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.

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.

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.

Evolution of Sea Turtles video has no idea where turtles came from

 A new Ben Thomas video brings us old and invalid view on turtle origins.

I wrote in the comments section:
“Several traditional, but invalid hypotheses in this video. The ability to pull the head inside the shell, whether sideways or straight back is a highly derived character in the hardshell turtle lineage. Sea turtles and their ancestors never could do this. They branched off earlier. Only some soft shell turtles, like the Asian giant soft-shell turtle (Pelochelys) manage to pull half the skull inside a huge mass of scaly flesh by convergence. Eorhynchochelys is a giant eunotosaur. Both are derived from Acleistorhinus not close to turtles. Pappochelys is a basal sauropterygian, again not close to turtles. Sorry, Ben. Eunotosaurus details here:” http://www.reptileevolution.com/eunotosaurus.htm

“Hard shell and soft shell turtles had dual and parallel origins from the small, horned pareiasaurs Elginia and Sclerosaurus. We know turtle origins back to Silurian jawless fish. Cladogram of relationships that tests all published turtle origin candidates here: http://www.reptileevolution.com/reptile-tree.htm

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.

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 4. Subset of the LRT focusing on the the clade that includes Kudnu.

Figure 3. Subset of the LRT focusing on the the clade that includes Kudnu.

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

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.

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.

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

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

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.

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: 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 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.

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 1. Partial reconstruction of Sphodrosaurus based on tracings in figure 2.

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: Basal hardshell turtle Meiolania aquatic

Lichtig and Lucas 2018
discuss the giant, horned, club-tailed basal turtle, Meiolania (Fig. 1).They report, “Analyzing the habitus of Meiolania based on limb proportions, shell shape, and femoral morphology suggests that it was an aquatic turtle similar in all these morphologies to Chelydra [the smaller genus of snapping 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.

The authors continue:
“The round shape of the femoral head indicates a walking mode of locomotion,
as is seen in the bottom walking of Chelydra. Furthermore, the plastral fontanelle is not known in any turtle suggested to be terrestrial. A “tail club” has been suggested to indicate a terrestrial habitus, as swinging this as a weapon would be difficult to impossible in the water. This ignores the fact that the tail “clubs” of Meiolania and Proganochelys are too narrow to be used as a club. The body of the tail would contact a target before the “club’s”
impact, reducing the effect of any strike. In addition, no extant terrestrial turtle has such a large tail, but this is exactly what is seen in the bottom walking Chelydra and Platysternon.” Some good hypotheses there.

Maybe amphibious?
At home either in a pond or between ponds?

Ancestral pareiasaurs were also likely amphibious
according to bone micro anatomy studies (Kriloff et al. 2008).

References
Lichtig AJ and Lucas SG 2018. The late Cenozoic turtle Meiolania platyceps was aquatic. SVP abstracts.
Kriloff A, Germain D, Canoville A, Vincent P,  Sache M and Laurin M 2008.
Evolution of bone microanatomy of the tetrapod tibia and its use in palaeobiological inference. Journal of Evolutionary Biology. 21 (3): 807–826. doi:10.1111/j.1420-9101.2008.01512.x