Patranomodon and descendants

Rubidge and Hopson (1990, 1996) got it right.
Patranomodon (Figs. 1–3) is basal to the dicynodonts AND the venjukovamorphs the Therapsid Skull Tree (TST, 68 taxa; Fig. 4).

FIgure 1. Patranomodon with bones colored here helped to rescuer the taxon. The original drawing omitted the septomaxilla and the anterior rostrum and mandible. Now it really does look more like a basal dicynodont.

FIgure 1. Patranomodon with bones colored here helped to rescuer the taxon. The original drawing omitted the septomaxilla and the anterior rostrum and mandible. Now it really does look more like a basal dicynodont.

Figure 1b. Patranomodon post-crania assembled.

Figure 1b. Patranomodon post-crania assembled.

Rubidge and Hopson (1996) reported, Patranaomodon is primitive with respect to other anornodonts in having short palatal exposure of the premaxilla, an unreduced tabular, a slit-like interpterygoidal vacuity, a screw-shaped jaw articulation (which precludes fore-aft sliding of the lower jaw), and only three sacral vertebrae. The poorly-known Galechirus and Galepus from the younger Cistecephalus Assemblage Zone appear to be at a comparably primitive evolutionary grade, and the three genera are tentatively united in the family Galechiridae. The taxon Dromasauria is shown to be paraphyletic and therefore should be discarded.”

In the TST
both venjukoviamorphs and dicynodonts are large, terrestrial dromasaurs. Here (Fig. 2) are a set of skulls to scale demonstrating the ancestry of the vejukoviamorphs.

Figure 2. Patranomodon and Galeops are sisters, both in the ancestry of dicynodonts and venjukoviamorphs.

Figure 2. Patranomodon and Galeops are sisters, both in the ancestry of dicynodonts and venjukoviamorphs.

This second set of skulls
(Fig. 3) shows the ancestry of the dicynodonts to scale, according to the TST.

Figure 3. The ancestry of dicynodonts includes Patranomodon and Galeops.

Figure 3. The ancestry of dicynodonts includes Patranomodon and Galeops.

A recent look at dicynodonts
(Kammerer 2019) suggested that Biseridens was basal to the clade Dicynodontia, but that cladogram did not test the taxa shown here (Fig. 4).

Figure 4. TST revised with new data on Patranomodon and sister taxa.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

We’ll dive deeper
into Kammerer 2019 in the next few days. Currently I am updating all the data for the TST using photos (Fig. 1) to supplement earlier drawings to fine tune the scoring. Yes, it’s okay to correct earlier errors based on less accurate drawings.


References
Rubidge BS and Hopson JA 1990. A new anomodont therapsid from South Africa and its bearing on the ancestry of Dicynodontia. South African Journal of Science, 86(1), 43-45.
Rubidge BS and Hopson JA 1996. A primitive anomodont therapsid from the base of the Beaufort Group (Upper Permian) of South Africa. Zoological Journal of the Linnean Society, 117: 115–139. Doi:10.1111/j.1096-3642.1996.tb02152.x

wiki/Patranomodon

Hipposaurus moves to the base of the Anomodontia

New data,
a photograph, of the skull of Hipposaurus (Figs. 1, 2; Haughton 1929; WB123), moved this basal therapsid to the base of the Anomodontia (Fig. 3), one node down (more primitive) in the therapsid skull tree (TST, 67 taxa, Fig. 3) and the same in the large reptile tree (LRT, 1440 taxa).

Figure 1. Hipposaurus skull with colors applied and used to create reconstruction on the right. Note the squamosal is largely missing and splinters of bone fill the orbit. Here those splinters are used to recreate a standard squamosal for this clade.

Figure 1. Hipposaurus skull with colors applied and used to create reconstruction on the right. Note the squamosal is largely missing and splinters of bone fill the orbit. Here those splinters are used to recreate a standard squamosal for this clade.

Wikipedia reports,
Broom 1932 considered Hipposaurus a gorgonopsian in the family ‘Ictidorhinidae’. Ictidorhinus nests between Hipposaurus and the gorgonopsians in the TST (Fig. 3). So, for 1932, and prior to the advent of software-driven cladograms, that was a good assessment.

Figure 1. Published material on Hipposaurus permits one to create a reconstruction like this. Not far removed from its ophiacodont / haptodine / pelycosaur precursors, Hipposaurus had longer, more gracile limbs and a distinct sabertooth canine, like Haptodus or Cutleria on steroids!

Figure 2. Published material on Hipposaurus permits one to create a reconstruction like this. Not far removed from its ophiacodont / haptodine / pelycosaur precursors, Hipposaurus had longer, more gracile limbs and a distinct sabertooth canine, like Haptodus or Cutleria on steroids!

Hipposaurus boonstrai (Haughton 1929, skull length 21cm, length 1.2m) Capitanian, Mddle Permian ~260 mya is a basal therapsid. Derived from a sister to  CutleriaHipposaurus phylogenetically preceded the Anomodontia and all higher predatory synapsids, including mammals.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

Much larger than its ancestors, 
Hipposaurus kept the small round skull of its ancestors, but had longer, more slender limbs capable of a more erect pose and probably a faster gait.

Earlier we looked at Dimetropus tracks that were originally attributed to a high-walking Dimetrodon, but fits Hipposaurus those tracks much better. The basalmost therapsid, Cutleria (Lewis and Vaughn 1965; Early Permian) is another possibility known from fewer bones.

Figure 5. Hipposaurus to scale with related taxa. Cutleria is the basalmost therapsid. Stenocybus and the IVPP specimen are also basal anomodonts.

Figure 4. Hipposaurus to scale with related taxa. Cutleria is the basalmost therapsid. Stenocybus and the IVPP specimen are also basal anomodonts.

The relatively larger size of the WB 123 specimen skull of Hipposaurus
indicates it was a later, larger variety of the as yet unknown last common ancestor of anomodonts and kynodonts (Fig. 4).


References
Boonstra LD 1952. Die Gorgonospier-geslag Hipposaurus en die familie Ictidorhinidae: Tydskr. Wet. Kuns 12:142-149.
Broom R 1932. The mammal-like reptiles of South Africa and the origin of mammals. Witherby, London, 376 pp.
Haughton SH 1929. On some new therapsid genera: Annals of the South African Museum 28(1):55-78.
Lewis GE and Vaughn PP 1965. Early Permian Vertebrates from the Cutler Formation of the Placerville Area Colorado. United States Geological Survey Professional Papers 503-C:1-50.

wiki/Hipposaurus

Revisiting Anteosaurus ‘junior’

Earlier we looked at the Kruger et al. 2017 hypothesis
that specimen BP/1/7074 (Fig. 1) was a juvenile Anteosaurus (Fig. 1; Watson 1921). The Therapsid Skull Tree (TST, 67 taxa, Fig. 4). Here, with better skull data, BP/1/7074 still does not nest with Anteosaurus, but I completely understand the earlier hypothesis.

Figure 1. Anteosaurus magnifies compared to the smaller and coeval BP/1/7074 specimen others considered a juvenile. Other more closely related specimens in the TT are also shown alongside BP/1/7074 specimen.

Figure 1. Anteosaurus magnifies compared to the smaller and coeval BP/1/7074 specimen others considered a juvenile. Other more closely related specimens in the TT are also shown alongside BP/1/7074 specimen.

There are a variety of Anteosaurus skulls known.
Here (Fig. 2) is a second one, A. abeli, for comparison (no scale bars). Perhaps another Anteosaurus skull will attract BP/1/7074, but presently tested skulls do not yet do so. Titanophoneus potens (Fig. 1) still nests closer to Anteosaurus while coeval Australosyodon (Fig. 1) nests with BP/1/7074.

Figure 2. Anteosaurus abeli skull with right side grayed out and colors added.

Figure 2. Anteosaurus abeli skull with right side grayed out and colors added.

The whole concept of juveniles of larger genera
looking like neotonous adults of less related genera has a long history with basal therapsids. We looked at one example earlier here with tiny Abadalon.

Figure 6. Anteosaurus scale model.

Figure 3. Anteosaurus scale model.

The TST
(Fig. 4) has seen many score changes over the past weekend, yet remained the same… or almost the same. One taxon shown below will move over one node. I look forward to telling that story.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

For those who really want to know…
Hipposaurus
will move to the base of the Anomodontia.


References
Boonstra LD 1963. Diversity within the South African Dinocephalia. S. Afr. J. Sci. 59: 196-206.
Kammerer CF 2011. Systematics of the Anteosauria (Therapsida: Dinocephalia).
–Journal of Systematic Paleontology: Vol. 9, #2, pp. 261-304.
Kruger A 2014. Ontogeny and cranial morphology of the basal carnivorous dinocephalian, Anteosaurus magnificus from the Tapinocephalus assemblage zone of the South African Karoo. Masters dissertation, University of Wiwatersand, Johannesburg.
Kruger A, Rubidge BS and Abdala F 2017. A juvenile specimen of Anteosaurus magnificus Watson, 1921 (Therapsida: Dinocephalia) from the South African Karoo, and its implications for understanding dinocephalian ontogeny. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2016.1276106
Watson, DMS 1921. The Bases of Classification of the Theriodontia: Proceedings of the Zoological Society of London, 1921: 35-98.

wiki/Anteosaurus

Tiny Abdalodon: a basal cynodont, drags in Lycosuchus

Today’s blogpost returns to basal Therapsida,
after several years of ignoring this clade.

Kammerer 2016 reidentifies an old Procynosuchus skull 
as an even more basal cynodont, now named Abdalodon (Fig. 1). The problem is: cynodonts arise from basal theriodonts (Therocephalia) and Abdalodon nests with another flat-head taxon, Lycosuchus (Fig. 1), a traditional therocephalian in every other cladogram, but not the Therapsid Skull Tree (TST, 67 skull-only taxa, Fig. 2), a sister cladogram to the LRT.

So, where is the cynodont dividing line?
(= which tested taxon is the progenitor of all later cynodonts and mammals?)

It would help if we knew the phylogenetic definition
of Cynodontia because we should never go by traits (which may converge), but only by taxon + taxon + their last common ancestor and all descendants to determine monophyletic clades.

From the Kammerer 2016 abstract:
“Phylogenetic analysis recovers Abdalodon as the sister‐taxon of Charassognathus, forming a clade (Charassognathidae fam. nov.) at the base of Cynodontia. These taxa represent a previously unrecognized radiation of small‐bodied Permian cynodonts. Despite their small size, the holotypes of Abdalodon and Charassognathus probably represent adults and indicate that early evolution of cynodonts may have occurred at small body size, explaining the poor Permian fossil record of the group.”

Figure 1. Abdalodon nests with the many times larger therocephalian Lycosuchus in the LRT.

Figure 1. Abdalodon nests with the many times larger therocephalian Lycosuchus in the LRT.

Hopson and Kitching 2001 defined  Cynodontia
(Fig. 2) as the most inclusive group containing Mammalia, but excluding Bauria. In the TT Abdalodon nests with Lycosuchus on the cynodont side of Bauria.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

So that makes Lycosuchus a cynodont,
by definition.

Figure 2. Procynosuchus, a basal cynodont therapsid synapsid sister to humans in the large reptile tree (prior to the addition of advanced cynodonts including mammals).

Figure 3. Procynosuchus, a basal cynodont therapsid synapsid sister to humans in the large reptile tree (prior to the addition of advanced cynodonts including mammals). This skull has been overinflated dorsoventrally based on the preserved skull, which everyone must have thought was crushed in that dimension.

Earlier we looked at
some Wikipedia writers when they stated, “Exactly where the border between reptile-like amphibians (non-amniote reptiliomorphs) and amniotes lies will probably never be known, as the reproductive structures involved fossilize poorly…” 

Contra that baseless assertion,
with phylogenetic analysis and clades defined by taxa it is easy to determine which taxa are the last common ancestors, sisters to the progenitors of every derived clade in the TT, LRT or LPT. We can tell exactly which taxon was the first to lay amniotic eggs, without having direct evidence of eggs, simply because all of its ancestors in the LRT laid amniotic eggs. In the same way, we can figure out which taxon, among those tested, is the basalmost cynodont. Adding Bauria to the LRT made that happen today.

Let’s talk about size
The extreme size difference between Abdalodon and Lycosuchus (Fig. 1) brings up the possibility of cynodonts going through a phylogenetic size squeeze… retaining juvenile traits into adulthood… neotony… essentially becoming sexually mature at a tiny size for more rapid reproduction, reduced food needs, ease in finding shelters, etc. We’ve seen that before in several clades here, here and here, to name a few.

Figure 4. Charassognathus does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TT.

Figure 4. Charassognathus does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TT.

Kammerer 2016 mentioned another small taxon,
Charassognathus (Fig. 4). In the TST (Fig. 2) Charassognathus nests with Bauria and Promoschorhynchops, within the Therocephalia, distinct from, and not far from Abdalodon and the Cynodontia. So no confirmation here for Kammerer’s proposed clade, ‘Charassognathidae’ (see above).


References
Hopson JA and Kitching JW 2001. A Probainognathian Cynodont from South Africa and the Phylogeny of Nonmammalian Cynodonts” pp 5-35 in: Parish A, et al.  editors, Studies in Organismic and Evolutionary biology in honor of A. W. Crompton. Bullettin of the Museum of Comparative Zoology. Harvard University 156(1).
Kammerer CF 2016. A new taxon of cynodont from the Tropidostoma Assemblage Zone (upper Permian) of South Africa, and the early evolution of Cynodontia. Papers in Palaeontology 2(3): 387–397. https://doi.org/10.1002/spp2.1046

wiki/Bauria
wiki/Abdalodon
wiki/Lycosuchus

Reptilomorpha to scale

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

Giant Mesozoic flat heads: Siderops and Koolasuchus

Little Gerrothorax has a new giant sister, Siderops,
(Fig. 1) in the large reptile tree (LRT, 1440 taxa). This is a traditional nesting recovered by prior workers.

We’re still missing those poorly ossified fingers and toes.
Or did this clade have lobefins (Fig. 2)? Nothing past the wrist is known for any clade members (that I’ve seen). Could go either way with available data… so, don’t assume fingers and toes.

Figure 1. Siderops in several views from Warren and Hutchinson 1983, colors added. The related giant Koolasuchus and small Gerrothorax are added for scale.

Figure 1. Siderops in several views from Warren and Hutchinson 1983, colors added. The related giant Koolasuchus and small Gerrothorax are added for scale. Are these lobefins or did they have feet? And look at the size of those palatal fangs!

Speaking of clades,
both Siderops and Gerrothorax are traditionally considered temnospondyls, which all have fingers and toes. Here they nest prior to traditional temnospondyls, closer to flathead lobefin tetrapods, like Tiktaalik, in the LRT (subset Fig. 2).

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

Figure 2. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data.

Siderops kehli (Warren and Hutchinson 1983; Early Jurassic, 180mya; skull 50cm long, overall 2.5m long) was traditionally considered a chigutisaurid temnospondyl or a brachyopoid. Here Siderops nests with the much smalller Gerrothorax. No branchials and scales were reported. The back of the skull and the extremities are unknown, so modifications were made to reflect that lack of data here.

Koolasuchus cleelandi was a late surviving Early Cretaceous giant from this clade, presently known from just a few bones, like the mandible (Fig. 2).

Tomorrow we’ll take a look
at several giant ‘amphibians’ (= anamniote tetrapods) all to scale.


References
Warren A and Hutchinson M 1983. The last labyrinthodont? A new brachyopoid (Amphibia, Temnospondyli) from the Early Jurassic Evergreen Formation of Queensland, Australia. Philosophical Transactions of The Royal Society B Biological SciencesB 303:1–62.

wiki/Gerrothorax
wiki/Siderops

One of your ancestors, Tinirau enters the LRT

Not sure how I missed this key taxon for seven years…
Swartz 2012 described a transitional Middle Triassic marine sarcopterygian nesting between Ostelepis and Panderichthys at the base of the Tetrapoda in the large reptile tree (LRT, 1440 taxa).

Figure 1a. Tinirau in situ revised.

Figure 1. Tinirau clacke in situ and reconstructed in lateral view from Swartz 2012, colors added. Light/dotted lines are hypothetical. Based on phylogenetic bracketing, the dorsal fins may have been lost already, as in Panderichthys. This is one of your ancestors.

FIgure 1a. Revised reconstruction of Tinirau.

FIgure 1a. Revised reconstruction of Tinirau. Compare to figure 1.

Tinirau clacke (Swartz B 2012; Middle Devonian; UCMP 118605) Distinct from earlier lobefin fish, this one has a skull twice as wide as tall, the skull bones are more tetrapod-like, dorsal ribs and a pelvis make a tentative appearance.

Figure 2. Basal tetrapods to scale. Yellow taxa are temnospondyls. Red taxa are reptilomorphs. Breaking the old paradigm, Acanthostega and Icthyostega are more aquatic than their ancestor, Ossinodus, the first taxa with big limbs and a shorter torso. Silvanerpeton is the basal reptile in the LRT. Perryella is the basal reptilomorph.

Figure 2. Basal tetrapods to scale. Yellow taxa are temnospondyls. Red taxa are reptilomorphs. Breaking the old paradigm, Acanthostega and Icthyostega are more aquatic than their ancestor, Ossinodus, the first taxa with big limbs and a shorter torso. Silvanerpeton is the basal reptile in the LRT. Perryella is the basal reptilomorph.


References
Swartz B 2012. A marine stem-tetrapod from the Devonian of Western North America. PLoS ONE. 7 (3): e33683. doi:10.1371/journal.pone.0033683

wiki/Tinirau

The many faces of Styxosaurus

Styxosaurus snowii (Originally Cimoliasaurus snowii, Williston 1890, KUVP 1301; Welles 1943; Late Cretaceous, Campanian, 80mya; SDSMT 451; Figs. 1, 2) is another giant elasmosaurid with dog-like fangs related to Simolestes in the large reptile tree (LRT, 1438 taxa).

Figure 1. Skull of Styxosaurus (KUVP 1301) from Sachs, Lindgren and Kear 2018, colorized using DGS methods.

Figure 1. Skull of Styxosaurus (KUVP 1301) from Sachs, Lindgren and Kear 2018, colorized using DGS methods. Broken teeth on this side of the skull repaired based on the dimensions of unbroken teeth on the other side of the skull.

Several new papers
(refs below) have taken another look at the skull of Styxosaurus, now known for about 130 years. Prior freehand drawings of the skull (Fig. 2) seem to overlook certain interesting details, many of which are critical for accurate scoring.

Figure 2. The changing face of Styxosaurus from Welles 1890, Otero 2016 and colorized here.

Figure 2. The changing face of Styxosaurus from Welles 1890, Otero 2016 and colorized here. Maybe a little easier to see each bone when colored? 

Overall,
a skeletal reconstruction of Styxosaurus required just a little updating (Fig. 3).

Figure 3. Styxosaurus skeleton as originally drawn and revised here.

Figure 3. Styxosaurus skeleton as originally drawn and revised here.

A biting animation
(Fig. 4) of Styxosaurus shows the interweaving of the oversized teeth. Note the elongate posterior dentary teeth. As in Tricleidus, these would have made effective foot traps when water was being expelled whenever the jaw closed.

Figure 6. Styxosaurus mandible animated.

Figure 4. Styxosaurus mandible animated.


References
Otero RA 2016. Taxonomic reassessment of Hydralmosaurus as Styxosaurus: new insights on the elasmosaurid neck evolution throughout the Cretaceous. PeerJ Figure 3. Styxosaurus skeleton as originally drawn and revised here.
Sachs S, Lindgren J and Kear B 2018. Reassessment of the Styxosaurus snowii (Williston, 1890) holotype specimen and its implications for elasmosaurid plesiosaurian interrelationships. Alcheringa: An Australasian Journal of Palaeontology, DOI: 10.1080/03115518.2018.1508613
Welles SP 1943. Elasmosaurid plesiosaurs with a description of the new material from California and Colorado. University of California Memoirs 13:125-254. figs.1-37., pls.12-29.
Welles SP and Bump J 1949. Alzadasaurus pembertoni, a new elasmosaur from the Upper Cretaceous of South Dakota. Journal of Paleontology 23(5): 521-535.
Williston SW 1890a. Structure of the Plesiosaurian Skull. Science. 16 (405): 262.
Williston SW 1890b. A New Plesiosaur from the Niobrara Cretaceous of Kansas. Transactions of the Annual Meetings of the Kansas Academy of Science. 12: 174–178.

wiki/Styxosaurus