Metoposaurus gets one more finger

Konietko-Meier et al. 2020 discover digit 5
where they did not expect to find one, on Metoposaurus (Figs. 1-3).

Figure 4. Ozimek hitching a ride on top of Metoposaurus.

Figure 1. Ozimek hitching a ride on top of Metoposaurus. Note the relatively large manus and pes here compared to figure 2.

We’ve long wondered, how many fingers did the first tetrapod have? 
If more than five, when did four or five come to be?
If five, when did four or more than five come to be?
If four, when did five or more than five come to be?

Figure 3. Metoposaurus in several views.

Figure 2. Metoposaurus in several views. Smaller hands and feet on this data lacking digit 5.

From the Konietko-Meier et al. 2020 introduction:
“In contrast to crown tetrapods that rarely have more than five digits, basal tetrapod groups possessed more digits, such as Acanthostega gunnari Jarvik, 1952 which had eight in the forelimb (Coates and Clack, 1990) and Ichthyostega Säve-Söderbergh, 1932 with seven digits in the hindlimb (Säve-Söderbergh, 1932; Jarvik,1996). This fact indicates that polydactyly is the plesiomorphic condition for the tetrapod autopodium (Laurin et al., 2000).”

No. That’s a myth. The large reptile tree (LRT, 1713+ taxa; subset Fig. 4) recovered four fingers in basal tetrapods. Five fingers are derived in several convergent clades. More than five fingers occurs only in Acanthostega and kin, a derived clade without descendants. (Maybe Ichthyostega, too, but we have no hands for it).

Figure 2. Metoposaurus manus with five digits from Konietko-Meier et al. 2020. Colors and PILs added here.

Figure 3. Metoposaurus manus with five digits from Konietko-Meier et al. 2020. Colors and PILs added here. Note the foreshortening of the distal phalanges somewhat corrected here and in diagram at right. Not sure why p5.1 is so long in the diagram.

From the Konietko-Meier et al. 2020 abstract:
“Temnospondyli are commonly believed to have possessed four digits in the manus
and five in the pes. However, actual finds of articulated autopodia are extremely rare. The most important observation is the presence of five metacarpals in this specimen. This allows reconstructing the manus as pentadactyl.”

Figure 4. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

Figure 4. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

From the Konietko-Meier et al. introduction:
“The first known record of a pentadactyl hand belongs to the Early Carboniferous stegocephalian Casineria kiddi (Paton et al., 1999).”

Chronology does not always mirror phylogeny. Casineria nests as an archosauromorph reptile, off the bottom of the chart (Fig. 4). Many more primitive taxa had only five digits. The Late Devonian reptilomorph, Tulerpeton, had only five fingers, as we learned earlier.

Among temnospondyls in the LRT
(Fig. 4) the derived taxa leaving no descendants, Parotosuchus and Paracyclotosaurus, were illustrated with five fingers. Trematosaurus is known from skull material only. These fifth fingers are appearing de novo, not as reversals.

Proterogyrinus
developed five fingers. Fingers are not preserved in related taxa, none of which left descendants.

Dissorophids
developed five fingers without leaving descendants.

Reptilomorpha,
starting with Utegenia + Seymouriamorpha, developed five fingers and we are their descendants.

The Konietko-Meier et al. chart
(their Fig. 4) indicates the outgroup taxon, Greererpeton (Fig. 5; Godfrey 1986, 1989 had five fingers.

This is an error. Only the PhD thesis illustrates fingers and only four are illustrated (Fig. 5). Maybe the five-digit pes was accidentally added to the manus database?

Figure 5. Data for Greererpeton from Godfrey 1986.

Figure 5. Data for Greererpeton from Godfrey 1986. Only the pes has five digits.

From the Konietko-Meier et al. introduction:
“Reconstruction of the evolution of digit reduction of the most basal and post-Devonian stegocephalians is not possible because of the lack of informative fossils. It is known that reductions in the number of digits have occurred frequently during tetrapod evolution, but it is still not known exactly when or even how many times the number of digits was reduced to five or less (Laurin et al., 2000).”

The LRT clarifies this problem. Reductions in the number of digits occurred less frequently than envisioned by Konietko-Meier et al. since ‘four fingers’ is the primitive and plesiomorphic condition, even in Greererpeton.


References
Godfrey SJ 1989. The postcranial skeletal anatomy of the Carboniferous tetrapod Greererpeton burkemorani Romer, 1969. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 323(1213), 75–133.
Konietzko-Meier D, Teschner EM, Bodzioch A and Sander PM 2020. Pentadactyl manus of the Metoposaurus krasiejowensis from the Late Triassic of Poland, the first record of pentadactyly among Temnospondyli. Journal of Anatomy 00:1–11. DOI: 10.1111/joa.13276

The largest amphibians of all time

Yesterday we looked at Siderops, a big plagiosaur and peeked at Koolasuchus, a giant plagiosaur. That makes today a good today to review the largest amphibians of all time (Fig. 1, click to enlarge).

Figure 1. Click to enlarge. The largest amphibians of all time include Mastodonsaurus, Prionosuchus, Koolasuchus, Siderops, Crassigyrinus and the extant Andrias, the giant Chinese salamander.

Figure 1. The cover of Giants, the book that launched my adult interest in dinosaurs, pterosaurs and everything inbetween.

Figure 2. The cover of Giants, the book that launched my adult interest in dinosaurs, pterosaurs and everything inbetween.

Back in 1989
and eager to locate the largest amphibian of all time, I added Prionosuchus (Fig. 1) to the popular natural history book, “Giants of Land, Sea and Air – Past and Present” (Fig. 2). Since the largest Prionosuchus is only known from fragments and slivers, much had to be restored using phylogenetic bracketing.

Now
Mastodonsaurus is probably just as long, but much bulkier, making it the largest amphibian of all time. It was the size of a Hippopotamus (Fig. 3).

The largest living amphibian is Andrias, the Chinese salamander.

Mastodonsaurus jaegeri (Jaeger 1828; Schoch 1999; Middle Triassic; skull length 1.2m; overall length 6m) is the largest lepospondyl in the LRT. Traditionally it was considered a temnospondyl, but if so that would make all amniotes temnospondyls, too, which was not the intention of the definition. Anterior dentary tusks fit through new skull openings (in red above) anterior to the nares. Intercostal plates overlapped succeeding ribs. Mastodonsaurusinhabited swampy ponds.

Andrias davidianus (Blanchard 1871; 1.8m in length; extant) the Chinese giant salamander, is a sister to Rana, the bullfrog and derived from a sister to Gerobatrachus.

Figure 1. Living hippopotamus. Now I ask you, does this look like a relative to deer and giraffes? Or to mesonychids?

Figure 3. Living hippopotamus, an amphibious mammal related to Mesonyx.

References
Blanchard É 1871.Note sur une nouvelle Salamandre gigantesque (Sieboldia Davidiana Blanch.) de la Chine occidentale. Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences. Paris 73: 79.
Jaeger GF 1828. 
Über die fossile Reptilien, welche in Württemberg aufgefunden worden sind. 48 pp., 6 pls.; Stuttgart (Metzler).
Schoch RR 1999. 
Comparative osteology of Mastodonsaurus giganteus (Jaeger, 1828) from the Middle Triassic (Lettenkeuper: Longobardian) of Germany (Baden-Württemberg, Bayern, Thüringen). Stuttgarter Beiträge zur Naturkunde Serie B. 278: 1–175. PDF

wiki/Mastodonsaurus
wiki/Andrias

Cochleosaurus joins the LRT

Updated January 30, 2019
with a new nesting for Cochleosaurus.

This examination of Cochleosaurus
was undertaken when this taxon appeared in the cladogram of Arbez, Sidor and Steyer 2018 in their study of the basal tetrapod, Laosuchus. In order to understand their work better, I added all their taxa to the LRT.

igure 1. Cochleosaurus in situ and restored by Rieppel 1980 and Godfrey and Holmes 1995. Here the septomaxilla is reidentified as the lacrimal and the lacrimal is the palatine exposed on the surface as in all sister taxa of its clade.

Figure 1. Cochleosaurus in situ and restored by Rieppel 1980 and Godfrey and Holmes 1995. Here the septomaxilla is reidentified as the lacrimal and the lacrimal is the palatine exposed on the surface as in all sister taxa of its clade.

Cochleosaurus bohemicus (Fritsch 1885; C. forensis Rieppel 1980; Moscovian, Late Carboniferous; 310 mya; 1.2-1.6m) was named for the spoon-like processes at the back of the skull. Traditionally considered a temnospondyl (a clade not recovered by the large reptile tree (1391 taxa), here it nests with Nigerpeton (Fig. 2), Saharastega and Chenoprosopus, taxa that share a high lateral naris, among other traits.

Figure 2. Nigerpeton nests with its contemporary, Saharastega (figure 1) and has dorsal nares and a concave rostrum.

Figure 2. Nigerpeton nests with its contemporary, Saharastega (figure 1) and has dorsal nares and a concave rostrum.

References
Fritsch A. 1885. Fauna der Gaskohle und der Kalksteine der Permformation Bohmens. vol. 2, Prague, 107 pp.
Godfrey SJ and Holmes R 1995. The Pennsylvanian temnospondyl Cochleosaurus florensisRieppel, from the lycopid stump fauna at Florence, Nova Scotia. Breviora 500:1–25.
Rieppel O. 1980. The edopoid amphibian Cochleosaurus from the Middle Pennsylvanian of Nova Scotia. Palaeontology 23(1):143–149.

wiki/Cochleosaurus

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 xx 2018 with Laosuchus nesting with chroniosuchians in the absence of Solenodonsaurus.

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.

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.

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

 

Koilops: a new sister for Greerepeton

Updated March 15, 2019 and March 20, 2020
with a new interpretation of the skull sutures of the stem tetrapod Tiktaalik. Now, with the addition of more closely related taxa, Koilops is a finned fish that nests basal to Elpistostege,  Spathicephalus and Tiktaalik off the main lineage of the fin to finger transition.

Figure 2. Koilops is a flat-headed sister to Spathicephalus, but with teeth, larger orbits and a shorter snout

Figure 2. Koilops is a flat-headed sister to Spathicephalus, but with teeth, larger orbits and a shorter snout

Koilops herma (Clack et al. 2016; NMS G. 2013.39/14) Tournasian, early Carboniferous ~375 mya) is a temnospondyl with a flat skull and large orbits nesting between Greererpeton and Spathicephalus. The nares were close to the rim of the short rorstrum. The pineal foramen was enormous. The teeth were small and sharp. The nasals were broad.


References
Clack et al. (14 other authors) 2016. Phylogenetic and environmental context of a Tournaisian tetrapod fauna. Nature ecology & evolution 1(0002):1-11.

Marjanovic and Laurin 2016: Basal tetrapods, continued…

Sorry this took so long…
As you’ll see there was a lot of work and prep involved that has been several weeks in the making. Thank you for your patience.

Earlier I introduced the Marjanovic and Laurin 2016 study
the way they did, by reporting their confirmation of the Ruta and Coats 2007 basal tetrapod topology that they were testing prior to reevaluating the data. I noted then that both studies (Fig. 5) included many so-called pre-reptiles, including  Bruktererpeton, Chroniosaurus, Solenodonsaurus, Limnoscelis, Tseajaia, DiadectesOrobates and Westlothiana,should not be in the pre-amniote inclusion set. Those taxa nest within the Reptilia in the large reptile tree (LRT, subset Fig. 4) with Silvanerpeton and Gephyrostegus at the base of the Reptilia (= Amniota). As reported earlier, those two are the amphibian-like reptiles that first developed the amniotic egg that defines the clade Amniota, a junior synonym of the Reptilia, based on the tree that recovers them at the base of both major branches, the new Archosauromorpha and the new Lepidosauromorpha early in the Viséan.

How can one readily compare two competing cladograms? 
You would not want to sit through a comparison of tens of thousands of scores for competing trees in a short blog like this. But we can compare images of taxa (Figs. 1–3. 6–8) placed in their phylogenetic order, subdivided for clarity into the three major lineages of basal tetrapods:

  1. Basalmost tetrapods and the lineage that led to Reptilia
  2. Members of the Lepospondyli
  3. Members of the Microsauria

These images will serve as a ready reference for today’s topics. As a preview, in summary:

The Marjanovic and Laurin (ML) 2016 tree nests

  1. frogs like Rana and salamanders like Andrias with microsaurs.
  2. small amphibamids, Cacops and Micromelerpeton nest with temnospondyls.
  3. basal Amniota splits into Synapsida (Caseasauria + Archaeovenator) and Sauropsida (Captorhinus, Paleothyris, Petrolacaosaurus) arising from an unknown genus basal to Diadectomorpha + Amniota
  4. The clade Amphibia arises near Solenodonsaurus + the crown-group Tetrapoda
  5. The clade Microsauria is divided into three parts separated by non-microsaurs with origins near Westlothiana.

The LRT nests

  1. frogs and salamanders nest with lepospondyls.
  2. small amphibamids, Cacops and Micromelerpeton nest with lepospondyls.
  3. basal Amniota splits into Archosauromorpha  (several basal taxa, Archaeovenator, Paleothyris and Petrolacaosaurus) and Lepiodosauromorpha (several basal taxa, Caseasauria and Captorhinus) with both major clades arising from Gephyrostegus bohemicus a late-surving Westphalian taxon, and Silvanerpeton, a Viséan taxon.
  4. The clade Amphibia arises near Balanerpeton and the amphibamids.
  5. The clade Microsauria has a single origin near Kirktonecta 

What you should be looking for
is a gradual accumulation of traits in every lineage. And look for taxa that don’t fit in the order presented. This can be done visually with these figures, combining hundreds of traits into one small package. Rest assured that all scoring by ML and the competing analysis in the LRT were done with the utmost care and diligence. So, some biased or errant scoring must have taken place in one study or the other or both for the topologies to differ so great. Bear in mind that ML had firsthand access to fossils and may have bowed to academic tradition, while I had photos and figures to work with and no allegiance to academic tradition.

First
the large reptile tree (LRT) taxa (Figs. 1–3) had two separate origins for limbed vertebrates.

Figure 1. CLICK TO ENLARGE. Basal tetrapod subset according to the LRT. These taxa lead to Reptilia, Lepospondyli and through that clade, the Microsauria. Note the convergent development of limbs and digits arising out of Osteolepis.

Figure 1. CLICK TO ENLARGE. Basal tetrapod subset according to the LRT. These taxa lead to Reptilia, Lepospondyli and through that clade, the Microsauria. Note the convergent development of limbs and digits arising out of Osteolepis.

In both studies
basal tetrapod outgroups are tail-propelled sarcopterygians having muscular fins not yet evolved into limbs with digits. Behind the skull are opercular bones that are lost in taxa with limbs. An exoskeleton of bony scales disappears in taxa with limbs. Snout to tail tip length averages 50 cm.

In the LRT
locomotion switches to the limbs in temnospondyls, which tend to be larger (1m+ and have overlapping dorsal ribs. The Greererpeton branch flattens out the ribs and skull, reducing both the tail and the limbs to likely become sit-and-wait predators. Phylogenetic size reduction and limb elongation is the trend that leads to Reptilia (Gephyrostegus). However an early exception, Crassigyrinus (Fig. 1), elongates the torso and reduces the limbs to adopt an eel-like lifestyle. Kotlassia adopts a salamander-like lifestyle from which Utegenia and the Lepospondyli arise (Fig. 2) alongside Reptilia.

Figure 2. CLICK TO ENLARGE. Subset of the LRT representing lepospondyli leading to frogs.

Figure 2. CLICK TO ENLARGE. Subset of the LRT representing lepospondyli leading to frogs.

In the LRT,
short-tailed, salamander-like Utegenia (derived from the Seymouriamorpha, Fig. 2) is a late-surving basal member of the generally small-sized clade Lepospondyli, which ultimately produces salamanders and frogs. A side branch produces the larger, temnospondyl-like Cacops, which develops a bony ridge atop the dorsal spines. Note the nesting here of Gerobatrachus as a salamander and frog relative, distinct from the ML tree (Fig. 6).

Figure 3. CLICK TO ENLARGE. Subset of the LRT focusing on Microsauria.

Figure 3. CLICK TO ENLARGE. Subset of the LRT focusing on Microsauria.

In the LRT
the Microsauria are derived here from the small basal amphibamids, Caerorhachis and more proximally, Kirktonecta. Microsaurs range from salamander-like to lizard-like to worm-like. The tail elongates to become the organ of locomotion in the Ptyonius clade. The head and torso flatten in the Eoserpeton clade.

Below
is the pertinent subset of the LRT (Fig. 4) with a representative, but not complete or exhaustive set of taxa. A summary of the tree’s differences with the ML tree is presented above. The ML tree is summarized below in three parts (6-8).

Figure 4. Subset of the LRT focusing on basal tetrapods.

Figure 4. Subset of the LRT focusing on basal tetrapods.

The Marjanovic and Laurin 2016 tree
(Fig. 5) presents a topology that is similar to the LRT in parts, but distinct in other parts, as summarized above. I realize this presentation is illegible at this column size due to the large number of taxa. Click on it to enlarge it. At the top and down the right column are basal taxa leading to temnspondyls and reptiles at bottom right. Working from the bottom up the left side are the microsaurs ending with the lissamphibians (frogs and salamanders) at the top/middle of the left column.

Figure 4. CLICK TO ENLARGE. The reevaluated Marjanovic and Laurin tree from which taxa on hand were set to match the tree topology (Figs. 5-7).

Figure 5. CLICK TO ENLARGE. The reevaluated Marjanovic and Laurin tree from which taxa on hand were set to match the tree topology (Figs. 5-7).

The ML tree
subdivides into there parts (Figs 6-8): basal taxa, some leading to temnospondyls and amphibamids; taxa leading to and including Amniota; and finally microsaurs leading to and including extant amphibians.

Figure 5. Basal tetrapods according to Marjanovic and Laurin 2016. Figures 6 and 7 lead to Amniota and Microsauria respectively.

Figure 6. Basal tetrapods according to Marjanovic and Laurin 2016. Figures 6 and 7 lead to Amniota and Microsauria respectively.

In the ML topology,
Ichthyostega, a taxon with a very large pectoral girdle, ribs, and pelvis, gives rise the the altogether smaller and more fish-like Acanthostega, which gives rise to members of the Whatcheeridae, tall-skulled Crassigyrinus and flat-skulled Osinodus. The traditional Colosteidae arise next. They have a variety of long shapes with short-legs. Oddly from this seemingly primitive clade arises small, short-torsoed, long-legged Eucritta followed by long torsoed, short-legged Proterogyrinus followed by a large clade of short-torsoed, long-legged taxa, including the >1m temnospondyls and the <30cm amphibamids.

Figure 7. CLICK TO ENLARGE. These are taxa listed on the Marjanovic and Laurin 2016 that lead to Reptilia (Amniota).

Figure 7. CLICK TO ENLARGE. These are taxa listed on the Marjanovic and Laurin 2016 that lead to Reptilia (Amniota).

In the ML tree
Gephyrostegus arises from the small temnospondyl, Balanerpeton, and and gives rise to Chroniosaurus, Solenodonsaurus, the Seymouriamorpha (including Utegenia) and the Diadectomorpha, nesting as the sister clade to the Amniota. Thus, no phylogenetic miniaturization was present at the origin of the Amniota in the ML tree. Moreover, dozens of taxa were not included here that nest at the base of the Amniota (Reptilia) in the LRT.  Basal amniotes in the ML tree are all Latest Carboniferous to Early Permian, while in the LRT basal amniotes arrived at least 40 million years earlier in the Visean (Early Carboniferous) and had radiated widely by the Late Carboniferous, as shown by the ML taxaon list. No amphibian-like reptiles made it to their Amniota.

FIgure 7. Microsauria according to Marjanovic and Laurin 2016. Here frogs and caecilians nest within the Microsauria.

FIgure 8. CLICK TO ENLARGE. Microsauria according to Marjanovic and Laurin 2016. Here frogs and caecilians nest within the Microsauria.

In the ML tree
the three microsaur clades (Fig. 5) arise from the Viséan taxon, Westlothiana (Fig. 8), which nests as a derived reptile when tested against more amniotes in the LRT. Utaherpeton is a basal microsaur in both trees, but it gives rise to the eel-like Acherontiscus and kin in the ML tree. Westlothiana further gives rise to Scincosaurus and kin, including the larger Diplocaulus. Thirdly, Westlothiana gives rise to lizard-like Tuditanus which gives rise to big-skulled Pantylus and tiny-limbed Microbrachis, shark-nosed Micraroter and Rhynchonkos. In both trees, Batropetes bucks the long-body, short-leg trend. In both trees Celtedens, representing the salamander-like albanerpetontids, gives rise to extant salamanders and frogs

So the possibilities are:

  1. Only one tree is completely correct
  2. Only one tree is mostly correct.
  3. Both trees have some correct and incorrect relationships

Problems

  1. Basal tetrapods tend to converge on several traits. For instance in the LRT, the palate is ‘open’ with narrow pterygoids in both temnospondyls and lepospondyls.
  2. Many small derived taxa lose and fuse skull bones
  3. Many taxa fuse vertebral bones as they evolve away from the notochord-based semi-encircling vertebrae of fish toward more complete vertebrae in which the neural spine, pleurocentrum and intercentrum tend to fuse, sometimes in convergent pattern, as widely recognized in basal reptiles and microsaurs.
  4. In basal tetrapods, fingers are not often preserved. So when four fingers appear their identity has to be ascertained. In the LRT mc5 and digit 5 are absent in Lepospondyls. In the LRT mc1 and digit 1 are absent in the temnospondyls. Five fingers and/or metacarpals are preserved in the few other non-amniote, basal tetrapods that preserve fingers (Proterogyrinus, Seymouria). The ML tree assumes that when four digits are present, they represent digits 1–4.

Ultimately
maximum parsimony and Occam’s Razor should rule unless strong evidence to the contrary is provided. After evidence is presented, it’s up to colleagues to accept or reject or ignore hypotheses.

References
Marjanovic D and Laurin M 2016. Reevaluation of the largest published morphological data matrix for phylogenetic analysis of Paleozoic limbed vertebrates. PeerJ. Not peer-reviewed. 356 pp.
Ruta M and Coates MI 2007
. Dates, nodes and character conflict: addressing the lissamphibian origin problem. Journal of Systematic Palaeontology 5-69-122.

Basal tetrapod cladogram: Marjanovic and Laurin 2016, PeerJ

Recently I added
several basal tetrapod taxa to the large reptile tree (LRT, now 950 taxa) in order to better understand the origin of the clade Reptilia (= Amnlota). Along the way, the software recovered some contra-traditional nestings which revived typically cordial correspondences with Drs. David Marjanovic and Jason Pardo, both of whom have studied basal tetrapods extensively. I don’t have all of the latest literature and I appreciate that these researchers open doors I may not have seen.

Less recently
Marjanovic and Laurin (2016) reexamined a earlier report on lissamphibian origins by Ruta and Coates (2007). Marjanovic and Laurin (ML) report “thousands of suboptimal scores due to typographic and similar errors and to questionable coding decisions: logically linked (redundant) characters, others with only one described state, even characters for which most taxa were scored after presumed relatives. Even continuous characters were unordered, the effects of ontogeny were not sufficiently taken into account, and data published after 2001 were mostly excluded.”

Figure 1. Click to enlarge. Wait 10 seconds for animation to begin. Basal tetrapod tree form Marjanovic and Laurin 2016.

Figure 1. Basal tetrapod tree form Marjanovic and Laurin 2016. After 10 seconds those moving lines that appear on the right will make sense when you CLICK TO ENLARGE and see how they connect taxa on competing trees.

ML document and justify all changes
to the earlier matrix, then add 48 taxa to the original 102. They report,  “From the late19th century to now, the modern amphibians have been considered temnospondyls by some (refs omitted), lepospondyls by others and polyphyletic yet others, with Salientia being nested among the temnospondyls, Gymnophionomorpha among the lepospondyls, and Caudata either in the lepospondyls (all early works) or in the temnospondyls (works published in the 21st century).”

“The present work cannot pretend to solve the question of lissamphibian origins or any other of the controversies in the phylogeny of early limbed vertebrates (of which there are many, as we will discuss). It merely tries to test, and explain within the limitations of the dataset, to what degree the trees found by RC07 still follow from their matrix – the largest published one that has been applied to those questions – after a thorough effort to improve the accuracy of the scoring and reduce character redundancy has been carried out to the best of our current knowledge. However, we think this effort forms a necessary step towards solving any of those problems. Further progress may come from larger matrices…”

“Our matrix has only 276 characters, a strong decrease from the 339 of RC07. For the most part, this is due to our mergers of redundant characters and does not entail a loss of information.”

After all that work and all those changes and additions,
ML report their repaired tree “topology is identical to Ruta and Coates 2007.”

Unfortunately that tree is vastly different
from the one recovered in the LRT, which has far fewer taxa, but an equal or greater gamut. Let’s figure out why the topologies differ and are similar. I’ll start slow with the similarities and the metaphorical ‘low-hanging fruit.’ The difficult topics we will handle later. I took the last few weeks (far too little time) to better understand basal tetrapods having zero knowledge of most taxa before starting. I have not been able to cover all the taxa employed by the ML tree.

Similarities:

  1. Both trees include fish and fish-like tetrapods at the base
  2. Both trees include microsaurs, reptiles and extant amphibians as derived taxa
  3. Both trees agree on the inclusion set for microsaurs and holospondyls
Figure 6. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.Figure 6. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.

Figure 2. Subset of the large reptile tree focusing on basal tetrapods, updated with Gerrothorax.

Differences:

Due to taxon exclusion,
the ML tree nests several reptiles as non-reptiles. These include:

  1. Sivanerpeton – basal reptile/amniote
  2. Gephyrostegus (bohemicus) –  basal reptile/amniote
  3. Bruktererpeton – Lepidosauromorpha
  4. Solenodonsaurus (+ Chroniosaurus, Chroniosuchus) – Archosauromorpha
  5. Tseajaia – Lepidosauromorpha
  6. Limnoscelis – Lepidosauromorpha
  7. Orobates – Lepidosauromorpha
  8. Diadectes – Lepidosauromorpha
  9. Westlothiana – Archosauromorpha

Where each taxon nests in the LRT follows each dash.

Due to taxon exclusion,
the ML tree nests several taxa as ‘Sauropsida’ a clade that no longer has utility based on the new basal reptile dichotomy Archosauromorpha and Lepidosauromorpha. These include:

  1. Captorhinus – Lepidosauromorpha
  2. Paleothyris/Protorothyris – two distinct Archosauromorpha
  3. Petrolacosaurus – Archosauromorpha

Chroniosuchia
ML report, “Chroniosaurus has a fully resolved position one node more crown ward than Gephyrostegidae, Bruktererpeton or Temnospondyli and one node more rootward than Solenodonsaurus.”  This is a similar nesting to the LRT except that all listed taxa other than Temnospondyli nest within the Reptilia. ML are missing several taxa that would have changed their tree topology (see the LRT for that list).

 

Microbrachis
I caught a little heat for not using the latest drawings of Microbrachis earlier. The new tracings (Fig. 3) come from Vallin and Laurin 2004. Note the tracings of the in situ specimen (color) do precisely match the freehand reconstruction they offered. All scoring changes further cemented prior LRT relationships.

Figure 3. Microbrachis images from Vallin and Laurin 2008. Color added here.

Figure 3. Microbrachis images from Vallin and Laurin 2004. Color added here.

More later.

References
Marjanovic D and Laurin M 2016. Reevaluation of the largest published morphological data matrix for phylogenetic analysis of Paleozoic limbed vertebrates. PeerJ. Not peer-reviewed. 356 pp.
Ruta M and Coates MI 2007
. Dates, nodes and character conflict: addressing the lissamphibian origin problem. Journal of Systematic Palaeontology 5-69-122.
Vallin G and Laurin M 2004. Cranial morphology and affinities of Microbrachis, and a reappraisal of the phylogeny and lifestyle of the first amphibians. Journal of Vertebrate Paleontology: Vol. 24 (1): 56-72 online pdf

wiki/Microbrachis

 

An ‘amphibian’ with an antorbital fenestra

Surprised to find this: 
Acheloma (Cope 1882; Dilkes and Reisz 1987; Early Permian, 275 mya; aka Trematops), a trematopsid amphibamid lepospondyl basal tetrapod had a confluent antorbital fenestra and naris. Bolt 1974 considered this a “very elongate external naris” and then considered two hypotheses for its origin and use:

  1. as a nasal salt gland (rather improbable, but still possible, according to Bolt)
  2. to transfer of forces away from the antorbital bar (Bolt’s preferred hypothesis)

Bolt also noted
that earlier papers referred this morphology to a confluent antorbital vacuity, but dismissed the notion by saying, “There is no evidence that any labyrinthodont, including the ancestors of trematopsids, possessed such an [completely separate] antorbital vacuity.” IMHO, this convergent trait need not have been completely separate to qualify as an antorbital vacuity/fenestra. As Bolt noted, in nearly every case, there is a slight constriction in this vacuity marking the end of the naris and the beginning of the antorbital vacuity (Fig. 1).  A nasal flange descends inside the vacuity.

Earlier
we looked at the antorbital fenestra in other tetrapods here.

Figure 1. Acheloma dunni skull with a confluent antorbital fenestra and naris.

Figure 1. Acheloma dunni skull with a confluent antorbital fenestra and naris. Scale bar = 5 cm.

Perhaps of interest to this discussion
is the relatively large diameter palatal teeth on the vomers, palatines and ectopterygoids (Fig. 1). Bolt also found evidence for a nasal flange in related Doleserpeton and Tersomius, but not in unrelated Seymouria and Eryops.

Olson 1941 had this odd explanation:
The anterior part was for smelling, the longer posterior part was for respiration and the reason for this was the internal naris lies beneath only the posterior part. Bolt noted the shortest route was not always the only route in tetrapods. Air passages can be quite complicated.

The odd otic notch
that likely housed an eardrum in related taxa, is long and narrow in Acheloma. Dilkes and Reisz (1987) noted, “The shape of the otic notch, however, argues against an impedence-matching hearing system because the vibrational properties of the postulated tympanum would be profoundly different from one with the same surface area but circular in outline.”

Acheloma cumminsi was originally considered a temnospondyl, but here nests between Dendrerpeton and Cacops within the lepospondyls with many traits convergent with temnospondyls, like that large wide skull and large overall size. The related Acheloma dunni (Fig. 1) had giant palatal teeth.

As promised earlier:
lepospondyl traits of Acheloma and Cacops not present in temnospondyls from the character list of the LRT. Let me know if you see errors here:

  1. Ventral naris chiefly maxilla in lateral view
  2. Prefrontal separate from postfrontal
  3. Preorbital length of skull sub-equal to postorbital length of skull
  4. Naris shape in lateral view < 2x longer than tall
  5. Palatine exposure on the external skull below orbit.
  6. Squamosal posterior rim is a ‘big curve’
  7. Squamosal descends to ventral skull
  8. Mandible tip straight, does not rise
  9. Cervical centrum longer than tall
  10. Cervical neural spines not taller than centra
  11. Pleurocentra larger than intercentra
  12. Two sacral vertebrae
  13. Sacral spines not > acetabulum depth
  14. Anterior chevron shapes, not wider proximally
  15. Anterior caudal neural spines not higher than centra
  16. Clavicle shorter than scapula
  17. Humerus not ‘L’-shaped
  18. Manual metacarpals 1-3 align
  19. Longest metacarpals: 2, 3 and sometimes 4
  20. Longest manual digit: three and four
  21. Manual unguals sharp pointed
  22. Metacarpal 5 absent – except in Cacops. Acheloma has 5 carpals.
  23. Posterior ilium not longer than anterior ilium
  24. Pubic apron wide
  25. Longest metatarsals: 3 and 4
  26. Pedal 3.1 not > p2.1
  27. Overall size not > 60 cm in length

Shifting
Acheloma, Broilleus and Cacops to Eryops adds 24 steps at present. Shifting those three + Dendrepeton and Tersomius adds 17 steps at present. Shfting those five + the three members of the Amphibamus clade adds 35 steps at present.

On a side note:

Having a fifth finger on basal tetrapods (no matter how you count them, 1-4 or 2-5) is rare after Acanthostega partly because a complete manus is rare in basal tetrapods and partly because many taxa have only four fingers. Proterogyrinus, Seymouria, Cacops and basal reptiles all have five fingers preserved. Presently that’s a discontinuous list, but those five fingers could be homologous. If you know of any other related examples, let me know. I need that data.

References
Bolt JR 1974. Osteology, function, and evolution of the trematopsid (Amphibia: Labyrinthodontia) nasal region. Fieldiana: Geology 33(2): 11-30.
Cope ED 1882. Third contribution to the history of the vertebrata ofthe Permian Formation of Texas. Proc. Phil. Soc., 20: 447-461.
Dilkes DW and Reisz R 1987. Trematops milleri identified as a junior synonym of Acheloma cumminsi with a revision of the genus. American Museum Novitates 2902.
Olson EC 1941. The family Trematopidae. Journal of Geology 49:149-176.

wiki/Acheloma

Four more basal tetrapods added to the LRT

Spoiler alert:
No basic changes to the large reptile tree topology (LRT, Fig. 1, 938 taxa). The biggest difference from traditional trees continues to be the separation of dissorophoids, including Cacops, from temnospondyls. Cacops and kin are still nesting with the lepospondyls, including all microsaurs and extant amphibians

Figure 1. Subset of the LRT showing basal tetrapods. Four more are added here with no change in tree topology.

Figure 1. Subset of the LRT showing basal tetrapods. Four more are added here with no change in tree topology.

Tomorrow or shortly thereafter
I’ll start reporting some numbers and describing some interesting taxa. For those interested, whenever I add taxa, I revisit and update old taxa including their scores. So if you want an updated .nex file, now is a better time than ever, with errors minimized.

 

Better data for the manus of Eryops

Just found this reference
Dr. David Dilkes (2015) provides photo data (Fig. 1) on the carpus and manus of Eryops the giant temnospondyl. Earlier the best data I had was a decades old (Romer era) reconstruction and based on that manus and those of its sister taxa. With that data it appeared that the four digits preserved were 2–5, not 1–4 as traditionally considered. Dilkes likewise follows tradition in listing the fingers as 1–4.

Figure 1. Forelimb of Eryops from Dilkes 2005. Here freehand drawings of the manus cannot compete with a taking a tracing of the photo and restoring the digits and carpal elements to their in vivo positions. Note the subtle differences that happen in the freehand drawing by Dilkes and the Romer era illustrator.

Figure 1. Forelimb of Eryops from Dilkes 2005. Here freehand drawings of the manus cannot compete with  a tracing of the photo and restoring the digits and carpal elements to their in vivo positions (middle). Note the subtle differences that happen in the freehand drawing by Dilkes (above) and the Romer era illustrator (below).

The present data further cements
the hypothesis that the fingers of Eryops are 2–5, not 1–4.

And further cements
the hypothesis that freehand drawing is not as accurate as tracing a photo of the bones.

Today’s post also demonstrates
that better data, no matter where it comes from or makes your hypothesis go, must be incorporated. And finally…

Today’s post also demonstrates
that good Science can take place with second-hand data.

References
Dilkes D 2015. Carpus and tarsus of Temnospondyli. Vertebrate Anatomy Morphology Palaentology 1(1):51-87.