New paper on Eldeceeon, one of our earliest reptile ancestors

Ruta, Clack and Smithson 2020
bring us new two new specimens of the amphibian-like reptile, Eldeceeon (pronounced ‘L-D-C-on’, Smithson 1994; Viséan, 335mya), adding to the two previously described specimens (Fig. 1). These two are the basalmost taxa in the Archosauromorpha in the large reptile tree (LRT, 1725+ taxa, subset Figs. 4, 5). The authors confirm a relationship to Silvanerpeton (Fig. 2), the last common ancestor of all reptiles in the LRT. They share a deep pelvis for large egg laying and a large lumbar region  for egg-carrying in females. This trait is shared with males unless all specimens around this node found so far are all females.

Figure 1. The two earlier specimens attributed to Eldeceeon that nest together at the base of the Archosauromorpha. Note the extended lumbar region and deep pelvis ideal for laying large eggs on both specimens.

Unfortunately, 
the authors consider these taxa “either as the most plesiomorphic stem amniote clade or as a clade immediately crownward of anthracosauroids.” 

They didn’t test enough taxa to nest Elcedeceeon and Silvanerpeton as basal amniotes (= reptiles), nor did they test enough taxa to recover a basal dichotomy in the Viséan at the base of the Reptilia. One branch, the Archosauromorpha, gives rise to synapsids and non-lepidosaur diapsids. At its base, Eldeceeon is an amphibian-like reptile that laid (by phylogenetic bracketing) amniotic eggs.

From the abstract:
“A detailed account of individual skull bones and a revision of key axial and appendicular features are provided, alongside the first complete reconstructions of the skull and lower jaw and a revised reconstruction of the postcranial skeleton.”

Actually those first complete reconstructions were done here in 2014. Worse yet, the authors created by freehand one chimaera reconstruction (their figure 7e), not appreciating the distinctions between the two previously known specimens (Fig. 1).

From the abstract
“The late Viséan anthracosauroid Eldeceeon rolfei from the East Kirkton Limestone of Scotland is re-described. Information from two originally described and two newly identified specimens broadens our knowledge of this tetrapod. 

Figure 2. Four cladograms from Ruta, Clack and Smithson 2020 seeking a nesting place for included taxa. Compare to Figure 4, a subset of the LRT. They need more outgroup taxa to solve their self-confessed phylogenetic problems.

From the Discussion
“The most vexing aspect of the Eldeceeon postcranium is the configuration of its rib cage, with long and curved ribs confined to the anterior half of its trunk. We hypothesise that the space between the most posterior trunk ribs and the pelvis was occupied by an unusually large puboischiofemoralis internus 2 (PIFI2).”

All basal amniotes have this sort of lumbar region. Gravid lizards use this space to carry eggs (Fig. 3). Ruta, Clack and Smithson overlook this possibility because their cladograms (Fig. 2) do not nest Eldeceeon and kin among the reptiles.

Figure 3. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

In the LRT Anthracosaurus
(Fig. 4) nests far from Eldeceeon (Fig. 5), Silvanerpeton, Gephyrostegus and other stem reptiles (= Reptilomorpha). Anthracosaurus nests in the same basal tetrapod clade as Ichthyostega and Proterogyrinus in the LRT. So taxon exclusion has mixed up the order of taxa in the cladogram of Ruta, Clack and Smithson 2020. More taxa solve such phylogenetic problems.

Other taxa are also adversely affected by taxon exclusion.
Ruta, Clack and Smithson report, “Eucritta melanolimnetes Clack, 1998 shares characters with groups as diverse as baphetids, temnospondyls, and anthracosaurs (Clack 2001); perhaps unsurprisingly, this combination of features has resulted in alternative phylogenetic placements for this taxon, either as a derived stem tetrapod or as a basal crown tetrapod shifting between alternate positions on either side of the lissamphibian–amniote dichotomy”. In the LRT (subset Fig. 2) Eucritta is a sister to Tulerpeton, the proximal outgroup clade to the Amniota + Gephyrostegus, which may be an amniote, too. It is the proximal outgroup to the Amniota in the LRT and includes all of the basal amniote traits.

Figure 4. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits. Eldeceeon arises after Silvanerpeton. Compare to cladograms in figure 2.

Eldeceeon rolfei (Smithson 1994) ~27 cm in total length, Early Carboniferous ~335 mya, is from the same formation that yielded Silvanerpeton and Westlothiana in the Viséan. Derived from a sister to Tulerpeton, Eldeceeon was basal to Diplovertebron and Solenodonsaurus in the LRT (Fig. 5). Relative to G. bohemicus, the skull of Eldeceeon was shorter and taller. The dorsal ribs are missing from the posterior half of the torso. This is an adaption to carrying larger eggs in gravid females. The pectoral girdle was more gracile. yet still deep. These two specimens nest together, but are distinct enough to warrant distinct species names.

Figure 5. Subset of the LRTfrom 2019 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.

Add taxa
to see the big picture. That always solves problems. Taxon exclusion continues to be the number one problem in paleontology.

Don’t create reconstruction chimaeras.
That never works out well. Too often the chimaera is created freehand.

The LRT is free, online and worldwide,
just so workers can check out the current list of sister taxa pertinent to any taxon under study. Someday it will be used. Not this time, but someday.

More on Anthracosaurus
and the traditional clade ‘Anthracosauria’ follows below the References. This clade turns out to be much smaller than current textbooks and lectures might indicate. Anthracosaurus is a terminal taxon leaving no descendants tested in the LRT.

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References
Ruta M, Clack JA and Smithson TR 2020. A review of the stem amniote Eldeceeon rolfei from the Viséan of East Kirkton, Scotland. Earth and Environmental Science Transactions of The Royal Society of Edinburgh (advance online publication)
DOI: https://doi.org/10.1017/S1755691020000079
Smithson TR 1994. Eldeceeon rolfei, a new reptiliomorph from the Viséan of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (3-4): 377–382.

wiki/Eldeceeon

Figure 3. The complete skull of Anthracosaurus greatly resembles its relative, Neopteroplax. These are basal flathead taxa with orbits high on the skull, distinct from reptilomorphs with smaller skulls and lateral orbits.

https://en.wikipedia.org/wiki/Anthracosauria
“Anthracosauria” is sometimes used to refer to all tetrapods more closely related to amniotes such as reptiles, mammals, and birds, rather than lissamphibians such as frogs and salamanders. An equivalent term to this definition would be Reptiliomorpha. Anthracosauria has also been used to refer to a smaller group of large, crocodilian-like aquatic tetrapods also known as embolomeres.

Gauthier, Kluge and Rowe (1988) defined Anthracosauria as a clade including “Amniota plus all other tetrapods that are more closely related to amniotes than they are to amphibians” (Amphibia in turn was defined by these authors as a clade including Lissamphibia and those tetrapods that are more closely related to lissamphibians than they are to amniotes).

Similarly, Michel Laurin (1996) uses the term in a cladistic sense to refer to only the most advanced reptile-like amphibians. Thus his definition includes Diadectomorpha, Solenodonsauridae and the amniotes.

Laurin (2001) created a different phylogenetic definition of Anthracosauria, defining it as “the largest clade that includes Anthracosaurus russelli but not Ascaphus true“. [Ascaphus is the extant tailed frog.]

Michael Benton (2000, 2004) makes the anthracosaurs a paraphyletic order within the superorder Reptiliomorpha, along with the orders Seymouriamorpha and Diadectomorpha, thus making the Anthracosaurians the “lower” reptile-like amphibians. In his definition, the group encompass the Embolomeri, Chroniosuchia and possibly the family Gephyrostegidae.

None of these apply to Anthrosaurus in the LRT.

Distinct from prior authors, the LRT recovers Limnoscelis, Diadectes and other diadectomorphs deep with the Lepidosauromorpha branch of the Reptilia. More taxa solved this problem, too.

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.

“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.

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.

 

Erpetosuchus now nests outside of the Archosauria + Poposauria in the LRT

Based on its uniquely inset tooth row
(Figs. 1–3) Erpetosuchus (Newton 1894; Late Carnian, Late Triassic) has been a traditional enigma taxon.

Figure 1. Erpetosuchus in several views. Here the post-crania of Parringtonia is added.

According to Wikipedia,
“The relationship of Erpetosuchus to other archosaurs is uncertain. In 2000 and 2002, it was considered a close relative of the group Crocodylomorpha, which includes living crocodylians and many extinct relatives. However, this relationship was questioned in a 2012 analysis that found the phylogenetic placement of Erpetosuchus to be very uncertain.”

“Benton and Walker (2002) found the same sister-group relationship and proposed the name Bathyotica for the clade containing Erpetosuchus and Crocodylomorpha.”

“Nesbitt and Butler (2012) included Erpetosuchus within a more comprehensive phylogenetic analysis and found it to group with the archosaur Parringtonia (Fig. 1) from the Middle Triassic of Tanzania. Both were part of the clade Erpetosuchidae. Nesbitt and Butler did not find support for the sister-group relationship between Erpetosuchus and Crocodylomorpha. Instead, erpetosuchids formed a polytomy or unresolved evolutionary relationship at the base of Archosauria along with several other groups. It could take many positions within Archosauria, but none were as a sister taxon of Crocodylomorpha.”

Figure 2. Erpetosuchus, Tarjadia, Parringtonia now nest with Decurisuchus outside of the Archosauria + Poposauria. Note the extreme anterior lean of the quadrate and quadratojugal here, convergent with crocodyliformes.

A recent review of the Crocodylomorpha
subset of the large reptile tree (LRT, 1660+ taxa; Fig. 4) knocked Erpetosuchus out of the Crocodylomorpha and out of the Archosauria. Erpetosuchus and other members assigned to the Erpetosuchidae (Pagosvenator, Parringtonia, Tarjadia (Figs. 2-3), but not the basal marine crocodile Dyoplax, at least not yet) now nest with Decuriasuchus (Figs. 2–3) in the LRT. This clade nests between Rauisuchia and Poposauria + Archosauria (Fig. 4).

Figure 3. Erpetosuchus and kin illustrated to scale. Parringtonia + Tarjadia + Erpetosuchus now nest with Decuriasuchus basal to Poposaurs + Archosauria.

The small size of Erpetosuchus
(Fig. 3) is a derived trait, following several much larger ancestors. Alas, as far as we know, Erpetosuchus was a terminal taxon, leaving no descendants.

Figure 4. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Why was Erpetosuchus traditionally considered ‘crocodile-like’?
The extreme anterior lean of the quadrate and quadratojugal are typical crocodile traits shared by convergence with members of the clade Erpetosuchidae (including Decuriasuchus).

Eagle-eyed readers may note
a few other changes in the Crocodylomorpha subset of the LRT (Fig. 4). We’ll deal with these in future blogposts.

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References
Benton MJ and Walker AD 2002. Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland, Zoological Journal of the Linnean Society 136:25-47.
Nesbitt SJ and Butler RJ 2012. Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae. Geological Magazine: 1. doi:10.1017/S0016756812000362
Nesbitt SJ, Stocker MR, Parke WGr, Wood TA, Sidor CA and Angielczy KD 2018. The braincase and endocast of Parringtonia gracilis, a Middle Triassic suchian (Archosaur: Pseudosuchia) Journal of Vertebrate Paleontology 37, Memoir 17: Vertebrate and Climatic Evolution in the Triassic Rift Basins of Tanzania and Zambia.
Newton TE 1894. Reptiles from the Elgin Sandstone—Description of two new genera. Philosophical Transactions of the Royal Society of London, B, 185:573–607.

wiki/Tarjadia
wiki/Parringtonia
wiki/Erpetosuchus

http://reptileevolution.com/decuriasuchus.htm

A 2020 primer on reptile tarsals

This blogpost had its genesis 
with a new paper by Blanco, Ezcurra and Bona 2020, who studied archosaur and stem archosaur ankles. They reported, “Here, we integrate embryological and palaeontological data and quantitative methodologies to test the hypothesis of fusion between the centrale and astragalus, or the alternative hypothesis of a complete loss of this element.”

More on the results of that paper
after this short primer.

Not sure how much readers know about this subject.
Ankles used to be ‘the thing’ back in the 1980s when terms like “crocodile normal” and “crocodile reversed” were common and influential. Today, with over 230 tested traits in the large reptile tree (LRT, 1658+ taxa), a few ankle traits fade to insignificance. Tiny details, like pegs and sockets, are ignored here. Instead this primer will start with broader, readily visible patterns of presence, absence and fusion.

Figure 1. Basal tetrapod ankles with tarsal elements identified by color.

The origin of carpals preceded the origin of tarsals.
The most primitive (but late appearing) tetrapods, like Trypanognathus, had poorly ossified tarsals and tiny limbs and digits. The most primitive appearances of tarsals in the LRT comes tentatively with Early Carboniferous Pholidogaster (Fig. 1) and completely with Early Carboniferous Greererpeton (Fig. 1). Both are more primitive in the LRT than the traditional fin-to-finger transitional Late Devonian taxa, Acanthostega and Ichthyostega, with their robust limbs and supernumerary digits. We don’t have fossils yet, but we have tracks of Middle Devonian tetrapods. Five is the primitive number of pedal digits in Pholidogaster. Four remains the primitive number of manual digits.

Remember, the first reptile,
Silvanerpeton, is from coeval Early Carboniferous strata. That means we’re missing many intervening taxa from earlier (Late Devonian) layers.

Starting with the sub-equal distal tarsals of Greererpeton
the medial distal tarsals of Gephyrostegus shrink, matching the smaller diameters of the medial metatarsals. The medial centrales also shrink. Two proximal tarsals fuse to become the astragalus and together with the new calcaneum (Pholidogaster lacks one) form the largest tarsal elements, strengthening the tarsus into a tighter, stronger set.

Note the slight rotation of the hind limb of Gephyrostegus
(Fig. 1) relative to the axis of the toes, corresponding to the increased asymmetry of the digit lengths. Distinct from the more fish-like Greererpeton, short-bodied, big-footed Gephyrostegus was able to clamber about on a myriad of landforms, stems and branches with its belly raised off the substrate (Fig. 2).

Figure 2. Gephyrostegus in anterior view demonstrating the need for shorter medial toes in tetrapods with a sprawling gait. This insures the toes to not scrape the substrate during the recovery phase and also assures that all the toes contribute to the propulsive phase.

Immediately following Silvanerpeton in the LRT
the Reptilia (=Amniota) split to form two major clades, the Archosauromorpha and the Lepidosauromorpha. At first, both were amphibian-like reptiles (laying amnion-layered eggs) with many traditional amphibians in their number here transferred to the Reptilia based on the last-common ancestor in the LRT method of classification, rather than a list of traditional skeletal traits.

Archosauromorpha step one: Gephyrostegus to Petrolacosaurus
Gephyrostegus (Fig. 3) is the proximal outgroup to the clade Reptilia. Five distal tarsals are present. 4 and 5 are larger than 1, 2 and 3. Four centrale are present. Two proximal tarsals are present, the astragalus (= tibiale) and calcaneum (= fibulae). No intermedium is present.

Petrolacosaurus (Fig. 3) is a basal diapsid. Here Two medial centrale fuse together. Another centrale fuses to the astragalus. The lateral centrale fuses to distal tarsal 4 doubling its size. Distal tarsal 5 shrinks to half. That makes pedal 5 not line up with the other four tarsals.

We’ll return to archosauromorphs below
after dealing with the lepidosauromorphs in order. But first compare the minor differences between the two major reptile clades following Gephyrostegus (Figs. 3, 4).

Figure 3. Gephyrostegus, a reptile outgroup, compared to Petrolacosaurus, a Late Carboniferous archosauromorph basal to archosauriforms and archosaurs. Compare to figure 2.

Lepidosauromorpha step one: Gephyrostegus to Nyctphruretus
Compared to Gephyrostegus, in the owenettid Nyctiphruretus (Fig. 4) two medial centrale fuse together by convergence. Two lateral centrale fuse to distal tarsal 4 tripling its size. Distal tarsal 5 enlarges. Distinct from Petrolacosaurus (Fig. 3), all five metatarsals remain aligned proximally and the hind limb becomes more aligned with the axis of the toes again.

Figure 4. Gephyrostegus compared to the basal lepidosauromorph. Note the fusion of the some centrales into distal tarsal 4.

Lepidosauromorpha step two: Nyctiphruretus to Huehuecuetzpalli
Huehuecuetzpalli (Fig. 5) is a more arboreal late-survivor in the Early Cretaceous from an Early Triassic radiation of tritosaur lepidosaurs. All distal tarsals are reduced. One and two are absent. Five is fused to metatarsal five creating a twisted ‘hook’. The last centrale is fused to the astragalus and the hind limb is strongly rotated relative to the toes.  The calcaneum is smaller and able to detach from the fibula.

Are you starting to see that bones have a history of homology? Most tarsal fusion is not at all apparent unless comparisons are made in a phylogenetic context. Of course, this affects scoring in analysis.

Figure 5. Lepidosauriform tarsals. The centrale is larger than the distal tarsal 2 in Late Permian Nyctphuretus. Huehuecuetzpalli is Early Cretaceous, so like fenestrasaurs, its ankle also evolved since the Early Triassic split to lose smaller tarsals.

Lepidosauromorpha step three: Macrocnemus to Peteinosaurus
Compared to taxa above (Fig. 5), Middle Triassic Macrocnemus (Fig. 6) loses distal tarsal 2 and retains the medial centrale.

Increasingly bipedal Langobardisaurus (Fig. 6) loses distal tarsal 1. The centrale is larger. The other tarsals are smaller.

Increasingly bipedal and sometimes flapping Cosesaurus (Fig. 6) loses distal tarsal 2. The centrale mimics distal tarsal 2. Distal tarsal 4 is not much larger than the centrale. The tibia migrates back in line with the axis of the pes.

Completely bipedal and flapping Peteinosaurus (Fig. 6) has a simple hinge ankle joint with alll four tarsal elements relatively larger and more similar in size.

Figure 6. Tritosaur lepidosaur tarsals from Peters 2000. Note how the centrale moves distally to replace or fuse with distal tarsal 1 and 2. Or is the centrale really distal tarsal 2?

Archosauromorpha step two: Petrolacosaurus to Protorosaurus
Compared to the basal archosauromorph diapsid, Petrolacosaurus (Figs. 3, 7) In Protorosaurus (Fig. 7) distal tarsal 5 fuses to metatarsal 5, as in the lepidosaur tritosaur, Huehuecuetzpalli (Fig. 5) by convergence. The astragalus moves to a more central position as the medial centrale articulates directly with the tibia in a short-lived experiment that does not continue with taxa more directly in the archosauriform lineage (Fig. 8).

Figure 7. Petrolacosaurus and Protorosaurus pedes to establish homologies.

Archosauromorpha step three: Protorosaurus to Archosauriforms
Compared to Protorosaurus (Fig. 8), the tarsals are little changed in the basal archosauriform, Proterosuchus, with the note that, as mentioned above, the centrale does not contact the tibia. The distal tarsals are sub-equal in size. The calcaneum is laterally extended, backing up the similarly extended mt5.

In Euparkeria (Fig. 8) the tarsus is similar with symmetrical and block-like proximal tarsals. The calcaneum does not back up mt 5. Pedal digit 3 longer than 4 signaling a less sprawling, more upright, form of locomotion with a simple hinge ankle joint.

In increasingly bipedal PVL 4597 (Fig. 8), basalmost archosaur, distal tarsals 1 and 2 are absent, 3 and 4 are fused. The calcaneum has a posterior process, the ‘heel’. Mt 1 is longer creating a more symmetrical pes with a simpler hinge ankle joint.

Figure 8. Archosauriform pedes compared to Protorosaurus.

Archosauromorpha step four: PVL 4597 to higher Archosauria
Compared to PVL 4597 (Fig. 9), the tarsus of the basal dinosaur Herrerasaurus (Fig. 9) is further reduced, and so is the calcaneum. The astragalus develops an anterior ascending process that also seen in Crocodylus (Fig. 9), which no longer has a simple-hinge ankle joint. Here fused distal tarsal 4/5 is thicker and the astragalus contacts mt 1, slightly rotating the tibia medially for a more sprawling configuration. Distinct from other archosaurs, mt 1 is the most robust in the set and mt 5 becomes a robust vestige in Crocodylus.

Figure 9. Archosaur tarsals compared.

Blanco, Ezcurra and Bona 2020 report, 

1. “the astragalus developed ancestrally from two ossification centres in stem archosaurs 
2. the supposed tibiale of bird embryos represents a centrale.
3. The tibiale never develops in diapsids.”

In counterpoint,

1. Figure 1 indicates the two ossification centers go back to the basal tetrapod, Greererpeton. Protorosaurus was an oddball with the centrale contacting the tibia.
2. Figure 1 indicates it is inappropriate to call the proximal tarsal in any reptile the ‘tibiale’ as the astragalus is present prior to basalmost taxa.
3. See above.

Blanco et al. report,
“The proximal tarsus of archosaurs is ancestrally composed of a medial astragalus that articulates proximally with the tibia and fibula and a lateral calcaneum that articulates proximally with the fibula.” The authors do not identify the owner of such a tarsus, but let us presume it is that oddball Protorosaurus (Figs. 7, 8).

Blanco et al. reach back to captorhinids
to suggest an outgroup to archosaurs. Unfortunately, captorhinds are basal lepidosauromorphs in the LRT. So the authors are looking where they should not be looking for progenitors.

The Blanco et al. membership list of Archosaurs is over extended.
Blanco et al. employ the invalid clades ‘Pseudosuchia‘ and ‘Avemetarsalia‘, which includes the lepidosaur pterosaurs. They also employ the lepidosaur, Macrocnemus (Fig. 6) as an archosauriform outgroup. Their Archosauromorpha include the archosauriforms, Proterosuchus and Erythrosuchus and the archosaurs Caiman, Lewisuchus and Rhea. They are not aware that the old definition of Archosauromorpha now includes synapsids when given the taxon list of the LRT.

Figure 10. Basal pterosaur and basal dinosaur pedes (feet) compared. While convergent in many respects, certain traits separate these two unrelated clades.

Pterosaurs are traditionally considered archosaurs, 
but that was shown to be invalid twenty years ago. Perhaps it would help if a basal archosaur dinosaur and a basal lepidosaur pterosaur were shown side-by-side (Fig. 10). We’ve already seen many instances of convergence in the tarsal evolution of archosauromorphs and lepidosauromorphs. This is just one more instance of the same. It is time for paleontologists to stop dragging their tails and get up to speed in this arena.

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References
Blanco MVF, Ezcurra MD and Bona P 2020. New embryological and palaeontological evidence sheds light on the evolution of the archosauromorph ankle. Nature Scientific Reports (2020)10:5150. https://doi.org/10.1038/s41598-020-62033-8
Peabody FE 1951. The origin of the astragalus of reptiles. Evolution 5(4):339–344.

Archosauromorph Misinformation in the Encyclopedia of Geology, 2nd edition

In the 2nd edition of Encyclopedia of Geology,
Ezcurra, Jones, Gentil and Butler 2020 provide their guide to:

“How to Recognize Fossils of Archosauromorpha and Archosauriformes
The earliest archosauromorph lineages (e.g., Protorosaurus speneri, early tanystropheids) have a general body plan that resembles that of large modern lizards (e.g., varanids, teiids), but they are characterized by a series of unique evolutionary novelties in their skeleton that appeared in the common ancestor of the group during the Permian.

These diagnostic anatomical features include:

1. snout representing around half or more of the skull length,
2. posterior margin of skull roof defined by a low vertical lamina, 
3. absence of a notochordal canal in the vertebral centra (with the exception of Aenigmastropheus, the earliest diverging archosauromorph), 
4. neck with at least a slightly sigmoid profile,
5. third cervical vertebra longer than the second one,
6. anterior cervical vertebrae with rib facets on the centrum,
7. last cervical and trunk vertebrae with bony buttresses (laminae) reinforcing rib articulations,
8. absence of intercentra (ossifications that lie between the vertebral centra) posterior to the second cervical vertebra,
9. very long cervical ribs extend parallel to the neck and possess an anterior process,
10. long transverse processes in trunk vertebrae,
11. humerus with low degree of torsion between the ends of the bone,
12. and absence of an ossified distal carpal 5 (small wrist bone above the lateral-most digit).

“Most of the diagnostic features that characterize the archosauromorph body plan are concentrated in the vertebral column and are related to the elevation of the head above the level of the trunk and possible reduction of the mass of the vertebrae without a loss in strength. However, the functional significance of these changes and potential paleoecological implications remain mostly unexplored.”

Figure 1.  From Ezcurra et al. 2020 with an overlay based on LRT results. The authors have not done their own testing, but are relying on popular consensus. That’s not good science.

Despite their sincere attempts, this is misinformation at its core. 

1. Due to taxon exclusion Ezcurra et al. have no idea that the validated split between Lepidosauromorpha and Archosauromorpha occurred following Silvanerpeton in the Viséan (Early Carboniferous. The authors report: “middle-late Permian” for that split.
2. No one can make a list of traits that all Archosauromorpha have in common and determine clade membership on that basis. In this respect the authors are attempting to  “Pull a Larry Martin“. You can only determine clade membership by a cladogram and look for that last common ancestor.
3. Thus the only way to recognize an archosauromorph (definition: all taxa closer to archosaurs than to lepidosaurs) is to see where a taxon nests on a wide gamut cladogram like the large reptile tree (LRT, 1655+ taxa), where mammals and their synapsids ancestors are also members of the new Archosauromorpha. 

Ezcurra et al. consider the following members of the Lepidosauromorpha
to be basal members of the Archosauromorpha.

1. Tanystropheidae. (Tanystropheus + Macrocnemus and kin) The LRT nests that clade in the Tritosauria and that clade in the Lepidosauria. Huehuecuetzpalli is in that lineage.
2. Allokotosauria (Azendohsaurus + Trilophosaurus and kin) The LRT nests that clade in between Sphenodontia (= Rhynchocephalia) and Rhynchosauria within the Lepidosauria.
3. Rhynchosauria (see above).

Ezcurra et al. consider the following clades
to be basal members of the Archosauromorpha.

1. Prolacertidae (Prolacerta and kin, but not Protorosaurus) The LRT supports this assignment.
2. Proterosuchidae (Proterosuchus and kin).The LRT supports this assignment.
3. Erythrosuchidae (Erythrosuchus and kin). The LRT supports this assignment.
4. Euparkeriidae (Euparkeria and kin). The LRT supports this assignment.
5. Proterochampsidae (Proterohampsa and kin). The LRT supports this assignment.
6. Doswelliidae (Doswellia and kin).The LRT supports this assignment except Vancleavea is a thalattosaur, an archosauromorph not related to Doswellia.

Ezcurra et al. consider the following clades
to be arguable basal members of the Archosauromorpha. Arguable? Test them! Based on their text and cladogram (Fig. 1) it is clear that Ezcurra’s team is following the authority of previous authors, not sure where some clades nest, rather than running the analysis themselves.

1. Choristodera (Champsosaurus and kin) The LRT supports this assignment.
2. Testudines (turtles, traditionally). The LRT nests this clade within the Lepidosauromorpha. Purported ancestors: Pappochelys is a sauropterygian archosauromorph in the LRT. Eunotosaurus is a lepidosauromorph not related to turtles, which arise from pareiasaurs in the LRT.
3. Sharovipterygidae (Sharovipteryx and kin). The LRT nests this clade between tanystropheids and pterosaurs in the Tritosauria in the Lepidosauria. Ozimek is a long-limbed protorosaur, not related.
4. Kuehneosauridae (Kuehneosaurus and kin. The LRT nests this clade among basalmost lepidosauriformes.
5. Phytosauria (Phytosaurus and kin). The LRT supports this assignment.

It should be noted that Ezcurra et al. consider the clade
Pterosauria to be a part of the Avemetarsalia within the Archosauria. This myth was proven wrong twenty years ago. The LRT nests pterosaurs with tanystropheids and sharovipterygids within the Tritosauria and Lepidosauria. The authors have not done their own testing, but are relying on popular consensus. That’s not good science. Now, sadly, that misinformation is set in stone in the pages of the Encyclopedia of Geology.

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References
Ezcurra MD, Jones AS, Gentil AR and Butler RJ 2020. Early Archosauromorphs: The crocodile and dinosaur precursors. Chapter in Encyclopedia of Geology, 2nd edition. Elsevier Inc. https://doi.org/10.1016/B978-0-12-409548-9.12439-X

Was Vellbergia really a juvenile basal lepidosaur? Let’s check…

Earlier we looked at tiny Vellbergia
(Sobral, Simoes and Schoch 2020; Middle Triassic) represented by a disarticulated tiny skull (Fig. 1). The large reptile tree (LRT) nested this hatchling with the much larger adult Prolacerta (Fig. 1). The MPT was 20263 steps for 1654 taxa.

The LRT nesting ran counter to the SuppData cladogram
of Sobral, Simoes and Schoch 2020, who nested Vellbergia among basal lepidosaurs, the closest of which are shown here (Fig. 1). Earlier I did not show the competing lepidosaur candidates. That was an oversight rectified today.

Figure 1. Vellbegia compared to the lepidosaurs it would nest with if Prolacerta and all Archosauromorpha were deleted. Gray areas on Vellbergia indicate restored bone that is lost in the fossil.

To test the lepidosaur hypothesis of relationships,
I deleted all Archosauromorph taxa, including Prolacerta, from the LRT to see where among the Lepidosauromorpha Vellbergia would nest. With no loss of resolution, Vellbergia nested between Palaegama and Tjubina + Huehuecuetzpalli at the base of the Tritosauria plus Fraxinisaura + Lacertulus (Fig. 1) at the base of the Protosquamata. The resulting MPT was 20276 steps, only 13 more than the Prolacerta hypothesis of interrelationships.

That is a remarkably small number considering the great phylogenetic distance between these taxa in the LRT.

Rampant convergence
is readily visible among the competing taxa (Fig. 1). No wonder Prolacerta was named “before Lacerta“, the extant squamate. According to Wikipedia, “Due to its small size and lizard-like appearance, Parrington (1935) subsequently placed Prolacerta between basal younginids and modern lizards. In the 1970s (Gow 1975) the close link between Prolacerta and crown archosaurs was first hypothesized.” That was prior to cladistic software and suffered from massive taxon exclusion.

Allometry vs. Isometry
One of the lepidosaurs shown above, Huehuecuetzpalli (Fig. 1), is known from both an adult and juvenile. The older and younger specimens were originally (Reynoso 1998) considered identical in proportion. Such isometry is an ontogenetic trait shared with other tritosaur lepidosaur clade members, including pterosaurs. On the other hand, if Vellbergia was a hatchling of Prolacerta, some measure of typical archosauromorph allometry should be readily apparent… and it is… including incomplete ossification of the nasals, frontals and parietals along with a relatively larger orbit and shorter rostrum, giving Vellbergia a traditional ‘cute’ appearance appropriate for its clade.

Size
Sobral, Simoes and Schoch considered Vellbergia a juvenile, but it is similar in size to the adult lepidosaurs shown here (Fig. 1). On the other hand, Vellbergia is appropriately smaller than Prolacerta, in line with its hatchling status.

Time
Remember also that Vellbergia is from the Middle Triassic. Prolacerta is from the Early Triassic. They were not found together and some differences are to be expected just from the millions of years separating them.

For comparison: another juvenile Prolacerta,
this time from Early Triassic Antarctica (Spiekman 2018; AMNH 9520), is much larger than Vellbergia from Middle Triassic Germany (Fig. 2), but just as cute. Note the relatively larger orbit and shorter rostrum compared to the adult Prolacerta (Fig. 1), traits likewise found in Vellbergia.

Figure 2. Small Prolacerta specimen AMNH 9520 from Spiekman 2018 compared to scale with Vellbergia. Sclerotic rings (SCL) identified by Spiekman 2018 are re-identified as pterygoids here.

Generally
crushed, disarticulated and incomplete juvenile specimens of allometric taxa are difficult to compare with adults. Even so, what is left of hatchling Vellbergia tends to resemble the larger juvenile and adult specimens of Prolacerta more than hatchling Vellbergia resembles the similarly-sized adult lepidosaurs it nests with in the absence of Prolacerta from the taxon list.

Phylogenetic analysis is an inexact science.
Nevertheless no other known method breaks down and rebuilds thousands of taxa more precisely. Only taxon exclusion appears to trip up workers at present.

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References
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Parrington FR 1935. On Prolacerta broomi gen. et sp. nov. and the origin of lizards. Annals and Magazine of Natural History 16, 197–205.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.
Sobral G, Simoes TR and Schoch RR 2020. A tiny new Middle Triassic stem-lepidosauromorph from Germany: implications fro the early evolution of lepidosauromorphs and the Vellberg fauna. Nature.com Scientific Reports 10, Article number: 2273.
Spiekman SNF 2018. A new specimen of Prolacerta broomi from the lower Fremouw Formation (Early Triassic) of Antarctica, its biogeographical implications and a taxonomic revision. Nature.com/scientificreports (2018)8:17996

wiki/Prolacerta

Kadimakara: holotype and referred specimen reconstructed as protorosaurs

Lately I found more data on Kadimakara
(Bartholomai 1979 ) than I had ever seen before (Figs 1, 2).

Figure 1. What remains of Kadimakara, above, and the referred specimen, below.

Too little data to add to the LRT,
but everyone seems to agree the prolacertiformes (protorosauria) is the clade these taxa belong to. Until further notice, I tend to agree.

Figure 2. Kadimakara holotype restored with Prolacerta, above. Referred specimen restored below.

The two taxa do not seem to be conspecific
even though no two parts overlap.

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References
Bartholomai A 1979. New lizard-like reptiles from the Early Triassic of Queensland. Alcheringa. 3 (3): 225–234.

wiki/Kadimakara_australiensis

A reexamination of Milosaurus: Brocklehurst and Fröbisch 2018

I just found out that not one but two Aerosaurus specimens were tested and are to be found in the SuppData for this paper. So, what happened here? I’ll dig deeper to look for a solution. 

Solution: The cladistic analysis in the Brocklehurst and Fröbisch 2018 Milosaurus study recovered nearly 2000 most parsimonious trees for 60 taxa. So the phylogeny is not well resolved. By contrast the LRT is well resolved. Relatively few of the characters could be scored for Milosaurus in the Brocklehurst and Fröbisch study. None overlapped with Ianthodon, the purported closest relative. By contrast the LRT found a suite of traits that were shared by Milosaurus and Aerosaurus to the exclusion of all other tested taxa. 

Brocklehurst and Fröbisch 2018 reexamine
“a large, pelycosaurian-grade synapsid” not from the Early Permian, but from the Latest Carboniferous of Illinois Milosaurus (Fig. 1) was first described by DeMar 1970 as a member of the Varanopsidae (= Varanopidae). Brocklehurst and Fröbisch note, “Milosaurus itself has received little attention since its original description. The only attempt to update its taxonomic status was by Spindler et al. (2018). These authors included Milosaurus in a phylogenetic analysis that, although principally focused on varanopids, contained a small sample of pelycosaurs from other families. Milosaurus was found nested within Ophiacodontidae, as the sister to Varanosaurus.”

Ultimately
Brocklehurst and Fröbisch nested Milosaurus with Haptodus within the Eupelycosauria.

Figure 1. The pes of Milosaurus (FMNH PR 701) in situ, reconstructed and compared to Aerosaurus, its smaller sister in the LRT. PILs added to restore distal phalanges.

By contrast
the large reptile tree nested Milosaurus with Aerosaurus (Fig. 1; Romer 1937, A. wellesi Langston and Reisz 1981), a taxon not listed by Brocklehurst and Fröbisch. Based on the pes alone, Milosaurus was twice the size of Aerosaurus. Aerosaurus is a basal synapsid more primitive than Haptodus and the Pelycosauria. Aerosaurus and Milosaurus nest between Elliotsmithia + Apsisaurus and Varanops.

Unfortunately
Brocklehurst and Fröbisch included the unrelated clade Caseasauria in their study of Synapsida, and did not include Aerosaurus. They also include Pyozia, not realizing it is a proto-diapsid derived from and distinct from varanopid synapsids. So, once again, taxon exclusion and inappropriate taxon inclusion are the reasons for this phylogenetic misfit.

Distinct from Haptodus, and similar to Aerosaurus
in Milosaurus metatarsals 2 and 3 align with p1.1, not mt1. The base of mt 5 is quite broad. Other traits also attract Milosaurus to Aerosaurus, including an unfused pubis + ilium. I was surprised that so few traits nested Milosaurus in the LRT as it continues to lump and split taxa with the current flawed list of multi-stage characters.

References
Brocklehurst N and Fröbisch J 2018. A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids. Journal of Vertebrate
Paleontology, DOI: 10.1080/02724634.2018.1508026
DeMar R. 1970. A primitive pelycosaur from the Pennsylvanian of Illinois. Journal of Paleontology 44:154–163.
Langston W Jr and Reisz RR 1981. Aerosaurus wellesi, new species, a varanopseid mammal-like reptile (Synapsida: Pelycosauria) from the Lower Permian of New Mexico. Journal of Vertebrate Paleontology 1:73–96.
Romer AS 1937. New genera and species of pelycosaurian reptiles. Proceedings of the New England Zoological Club 16:90-96.

wiki/Aerosaurus

Another cherry-deleted Professor Benton supertree

Allen et al. 2018
(includes Professor MJ Benton as a co-author) recently produced an ‘archosauromorph’ supertree (Fig. 1, click to enlarge) that (according to the LRT) includes more than two dozen lepidosaurormorphs and one thalattosaur due to improper taxon inclusion brought about by massive taxon exclusion. You might remember Hone and Benton 2007, 2009 previously had troubles building their pterosaur origin supertree because they cherry-deleted pertinent taxa _that they said they were going to test_ in order to avoid confirming the four trees recovered in Peters 2000. Allen et al. repeat that mistake by deleting those taxa again, along with deleting other well-known and pertinent taxa in their latest illogical supertree fiasco (Fig. 1 frame 1).

Figure 1. 2-frame GIF. The circle cladogram is from Allen et al. 2018. The overlay shows clades recovered by the LRT. Click to enlarge and make legible.

By contrast
the large reptile tree (LRT, 1305 taxa) is a single fully resolved cladogram that includes ancestral taxa going back to basal tetrapods. By doing so, the tree topology reveals that lepidosauromorphs split from archosauromorphs immediately following the invention of the amniote membrane. The interrelationships of all included taxa are recovered in the LRT with confidence because every candidate for sisterhood for every included enigma taxon are included in the LRT.

Unfortunately Allen et al. have a much smaller study with cherry-picked taxa
that misinform (= produce false positives) due to taxon exclusion. Allen et al. recovered 8 supertrees with no utility. They do not understand the basic Archosauromorpha / Lepidosauromorpha division within the Reptilia (= Amniota). Many of their other errors and misunderstandings appear as a result.

Odd sister taxa recovered in the Allen et al. 2018 tree include:

1. Basalmost archosauromorph: Jesairosaurus, which is basal to the lepidosauriform drepanosaurs in the LRT
2. Rhynchosaur and trilophosaur outgroup taxon: Pamelaria, a derived protorosaur in the LRT.
3. The thalattosaur Vancleavea is still not being tested with other thalattosaurs, but in Allen et al. is derived from Yarasuchus.
4. Lepidosauromorph, lepidosauriform, lepidosaur, tritosaur, fenestrasaur pterosaurs are still not being tested with other published fenestrasaurs (Cosesaurus, Sharovipteryx, etc.), but appear in the supertree derived from Vancleavea + Tarjadia + Doswellia and Proterochampsa + Cerritosaurus. This time Benton’s 1999 subject of study and former sister to pterosaurs, Scleromochlus, does not appear in the taxon list or the reference list (see what I mean about cherry-picking trees and papers?)
5. Lagerpeton nests as a sister to pterosaurs. In the LRT Lagerpeton nests with Tropidosuchus.
6. The basal bipedal crocodylomorphs, Lewisuchus and Saltopus nest with the poposaurs Silesaurus and Sacisaurus far apart from other bipedal or near bipedal crocs like Tarjadia, and on a distant branch, Litargosuchus, Hesperosuchus and Terrestrisuchus. Missing from the taxon list is a Tarjadia sister in the LRT: Erpetosuchus.
7. Other basal bipedal crocs (Hesperosuchus) leading to higher crocs (Protosuchus) are derived from Postosuchus, with a juvenile Postosuchus (CM73372) at its base. Missing from this taxon list are Trialestes, Junggarsuchus and Pseudhesperosuchus, taxa close to the origin of Dinosauria.
8. Ornithischia arises from the poposaur, Sacisaurus, outside of the Dinosauria (with Herrerasaurus and kin at its base).
9. The basal theropod, Tawa, nests far from other theropods.
10. Parasuchians are _still_ the sister clade to the pterosaur/poposaur/dinosaur clade and nest basal to Ornithosuchus and Rauisuchia + Ticinosuchus. In the LRT parasuchians arise from Elachistosuchus and Diandongosuchus taxa missing from Allen et al.
11. Aetosaurs arise from the misplaced basalmost poposaur, Turfanosuchus, the misplaced basalmost croc, Gracilisuchus, and the misplaced fugusuchid, Revueltosaurus.
12. Missing from the taxon list is Vjushkovia, the basalmost rauisuchid, and Decuriasuchus, which ties Vjushkovia to Turfanosuchus and the base of the Archosauria (crocs + dinos only in the LRT).

The Allen et al. study adds nothing but confusion to the Archosauromorpha. 
It is indeed unfortunate that the next generation of paleontologists (Benton’s co-authors, including Allen) were apparently forced to keep their blinders on in order to succeed in an academic system that ignores, rather than tests pertinent published taxa.

When one creates a cladogram,
one has the responsibility to review each node to make sure all sister taxa look similar to one another at every node. If not, add taxa until they do.

In order for Allen et al. to understand
the separation of the new Lepidosauromorpha from the new Archosauromorpha, they need to include a long list of taxa going back to the Viséan Silvanerpeton and the Westphalian Gephyrostegus, where the two branches of the Reptilia split. They can do that easily by including the LRT in their next supertree analysis.

References
Allen BJ, Stubbs TL, Benton MJ and Puttick MN 2018. Archosauromorph extinction selectivity during the Triassic-Jurassic mass extinction. Palaeontology 2108: 1–14. doi: 10.1111/pala.12399
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

Laosuchus naga enters the LRT

Updated January 30, 2019
with a new nesting of Laosuchus between Eryops and the Cochleosaurus clade, not as a chroniosuchid, as originally nested.

The question today is:
what are chroniosuchians? Are they reptiles or not? Arbez, Sidor and Steyer 2018 say: ‘not’ (Fig. 1). Here that mistake is due to tradition and taxon exclusion, based on their cherry-picked outgroups. Heretically. chroniosuchians are amphibian-like reptiles.

Figure 1. Cladogram from Arbez, Sidor and Steyer 2018 with Laosuchus nesting with chroniosuchians in the absence of Solenodonsaurus.

Arbez, Sidor and Steyer report from their abstract:
“Chroniosuchians were a clade of non-amniotic tetrapods known from the Guadalupian (middle Permian) to Late Triassic, mainly from Russia and China.” Asaphestera is the proximal outgroup followed by Limnoscelis, Seymouria, Gephyrostegus and other taxa.

By contrast and using more outgroup taxa
the large reptile tree (LRT 1391 taxa, ) nests chroniosuchians within the base of the archosauromorph branch of reptiles. When more taxa are included in the LRT, Limnoscelis and Gephyrostegus nest as reptiles (= amniotes) while Asaphestra and Seymouria nest as unrelated traditional microsaur lepospondyls and seymouriamorphs respectively.

Arbez, Sidor and Steyer 2018 introduce a new taxon,
Laosuchus naga (Fig 3), as a long-snouted chroniosuchian, but here nests with long-snouted eryopid temnospondyls. 

Figure 1. Laosuchus in dorsal and lateral views. Colors added with some difficulty here as all the bones are fused and their surfaces are ornamented.

Laosuchus naga traits include:

1. an extremely reduced pineal foramen
2. absence of palatal dentition
3. well-developed transverse flange of the pterygoid that contacts the maxilla
4. internal crest on and above the dorsal side the palate
5. otic notch closed by the tabular horn and the posterior part of the squamosal, forming a continuous wall
6. thin and high ventromedial ridge on parasphenoid.

Figure 4. Solenodonsaurus skull in situ and reconstructed. That brown bone on top of the frontal/parietal suture is a displaced lacrimal that nicely fills the gap in the reconstruction.

Something I learned while reexamining Solenodonsaurus
The displaced bone atop the skull is actually part of the broken lacrimal. The quadratojugal is displaced on the posterior mandible. The prefrontal is broken but not very displaced. The posterior jugal is broken into several pieces. Using DGS allows one to cut and paste and fit these puzzle pieces back into the missing parts of the skeleton where they belong. If they don’t fit, they don’t belong, but they never fit perfectly. It’s like putting Humpty Dumpty together again. There are always a few pieces left over.

References
Arbez T, Sidor CA and Steyer J-S 2018. Laosuchus naga gen. et sp. nov., a new chroniosuchian from South-East Asia (Laos) with internal structures revealed by micro-CT scan and discussion of its palaeobiology. Journal of Systematic Palaeontology DOI: 10.1080/14772019.2018.1504827

http://zoobank.org/urn:lsid:zoobank.org:pub:11D07FA3-0F4C-4EF9-A416-E8E6BE76C970