, convergent with meiolaniids.

Moreover, only the shells of the two clades of turtles are unique unto themselves, as most other of their body parts are microevolutionary adjustments from their separate micro pareiasaur bauplans. And, based on current fossil chronology, they had 25 to 45 million years to develop their respective shells from their proximal outgroup sisters.

References
Gilbert SF, Loredo GA, Brukman A, Burke AC. 2001.  Morphogenesis of the turtle shell: the development of a novel structure in tetrapod evolution. Evol Dev 2001;3:47 ± 58.
Götte A 1899. Über die Entwicklung des knoÈ chernen RuÈ ckenschildes (Carapax) der SchildkroÈten. Z wiss Zool 1899;66:407±434.
Lee MSY 1996. Correlated progression and the origin of turtles. Nature 1996;379:811- 815.
Rieppel O 1996. Turtles as diapsid reptiles. Nature 384 (6608), 453-455
Rieppel O 2001. Turtles as hopeful monsters. BioEssays 23:987-991.|
Rieppel O 2012. The Evolution of the Turtle Shell. Morphology and Evolution of Turtles. Part 2, 51-61. DOI: 10.1007/978-94-007-4309-0_5
Rieppel O 2017. Turtles as Hopeful Monsters. Origins and Evolution. Indiana University Press. 212 pp.. Online here.
Ruckes H. 1929 (12) Studies in chelonian osteology. Part II. The morphological relationships between girdles, ribs and carapace. Ann NY Acad Sci 1929;31:81-120.

Rieppel book summary online

The plate and counterplate of Sclerosaurus

Earlier the large reptile tree nested the small pareisaur Sclerosaurus armatus (von Meyer 1857; Early to Middle Triassic; 30 cm long; Fig.1) at the base of the soft shell turtle clade (Fig. 2). This is at odds with current thinking (see below). Here the software program Adobe Photoshop enables researchers to superimpose the fossil plate upon the counterplate to provide a more complete set of data. This is the DGS method, a tried and true method for identifying bones to aid in interpretation as a prelude to creating a reconstruction. It’s much better than simply putting a label or arrow somewhere on the unoutlined bone. The only limitations are in the data available and the expertise of the interpreter.

Figure1. Click to enlarge. The plate and counter plate of Sclerosaurus, an ancestral taxon to soft shell turtled. Girdles and extremities are reconstructed. Frames change every 5 seconds. Here imposing the  plate and counter plate upon one another in Photoshop helps to reconstruct the specimen. The humerus has been rotated about 180 degrees during taphonomy.

Sclerosaurus armatus (Meyer 1859, Sues and Reisz 2008; 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. After Procolophon, Sues and Reisz (2008) considered Tichvinskia, Hypsognathus, Leptopleuron and Scoloparia sister taxa to Sclerosaurus. These all nest with Diadectes in the large reptile tree, not pareiasaurs.

Wikipedia also reports that Sclerosaurus is a procolophonid. Shifting Sclerosaurus to the procolophonids in the large reptile tree adds 55 steps.

Figure 2. 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.

Here, based on data from Sues and Reisz (2008), Sclerosaurus nests between pareiasaurs and basal soft-shell turtles like Odontochelys and Trionyx. It is a sister to Arganaceras, but was smaller with larger supratemporal horns.

FIgure 3. Sclerosaurus face.

Figure 4. Sclerosaurus reconstructed.

References
Meyer H von 1859. Sclerosaurus armatus aus dem bunten Sandestein von Rheinfelsen. Palaeontographica 7:35-40.
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

wiki/Sclerosaurus

 

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 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. 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.

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 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.

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. 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

Procolophonid phylogeny – problems and solutions

Cisneros 2008 reviewed the “procolophonids” as traditionally assumed (Fig. 1) and created a  focused phylogenetic family tree with Nyctiphruretus and Owenettids at the base and Procolophon, Hypsognathus and Sclerosaurus as derived taxa (Fig.1). Unfortunately, this topology was not replicated in the large reptile tree. Moreover, the Cisnernos tree appears to be upside down.*

Figure 1. The traditional procolophonid family tree according to Cisneros 2008. Highlighted taxa are found scattered in the large reptile tree (figure 2). Nyctiphruretus is the outgroup. Owenettidae is the secondary outgroup. The large reptile tree found Orobates to be the outgroup for Procolophon and kin (Fig. 2). Nowhere here are any diadectids, the sister group to Procolophon and kin in the large reptile tree. 

Figure 2. A segment of the large reptile tree with a gamut more or less equal to the Cisneros 2008 tree demonstrating the large number of excluded intervening taxa discovered by increasing the inclusion set. Highlighted taxa are found in the Cisneros 2008 tree (figure 1).

The large reptile tree
found a different topology (Fig. 2) with Hypsognathus and Procolophon at the base derived from a sister to Orobates. Sclerosaurus nested with pareiasaurs. Nyctiphruretus and owenettids nested as derived taxa basal to lepidosaurs (outgroup to Paliguana). Clades were widely separated from one another by numerous taxa.

Background
Cisneros 2008 reviewed the prior literature on the subject, noting with regularity that owenettids were previously not associated with procolphonids and otherwise often are found to each be monophyletic taxa. That all changed when Reisz and Laurin (1991) considered Owenetta to be a procolophonid. DeBraga and Rieppel (1997) found an Owenettidae-Procolophonidae clade. DeBraga (2003) placed Sclerosaurus within the Procolophonidae.

The problem
with Cisneros 2008 and the other prior papers listed above appears to be a reliance on small traditional inclusion sets without basing them on a verified and valid larger gamut study, like the large reptile tree (Fig. 2). Such a large study establishes broader relationships. Then more focused studies, like Cisneros 2008, can proceed with greater confidence and fewer taxon inclusion/exclusion errors.

This is the reason to have a large gamut study of the reptile family tree — to avoid such assumptions based on tradition, not testing. Larger trees also establish outgroups better.

Real procolophonids
Are restricted to Hypsognathus and Procolophon (from the large reptile tree), plus the procolophonid cousins listed in figure 1. Sclerosaurus, nyctiphruretids and owenettids belong to small non-procolophonid clades on the new Lepidosauromorpha branch leading to lepidosaurs, further to the right in the tree, far from the true procolophonids.

References
Cisneros JC 2008. Phylogenetic relationships of procolophonid parareptiles with remarks on their geological record. Journal of Systematic Palaeontology 6(3): 345-366.
deBraga M 2003. The postcranial skeleton, phylogenetic position, and probable life style of the Early Triassic reptile Procolophon trigoniceps. Canadian Journal of Earth Sciences 40: 527–556.
DeBraga M and Rieppel O 1997. Reptile phylogeny and the interrelationships of turtles. Zoological Journal of the Linnean Society 120: 281–354.
Reisz RR and Laurin M 1991. Owenetta and the origin of turtles. Nature 349: 324–326.

* We’ve seen such trees before here, with phylogenetic relationships perfectly ordered but upside-down.

A tree topology change – turtles and pareiasaurs move from diadectids to millerettids

I spent last week adding taxa and running through potential problems with the large reptile tree. Several matrix boxes were rescored. The result shifted turtles + pareiasaurs from Diadectides + Procolophon  to Milleretta RC70 + Odontochelys (a near-turtle now, not a real turtle), which we discussed earlier.

An interesting shift. 
Moving pareiasaurs + Proganochelys back to Diadectes + Procolophon now adds 22 steps. Moving pareiasaurs + turtles to Eunotosaurus (following the results of Lyson et al. 2013) adds 28 steps.

The RC14 specimen of Milleretta is still in the same clade as Acleistorhinus + Eunotosaurus + Austraolthyris + Feeserpeton + Belebey + Bolosaurus. 

Maybe not as crazy as it sounds
It’s the “plain brown sparrows” like Milleretta, that lie at the bases of major clades, not the highly derived taxa, like Procolophon and Diadectes. Those become extinct. The various specimens of Milleretta have long been ignored, but they really are the keys to understanding the reptile family tree.

References
Broom R 1913. On the Structure and Affinities of Bolosaurus. Bulletin of the American Museum of Natural History 32:509-516
Broom R 1938 On the Structure of the Reptilian Tarsus: Proceedings of the Zoological Society of London, v. 133, 108, p. 535-542.
Broom R 1948. A contribution to our knowledge of the vertebrates of the Karroo beds of South Africa: Transactions of the Royal Society of Edinburgh, Endinburgh 61: 577-629.
Case EC 1907. Description of the Skull of Bolosaurus striatus Cope. Bulletin of the American Museum of Natural History 23:653-658
Cope ED 1878. Descriptions of extinct Batrachia and Reptilia from the Permian formations of Texas. Proceedings of the American Philosophical Society 17:505-530
Gow CE 1972. The osteology and relationships of the Millerettidae (Reptilia: Cotylosauria). Journal of Zoology, London 167:219-264.
Watson DMS 1954. On Bolosaurus and the origin and classification of reptiles.Bulletin of the Museum of Comparative Zoology at Harvard College,, v. 111, no. 9444-449.

wiki/Milleretta
wiki/Bolosaurus

The origin of pareiasaurs (and turtles).

Revised July 13, 2014 with a new image of Sclerosaurus.

Figure1. Pareiasaur (Anthodon) and its phylogenetic predecessor, Stephanospondylus, a robust millerettid and an ancestor to turtles. Note the close correspondence of dorsal skull elements.

Earlier we looked at the ancestry of hard shell turtles (starting with Proganochelys) and soft shell turtles (starting with Odontochelys). According to the large reptile tree, the closest sister taxon to turtles is the clade Pareiasauria, represented above by Anthodon (Fig. 1). Stephanospondylus is basal to pareiasaurs followed more distantly diadectids, bolosaurids and ultimately Milleretta. So pareiasaurs AND turtles are sisters to diadectids and millerettids,

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

Sues and Reisz (2008) considered Sclerosaurus a procolophonid, but their concept of a procolophonid was much greater (includes more taxa) than is appropriate, according to the results of the large reptile tree.

References
Broom R 1938 On the Structure of the Reptilian Tarsus: Proceedings of the Zoological Society of London, v. 133, 108, p. 535-542.
Broom R 1948. A contribution to our knowledge of the vertebrates of the Karroo beds of South Africa: Transactions of the Royal Society of Edinburgh, Endinburgh 61: 577-629.
Gow CE 1972. The osteology and relationships of the Millerettidae (Reptilia: Cotylosauria). Journal of Zoology, London 167:219-264.
Hartmann-Weinberg AP 1933. Evolution der Pareiasauriden: Trudy Palaeontological institute Academe Nauk, SSSR, 1933, n. 3, p. 1-66.
Lee MSY 1997. Pareiasaur phylogeny and the origin of turtles. Zoological Journal of the Linnean Society 120: 197-280.
Owen R 1876. Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the Collection of the British Museum. London, British Museum (Natural History).
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

wiki/Anthodon
wiki/Deltavjatia
Deltavjatia paleocritti
wiki/Pareiasaur
Sclerosaurus paleocritti
wiki/Milleretta

Lee 1993 – An Important Contribution to Turtle Origins

Earlier we looked at several convergent turtle-like taxa. Today we’ll take a good look at the pareiasaurs, the second* closest taxon to the turtles themselves.

The origin of turtles
is one of the most hotly debated topics in paleontology. Unique among living amniotes, turtles have a carapace, plastron and a shoulder girdle within the rib cage. Some DNA studies point to an archosaur link. Other studies link turtles to lizards. Only the large reptile tree looked at over 335 possible nesting sites for turtles and came up with one.

Dr. Michael S. Y. Lee (1993) provided the best published morphological report on turtle origins to date. This paper precedes the discovery of Odontochelys (Li et al. 2008), overlooks Stephanospondylus (Geinitz and Deichmuller 1882) and nests turtles with pareiasaurs like Deltavjatia (Hartmann-Weinberg 1937).

Figure 1. The pareiasaur Deltavjatia identifying turtle traits: A2 – Foramen palatinum medially located (similar to the suborbital fenestra). A8 – Supraoccipital forms a long, high, narrow and median ridge sutured to the skull roof along its entire length. A12 – Scapula with acromion process on the anterior margin. A13 – Humerus with ectepicondylar foramen. B1 – (Fig. 1) Twenty or fewer presacral vertebrae. B2 – Tall and narrow scapula (4x higher than wide). B3 – Shoulder glenoid not screw-shaped, but bipartite. B4 – Scapula oriented anterodorsally, not horizontally. B8 – Thick dermal armor over the dorsal region.

In Lee (1993) pareiasaurs were found to share 16 derived traits with turtles. These traits are identified with an “A“.

Cranial traits synapomorphies:
A1 – (Fig. 2) Choana (internal nares) located far medially.
A2 – (Figs. 1,2) Foramen palatinum medially located (similar to the suborbital fenestra).
A3 – (Fig. 2) Massive horizontal paroccipital process sutured to squamosal.
A4 – (Fig. 2) Long lateral flange of the exoccipital on the posterior face of the paroccipital process.
A5 – (Fig. 2) Basisphenoid and basioccipital ossified together.
A6 – (Fig. 2) Ossified medial wall of prootic.
A7 – (Fig. 2) Transverse flange of pterygoid reduced and forwardly directed.
A8 – (Fig. 1`) Supraoccipital forms a long, high, narrow and median ridge sutured to the skull roof along its entire length.
A9 – The entire palate is raised well above the ventral margin of the maxilla.

Figure 2. More turtle traits in pareiasaurs. A1 – Choana located medially. A2 -Foramen palatinum medially located. A3 – Massive horizontal paroccipital process sutured to squamosal. A4 – Long lateral flange of the exoccipital on the posterior face of the paroccipital process. A5 – Basisphenoid and basioccipital ossified together. A6 – Ossified medial wall of prootic. A7 – Transverse flange of pterygoid reduced and forwardly directed. A9 – The entire palate is raised well above the ventral margin of the maxilla.

Postcranial Trait Synapomorphies
A10 – (Fig. 3) Prominent lateral projections on at least the first 14 caudal vertebrae.
A11 – (Fig. 3) Chevrons not wedged between adjacent centra.
A12 – (Figs. 1, 3) Scapula with acromion process on the anterior margin
A13 – (Fig. 1) Humerus with ectepicondylar foramen.
A14 – (Fig. 3) Femur with a major trochanteron the posterior margin.
A15 – (Fig. 3) Reduced pedal digit 5.
A16 – Prominent dorsal buttress, V-shaped in ventral view, overhanging the acetabulum.

Figure 3. Postcranial turtle traits in pareiasaurs. A10 – Prominent lateral projections on at least the first 14 caudal vertebrae. A11 – Chevrons not wedged between adjacent centra. A12 – Scapula with acromion process on the anterior margin. A14 – Femur with a major trochanteron the posterior margin. A15 – Reduced pedal digit 5.

Sclerosaurus
Nine more traits are shared by Proganochelys, pareiasaurs and Sclerosaurus, the smaller, flatter, pareiasaur sister. These are identified with a “B” by Lee (1993).

B1 – (Fig. 1) Twenty or fewer presacral vertebrae.
B2 – (Figs. 1, 3) Tall and narrow scapula (4x higher than wide).
B3 – (Figs. 1, 3) Shoulder glenoid not screw-shaped, but bipartite.
B4 – (Figs, 1-3) Scapula oriented anterodorsally, not horizontally.
B5 – Reduced manual phalangeal formula (23332)
B6 – (Fig. 3) Astragalus and calcaneum fused
B7 – (Fig. 3) Reduced pedal phalangeal formula (23343)
B8 – (Fig. 1) Thick dermal armor over the dorsal region.
B9 – Loss of gastralia.

The large reptile tree found Sclerosaurus to be a derived pareiasaur, not closer to turtles. Chronologically Stephanospondylus preceded turtles and Sclerosaurus by 70 million years. Stephanspondylus preceded pareiasaurus by 35 million years, plenty of time for these radiations to occur. Look for primitive turtles in the mid to late Permian, concurrent with pareiasaurs.

But wait, there’s more…
The large reptile tree used only a few of the above traits yet to likewise nest turtles with pareiasaurs and Sclerosaurus. Stephanospondylus does not preserve any palate, tail, manus femur, pes or armor data.

The scapula question
Lee notes that pareiasaurs and Sclerosaurus possess 5 cervicals and 14-15 dorsals for a total of 19 to 20. Turtles possess 8 cervicals and 10 dorsals, meaning that 3 turtle cervicals are former dorsals. This change was accompanied by a posterior shift of the pectoral girdle (Watson 1914) that is recapitulated during turtle ontogeny (embryogenesis).

All known pareiasaurs are too pareiasaur-y to be ancestral to turtles
*Stephanospondylus is a key taxon linking diadectids to pareiasaurs and turtles that avoids being to “pareiasaur-y.” No known archosaur shares so many turtle traits. No known sauropterygian comes close either. Out of 335+ taxa, Stephanospondylus remains the best candidate I’ve found. But, sans that taxon, turtles would nest just outside the Pareiasauria.

Hats off to Dr. Lee for doing a great job.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Geinitz HB and Deichmüller JV 1882. Die Saurier der unteren Dyas von Sachsen. Paleontographica, N. F. 9:1-46.
Hartmann-Weinberg AP 1933. Evolution der Pareiasauriden: Trudy Palaeontological institute Academe Nauk, SSSR, 1933, n. 3, p. 1-66.
Lee MSY 1993. The Origin of the Turtle Body Plan: Bridging a Famous Morphological Gap. Science 264:1716-17-1719.
Li C, Wu X-C, Rieppel O, Wang L-T, Zhao L-J 2008. An ancestral turtle from the Late Triassic of southwestern China. Nature 456: 497-501.
Romer AS 1925. Permian amphibian and reptilian remains described as Stephanospondylus. Journal of Geololgy 33: 447-463.
Stappenbeck R 1905. Uber Stephanospondylus n. g. und Phanerosaurus H. v. Meyer: Zeitschrift der Deutschen Geologischen Gesellschaft, v. 57, p. 380-437.
Watson DMS 1914. Eunotosaurus africanus Seeley and the ancestors of the Chelonia. Proceedings of the Zoological Society of London 11:1011.

Palaos discussion

Pareiasaurs. Giant Millerettids.

Updated April 10, 2015. This error was corrected in the reptile tree long ago, but the post was not updated until today.

The recent paper on Arganaceras (Jalil and Janvier 2005), the horn-snouted pareiasaur, got me thinking about pareiasaur phlogeny, a dodgy issue involving turtles and lanthanosuchids, not to mention diadectids, which aren’t even supposed to be reptiles~!

Figure 1. Arganaceras, as originally reconstructed and modified.

Arganaceras 
A recent paper by Jalil and Janvier (2005) described a new Late Permian pareiasaur with twin nasal horns, Arganaceras vacanti. They nested it as a “much derived form ” close to Elginia, a pareiasaur with atypical bull-like horns developing from enlarged and pointed supratemporals (Fig. 1). For comparison, Deltavjatia (Fig. 2) was a more typical basal pareiasaur.

Figure 2. The pareiasaur Deltavjatia.

Revised Reconstruction
Two reconstructions of Arganaceras are shown (Fig. 1), the original and an alternate with modifications. From examination of the printed materials and comparisons to sisters, it appears that the lacrimal should be a small bone and the frontal should broadly contact the orbit. No other pareiasaur has such a large lateral naris, so by reversing the nasal bone a more typical morphology reappears.

Arganaceras was not tested yet against a large number of pareiasaurs, but at present it nests as a basal one. Elginia was indeed a sister, but it also branched off near the base along with Arganaceras.

A Pareiasaur Skull Table
Below are several diadectid/pareiasaur/turtle skulls in dorsal view and in phylogenetic order. In some the orbits are not visible in dorsal view. In others they are barely visible in lateral view. In some the quadratojugal expands laterally to form cheek extensions, but not in others. In some horns develop from the supratemporals. Others develop horns elsewhere. Turtles developed a shell. Others were more lightly armored. Lanthanosuchus was the first in the lizard lineage to develop a lateral temporal fenestra. So, beyond traditional views that consider them odd offshoots, pareiasaurs were instead key taxa, vital to our understanding of reptile evolution during the Permian.

Figure 3. Click to Enlarge. Basal diadectomorphs featuring Pareiasaurs, Procolophonids, Lanthanosuchids and Turtles. New data shows that Milleretta was basal to both diadectomorphs and the pareiasaur/turtle clade.

Procolophonids?
Taxa with over-sized orbits, such as Hypsognathus, have been traditionally considered procolophonids. Such overextended orbits are thought to have also contained jaw muscles. Here only Hypsognathus nests with Procolophon. Be that as it may, the present tree indicates that some phylogenetic distance separated Nyctiphruretus and Macroleter from Procolophon. The putative procolophonids, Owenetta and Barasaurus were further removed, derived from Macroleter and kin.

Turtles in Convergence
Turtles nest as sisters to pareiasaurs, but from above Odontochelys appears to share more traits with Orobates and Proganochelys appears closer to Diadectes. These convergences only emphasize the problems paleontologists have had trying to nest turtles with other reptiles. And thank goodness for PAUP*!

As More Taxa Are Added This Tree May Change
These millerettid descendants have never been tested together, which is the reason why this tree varies from the one posted on Wiki. Don’t take this as the final word either. (Updated April 10, 2015, thank you, L.A. for noticing the problem.) See the large reptile tree for the latest nestings. When this post was first created in 2011, there were far fewer taxa and some of the data was poor.

References
Jalil N-E and Janvier P 2005. Les pareiasaures (Amniota, Parareptilia) du Permien supérieur du Bassin d’Argana, Maroc. Geodiversitas 27(1):35-132.