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Live birth in ‘Dinocephalosaurus’? Maybe. Maybe not.

Wednesday, February 15, 2017 11:56
% of readers think this story is Fact. Add your two cents.

(Before It's News)

Yesterday Liu et al. 2017 reported on
a pregnant Dinocephalosaurus (Figs. 1-5). This is wonderful and exciting news. However, the embryo is NOT in the process of passing through the cloaca, as we’ve seen in ichthyosaurs. The embryo is much higher in the abdomen, still in the uterus. So the headline “Live birth in an archosauromorph reptile” is… at best… premature. Live birth is still a possibility. A critical examination of the data reveals a few more major and minor problems.

Dinocephalosaurus in resting, feeding and breathing modes. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2012/07/dinocephalosaurus_act.jpg?w=584&h=536?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2012/07/dinocephalosaurus_act.jpg?w=584&h=536?w=584″ class=”size-full wp-image-6782″ src=”https://pterosaurheresies.files.wordpress.com/2012/07/dinocephalosaurus_act.jpg?w=584&h=536″ alt=”Dinocephalosaurus in resting, feeding and breathing modes.” width=”584″ height=”536″ srcset=”https://pterosaurheresies.files.wordpress.com/2012/07/dinocephalosaurus_act.jpg?w=584&h=536 584w, https://pterosaurheresies.files.wordpress.com/2012/07/dinocephalosaurus_act.jpg?w=150&h=138 150w, https://pterosaurheresies.files.wordpress.com/2012/07/dinocephalosaurus_act.jpg?w=300&h=276 300w, https://pterosaurheresies.files.wordpress.com/2012/07/dinocephalosaurus_act.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 1. The holotype (not the new specimen) of Dinocephalosaurus in resting, feeding and breathing modes. In breathing mode the throat sac would capture air that would not be inhaled until the neck was horizontal at the bottom of the shallow sea. Orbits on top of the skull support this hypothesis. Image from Peters 2005. The new specimen has a longer neck, a more robust tail, and a different pedal morphology.

Unfortunately
the authors nested Dinocephalosaurus within the Archosauromorpha (Fig. 2). That is incorrect. Dinocephalosaurus nests within the new Lepidosauromorpha in the large reptile tree (LRT, 952 taxa), which minimizes the taxon exclusion problem suffered by the much smaller taxon list in the Liu et al. 2017 tree.

Figure 6. Cladogram from Liu et al. 2017 with colors added based on results from the LRT. Taxon exclusion is a major problem here. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/02/liu_dinocephalosaurus_cladogram.jpg?w=584&h=800?w=219″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/02/liu_dinocephalosaurus_cladogram.jpg?w=584&h=800?w=584″ class=”size-full wp-image-26100″ src=”https://pterosaurheresies.files.wordpress.com/2017/02/liu_dinocephalosaurus_cladogram.jpg?w=584&h=800″ alt=”Figure 6. Cladogram from Liu et al. 2017 with colors added based on results from the LRT. Taxon exclusion is a major problem here. ” width=”584″ height=”800″ srcset=”https://pterosaurheresies.files.wordpress.com/2017/02/liu_dinocephalosaurus_cladogram.jpg?w=584&h=800 584w, https://pterosaurheresies.files.wordpress.com/2017/02/liu_dinocephalosaurus_cladogram.jpg?w=110&h=150 110w, https://pterosaurheresies.files.wordpress.com/2017/02/liu_dinocephalosaurus_cladogram.jpg?w=219&h=300 219w, https://pterosaurheresies.files.wordpress.com/2017/02/liu_dinocephalosaurus_cladogram.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 2. Cladogram from Liu et al. 2017 with colors added based on results from the LRT. Taxon exclusion is a major problem here. Note in the Liu et al. cladogram members of the Protorosauria are divided into three clades. In sympathy, members of the Tritosauria and Protorosauria do indeed converge with one another. More taxa clears up the problem shown here of cherry-picking taxa.

Dinocephalosaurus actually nests
within the lepidosaur clade, Tritosauria, a clade that also includes Tanystropheus, pterosaurs and several other taxa (Fig. 7) that had been mistaken for protorosaur relatives in the Liu et al and other prior studies.

As a lepidosaur, 
Dinocephalosaurus would have been able to retain embryos within the mother far longer that in extant archosauromorphs. And based on the extreme thinness of pterosaur eggshells (closest known relatives with embryos, Fig. 7), those leathery eggshells only develop just prior to egg laying. So live birth is only one of a spectrum of options for Dinocephalosaurus. As in pterosaurs, the eggs could have hatched shortly after the female laid them on the shoreline.

Dinocephalosaurus. Note the very narrow cranial portion of the skull and the very wide cheeks. That, by it self, opens the orbits dorsally. Sure there’s some lateral exposure, but those eyes are looking up! ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2012/11/dinocephalosaurus.jpg?w=584&h=269?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2012/11/dinocephalosaurus.jpg?w=584&h=269?w=584″ class=”size-full wp-image-8339″ src=”https://pterosaurheresies.files.wordpress.com/2012/11/dinocephalosaurus.jpg?w=584&h=269″ alt=”Dinocephalosaurus. Note the very narrow cranial portion of the skull and the very wide cheeks. That, by it self, opens the orbits dorsally. Sure there’s some lateral exposure, but those eyes are looking up!” width=”584″ height=”269″ srcset=”https://pterosaurheresies.files.wordpress.com/2012/11/dinocephalosaurus.jpg?w=584&h=269 584w, https://pterosaurheresies.files.wordpress.com/2012/11/dinocephalosaurus.jpg?w=150&h=69 150w, https://pterosaurheresies.files.wordpress.com/2012/11/dinocephalosaurus.jpg?w=300&h=138 300w, https://pterosaurheresies.files.wordpress.com/2012/11/dinocephalosaurus.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 3. The holotyype of Dinocephalosaurus. Although extremely similar, the new specimen is different in several ways. See below.

Liu et al. report that live birth is unknown in the Archosauromorpha.
However, in the LRT mammals and enaliosaurs (sauropterygians + ichthyosaurs) are both archosauromorphs that experience live birth. Hyphalosaurus, a choristodere archosauromorph, had extremely thin eggshells and retained developing embryos inside the mother until laying those eggs.

Figure 5. Hypothetical Tanystropheus embryo compared to Dinocephalosaurus embryo. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus_tanystropheus_embryo_egg.jpg?w=584&h=797?w=220″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus_tanystropheus_embryo_egg.jpg?w=584&h=797?w=584″ class=”size-full wp-image-26099″ src=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus_tanystropheus_embryo_egg.jpg?w=584&h=797″ alt=”Figure 5. Hypothetical Tanystropheus embryo compared to Dinocephalosaurus embryo. ” width=”584″ height=”797″ srcset=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus_tanystropheus_embryo_egg.jpg?w=584&h=797 584w, https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus_tanystropheus_embryo_egg.jpg?w=110&h=150 110w, https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus_tanystropheus_embryo_egg.jpg?w=220&h=300 220w, https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus_tanystropheus_embryo_egg.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 4. Hypothetical Tanystropheus embryo compared to part of an embryo of the new specimen attributed to Dinocephalosaurus.

More about that embryo
What little is preserved of the Dinocephalosaurus embryo (Fig. 4) is curled up in its amniotic sac, as one would expect for any reptile embryo still in utero. For comparison, note the hypothetical Tanystropheus embryo alongside it. That long neck has to go somewhere and Dinocephalosaurus provides further evidence that juvenile tritosaurs were isometric duplicates of their adult parents. That long neck did not develop with maturity. Among other tritosaurs we see juveniles similar in proportion to adults in the basal form, Huehuecuetzpalliand all pterosaur embryos.

Liu et al. further report. “Despite the complexity of this transition, viviparity has evolved at least 115 times in extant squamates (lizards and snakes), in addition to a single time in the common ancestor of therian mammals. Moreover, viviparity is a common reproductive mode in extinct aquatic reptiles including eosauropterygians, ichthyosaurs, mosasauroids, some choristoderans and likely mesosaurs.” Since mosasauroids are extinct squamates that makes at least 116 times for lepidosaurs.    Some living squamates produce eggs that hatch shortly after they are expelled, a sort of transition from oviparity to viviparity. That’s where pterosaurs fall and perhaps Dinocephalosaurus.

More cladogram issues
The Liu et al. figure 1 cladogram shows a polytomy of most reptilian clades arising during the Permian. No such polytomy appears in the LRT in which Archosauromorpha diverged from the Lepidosauromorpha tens of millions of years earlier in the Viséan (Lower Carboniferous). Liu et al. mistakenly report that trilophosaurs, rhynchosaurs and pterosaurs are archosauromorph reptiles. They are lepidosauromorph reptiles in the LRT.

Figure 1. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalo2-recon588.jpg?w=584&h=1575?w=111″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalo2-recon588.jpg?w=584&h=1575?w=380″ class=”size-full wp-image-26098″ src=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalo2-recon588.jpg?w=584&h=1575″ alt=”Figure 1. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4.” width=”584″ height=”1575″ srcset=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalo2-recon588.jpg?w=584&h=1575 584w, https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalo2-recon588.jpg?w=56&h=150 56w, https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalo2-recon588.jpg?w=111&h=300 111w, https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalo2-recon588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 5. The new Dinocephalosaurus has traits the holotype does not have, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with a more elongate pedal digit 4. The partial embryo is in magenta at left.

The new specimen looks like a Dinocephalosaurus, but is it one?
Distinct from the holotype, the new specimen has a deep robust tail with deep chevrons (Fig. 5) as in Litorosuchus (Fig. 6), also from China, but from higher strata. They all share a common ancestor in one of the highly variable Macrocnemus specimens (Fig. 7). The toes of the new specimen are more asymmetric. The neck probably has more vertebrae (several are lost, but note the longest ones are NOT at the base of the neck in the holotype). Unfortunately little more can be said with so much of the mother lacking at present. We’ve already seen a Chinese Tanystropheus similar to, but not identical to the European Tanystropheus. We can imagine even greater variation within the available gamut of the present sparse fossil evidence.

Figure 3. Litorosuchus compared to Macrocnemus and kin at two scales. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2016/11/tanystropheus-and-kin.jpg?w=584&h=858?w=204″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2016/11/tanystropheus-and-kin.jpg?w=584&h=858?w=584″ class=”size-full wp-image-24907″ src=”https://pterosaurheresies.files.wordpress.com/2016/11/tanystropheus-and-kin.jpg?w=584&h=858″ alt=”Figure 3. Litorosuchus compared to Macrocnemus and kin at two scales.” width=”584″ height=”858″ srcset=”https://pterosaurheresies.files.wordpress.com/2016/11/tanystropheus-and-kin.jpg?w=584&h=858 584w, https://pterosaurheresies.files.wordpress.com/2016/11/tanystropheus-and-kin.jpg?w=102&h=150 102w, https://pterosaurheresies.files.wordpress.com/2016/11/tanystropheus-and-kin.jpg?w=204&h=300 204w, https://pterosaurheresies.files.wordpress.com/2016/11/tanystropheus-and-kin.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 6. Litorosuchus compared to Macrocnemus and kin at two scales. Litorosuchus has deep chevrons and a robust tail, as in the new specimen, lacking in Dinocephalosaurus.

Figure 2. Given the scrappy, skull-less data, the putative Dinocephalosaurus either nests with its namesake or by convergence with Litorosuchus which shares deep chevrons and a robust tail, among other traits. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus2.gif?w=584?w=128″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus2.gif?w=584?w=310″ class=”size-full wp-image-26103″ src=”https://pterosaurheresies.files.wordpress.com/2017/02/dinocephalosaurus2.gif?w=584″ alt=”Figure 2. Given the scrappy, skull-less data, the putative Dinocephalosaurus either nests with its namesake or by convergence with Litorosuchus which shares deep chevrons and a robust tail, among other traits. ” />

Figure 7. Given the scrappy, skull-less data, the putative Dinocephalosaurus either nests with its namesake or by convergence with Litorosuchus which shares deep chevrons and a robust tail, among other traits.

It really is too much
to expect identical specimens to come from distinct fossil bearing strata. So variation within Dinocephalosaurus is a possibility. But so is convergence from the lineage of Litorosuchus.

Next steps
The paleo-community needs to include more specimen-based taxa in their cladograms or the Liu et al. problem (not restricted to them!) is going to continue ad infinitum. I know that’s a lot of work. But it can be done (I’ve done it!) and it needs to be done. Just start with a large gamut analysis and keep adding taxa to it. That will make the current phylogenetic problems go away.

Final note
Images of tanystropheids and dinocephalosaurs swimming horizontally through open waters (Liu et al. 2017 their figure 3) may not be an accurate portrayals of their daily lives. Other options have been published (Fig. 1) or appear online (Fig. 8). Odd-looking tetrapods often have uncommon niches and atypical behaviors.

Tanystropheus underwater among tall crinoids and small squids. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2012/07/tanystropheus-crinoid.jpg?w=584&h=858?w=204″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2012/07/tanystropheus-crinoid.jpg?w=584&h=858?w=584″ class=”size-full wp-image-6784″ src=”https://pterosaurheresies.files.wordpress.com/2012/07/tanystropheus-crinoid.jpg?w=584&h=858″ alt=”Tanystropheus underwater among tall crinoids and small squids.” width=”584″ height=”858″ srcset=”https://pterosaurheresies.files.wordpress.com/2012/07/tanystropheus-crinoid.jpg?w=584&h=858 584w, https://pterosaurheresies.files.wordpress.com/2012/07/tanystropheus-crinoid.jpg?w=102&h=150 102w, https://pterosaurheresies.files.wordpress.com/2012/07/tanystropheus-crinoid.jpg?w=204&h=300 204w, https://pterosaurheresies.files.wordpress.com/2012/07/tanystropheus-crinoid.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 8. Tanystropheus in a vertical strike elevating the neck and raising its blood pressure in order to keep circulation around its brain and another system to keep blood from pooling in its hind limb and tail.

References
Li C, Rieppel O and LaBarbera MC 2004. A Triassic aquatic protorosaur with an extremely long neck. Science 305:1931.
Liu, J. et al. 2017. Live birth in an archosauromorph reptile. Nature Communications 8, 14445 doi: 10.1038/ncomms14445
Peters D, Demes B and Krause DW 2005. Suction feeding in Triassic Protorosaur? Science, 308: 1112-1113.



Source: https://pterosaurheresies.wordpress.com/2017/02/16/live-birth-in-dinocephalosaurus-maybe-maybe-not/

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