Recalibrating clade origins, part 3

Earlier
we looked at the first part and second part of Marjanovic’s 2019 chronological recalibration of vertebrate nodes.  Today we continue.

Testudines (Panpleurodira – Pancryptodira)
Unfortunately Marjanovic relies on tradition when he splits turtles into pleurodiran (side-neck) and cryptodiran (hidden-neck) clades. He reports, “With one short series of exceptions (Gaffney et al., 2006, 2007; Gaffney and Jenkins, 2010), all treatments of Mesozoic turtle phylogeny from the 21st century have consistently found Proterochersis and all other turtles older than Late Jurassic to lie outside the crown group. The oldest known securely dated crown-group turtle is thus the mid-late Oxfordian (158 Ma) stem-panpleurodire Caribemys. The observed absence of cryptodires is likely real; combining this with more rootward Middle and Early Jurassic stem turtles from other continents, I suggest a hard maximum age of 175 Ma based on the beginning of the Middle Jurassic (174.1 ± 1.0 Ma ago: ICS).”

Neither sea turtles nor soft-shell turtles hide their head within their carapace, nor could their ancestors do so. In the large reptile tree (LRT, 1630+ taxa; Fig. 1) the basal dichotomy between soft shell and hard shell turtles extends back to small horned pareiasaurs from the Latest Permian (255 mya). Thus the crown group of all living turtles also includes all extinct turtles. Cryptodires and pleurodires appeared later, both within the hardshell clade, timed as noted above.

Figure 1. 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.

Lepidosauria (Rhynchocephalia + Squamata)
Marjanovic reports, “The minimum age of this calibration, given as 238 Ma, has to be slightly revised to 244 Ma (hard) based on Megachirella, the oldest known stem-squamate, which is older than the oldest known rhynchocephalian (238–240 Ma). An Early Triassic or perhaps Late Permian maximum age seems reasonable, but, given the rarity of stem-lepidosauromorphs and of Permian diapsids in general, I rather propose to use the ecologically similar small amniotes of Richards Spur (289 ± 0.68 Ma, see Node 107) to support a soft maximum age of 290 Ma.”

In the LRT the last common ancestors of rhynchocephalians + squamates (Fig. 2) include the basal rhynchocephalian (not stem-squamate) Megachirella (earliest Middle Triassic, 244 mya) and the earlier Palaegama (Late Permian). A proximal outgroup taxon is Tridentinosaurus (Earliest Permian, 295mya) approximating Marjanovic’s proposal.

Figure 1.  Subset of the LRT focusing on lepidosaurs and snakes are among the squamates.

Toxicofera (Pythonomorpha + Anguimorpha including Iguanomorpha)
Marjanovic reports, “I agree with Irisarri et al. (2017) in not assigning a maximum age other than that for Node 125 (Lepidosauria, see above).”

In the LRT Toxicofera is a junior synonym for Squamata (Fig. 2). The basalmost squamate taxon in the LRT is Euposaurus (Late Jurassic, Kimmeridgian, 155 mya). An Early Permian outgroup taxon, MNC-TA1045 (Spindler 2017) in a traditionally unrecognized clade, Protosquamata, which includes extinct taxa only. Lacertulus (Late Permian, not mentioned by Marjanovic) is a basal taxon.

Iguania (Chamaeleonformes + Iguanoidea)
Marjanovic reports, “I cannot assign a maximum age other than that for Node 125.” (See above).

In the LRT Euposaurus (overlooked by Marjanovic, and see above, Fig. 2), is the basalmost member of the Iguania and Squamata.

More tomorrow…

---

References
Marjanovic D 2019. Recalibrating the transcriptomic timetree of jawed vertebrates.
bioRxiv 2019.12.19.882829 (preprint)
doi: https://doi.org/10.1101/2019.12.19.882829
https://www.biorxiv.org/content/10.1101/2019.12.19.882829v1

https://www.biorxiv.org/content/10.1101/2019.12.19.882829v1.full.pdf

Desmatochelys enters the LRT after bone reinterpretation

Certain aspects
of certain turtle skulls have been traditionally misinterpreted, as reported earlier.

Figure 1. The skull of the Cretaceous sea turtle, Desmatochelys, is relabeled here with the addition of color.

A not so recent paper on the sea turtle, Desmatochelys
(Fig. 1), by Cadena and Parham 2015 misidentified several skull bones, here corrected.

---

References
Cadena EA and Parham. JF 2015. Oldest Known Marine Turtle? A New protostegid from the Lower Cretaceous of Colombia. PaleoBios. 32(1).

SVP abstracts – Are meiolaniform turtles stem turtles?

Kear et al. 2019 talk about
‘stem’ turtles with skull horns and club tails: the meiolaniforms.

From the abstract:
“Meiolaniforms (Meiolaniformes) are an enigmatic radiation of stem turtles with an exceptionally protracted 100 million-year evolutionary record that spans the mid-Cretaceous (Aptian–Albian) to Holocene. Their fossils have been documented for over 130 years, with the most famous examples being the derived Australasian and southern South American meiolaniids – bizarre horned turtles with massive domed shells and tail clubs that are thought to have been terrestrial and probably herbivorous.”

In the large reptile tree (LRT, 1592 taxa, subset Fig. 2) meiolaniforms (Fig. 1) are not enigmatic. They are basalmost hard-shell turtles derived from similarly-horned Elginia-type small pareiasaurs in parallel with Sclerosaurus-type small pareiasaurs basal to soft-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.

“Despite a long history of research, the phylogenetic affinities of meiolaniids have proven contentious because of ambiguous character state interpretations and incomplete fossils
representing the most ancient Cretaceous meiolaniform taxa.”

This problem is contentious only because of taxon exclusion. Prior workers have not included analyses of meiolaniforms and Elginia.

“Here, we therefore report the significant discovery of the stratigraphically oldest demonstrable meiolaniform remains, which were excavated from Hauterivian–Barremian high-paleolatitude (around 80°S) deposits of the Eumeralla Formation in Victoria, southeastern Australia. Synchrotron microtomographic imaging of multiple virtually complete skulls and shells provides a wealth of new data, which we combine with the most comprehensive meiolaniform dataset and Bayesian tip-dating to elucidate relationships, divergence timing and paleoecological diversity.”

Did the authors include Elginia, Sclerosaurus, Arganceras and Bunostegos? The abstract does not mention them.

“Our results reveal that meiolaniforms emerged as a discrete Austral Gondwanan lineage,
and basally branching sister group of crown turtles (Testudines) during the Jurassic.”

The LRT invalidated a monophyletic Testudines. Rather soft-shell and hard-shell turtles had separate parallel origins from within the small horned pareisaurs.

Figure 5. Subset of the LRT focusing on turtle origins and unrelated eunotosaurs.

“We additionally recover a novel dichotomy within Meiolaniformes, which split into a unique Early Cretaceous trans-polar radiation incorporating apparently aquatic forms with flattened shells and vascularized bone microstructure, versus the larger-bodied terrestrial meiolaniids that persisted as Paleogene–Neogene relic species isolated in Patagonia and Australasia.”

That’s interesting. The LRT sort of separates the meiolaniform Niolama from the meiolaniform Meiolania + Proterochersis + Proganochelys. The latter taxon also has a club tail. Perhaps more meiolanforms would continue to nest with one or the other.

“Finally, our analyses resolve the paraphyletic stem of crown Testudines, which otherwise includes endemic clades of Jurassic–Cretaceous turtles distributed across the northern Laurasian landmasses. These had diverged from the Southern Hemisphere meiolaniforms by at least the Middle Jurassic, and thus parallel the vicariant biogeography of crown turtles, which likewise diversified globally in response to continental fragmentation and possibly climate.”

Outgroups are key to understanding turtle evolution in the LRT. So is taxon inclusion. Based on the dual origin of turtles from horned small pareiasaurs in the LRT, the list of stem turtles now includes pareiasaurs, if the concept of a monophyletic turtle still stands with a last common ancestor lacking a carapace and plastron within the pareiasaurs.

---

References
Kear BP et al. 2019. Cretaceous polar meiolaniform resolves stem turtle relationships. Journal of Vertebrate Paleontology abstracts.

Did the turtle nuchal evolve from cleithra?

Lyson et al.  2013
propose a homology of the turtle nuchal (central anterior roof-like bone of the carapace) with the primitive cleithra (singular: cleithrum, slender, stem-like bone anterior to the scapula). In order to do so, they produced a set of turtle ancestors (or engineering models) that is not validated by the large reptile tree (LRT, 1395 taxa).

Frogs, lepidosaurs, diadectids and para-caseasaurs,
according to Lyson et al., model the ancestry of turtle shoulders and shells (Fig. 1).

Figure 1. On the left, from Lyson et al. 2013 with graphics added. On the right taxa basal to turtles according to the LRT. The right sequence documents a more gradual accumulation of traits. Even so, the gap between Bunostegos and Meiolania includes the complete development of the carapace and plastron… but almost everything else was present. A skull-only taxon, Elginia, nests between the two.

By contrast,
in the LRT Milleretta, is basal to Stephanospondylus, which is basal to diadectids on one branch and pareiasaurs, like Bunostegos, and the basal turtle Meiolania, on the other, documenting a more gradual accumulation of traits without introducing frogs and lepidosaurs. In the LRT, the gap between Bunostegos and Meiolania includes the unchronicled development of the carapace and plastron. Given that issue, almost everything else was present in the skeleton. A skull-only taxon, Elginia (not shown in Fig. 1), nests between the two. There is an online paper on turtle ancestors here.

Taxon exclusion is once again the problem.
Since Lyson et al. used inappropriate and unrelated taxa to demonstrate their hypothesis, it was invalid from the get-go. To my knowledge (let me know if I am wrong):

1. No one recently suggested that frogs, like Rana, are basal to turtles.
2. No one recently suggested that Diadectes is basal to turtles.
3. No one recently suggested that Sphenodon is basal to turtles.
4. Several authors (many from the Lyson et al. list) have suggested that Eunotosaurus was basal to turtles, but they did not test the above-listed LRT competing candidates when they published.

From Wikipedia Diadectidae
“Paleontologist E.C. Case compared diadectids to turtles in 1907, noting their large pectoral girdles, short, strong limbs, and robust skulls. Case described them as “lowly, sluggish, inoffensive herbivorous reptiles, clad in an armor of plate to protect them from the fiercely carnivorous pelycosaurs.”

The better method
for figuring out anything about turtles is to employ the valid ancestors of turtles, validated by testing against all other published candidates. I know, from testing, that all other candidates, like Eunotosaurus, nest far from turtles.

Getting back to our headline
and the title of the Lyson et al. paper, the genesis of the turtle carapace in hard-shell turtles is not preserved in the fossil record at present. Even so, the rarely preserved cleithrum gives little to no indication that it evolved into an anterior carapace bone… at present. Some day it may.

Lyson et al. note:
“unlike the other midline carapacial elements, the nuchal develops from paired mesenchymal condensations each of which contains a separate ossification center… first observed by Vallén (1942) and led him to conclude the nuchal was homologous with the supracleithra.”

The supracleithrum
by definition, “is a bone of the pectoral girdle situated dorsal to the cleithrum in some fishes and amphibians.”  That definition does not include reptiles.

If we look for a pre-nuchal in pareiasaurs
it is easy to find parasagittal osteoderms (Fig 2). Lyson et al. do not mention the word ‘pareiasaur’ in their paper.

Figure 2. The pareiasaur, Deltavjatia, with osteoderms in orange. Note the anterior set is simple and paired, as hoped for by Lyson et al. but not found, except in turtle embryos, by Lyson et al.

Taxon exclusion can ruin a paper.
You can talk about thousands of characters for Eunotosaurus, but if you don’t include one pareiasaur, you’ll in the wrong ballpark on game day. Deltavjatia (Fig. 2) does not preserve a cleithrum. Rather, given its close, but not direct relation to turtles, the turtle nuchal likely arises from the osteoderms that are in place in Deltavjatia. They are the right size, in the correct orientation, and used for the same reason. So the nuchal probably arose from the foremost osteoderms on the torso, while those on the neck became neck armor. Remember, early turtles could not withdraw their neck.

It’s probably worthwhile to remind you of other body parts
that evolve in the ancestry of turtles until they become turtle traits at this time.

Figure 3. Turtle pelvis evolution. Here are the changes in the pelvis of pre-turtles and basal hard-shelled turtles.

Take the turtle pelvis, for instance.
Similar precursors can be seen in stem turtle pareiasaurs (Fig. 3). And the skull is interesting. Workers have discussed Elginia with pareiasaurs and Meiolania with turtles, but never Meiolania with pareiasaurs or Elginia with turtles. That you heard here first in a three-part series five years ago.

Figure 4. Hard shell turtle evolution featuring the skulls of  Bunostegos, Elgenia, Meiolania and Proganochelys – NOT to scale. Note the long list of shared traits, longer than in any competing candidate.

If you know one of the seven authors
of Lyson et al. 2013, please make sure they become aware of this critique. A few of them are among those who rejected the submitted manuscript on the origin of turtles. Evidently they prefer the invalid status quo rather than this novel hypothesis for turtle origins.

References
Case EC 1907. Restoration of Diadectes. The Journal of Geology. 15 (6): 556–559.
Lyson TR, Bhullar B-AS, Bever GS, Joyce WG, de Queiroz K, Abzhanov A and Gauthier JA 2013. Homology of the enigmatic nuchal bone reveals novel reorganization of the shoulder girdle in the evolution of the turtle shell. Evolution & Development 15(5):317–325. DOI: 10.1111/ede.12041
Vallén E 1942. Beiträge zur Kenntnis der Ontogenie und der vergleichenden. Anatomie des Schildkrötenpanzers. Acta Zool. Stockholm 23: 1–127.

SVP 2018: Turtle ribs in softshell embryos

Hirasawa et al. 2018
studied the embryonic development of the Chinese soft-shell turtle, Pelodiscus sinensis, seeking clues to the origin of turtles.

Backstory:
The large reptile tree (LRT, 1313) tests a wide gamut of candidates, including all prior turtle ancestor candidates and a thousand more. It recovers a dual origin of turtles (hardshell and soft-shell) from two separate small horned pareiasaurs, Elginia and Sphodrosaurus.

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

Hirasawa et al. report, “The turtles’ body plan differs from that of the other tetrapods in the solid dorsal and ventral shells (carapace and plastron).” Actually, no. The placodont Henodus has a similar carapace and plastron.

Hirasawa et al. report, “It has been widely accepted that the carapace and plastron evolved from the ribs and clavicular girdle plus gastralia, respectively, but the evolutionarytransition was poorly preserved in the fossil record.” In the LRT turtle ancestors did not have gastralia until the recent discovery that Sphodrosaurus was ancestral to soft-shell turtles and lateral (not medial) ‘gastralia’ (actually plastron progenitors) first appear.

FIgure 2. Partial reconstruction of Sphodrosaurus based on tracings in figure 2. Plastron primordia appear in cyan (and so does the humerus and two sacrals, sorry!)

Hirasawa et al. report, “In the turtle embryo, the rib primordia are not extended to the lateral body wall unlike those of the other amniotes, and only the deep layer of the body wall muscle develops in the lateral body wall. Concomitantly, the sternum, which develops adjacent to the ventral ends of the ribs in the other amniotes, does not develop in the turtle embryo.” Actually the sternum is a rare ossification in tetrapods, not found in turtles, or LRT turtle ancestors. However the interclavicle is present in the turtle plastron.

Hirasawa et al. report, “Among fossil taxa, sauropterygians have repeatedly been placed in the closest position to turtles by phylogenetic analyses in previous studies.” In the LRT sauropterygians are not related to turtles except at the origin of the amnion in Viséan amphibian-like reptiles like Silvanerpeton.

The LRT is online for anyone to test taxa
relevant to the ancestry of turtles or any other included taxon or clade.

References
Hirasawa R et al. 2018. Developmental biological inferno on the evolution from the ribcage to the turtle shell. SVP abstract.

SVP 2018: New data on Chinlechelys (Triassic turtle)

Lucas and Licthtig 2018
present new details on the morphology of Chinlechelys, a Late Triassic turtle.

Figure 1. Chinlechelys compared to Proganochelys. The cervical armor is relatively larger, the humerus is relatively smaller. Evidently more is known now.

The authors report, “a significant portion of the carapace. This new material includes thoracic vertebrae 1–3 and 5–8 as well as the isolated axillary notch and a small carapace fragment. A fragment originally described as cervical armor on further inspection is found to be a portion of the posterior carapace margin. This fragment shows a distinct radial sculpture like that of the posterior marginals of Proganochelys.  The peripheral previously published is not from the posterior of the carapace, but rather from its lateral margin.  

“Four bones concreted together tentatively considered the posterior left corner of a skull are unusual in their morphology relative to other turtles. The long quadratojugal is similar to that of dwarf pareiasaurs in its long length and the presence of a ventral ridge parallel to the lateral margin. The squamosal has a distinct ventral conch similar to Anthodon and more anterior and ventral than the otic notch of Proganochelys. Overall, this makes a very unusual turtle, but some of this may not be as odd as it seems as many of these features are unclear in other Triassic turtles like Proganochelys. The preserved ribs and overlying neutrals and costals support the idea that the costals and ribs were originally two separate ossifications that were fused latter in evolution.”

I’m sure we’ll be hearing more later.
All of this appears to support the dual origin of turtles from pareiasaurs as recovered by the large reptile tree (LRT, 1311 taxa).

References
Lucas SG and Lichtig AJ 2018. New morphology of Chinlechelys, a Late Triassic turtle from New Mexico, U.S.A. SVP abstract.

Eorhynchochelys: a giant eunotosaur, not a stem turtle

Figure 1. Skull of Eorhynchochelys sinensis with DGS colors applied to bones. These differ somewhat from the original bone drawing. This is a standard eunotosaur skull, not a pareiasaur or turtle skull. I see tiny premaxillary teeth, btw.

Li, Fraser, Rieppel and Wu 2018
introduce Eorhynchochelys sinensis (Figs. 1,2), which they describe in their headline as ‘a  Triassic stem turtle’ and in their abstract as ‘a Triassic turtle.’ Unfortunately, Eorhynchochelys is not related to turtles. Instead it is a spectacular giant eunotosaur (sister to Eunotosaurus).

Figure 2. Eorhynchochelys in situ alongside manus, pes, pectoral and pelvic girdle, plus Eunotosaurus to scale. By convergence Eorhynchochelys resembles Cotylorhychus.

The problem is, once again, taxon exclusion.
Li et al. employed far too few taxa (Fig. 3) and no pertinent turtle ancestor taxa (see Fig. 4).

Figure 3. Cladogram of turtle relationships by Li et al. 2018. Yellow-green areas are lepidosauromorphs in the LRT demonstrating the mix of clades present here due to massive taxon exclusion. The LRT has 40x more taxa.

We know exactly from which taxa turtles arise.
In the large reptile tree (LRT, 1271 taxa, Fig. 4): 1) hard shell turtles arise from the small, horned pareiasaur, Elginia. The basalmost hard shell turtle is Niolamia, not Proganochelys. 2) soft shell turtles arise from the small, horned pareiasaurs, Sclerosaurus and Arganaceras. The basalmost soft shell turtle is Odontochelys. None of these taxa have temporal fenestrae. We looked at turtle origins earlier here. Turtle origins were published online in the form of a manuscript earlier here.

Figure 4. Subset of the LRT focusing on turtle origins and unrelated eunotosaurs.

Unrelated
Pappochelys nests with basal placodonts. Eunotosaurus nests with the caseid clade, close to Acleistorhinus and Australothyris, all taxa with a lateral temporal fenestra. Li et al. suggested that this lateral temporal fenestra indicated that turtles were diapsids. That has been falsified by the LRT which shows that turtles never had temporal fenestra all the way back to Devonian tetrapods.

Eorhynchochelys sinensis (Li et al. 2018; Late Triassic) was considered the earliest known stem turtle with a toothless beak, but here nests as a giant aquatic eunotosaur with tiny premaxillary teeth. In size and overall build it converges with Cotylorhynchus.

References
Li C, Fraser NC, Rieppel O and Wu X-C 2018. A Triassic stem turtle with an edentulous beak. Nature 560:476–479.

What would turtles be, if pareiasaurs were not known?

This is lesson 3 in taxon exclusion…
to see where select clades would nest in the absence of their proximal taxa.

Two clades of turtles
(soft-shell and hard-shell) arise from two different parieasaurs (Fig. 1) in the large reptile tree (LRT, 1242 taxa).

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

The question is: what if pareiasaurs were never discovered?

1. Then turtles arise from Stephanospondylus. And if that taxon is absent…
2. Then turtles arise from limbless microsaurs (like Lysorophus and Adelospondylus ). What?? With the very weird, tube-snout soft-shell, Ocepecephalon (post-crania unknown) nesting as the basalmost turtle. And if all non-reptile tetrapods and lepidosauromorphs are absent…
3. Then turtles arise from cynodonts, between Procynosuchus and Thrinaxodon. In that case, turtles start with Baena and Glyptops on one branch, and soft-shell turtles on the other.
4. Removing all soft-shell turtles nests hard-shell turtles between the fish, Osteolepis, and chroniosuchids (not Eldeceeon), (when non-reptile tetrapods and lepidosauromorphs are absent as in #3), which is close to the original topology.
5. Otherwise hard-shell turtles arise from the microsaur, Batropetes clade, with the turtle Kallokibotion at the base of the hard-shell turtles.

Does this all make sense?
No. But in the absence of pareiasaurs (and later, soft shell turtles) PAUP is going to find the least different taxa from a wide gamut list (see above).

Notably
neither Eunotosaurus nor Pappochelys were picked by PAUP, which found more parsimonious candidates elsewhere. Eunotosaurus and Pappochelys were cherry-picked taxa, promoted to be turtle ancestors by biased workers. These two taxa nested with turtles by default in the absence of more similar candidate sisters for all involved taxa.

Taxon exclusion
has been the number one problem in traditional paleontology. That’s why the LRT includes such a wide gamut of taxa. The result is a minimizing of taxon exclusion and the problems that attend it.

Arvinachelys: another pig-nose turtle

Arvinachelys goldeni (Lively 2015; Late Cretaceous; UMNH VP 21151; 60cm in length; Figs. 1, 2) was promoted as a unique pig-nose turtle, having twin narial openings. That trait is now shared with Kallokibotion (Nopsca 1923; Pérez-García and Vlad Codrea 2018; Fig. 2), which we looked at earlier here. This is a near-basal turtle nesting near baenids and before any extant taxa (crown group) among the hard-shell turtles.

Arvinachelys is not closely related
to the living pig-nose turtle, Carettochelys.

Lively 2015
fused many of the skull bones together in his µCT scan (Fig. 1). I was able to trace outlines for several fused elements. I also relabeled the squamosal as the supratemporal. Lively did not identify the top half of the premaxilla, separated from the bottom half in the adult skull. Though rare, such splits do occur in certain other turtles, Lively did not identify the bottom half of the jugal, recolored here.

Figure 1. Arvinachelys as originally figured, then with several fused bones segregated with colors.

Figure 3. Kallokibotion (at right) compared to Meiolania. The former also has divided narial openings and precedes Arniachelys phylogenetically.

Publicity
Journalist call this turtle’s twin nares ‘bizarre’ and ‘weird’, even though basal turtles, like Proganochelys share this trait. When you think about it, there are several turtles that are much more weird than Arvinachelys. Superlatives, whether warranted or not, seem to drive paleo publicity.

https://www.earthtouchnews.com/discoveries/fossils/this-ancient-pig-nosed-creature-might-be-the-weirdest-turtle-that-ever-lived/

https://www.cnn.com/2015/10/24/us/goldens-bacon-turtle-fossil-feat/index.html

http://time.com/4083220/pig-snouted-turtle-fossil/

References
Lively J 2015. A new species of baenid turtle from the Kaiparowits Formation (Upper Cretaceous: Campanian) of southern Utah. Journal of Vertebrate Paleontology. doi:10.1080/02724634.2015.1009084
Pérez-García A and Vlad Codrea 2018. New insights on the anatomy and systematics of Kallokibotion Nopcsa, 1923, the enigmatic uppermost Cretaceous basal turtle (stem Testudines) from Transylvania. Zoological Journal of the Linnean Society. 182(2):419–443. doi:10.1093/zoolinnean/zlx037.

 

More turtles with temporal fenestrae

Figure 1. Skull of the basal hard-shell turtle, Baena. Some of these bone IDs and their sutures differ from those from Gaffney 1979. Principally, the gray/red bone is the supratemporal, considered absent by all turtle experts when they do not recognize the pareiasaur origin of the clade.

Yesterday we looked at several turtles with a lateral temporal fenestra. Today a few more are presented including Baena and Kayentachelys, turtles recently added to the large reptile tree (LRT, 1201 taxa).

Figure 2. Kayentachelys skull with bones colored differently than in the original drawings.

These two extinct turtles
nest between basalmost forms and extant turtles.

By convergence
several turtle clades (Fig. 3) developed various skull fenestrae, including soft-shell turtles beginning with Arganaceras (not sure if it’s a turtle or not yet) and Odontochelys.

Figure 3. Subset of the large reptile tree (LRT, 1199 taxa) with the addition of three basal turtles. The Mongolochelys/Chubutemys clade did not develop temporal fenestrae. Foxemys and Macrochelys had tentative occipital invagination that extended further with more derived taxa in their respective clades.

Among the most striking of the fenestrated turtle skulls
are the [cryptodire = straight neck in dorsal view, S-curve in lateral view] common Eastern box turtle (genus: Terrapene, Fig. 4) and the [pleurodire = S-curve side neck in dorsal view] matamata (genus: Chelus, Fig. 5). It’s difficult to label these two ‘anapsids’ based on their skull morphology, but that’s the traditional label.

Figure 4. Terrapene, the box turtle, with skull bones colorized. Note the fenestrated skull. See how colors make bones so much easier to understand. You’ll note many academic papers have been following this trend lately.

Figure 5. Chelus frmbiata, the mata-mata has a temporal fenestra. Not sure if it’s a lateral or upper type. Note also the mistake made by Dr. Gaffney in overlooking the squamosal and quadratojugal, and mislabeling the supratemporal. This is one skull you can easily get lost in—if you don’t color the bones. Finally, note the sidesweep of the cervicals in this pleurodire turtle.

References
Gaffney ES 1979. The Jurassic Turtles of North America. Bulletin of the American Museum of Natural History 162(3):91-136.