SVP abstracts 2017: Eudibamus forelimb description

Sumida et al. 2017 bring us new information
on the pectoral region of Eudibamus, (Figs. 1,2) an early likely biped in the sprawling manner of the unrelated extant iguanian lizards, Chlamydosaurus and Basiliscus by convergence.

Unfortunately,
Sumida et al. continue to cling to the invalidated tradition that Eudibamus is a bolosaurid, largely based on convergent tooth shapes and taxon exclusion in their analyses.

Figure 1. Basal diasids and proto-diapsids. Largely ignored these putative synapsids actually split from other synapsids while retaining the temporal fenestra trait that serves as the basis for the addition of upper temporal fenestra in diapsids. Included here are Protorothyris, Archaeovenator, Mycterosaurus, Heleosaurus, Mesenosaurus, Broomia, Milleropsis, Eudibamus, Petrolacosaurus, Spinoaequalis, and Tangasaurus.

Figure 1. Basal diasids and proto-diapsids. Largely ignored these putative synapsids actually split from other synapsids while retaining the temporal fenestra trait that serves as the basis for the addition of upper temporal fenestra in diapsids. Included here are Protorothyris, Archaeovenator, Mycterosaurus, Heleosaurus, Mesenosaurus, Broomia, Milleropsis, Eudibamus, Petrolacosaurus, Spinoaequalis, and Tangasaurus.

From the Sumida et al. abstract
Eudibamus cursoris, a bolosaurid parareptile, from the Early Permian Tambach Formation (approximately 290 mybp), Thüringer Wald (Thuringian Forest), of central Germany, has been interpreted as the earliest known facultative biped. This was initially proposed based on the postcranial limb proportions in the type specimen (MNG [Museum der Natur, Gotha, Germany] 8852), but the forelimb itself has never been formally described. A nearly complete left, and partial right forelimb are preserved in the type specimen. The forelimb is less than 60% the length of the hindlimb. Only a thin, blade-like scapula is visible. Brachial, antebrachial, and manual elements are slender and elongate compared to those of other basal amniotes. The humerus has two well developed distal condyles with terminally facing articular facets. Delto-pectoral attachments were along a narrow ridge. The radius and ulna are nearly subequal in length. Conspicuously, the ulna lacks a well developed olecranon process. Carpals are proximodistally elongate compared to other basal amniotes. The intermedium and lateral centrale and the radiale and medial centrale articulate end-to-end, and their combined lengths equal that of the ulnare; the intermedium and radiale, and the medial and lateral centralia are equal in length. Four distal carpals are visible, it is unclear whether whether the fifth is truly absent or simply unossified. The distal carpal associated with digit two is reduced to a tiny pebble of bone, whereas that associated with digit four is largest and somewhat wedge shaped. Four metacarpals, likely equivalent to digits two-five, are present. The proximal portion of metacarpal two is present but length of the entire element cannot be determined. No elements of digit one can be seen, though its absence could be an artifact of preservation; however, the presence of only four distal carpals suggests Eudibamus may have had only four manual digits. Three phalanges are preserved in digits three and four. Both come to blunt tips and neither exhibits a significantly elongate penultimate element. The overall limb proportions seen in Eudibamus could suggest facultative bipedality or vertical clinging and leaping. However, vertical clingers and leapers normally have at least one is proportionately elongate manual digit and well-developed manual claws. Neither phalangeal proportions, nor the two well-developed terminal phalanges show such adaptations in Eudibamus and its interpretation as a facultative biped remains the most plausible interpretation of its postcranial anatomy.”

Figure 1. Click to enlarge. Eudibamus in situ (above), traced (middle) and reconstructed (below). The revised skull retains a large orbit and has a shorter rostrum.

Figure 1. Click to enlarge. Eudibamus in situ (above), traced (middle) and reconstructed (below). The revised skull retains a large orbit and has a shorter rostrum.

First of all,
Parareptilia has been invalidated as a monophyletic clade since 2012. 

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Since 2011
Eudibamus has nested with other slender, speedy, basalmost archoauromorph diapsids (Araeoscelis, Petrolacosaurus and kin) (Fig. 1) in the large reptile tree, far from the squat, slow, bolosaurids, like Bolosaurus and Belebey that nest with diadectids and pareiasaurs.

Let’s look again
at the pectoral region and forelimb of Eudibamus as listed by Sumida et al. above. Note how many of these traits are also present in basal archosauromorph diapsid taxa and their outgroups shown in figure 1 above. Bolosaurids, by contrast, are known chiefly by skull material, so direct comparisons to forelimbs cannot be made.

Imagine the co-authors, grad students 
who disagree with Dr. Sumida on the phylogenetic position of Eudibamus, perhaps after testing a larger gamut of taxa or by reading this blog. All co-authors sign that they agree with what is in the abstract. This is how paleontology puts on blinders, clings to traditions and generally avoids rocking the hypotheses of senior professors.

Fortunately
non-academic renegades and independent researchers have no such restrictions, but are free to explore and experiment.

References
Sumida SS et al. 2017. Structure of the pectoral limb of the early Permian bolosaurid reptile Eudibamus cursors: further evidence supporting it as the earliest known facultative biped. SVP abstracts 2017.

Sumida 2009 Ted Talk video
What is Eudibamus?

Advertisements

Go back far enough in dinosaur ancestry and you come to: Heleosaurus

With our never-ending fascination with dinosaurs
it’s interesting to list some of the taxa in their deep, deep!, deep!! ancestry. One such ancestor is Heleosaurus (Fig. 1; Broom 1907; Middle Permian ~270 mya, ~30 cm snout to vent length), the first known basal prodiapsid, the clade the includes diapsids (sans lepidosaurs, which are unrelated but share the same skull topology by convergence).

Figure 1. Heleosaurus is closer to the main lineage of dinosaurs. It retained canine fangs.

Figure 1. Heleosaurus is close to the main lineage of dinosaurs. It retained canine fangs. Note the squamosal distinct from the quadratojugal, as in Nikkasaurus. Also note the continuing lacrimal contact with the naris, as in Protorothyris.

But first
I want to discuss a derived Heleosaurus cousin, Nikkasaurus (Ivahnenko 2000; Fig. 2), also one of the most basal prodiapsids.

It is only by coincidence
that Ivahnenko labeled Nikkasaurus one of his ‘Dinomorpha,’ a clade name ignored by other authors. Wikipedia considers Nikkasaurus one of the Therapsida and possibly a relic of a more ancient stage of therapsid development. Like Heleosaurus, Nikkasaurus had a single synapsid-like lateral temporal fenestra. Only their nesting outside of that clade and basal to the clade Diapsida in the LRT tell us what they really are. Most of the time, as you know, we can tell what a taxon is simply by looking at it. In this case, as in only a few others, we cannot do so readily.

Figure 1. Nikkasaurus, one of the most primitive prodiapsids, direct but ancient ancestors of dinosaurs.

Figure 2. Nikkasaurus, one of the most primitive prodiapsids, direct but ancient ancestors of dinosaurs.

Nikkasaurus tatarinovi (Ivahnenko 2000) Middle Permian was a tiny basal prodiapsid with a large orbit. It retained a large quadratojugal. The fossil is missing the squamosal. Others mistakenly considered the quadratojugal the squamosal, as in therapsids. That’s an easy mistake to make. Compare this bone to the QJ in Heleosaurus (Fig. 1), another prodiapsid. Nikkasaurus has small sharp teeth and no canine fang. Nikkasaurus is a sister to Mycterosaurus. They both share a large orbit and fairly long snout. What appears to be a retroarticular process may be something else awaiting inspection in the actual fossil. Based on all other data points, I don’t trust that post-dentary data. It doesn’t match the in situ figure.

Distinct from other prodiapsids,
the Nikkasaurus, Mycerosaurus and Mesenosaurus maxilla extended dorsally, overlapping the lacrimal and contacting the nasal, as it does in Dimetrodon and basal therapsids like Hipposaurus and Stenocybus. This trait tends to be homoplastic / convergent in all derived taxa, but the timing differs in separate clades.

Figure 1. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it.

Figure 2. Nikkasaurus and what little is known of its postcrania. Above, in situ. Below, tentative reconstruction. If anyone has a picture of the fossil itself, please send it. Note the posterior mandible mismatch in the purported retroarticular process. I suspect the process is not there.

And finally we come back to Heleosaurus.
Slightly closer to the lineage of dinosaurs is the slightly more basal prodiapsid, Heleosaurus (Fig. 2), which retained canine fangs, had a more typical posterior mandible and retained a lacrimal / naris contact. This naris trait was retained by Petrolacosaurus, Eudibamus, Spinoaequalis and other basal diapsids (archosauromorpha with both upper and lateral temporal fenestra ). The maxilla did not rise again to cut off lacrimal contact with the naris in the ancestry of dinosaurs until the small Youngina specimens huddled together, SAM K 7710 and every more derived taxon thereafter, up to and including dinos.

References
Broom R 1907. On some new fossil reptiles from the Karroo beds of Victoria West, South Africa. Transactions of the South African Philosophical Society 18:31–42.
Ivahnenko MF 2000. 
Cranial morphology and evolution of Permian Dinomorpha (Eotherapsida) of eastern Europe. Paleontological Journal 42(9):859-995. DOI: 10.1134/S0031030108090013

It’s not Hovasaurus – and it’s not in a museum

A slight departure today
to the world of fossil commerce. This reptile is new to Science, so it should be presented to a museum for study, but it’s for sale online. And it was misidentified by the proprietors (who have been notified).

Figure 1. Specimen wrongly interpreted as Hovasaurus from FineFossils.com

Figure 1. Specimen wrongly identified as Hovasaurus from FineFossils.com

Cruising around the Internet
I found this specimen (Fig. 1) at FineFossils.com misidentified as Hovasaurus (Fig. 2). The differences are pretty obvious, so I won’t belabor them here. The new specimen is from the same strata and location as Hovasaurus, which is probably the reason for the mistake.

Figure 1. Tangasaurus, Hovasaurus and Thadeosaurus, three marine younginiformes, apparently have no scapula.

Figure 2. Tangasaurus, Hovasaurus and Thadeosaurus, three marine younginiformes compared. Hovasaurus, as you can see bears little resemblance to the FineFossils.com specimen mislabeled as Hovasaurus.

From the FineFossils
website: Hovasaurus boulei was a small aquatic Diapsid reptile, of the order Eosuchia, and dates from the late Permian Period, 260m to 251m years old. This specimen was discovered in the Middle Sankamena Formation, Sankamena Valley, Madagascar. It is very rare to find such a complete specimen in perfect condition, displaying a wonderfully preserved skeleton.

These reptiles are known to have a laterally flattened tail [but this one does not have such a tail!], very much like a modern day sea snake, making them extremely agile in the water.  Stones have been found in the abdomens of these creatures [but no stones were found here], indicating that they swallowed small stones to give them ballast, preventing them from floating to the surface when they were hunting prey underwater. 

This Hovasaurus is an amazing example of this very ancient reptile, and is of museum quality [other than the upside-down skull, the specimen has no obvious errors]. We have seen other specimens, but the majority are dis-articulated or incomplete.
The only restoration to this piece is at the tip of the tail.

Size:    matrix  47cms x 15cms
Size:    reptile   46cms long

The description of this specimen
recalls the mid 1800s in the earliest days of fossil collection when every pterosaur discovered was referred to  Pterodactylus, despite readily observable differences from the holotype. This specimen (Fig. 1)  is probably more marketable with a name. The name might also imply it is common enough to be sold to private individuals, like the Green River fossil fish magnets that adorn American refrigerators.

Figure 3. The FineFossils.com specimen traced and reconstructed. This previously unknown specimen nests at the base of the Diapsida, close to Eudibamus, but has an extended rostrum.

Figure 3. The FineFossils.com specimen traced and reconstructed. This previously unknown specimen nests at the base of the Diapsida, close to Eudibamus, but has an extended rostrum.

In this case, however,
the specimen is new to Science. It has not been assigned a generic name. It has not been studied yet (other than by what you’re reading here). The FineFossils specimen has a longer rostrum than other basal diapsids and hints at a broader radiation at this node. It is basal to Eudibamus, Aphelosaurus, Petrolacosaurus (Fig. 4) and Araeoscelis on one branch. It is basal to Spinoaequalis and all the marine and terrestrial Younginiforms, including birds and crocs, ichthyosaurs and plesiosaurs, on the other branch. The rostrum appears to have an antorbital fenestra (Fig. 4), but that is due to crushing and shifting of the elements.

Figure 4. Fine fossils skull wrongly attributed to Hovasaurus traced and reconstructed. This is an unnamed genus new to Science.

Figure 4. Fine fossils skull wrongly attributed to Hovasaurus traced and reconstructed. This is an unnamed genus new to Science. The apparent antorbital fenestra is an illusion produced by taphonomic shifting.

So, if anyone has deep pockets out there
you can make a purchase and a museum donation that will be much appreciated by reptile paleontologists everywhere. This is a unique specimen nesting at a key node on the family tree that I can only chat about online, since it currently has no museum number. It can’t find a permanent place on the large reptile tree without that museum number.

It would be worthy of a publication!

It’s rare. It’s unique.
And if you work it right, it might be named for you as in ‘Rogersaurus’, ‘Marysaurus’ or, better yet… Diapsidsaurus longirostrum would make a suitable name for the reasons listed above.

Figure 2. Petrolacosaurus is an earlier sister to Araeoscelis with a definite diapsid temporal configuration, but oddly the upper temporal fenestra is largely lateral in this taxon.

Figure 5. Petrolacosaurus is an earlier sister to Araeoscelis with a definite diapsid temporal configuration, but oddly the upper temporal fenestra is largely lateral in this taxon. The parietals are quite broad.

Speaking of basal diapsids
Once hailed as the most basal disapsid, Petrolacosaurus (Lane 1945, Reisz 1977) is now much more derived with several more primitive diapsid taxa preceding it on the large reptile tree, including the FineFossils.com specimen. All this hints at an earlier radiation, the kind we talked about earlier here.

References
Lane HH 1945. New Mid-Pennsylvanian Reptiles from Kansas. Transactions of the Kansas Academy of Science 47(3):381-390.
Reisz RR 1977. Petrolacosaurus, the Oldest Known Diapsid Reptile. Science, 196:1091-1093. DOI: 10.1126/science.196.4294.1091

wiki/Petrolacosaurus

When Synapsids and Diapsids split

At some point
on every reptile cladogram the Synapsida emerges and somewhere else the Diapsida emerges.

In contrast to all prior cladograms,
on the large reptile tree, the traditional Diapsida is diphylletic, with lepidosaurs no longer related to archosaurs except by way of the basalmost Viséan reptiles (at the archosauromorph/ lepidisauromorph split). The reduced Diapsida (sans lepidosaurs) arises from the Prodiapsida, which splits from the Synapsida at the common base of both clades, near Protorothyris (Fig. 1), a basal archosauromorph. What happened at that split is today’s topic.

One of the basalmost synapsids
is Varanosaurus. One of the basal prodiapsids is Heleosaurus (Fig. 1). Both have a synapsid temporal morphology. Among traditional paleontologists, both are considered traditional synapsids.

Now let’s take a look
at some of the characters that split these sister taxa that otherwise share so many traits and put forth some hypotheses as to what they may mean in the grand scope of reptile evolution.

Figure 1. Taxa at the split between Synapsida and Diapsida (Prodiapsida): Varanosaurus and Heleosaurus to scale along with their common ancestor, Protorothyris.

Figure 1. Taxa at the split between Synapsida and Diapsida (Prodiapsida): Varanosaurus and Heleosaurus to scale along with their common ancestor, Protorothyris.

In many respects,
Varanosaurus was just a bigger Heleosaurus. And both were much larger than their predecessor, Protorothyris. So size was a major factor in the Early Permian. Basal synapsids were larger than prodiapsids and both were larger than their Carboniferous predecessors.

Distinct from Varanosaurus,
Heleosaurus had 19 rather minor traits in the large reptile tree. As a rule they’re not very interesting or informative (but see the next topic header):

  1. Remained < 60 cm long
  2. Slightly wider skull relative to height at orbit
  3. The nasal shape retains ‘narrows anteriorly’ description (not arrowhead)
  4. Orbit stays in anterior half of the skull
  5. Supratemporal/squamosal overhang
  6. Shorter jugal quadratojugal process
  7. Quadrate rotates to vertical
  8. Lateral temporal fenestra larger, circumtemporal bones more gracile
  9. Occiput remains close to quadrates
  10. Basipterygoid lateral processes prominent
  11. Mandible tip straight
  12. Mandible fenestra remains absent
  13. Olecranon process not present (Heleosaurus clade only)
  14. Clavicles medially not broad
  15. Radius + ulna > 3x longer than wide
  16. Retained pubis angled ventrally
  17. Acetabulum opens ventrally (Heleosaurus clade only)
  18. Tibia < 2x ilium length
  19. Dorsal osteoderms present (restricted to Heleosaurus

In summary,
these Heleosaurus traits break down to four major and a few minor distinctions from Varanosaurus:

  1. Smaller size, larger orbit, shorter rostrum, relatively less bone in the skull – all attributable to neotony (retention of embryo/juvenile traits)
  2. Relatively longer hind limbs and more slender tail (shorter chevrons and transverse processes (ribs). Together these two make prodiapsids speedy, not lumbering. Ideal for avoiding larger enemies and attacking insect prey.
  3. Relatively larger orbit: possible nocturnal hunter.
  4. Longer, more gracile ribs: fast locomotion requires more efficient and rapid respiration provided by expanding ribs
  5. Minor traits: Fewer teeth, ‘solid’ palate, larger choanae: all part of the insectivore, rapid respiration bauplan.

In my opinion
the smaller size of Heleosaurus helped it retain an insect diet, rather than moving into carnivory, piscivory or herbivory, as proposed for the pelycosaurs. Heleosaurus was probably faster and more agile than its larger and smaller relatives, better adapted to hunt insects and avoid predators.

Later taxa
‘improved’ on these traits as the clade Diapsida appeared, followed quickly by a division into terrestrial younginiforms and aquatic younginiforms.

These lizardy archosauromorph diapsids competed with
outwardly similar lepidosauromorphs lepidosaur pseudo-diapsids, like Tjubina. The lepidosaur branch retained insectivory, for the most part. The archosauromorph branch did not, for the most part, with the exception that several extant mammals and birds today are insectivores.

Maybe Araeoscelis DOES have a lateral temporal fenestra

Among basal diapsids,
Araeoscelis (Fig. 1, Williston 1910) has been the traditional outlier, closing up its lateral temporal fenestra shortly after gaining its upper temporal fenestra. Taking another look at the published drawings and moving the bones around a little, exposes a tiny lateral fenestra (Fig. 1). This is not traditional thinking, but also removes an odd autapomorphy.

Short reminder:
Araeoscelis is one sort of diapsid, the sort that ultimately led to dinos and birds. This entire clade is convergent with the diapsid configuration that developed in lepidosaurs according to the large reptile tree.

Figure 1. Araeoscelis fossi skull drawings from Reiz et al. 1984. Reconstructed in the middle.

Figure 1. Araeoscelis fossi skull drawings from Reiz et al. 1984. Reconstructed in the middle.

It’s worthwhile here to bring up Petrolacosaurus (Fig. 2) for comparison.

Figure 2. Petrolacosaurus is an earlier sister to Araeoscelis with a definite diapsid temporal configuration, but oddly the upper temporal fenestra is largely lateral in this taxon.

Figure 2. Petrolacosaurus is an earlier sister to Araeoscelis with a definite diapsid temporal configuration, but oddly the upper temporal fenestra is largely lateral in this taxon. The parietals are quite broad.

Note
in Petrolacosaurus the upper temporal fenestra is high on the lateral side of the skull and the jaw joint is in line with the jaw line, distinct from Araeoscelis. The new data shifts nothing in the large reptile tree.

IMHO,
the reduction of the lateral temporal fenestra in Araeoscelis.has something to do with the decent of the jaw joint and the blunting/thickening of the teeth. It was eating something that was tougher or crunchier than Petrolacosaurus preferred.

Araeoscelis is a terminal taxon, leaving no known descendant taxa.

References
Reisz RR, Berman DS and Scott D 1984. The anatomy and relationships of the lower Permian reptile Araeoscelis. Journal of Vertebrate Paleontology 4: 57-67.
Vaughn PP 1955. The Permian reptile Araeoscelis re-studied. Harvard Museum of Comparative Zoology, Bulletin 113:305-467.
Williston SW 1910. New Permian reptiles; rhachitomous vertebrae. Journal of Geology 18:585-600.
Williston SW 1913. The skulls of Araeoscelis and Casea, Permian reptiles. Journal of Geology 21:743-747.
wiki/Araeoscelis

Eudibamus skull revisited

Unfortunately,
requests for hi-rez images of the skull of Eudibamus (Berman et al. 2000) have gone unanswered.

Fortunately,
an image from a Stuart Sumida lab pdf file (Fig. 1) provides the best image I’ve seen so far. Even so, it could be better.

Figure 1. GIF movie of the skull of Eudibamus along with a DGS interpretation of the elements. A reconstruction (Fig. 2) appears to 'make sense" but I'd still like to see better resolution.

Figure 1. GIF movie of the skull of Eudibamus along with the original (line art) interpretation and a DGS interpretation of the elements. Where are the teeth in the line art? They are not indicated. A reconstruction based on the DGS tracings (Fig. 2) appears to ‘make sense” but I’d still like to see better resolution. The presumed mandible here does not have the appearance of the rest of the bones. The mandible is based on a possible impression that looks like it has teeth. These could be pick marks. Black lines in the color tracing appear to represent palatal elements that basically match those of Petrolacosaurus.

Eudibamus is still considered a bolosaurid
(Fig. 2) in traditional paleontology, but it nests with basal diapsids, like Petrolacosaurus, in the large reptile tree. We looked at Eudibamus earlier here, here and here.

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

Figure 2. Eudibamus skull revised here with new data compared to bolosaurids, on the left, and basal diapsids, on the right. Post crania for bolosaurids is very fragmentary. Bolosaurids are related to pareiasaurs and turtles, all derived from millerettids. Can you see why Eudibamus was confused with bolosaurids?

This skull remains confusing.
This is only an attempt at understanding it. Higher resolution and color would be helpful. The original authors did not publish a skull reconstruction, nor did they label individual skull bones. I wonder if they were just as confused, even with the skull in front of them.

 Eudibamus reconstruted.

Figure 3. Eudibamus reconstructed. This will probably not be the last such attempt. But I think it is the most accurate so far.

References
Berman, DS, Reisz RR, Scott D, Henrici AC, Sumida SS and Martens T 2000. Early Permian bipedal reptile. Science 290: 969-972.

The Marine (Aquatic) Younginiformes

Whenever one thinks of marine reptiles,
the giant mosasaurs, ichthyosaurs and plesiosaurs immediately come to mind. Dig a little deeper and the placodonts, mesosaurs and thalattosaurs pop up. Basal to all these taxa are the pachypleurosaurs. Basal to the pachypleurosaurs are the marine younginiformes (Fig. 1), beginning with Galesphyrus. The odd saurosphargids are newcomers to this list (Fig. 2) nesting between basal younginiforms and pachypleurosaurs.

Yesterday we looked at the outgroup taxon to the younginiformes, Spinoaequalis. Today we’ll discuss the basal marine younginiformes beginning with Galesphyrus (Fig. 1).

Figure 3. Spinoaequalis and descendant marine younginiformes.

Figure 3. Spinoaequalis and descendant marine younginiformes. These give rise to plesiosaurs, placodonts, mesosaurs, ichthyosaurs and thalattosuchians. Click to enlarge. Note hoe hew taxa adequately preserve the skull. The flattening of the pectoral girdle is notable here.

1. Galesphyrus (Carroll 1976; Late Permian ~260 mya) This headless articulated partial skeleton had no obvious aquatic adaptations, other than, perhaps, those big, broad feet (and also note that wider tarsus and more widely separated tibia and fibula). The hourglass-shaped proximal carpal is a trait shared with basal diapsids, like AraeoscelisGalesphyrus had more robust limbs and relatively larger feet than Spinoaequalis. Most of the tail is unknown.

2. Youngina capensis? BPI 3859 (Broom 1922; Late Permian ~260 mya). The genus Youngina was once considered basal to both lepidosaurs and archosaurs. The BPI 3859 specimen does not nest with the holotype. So the BPI 3859 specimen is not a Youngina. The BPI 3859 specimen has a taller scapula than Galesphyrus. Few other traits are preserved in common.

3. Acerosodontosaurus piveteaui (Currie 1980; Bickelmann, Müller and Reisz 2009; Late Permian ~260 mya). Acerosodontosaurus descended from a sister to Galesphyrus was a sister to the BPI 3859 specimen attributed to Youngina (see below) and phylogenetically preceded Hovasaurus, Claudiosaurus and Thadeosaurus and Tangasaurus.

4. Thadeosaurus colcanapi (Carroll 1981; Late Permian, ~260 mya), nests between Acerosodontosaurus and ClaudiosaurusTangasaurus and Hovasaurus are sister taxa. The scapula and coracoid were fused only in adults. Many specimens are known including several juveniles. None preserve the skull very well. A juvenile skull gives provides the most data.

5. Hovasaurus boulei (Piveteau 1926, Currie 1981; Late Permian to Early Triassic ~250mya ) was originally considered a tangasaurid. Here Hovasaurus nests as a sister to Tangasaurus and Thadeosaurus. Distinct from Thadeosaurus, the cervicals were more robust. The torso was shorter and deeper with longer dorsal ribs. The presacral number was 26. Accessory articulations were present on the vertebra. The tail had higher neural spines and deeper chevrons. The chevrons were broader distally. The scapulocoracoid was larger and the scapula was part of the chest shield. The metarsals were shorter. Pedal digit 5 was longer relative to digit 4.This genus is known from several specimens varying in size. Gravel was found in the belly of several specimens, likely used for ballast or digestion.

6. Tangasaurus mennelli (Haughton 1924; Late Permian) was known from only two specimens collected in 1922. Later, Currie (1982) reported over 300 partial specimens were attributed to Tangasaurus, but reattributed most of them elsewhere. Haughton (1924) described a long, powerful, flattened tail and presumed an aquatic existence. The great size of the transverse processes at the base of the tail are notable. So is their anterior curvature. These reflect the size of the caudofemoralis muscles driving the large hind limbs. Note the large coracoid, central sternum, short ribs, massive humerus (especialy distally) and high caudal spines creating a sculling tail ideal for swimming.

7. Claudiosaurus germaini (Carroll 1981; Late Permian ~260 mya) was originally described as a close relative of Thadeosaurus, and indeed it is. Claudiosaurus also nests with Adelosaurus and Atopodentatus. The skulls of predecesor taxa, like Hovasaurus, are poorly known, so distinct from Spinoaequalis, the reduced skull of Claudiosaurus had a premaxilla enlarged to a third or more of the rostral length. The premaxilla ascending process split the nasals. The naris is elongated horizontally  perhaps just contacting the lacrimal. The jugal was gracile. The supratemporal was a small oval.  A quadratojugal was present contacting both the jugal and the squamosal + quadrate, but other workers have not recognized that loose bone as the quadratojugal. A retroarticular process was present. The number of cervicals increased to at least nine and they decreased in size cranially. The posterior cervicals were as tall as the little skull. The cervical neural spines were taller than each centrum. Intercentra were absent. The pre sacral number of vertebrae dropped to 24.  Metacarpals 3 and 4 were subequal.

8. Adelosaurus huxleyi (Hancock and Howse 1870, Evans 1988) was originally considered to be a small and distinct species of Protorosaurus. Here, derived from a sister to Claudiosaurus, Adelosaurus was basal to, Atopodentatus and the rest of the marine younginiformes and enaliosaurs. Smaller than Claudiosaurus, Adelosaurus had more robust ribs. The humerus did not have an expanded distal end. The hind limb was more gracile. The proximal metatarsals were all subequal in width, except perhaps, metatarsal 5. Adelosaurus was one of the most terrestrial of the known enaliosaurs, showing few aquatic characters, but the disc-like shape of the scapulocoracoid is a trait that was retained. Evans (1988) considered the incomplete ossification of joint surfaces as evidence for immaturity or an aquatic lifestyle. Most taxa around this node have been considered immature for the same reasons.

Figure 3. Basal marine younginiformes, including Galesphyrus, Tangasaurus, Claudiosaurus and others. This is a subset of the large reptile tree.

Figure 3. Basal marine younginiformes, including Galesphyrus, Tangasaurus, Claudiosaurus and others. This is a subset of the large reptile tree. Spinoaequalis is also basal to the terrestrial younginiformes. 

In future posts
we’ll look at the terrestrial younginiformes that ultimately gave rise to the Archosauriformes. New data has clarified relationships at those nodes (Fig. 2).

References
Bickelmann C, Müller J and Reisz RR 2009. The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of “younginiform” reptiles. Canadian Journal of Earth Sciences 46:651-661.
Broom, R. 1922. An imperfect skeleton of Youngina capensis, Broom, in the collecton of the Transvaal Museum. Annals of the Transvaal Museum 8:273–277.
Carroll RL 1976. Galesphyrus capensis, a younginid eosuchian from South Africa. Annals of the South African Museum 72(4):59-68.
Carroll RL 1981. Plesiosaur ancestors from the Upper Permian of Madagascar. Philosophical Transactions of the Royal Society London B 293: 315-383.
Currie PJ 1980. A new younginid (Reptilia: Eosuchia) from the Upper Permian of Madagascar. Canadian Journal of Earth Sciences 17(4):500-51.
Currie PJ 1981. Hovasaurus bolei, an aquatic eosuchian from the Upper Permian of Madagascar. Palaeontologica Africana, 24: 99-163.
Evans 1988. The Upper Permian reptile Adelosaurus from Durham. Palaeontology 31(4): 957-964. online pdf
Gardner NM, Holliday CM and O’Keefe FR 2010. The braincase of Youngina capensis (Reptilia, Diapsida): New insights from high-resolution CT scanning of the holotype. Paleonotologica Electronica 13(3).
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Hancock A and Howse R 1870. On Protorosaurus speneri von Meyer, and a new species, Protorosaurus huxleyi, from the Marl Slate of Middridge, Durham. Quarterly Journal of the geological Society of London 26, 565-572.
Olsen EC 1936. Notes on the skull of Youngina capensis Broom. Journal of Geology, 44 (4): 523-533.
Piveteau, J. 1926. Paleontologie de Madagascar XIII. Amphibiens et reptiles permiens. Annls  Paleont. 15: 53-180.