SVP abstracts 17: Pederpes is a junior synonym for Whatcheeria

Otoo et al. 2020 bring us
a new reconstruction of Whatcheeria (Figs. 1, 2), evidently updated from a 2018 abstract by the same authors (less one).

Figure 1. Whatcheeria fossil.

Figure 1. Whatcheeria fossil.

From the Otoo et al. abstract:
“The early tetrapod Whatcheeria is represented by hundreds of specimens from the Mississippian Delta locality (Iowa, U.S.A.). Research on the postcranial anatomy allows a full-body reconstruction to be produced for the first time. The ribcage is strongly regionalized, with long anterior trunk ribs bearing large uncinate processes, and short posterior trunk ribs. The girdles and limbs are massive; in particular, the processes of the humerus are very large, and imply bulky forelimb and shoulder musculature, especially relating to the retraction of the forelimb. The cervical region is elongated and the tail is reduced in length relative to contemporary tetrapods such as embolomeres and colosteids.”

Whatcheeria nests in the large reptile tree (LRT, subset Fig. 3) alongside Pederpes (Fig. 4). The two share all traits scored in the LRT and are coeval in the Early Carboniferous.

Figure 2. Whatcheeria skull.

Figure 2. Early Carboniferous Whatcheeria skull.

More from the Otoo et al. abstract:
“The resulting proportions are more similar to terrestrial taxa such as Seymouria and Eryops. These taxa also share with Whatcheeria robust humeri with large processes, large olecranon processes, large scapular blades, and regionalized ribcages. Such similarities suggest convergent life habits, with an anteriorly stiffened trunk to increase the effectiveness of the powerful forelimbs and reduce lateral motion of the body.”

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

Figure 3. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

More from the Otoo et al. abstract:
“We hypothesize that Whatcheeria represents an independent experiment in appendicular-dominated locomotion, with improved ability to explore terrestrial environments The large (>2 m maximum) body size of Whatcheeria is larger than most Mississippian tetrapods, particularly those for which there is the most compelling evidence of terrestriality (e.g., Balanerpeton, Westlothiana). Aquatic locomotion may have been accomplished by bottom-walking, or rowing with the forelimbs.”

“Our new data include additional synapomorphies between Whatcheeria and Pederpes, and suggest that the latter is a juvenile.

Whatcheeria and Pederpes nest together in the LRT (Fig. 4). Of 235 traits, none differ between the two. Based on scale bars the two are identical in size, with 10cm measuring the snout to the posterior orbit on both. Pederpes (Clack 2002) is thus a junior synonym for Whatcheeria (Lombard and Bolt 1995). Hmmm. Wonder how this one got away from the experts over the last 18 years. Whatcheeria entered the LRT in 2017, so I had three years to see this, too.

Figure 3. Pederpes is a basal taxon in the Whatcheeria + Crassigyrinus clade.

Figure 4. Early Carboniferous Pederpes is a basal taxon in the Stegocephalia.

More from the Otoo et al. abstract:
These data contribute to a new diagnosis for the Whatcheeriidae and a reassessment of material and taxa referred or compared to the family; significantly, Ossinodus is not a whatcheeriid and represents a distinct morphotype.

The LRT (subset Fig. 3, Fig. 5) agrees with this.

Figure 2. Ossinodus, Pederpes were more primitive than the more aquatic Icthyostega.

Figure 5. Ossinodus,is more primitive than the more aquatic Icthyostega. Pederpes is more derived, but close. The black areas of Ossinodus are known. The rest is restoration.

More from the Otoo et al. abstract:
“However, these data do move Whatcheeria crownward in phylogenetic analyses. Rather, our findings highlight the disparity of stem tetrapods, and emphasizes Whatcheeria’s status as an early-diverging experiment in a morphology later revisited by crown tetrapods.”

The LRT (subset Fig. 3) does not agree with this conclusion. Ossinodus (Fig. 5) nests basal to both stegocephalians (including Whatcheeria) and crown tetrapods. It is the most basal tetrapod with substantially larger limbs than those of basalmost tetrapods like Trypanognathus. Ichthyostega and Pederpes are taxa leaving no Permian and Mesozoic descendants.


References
Ahlberg PE and Milner AR 1994. The origin and early diversification of tetrapods. Nature 368, 507-514.
Clack JA 2002. Gaining Ground: The origin and evolution of tetrapods. Indiana University Press.
Clack JA 2002. An early tetrapod from ‘Romer’s Gap’. Nature. 418 (6893): 72–76. doi:10.1038/nature00824
Lydekker R 1890. On two new species of labyrinthodonts. Quarterly Journal of the Geological Society, London 46, 289-294.
Lombard RE and Bolt, J.R 1995. A new primitive tetrapod, Whatcheeria deltae, from the Lower Carboniferous of Iowa. Palaeontology 38(3):471–495.
Otoo B, Bolt J, Lombard E and Coates M 2020. A new reconstruction of Whatcheeria and the ecomorpholigcal disparity of early tetrapods. SVP abstracts 2020.
Otoo BK, Bolt JR, Lombard E 2018. A leg up: Whatcheeria and its new contributions to tetrapod anatomy. SVP abstracts.
Panchen AL 1991. The early tetrapods: classification and the shapes of cladograms in: Origins of the Higher Groups of Tetrapods: Controversy and Consensus. Eds. Schultze HP and Trueb L. Comstock Publishing Associates, Cornell University Press, Ithaca and London.

wiki/Pederpes
wiki/Whatcheeria

https://pterosaurheresies.wordpress.com/2018/10/30/svp-2018-new-whatcheeria-data-from-nearly-100-specimens/

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

 

Recalibrating clade origins, part 2

Marjanovic 2019 reports on
the origin of several clades based on fossils and molecules. Yesterday we looked at part 1, which focused on the abstract. Today: the origin of several more listed clades.

Gnathostomata (Chondrichthyes + Osteichichthyes)
Marjanovic cautiously proposes the mid-Florian (Early Ordovician, 475 mya) for the origin using traditional taxa and cladograms.

By contrast, the LRT splits off quasi-jawless sturgeons before the appearance of jawed sharks + other bony fish. It also splits off the jawed Loganellia + Rhincodon + Manta clade before the Polyodon + ratfish + sharks + skates clade and the Pachycormus + Hybodus clade before the dichotomy that resulted in the rest of the bony fish (the now polyphyletic ‘Osteichthyes‘)… so direct comparisons are not apples and apples here. Sturgeons first appear much later in the fossil record. Loganellia appears in the Early Silurian with an earlier genesis. So Marjanovic’s estimate may be a little early.

Osteichthyes (Actnopterygii + Sarcopterygii)
Marjanovic reports, “The oldest known uncontroversial crown-group osteichthyan is the oldest known dipnomorph, Youngolepis.” He suggests, “the minimum age for this calibration is the same as that for the next node,” the Silurian/Devonian boundary, 420 mya.

The LRT includes placoderms within one branch of the bony fish, so Entelognathus along with the stem-lungfish Guiyu, both in the Late Silurian are older than Marjanovic suggests with an earlier genesis. Sturgeons, which traditional workers consider a member of the Osteichyes, phylogenetically preceded Longanellia, which is known from Early Silurian strata. So, again we’re not comparing similar cladograms here. The LRT tests a wider gamut of taxa, which is an advantage in that it opens further possibilities than tradition dictates.

Dipnomorpha + Tetrapodomorpha (lungfish + lobe fin ancestors of tetrapods)
Marjanovic reports, “I suggest a hard minimum age of 420mya.” (See above).

The LRT includes Late Siluirian Guiyu within the stem-lungfish clade. so the split occurred earlier.

Tetrapoda (Amphibia + total group of Amniota)
Marjanovic reports, “the richer and better studied Famennian (end-Devonian) record, which has not so far yielded tetrapods close to the crown-group but has yielded more stemward tetrapods and other tetrapodomorphs (Marjanović and Laurin, 2019), should be used to place a soft maximum age around very roughly 365 Ma.”

Figure 3. Tersomius texensis, an amphibamid lepospondyl close to Dendrerpeton.

Figure 1. Tersomius texensis, an amphibamid lepospondyl close to Dendrerpeton.

In the LRT the last common ancestor of Amphibia + Amniota is Tersomius (Fig. 1), a late survivor in the Early Permian of an earlier genesis and radiation. The oldest taxa from this clade in the LRT are the basal amniotes / amphibian-like reptiles, Silvanerpeton and Eldeceeon from the Viséan (335 mya), with a long list of late surviving taxa between them and Tersomius, some eight nodes beyond the Late Devonian Acanthostega and Ichthyostega (365 mya). So the Tournaisian (355 mya) split suggested by Marjanovic seems about right.

Amniota (Theropsida + Sauropsida)
Marjanovic reports, “I refrain from recommending a maximum age other than that of the preceding Node, even though such an early age would imply very slow rates of morphological evolution in the earliest thero- and sauropsids.”

The LRT recovers a different basal dichotomy (Archosauromorpha + Lepidosauromorpha) and a different last common ancestor for all amniotes (Silvanerpeton) than Marjanovic is working with. Silvanerpeton is Viséan in age (~335 mya). In the LRT ‘Amniota’ is a junior synonym for Reptilia.

Crown group of Diapsida (Lepidosauromorpha + Archosauromorpha)
Marjanovic reports, “I cannot express confidence in a maximum age other than that of  Node 106, which I cannot distinguish from the maximum age of Node 105 as explained above. This leaves Node 107 without independent calibrations in the current taxon sample.”

The LRT finds two origins for reptiles with a diapsid skull architecture. So the tradtional clade ‘Diapsida’ is also a junior synonym for Reptilia and Marjanovic is using an outdated and under represented cladogram. Lepidosauromorph diapsids first appear with Paliguana in the earliest Triassic. Archosauromorph diapsids first appear with Erpetonyx and Petrolacosaurus in the Late Carboniferous with an earlier genesis. These taxa are not mentioned by Marjanovic.

Archosauria (Crocodile total group + Bird total group)
Marjanovic reports, “I accept the Permian-Triassic boundary (251.902 ± 0.024 Ma: ICS; rounded to 252) as the soft maximum age on the grounds that a major radiation of archosauromorphs at the beginning of the Triassic seems likely for ecological reasons.”

The LRT restricts membership within the Archosauria to just Crocodylomorpha + Dinosauria. So the maximum age for this dichotomy is younger and the last common ancestor is the PVL 4597 specimen (late Middle Triassic, 230mya) traditionally assigned to Gracilisuchus, but nesting apart from the holotype.

The LRT finds the Archosauriformes first appeared in the Late Permian (260mya), arising from a sister to Youngoides romeri (FMNH UC1528) thereafter splitting into clades arising from the larger Proterosuchus and the smaller Euparkeria.

Alligatoridae (Alligatorinae + Caimaninae)
Marjanovic reports, “Given this uncertainty, I have used a hard minimum age of 65 Ma for present purposes, but generally recommend against using this cladogenesis as a calibration for time trees.”

The LRT does not include pertinent taxa surrounding this split.

Figure 1. Megapodius is the extant bird nesting at the base of all neognathae (all living birds except ratites).

Figure 2. Megapodius is the extant bird nesting at the base of all neognathae (all living birds except ratites). And it looks like a basal bird. It also looks a bit like the Solnhofen bird, Jurapteryx. It is easy to imagine diverse forms arising from this bauplan and the LRT indicates that is exactly what happened.

Crown group of Neognathae (Gallanseres + Neoaves)
Marjanovic further defines this clade as, “The last common ancestor of Anas, Gallus and Meleagris on one side and Taeniopygia.” More commonly Marjanovic nests a duck, a chicken and a turkey on one side and a zebra finch on the other as the basal dichotomy of all living birds, sans ostriches, kiwis and kin. Marjanovic reports, “As the soft maximum age I tentatively suggest 115 Ma, an estimate of the mid-Aptian age of the (likewise terrestrial) Xiagou Fm of northwestern China, which has yielded a diversity of stem-birds but no particularly close relatives of the crown.”

Taxa listed by Marjanovic are all highly derived taxa in the LRT where the scrub fowl, Megapodius (Fig. 2) and the tinamou, Crypturus, are basal neognaths. These would have had their genesis in the Earllest Cretaceous given that Early Cretaceous clades that redevelop or retain teeth are more derived.

More tomorrow…


References
Marjanovic D 2019. Recalibrating the transcriptomic timetree of jawed vertebrates.
bioRxiv 2019.12.19.882829 (preprint)
doi: https://doi.org/10.1101/2019.12.19.882829
https://www.biorxiv.org/content/10.1101/2019.12.19.882829v1

Tetrapod ancestors updated back to Cambrian finless fish

Pictures tell the story, for the most part today.
The large reptile tree
(LRT, 1615+ taxa) presents an occasionally novel and growing list of taxa between Cambrian pre-fish and the first listed tetrapod, Laidleria (Fig. 1 bottom). This list is updated from the previous time this list was first presented without so many basal chordates. Note, it still does not include traditional members, Acanthostega and Ichthyostega. which nest at more derived nodes as they venture back into a more fish-like niche.

Figure 1. These taxa are those closest to main line of tetrapod ancestors. That makes these taxa human ancestors, too.

Figure 1. These taxa are those closest to main line of tetrapod ancestors. That makes these taxa human ancestors, too.

Qiao et al. 2016 report,
“Our findings consistently corroborate the paraphyly of placoderms, all ‘acanthodians’ as a paraphyletic stem group of chondrichthyans, Entelognathus as a stem gnathostome, and the Guiyu-lineage as stem sarcopterygians.”

Figure 3. Traditional cladogram from Lingham-Soliar 2014.

Figure 2. Traditional cladogram from Lingham-Soliar 2014. This has been invalidated by the LRT.

Figure 4. Subset of the LRT with the addition of several jawless taxa.

Figure 3. Subset of the LRT with the addition of several jawless taxa.

References
Brazeau MD and Friedman M 2015. The origin and early phylogenetic history of jawed vertebrates. Nature. 2015;520(7548):490–7. pmid:25903631.
Davis SP, Finarelli JA and Coates MI 2012. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature. 2012;486(7402):247–250. pmid:22699617
Dupret V, Sanchez S, Goujet D, Tafforeau P and Ahlberg PE 2014. A primitive placoderm sheds light on the origin of the jawed vertebrate face. Nature. 2014;507:500–503. pmid:24522530
Lingham-Soliar T 2014. The vertebrate integument volume 1. origin and evolution. Springer.com  PDF
Qiao T, King B, Long JA, Ahlberg PE and Zhu M 2016. Early gnathostome phylogeny revisited: multiple method consensus. PLoS ONE 11(9): e0163157. https://doi.org/10.1371/journal.pone.0163157
Zhu M, Zhao W-J, Jia L-T, Lu J, Qiao T and Qu Q-M. 2009. The oldest articulated osteichthyan reveals mosaic gnathostome characters. Nature. 2009;458:469–474. pmid:19325627
Zhu M, Yu X-B, Ahlberg PE, Choo B, Lu J, Qiao T, et al. 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 2013;502(7470):188–193. pmid:24067611
Zhu M, Yu X-B and Janvier P 1999. A primitive fossil fish sheds light on the origin of bony fishes. Nature. 1999;397:607–610.

https://pterosaurheresies.wordpress.com/2019/10/24/tetrapod-evolution-without-ichthyostega-and-acanthostega/

The origin of the tetrapod quadratojugal

As we’ve seen
over the past several dozen fish additions to the large reptile tree (LRT, 1583 taxa) facial bones homologous with those of tetrapods often divide and fuse. We’ve already seen multipart jugals, lacrimals, nasals and squamosals in fish. This can be confusing and is probably the reason why fish facial bones are traditionally not labeled with tetrapod nomenclature. Expect homology arguments to last for decades, but here all fish facial bones are colored with tetrapod homologs.

Figure 1. Gogonasus skull demonstrating the genesis of the split between the toothy maxilla and the toothless quadratojugal.

Figure 1. Gogonasus skull demonstrating the genesis of the split between the toothy maxilla and the toothless quadratojugal.

The one bone that first appears by a split
of the maxilla into anterior toothy and posterior toothless portions is the quadratojugal. Phylogenetically the quadratojugal first appears on Gogonasus (Fig. 1). Prior taxa lack it. Later taxa have it. Even so, until the cladogram got figured out, this was puzzling.

Figure 1. Subset of the LRT alongside the definitions published in Laurin, Girondot and de Ricqles 2000.

Figure 2. Subset of the LRT alongside the definitions published in Laurin, Girondot and de Ricqles 2000. Note the Gogonasus node, where the quadratojugal first appears.

Gogonasus andrewsae (Long 1985, Long et al. 1997; Late Devonian, 380 mya; NMV P221807; 30-40cm in length) is the best preserved specimen of its type. This is the crossopterygian transitional between rhizodontids, coelocanths and higher tetrapodomorphs. The maxilla splits in two creating the tetrapod quadratojugal. The squamosal splits in two creating the tetrapodomorph preopercular. A pineal opening appears, so does the tetrapodomorph choana. The lacrimal contacts the external naris. This is the crossopterygian that gave rise to tetrapodomorphs and tetrapods, rhizodontids and gulper eels.


References
Long JA 1985. A new osteolepidid fish from the Upper Devonian Gogo Formation of Western Australia, Recs. Western Australia Mueum 12: 361–377.
Long JA et al. 1997. Osteology and functional morphology of the osteolepiform fish Gogonasus Long, 1985, from the Upper Devonian Gogo Formation, Western Australia. Recs. W. A. Mus. Suppl. 57, 1–89.

wiki/Gogonasus

Third eye distribution in 1413 LRT tetrapods

The mysterious pineal/parietal eye/opening.
Some tetrapods have one between the parietals (Fig. 1). Others seal off that opening. Some either greatly expand the pineal or reduce the length of the parietal creating a ‘large’ opening relative to the length of the parietal. The pineal body varies greatly in size. In humans it is tucked in below the cerebrum and cerebellum. By contrast, in lampreys it extends high above the brain and is light sensitive (Fig. 2). According to Wikipedia, “The [third] eye is photoreceptive and is associated with the pineal gland, regulating circadian rhythmicity and hormone production for thermoregulation.

Wikipedia reports, 
“The tuatara has a third eye on the top of its head called the parietal eye. It has its own lens, a parietal plug which resembles a cornea, retina with rod-like structures, and degenerated nerve connection to the brain. The parietal eye is only visible in hatchlings, which have a translucent patch at the top centre of the skull. After four to six months, it becomes covered with opaque scales and pigment. Its purpose is unknown, but it may be useful in absorbing ultraviolet rays to produce vitamin D, as well as to determine light/dark cycles, and help with thermoregulationOf all extant tetrapods, the parietal eye is most pronounced in the tuatara. It is part of the pineal complex, another part of which is the pineal gland, which in tuatara secretes melatonin at night. Some salamanders have been shown to use their pineal bodies to perceive polarised light, and thus determine the position of the sun, even under cloud cover, aiding navigation.

The distribution pattern in extinct tetrapods
is readily apparent in a broad sense ( Fig. 1). Even so, exceptions appear often. Reversals appear rarely. It is interesting to note the last time a third eye opening appeared in the skulls of various lineages. The large reptile tree (LRT, 1413 taxa) scores for 231 traits, one of which is #39, the pineal foramen.  Scoring choices include:

  1. Present and tiny <.20 parietal length
  2. Absent
  3. Present and large ≥ .20 parietal length
  4. Between the frontals (= anterior to the parietals)
Figure 1. Click to enlarge. This is the complete LRT highlighting the distribution of the pineal opening.

Figure 1. Click to enlarge. This is the complete LRT highlighting the distribution of the pineal opening.

The primitive state is: ‘between the frontals’.
This occurs in basal fish, prior to sarcopterygians. This state also occurs by reversal in several iguanid squamates related to Chlamydosaurus.

The derived state is ‘absent’.
This occurs in a wide variety of taxa from derived eryopids to mammals, several squamates, macrocnemids (including fenestrasaurs) and euarchosauriformes among others.

Most basal tetrapods
have a ‘tiny’ pineal opening.

Most basal reptiles
have a large pineal opening.

Figure 3. Pineal body in a primitive jawless fish, like the lamprey.

Figure 3. Pineal body in a primitive jawless fish, like the lamprey.

According to Wikipedia
“The pineal gland is a small endocrine gland in the brain of animals with backbones. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles.”

Figure 1. The basal synapsid, Vaughnictis, and the basal caseasaur, Eothyris. For starters, synapsids have a taller than wide skull and caseasaurs have a wider skull. See text for other details.

Figure 3. The basal synapsid, Vaughnictis, and the basal caseasaur, Eothyris. Both branches of basal reptilesw (Fig. 1) retained a pineal/parietal opening for the third eye.

“The results of various scientific research in evolutionary biology, comparative neuroanatomy and neurophysiology, have explained the phylogeny of the pineal gland in different vertebrate species. From the point of view of biological evolution, the pineal gland represents a kind of atrophied photoreceptor. In the epithalamus of some species of amphibians and reptiles, it is linked to a light-sensing organ, known as the parietal eye, which is also called the pineal eye or third eye.”


References
Zhu M, Yu X-B, Ahlberg PE, Choo B and 8 others 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 502:188–193.

wiki/Parietal_eye
wiki/Pineal_gland
wiki/Tuatara

Dr J Gauthier lecture video on birds + dinos

If you watch this…
Stay for the brilliant question and answer period at the end.

And…
returning to an earlier subject…
Geologist Randall Carlson reports on Joe Rogan Experience #606 (1:35:44) —  “See, here’s the thing. Modern science does tend to get over specialized. And so what happens is, they guy looking at extinctions might not be looking at glacial melting. The guy looking at glacial melting… the geologist is not looking at what’s going on in the sky. They’re not looking at traditions, you know, traditions from thousands of years ago. What it does is, because of the powerful of this specialization, this specialization is extremely powerful, but the thing of it is… it’s easy to miss the big picture. What that does is, it opens the door for generalists, guys who are just, people who are just, men or women, anybody who is curious about this stuff, look into it and try to see the big picture.”

In other words…
taxon exclusion problems can be solved by a wide gamut analysis of the entire range of tetrapods now known.

Joe Rogan says (1:37:46),
“People love to be able to dismiss anything that’s not mainstream, right?” To which Randall Carlson replies, “Because there’s this cult of authority.” Randall Carlson continues (1:38:40) “They’ve got this idea in their mind that there’s this authority that’s got it all explained, which makes it easy, because if somebody’s got this all explained, then we don’t need to concern ourselves with it or think about it. Right? So, what I see is, ‘Okay… forget about who says what. Look at the facts. Let the facts dictate to us what the meaning of all this is. And let’s look at all points of view.” 

The idea that a meteor impact ended the last Ice Age,
and killed the northern megafauna first proposed by Randall Carlson and others gained new hard evidence with the recent discovery of a Paris-sized crater on the north rim of Greenland. Details and videos here: https://earthsky.org/earth/meteorite-crater-under-greenland-ice

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

Ichthyostega and Acanthostega: secondarily more aquatic

More heresy here
as the large reptile tree (LRT, 1036 taxa) flips the traditional order of fins-to-feet upside down. Traditionally the late Devonian Ichthyostega and Acanthostega, bridge the gap between lobe-fin sarcopterygians, like Osteolepis.

In the LRT
Acanthostega, ‘the fish with limbs’, nests at a more derived node than its precursor, the more fully limbed, Ossinodus (Fig. 1). Evidently neotony, the retention of juvenile traits into adulthood, was the driving force behind the derived appearance of Acanthostega, with its smaller size, stunted limbs, smaller skull, longer more flexible torso and longer fin tail.

Figure 1. Ossinodus is the more primitive taxon in the LRT compared to the smaller Acanthostega, the tadpole of the two.

Figure 1. Ossinodus is the more primitive taxon in the LRT compared to the smaller Acanthostega, essentially the neotenous ‘tadpole’ of the two.

Likewise
Ichthyostega is more derived than both fully-limbed Ossinodus and Pederpes, which had five toes. As in Acanthostega, the return to water added digits to the pes of Ichthyostega. In both taxa the interosseus space between the tibia and fibula filled in to produce a less flexible crus.

Figure 2. Ossinodus, Pederpes were more primitive than the more aquatic Icthyostega.

Figure 2. Long-limbed Ossinodus and Pederpes were more primitive than the more aquatic Icthyostega.

So, Acanthostega and Ichthyostega were not STEM tetrapods.
Instead, they were both firmly nested within the clade Tetrapoda. Ossinodus lies at the base of the Tetrapoda. The proximal outgroups are similarly flattened Panderichthys and Tiktaalik. The extra digits displayed by Acanthostega and Ichthyostega may or may not tell us what happened in the transition from fins to feet. We need to find a derived Tiktaalik with fingers and toes.

Figure 3. Tiktaalik specimens compared to Ossinodus.

Figure 3. Tiktaalik specimens compared to Ossinodus.

In cases like these
it’s good to remember that ontogeny recapitulates phylogeny. Today and generally young amphibians are more fish-like (with gills and fins) than older amphibians.

It’s also good to remember
that the return to the water happened many times in the evolution of tetrapods. There’s nothing that strange about it. Also the first Devonian footprints precede the Late Devonian by tens of millions of years.

Figure 4. From the NY Times, the traditional view of tetrapod origins.  Red comment was added by me.

Figure 4. From the NY Times, the traditional view of tetrapod origins. 

Phylogenetic analysis teaches us things
you can’t see just by looking at the bones of an individual specimen. A cladogram is a powerful tool. The LRT is the basis for many of the heretical claims made here. You don’t have to trust these results. Anyone can duplicate this experiment to find out for themselves. Taxon exclusion is still the number one problem that is largely solved by the LRT.

You might remember
earlier the cylindrical and very fish-like Colosteus and Pholidogaster convergently produced limbs independently of flattened Ossinodus, here the most primitive taxon with limbs that are retained by every living tetrapod. By contrast, the Colosteus/Pholidogaster experiment did not survive into the Permian.

References
Ahlberg PE, Clack JA and Blom H 2005. The axial skeleton of the Devonian trtrapod Ichthyostega. Nature 437(1): 137-140.
Clack JA 2002.
 Gaining Ground: The origin and evolution of tetrapods. Indiana University Press.
Clack JA 2002. An early tetrapod from ‘Romer’s Gap’. Nature. 418 (6893): 72–76. doi:10.1038/nature00824
Clack JA 2006. The emergence of early tetrapods. Palaeogeography Palaeoclimatology Palaeoecology. 232: 167–189.
Jarvik E 1952. On the fish-like tail in the ichtyhyostegid stegocephalians. Meddelelser om Grønland 114: 1–90.
Jarvik E 1996. The Devonian tetrapod Ichthyostega. Fossils and Strata. 40:1-213.
Säve-Söderbergh G 1932. Preliminary notes on Devonian stegocephalians from East Greenland. Meddelelser øm Grönland 94: 1-211.
Warren A and Turner S 2004. The first stem tetrapod from the Lower Carboniferous of Gondwana. Palaeontology 47(1):151-184.
Warren A 2007. New data on Ossinodus pueri, a stem tetrapod from the Early Carboniferous of Australia. Journal of Vertebrate Paleontology 27(4):850-862.

wiki/Ichthyostega
wiki/Acanthostega
wiki/Ossinodus
wiki/Pederpes

Tulerpeton restoration

A reconstruction
puts the in situ bones back into their in vivo places.

A restoration
imagines the bones and soft tissues that are missing from the data. Adding scaled elements from a sister taxon is usually the best way to handle a restoration as we await further data from the field.

Figure 1. Tulerpeton restored based on the bauplan of Silvanerpeton and to the same scale.

Figure 1. Tulerpeton restored based on the bauplan of Silvanerpeton and to the same scale.

We looked at
Tulerpeton, the Upper Devonian taxon known chiefly from its limbs, earlier. I reconstructed the limbs several ways, but did not attempt a restoration. Here (Fig. 1) that oversight is remedied based on the bauplan of Viséan sister, Silvanerpeton. 

Among the overlapping elements,
in Tulerpeton the pectoral girdle and forelimbs are larger. An extra digit is present laterally.

References
Clack JA 1994. Silvanerpeton miripedes, a new anthracosauroid from the Visean of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (for 1993), 369–76.
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/Silvanerpeton
wiki/Tulerpeton