Sookias et al. 2020: Euparkeria updated, cladogram outdated

Cutting to the chase: 
No one has studied and published on Euparkeria (Figs. 3-6) more than Roland Sookias and his colleagues (Sookias et al.  2014, Sookias 2016, Sookias et al. 2020). Unfortunately taxon exclusion mars all of his work (Figs. 1, 2), including his latest, otherwise terrific paper presenting close-up and µCT scans from the ten specimens found in a single locality, all attributed to Euparkeria. This paper is so rich in data, but so poor and misleading in systematics.

From the abstract:
“The archosauriform Euparkeria capensis from the Middle Triassic (Anisian) of South Africa has been of great interest since its initial description in 1913, because its anatomy shed light on the origins and early evolution of crown Archosauria and potentially approached that of the archosaur common ancestor.”

In the large reptile tree (LRT, 1714+ taxa, subset Fig. 1) Euparkeria nests far from Archosauria (= the last common ancestor of birds + crocs). Instead Euparkeria nests at the base of the Euarchosauriformes (= all archosauriforms closer to Euparkeria than to Proterosuchus and the pararchosauriforms, Fig. 1). These clades were separated in 2012 here, and that split has remained steady despite many additional taxa.

Figure 1. Subset of the LRT focusing on Archosauriformes. Clade colors match figure 2 overlay.

Figure 1. Subset of the LRT focusing on Archosauriformes. Clade colors match figure 2 overlay.

Phylogenetic analysis
Sookias et al. 2020 worked from a dataset in Sookias 2016. Sookias 2016 was built on the invalidated Nesbitt 2011 and Sookias et al. 2014. The Sookias et al. 2020 results are typical whenever taxon exclusion shuffles the clades, mixing unrelated taxa together. Clades nest where they do in Sookias 2020 by default. That’s how you get crocs and phytosaurs nesting together and euparkeriids arising from erythrosuchids (Fig. 2), rather that the other way around, as in the LRT (Fig. 1). We’re also wary of any cladogram that includes suprageneric taxa.

Figure 2. Sookias et al. 2020 cladogram lacks enough taxa compared to the LRT (Fig. 2) and so shuffles clades here. Here crocs nest within 'Other Pseudosuchia' and pterosaurs nest within Ornithodira, two clades invalidated by the LRT by adding taxa. Promoting this outdated myth of interrelationships in 2020 is not professional.

Figure 2. Sookias et al. 2020 cladogram lacks enough taxa compared to the LRT (Fig. 2) and so shuffles clades here. Here crocs nest within ‘Other Pseudosuchia’ and pterosaurs nest within Ornithodira, two clades invalidated by the LRT by adding taxa. Promoting this outdated myth of interrelationships in 2020 is not professional. Dongusuchus and Dorosuchus are know from bits and pieces of the post-crania.

Euparkeria has been studied previously,
but never so completely as in Sookias et al. 2020. As in Ewer (1965, Fig. 3) Sookias et al. present a freehand diagram chimaera skull (Figs. 4, 5) that combines data from several specimens they consider to be conspecific.

Figure x. Previous views of Euparkeria.

Figure 3. Previous views of Euparkeria.

Comparing a photo of the SAM 5867 specimen
to the Sookias et al. diagram may be instructive. Did they get all the details right?

Figure x. How does the skull of the 5867 specimen of Euparkeria compare to the diagram? Here they are to the same scale.

Figure 4. How does the skull of the 5867 specimen of Euparkeria compare to the diagram? Here they are to the same scale. You decide on the details.

Several color photos were included in Sookias et al. 2020,
so it is surprising that their diagram lacks colors (Fig. 5 left column). When colors are added, the bones lump and separate as well as the LRT lumps and separates taxa.

Figure x. Diagram from Sookias 2020 at left. Rearranged and colored at right for ease of viewing.

Figure 5. Diagram from Sookias et al.  2020 at left. Rearranged and colored at right for ease of viewing.

Using a little DGS on a skull tracing of the SAM 4067a specimen
(Fig. 6) permits one to copy and paste elements from the left and right to create a reconstruction (Fig. 6) without reverting to the unconscious bias that attends all freehand drawings. Broom 1913 assigned this specimen to Browniella africana. Haughton 1922 considered Browniella a junior synonym and this synonymy has been accepted by all prior workers. No prior workers provided a reconstruction for accurate scoring. They just  ‘eye-balled’ the roadkill skull.

Figure 1. The SAM 4967a specimen attributed to Euparkeria. Images from Sookias et al. 2020 with colors and reconstruction added here.

Figure 6. Browniella africana, the SAM 4967a specimen attributed to Euparkeria. Images from Sookias et al. 2020 with colors and reconstruction added here.

Euparkeria capensis (Broom 1913, SAM 5867) Early Triassic, ~247 mya, 60 centimeter length is derived from the FMNH UC 1528 specimen of Youngoides (Fig. 7), a taxon ignored by Sookias et al. An unpublished paper can be found on ResearchGate.net.

The SAM 5867 specimen of Euparkeria nests between Pararchosauriformes, like Polymorphodon (Fig. 8), and all higher Euarchosauriformes like Garjainia (Fig. 9). The SAM 5867 specimen nests at the base of the Euparkeriidae, which presently include only two other tax, the SAM 4067a specimen (Fig. 6) and Osmolskina, which nest with each other (Fig. 1).

Figure 1. Youngoides romeri FMNH UC1528 demonstrates an early appearance of the antorbital fenestra in the Archosauriformes. This specimen is the outgroup to Proterosuchus, the traditional basal member of the Archosauriformes. 

Figure 7. Youngoides romeri FMNH UC1528 demonstrates an early appearance of the antorbital fenestra in the Archosauriformes. This specimen is the outgroup to the Archosauriformes.

Figure 1. Skull elements of Polymorphodon.

Figure 8. Skull elements of Polymorphodon, basal to proterochampsids.

Figure 1. Garjainia at several scales and views.

Figure 9. Garjainia at several scales and views.

Osmolskina czatkowicensis (Borsuk-Biaynicka and Evans 2009), Early Triassic,

Browniella africana  (Fig. 6, SAM 4067A) is a eurparkeriid more closely related to Osmolskina in the LRT.

Sometimes additional detail comes in handy.
And Sookias et al.  2020 provided that additional detail.

Unfortunately, without a valid phylogenetic context
you won’t know the outgroups, ingroups, ancestors and descendants of any taxon under your µCT scanner. Sometimes you need a metaphorical ‘panoramic camera’ like the LRT, for that wide gamut view that minimizes taxon exclusion.


References
Broom R 1913. On the South-African Pseudosuchian Euparkeria and Allied Genera. Proceedings of the Zoological Society of London 83: 619–633.
Borsuk-Bialynicka M and Evans SE 2009. Cranial and mandibular osteology of the Early Triassic archosauriform Osmolskina czatkowicensis from Poland. Palaeontologia Polonica 65, 235–281.
Ewer RF 1965. The Anatomy of the Thecodont Reptile Euparkeria capensis Broom Philosophical Transactions of the Royal Society London B 248 379-435.
doi: 10.1098/rstb.1965.0003
Haughton S 1922. On the reptilian genera Euparkeria Broom, and Mesosuchus Watson. Transactions of the Royal Society South Africa 10, 81–88. (doi:10.1080/00359192209519270
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bull. Am. Mus. Nat. Hist. 352, 1–292. (doi:10.1206/352.1)
Nesbitt SJ et al. 2017 The earliest bird-line archosaurs and the assembly of the dinosaur body plan. Nature 544, 484–487.
Sookias RB, Sullivan C, Liu J, Butler RJ. 2014 Systematics of putative euparkeriids (Diapsida: Archosauriformes) from the Triassic of China. PeerJ2, e658 (doi:10.7717/peerj.658)
Sookias RB 2016. The relationships of the Euparkeriidae and the rise of Archosauria. Royal Soceity open science 3, 150674. (doi:10.1098/rsos. 150674)
Sookias RB, Dilkes D, Sobral G, Smith RMH, Wolvaardt FP, Arcucci AB, Bhullar B-AS and Werneburg I 2020. The craniomandibular anatomy of the early archosauriform Euparkeria capensis and the dawn of the archosaur skull. R. Soc. Open Sci. 7: 200116.
http://dx.doi.org/10.1098/rsos.200116

https://www.researchgate.net/publication/328388486_Youngoides_romeri_and_the_origin_of_the_Archosauriformes

wiki/Osmolskina
http://reptileevolution.com/euparkeria.htm
http://reptileevolution.com/osmolskina.htm

Erpetosuchus now nests outside of the Archosauria + Poposauria in the LRT

Based on its uniquely inset tooth row
(Figs. 1–3) Erpetosuchus (Newton 1894; Late Carnian, Late Triassic) has been a traditional enigma taxon.

Figure 1. Erpetosuchus in several views. Here the post-crania of Parringtonia is added.

Figure 1. Erpetosuchus in several views. Here the post-crania of Parringtonia is added.

According to Wikipedia,
“The relationship of Erpetosuchus to other archosaurs is uncertain. In 2000 and 2002, it was considered a close relative of the group Crocodylomorpha, which includes living crocodylians and many extinct relatives. However, this relationship was questioned in a 2012 analysis that found the phylogenetic placement of Erpetosuchus to be very uncertain.”

“Benton and Walker (2002) found the same sister-group relationship and proposed the name Bathyotica for the clade containing Erpetosuchus and Crocodylomorpha.”

“Nesbitt and Butler (2012) included Erpetosuchus within a more comprehensive phylogenetic analysis and found it to group with the archosaur Parringtonia (Fig. 1) from the Middle Triassic of Tanzania. Both were part of the clade Erpetosuchidae. Nesbitt and Butler did not find support for the sister-group relationship between Erpetosuchus and Crocodylomorpha. Instead, erpetosuchids formed a polytomy or unresolved evolutionary relationship at the base of Archosauria along with several other groups. It could take many positions within Archosauria, but none were as a sister taxon of Crocodylomorpha.”

Figure 2. Erpetosuchus, Tarjadia, Parringtonia now nest with Decurisuchus outside of the Archosauria + Poposauria.

Figure 2. Erpetosuchus, Tarjadia, Parringtonia now nest with Decurisuchus outside of the Archosauria + Poposauria. Note the extreme anterior lean of the quadrate and quadratojugal here, convergent with crocodyliformes.

A recent review of the Crocodylomorpha
subset of the large reptile tree (LRT, 1660+ taxa; Fig. 4) knocked Erpetosuchus out of the Crocodylomorpha and out of the Archosauria. Erpetosuchus and other members assigned to the Erpetosuchidae (Pagosvenator, Parringtonia, Tarjadia (Figs. 2-3), but not the basal marine crocodile Dyoplax, at least not yet) now nest with Decuriasuchus (Figs. 2–3) in the LRT. This clade nests between Rauisuchia and Poposauria + Archosauria (Fig. 4).

Figure 1. Erpetosuchus and kin illustrated to scale. Parringtonia + Tarjadia + Erpetosuchus now nest with Decuriasuchus basal to Poposaurs + Archosauria.

Figure 3. Erpetosuchus and kin illustrated to scale. Parringtonia + Tarjadia + Erpetosuchus now nest with Decuriasuchus basal to Poposaurs + Archosauria.

The small size of Erpetosuchus
(Fig. 3) is a derived trait, following several much larger ancestors. Alas, as far as we know, Erpetosuchus was a terminal taxon, leaving no descendants.

Figure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Figure 4. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

Why was Erpetosuchus traditionally considered ‘crocodile-like’?
The extreme anterior lean of the quadrate and quadratojugal are typical crocodile traits shared by convergence with members of the clade Erpetosuchidae (including Decuriasuchus).

Eagle-eyed readers may note
a few other changes in the Crocodylomorpha subset of the LRT (Fig. 4). We’ll deal with these in future blogposts.


References
Benton MJ and Walker AD 2002. Erpetosuchus, a crocodile-like basal archosaur from the Late Triassic of Elgin, Scotland, Zoological Journal of the Linnean Society 136:25-47.
Nesbitt SJ and Butler RJ 2012. Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae. Geological Magazine: 1. doi:10.1017/S0016756812000362
Nesbitt SJ, Stocker MR, Parke WGr, Wood TA, Sidor CA and Angielczy KD 2018. The braincase and endocast of Parringtonia gracilis, a Middle Triassic suchian (Archosaur: Pseudosuchia) Journal of Vertebrate Paleontology 37, Memoir 17: Vertebrate and Climatic Evolution in the Triassic Rift Basins of Tanzania and Zambia.
Newton TE 1894. Reptiles from the Elgin Sandstone—Description of two new genera. Philosophical Transactions of the Royal Society of London, B, 185:573–607.

wiki/Tarjadia
wiki/Parringtonia
wiki/Erpetosuchus

http://reptileevolution.com/decuriasuchus.htm

Non-dinosaurian Dinosauromorpha (Langer et al. 2013)

Continuing to push Lagerpeton as a “dinosauromorph” (which is traditional thinking), Langer et al. (2013) continues to ignore certain basic facts starting in the feet that divide pararchosauriforms (including Lagerpeton) and euarchosauriforms (including dinosaurs) into two major clades.

The feet of Euarchosauriformes (above in white) and Pararchosauriformes (below in grey). No higher euarchosauriformes have a longer digit 4 than 3. Both sets of feet share more traits with each other, which removes Lagerpeton from the lineage of dinosaurs, but puts it in the line of descent from Diandongosuchus.

Figure 1. Click to enlarge. The feet of Euarchosauriformes (above in white) and Pararchosauriformes (below in grey). No higher euarchosauriformes have a longer digit 4 than 3. Both clades share more foot traits with each other, which removes Lagerpeton from the lineage of dinosaurs in the Euarchosauriformes, and puts it in the line of descent from Diandongosuchus (with its long digit 4) and/or Proterochampsa (with its short digit 1). Also note that the ascending process of the astragalus is posterior in Lagerpeton, anterior in dinosaurs.

Euarchosauriformes
It’s unfortunate that so few euarchosauriform feet are known that include a complete digit 4, but what we do know demonstrates that digit 4 is always shorter than 3 and metatarsal 4 is always shorter than mt3.

Pararchosauriformes
In this clade pedal digit 4 can sometimes be longer than 3 and metarsal 4 is never shorter than mt3. Sometimes pedal digit 4 is reduced to a vestige, other times, even within a genus, it is not. In any case, Lagerpeton belongs in this clade, a small biped at the acme of a  large, flat-headed, quadrupedal clade. It does not belong with dinosaurs or their short pedal digit 4 kin. In Lagerpeton, the astragalus flange rises in back of the tibia, not in the front, as in dinosaurs.

The way to separate the Euarchosauriformes from the Pararchosaurifomes
is to introduce protorosaurs, Youngina, Youngoides, Choristodera, Doswellia and the traditional archosauriformes, as demonstrated by the large reptile tree.

Mistaking Early Triassic bipedal lizard tracks for dinosauromorph tracks
Earlier we discussed the mistakes of Brusatte et al. (2012) who claimed that certain ichnites related to Rotodactylus in the Early Triassic belonged to lagerpetids, when in reality they belong to cosesaurids, in the ancestry of pterosaurs.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Langer MC, Nesbitt SJ, Bittencourt JS and Irmis RB 2013.  Non-dinosaurian Dinosauromorpha.  Geological Society, London, Special Publications v.379, first published February 13, 2013; doi 10.1144/SP379.9 From: Nesbitt SJ, Desojo JB and Irmis RB eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.9 # The Geological Society of London 2013.

Archosauria: Watch out how you use this taxon!

According to EvoWikiArchosauria (Cope 1869 emended by Gauthier 1984 “ruling reptiles”) sensu stricto, or sensu Gauthier, is the crown clade of Archosauromorpha and is defined as “the common ancestor of birds and crocodiles and all descendants thereof.

In older, traditional smaller reptile trees, pterosaurs are included in the Archosauria as they were once, and are still traditionally considered close to dinosaurs, despite the fact that the two share very few traits. No series of taxa within or just outside the Archosauria demonstrate a gradual accumulation of pterosaurian traits. Rather, that gradual accumulation of traits is found in a series of now extinct tritosaur lizards, once and traditionally mistakenly considered prolacertiformes or protorosaurs.

Figure 1. Segment of the large reptile tree showing the Euarchosauriformes. The Archosauria is highlighted at the bottom.

Figure 1. Segment of the large reptile tree showing the Euarchosauriformes. The Archosauria is highlighted at the bottom.

The large reptile tree (Fig. 1) demonstrates that the outgroup for the dinosaurs (including birds) is the crocodylomorpha. So birds and crocs share last common ancestor around Turfanosuchus and Decuriasuchus. So the Archosauria is now restricted to just the Crocodylomorpha and the Dinosauria and the smaller clades and taxa they include. Note the basal placement of rauisuchoids preceding the archosauria.

Because prior studies did not include so many basal taxa, they included many additional ‘by default’ mismatches nesting between crocs and dinos. Let’s have a look at them.

 A tree recovered from Gauthier 1986

Figure 2. A tree recovered from Gauthier 1986 (form Wiki) Pararchosauriformes are in green boxes. Pterosaurs are included within Ornithodira. Crocs and dinos here are greatly separated, so all basal forms back to a last common ancestor are included within the Archosauria.

Gauthier 1986
This very early smaller study included Proterochampsidae and Parasuchia, two suprageneric clades now known to nest outside the Euarchosauriformes when more taxa, like various Youngina and Choristodera, are included. It also employed suprageneric taxa instead of generic taxa (which always invites trouble), and certainly two few taxa to demonstrate a gradual accumulation of traits in derived forms. Gauthier employs the Ornithodira, which includes pterosaurs. Not sure how you would score such a taxon, with wings or without?

The Archosauria according to Sereno 1991 from Wiki.

Figure 3. The Archosauria according to Sereno 1991 from Wiki. Light red arrows shows that crocs and dinos are still far apart here.

Sereno 1991
Five years later, but still early in the world of PAUP, Sereno (1991) moves Euparkeria outside of the Archosauria. Crocs nest within Suchia here. Ornithodira is divided into three clades. Pterosauria is highlighted because it doesn’t belong here, but in lizards (not employed). As in Gauthier (1986) Proterochampsidae and Parasuchia are also not correctly nested within these Euarchosauriformes, but nest here by default.

Benton 2004 diagrams the Archosauria.

Figure 4. Benton 2004 diagrams the Archosauria but includes two lepidosauromorphs and separates the crocs into three widely divided clades.  Lagerpeton is more closely related to Proterochampsidae than dinos when Tropidosuchus is employed, which is not the case here. Clearly there needed to be more attention paid to basal crocodylomorphs that nest in three widely varied nodes here. Suprageneric taxa, like Crocodylomorpha, are probably the cause of the problem.

Benton 2004
Thirteen years later, and four years after Peters (2000), Benton (2004, Fig. 4) expanded on earlier studies, still employing suprageneric taxa, but moving towards employing more generic taxa. The topology was largely the same, though, as in prior studies (Figs. 2, 3). Yes, unbelievably, that’s  Hyperdapedon as a basal taxon.

Archosauria according to Brusatte 2010. Various clades found in the large reptile tree are identified by color boxes.

Figure 5. Archosauria according to Brusatte 2010. Various clades found in the large reptile tree are identified by color boxes. Yes, there appear to be problems here as compared to the large reptile tree results. 

Brusatte et al. 2010
Six years later, and a full ten years after Peters (2000), Brusatte et al. (2010) employed still more generic taxa, keeping Pterosauria and Phytosauria but dropping Proterochampsidae. Here Gracilisuchus and Erpetosuchus correctly nested with Crocodylomorpha, but Scleromochlus did not. Taxa found to nest as poposaurids in the large reptile tree are divided, unresolved and widely separated here. Note that no taxa are shown to be basal to the Archosauria (which is always a problem!) and the basal taxa in each branch (Scleromochlus, Pterosauria, Phytosauria (=Parasuchia) and Aetosauria do not resemble one another — but they should if they truly reflect and model actual evolutionary paths.

Only the large reptile tree provides the gradual accumulation of traits in all derived taxa from more primitive taxa. So when you talk about archosaurs, it would be a good idea to restrict your discussion to crocs and dinos, which by definition, make up this clade. Keep the poposaurs within the Dinosauria. The others are all outliers.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Cope ED 1869.
Synopsis of the extinct Batrachia, Reptilia and Aves of North America. Transactions of the America Philosophical Society 14: 1–252.
Gauthier J1984. A cladistic analysis of the higher systematic categories of the Diapsida. [dissertation]. Available from University Microfilms International, Ann Arbor, #85-12825, vii + 564 pp.
Gauthier J 1986. Saurischian monophyly and the origin of birds. Memoirs of the California Academy of Sciences 8: 1-55.
Sereno PC 1991. Basal archosaurs: phylogenetic relationships and functional implications. J Vert Paleo 11 (Supp) Mem 2: 1–53.

The Origin of Dinosaurs Goes Way, Way Back

Dinosaurs: A Concise Natural History by Fastovsky and Weishampel 2012

Dinosaurs: A Concise Natural History by Fastovsky and Weishampel 2012

Hot on the heels of the rediscovery of Nyasasaurus (did it have heels?), a new book by Fastovsky and Weishampel (2012) Dinosaurs: A Concise Natural History (2nd Ed) discusses the origin of dinosaurs and many other dino topics. That publication inspired this post.

Earlier we looked at various competing hypotheses for the origin of the dinosaurs, closer to their departure from other reptiles, and why pterosaurs and phytosaurs have no business in the lineage of dinosaurs. Earlier we also looked at the base of the Archosauria and the Origin of the Dinosauria. Here we’re going to take this story way, way back and cover more bases.

We’re going to take dinosaur origins back to Ichthyostega, an early tetrapod. Why? Because we can! We have the only large reptile tree that documents every evolutionary step it took to create dinosaurs from their ancestral pollywogs in the Devonian. And we’ll met several dozen very interesting taxa along the way. For more details I encourage you to click on the links that interest you. There are more details and images there. And please remember, these are NOT the direct ancestors, but the closest reps we have to that unbroken string of unknown parents, grandparents, great grandparents, etc. etc.

Icthythostega (still pretty fishy), Pederpes (down to only five toes), Proterogyrinus (nostrils move to the snout tip), Eldeceeon (long toes), Seymouria (more terrestrial but convergently off to the side), Utegenia (more aquatic and off to the froggy side), Silvanerpeton (closer to Eldeceeon, with larger eyes, longer fifth toe) and Gephyrostegus (ankle includes fused elements creating an astragalus, a premaxilla/maxilla notch is present, more gracile limbs and a trend toward a much smaller size, which makes amniotic eggs possible) brings us to the base of the Reptilia.

Cephalerpeton (lose of palatal fangs, fusion of the intertemporal, straight posterior squamosal and longer, more gracile limbs) nests at the base of the otherwise diphyletic Reptilia.

Westlothiana (a little too long waisted, but no tabular horns, mandible reduced to three major bones in lateral view, the premaxilla did not descend), nests at the base of the new Archosauromorpha, followed by Paleothyris (now that’s more like it, short-waisted, athletic, enlarged canines, longer rostrum, high coronoid process, ossified scapulocoracoid, more gracile limbs and toes), Brouffia (minor improvements), Coelostegus (maxilla deeper, supratemporals angled down, vertebrae taller), Hylonomus (jugal invades the squamosal, gastralia present), Protorothyris (larger skull and deeper canine) and Aerosaurus (reduced squamosal, first appearance of the lateral temporal fenestra, but getting too robust in the postcrania) take us to the base of the Synapsida.

Heleosaurus (not so robust, smaller skull, longer neck, pelvis larger than scapulocoracoids, longer limbs, reduced to absent posterior ribs), Milleropsis (finally a tail is preserved and it is whip-like, metacarpal 3 is longer than 4, possible biped), Eudibamus (longer neck, upper temporal fenestra gives us a diapsid configuration, definite biped with another attenuated tail, but the toes were way too asymmetrical), Spinoaequalis (taller tail spines link this taxon to water, ulna and radius are longer and straighter, the tibia and fibula have less interossial space) and Petrolacosaurus (shorter rostrum, larger orbit, longer neck, whip-like tail, tibia and fibula bowed apart) take us past the base of the Diapsida.

Acerosodontosaurus (a little too robust, with smaller cervicals and with forelimbs too long and robust,) and Adelosaurus (smaller and more gracile with shorter fingers and toes) lead toward the Enaoliosauria, a large clade of aquatic and marine reptiles.

Tangasaurus (neck getting way too long, but limbs large and subequal) nests at the base of the Tangasauria (the more terrestrial lineage) followed by Thadeosaurus (gracile palatal elements, sterna appear for a short time), Orovenator (large naris, descending premaxilla, gracile posterior skull elements, skull taller than wide, rostrum concave dorsally) and Youngina (BPI3859) (taller lateral temporal fenestra, maxilla taller, pubis and ischium separate elements) take us to the base of the Protorosauria, which diverge at this point.

Youngina (AMNH5661) (skull a little too flat and wide, heading toward pararchosauriformes) and Youngoides (UC1528)  (smaller temporal fenestra, frontals without posterior process, pineal foramen tiny, quadrate leans anteriorly, possible antorbital fenestra) take us to the base of the Archosauriformes.

Now we come to more familiar territory, the base of the Euarchosauriformes, with Proterosuchus (first verified appearance of the antorbital fenestra, drooping premaxilla, mandibular fenestra, more robust taller cervicals, lower limb elements not bowed), Fugusuchus (larger more robust skull, fewer larger teeth), Garjainia (convex maxilla, naris rises on nose tip, shorter tail, deeper chest, deeper pelvis directed ventrally, more upright limbs), Euparkeria (smaller, more gracile, longer tail, higher naris, hooked fifth metatarsal), Ornithosuchus (a side branch experimenting with both convergent bipedality (deeper pelvis) and a deeper, narrower skull) and Vjushkovia (not so derived, taking its time evolving evidently, but with a high naris and pedal digit 3 longer than 4) take us to the base of the Rausuchia and a fish-eating side branch that includes the long-necked Yarasuchus and Ticinosuchus, which had lost its premaxillary teeth.

Now we hit the base of the Archosauria represented by Decuriasuchus (super slender forelimbs and pectoral girdle), Turfanosuchus (looks like a reptilian horse with a smaller skull, longer neck and a high carriage) and Gracilisuchus (at the base of the crocodylomorpha). Some early members were bipeds.

Figure 1. Lewisuchus, a tiny predecessor to crocs and dinos (including birds).

Figure 1. Lewisuchus, a tiny predecessor to crocs and dinos (including birds).

Lewisuchus is known from too few pieces, but might be just what we’re looking for in a basalmost dino. It likely had much longer hind limbs than forelimbs, considering the general proportions that are known. And it was much smaller than its closest kin. Such traits could lead toward crocs or dinos, but at this point the back of the skull suggests this taxon leads to a third bipedal lineage without many descendants.

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Trialestes (had croc-like elongated carpals, a tridactyl pes, pelvis perforated, femoral head inturned, vertebral centra with excavated lateral surfaces, longer radius than humerus, but late Triassic) and probably Nyasasaurus (large deltopectoral crest and Early Middle Triassic) nest at the base of the Dinosauria, specifically the Theropoda. Panphagia and Pampadromaeus nest at the base of the Phytodinosauria (sauropodomorphs + the other herby dinos, enlargement of premaxillary teeth, longer neck). Pisanosaurus (shorter neck, blunter teeth) nests at the base of the Poposauridae (traditionally considered dinosaur-like rauisuchians due to the extended calcaneum, but here nesting with dinos). Massospondylus (more cervicals, shorter forelimb, two lateral fingers vestigial) nests at the base of the Sauropodomorpha. Daemonosaurus (reduced antorbital fenestra, longer premaxillary fangs, postnarial process of premaxilla longer, shorter jaw) nests at the base of the Ornithischia.

Figure 1. The origin of dinosaurs as portrayed by the phylogenetic series of closest known sister taxa to the actual unknown undiscovered true lineage of dinosaurs. A. Youngina, B. Proterosuchus, C. Garjainia, D. Euparkeria, Vjushkovia, 1. Ticinosuchus, 2. Yarasuchus, 3. Decuriasuchus, 4. Turfanosuchus, 5. Gracilisuchus, 6. PVL 4597, 7. Trialestes, 8. Herrerasaurus, 9. Marasuchus, 10. Daemonosaurus.

Figure 3. The origin of dinosaurs as portrayed by the phylogenetic series of closest known sister taxa to the actual unknown undiscovered true lineage of dinosaurs. A. Youngina, B. Proterosuchus, C. Garjainia, D. Euparkeria, Vjushkovia, 1. Ticinosuchus, 2. Yarasuchus, 3. Decuriasuchus, 4. Turfanosuchus, 5. Gracilisuchus, 6. PVL 4597, 7. Trialestes, 8. Herrerasaurus, 9. Marasuchus, 10. Daemonosaurus.

YouTube has a short video on the Origin of Dinosaurs that pretty much follows the traditional route.

Please remember that, despite tradition and textbooks, the Phytosauria, Proterochampsia and Pterosauria have nothing to do with dinosaur origins. The Proterochampsia include Dromomeron and Lagerpeton, as close relatives to Tropidosuchus, another convergent biped. A large reptile tree demonstrates this. And this experiment can be repeated if anyone cares to add a taxa or two.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Various other online refs
Discovery News
Wiki-Dinosaur
Science News