Megaevolutionary dynamics in reptiles: Simoes et al. 2020

Simoes et al 2020 discuss
“rates of phenotypic evolution and disparity across broad scales of time to understand the evolutionary dynamics behind the origin of major clades, or how they relate to rates of molecular evolution.”

“Here, we provide a total evidence approach to this problem using the largest available data set on diapsid reptiles.”

Unfortunately not large enough to understand that traditional ‘diapsid’ reptiles are diphyletic, splitting in the Viséan and convergently developing two

“We find a strong decoupling between phenotypic and molecular rates of evolution,”

Yet another case of gene-trait mismatch in analysis.

“and that the origin of snakes is marked by exceptionally high evolutionary rates.”

Taxon exclusion is the reason for this exclusion.

Figure 1. Cladogram from Simoes et al. 2020. Gray tones added to show Lepidosauromorpha in the LRT.

Figure 1. Cladogram from Simoes et al. 2020. Gray tones added to show Lepidosauromorpha in the LRT.

“Here, we explore megaevolutionary dynamics on phenotypic and molecular evolution during two fundamental periods of reptile evolution: i) the origin and early diversification of the major lineages of diapsid reptiles (lizards, snakes, tuataras, turtles, archosaurs, marine reptiles, among others) during the Permian and Triassic periods,”

In the LRT the new archosauromorphs split from new lepidosauromorphs in the Viséan (Early Carboniferous).

“as the origin and evolution of lepidosaurs (lizards, snakes and tuataras) from the Jurassic to the present.”

In the LRT lepidosaurs had their origin in the Permian and the Simoes team ignores the Triassic radiation of lepidosaurs leading to tanystropheids and pterosaurs.

So without a proper and valid phylogenetic context,
why continue? How can they possibly discuss ‘rates of change’ if they do not include basal taxa from earlier period?

“Our results indicating exceptionally high phenotypic evolutionary rates at the origin of snakes further suggest that snakes not only possess a distinctive morphology within reptiles,  but also that the first steps towards the acquisition of the snake body plan was extremely fast.”

In the LRT many taxa are included in the origin of snakes from basal geckos. These are missing from Simoes list of snake ancestor.

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

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

In the LRT all sister taxa resemble one another
and document a gradual accumulation of derived traits.

If you have any particular evolutionary questions,
they were probably answered earlier in previous posts. Use the keyword box at upper right to seek your answer.

 

The affinities of ‘Parareptilia’ and ‘Varanopidae’: Ford and Benson 2020

Readers will know the knives are out for this one
by Ford and Benson 2020 since the large reptile tree (LRT, 1625+ taxa) finds the Parareptilia is polyphyletic and the Varanopidae (1940) is a junior synonym for Synapsida (1903). And yes, Ford and Benson’s cladogram (Fig. 1) suffers from (altogether now): taxon exclusion. The Ford and Benson paper, like many before it, keeps perpetuating the myth of the Parareptilia and other traditional clades.

Figure 1. Cladogram by Ford and Benson 2020, with orange overlay showing taxa in the Archosauromorpha in the LRT. Massive taxon exclusion is the problem with the Ford and Benson tree.

Figure 1. Cladogram by Ford and Benson 2020, with orange overlay showing taxa in the Archosauromorpha in the LRT. Massive taxon exclusion is the problem with the Ford and Benson tree.

From the abstract:
“Amniotes include mammals, reptiles and birds, representing 75% of extant vertebrate species on land. They originated around 318 million years ago in the early Late Carboniferous and their early fossil record is central to understanding the expansion of vertebrates in terrestrial ecosystems.

By contrast, in the LRT the last common ancestor of all amniotes (= reptiles) is Silvanerpeton from the Viséan (Early Carbonferous, 335mya, not listed in Fig. 1) with a likely genesis earlier since the Viséan includes several other  amphibian-like reptiles, also not listed. Ford and Benson need to dip much deeper into the basal Tetrapoda to figure out which taxon is the last common ancestor of the Amniota and which taxa precede it. They make the mistake of considering Tseajaia and Limnoscelis pre-amniotes.The LRT nests them both deep within Amniota / Reptilia.

“We present a phylogenetic hypothesis that challenges the widely accepted consensus about early amniote evolution, based on parsimony analysis and Bayesian inference of a new morphological dataset.”

That would be great, so long as they include pertinent taxa, which they do not.

“We find a reduced membership of the mammalian stem lineage, which excludes varanopids.”

That’s odd because when you add pertinent taxa, the LRT finds an increased membership in the diapsid/mammal stem lineage, the new Archosauromorpha.

“This implies that evolutionary turnover of the mammalian stem lineage during the Early–Middle Permian transition (273 million years ago) was more abrupt than has previously been recognized.”

No one can make valid implications from the Ford and Benson cladogram. It is largely incomplete.

“We also find that Parareptilia are nested within Diapsida.”

This is only possible due to massive taxon exclusion. Ford and Benson omit many taxa that would change the topology of their tree. The Parareptilia include a diverse and polyphyletic assembly of taxa according to the LRT. Ford and Benson are not aware that Lepidosauria are no longer members of the archosauromorph Diapsida.

“This suggests that temporal fenestration, a key structural innovation with important functional implications, evolved fewer times than generally thought, but showed highly variable morphology among early reptiles after its initial origin.”

Just the opposite. In the LRT fenestration evolved MORE times than generally thought.

“Our phylogeny also addresses controversies over the affinities of mesosaurids, the earliest known aquatic amniotes, which we recover as early diverging parareptiles.”

That can only happen with massive taxon exclusion. We’ve known for several years that mesosaurs nest as derived pachypleurosaurs close to thalattosaurs and ichthyosaurs in the LRT. Those pertinent taxa are omitted in Ford and Benson’s paper.

From the introduction:
“The current paradigm of early amniote evolution was established in the late twentieth century. It includes a deep crown group dichotomy between Synapsida (total group mammals) and Reptilia (total group reptiles, including birds), followed by an early divergence of Parareptilia from all other reptiles (Eureptilia).”

Add taxa and the first dichotomy separates the new Archosauromorpha from the new Lepidosauromorpha. This has been online since July 2011 and represents the current paradigm. Ford and Benson are digging into old myths and traditions.

“Furthermore, both molecular and morphological studies have recovered turtles, which lack fenestrae, as diapsids.”

Since molecular studies do not replicate trait studies in deep time molecular studies must be wrong (probably due to epigenetics) and do not employ fossil taxa. So forget genomics in paleontology. Genomics delivers false positives.

“Our analysis includes 66 early fossil members of the amniote crown group, and four crownward members of the amniote stem group, giving a total of 70 operational taxonomic units.” 

By contrast the LRT includes 1625+ taxa not biased by prior studies, including dozens of basal vertebrates and basal tetrapods.

“The goal of our study is to examine the deep divergences of the amniote crown group.” 

If so, then Ford and Benson need to add dozens to hundreds of more taxa to their incomplete study. A suggested list is found here.

“We excluded recumbirostrans from our analysis. Recumbirostrans have generally been assigned to non-amniote microsaurs, but were recently recovered as early crown group amniotes.”

By contrast the LRT includes seven taxa listed by Wikipedia/Recumbirostra. We learned earlier that previous workers have deleted taxa that otherwise deliver unwanted results. Not sure what is happening in the Ford and Benson paper after their omission of this clade. Those seven recumbirostran taxa nest outside the Reptilia /Amniota in the LRT.

From the Results:
“All our analyses recover parareptiles and neodiapsids as a monophyletic group within Diapsida.”

These are false positive results due to taxon exclusion as shown here.

From the Discussion:
“The sister relationship between parareptiles and neodiapsids, and their relationship to Varanopidae, implies a single origin of temporal fenestration before the common ancestor of these clades.” 

These are false positive results due to taxon exclusion as shown here. We’ve known the clade Diapsida is polyphyletic since July 2011 with a last common ancestor in Early Carboniferous amphibian-like reptiles.

Happy holidays, dear readers. 


References
Ford DP and Benson RBJ 2020. The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae. Nature ecology & evolution 4:57–65. SuppData

Modesto SP 2020. Rooting about reptile relationships. Nature Ecology & Evolution 4:10–11.

 

New ‘Mesenosaurus’ closer to other taxa in the LRT

Maho, Gee and Reisz 2019
introduce us to a new Early Permian skull-only specimens (OMNH 73208, OMNH 73209 and OMNH 73500; Figs. 1, 2) they attribute to a new species of an old genus, Mesenosaurus efremovi

Figure 1. ?Mesenosaurus efremovi, left and right sides from Maho et al. 2019. Colors added using DGS techniques.

Figure 1. ?Mesenosaurus efremovi, left and right sides from Maho et al. 2019. Colors added using DGS techniques. Note the antorbital fossa without a fenestra.

The original art in Maho et al. 2019
(Fig. 1) was used to create this reconstruction (Fig. 2) using DGS techniques, using the best bones from the left and right to make this reconstruction. There are no surprises here.

Figure 2. ?Mesenosaurus efremovi reconstructed using DGS techniques.

Figure 2. ?Mesenosaurus efremovi reconstructed using DGS techniques. See figure 1.

After testing OMNH 73209
(Figs. 1, 2) in the large reptile tree (LRT, 1592 taxa, subset Fig. 4) this specimen nests a node away from three other Mesenosaurus specimens. So, distinct from Maho et al. 2019 (Fig 3), this specimen is not congeneric with other Mesenosaurus in the LRT (Fig. 4).

Figure 3. From Maho et al. 2019, their cladogram of Mesenosaurus relationships.

Figure 3. From Maho et al. 2019, their cladogram of Mesenosaurus relationships.

Further complicating matters,
Maho et al. contend that Mesenosaurus is a varanopid (Fig. 3). This is an outmoded traditional hypothesis invalidated in 2014 by the LRT. Mesenosaurus and kin are Protodiapsids, nesting between the basalmost synapsid, Vaughnictis and archosauromorphs with a diapsid skull architecture, labeled Diapsida in the LRT.

Figure 4. Subset of the LRT focusing on the clade Protodiapsida nesting between basalmost synapsids and archosauromorph diapsids.

Figure 4. Subset of the LRT focusing on the clade Protodiapsida nesting between basalmost synapsids and archosauromorph diapsids.

As we learned earlier in 2011
lepidosauriformes also developed a diapsid skull architecture by convergence, here labeled Lepidosauriformes. That news has not reached the three authors, Maho, Gee and Reisz, nor have they tested a sufficient number of pertinent taxa to recover that basal dichotomy, known for the last eight years.

Figure 1. Mesenosaurus skulls compared to sisters Heleosaurus and Mycterosaurus. Note the greater angularity of the skull shapes along with the wider posterior skulls in derived taxa (toward the bottom). The SGU specimen needs better data on the squamosal, which is illustrated as missing its ventral/lateral portion here.

Figure 5. Mesenosaurus skulls compared to sisters Heleosaurus and Mycterosaurus. Note the greater angularity of the skull shapes along with the wider posterior skulls in derived taxa (toward the bottom). The SGU specimen needs better data on the squamosal, which is illustrated as missing its ventral/lateral portion here.

According to the LRT
the various Mesenosaurus specimens (Fig. 5) demonstrate a wider variety of skull shapes than do many congeneric taxa.

Figure 2. A subset of the large reptile tree showing the relationships of protosynapsids, synapsids, protodiapsids and diapsids. Traditionally nested with synapsids as varanopids, the protodiapsids have rarely, if ever, been tested with diapsids.

Figure 6. A subset of the large reptile tree showing the relationships of protosynapsids, synapsids, protodiapsids and diapsids. Traditionally nested with synapsids as varanopids, the protodiapsids have rarely, if ever, been tested with diapsids.

Varanopids have a smaller clade membership
than the authors suppose when more taxa are tested. All they have to do is add taxa to see their varanopid clade become a dichotomy (Fig. 6) leading to mammals on one line and dinosaurs and giant sea reptiles on the other. All this was overlooked by the PhDs.


References
Maho S, Gee BM, Reisz RR 2019. A new varanopid synapsid from the early Permian of Oklahoma and the evolutionary stasis in this clade. R. Soc. open sci. 6: 191297. http://dx.doi.org/10.1098/rsos.191297

https://pterosaurheresies.wordpress.com/2014/03/03/basal-diapsida-and-proto-diapsida/

Early Permian Cabarzia enters the LRT on two legs

Spindler, Werneberg and Schneider 2019
bring us news of a new headless, but otherwise complete skeleton from the Early Permian of Germany. The authors considered Cabarzia trostheidei (Figs. 1, 2, 5; NML-G2017/001) a close match to the Middle Permian protodiapsid Mesenosaurus (Fig. 2) from the Middle Permian of Russia and the oldest evidence for bipedal locomotion, 15 million years earlier than Eudibamus.

Figure 1. Cabarzia in situ and tracing distorted to fit the photo from Spindler, et al. 2019. Inserts show manus and pes with DGS colors and reconstructions. Scale bar = 5 cm.

Figure 1. Cabarzia in situ and tracing distorted to match the photo from Spindler, et al. 2019. Inserts show manus and pes with DGS colors and reconstructions. Scale bar = 5 cm. Pelvis enlarged in figure 4.

In slight contrast
the large reptile tree (LRT, 1385 taxa; subset Fig. 4) nests Cabarzia on the synapsid side of the Synapsida-Protodiapsida split within the new Archosauromorpha. Skull-less Cabarzia nests with the synapsids, Apsisaurus and Aerosaurus, also from the Early Permian. This is only a node or two away from Mesenosaurus.

In an earlier Spindler et al. 2016 phylogenetic analysis,
the last outgroup to the Synapsida-Protodiapsida split, Vaughnictis nested with the new Lepidosauromorpha caseid, Oedaleops (Fig. 3) far from the synapsids, but close to Feeserpeton and other taxa with a lateral temporal opening not related to synapsids. That error and the mistaken monophyly of the clade Varanopidae, are common to in all current paleontological books. Both are due to taxon exclusion at the base of the Reptilia (see below) and the lack of diapsid taxa in synapsid studies and vice versa.

Figure 2. Two specimens attributed to Mesenosaurus compared to scale with Cabarzia. Scale bar = 5cm.

Figure 2. Two specimens attributed to Mesenosaurus compared to scale with Cabarzia. Scale bar = 5cm.

Spindler et al. 2016 (the Ascendonanus paper)
presented a phylogenetic analysis that included Vaughnictis, which nested with the Lepidosauromorph caseid, Oedaleops, (Fig. 3) without providing enough taxa to recover a basal Lepidosauromorpha-Archosauromorpha split recovered by the LRT that separates caseids from synapsids and nests them with other bulky herbivores with a lateral temporal fenestra, like Eunotosaurus. Cabarzia was then known as the Cabarz specimen, then considered a member of the Varanopidae (Fg. 3).

FIgure 3. Spindler et al. 2016 cladogram suffering from massive taxon exclusion.

FIgure 3. Spindler et al. 2016 cladogram suffering from massive taxon exclusion. The red panel highlights taxa that nest within the new Lepidosauromorpha in the LRT. The dark gray panel highlands various actual and putative varanopids nesting paraphyletically. In the LRT they nest together. Note the proximity of the Cabarz specimen (Cabarzia) to Elliotsmithia, but some distance from Apsisaurus, Aerosaurus, Varanops and and Varanodon.

The LRT
(subset Fig. 4) does not suffer from taxon exclusion. At least, so far… Rather this wide gamut study illuminates previously unrecognized splits, like those within the traditional Varanopidae that produced the Protodiapsida.

Figure 4. Subset of the LRT focusing on basal Archosauromorpha including Vaughnictis and Cabarzia nesting at the base of the Protodiapsid-Synapsid split. Note all the large varanopids nest together here in the Synapsida, separate from small varanopids in the Protodiapsida.

Figure 4. Subset of the LRT focusing on basal Archosauromorpha including Cabarzia nesting at the base of the -Synapsida. Note all the large varanopids nest together here in the Synapsida, separate from small varanopids in the Protodiapsida.

Bipedal locomotion
Spindler et al. report, “Although the proportions of the entire postcranium of Cabarzia roughly resemble those of Eudibamus, these genera can easily be distinguished based on their vertebrae.” 

Citing Berman et al. 2000b and Sumida et al. 2013,
Spindler et al. list the adaptations of functional bipedalism. (my notes added)

  1. short neck (but Chlamydosaurus has a long neck)
  2. long hindlimbs
  3. short forelimbs
  4. short and slender trunk
  5. and a long robust tail (but Chlamydosaurus has a long attenuated tai)
  6. a rearward shift of the center of body mass

Spindler et al. 2018 note: “Decreased asymmetry of the hindlimb is seen in basal varanopids and mesenosaurines. Eudibamus has remarkably narrow caudal vertebrae; this may indicate that it evolved active bipedalism, facilitating slow bipedal locomotion.” We talked earlier here about the basal diapsid with a long neck and super slender tail, Eudibamus and its putative bipedal abilities. Spindler et al. do not cite the most active scientist currently working with bipedal lizards, Bruce Jayne and his video of lizards on treadmills.

FIgure 4. Pelvis of Cabarzia colored with DGS. Note the offset femoral head perforating the pelvis, the anterior process of the illiim and the four sacral vertebrae, all pointing to bipedal locomotion. Some of this was overlooked by Spindler et al.

FIgure 4. Pelvis of Cabarzia colored with DGS. Note the offset right femoral head perforating the pelvis, the anterior processes of the illi a and the four sacral vertebrae, all pointing to bipedal locomotion. Some of this was overlooked by Spindler et al. The left femur is too long due to the split. The pink linear bones are probably displaced gastralia.

The traditional touchstones of bipedal locomotion in lizards
(e.g. Chlamydosaurus kingii) are also present in Cabarzia. These include (according to Shine and Lambeck 1978, Snyder 1954; my notes added in bold):

  1. Bipedal reptiles are generally small, having experienced phylogenetic miniaturization –  outgroup taxa, Protorothyris and Vaughnictis, are not larger than Cabarzia.
  2. Bipeds are terrestrial and/or arboreal – present in most tetrapods
  3. Longer hind limbs than forelimbs – present in many tetrapods
  4. Anterior process of the illiim, no matter how small – present in Cabarzia 
  5. Typically stronger or more sacral connections to the ilium – present in Cabarzia 
  6. Typically a long neck and short torso  unknown in Cabarzia 

In Cabarzia we also find

  1. perforated acetabulum
  2. elongate and offset cylindrical femoral head

Overlooked by Spindler et al.:
Cabarzia provides a more complete look at the post-crania of basalmost synapsids, which include humans. No one has ever considered the possibility that bipedal locomotion in the Early Permian was part of that story. It is also common knowledge that more derived taxa in the lineage of synapsids, therapsids and mammals retained  quadrupedal locomotion, an imperforated acetabulum and only two sacrals. So bipedalism was a dead-end for Cabarzia, producing no known ancestors.

Figure 5. Cabarzia compared to Vaughnictis and Apsisaurus to scale. Finger 1 and other phalanges were identified in published photos of this specimen (Fig. 1) using DGS tracing and reconstruction methods.

Figure 5. Cabarzia compared to Vaughnictis and Apsisaurus to scale. Finger 1 and other phalanges were identified in published photos of this specimen (Fig. 1) using DGS tracing and reconstruction methods.

Despite the similar and coeval red bed matrices
of Aerosaurus, ApsisaurusVaughnictis and Cabarzia, the former three come from the western USA (Colorado) while Cabarzia comes from central Germany. Back then they were closer to one another, not separated by an Atlantic Ocean (Fig. 6).

Figure 6. Early Permian Earth, prior to the separation of Europe from North America.

Figure 6. Early Permian Earth, prior to the separation of Europe from North America.

References
Shine R and Lambeck R 1989.Ecology of Frillneck Lizards, Chlamydosaurus kingii (Agamidae), in Tropical Australia. Aust. Wildl. res. Vol. 16: 491-500.
Snyder RC 1954.
 The anatomy and function of the pelvic girdle and hind limb in lizard locomotion. American Journal of Anatomy 95:1-46.
Spindler F, Werneberg R and Schneider JW 2019. A new mesenosaurine from the lower Permian of Germany and the postcrania of Mesenosaurus: implications for early amniote comparative osteology. PalZ Paläontologische Gesellschaft

 

SVP 2018: The evolution of varanopids

Reisz 2018 reports,
“Varanopidae is a clade of small to medium sized carnivorous synapsids whose fossil
record spans the Late Pennsylvanian to late Permian, one of the longest known temporal
ranges of any Paleozoic eupelycosaur clade. It has also been recently suggested that this clade may not be part of Synapsida, but may instead nest within Diapsida.”

In the large reptile tree (LRT, 1306 taxa, subset Fig. 1) Vaughnictis is the last common ancestor of Diapsida and Synapsida. Varanodon nests within the Synapsida. A series of former varanopids nest as pre-diapsids.

Figure 6. Subset of the large reptile tree showing the nesting of Vaughnictis at the base of the Synapsida and Prodiapsida.

Figure 1. Subset of the large reptile tree showing the nesting of Vaughnictis at the base of the Synapsida and Prodiapsida. Higher synapsids arise from Ophiacodon. Diapsids arise from the Broomia clade. If Reisz isn’t getting this topology, he may have to add taxa. 

Reisz 2018 concludes,
“A revised and expanded data matrix and phylogenetic analysis that integrates Permo-Carboniferous synapsids and reptiles does recover a monophyletic Varanopidae within Synapsida, with Varanodon and its varanodontine sister taxa, Watongia, Varanops, Tambacarnifex, as apex, gracile predators of the early Permian, contemporaries of the larger, more massively built sphenacodontid synapsids.”

Unfortunately taxon exclusion
prevents Dr. Reisz from seeing the big picture (subset Fig. 1), published online in 2015 here and expanded since then.

References
Reisz RR 2018. Varanodon and the evolution of varanopid synapsids. SVP abstracts.

It’s not Hovasaurus – and it’s not in a museum

A slight departure today
to the world of fossil commerce. This reptile is new to Science, so it should be presented to a museum for study, but it’s for sale online. And it was misidentified by the proprietors (who have been notified).

Figure 1. Specimen wrongly interpreted as Hovasaurus from FineFossils.com

Figure 1. Specimen wrongly identified as Hovasaurus from FineFossils.com

Cruising around the Internet
I found this specimen (Fig. 1) at FineFossils.com misidentified as Hovasaurus (Fig. 2). The differences are pretty obvious, so I won’t belabor them here. The new specimen is from the same strata and location as Hovasaurus, which is probably the reason for the mistake.

Figure 1. Tangasaurus, Hovasaurus and Thadeosaurus, three marine younginiformes, apparently have no scapula.

Figure 2. Tangasaurus, Hovasaurus and Thadeosaurus, three marine younginiformes compared. Hovasaurus, as you can see bears little resemblance to the FineFossils.com specimen mislabeled as Hovasaurus.

From the FineFossils
website: Hovasaurus boulei was a small aquatic Diapsid reptile, of the order Eosuchia, and dates from the late Permian Period, 260m to 251m years old. This specimen was discovered in the Middle Sankamena Formation, Sankamena Valley, Madagascar. It is very rare to find such a complete specimen in perfect condition, displaying a wonderfully preserved skeleton.

These reptiles are known to have a laterally flattened tail [but this one does not have such a tail!], very much like a modern day sea snake, making them extremely agile in the water.  Stones have been found in the abdomens of these creatures [but no stones were found here], indicating that they swallowed small stones to give them ballast, preventing them from floating to the surface when they were hunting prey underwater. 

This Hovasaurus is an amazing example of this very ancient reptile, and is of museum quality [other than the upside-down skull, the specimen has no obvious errors]. We have seen other specimens, but the majority are dis-articulated or incomplete.
The only restoration to this piece is at the tip of the tail.

Size:    matrix  47cms x 15cms
Size:    reptile   46cms long

The description of this specimen
recalls the mid 1800s in the earliest days of fossil collection when every pterosaur discovered was referred to  Pterodactylus, despite readily observable differences from the holotype. This specimen (Fig. 1)  is probably more marketable with a name. The name might also imply it is common enough to be sold to private individuals, like the Green River fossil fish magnets that adorn American refrigerators.

Figure 3. The FineFossils.com specimen traced and reconstructed. This previously unknown specimen nests at the base of the Diapsida, close to Eudibamus, but has an extended rostrum.

Figure 3. The FineFossils.com specimen traced and reconstructed. This previously unknown specimen nests at the base of the Diapsida, close to Eudibamus, but has an extended rostrum.

In this case, however,
the specimen is new to Science. It has not been assigned a generic name. It has not been studied yet (other than by what you’re reading here). The FineFossils specimen has a longer rostrum than other basal diapsids and hints at a broader radiation at this node. It is basal to Eudibamus, Aphelosaurus, Petrolacosaurus (Fig. 4) and Araeoscelis on one branch. It is basal to Spinoaequalis and all the marine and terrestrial Younginiforms, including birds and crocs, ichthyosaurs and plesiosaurs, on the other branch. The rostrum appears to have an antorbital fenestra (Fig. 4), but that is due to crushing and shifting of the elements.

Figure 4. Fine fossils skull wrongly attributed to Hovasaurus traced and reconstructed. This is an unnamed genus new to Science.

Figure 4. Fine fossils skull wrongly attributed to Hovasaurus traced and reconstructed. This is an unnamed genus new to Science. The apparent antorbital fenestra is an illusion produced by taphonomic shifting.

So, if anyone has deep pockets out there
you can make a purchase and a museum donation that will be much appreciated by reptile paleontologists everywhere. This is a unique specimen nesting at a key node on the family tree that I can only chat about online, since it currently has no museum number. It can’t find a permanent place on the large reptile tree without that museum number.

It would be worthy of a publication!

It’s rare. It’s unique.
And if you work it right, it might be named for you as in ‘Rogersaurus’, ‘Marysaurus’ or, better yet… Diapsidsaurus longirostrum would make a suitable name for the reasons listed above.

Figure 2. Petrolacosaurus is an earlier sister to Araeoscelis with a definite diapsid temporal configuration, but oddly the upper temporal fenestra is largely lateral in this taxon.

Figure 5. Petrolacosaurus is an earlier sister to Araeoscelis with a definite diapsid temporal configuration, but oddly the upper temporal fenestra is largely lateral in this taxon. The parietals are quite broad.

Speaking of basal diapsids
Once hailed as the most basal disapsid, Petrolacosaurus (Lane 1945, Reisz 1977) is now much more derived with several more primitive diapsid taxa preceding it on the large reptile tree, including the FineFossils.com specimen. All this hints at an earlier radiation, the kind we talked about earlier here.

References
Lane HH 1945. New Mid-Pennsylvanian Reptiles from Kansas. Transactions of the Kansas Academy of Science 47(3):381-390.
Reisz RR 1977. Petrolacosaurus, the Oldest Known Diapsid Reptile. Science, 196:1091-1093. DOI: 10.1126/science.196.4294.1091

wiki/Petrolacosaurus

When Synapsids and Diapsids split

At some point
on every reptile cladogram the Synapsida emerges and somewhere else the Diapsida emerges.

In contrast to all prior cladograms,
on the large reptile tree, the traditional Diapsida is diphylletic, with lepidosaurs no longer related to archosaurs except by way of the basalmost Viséan reptiles (at the archosauromorph/ lepidisauromorph split). The reduced Diapsida (sans lepidosaurs) arises from the Prodiapsida, which splits from the Synapsida at the common base of both clades, near Protorothyris (Fig. 1), a basal archosauromorph. What happened at that split is today’s topic.

One of the basalmost synapsids
is Varanosaurus. One of the basal prodiapsids is Heleosaurus (Fig. 1). Both have a synapsid temporal morphology. Among traditional paleontologists, both are considered traditional synapsids.

Now let’s take a look
at some of the characters that split these sister taxa that otherwise share so many traits and put forth some hypotheses as to what they may mean in the grand scope of reptile evolution.

Figure 1. Taxa at the split between Synapsida and Diapsida (Prodiapsida): Varanosaurus and Heleosaurus to scale along with their common ancestor, Protorothyris.

Figure 1. Taxa at the split between Synapsida and Diapsida (Prodiapsida): Varanosaurus and Heleosaurus to scale along with their common ancestor, Protorothyris.

In many respects,
Varanosaurus was just a bigger Heleosaurus. And both were much larger than their predecessor, Protorothyris. So size was a major factor in the Early Permian. Basal synapsids were larger than prodiapsids and both were larger than their Carboniferous predecessors.

Distinct from Varanosaurus,
Heleosaurus had 19 rather minor traits in the large reptile tree. As a rule they’re not very interesting or informative (but see the next topic header):

  1. Remained < 60 cm long
  2. Slightly wider skull relative to height at orbit
  3. The nasal shape retains ‘narrows anteriorly’ description (not arrowhead)
  4. Orbit stays in anterior half of the skull
  5. Supratemporal/squamosal overhang
  6. Shorter jugal quadratojugal process
  7. Quadrate rotates to vertical
  8. Lateral temporal fenestra larger, circumtemporal bones more gracile
  9. Occiput remains close to quadrates
  10. Basipterygoid lateral processes prominent
  11. Mandible tip straight
  12. Mandible fenestra remains absent
  13. Olecranon process not present (Heleosaurus clade only)
  14. Clavicles medially not broad
  15. Radius + ulna > 3x longer than wide
  16. Retained pubis angled ventrally
  17. Acetabulum opens ventrally (Heleosaurus clade only)
  18. Tibia < 2x ilium length
  19. Dorsal osteoderms present (restricted to Heleosaurus

In summary,
these Heleosaurus traits break down to four major and a few minor distinctions from Varanosaurus:

  1. Smaller size, larger orbit, shorter rostrum, relatively less bone in the skull – all attributable to neotony (retention of embryo/juvenile traits)
  2. Relatively longer hind limbs and more slender tail (shorter chevrons and transverse processes (ribs). Together these two make prodiapsids speedy, not lumbering. Ideal for avoiding larger enemies and attacking insect prey.
  3. Relatively larger orbit: possible nocturnal hunter.
  4. Longer, more gracile ribs: fast locomotion requires more efficient and rapid respiration provided by expanding ribs
  5. Minor traits: Fewer teeth, ‘solid’ palate, larger choanae: all part of the insectivore, rapid respiration bauplan.

In my opinion
the smaller size of Heleosaurus helped it retain an insect diet, rather than moving into carnivory, piscivory or herbivory, as proposed for the pelycosaurs. Heleosaurus was probably faster and more agile than its larger and smaller relatives, better adapted to hunt insects and avoid predators.

Later taxa
‘improved’ on these traits as the clade Diapsida appeared, followed quickly by a division into terrestrial younginiforms and aquatic younginiforms.

These lizardy archosauromorph diapsids competed with
outwardly similar lepidosauromorphs lepidosaur pseudo-diapsids, like Tjubina. The lepidosaur branch retained insectivory, for the most part. The archosauromorph branch did not, for the most part, with the exception that several extant mammals and birds today are insectivores.

Maybe Araeoscelis DOES have a lateral temporal fenestra

Among basal diapsids,
Araeoscelis (Fig. 1, Williston 1910) has been the traditional outlier, closing up its lateral temporal fenestra shortly after gaining its upper temporal fenestra. Taking another look at the published drawings and moving the bones around a little, exposes a tiny lateral fenestra (Fig. 1). This is not traditional thinking, but also removes an odd autapomorphy.

Short reminder:
Araeoscelis is one sort of diapsid, the sort that ultimately led to dinos and birds. This entire clade is convergent with the diapsid configuration that developed in lepidosaurs according to the large reptile tree.

Figure 1. Araeoscelis fossi skull drawings from Reiz et al. 1984. Reconstructed in the middle.

Figure 1. Araeoscelis fossi skull drawings from Reiz et al. 1984. Reconstructed in the middle.

It’s worthwhile here to bring up Petrolacosaurus (Fig. 2) for comparison.

Figure 2. Petrolacosaurus is an earlier sister to Araeoscelis with a definite diapsid temporal configuration, but oddly the upper temporal fenestra is largely lateral in this taxon.

Figure 2. Petrolacosaurus is an earlier sister to Araeoscelis with a definite diapsid temporal configuration, but oddly the upper temporal fenestra is largely lateral in this taxon. The parietals are quite broad.

Note
in Petrolacosaurus the upper temporal fenestra is high on the lateral side of the skull and the jaw joint is in line with the jaw line, distinct from Araeoscelis. The new data shifts nothing in the large reptile tree.

IMHO,
the reduction of the lateral temporal fenestra in Araeoscelis.has something to do with the decent of the jaw joint and the blunting/thickening of the teeth. It was eating something that was tougher or crunchier than Petrolacosaurus preferred.

Araeoscelis is a terminal taxon, leaving no known descendant taxa.

References
Reisz RR, Berman DS and Scott D 1984. The anatomy and relationships of the lower Permian reptile Araeoscelis. Journal of Vertebrate Paleontology 4: 57-67.
Vaughn PP 1955. The Permian reptile Araeoscelis re-studied. Harvard Museum of Comparative Zoology, Bulletin 113:305-467.
Williston SW 1910. New Permian reptiles; rhachitomous vertebrae. Journal of Geology 18:585-600.
Williston SW 1913. The skulls of Araeoscelis and Casea, Permian reptiles. Journal of Geology 21:743-747.
wiki/Araeoscelis

Spinoaequalis and the origin of two clades of Younginiformes

Unless there is more breaking news, like Yi qi, the next few sessions will cover some news at the base of the younginiformes and archosauriformes.

Spinoaequalis schultzei (deBraga and Reisz 1995; Late Carboniferous ~306 mya; ~30 cm in length; Fig. 1), was originally considered a basal diapsid close to Petrolacosaurus and Araeoscelis, but with a deep, sculling tail. Here that nesting is confirmed with a closer relationships to Eudibamus.

 

More importantly,
Spinoaequalis nests at the base of the marine younginiformes, like Galesphyrus and the terrestrial younginformes, like Youngina SAM K7710 (see links below and Fig. 1). In other words these are all the taxa higher than Carboniferous diapsids (araeoscelids).

The deep tail is an autapomorphy of Spinoaeaqualis not expressed in descendant taxa, except, perhaps and separated by several nodes, Hovasaurus.

Figure 1. Spinoaequalis (above) to scale with a member of the juvenile den specimen of Youngina SAM K1770. These are sister taxa. The SAM specimens are not juveniles, but nest at the base of all terrestrial Younginisofmes + Protorosauria + Archosauriformes.

Figure 1. Spinoaequalis (above) to scale with a member of the purported juvenile den specimen of Youngina, SAM K1770. These are sister taxa. The SAM specimens are not juveniles, but nest at the base of all terrestrial Younginisofmes + Protorosauria + Archosauriformes. Another sister, Galesphyrus, nests at the base of all aquatic younginformes.

Spinoaequalis is much more important than deBraga and Reisz ever realized due to its nesting at the base of all terrestrial younginiformes (including archosauriformesdinosaurs including birds) …

Figure 2. Spinoaequalis and a number of basal terrestrial yonginiformes, many of which are represented by skulls only.

Figure 2. Spinoaequalis and a number of basal terrestrial yonginiformes, many of which are represented by skulls only. Click to enlarge. One other mislabeled Youngina specimen nests among the marine clade (Fig. 3).

…and at the base of all marine younginformes (including ichthyosaurs and sauropterygians).

Figure 3. Spinoaequalis and descendant marine younginiformes.

Figure 3. Spinoaequalis and descendant marine younginiformes. These give rise to plesiosaurs, placodonts, mesosaurs, ichthyosaurs and thalattosuchians. Click to enlarge. Note the nesting of one purported Youngina specimen separate from all others listed here.

And here (Fig. 4) is the tree and taxa we’ll be looking at over the next few blogposts. Note this is not the tree topology promoted by prior published work. The entire reptile tree can be viewed here.

Figure 3. Subset of the large reptile tree focusing on the Protodiapsida, the Diapsida, Marine Younginiformes and Terrestrial Younginiformes, including Protorosaurs and Archosauriformes. Click to enlarge.

Figure 4. Subset of the large reptile tree focusing on the Protodiapsida, the Diapsida, Marine Younginiformes and Terrestrial Younginiformes, including Protorosaurs and Archosauriformes.
Click to enlarge.

References
deBraga M and Reisz RR 1995. A new diapsid reptile from the uppermost Carboniferous (Stephanian) of Kansas. Palaeontology 38 (1): 199–212. palass-pub.pdf

wiki/Spinoaequalis

Variation in Mesenosaurus and Mycterosaurus

Updated February 23, 2015 with a new image of Mycterosaurus.

Mesenosaurus romeri (Efremov 1938, Reisz and Berman 2001) Late Carboniferous to Early Permian ~300 to ~260 mya was originally considered a varanopseid, like Varanops, but it lies outside the varanopsids and outside the synapsids when tested against a larger list of taxa. Here Mesenosaurus was derived from a sister to Archaeovenator and phylogenetically preceded Milleropsis within the Protodiapsida and Eudibamus and Petrolacosaurus within the Diapsida (sans Lepidosauriformes, which nest elsewhere).

The clade of Heleosaurus + Mycterosaurus is a sister to Mesenosaurus (Fig. 1).

Figure 1. Mesenosaurus skulls compared to sisters Heleosaurus and Mycterosaurus. Note the greater angularity of the skull shapes along with the wider posterior skulls in derived taxa (toward the bottom). The SGU specimen needs better data on the squamosal, which is illustrated as missing its ventral/lateral portion here.

Figure 1. Mesenosaurus skulls compared to sisters Heleosaurus and Mycterosaurus. Note the greater angularity of the skull shapes along with the wider posterior skulls in derived taxa (toward the bottom). The SGU specimen needs better data on the squamosal, which is illustrated as missing its ventral/lateral portion here.

The Mycterosaurus question
The Mycterosaurus in figure 1 was illustrated by Williston in 1915. Bones attributed to Mycterosaurus by Reisz et al. 1996 are shown in figure 2. The tooth shapes are not the same. The depth of the maxilla is not the same. Yet the tooth shapes in the Williston image are not the same as those in Heleosaurus and Mesenosaurus. The Reisz et al. images are more similar.

Figure 2. Mycterosaurus bones from a fissure fill formation. Typically such bones are individually preserved, so their association with each other and with a certain genus and species is due to the expert eye of a paleontologist. I note differences in the shapes of Mycterosaurus here compared to the Williston specimen/reconstruction in figure 1. So, the data is confusing.

Figure 2. Mycterosaurus bones from a fissure fill formation. Typically such bones are individually preserved, so their association with each other and with a certain genus and species is due to the expert eye of a paleontologist. I note differences in the shapes of Mycterosaurus here compared to the Williston specimen/reconstruction in figure 1. So, the data is confusing.

Sometimes one trusts an illustration…
especially if that’s the only available data. Other times, especially if the illustration is old, the trust is reduced. Howecer, the holotype is the benchmark. Fissure fill specimens, disarticulated as they are, and recent figures are typically more accurate. But how do they relate to the holotype?

If anyone has better data on the holotype of Mycterosaurus,
like a photograph of, please send it and the accuracy of the large reptile tree will be enhanced.

References
Efremov JA 1938. Some new Permian reptiles of the USSR. Academy of Sciences URSS, C. R., 19: 121-126.
Reisz RR and Berman DS 2001. The skull of Mesenosaurus romeri, a small varanopseid (Synapsida: Eupelycosauria) from the Upper Permian of the Mezen River basin, northern Russia. Annals of the Carnegie Museum 70: 113-132. online pdf
Reisz RR, Wilson H and Scott D 1996. Varanopseid synapsid skeletal elements form Richards Spur, a Lower Permian fissure fill near Ft. Sill, Oklahoma. Oklahoma Geology Notes 56 (3):160-170.

wiki/Mesenosaurus