Tulerpeton pes options

Earlier the pedal elements of the amphibian-like reptile Tulerpeton were moved around to produce a reasonable reconstruction. Today I offer a few more options (Fig. 1) including one with six toes. All appear to be reasonable.

Figure 1. Tulerpeton pes reconstruction options using published images of the in situ fossil.

Figure 1. Tulerpeton pes reconstruction options using published images of the in situ fossil.

None of these reconstructions
changes the nesting of Tulerpeton as the basalmost Reptile (=Amniote). Such long toes with so many phalanges in these patterns of relative length are not found in basal tetrapods.

Figure 1. Tulerpeton parts from Lebedev and Coates 1995 here colorized and newly reconstructed. Manus and pes enlarged in figure 2.

Figure 2 Tulerpeton parts from Lebedev and Coates 1995 here colorized and newly reconstructed. Manus and pes enlarged in figure 2.

A little backstory
Tulerpeton curtum (Lebedev 1984, Fammenian, Latest Devonian, 365 mya) was described as, “one of the first true tetrapods to have arisen.” Here it nests as the basalmost reptile, pushing Gephyostegus bohemicus back to the pre-amniotes. Very little other than the limbs are known. In life it would have been similar to and the size of Gephyrostegus, Urumqia and EldeceeonTulerpeton lived in shallow marine waters.

References
Coates MI and Ruta M 2001 2002. Fins to limbs: What the fossils say. Evolution & Development 4(5): 390–401.
Lebedev OA 1984. The first find of a Devonian tetrapod in USSR. Doklady Akad. Navk. SSSR. 278: 1407–1413.
Lebedev OA and Clack JA 1993. Upper Devonian tetrapods from Andreyeva, Tula Region, Russia. Paleontology36: 721-734.
Lebedev OA and Coates MI 1995. postcranial skeleton of the Devonian tetrapod Tulerpeton curtum Lebedev. Zoological Journal of the Linnean Society. 114 (3): 307–348.

wiki/Tulerpeton

 

 

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PILs (Parallel Interphalangeal Lines) and Paddles

Paddle PILs
Peters (2000, 2010, 2011) described PILs (Parallel Interphalangeal Lines) that can be drawn through any tetrapod manus or pes. Primitively three sets are present, medial, transverse and lateral. The lines indicate phalanges that act in sets while grasping (flexion) or during locomotion (extension). As digits are reduced, as in theropod or horse feet, the PILs tend to merge.

Figure 1. On left: Tylosaurus pelvis with an anteriorly-leaning ilium. On right: Tylosaurus forelimb paddle. Note the PILs are not continuous but  stop at digit 2, the main spar of this aquatic "wing".

Figure 1. On left: Tylosaurus pelvis with an anteriorly-leaning ilium. Note the acetabulum is not facing the reader. This is the medial view of the pelvis. In the middle, the two sacral vertebrae of Tylosaurus. On right: Tylosaurus forelimb paddle. Note the PILs are not continuous but stop at digit 2, the main spar of this aquatic “wing”.

Tetrapods with flippers or paddles present a special case,
but even then, PILs are present. Recently I took a look at the manus of Tylosaurus and noticed that the PILs were not continuous from side to side, as they are typically (but not universally) in terrestrial tetrapods. With Tylosaurus the transverse set was not apparent. The medial set extended to digit 2. So did the lateral set. Digit 2 in the wing-like paddle of Tylosaurus is analogous to the main wing spar of an airplane wing. And that spar is not supposed to bend. Apparently in this case, the absence of transverse PILs that would have allowed flexion and extension showed that the flipper was most efficient when it did not flex and extend much.

Pelvis
In most tetrapods the ilium extends posteriorly. In many the ilium also extends anteriorly, creating a long lateral plate for the attachment of many large muscles. In aquatic forms the ilium is generally reduced. As you might expect, in some taxa that also reduces the number of sacral vertebrae. In others, oddly, the number of sacrals can double to four. In many aquatic taxa, and a few arboreal forms, the ilium has no posterior process, but extends dorsally. Rarely, as in Tylosaurus (Fig. 1) the ilium tilts anteriorly. Only the presence of the laterally-facing acetabulum assures you that this orientation is correct. I’m not sure why this is so. That ilium angle is 90º from the scapula angle in a bird, bat or pterosaur, animals that fly through the air and employ the scapula to anchor muscles that raise the wing (the details differ between all three flyers, btw, with birds employing a pulley-like bone to bend the action of a pectoral muscle to aid in wing elevation). Tylosaurus may have had the same problem to overcome, paddle elevation, but used a tall narrow anchor, rather than a low, long anchor to do the job.

Lingham-Soliar (1992) described subaqueous flying in a mosasaur, but concentrated on the pectoral area and forelimb, ignoring the pelvis and hind limb.

References
Lingham-Soliar T 1992. A new mode of locomotion in mosasaurs: subaquaeous flying in Plioplatecarpus marshii. Journal of Vertebrate Paleontology 12:405-421. 
Peters D 2000. Description and interpretation of interphalangeal iines in tetrapods
Ichnos, 7:11-41.
Peters D 2010. In defence of parallel interphalangeal lines. Historical Biology iFirst article, 2010, 1–6 DOI: 10.1080/08912961003663500
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605

Synapsid manus and pedes study

A recent online paper by Kümmel and Frey (2014) describes the mobility of the ‘thumb’ and medial toe in non-mammalian Synapsida and one extant mammal.

Figure 1. Manus of Galesaurus, an arboreal dromasaur, anomodont, synapsid.

Figure 1. Manus of Galesaurus, a basal cynodont synapsid. PILs added. This is where grasping first emerged, later dropped by many later mammal clades, but retained by primates and other arboreal forms.

From their abstract
The the reduction of autopodial rotation can be estimated, e.g., from the decrease of lateral rotation and medial abduction of the first phalanx in the metapodiophalangeal joint I. Autopodial rotation was high in Titanophoneus and reduced in derived Cynodontia. In Mammaliamorpha the mobility of the first ray suggests autopodial rolling in an approximately anterior direction. Most non-mammaliamorph Therapsida and probably some Mesozoic Mammaliamorpha had prehensile autopodia with an opposable ray I. In forms with a pronounced relief of the respective joints, ray I could be opposed to 90° against ray III. A strong transverse arch in the row of distalia supported the opposition movement of ray I and resulted in a convergence of the claws of digits II–V just by flexing those digits. A tight articular coherence in the digital joints of digits II–V during strong flexion supported a firm grip capacity.

Figure 2. Pes of Titanophoneus-like synapsid from Kümmel and Frey. PILs added. Approximately middle of the propulsion phase (A), followed by plantar flexion of metatarsalia II–V and distale I (B). C shows the start of the raising phase of the metapodialia and D the start of the raising phase of the digits

Figure 2. Pes of Titanophoneus-like synapsid from Kümmel and Frey. PILs added. Approximately middle of the propulsion phase (A), followed by plantar flexion of metatarsalia II–V and distale I (B). C shows the start of the raising phase of the metapodialia and D the start of the raising phase of the digits

Not mentioned, or referenced, but clearly visible
is the presence of PILs (parallel interphalangeal lines) that enable the phalanges to work in sets.

If you ever wondered where your grasping hand first appeared, it is here (Figure 1) in cynodonts.  No matter that grasping later disappeared in many later mammal clades, it was retained by arboreal and carnivorous clades.

The authors discuss the alignment of the phalanges without discussing the 14-year-old paper on PILs (Peters 2000), which might have been appropriate in this study. So, it’s brought up here.

The arching of the metacarpals an metapodials is also shown here. A similar arching was shown to exist in the pes of Pteranodon (Peters 2000). That arching in the human metacarpals produces a fist clearly aligns the knuckles for branch grabbing. Otherwise, when flattened and useful only for clapping and slapping, the knuckles are not clearly aligned.

References
Kümmell SB and Frey 2014. Range of Movement in Ray I of Manus and Pes and the Prehensility of the Autopodia in the Early Permian to Late Cretaceous Non-Anomodont Synapsida. PLoS ONE 9(12): e113911.doi:10.1371/journal.pone.0113911 http://www.plosone.org/article

Peters D 2000. Description and interpretation of interphalangeal iines in tetrapods
Ichnos, 7:11-41.

 

Let’s add PILs to the Poposaurus foot

and see what happens…

The question posed by Farlow et al (2014) is were the toes of Poposaurus (Figs. 1-3) splayed or nearly parallel? Farlow (Fig. 1) showed both possibilities in a digitigrade fashion. Here (Fig. 1) I added PILs (parallel interphalangeal lines, (Peters 2000, 2011) to see which possibility produced the simplest set of PILs.

Figure 1. From Farlow et al. 2014) showing the Poposaurus foot in plantigrade and digitigrade poses. In the ghosted addition I added a digitigrade configuration, but so high as in the Farlow examples. In any case, digit 1 impresses, but shares no PILs, so it acts as a vestige, no longer part of the phalangeal sets.

Figure 1. From Farlow et al. 2014) showing the Poposaurus foot in plantigrade and digitigrade poses. In the ghosted addition I added a digitigrade configuration, but so high as in the Farlow examples. In any case, digit 1 impresses, but shares no PILs, so it acts as a vestige, no longer part of the phalangeal sets. The metatarsals in ventral view are also ghosted to better show the bones that would have contributed to making a footprint. Note: the medial and lateral PILs are complete, but the transverse set is not, but becomes more so with the spreading toes.

Farlow et al. created their splayed foot by spreading the digits as far as they could go on the distal metatarsals. Another way to do this would be to rotate the medial and lateral metatarsals, creating a metatarsal arc, but this was not attempted by Farlow et al. Even a slight axial rotation of these metatarsals would have splayed the digits just a little bit more.

And that’s really all you need.

Here (Fig. 2) we look at an even more splayed foot and now we have complete PILs even in the transverse set, which is the one Poposaurus would have used for locomotion, as in birds and theropods.

Figure 2. When you splay the digits of Poposaurus just a little bit more, the transverse PILs become complete and uninterrupted. This, then, is the most likely configuration of the pes.

Figure 2. When you splay the digits of Poposaurus just a little bit more, the transverse PILs become complete and uninterrupted. This, then, is the most likely configuration of the pes. PILs work!

Now all the PIL sets (except, again, digit 1, which just had to get out of the way) are able to operate at maximum efficiency. They are complete and uninterrupted, as in all other tetrapods.

BTW, Poposaurus is basal to Silesaurus in the large reptile tree, and Silesaurus does not preserve digit 1.

 

Figure 1. Poposaurs to scale and in phylogenetic order (top to bottom). Sacisaurus is at the base. Silesaurus and Lotosaurus are derived. Poposaurus is one of the largest, along with Lotosaurus.

Figure 3. Poposaurs to scale and in phylogenetic order (top to bottom). Sacisaurus is at the base. Silesaurus and Lotosaurus are derived. Poposaurus is one of the largest, along with Lotosaurus.

Three days ago we took our first look at the Farlow et al. 2014 paper.

References
Farlow JO, Schachner ER, Sarrazin JC, Klein H and Currie PJ 2014. Pedal Proportions of Poposaurus gracilis: Convergence and Divergence in the Feet of Archosaurs. The Anatomical Record. DOI 10.1002/ar.22863
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos, 7: 11-41.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605