What is Dyoplax?

Figure 1. Dyoplax arenaceus Fraas 1867 is a mold fossil recently considered to be a sphenosuchian crocodylomorph. Here it nests as a basal metriorhynchid (sea crocodile) in the Late Triassic.

Figure 1. Dyoplax arenaceus Fraas 1867 is a mold fossil recently considered to be a sphenosuchian crocodylomorph. Here it nests as a basal metriorhynchid (sea crocodile) in the Late Triassic.

Dyoplax arenaceus (Fraas 1867, Lucas, Wild and Hunt 1998) is a unique Late Triassic crocodylomorph, one of the three original crocodylomorphs in the 19th century along with two aetosaurs.

No bones are present.
Like Cosesaurus it is a natural cast mold. Fraas thought it had the head of a lizard, but the armor of a gavial. Lucas et al. nested it as the oldest sphenosuchian crocodylomorph. Maish et al. nested it with Erpetosuchus.

Here
Dyoplax nests as a basal metriorhynchid, those Jurassic sea crocodiles with flippers for fore limbs and a curved fish-like tail (Fig. 2), which was probably too early to be present. Unfortunately the tail tip and limb tips are missing from the fossil (Fig. 1)

The fossil appears to have no arch of bones separating the upper and lateral temporal fenestrae, but the intervening squamosal appears to be flipped and displaced near the neck ribs. (Black arrow in fig. 1)

Figure 2. Several Jurassic sea crocs, apparently derived from Late Triassic Dyoplax.

Figure 2. Several Jurassic sea crocs, apparently derived from Late Triassic Dyoplax.

Boy, it’s been awhile
since I posted anything. Feels good to be back… but for how long?

References
Fraas O 1867. Dyoplax arenaceus, ein neuer Stuttgarter Keuper-Saurier. Jh. Verein vaterländ. Naturk. Württemberg 23:108-112; Stuttgart.
Lucas SG, Wild R, Hunt AP 1998. Dyoplax O. Fraas, a Triassic sphenosuchian from Germany. Stuttgarter Beiträge zur Naturkunde, B. 263: 1–13.
Maisch MW;  Matzke AT; Rathgeber T 2013. Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen. 267 (3): 353–362.

 

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Happy Holidays, Everyone!

I wish you all the best!
Here at the David Peters Studio I have not kept up with my usual one-a-day posts (and feeling guilty about it). Having already covered just about every clade out there, I’m reduced to commenting about the paleo news as it comes out and rechecking all the links and data at ReptileEvolution.com, which this blog post supports.

I’ve also managed to squeeze out
a few papers. Digging deeper into various subjects always brings up some dirt and some gold. There’s no reward in publishing a paper, other than the personal satisfaction in knowing you’ve shed a little light on the dark corners of a subject.

It’s important for all of us to be life-long learners.

Thank you
for your readership.

The 11th Archaeopteryx: closer to Sapeornis

Figure 1. The 11th specimen attributed to Archaeopteryx in situ. See figure 2 for a reconstruction. This specimen remains in private hands without a museum number.

Figure 1. The 11th specimen attributed to Archaeopteryx in situ. See figure 2 for a reconstruction. This specimen remains in private hands without a museum number. Note all the soft tissue feathers preserved here.

Archaeopteryx number 11
(Figs. 1, 2) has no museum number and is in private hands, but Foth et al. 2014 published a description in Nature. These authors unfortunately considered this specimen just another Archaeopteryx, but one well supplied with feather impressions. In the large reptile tree (LRT, subset Fig. 3) this Solnhofen bird nests at the base of the node that produced two specimens of Sapeornis, a clade convergent with Euronithes in having a pygostyle.  The 11th specimen is complete and articulated, but lacks a large part of the cranium.

Figure 2. Most of the complete Solnhofen birds, including Archaeopteryx and the eleventh specimen to scale.

Figure 2. Most of the complete Solnhofen birds, including Archaeopteryx and the eleventh specimen to scale.

Foth et al. 2014 do not mention
the lack of a sternum. Sapeornis likewise lacks a sternum even though more primitive taxa have one.

Figure 4. The eleventh Archaeopteryx nests with Sapeornis.

Figure 4. The eleventh Archaeopteryx nests with Sapeornis.

At first glance
this appears to be an ordinary Archaeopteryx. However, when you put the dividers on the bones you find that it differs in subtle ways from the holotype and is more similar to Sapeornis and its sisters. As I mentioned yesterday, it would be a good thing for all early bird workers to start considering the Solnhofen birds individual genera, not a single genus. It’s just a lazy habit we have to overcome.

References
Foth C, Tischlinger H and Rauhut OWM 2014. New specimen of Archaeopteryx provides insights into the evolution.of pennaceous feathers. Nature 511:79–83.DOI: 10.1038/nature13467

Ostromia: The Haarlem specimen of Archaeopteryx

Updated January 17, 2018 with a new tracing and nesting of Ostromia as a sister to Eosinopteryx in the proximal outgroup clade to the birds. 

A recent paper
by Foth and Rauhut 2017 reexamined the incomplete Haarlem specimen on plate and counter plate (TM 6928, 6929, Figs. 1–3) originally attributed to a pterosaur (Pterodactylus crassipes, von Meyer 1857) and later to Archaeopteryx crassipes (Ostrom 1970). The co-authors renamed the specimen Ostromia crassipes and nested it with Anchiornis (Fig. 2), a larger troodontid with a short coracoid outside of the bird clade in the large reptile tree (LRT).

Figure 1. The Haarlem specimen of Archaeopteryx now named Ostromia crassipes.

Figure 1. The Haarlem specimen of Archaeopteryx now named Ostromia crassipes.

Foth and Rauhut 2017
considered Anchiornis“the possibly oldest and most basal clade of avialan, here named Anchiornithidae.” And they considered Ostromia the first and only anchiornithid outside of the Tiaojushan Formation of China.

Figure 1. Anchiornis, the pre-bird troodontid, to scale with Ostromia, the Solnhofen bird, the Haarlem specimen.

Figure 1. Anchiornis, the pre-bird troodontid, to scale with Ostromia, the Solnhofen pre-bird, the Haarlem specimen.

The authors employed a previously published phylogenetic analysis
from Foth et al. 2014. which looked at the privately owned 11th specimen of Archaeopteryx. Unfortunately their cladogram lumped all Archaeopteryx specimens (Fig. 3) together. So we’re dealing with a possible taxonomic chimaera and a certain taxon exclusion.

Figure 3. Several Solnhofen birds, including Archaeopteryx, compared to Ostromia to scale.

Figure 3. Several Solnhofen birds, including Archaeopteryx, compared to Ostromia to scale.

The variety shown by the Solnhofen birds
(Fig. 3) should invite phylogenetic analysis (Fig. 4). But Foth et al. (2014, 2017) did not respond to the invitation. If they had done so, perhaps they would have replicated the results of the LRT in nesting Ostromia with other coeval Archaeopteryx specimens. Their Ostromia nests here with Eosinopteryx, not with Anchiornis.

In size, strata and morphology
Ostromia nests rather closely to the other Solnhofen birds in the LRT, but in the proximal outgroup, along with Eosinopteryx and Xiaotingia.

I encourage bird workers
to not lump the Solnhofen birds together as a single taxonomic unit, but to split them into individual specimens. There’s a treasure to be found there. Each one deserves to be its own species, if not its own genus.

References
Foth C and Rauhut OWM 2017. Re-evaluation of the Haarlem Archaeopteryx and the radiation of maniraptoran theropod dinosaurs. BMC Evolutionary Biology 17:236
Foth C, Tischlinger H, Rauhut OWM 2014. New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers. Nature 511:79–82.
Ostrom JH 1970. Archaeopteryx: notice of a “new” specimen. Science. 1970;170:537_538.
Von Meyer H 1861. Archaeopteryx lithographica und Pterodactylus. N Jb Min Geognosie Geol Petrefaktenkd. 1861:678–679.

TM = Teylers Museum in Haarlem, the Netherlands

Phylogenetic miniaturization preceding the origin of Reptilia

We looked at
Ossinodus and Acanthostega a few days ago. Today the relatives of those two, from Osteolepis to Gephyrostegus are shown to scale (Fig. 1). Look how small the first reptiles were. Certainly the transition to land was aided by having less weight to lug around without the support of water.

Figure 1. Taxa preceding reptiles in the LRT.  Look how small the first reptiles were. Certainly the transition to land was aided by having less weight to lug around without the support of water. 

Figure 1. Taxa preceding reptiles in the LRT. Look how small the first reptiles were. Certainly the transition to land was aided by having less weight to lug around without the support of water. 

Ossinodus still hasn’t gotten enough press
related to its placement in the origin of four legs with toes from fins. Tiktaalik (with lobefins) is its proximal outgroup. Or to the fact that Ossinodus is our first sabertooth! We need to find a complete manus and pes for Ossinodus to see if it had five toes ore more. Presently we don’t know.

Pederpes has five toes. The manus is not well enough known. The narrow skull suggested that Pederpes breathed by inhaling with a muscular action like most modern tetrapods, rather than by pumping air into the lungs with a throat pouch the way many modern amphibians do. The problem with this is Pederpes is basal to both lizards and frogs, which still breathe by buccal (throat pouch) pumping.

Ichthyostega had more than five toes, Which toes are homologous with our five are indicated here (Fig. 2). The extra digits appear between 1 and 2. Does anyone understand why this is so?

Figure 2. Ichthyostega pes with homologous digits numbered. The extra digits appear here between 1 and 2, perhaps due to a return to a more aquatic lifestyle (perhaps more swimming and less bottom walking).

Figure 2. Ichthyostega pes with homologous digits numbered. The extra digits appear here between 1 and 2, perhaps due to a return to a more aquatic lifestyle (perhaps more swimming and less bottom walking).

Arikanerpeton is a basal seymouriamorph in the large reptile tree (LRT). Utegenia is a basal lepidospondyl. Both are close but not very close to origin of reptiles. Perhaps the more direct route, at present, is through Eucritta. That taxon has small hands, but large asymmetric feet with long toes, like reptiles. The long toes of Eucritta (Fig. 3) are not at the ends of long legs, but really short legs, an odd combination.

Figure 3. Eucritta has long toes, but short legs. There's a story there that is presently hard to understand.

Figure 3. Eucritta has long toes, but short legs. There’s a story there that is presently hard to understand. Not sure how deep the pelvis was. Could go either way with present data. 

One wonders if
bullet-shaped Eucritta, coming after longer-legged Tulerpeton, was also secondarily aquatic, like Ichthyostega and Acanthostega.

References
Clack JA 1998. A new Early Carboniferous tetrapod with a mélange of crown group characters. Nature 394: 66-69.
Clack JA 2007. Eucritta melanolimnetes from the Early Carboniferous of Scotland, a stem tetrapod showing a mosaic of characteristics. Transactions of The Royal Society of Edinburgh 92:75-95.
Warren A and Turner S 2004. The first stem tetrapod from the Lower Carboniferous of Gondwana. Palaeontology 47(1):151-184.
Warren A 2007. New data on Ossinodus pueri, a stem tetrapod from the Early Carboniferous of Australia. Journal of Vertebrate Paleontology 27(4):850-862.

wiki/Ossinodus
wiki/Eucritta

Comment to Wang et al. 2017 published

Science
recently published a paper on an accumulation of pterosaur eggs by Wang et al. 2017. And I’m happy to report they just published my comment in an e-letter suggesting another interpretation of the data at hand. All the details were published earlier here at the pterosaurheresies blog site.

Figure 1. From Wang et al. 2017, a pterosaur egg and bone accumulation. Eggs float. So do hollow pterosaur bones.

Figure 1. From Wang et al. 2017, a pterosaur egg and bone accumulation. Eggs float. So do hollow pterosaur bones.

References
Wang X and 16 co-authors 2017. Egg accumulation with 3D embryos provides insight into the life history of a pterosaur. Science 358:1197–1201.

 

Ichthyostega and Acanthostega: secondarily more aquatic

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

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

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

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

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

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

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

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

Figure 3. Tiktaalik specimens compared to Ossinodus.

Figure 3. Tiktaalik specimens compared to Ossinodus.

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

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

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

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

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

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

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

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