Reviewing the ‘Colosteidae’

Updated June 23, 2017 with the removal of Phlegethontia after taxon additions attracted that taxon to the Aïstopoda, where it traditionally nests. 

I asked for the challenge.
Dr. David Marjanović (DM) responded. He thought the traditional collosteids should nest together, as they do in Marjanović and Laurin 2017. By contrast, in the large reptile tree (LRT, 1012 taxa) only two nest together. Dr. David Marjanović also did not like Colosteus and kin nesting between Osteolepis and Panderichthys. Rather, Marjanović and Laurin 2017 reported, “Colosteidae is consistently found in a position one node more rootward than Baphetoidea and one node more crownward than Crassigyrinus.” In the Marjanović and Laurin study, relatives of Baphetes include Spathicephalus, Eucritta and Megalocephalus and Crassigyrinus nests between the collosteids and Tulerpeton. The LRT does not support this topology.

The Colosteidae
is a clade of basal tetrapods that classically includes Pholidogaster, Colosteus, Greererpeton and the latest addition, Deltaherpeton (Fig. 1).

Figure 1. Classic Collosteidae include Collosteus, Pholidogaster, Greererpeton and Deltaherpeton all to scale.

Figure 1. Classic Collosteidae include Collosteus, Pholidogaster, Greererpeton and Deltaherpeton all to scale here. Classic synapomorphies are listed below. The LRT nests Colosteus and Pholidogaster together while the other two nest elsewhere.

Marjanović and Laurin report,
“Deltaherpeton is one of the oldest known colosteids.” Bolt and Lombard 2010 report, Deltaherpeton is unique among colosteids in having an internasal and single midline postparietal. An additional midline pair of cf. ‘interfrontonasals’ may be present. Synapomorphies which unite Deltaherpeton, Colosteus, Greererpeton, and Pholidogaster as Colosteidae are:

  1. premaxilla with fang pair;
  2. dentary with notch for receipt of premaxillary fang;
  3. mandible with single elongate exomeckelian fenestra;
  4. pre-narial infraorbital lateral line terminating at ventral margin of premaxilla just anterior to external naris; and
  5. post-narial infraorbital lateral line terminating at the ventral margin of the maxilla just posterior to the external naris.

Let’s test to see
if this list is just a Larry Martin list of a few traits that are overwhelmed by other synapomorphies in the LRT. And at the same time, let’s see if these few traits have a wider, but overlooked, distribution and to see if they are valid for every included taxon.

Premaxilla with (lateral) fang pair
is indeed present in the four named taxa, if only barely in Deltaherpeton. Overlooked, perhaps, the lateral premaxillary tooth is also the largest in Phlegethontia, Acanthostega, Ventastega, Pederpes, Sclerocephalus, Ichthyostega among taxa related to traditional colosteids. More on premaxillary fangs below.

Figure 2. Phlegethontia longissima skull (CGH 129) has relatively large temporal plates, a wide flat cranium and a long pointed rostrum.

Figure 2. Phlegethontia longissima skull (CGH 129) has relatively large temporal plates, a wide flat cranium and a long pointed premaxilla. Note the large lateral fangs and tiny anteromedial ones.

The dentary notch
Unfortunaely I see this trait only on Greererpeton and Pholidogaster. In Colosteus (Figs. 1, 6) and Delatherpeton (Figs 3, 5) it is not apparent.

Figure 3. Drawing of Deltaherpeton sutures in Lombard and Bolt 2010 and colorized here. Note the lack of data around the naris (white glow).

Figure 3. Drawing of Deltaherpeton sutures in Bolt and Lombard 2010 and colorized here. Note the lack of data around the naris (white glow).

Collosteid traits 3-5 (above)
include the elongate exomeckelian fenestra and the two lateral lines (Fig. 3) are difficult to see or not see in some taxa. Note in the labeled image of Deltaherpeton by Bolt and Lombard 2010 (Fig. 3). Even they were unable to draw the naris and its surrounding lateral lines (white glow), but provided a diagram (Fig. 3) on another figure. 

Figure 4. Panderichthys palates. Note the lateral line below the naris is not continuous, contra Lombard and Bolt.

Figure 4. Panderichthys palates from Vorobyeva and Schultze 1991. Note the lateral line below the naris is not continuous, contra Bolt and Lombard.

I have not looked for lateral line/naris patterns
in other taxa, but Bolt and Lombard note the lateral line is continuous and straight below the naris along a lateral rostral plate in Eusthenopteron, Panderichthys (Fig. 4) and Ichthyostega. The lateral rostral plate is below the naris in Eusthenopteron. In Panderichthys the lateral line does not cross the lateral rostral plate, if that is what it is, because it is illustrated by Vorobyeva and Schultze (1991) with teeth, so it may just be a broken portion of the maxilla and the lateral rostral plate is no longer present. The naris of Ichthyostega is at the jawline leaving little room for a lateral rostral plate on the exterior surface. Would have been better for Bolt and Lombard to provide both the data, for verification, and the diagram, because now doubts arise.

Figure 4. Deltaherpeton in situ with inset showing location of naris and circumarial bones.

Figure 5. Deltaherpeton in situ with inset showing location of tiny inset naris and circumarial bones.

Two taxa separate Greererpeton and Pholidogaster in the LRT:
Panderichthys and Tiktaalik. Both lack the lateral premaxillary fang. Notably and despite their antiquity, both are derived and distinct from related taxa in having a very flat skull with orbits close to the midline. All marginal teeth are relatively tiny, which is also distinct from related taxa. Apparently when the skull flattened in these two the lateral premaxillary fangs shrank. Perhaps we should look for them in undiscovered basal taxa, probably originating n the early Late Devonian and lasting who knows how long.

Figure 6. Colosteus relatives according to the LRT scaled to a common skull length. Their sizes actually vary quite a bit, as noted by the different scale bars. Only Pholidogaster and Colosteus are taxa in common with traditional colosteid lists.

Figure 6. Colosteus relatives according to the LRT scaled to a common skull length. Their sizes actually vary quite a bit, as noted by the different scale bars. Only Pholidogaster and Colosteus are taxa in common with traditional colosteid lists.

In the large reptile tree
(subset Fig. 3) flat Greererpeton nests with other flat taxa like Spathocephalus, Trimerorhachis and Gerrothorax and  Ossinodus. Deltaherpeton nests with other tall- and narrow-skulled taxa, like Crassigyrinus and Ventastega. Pholidogaster and Colosteus nest with other round skull taxa. Despite their readily apparent differences no other taxa in the LRT share as many traits with clade members. And these three are the few representatives of a radiation covering about 60 million years. Just think what the mammals did in 60 million years.

The taphonomic crushing of the Deltaherpeton skull suggests it was wider than it was. Finding the palate by excavating from the other side of the matrix would provide precise data.

Figure 4. Subset of the large reptile tree. Classic colosteids are highlighted and connected by green lines.

Figure 7. Subset of the large reptile tree. Classic colosteids are highlighted and connected by green lines.

Did temnospondyls return the water?
Or never leave it? Did tetrapods develop fingers and toes more than once? Did basal tetrapods develop the ability to raise their bellies off the substrate more than once? The LRT provides provisional answers to these questions (Fig. 7). Convergence is apparent here. The LRT collosteids are separated from start to finish by about 60 million years, so changes can be expected.

Synapomorphies
Rather than pulling a Larry Martin, I did not list the few or many traits shared by Collosteus relatives in the LRT. Those can be gleaned from the matrix and most certainly will find convergences elsewhere on the cladogram. Remember, its not just one or a dozen traits that nest taxa as a clade, but the suite of traits that can really only be recovered by software like PAUP.

As to Dr. Marjanović’s challenge:
The traditional list of collosteids certainly does fall into a much narrow spectrum of sizes (Fig. 1), as opposed to the LRT list of Collosteus relatives (Fig. 6). And I did reexamine several issues and red flags. Some scores were revised. Deltaherpeton shifted two nodes and I think I understand it much better now. The list of classic collosteid traits is not found in all members and some traits extend to other clades. Finally, the phylogenetic distance between classic collosteids is not far from each other in the LRT, and in both studies both collosteid clades nest toward the base of the Tetrapoda. The details will work themselves out with further study on both sides. All interpretations are provisional, especially in basal tetrapods given their lateral lines that sometimes look like sutures and both camouflaged by a maze of skull texture.

As a suggestion for the future:
if colleagues would colorize their skull photos, paying attention to broken pieces and parts that just barely peek out from overlying material, that would go a long way toward improving the present system of either just showing the specimen or creating a freehand outline of the specimen, or just labeling bones with abbreviations and arrows without noting sutures.

References
Marjanović D and Laurin M 2017. Reevaluation of the largest published morphological data matrix for phylogenetic analysis of Paleozoic limbed vertebrates. PeerJPrePrints (not peer-reviewed).
Vorobyeva EI and Schultze H-P 1991. Description and systematics of panderichthyid fishes with comments on their relationship to tetrapods, in Schultze and Trueb (eds.), Origins of the Higher Groups of Tetrapods Comstock, pp 68-109.

Where is the rest of Lanthanolania?

It was back in 2011
when the post-crania of Lanthanolania (Fig. 1) was reported in an abstract by Modesto and Reisz. Prior to that, in 2003, only the skull was described by the same authors. Over the last six years the post-crania of Lanthanolania has not been published.

From the 2011 SVPCA abstract:
“The evolutionary history of Diapsida during the Palaeozoic Era is remarkably poor. Following the reclassification of the Early Permian Apsisaurus witteri as a synapsid last year, only a handful of taxa span the large temporal gap between the oldest known diapsid Petrolacosaurus kansensis and the Late Permian neodiapsid Youngina capensis. These include two Middle Permian neodiapsids, the recently described Orovenator mayorum from Oklahoma, USA, and Lanthanolania ivakhnenkoi from the Mezen region, northern Russia. A recently collected, nearly complete skeleton of Lanthanolania permits a thorough reexamination of the phylogenetic relationships of these two taxa.

“Phylogenetic analysis of 188 characters and 30 diapsid taxa positions these two small forms as stem saurians and the oldest known neodiapsids (recently redefined by the authors as the sister taxon of Araeoscelidia). Interestingly, our results suggest that the lower temporal bar was lost by the ancestral neodiapsid relatively soon after the evolution of the diapsid temporal morphology, and conversely, that the temporal configuration of the Late Permian Youngina capensis is a secondary condition. In addition, the skeletal anatomy of Lanthanolania provides evidence of limb proportions that suggest that this small reptile is the oldest known bipedal diapsid.”

Figure 1. Kuehneosaurid skulls from Palaegama to Coelurosauravus and Mecistotrachelos, and to Lanthanolania, Pamelina, Kuehneosaurus, Icarosaurus and Xianglong. Some of these taxa were not previously recognized as kuehneosaurids or their ancestors.

Figure 1. Kuehneosaurid skulls from Palaegama to Coelurosauravus and Mecistotrachelos, and to Lanthanolania, Pamelina, Kuehneosaurus, Icarosaurus and Xianglong. Some of these taxa were not previously recognized as kuehneosaurids or their ancestors.

Earlier (2011) the large reptile tree (LRT) nested Lanthanolania with the so-called rib gliders between Coelurosauravus and Icarosaurus. Back then we looked at those issues here.

Modesto and Reisz (2003) had a hard time
nesting Lanthanolania and considered it ‘enigmatic’. The closest they came was to nest Lanthanolania at the base of the lepidosauriformes (Rhynchocephalia + Squamata) and in other tests, with Coelurosauravus, which they split apart from the lepidosauriformes by adding intervening unrelated ‘by default’ taxa.

Unfortunately
with their small taxon list, Modesto and Reisz (2003) did not recover the basal split among reptiles that had occurred between the new Lepidosauromorpha and Archosauromorpha at Gephyrostegus + kin at the earliest Carboniferous. Thus the formerly monophyletic clade Diapsida is diphyletic in the LRT. Modesto and Reisz  mixed taxa from the two major clades and that muddied their results. Parts of their results were essentially correct, just unintelligible due to the addition of unrelated intervening archosauromorph basal diapsids.

Traditional paleontology
has likewise never nested coelurosauravids with kuehneosaurids, like Icarosaurus, perhaps based in part on the rib/dermal rod issue.

Problems and guesses:

  1. “Phylogenetic analysis of 188 characters and 30 diapsid taxa positions these two small forms as stem saurians and the oldest known neodiapsids (recently redefined by the authors as the sister taxon of Araeoscelidia).” — Sauria (= last common ancestor of archosaurs and lepidosaurs), is a junior synonym for Reptilia in the LRT. Neodiapsida (= includes all diapsids apart from araeoscelidians (= Petrolacosaurus and Araeoscelida)) or all taxa more closely related to Youngina than to Petrolacosaurus. Thus, in their thinking, Sauria is a clade within Neodiapsida. Modesto and Reisz do not yet recognize that Diapsida is no longer a monophyletic clade. In the LRT Orovenator and Lanthanolania are not related. The former is a basal diapsid archosauromorph. The latter is a basal lepidosauriform lepidosauromorph.
  2. “Interestingly, our results suggest that the lower temporal bar was lost by the ancestral neodiapsid relatively soon after the evolution of the diapsid temporal morphology,” — According to the LRT, the lower temporal bar was not lost nor was it present in the lepidosauromorph ‘rib’ gliders, including Lanthanolania. By contrast, Orovenator is one of the most basal archosauromorphs with an upper temporal fenestra.  Petrolacosaurus is older.
  3. “and conversely, that the temporal configuration of the Late Permian Youngina capensis is a secondary condition.” — In the LRT, it is not a secondary configuration, but is derived from basal diapsid taxa like Orovenator.
  4. “In addition, the skeletal anatomy of Lanthanolania provides evidence of limb proportions that suggest that this small reptile is the oldest known bipedal diapsid.” — I can only guess why they promoted this hypothesis: short torso and long hind limbs? Icarosaurus has such proportions. So does Kuehneosaurus. So does their last common ancestor, Palaegama (Fig. 2) which lacks wire-like dermal ossifications.
Figure 3. Palaegama, close to the origin of all Lepidosauriformes.

Figure 2. Palaegama, close to the origin of all Lepidosauriformes.

The question today is
where is the paper that describes the above-mentioned post-crania of Lanthanolania? Is the post-crania definitely referable?

If the referred specimen came from similar sediments
the matrix was described in 2003 as ‘extremely hard to work with’. Perhaps it is still being worked on. Or it has been shelved.

Phylogenetic bracketing
indicates that the new specimen might or should have wing-like wire/rod dermal elements, like those found in both Coelurosauravus and Icarosaurus, but traditionally considered ribs in Icarosaurus. They are not ribs, as we learned earlier here. The real ribs are short and fused to the vertebrae, appearing to be long transverse processes, but no related taxa have long transverse processes and not all of the ribs are fused to the vertebrae, betraying their identity. Since a mass of dermal rods was not mentioned in the abstract, one  wonders if the new specimen was actually closer to Palaegama than to Lanthanolania?

Late news from Sean Modesto about Lanthanolania:
“The project is currently in the hands of Dr. Reisz. No “ETA” as yet!”

Problems like this one
are a good reason to include the taxa the LRT suggests one include in smaller, more focused studies.

References:
Modesto SP and Reisz RR 2003. An enigmatic new diapsid reptile from the Upper Permian of Eastern Europe. Journal of Vertebrate Paleontology 22 (4): 851-855.
Reisz RR and Modesto SP 2011. The neodiapsid Lanthanolania ivakhnenkoi from the Middle Permian of Russia, and the initial diversification of diapsid reptiles.SVPCA abstract published online.

 

The paint-by-numbers analogy to phylogenetic analysis

Figure 1. owl paint-by-numbers

Figure 1. Owl paint-by-numbers. If you accurately add color to each little shape, pretty soon a picture will emerge. You don’t have to compose it. That’s already been done for you. Follow this method and your result will echo the original composition,  lighting and subject matter to a great degree. 

Phylogenetic analysis is like a paint-by-numbers kit.
You fill in each little color by following the instructions. Or you fill in each little matrix box (taxon/character) with the correct score. Only afterwards do you see the big picture. Or only afterwards does the software produce the resulting cladogram, the big picture of hypothetical relationships.

By contrast, in traditional painting
the master artist starts with a loose sketch, then arranges elements in a composition to fit a triangle, a golden rectangle, or some other substructure. The colors, tints and shadows are added in large blocks to a canvas of the right size to fit a certain wall. Finally the details (lace, highlights, eyelashes, etc. are added.

Like a paint-by-numbers canvas,
the big picture in evolution has already happened. The “instructions” or “clues” come to us in the form of preserved and exposed traits in fossils and living taxa. We don’t have all the clues, and never will, but with what we do have we fill them in until a complete picture begins to emerge, blank spaces and all.

Likewise, the large reptile tree
(LRT) and large pterosaur tree (LPT) are large gamut cladograms that will never be completed. However, as new taxa are added the details and transitions between established taxa become finer and finer blends. The big picture, or tree topology, has been pretty steady for several years and hundreds of additions.

Make sure your taxa 
are all species or specimens. Those provide good data. Avoid suprageneric taxa. By combining traits from several genera you’ll muddy the canvas. The tiny features will be lacking. You’ll cherry-pick favorites and overlook obscure details that might be Important.

Science is for everyone
Not just for PhDs. If they can create a cladogram, so can you. They test published work for validity. So do I and so can you. Along the way, you will make mistakes. I do too. Others will point out mistakes. Defend your decisions where appropriate. Fix problems at every opportunity. Follow this method and your result will echo the original tree topology. Then keep adding taxa as they become available to fill in any blank spaces.

The first time an idea is proposed
it is rarely accepted. As time goes by, some hypotheses disappear. And some should disappear. Others, whether valid or not, get headlines because the PR machinery is tilted in their favor. Still others slowly grow in acceptance and are ultimately embraced because they reflect the original tree topology we’re all trying to see more clearly.

Good luck on all your endeavors.

Coincidence? Or Discovery?

A recent reply (see below) to an earlier post bears noting:

Diandongosuchus nests as a basal phytosaur when choristoderes and basal younginoids are included, far from Qianosuchus, which also does not nest with poposaurs, which are all bipedal (or formerly bipedal) herbivores, a far cry from Diandongosuchus.

Figure 1. Diandongosuchus nests as a basal phytosaur when choristoderes and basal younginoids are included, far from Qianosuchus, which also does not nest with poposaurs, which are all bipedal (or formerly bipedal) herbivores, a far cry from Diandongosuchus.

David Marjanović on April 12, 2017 at 3:16 am said: 
“The redescription of Diandongosuchus (Fig. 1) has now been published in open access. I’m afraid I can’t congratulate you. The new paper, and the SVP abstract before it, uses data you didn’t (and couldn’t) use – you were right for the wrong reasons. No congratulations for coincidences. :-|  “

Reply ↓
davidpeters1954 on May 22, 2017 at 8:31 pm said:
“So, phylogenetic analysis and expanding the inclusion set are the wrong reasons? Tsk, tsk, David. Your bias is showing.”

Back story:
Diandongosuchus (Li et al. 2012) was originally nested with poposaurs. Within a few days of its publication, Diandongosuchus was added as a taxon to the large reptile tree (LRT) and it nested not with poposaurs, but at the base of the phytosaurs. Several other blog posts here, here and here further illustrated the link.

Recently 
Stocker et al. 2016 also nested Diandongosuchus with phytosaurs and shortly thereafter news of that publication was posted here,

Botton line:
Stocker et al. did not recognize the earlier discovery. It was easy to Google. It would have been appropriate to add the original discoverer to the list of authors. This is common practice, even when that person is deceased. More recently Dr. Marjanović withheld congratulations and demeaned the scientific method by which the discovery was attained (an expanded taxon list employed in phylogenetic analysis) as “the wrong reasons.”

 

Carl Sagan once wrote:
“In a lot of scientists, the ratio of wonder to skepticism declines in time. That may be connected with the fact that in some fields—mathematics, physics, some others—the great discoveries are almost entirely made by youngsters.”

“The suppression of uncomfortable ideas may be common in religion or in politics, but it is not the path to knowledge; it has no in the endeavor of science. We do not know in advance who will discover fundamental insights.”

“There are many hypotheses in science which are wrong. That’s perfectly all right; they’re the aperture to finding out what’s right. Science is a self-correcting process. To be accepted, new ideas must survive the most rigorous standards of evidence and scrutiny.”

The hypothesis
that Diandongosuchus is more closely related to phytosaurs than to poposaurs originally appeared here in 2012 and was confirmed four years later by Stocker et al. That Dr. Marjanović does not approve of the earlier discovery tell us more about professional biases against ‘outsiders’, which we’ve seen before, than it does about the ‘coincidence’ he conjures.

 

References
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.
Stocker MR, Nesbitt SJ, Zhao L-J, Wu X-C and Li C 2016. Mosaic evolution in phytosauria: the origin of longsnouted morphologies based on a complete skeleton of a phytosaur from the Middle Triassic of China. Abstracts of the Society of Vertebtate Paleontology meeting 2016.

 

Vintana and the vain search for the clades Allotheria and Gondwanatheria

Figure 1. Vintana as originally illustrated. I added colors to certain bones. Note the high angle of the ventral maxilla and the deep premaxilla. Lateral view reduced to scale with other views.

Figure 1. Vintana as originally illustrated. I added colors to certain bones. Note the high angle of the ventral maxilla and the deep premaxilla. Lateral view reduced to scale with other views.

Earlier we looked at Vintana (Fig. 1, Krause et al. 2014a, b). To Krause et al. Vintana represented the first specimen in the clades Allotheria and Gondwanatheria to be known from more than teeth and minimal skull material.

To Krause et al. 
Allotheria included Multituberculata and nested between the clade Eutriconodonta (including Repenomamus and Jeholodens) and the clade Trechnotheria (including the spalacotheres Maotherium and Akidolestes) and Cronopio, Henkelotherium, Juramaia, Eomaia, Eutheria and Metatheria.

Taxon exclusion issues
The large reptile tree (LRT, 1005 taxa) did not recover the above clades or relationships. Alotheria does not appear in the LRT.

  1. Multituberculata, Henkelotherium and Maotherium nest within Glires (rats and rabbits and kin) in the LRT.
  2. Repenomamus and Jeholodens nest within the pre-mammalian trityllodontid cynodonts in the LRT.
  3. Akidolestes nests within basal Mammalia, close to Ornithorhynchus in the LRT.
  4. Cronopio and Juramaia nest within basal Mammalia between Megazostrodon and Didelphis in the LRT.
  5. Eomaia nests at the base of the Metatheria in the LRT.
  6. Vintana nests with Interatherium among the derived Metatheria (marsupials), with wombats, like Vombatus and Toxodon in the LRT.

Despite a paper in Nature
and a memoir of 222 pages in the Journal of Vertebrate Paleontology; despite CT scans and firsthand examination with electron microscopes; despite being examined and described by many of the biggest name and heavy hitters in paleontology… Krause et al. never understood that Vintana was just a derived wombat, evidently due to taxon exclusion problems.

Figure 3. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats, between Vombatus and the giant Toxodon.

Figure 2. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats,with Vintana,  between Vombatus and the giant Toxodon

The large reptile tree now includes
1005 taxa, all candidates for sisterhood with every added taxon. Despite the large gamut of 74 taxa employed by Krause et al. they did not include the best candidates for Vintana sisterhood. Perhaps the fault lies in the reliance of prior studies and paradigms. Perhaps the fault lies in the over reliance by Krause et al. and other mammal workers, on dental traits. Perhaps the fault lies in the absence of pertinent sisters to the above-named taxa, including Interatheriium for Vintana.

In any case
Vintana does not stand alone as the only taxon in its clade represented by skull material. Based on its sisterhood with Interatherium, we have  pretty good idea what its mandibles and post-crania looked like. Yes, Vintana is weird. But Interatherium is also weird in the same way, just not as weird.

The LRT has dismantled and invalidated
several other clades, too, Ornithodira and Parareptilia among them.

References
Krause DW, Hoffmann S, Wible JR, Kirk EC, and several other authors 2014a. First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature. online. doi:10.1038/nature13922. ISSN 1476-4687.
Krause DW et al. 2014b. Vintana sertichi (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology Memoir 14. 222pp.

wiki/Vintana
pterosaur heresies – Vintana

Animated chronology of basal tetrapods

An animated color-coded cladogram
(Fig. 1, subset of the large reptile tree) of basal tetrapods demonstrates a great Devonian radiation prior to the multiple convergent reduction in digit numbers that typify most tetrapods. And perhaps suggests a multiple origination for land-living tetrapods (i.e. metoposaurs and eryopids appear to have had different basal tetrapod ancestors than frogs and reptiles).

  1. Late Devonian – deep blue
  2. Early Carboniferous – light green
  3. Late Carboniferous – deep green
  4. Early Permain – light orange
  5. Late Permian – dark orange (brown)
  6. Early Triassic – pink
  7. Late Triassic – red
  8. Jurassic – cyan
  9. Post-Jurassic to extant – black
Figure 1. Subset of the LRT focusing on basal tetrapods.

Figure 1. Subset of the LRT focusing on basal tetrapods. Six frames change every 2 seconds. 

The cladogram also supports
the reptilian identification of Tulerpeton giving rise to the large number and radiation of Viséan (early Carboniferous) and later reptiles.

Note also
the radiation of derived legless microsaurs also from the Viséan (340 mya).

What you don’t see in this cladogram
are the many short ghost lineages of basal and other taxa implied by the presence of derived taxa known from earlier sediments. Of course, this is due to the somewhat random and certainly rare preservation and excavation of vertebrate fossils.

Even so
the general order of appearance of taxa in the cladogram seems to be correlated to phylogenetic relationships. Exceptions arise due to the random nature of fossil discovery. Give us another 200 years and see how the tree fills out!

Here, once again,
colorizing the taxa and putting them into an animated cladogram increases global understanding of basal tetrapod interrelationships that cannot be communicated in traditional print media.

Lambdotherium: not a basal brontothere — it’s another pig relative!

Earlier a putative stem brontothere, Danjiangia, was re-nested with basal artiodactyls in the large reptile tree (LRT, 1005 taxa).

Here another putative stem brontothere,
Lambdotherium (Cope 1880, Mader 1998; Eocene, 50mya; Fig. 1) likewise moves away from the basal brontothere, Eotitanops. In the LRT  Lambdotherium nests with Ancodus (Fig. 2), another basal artiodactyl close to extant pigs.

Figure 1. Lambdotherium traditionally nests with the basal brontothere, Eotitanops, but here nests with Ancodus, a basal artiodactyl.

Figure 1. Lambdotherium traditionally nests with the basal brontothere, Eotitanops (ghosted here), but here nests with Ancodus, a basal artiodactyl. Brontotheres have a very tall naris. Pigs do not. 

I don’t know of any post-crania
for Lambdotherium. Note that Ancodus (Fig. 2), like Eotitanops, has a pentadatyl manus. Lambdotherium was traditionally considered a brontothere based on its teeth. The LRT employs relatively few dental traits. And maybe some specimens need to be reexamined. The very high arch of the Lambdotherium squamosal, among many other traits, is more similar to pig-like taxa, than to basal brontotheres, which here nest closer to rhinos, than to horses, contra the Wikipedia report on brontotheres.

Distinct from both rhinos and horses,
brontotheres have four toes on the forefeet. All are derived from a sister to Hyrachyus, which likewise has four toes.

Figure 1. Ancodus nests as a more derived sister to Sus and it retains digit 1 on the manus and pes.

Figure 2. Ancodus nests as a more derived sister to Sus and it retains digit 1 on the manus and pes.

References
Cope ED 1880. The bad lands of the Wind River and their fauna. The American Naturalist 14(10):745-748.
Mader BJ 1998. Brontotheriidae. In Janis CM, Scott KM, and Jacobs LL (eds.), Evolution of Tertiary Mammals of North America 1:525-536.
Mihlbachler MC 2004. Phylogenetic Systematics of the Brontotheriidae (Mammalia, Perissodactyla). PhD dissertation. Columbia University. p. 757.
Mihlbachler MC 2008. Species taxonomy, phylogeny and biogeography of teh Brontotheriidae (Mammalia: Perissodactyla). Bulletin of the American Museum of Natural History 311:475pp.

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