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.

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 1. Click to enlarge. Stephanospondylus was considered a type of diadectid, but it nests with turtles and pareiasaurs, all derived from millerettids.

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

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

Resurrecting extinct taxa: Pareiasauria, Compsognathidae and Ophiacodontidae

Earlier we looked at
four clades thought to be extinct, but are not extinct based on their nesting in the large reptile tree (LRT, 1366 taxa). Today, three more:

Figure 2. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

Figure 1. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

Pareiasauria
According to Wikipedia, “Pareiasaurs (meaning “cheek lizards”) are an extinct group of anapsid reptiles classified in the family Pareiasauridae. They were large herbivores that flourished during the Permian period.”

In the LRT two clades of turtles (Fig. 1) are derived in parallel from two small horned pareiasaurs.

Figure 1. Lately the two clades based on two specimens of Compsognathus (one much larger than the other) have merged recently.

Figure 2.  Lately the two clades based on two specimens of Compsognathus (one much larger than the other) have merged recently.

Compsognathidae
According to Holtz 2004, “The most inclusive clade containing Compsognathus longipes but not Passer domesticsus.” Traditionally Compsognathus nests outside the Tyrannoraptora, a clade that traditionally leads to birds.

In the LRT Compsognathus specimens nest at the base of several theropod clades (Fig. 2) including the tyrannosaurs and Mirischia, Ornitholestes and the feathered theropods leading to birds.

Figure 1. Varanosaurus, Ophiacodon, Cutleria and Ictidorhinus. These are taxa at the base of the Therapsida. Ophiacodon did not cross into the Therapsida, but developed a larger size with a primitive morphology. This new reconstruction of Ophiacodon is based on the Field Museum (Chicago) specimen. Click to enlarge.

Figure  3. Varanosaurus, Ophiacodon, Cutleria and Ictidorhinus. These are taxa at the base of the Therapsida. Ophiacodon did not cross into the Therapsida, but developed a larger size with a primitive morphology. This new reconstruction of Ophiacodon is based on the Field Museum (Chicago) specimen. Click to enlarge.

Ophiacodontidae
According to Wikipedia, “Ophiacodontidae is an extinct family of early eupelycosaurs from the Carboniferous and Permian. Ophiacodontids are among the most basal synapsids, an offshoot of the lineage which includes therapsids and their descendants, the mammals. The group became extinct by the Middle Permian.”

In the LRT Ophiacodon (Fig. 3) and Archaeothyris, neither members of the Pelycosauria, are more directly related to basal therapsids, including derived the therapsids: mammals.

References
Holtz TR 2004. Basal tetanurae. PP. 71–110 in The Dinosauria, U of California Press.

/wiki/Pareiasaur
wiki/Ophiacodontidae

 

SVP 2018: New elginiid parieasaur skull from China

Liu and Bever 2018
describe a complete pareiasaur skull close to Eliginia (Fig. 1), the proximal outgroup to hardshell turtles in the large reptile tree, and no where else. The new specimen is significantly larger than Elginia. The authors refer the specimen to Sanchuansaurus, a taxon apparently known from far less material. Evidently this abstract does not represent the earlier Eliginia wuyongae (Fig. 1), which is not significantly larger than Elginia. Liu and Bever make no mention of the eliginiid relationship to basal hard-shell turtles.

Figure 2. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

Figure 1. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT. The new specimen is larger than Eliginia.

References
Liu J and Bever GS 2018. The first complete pareiasaaur skull from China and its implications for the taxonomy of Chinese pareiasaurs.

wiki/Shihtienfenia

First evidence for elginiid pareiasaurs in the Karoo (South Africa)

In the large reptile tree (LRT, 1308 taxa) pareisaurs split after Stephanospondylus into two clades: 1) traditional pareiasaurs and 2) turtle-ancestor pareiasaurs (Fig. 1). Only the latter clade develop distinct supratemporal horns.

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 1. 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. Horns only appear in elginid and sclerosaurid pareiasaurs.

On a recent trip
to the Sam Noble Oklahoma Museum of Natural History in Norman, Oklahoma, USA, I studied a pareiasaur horn, OMNH 708 (Fig. 2). For over a century elginiid pareiasaurs were only known from Scotland. This year other elginids were reported from China (Liu and Bever 2018), and others were reported in 2005 from Eastern Europe (Bulanov and Yashina 2005). OMNH 708 represents yet another specimen, perhaps the first from the Late Permian Karoo beds of South Africa. (Please, let me know of not so.)

Figure 1. OMNH 708, a Permian pareiasaur horn form the Karoo, South Africa.

Figure 1. OMNH 708, a Permian pareiasaur horn form the Karoo, South Africa.

The OMNH specimen
is much larger than the Scottish and Chinese specimens (Fig. 2), more in the size range of ancestral pareiasaurs and Stephanospondylus.

Figure 3. Elginia and OMNH 708 at two scales.

Figure 3. Elginia and OMNH 708 at two scales.

The only question that remains is
is this really a pareiasaur horn? Or has everyone misinterpreted it? It really looks like a cow or bison horn (Fig. 4), but its origin in Permian strata prohibits that.

Figure 4. A modern cow skull horn most closely resembles the Permian pareiasaur horn, by convergence, of course.

Figure 4. A modern cow skull horn most closely resembles the Permian pareiasaur horn, by convergence, of course.

Say, ‘hello’, to convergence, once again.

References
Bulanov VV and Yashina OV 2005. Elginiid pareisaurs of Eastern Europe. Paleontological Journal 39(4):428–432.

Liu J and Bever GS 2018. The tetrapod fauna of the upper Permian Naobaogou formation of China: A new species of Eliginia (Parareptilia, Pareiasauria). Papers in Paleontology 2018: 1-13.
Newton ET 1893. On some new reptiles from the Elgin Sandstone: Philosophical Transactions of the Royal Society of London, series B 184:473-489.

another-turtle-with-teeth-elginia-newton-1893/

another-turtle-with-teeth-elginia-part-2/

another-turtle-with-teeth-elginia-part-3/

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.

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 with colors added to bones and possible soft carapace impression.

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.

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.

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

Not even an elevated Dimetrodon made these Dimetropus tracks

Matching tracks to trackmakers
can only ever be a semi-rewarding experience. Estimates and exclusions can be advanced. Exact matches are harder to come by. This is due to both the vagaries and varieties of sequential footprints in mud or sand, and to the rarity of having skeletal data that matches.

Figure 1. Dimetrodon adult, juvenile, skull, manus, pes.

Figure 1. Dimetrodon adult, juvenile, skull, manus, pes. Note the asymmetry of the fingers and toes. Dimetropus tracks were named for this taxon.

Which brings us to Dimetropus
Traditionally Early Permian Dimetropus tracks (Fig. 2–8; Romer and Price 1940) have been matched to the coeval pelycosaur, Dimetrodon (Fig. 1)—but only by narrowing the gauge of the Dimetrodon feet and elevating the belly off the surface, as Hunt and Lucas 1998 showed.

Today we’ll take a look at some other solutions
not involving Dimetrodon doing high-rise pushups. Several distinctly different tracks have fallen into the Dimetropus wastebasket. Let’s look at three ichnospecimens.

Traditionally, and according to Wikipedia,
citing Hunt and Lucas 1998: “Trackways called Dimetropus (“Dimetrodon foot”) that match the foot configuration of large sphenacodontids show animals walking with their limbs brought under the body for a narrow, semi-erect gait without tail or belly drag marks. Such clear evidence for a more efficient upright posture suggests that important details about the anatomy and locomotion of Sphenacodon and Dimetrodon may not be fully understood.” Hunt and Lucas blamed traditional reconstructions of Dimetrodon for the mismatch. Instead they should have looked at other candidate trackmakers from the Early Permian. Note the asymmetric manus and pes of Dimetrodon (Fig. 1). Those don’t match the tracks no matter how high the belly is above the substrate. Dimetrodon is just fine the way it is.

Figure 1. Early Permian Dimetropus tracks matched to Middle Triassic Sclerosaurus, one of the few turtle-lineage pareiasaurs for which hands and feet are known.

Figure 2. Early Permian Dimetropus tracks matched to Middle Triassic Sclerosaurus, one of the few turtle-lineage pareiasaurs for which hands and feet are known.

A better match
can be made to the Middle Triassic pre-softshell turtle pareiasaur, Sclerosaurus (Fig. 2). Note the symmetric manus and pes like those of living turtles (Fig. 3) and the Dimetropus specimen in figure 2.

Figure 2. Snapping turtle tracks in mud. Note the relatively narrow gauge and symmetric imprints.

Figure 3. Snapping turtle tracks in mud. Note the relatively narrow gauge and symmetric imprints like those of Dimetropus.

Living turtle tracks
like those of the snapping turtle, Macrochelys (Fig. 3) are also symmetrical and surprisingly narrow gauge. Let’s not forget, Dimetropus tracks occur in Early Permian sediments, predating the earliest fossil turtles, like Proganochelys, first appearing in the Late Triassic. Let’s also not forget, in the large reptile tree (LRT, subset Fig. 7) Proganochelys is not the most basal turtle and valid predecessors (not eunotosaurs) had similar hands and feet.

FIgure 4. Dimetropus tracks compared to a large Dimetrodon matched to finger and toe tips. Hand too wide. Compared to a small Dimetrodon. Hand too small. Compared to a normal size Hipposaurus, good match even if not all the digits are known.

FIgure 4. Dimetropus tracks compared to a large Dimetrodon matched to finger and toe tips. Hand too wide. Compared to a small Dimetrodon. Hand too small. Compared to a normal size Hipposaurus, good match even if not all the digits are known.

A second set of Dimetropus tracks
(Fig. 4, right), have distinctive heels behind symmetric + asymmetric imprints. A large Dimetrodon could not have made these tracks because they are too narrow. A small Dimetrodon had extremities that were too small, as the animated GIF shows.

FIgure 3. Hipposaurus compared Dimetropus. The overall and leg length is right, as are many of the digits. Unfortunately the medial digits are too short in Hipposaurus. Hipposaurus has a narrower gauge and lifted its belly of the ground, as did the Dimetropus trackmaker.

FIgure 5. Hipposaurus compared Dimetropus. The overall and leg length is right, as are many of the digits. Unfortunately the medial digits are too short in Hipposaurus. Hipposaurus has a narrower gauge and lifted its belly of the ground, as did the Dimetropus trackmaker.

Fortunately,
we also have Middle Permian basal therapsid, Hipposaurus (Figs. 4, 5), a close relative of the last common ancestor of all pelycosaurs (see Haptodus and Pantelosaurus; Fig. 6). No doubt Hipposaurus elevated its torso on a narrow gauge track, with manus tracks slightly wider than pedal traces, as in Dimetropus. Both the carpus and tarsus are elongate, matching Dimetropus tracks.

Unfortunately,
we don’t have all the phalanges for the Hipposaurus manus and pes (Fig. 4). Drag marks can lengthen a digit trace. Flexing a claw into the substrate can shorten a digit trace. It is also important to note that during the last moment of the manus propulsion phase, the medial and lateral metacarpals can rotate axially, creating the impression of an ‘opposable thumb’ in the substrate. Note that no two ichnites are identical, despite being made one after another by the same animal.

Figure 5. Closeup of Hipposaurus manus and pes compared to random Dimetropus manus and pes tracks. Note, some digits remain unknown. Some digits might create drag marks. Others may dig in a claw or two apparently shortening the digit imprint.

Figure 6. Closeup of Hipposaurus manus and pes compared to random Dimetropus manus and pes tracks. Note, some digits remain unknown. Some digits might create drag marks. Others may dig in a claw or two apparently shortening the digit imprint.

At present
a more primitive sister to Hipposaurus is the best match for the Hunt et al. 1995 Dimetropus tracks and the Early Permian timing is right.

FIgure 6. Subset of the LRT focusing on Hipposaurus and its relatives, color coded to time.

FIgure 7. Subset of the LRT focusing on Hipposaurus and its relatives, color coded to time. Hipposaurus is nearly Early Permian and probably had its genesis in the Early Permian.

In the popular press
NewScientist.com reported, “We’ve drawn iconic sail-wearing Dimetrodon wrong for 100 years. Some palaeontologists did offer an explanation – that Dimetrodon thrashed its spine from side to side so much as it walked that it could leave narrow sets of footprints despite having sprawled legs.” That hypothesis, based on omitting pertinent taxa, is no longer necessary or valid.

Abbott, Sues and Lockwood 2017 reported the limbs of Dimetrodon were morphologically closest to those of the extant Caiman, which sits on its belly, but also rises when it walks.

It is unfortunate that no prior workers considered Hipposaurus, a nearly coeval taxon with Dimetropus having matching slender digits, long legs, an erect carriage, and just about the right digit proportions.

A third ichnotaxon,
Dimetropus osageorum (Sacchi et al. 2014), was considered a possible caseid, rather than a sphenacodontid, but caseids have more asymmetric digits (= a shorter digit 2). Unfortunately, taxon exclusion also hampered the Sacchi et al. study. They did not consider Early Permian stephanospondylids, Late Permian pareiasaurs in the turtle lineage and Triassic turtles. No skeletal taxon is a perfect match for this ichnotaxon, but the Late Cretaceous turtle, Mongolochelys, is close  (Fig. 8). It took some 200 million years after the trackmaker of Dimetropus for the lateral pedal digits to shrink, but everything else is a pretty good match.

Figure 7. Dimetropus oageorum from Sacchi et al. 2014 matched to Mongolochelys, a Late Cretaceous turtle. Only pareiasaurs and turtles, among basal taxa, have such a long manual and pedal digit 2.

Figure 8. Dimetropus oageorum from Sacchi et al. 2014 matched to Mongolochelys, a Late Cretaceous turtle. Only pareiasaurs and turtles, among basal taxa, have such a long manual and pedal digit 2. The reduction of pedal digits 4 and 5 are derived in this late surviving basal turtle.

Also compare the hands and feet
of Early Permian Dimetropus osageorum (Fig. 8) to the Middle Triassic Sclerosaurus (Fig. 2). Dimetropus is solid evidence that turtle-ancestor pareiasaurs were present in the Early Permian (see Stephanospondylus, an Early Permian turtle and pareiasaur ancestor).

Saachi et al. conclude, “At the same time, the process of attributing ichnotaxa, on the basis of well preserved tracks and by comparison with known skeletal remains, is validated.”  True. Unfortunately all prior workers overlooked a wider gamut of skeletal taxa to compare with their ichnotaxon in their search for a ‘best match.’ Perhaps they felt restricted by time (Early Permian). As the above notes demonstrate, that is not a good excuse.

References
Abbott CP, Sues H-D and Lockwood R 2017. The Dimetrodon dilemma: reassessing posture in sphenacodonts. GSA annual meeting in Seattle, WA USA 2017. DOI: 10.1130/abs/2017AM-307190
Hunt AP and Lucas SG 1998. Vertebrate tracks and the myth of the belly-dragging, tail-dragging tetrapods of the Late Paleozoic. Bulletin New Mexico Museum of Natural History and Science. 271: 67–69.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Romano M, Citton P and Nicosia U 2015. Corroborating trackmaker identification through footprint functional analysis: the case study of Ichniotherium and Dimetropus. Lethaia https://doi.org/10.1111/let.12136
Romer AS and Price LI 1940. Review of the Pelycosauria: Geological Society of America, Special Paper 28:538pp
Sacchi E, Cifelli R, Citton P, Nicosia U and Romano M 2014. Dimetropus osageorum n. isp. from the Early Permian of Oklahoma (USA): A trace and its trackmaker. Ichnos 21(3):175–192. https://doi.org/10.1080/10420940.2014.933070

Another overlooked turtle ancestor just got published

Considered
congeneric with Elginia mirabilis (from Late Permian Scotland), the new elginiid comes from Late Permian China (Figs. 1, 2). The authors (Liu and Bever 2018) correctly identified the material in a specific sense, but had no idea what they had in a broader sense, because they only tested Elginia against pareiasaurs.

It’s really part of the genesis of turtles (Fig. 2), and we’re glad to see it!

Once again,
taxon exclusion raises its blind head. We’ve known Elginia was a turtle ancestor since 2014 when that went online. Unfortunately co-author Bever had earlier published on the genesis of turtles, relying on pre-turtle-mimic Eunotosaurus. Both are tested in the large reptile tree (LRT, 1152 taxa) and Eliginia nests with turtles. Eunotosaurus does not. It is more closely related to Acleistorhinus and kin. When Liu and Bever include Meiolania and Niolamia (Fig. 2) in their analyses, then they’ll see how it all plays out.

Elginia wuyongae (Figs. 1, 2) is smaller than Elginia mirabilis, lacks long horns and nests between the big desert pareiasaur, Bunostegos (Fig. 2), and its Scottish namesake at the base of hard shell turtles. Importantly, E. wuyongae preserves a few post-cranial data, including the genesis of the hard-shell turtle carapace…which is incredible news!!!

But you’re hearing that here first.
Jiu and Bever did not understand the importance and so overlooked it.

Figure 1. Elginia wuyongae was just described. It shows the genesis of shell formation in hard shell turtles.

Figure 1. Elginia wuyongae was just described. It shows the genesis of shell formation in hard shell turtles. That tiny last sacral vertebra (near the four dots) suggests a tiny tail was present. 

Lacks a rostrum…
skull is pretty beaten up, parts missing, holes pocket bones, lacks a palate. Squamosal misidentified originally (repaired here). Still, you gotta love it! It has post-cranial clues lacking in other transitional taxa. And it fills a gap!

How can workers not notice the family resemblance? 

Figure 2. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

Figure 2. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT. Those other horned pareiasaurs are basal turtles, meiolaniids with substantial carapace and plastron. Both sides of the new Elginia skull are shown. The squamosal is tucked inside the overlapping supratemporal in these transitional taxa. 

The authors do mention the turtle connection, like so:
“…and their long-hypothesized, but now largely rejected, potential as the close relatives
of turtles (Rieppel & deBraga 1996; Lyson et al. 2010; Lee 2013; Lyson et al. 2013; Bever et al. 2015; Schoch & Sues 2015; Laurin & Pi~neiro 2017).” It’s not surprising how many workers think this – because they don’t test the taxa that need to be tested, as they are tested here in the LRT. Remember, a consensus of workers can be wrong.

On that note:
Liu and Bever are still clinging to the invalid clade Parareptilia.

References
Liu J and Bever GS 2018. The tetrapod fauna of the upper Permian Naobaogou formation of China: A new species of Eliginia (Parareptilia, Pareiasauria). Papers in Paleontology 2018: 1-13.

More evidence that Meiolania is a basal turtle

Figure 5. Meiolania, the most primitive of known turtles, has lateral forelimbs, like non turtles.

Figure 1. Meiolania, the most primitive of known turtles, has lateral forelimbs, like non turtles. Extant turtle elbows point anteriorly. 

Earlier we looked at the bizarre and seeming highly derived skulls of Meiolania (Fig. 1) and Niolamia, (Fig. 2) two large late-surviving meiolanid turtles that are only known from rather recent fossil material following an undocumented origin in the Late Permian or Early Triassic.  They both nested as sisters to Elginia (Fig. 2; Late Permian), a toothed turtle sister with horns. So the horns and frills are primitive, not derived.

Figure 2. Comparing the skulls of Elginia, with teeth, and the turtle, Niolamia, toothless.

Figure 2. Comparing the skulls of Elginia, with teeth, and the turtle, Niolamia, toothless.

Here’s a review
of various turtle ancestor candidates in graphic format (Fig. 3). A candidate touted by several recent authors, Eunotosaurus, is among those shown.

Figure 1. In traditional studies Eunotosaurus nests at the base of turtles, but that is only in the absence of the taxa shown here and correctly scored. Here Eunotosaurus is convergent with turtles, but not related. Turtles arise from small pareiasaurs.

Figure 3. In traditional studies Eunotosaurus nests at the base of turtles, but that is only in the absence of the taxa shown here and correctly scored. Here Eunotosaurus is convergent with turtles, but not related. Turtles arise from small pareiasaurs.

Cervical count
Pareiasaurs have 6 cervicals. Turtles have 8, several of which are tucked inside the shell. Proganochelys, often touted as the most basal turtle, has 8 cervicals. Horned Meiolania, at the base of the hard-shell turtles has 6 cervicals with ribs and 2 without ribs according to Gaffney (1985; Fig. 4). Most living turtles do not have cervical ribs. In Proganochelys cervical ribs are much reduced.

Note that in Odontochelys (Fig. 3 a similar situation arises where the all the vertebrae anterior to the expanded ribs are considered cervicals, even though two are posterior to the scapula. Similarly, in Proganchelys (Fig. 3) the last cervical is posterior to the scapula. In other tetrapods (let me know if I am forgetting any), all the cervicals are anterior to the scapula and a few dorsal vertebrae typically appear anterior to the scapulae. The tucking of the scapula beneath the ribs of turtles is a recurring problem with many offering insight.

Figure 1. Meiolania cervicals. Did Gaffney follow tradition when he identified 8 cervicals here? Only 6 have ribs and the shape changes between 6 and 7.

Figure 4. Meiolania cervicals. Did Gaffney follow tradition when he identified 8 cervicals here? Only 6 have ribs (yellow) and the shape changes between 6 and 7.

There are several different possible nesting sites
for turtles with regard to living reptiles (including mammals and birds, Fig. 5). Only the LRT (in yellow) has not made it to the academic literature (after several tries) because it is the only tree topology that splits Archosauromorpha from Lepidosauromorpha in the Viséan, further in the past than other workers venture to place reptiles that still look like amphibians. Until we get the basic topology down and agreed upon, it is going to be difficult to nest turtles properly.

Figure 2. Various hypotheses regarding turtle origins. The LRT is added in yellow.

Figure 5. Various hypotheses regarding turtle origins. The LRT is added in yellow. Most studies show Synapsida as the basal dichotomy, whereas the LRT divides Lepidosauromorpha from Archosauromorpha together with two separate origins for diapsid reptiles.

References
Gaffney ES 1985. The cervical and caudal vertebrae of the cryptodiran turtle, Meiolania platyceps, form the Pleistocene of Lord Howe Island, Australia. American Museum Novitates 2805:1-29.

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

Figure 1. Turtles as Hopeful Monsters by O. Rieppel 2017.

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.

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.

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. The plate and counter plate of Sclerosaurus, an ancestral taxon to soft shell turtled. Girdles and extremities are reconstructed.

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 TichvinskiaHypsognathus, 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 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 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 1. Sclerosaurus face.

FIgure 3. Sclerosaurus face.

Figure 4. Sclerosaurus reconstructed.

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