Perhaps Tulerpeton had only 5 fingers (and five toes)

Let’s get right to it.
Tulerpeton (Fig. 1) was originally described with six fingers. If not six fingers, where did that sixth finger come from?

The other hand.
Specifically, the tip of finger 4 from the left hand (Fig. 1) provides a suitable match.  The left hand is otherwise buried in the matrix beneath the well-exposed right hand.

Figure 1. Tulerpeton manus with digit 6 re-identified as the top of digit 4 from the other hand.

Figure 1. Tulerpeton manus with digit 6 re-identified as the top of digit 4 from the other hand. The drawing at left is the in situ presentation. The diagram at right is the traditional six-finger interpretation. The manus in the middle represents the new hypothesis of digit identity.

Tulerpeton sisters in the LRT
don’t have a digit 6. So, maybe the original description was a mistake.

Likewise, the pes of Tulerpeton
was also originally described with six digits (Fig. 2). However, a new interpretation first discussed here indicated only five toes were present. That sixth digit was created to fill a perceived space produced by broken and displaced phalanges.

Figure 1. Tulerpeton pes reconstruction options using published images of the in situ fossil.

Figure 2. Tulerpeton pes reconstruction options using published images of the in situ fossil.

References
Coates MI and Ruta M 2001 2002. Fins to limbs: What the fossils say. Evolution & Development 4(5): 390–401.
Lebedev OA 1984. The first find of a Devonian tetrapod in USSR. Doklady Akad. Navk. SSSR. 278: 1407–1413.
Lebedev OA and Clack JA 1993. Upper Devonian tetrapods from Andreyeva, Tula Region, Russia. Paleontology36: 721-734.
Lebedev OA and Coates MI 1995. postcranial skeleton of the Devonian tetrapod Tulerpeton curtum Lebedev. Zoological Journal of the Linnean Society. 114 (3): 307–348.
Mondéjar-Fernandez J, Clément G and Sanchez S 2014. New insights into the scales of the Devonian tetrapods Tulerpeton curtum Lebedeve, 1984. Journal of Vertebrate Paleontology 34:1454-1459.

wiki/Tulerpeton

 

Reptilomorpha to scale

Taxa closer to Reptilia
(e.g. Silvanerpeton) than to Lissamphibia (e.g. Rana) are considered Reptilomorpha  by definition (Säve-Söderbergh 1934). Contra tradition and paradigm (see below), in the large reptile tree (LRT, 1440 taxa) most of the following taxa (Fig. 1) are basal (non-reptle) taxa that fulfill this definition. Some outgroup taxa are also shown along with Silvanerpeton, the last common ancestor of all reptiles (= amniotes) in the LRT.

Figure 1. Members of the Reptilomorpha and their proximal outgroups illustrated to scale and in their phylogenetic order from top (primitive) to bottom (derived).

Figure 1. Members of the Reptilomorpha. starting with Caerorhachis and their proximal outgroups illustrated to scale and in their phylogenetic order from top (primitive) to bottom (derived). Not all reptilomrophs have long limbs and large feet, but these traits are generally not found in non-reptilomorphs. Frogs are important convergent exceptions.

The clade Reptilomorpha
includes all members of the clade Reptilia (= Amniota), but we’re going to focus on the stem amniotes today, basically from Caerorhachis to Gephyrostegus.

According to Wikipedia
“As the exact phylogenetic position of Lissamphibia within Tetrapoda remains uncertain, it also remains controversial which fossil tetrapods are more closely related to amniotes than to lissamphibians, and thus, which ones of them were reptiliomorphs in any meaning of the word. These include the diadectomorphsseymouriamorphs, most or all “lepospondyls”, gephyrostegids, and possibly the embolomeres and chroniosuchians. In addition, several “anthracosaur” genera of uncertain taxonomic placement would also probably qualify as reptiliomorphs, including SolenodonsaurusEldeceeonSilvanerpeton, and Casineria.”

Most of these taxa
nest within the clade Reptilia in the LRT. Taxon exclusion has been the traditional cause of this problem, something the LRT was designed to take care of with high confidence because all candidates are tested.

Origin of amniotes
Wikipedia reports, “Exactly where the border between reptile-like amphibians (non-amniote reptiliomorphs) and amniotes lies will probably never be known, as the reproductive structures involved fossilize poorly, but various small, advanced reptiliomorphs have been suggested as the first true amniotes, including SolenodonsaurusCasineria and Westlothiana.”

In the LRT, these three taxa nest well within the Reptilia.
Exactly where the last common ancestor of all living reptiles has been known for several years. Phylogenetic analysis makes this easy. Whichever taxon is the last common ancestor all living mammals, birds, lizards and crocodilians marks the border. Here in the LRT, that taxon is Silvanerpeton (Fig. 1) from the Viséan (Early Carboniferous) with an even earlier genesis because several reptile ingroup taxa are coeval in the Viséan.

Figure 1. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data.

Figure 1. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data. By this cladogram and by definition, Microsauria is a clade within Reptilomorpha. 

Not all reptilomrophs have long limbs and large feet,
but these traits are generally not found in non-reptilomorph basal tetrapods. By convergence, frogs (genus: Rana) are important exceptions. Needless to say, longer, stronger limbs are ideal for terrestrial excursions, despite the fact that some reptiles, like snakes and skinks, get along very well without them.

Earlier we talked about the lack of posterior dorsal ribs in the earliest reptiles. This provided additional space for gravid females to grow amniotic eggs prior to laying them. A deep pelvis permitted the expulsion of larger eggs. A deeper pelvis is found in Eusauropleura (Fig. 1) and more derived taxa. Platyrhinops (Fig. 1), in this regard a reptile-mimic, also had a deep pelvis and long legs by convergence.

The earliest fishapods,  
like Panderichthys and Tiktaalik had a wide flat body with dorsal ribs that were much wider than deep — less chance for tipping while walking. This wide, flat morphology is retained up to Utegenia, when the dorsal ribs start curving to enclose a deeper, narrower torso (by convergence with other taxa, like Ichthyostega. At the same time the orbits moved laterally.

Not all reptilomorphs are small,
but the earliest reptilomorphs were no larger than than the juveniles of their ancestor, Greererpeton (Fig. 1), distinct from the giant ‘amphibians’ we looked at earlier.


References
Carroll RL 1991. The origin of reptiles. Pp. 331–53 in Schultze H-P and Trueb L editors. Origins of the higher groups of tetrapods — controversy and consensus. Ithaca: Cornell University Press.
Gauthier J, Kluge AG and Rowe T 1988. The early evolution of the Amniota. In The Phylogeny and Classification of the Tetrapods: Volume 1: Amphibians, Reptiles, Birds. Edited by MJ Benton. Clarendon Press, Oxford, pp. 103–155.
Ruta M, Coates MI and Quicke DLJ 2003. Early tetrapod relationships revisited. Biological Reviews 78 (2): 251–345.
Säve-Söderbergh G 1934. Some points of view concerning the evolution of the vertebrates and the classification of this group. Arkiv för Zoologi. 26A: 1–20.

Anthracosaurus: beware the chimaera!

Figure 1. The complete skull of Anthracosaurus greatly resembles its relative, Neopteroplax.

Figure 1. The complete skull of Anthracosaurus greatly resembles its relative, Neopteroplax.

Anthracosaurus russelli (Huxley 1863, Panchen 1977, Clack 1987; Westphalian, Late Carboniferous, 310 mya, skull length 40cm; Figs. 1, 2) was originally considered a labyrinthodont. The wide, yet pointed, triangular skull and tall orbits recall traits found in labyrinthodonts, like Sclerocephalus, and in the basal tetrapod, Tiktaalik. Here, in the large reptile tree (LRT, 967 taxa),  Anthracosaurus nests with Neopteroplax (Fig. 3) as a derived embolomere, the clade that likely gave rise to Seymouriamorpha, Lepospondyli and Reptilia

At least one orbit
in Anthracosaurus has an inverted teardrop shape. The marginal and palatal fangs are quite large. Although flattened in dorsal view, comparisons suggest the jaw margin was convex, as in Neopteroplax.

Based on its size and nesting,
Anthracosaurus developed a labyrinthodont-like skull by convergence because Proterogyrinus is basal in the Embolomeri. Those giant marginal and palatal fangs indicate a predatory niche.

Figure 2. Left: Anthracosaurus chimaera from Clack 1987. Right: Older tracing in dorsal view of the complete skull and palatal view attributed to Anthracosaurus from an online photo.

Figure 2. Left: Anthracosaurus chimaera from Clack 1987. Right: Older tracing in dorsal view of the complete skull and palatal view attributed to Anthracosaurus from an online photo. The narrower skull is made of several different specimens (chimaera) and produces a loss of resolution in the LRT.

Clack 1987
illustrated a lateral and dorsal view of Anthracosaurus (Fig. 2) based on a chimaera of specimens. Unfortunately, plugging that data into the LRT produced loss of resolution over several nodes. Using the older single skull in dorsal view had no such problems.

We looked at the problems chimaera taxa produce
earlier here, and in six blogs that preceded that one.

Figure 3. Neopteroplax has a skull quite similar to the older single skull of Anthracosaurus and they nest together in the LRT.

Figure 3. Neopteroplax has a skull quite similar to the older single skull of Anthracosaurus and they nest together in the LRT.

The clade Anthracosauria has had problems
From Wikipedia: “Gauthier, Kluge and Rowe (1988) defined Anthracosauria as ‘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).”

In this definition non-amniote Anthracosauria does not include Anthracosaurus, but only Silvanerpeton and Gephyrostegus in the LRT because more basal taxa are also basal to amphibians.

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

In the LRT Diadectomorpha and Solenodonsauridae are amniotes.

“As Ruta, Coates and Quicke (2003) pointed out, this definition is problematic, because, depending on the exact phylogenetic position of Lissamphibia within Tetrapoda, using it might lead to the situation where some taxa traditionally classified as anthracosaurs, including even the genus Anthracosaurus itself, wouldn’t belong to Anthracosauria.

Indeed! And that happened in the LRT.

Laurin (2001) created a different phylogenetic definition of Anthracosauria, defining it as “the largest clade that includes Anthracosaurus russelli but not Ascaphus truei”.

In the LRT Ascaphus, the tailed frog, is derived from the large clade, the embolomeri, that includes Anthracosaurus. However the small clade that includes just Anthracosaurus and Neopteroplax does not include the tailed frog.

“However, 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.”

In the LRT the Embolomeri are basal to Eucritta and the Seymouriamorpha, which are basal to the Reptilia (= Amniota) and Lepospondyli (including Amphibia). The Chroniosuchia and Gephyrostegus are both amphibian-like reptiles in the LRT.

The clade Reptilomorpha suffers the same definition problems.
As Wikipedia reported, “As the exact phylogenetic position of Lissamphibia within Tetrapoda remains uncertain, it also remains controversial which fossil tetrapods are more closely related to amniotes than to lissamphibians, and thus, which ones of them were reptiliomorphs in any meaning of the word.”

Wouldn’t it be great if someone could put together
a large gamut phylogenetic analysis that could settle all those controversial issues?

References
Clack JA 1987. Two new speciemens of Anthracosaurus (Amphibia: Anthracosauria) from the Northumberland coal measures. Palaeontology 30(1):15-26.
Huxley TH 1863. Description of Anthracosaurus russelli, a new labyrinthodont from the Lanarkshire coalfield. Quartery Journal of the Geological Society 19:56-58.
Panchen AL 1975. A new genus and species of anthracosaur amphibian from the Lower Carboniferous of Scotland and the status of Pholidogaster pisciformis Huxley. Philosophical Transactions of the Royal Society of London, B. 269: 581-640.
Panchen AL 1977. On Anthracosaurus russelli Huxley (Amphibia: Labyrinthodontia) and the family Anthracosauridae. Philosophical Transactions of the Royal Society B. 279 (968): 447–512.