Resurrecting extinct taxa: Creodonta, Mesonychidae, Desmostylia and Gephyrostegidae

Taxonomy
“the branch of science concerned with classification, especially of organisms; systematics.”  Taxon: a taxonomic group of any rank, such as a species, family, or class.

The large reptile tree
(LRT, 1366 taxa) has resurrected several taxa (in this case, clades) long thought to be extinct.

Figure 1. Adding Sinopa to the LRT nests it here, between the extant quoll (Dasyurus) and the extant Tasmanian devil (Sarcophilus).

Figure 1. Members of the traditionally extinct Creodonta include the extant quoll (Dasyurus) and the extant Tasmanian devil (Sarcophilus).

Creodonta
According to Wikipedia: “Creodonta” was coined by Edward Drinker Cope in 1875. Cope included the oxyaenids and the viverravid Didymictis but omitted the hyaenodontids. In 1880. he expanded the term to include MiacidaeArctocyonidaeLeptictidae (now Pseudorhyncocyonidae), OxyaenidaeAmbloctonidae and Mesonychidae. Cope originally placed creodonts within the Insectivora. In 1884, however, he regarded them as a basal group from which both carnivorans and insectivorans arose. Hyaenodontidae was not included among the creodonts until 1909. Over time, various groups were removed, and by 1969 it contained, as it does today, only the oxyaenids and the hyaenodontids.

In the LRT, Oxyaena and Hyaenodon are members of an extinct clade. However, Sinopa is considered a hyaenodontid, and it nests between the extant quoll (genus: Dasyurus) and the extant Tasmanian devil (genus: Sarcophilus). Sarkastodon is considered an oxyaenid and it nests as a sister to Sarcophilus. So… either the quoll and Tasmanian devil are living members of the Creodonta, or we’ll have to redefine the Creodonta.

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

Desmostylia
According to Wikipedia: “Desmostylians are the only known extinct order of marine mammals. The Desmostylia, together with Sirenia and Proboscidea (and possibly Embrithopoda), have traditionally been assigned to the afrotherian clade Tethytheria, a group named after the paleoocean Tethys around which they originally evolved. The assignment of Desmostylia to Afrotheria has always been problematic from a biogeographic standpoint, given that Africa was the locus of the early evolution of the Afrotheria while the Desmostylia have only been found along the Pacific Rim. That assignment has been seriously undermined by a 2014 cladistic analysis that places anthracobunids and desmostylians, two major groups of putative non-African afrotheres, close to each other within the laurasiatherian order Perissodactyla.”

In the LRT, desmostylians are indeed derived from anthracobunids, which, in turn, are derived from hippos and mesonychids. Mysticeti, the clade of baleen whales are derived from desmostylians. So… baleen whales are extant desmostylians.

Figure 3. Four mesonychids to scale. Here Mesonyx, Anthracobune, Paleoparadoxia and Hippopotamus are compared.

Figure 3. Four mesonychids to scale. Here Mesonyx, Anthracobune, Paleoparadoxia and Hippopotamus are compared.

Mesonychidae
According to Wikipedia, “Mesonychidae is an extinct family of small to large-sized omnivorouscarnivorous mammals closely related to cetartiodactyls (even-toed ungulates & cetaceans) which were endemic to North America and Eurasia during the Early Paleocene to the Early Oligocene. The mesonychids were an unusual group of condylarths with a specialized dentition featuring tri-cuspid upper molars and high-crowned lower molars with shearing surfaces. They were once viewed as primitive carnivores, like the Paleocene family Arctocyonidae, and their diet probably included meat and fish. In contrast to this other family of early mammals, the mesonychids had only four digits furnished with hooves supported by narrow fissured end phalanges.”

In the LRT, mesonychids include hippos and baleen whales. So, they are extant mesonychids. On the other hand, Arctocyonidae includes Arctocyon, which nests in the unrelated marsupial clade, Creodonta (see above). Certain other traditional mesonychids, like Sinonyx and Andrewsarchus, are not mesonyhids, but nest with the elephant shrew, Rhychocyon, close to tenrecs.

Figure 1. Silvanerpeton and Gephyrostegus to the same scale. Each of the two frames takes five seconds. Novel traits are listed. This transition occurred in the early Viséan, over 340 mya. Gephyrostgeus is more robust and athletic with a larger capacity to carry and lay eggs.

Figure 1. Silvanerpeton and Gephyrostegus to the same scale. Each of the two frames takes five seconds. Novel traits are listed. This transition occurred in the early Viséan, over 340 mya. Gephyrostgeus is more robust and athletic with a larger capacity to carry and lay eggs.

Gephyrostegidae
According to Wikipedia, “Gephyrostegidae is an extinct family of reptiliomorph tetrapods from the Late Carboniferous including the genera GephyrostegusBruktererpeton, and Eusauropleura.”

In the LRT, Gephyrostegus is the last common ancestor of the Amniota (= Reptilia). So… gephyrostegids include all living mammals, archosaurs (crocs + birds) and lepidosaurs.

References

wiki/Gephyrostegidae
wiki/Mesonychidae
wiki/Desmostylia

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Dr J Gauthier lecture video on birds + dinos

If you watch this…
Stay for the brilliant question and answer period at the end.

And…
returning to an earlier subject…
Geologist Randall Carlson reports on Joe Rogan Experience #606 (1:35:44) —  “See, here’s the thing. Modern science does tend to get over specialized. And so what happens is, they guy looking at extinctions might not be looking at glacial melting. The guy looking at glacial melting… the geologist is not looking at what’s going on in the sky. They’re not looking at traditions, you know, traditions from thousands of years ago. What it does is, because of the powerful of this specialization, this specialization is extremely powerful, but the thing of it is… it’s easy to miss the big picture. What that does is, it opens the door for generalists, guys who are just, people who are just, men or women, anybody who is curious about this stuff, look into it and try to see the big picture.”

In other words…
taxon exclusion problems can be solved by a wide gamut analysis of the entire range of tetrapods now known.

Joe Rogan says (1:37:46),
“People love to be able to dismiss anything that’s not mainstream, right?” To which Randall Carlson replies, “Because there’s this cult of authority.” Randall Carlson continues (1:38:40) “They’ve got this idea in their mind that there’s this authority that’s got it all explained, which makes it easy, because if somebody’s got this all explained, then we don’t need to concern ourselves with it or think about it. Right? So, what I see is, ‘Okay… forget about who says what. Look at the facts. Let the facts dictate to us what the meaning of all this is. And let’s look at all points of view.” 

The idea that a meteor impact ended the last Ice Age,
and killed the northern megafauna first proposed by Randall Carlson and others gained new hard evidence with the recent discovery of a Paris-sized crater on the north rim of Greenland. Details and videos here: https://earthsky.org/earth/meteorite-crater-under-greenland-ice

Phylogenetic miniaturization has a name: the Lilliput effect

Just learned this yesterday
and glad to see someone else recognizes and has given a name to phylogenetic miniaturization. Size matters!!! …according to the large reptile tree and large pterosaur tree. New animal taxa tend to originally develop at a small size, as hypothesized by S.M. Stanley (1973).

According to Wikipedia
The Lilliput effect (Urbanek 1993) is a term used to describe a decrease in body size in animals which have survived a major extinction. There are several hypotheses as to why these patterns appear in the fossil record, some of which are: the survival of small taxa, dwarfing of larger lineages, and the evolutionary miniaturization from larger ancestral stocks”

Berv and Field 2017
find an Avian Liilliput Effect at the K-Pg boundary.

From the abstract:
“Survivorship following major mass extinctions may be associated with a decrease in body size—a phenomenon called the Lilliput effect. Body size is a strong predictor of many life history traits (LHTs), and is known to influence demography and intrinsic biological processes. Pronounced changes in organismal size throughout earth history are therefore likely to be associated with concomitant genome-wide changes in evolutionary rates. Here, we report pronounced heterogeneity in rates of molecular evolution (varying up to ∼20-fold) across a large-scale avian phylogenomic data set and show that nucleotide substitution rates are strongly correlated with body size and metabolic rate. We also identify potential body size reductions associated with the Cretaceous–Paleogene (K-Pg) transition, consistent with a Lilliput effect in the wake of that mass extinction event. We posit that selection for reduced body size across the K-Pg extinction horizon may have resulted in transient increases in substitution rate along the deepest branches of the extant avian tree of life. This “hidden” rate acceleration may result in both strict and relaxed molecular clocks over-estimating the age of the avian crown group through the relationship between life history and demographic parameters that scale with molecular substitution rate. If reductions in body size (and/or selection for related demographic parameters like short generation times) are a common property of lineages surviving mass extinctions, this phenomenon may help resolve persistent divergence time debates across the tree of life. Furthermore, our results suggest that selection for certain LHTs may be associated with deterministic molecular evolutionary outcomes.”

Still unrecognized by other pterosaur workers
the large pterosaur tree and large reptile tree recover a Lilliput effect at the base of every major pterosaur clade and elsewhere (turtles, reptiles, lizards, mammals, placentals, bats, etc. ) While other workers find the Lilliput effect in the aftermath of mass extinctions, the LRT found smaller taxa prior to mass extinctions survived the events, while others, like Late Cretaceous large pterosaurs, did not.

References
Berv JS and Field DJ 2017. Genomic Signature of an Avian Lilliput Effect across the K-Pg Extinction. Systematic Biology syx064
Harries PJ and Knorr PO 2009. What does the ‘Lilliput Effect’ mean? Palaeogeography, Palaeoclimatology, Palaeoecology 284:4–10. online
Stanley SM 1973. An explanation for Cope’s Rule”. Evolution. 27: 1–26. doi:10.2307/2407115
Urbanek A 1993.
Biotic crises in the history of Upper Silurian graptoloids: APalaeobiological model. Historical Biology, 7:29-50.

Surviving the Permian-Triassic boundary

For those of you
who typically ignore the letters to the editor, this is one exchange that you might find interesting.

Earlier Bill Erickson asked me 
“So, why, in your opinion, did diapsid reptiles suddenly — and I do mean suddenly — become so dominant beginning in or about Carnian time, and remain dominant thereafter throughout the Mesozoic, after millions of years of synapsid dominance beforehand in the mid-to-late Paleozoic and early Triassic?”

I answered
-Why- questions are very tough in Science, Bill. I don’t know the answer to your question. I don’t have an opinion either.

B. Erickson replied
“David – I’d agree for the most part, but I do think Peter Ward made a good case [in his book Gorgon.] that synapsids had a less efficient respiratory system than many archosaurs, and that lower atmospheric oxygen was a major driver in the end-Permian extinction. Of course, some synapsids, especially cynodonts, were diverse in early Triassic, and that’s another story.”

To which I replied
Bill, I have heard of Ward’s hypothesis and it makes a certain sense. Let me toss this off-the-cuff idea at you.

Synapsids, to my knowledge, survived the Permian extinction event by burrowing, or perhaps there was a part of the world they found refuge in. If the former, whether in dirt or leaf litter, both niches seem to support small to tiny tetrapods. See Pachygenelus, Megazostrodon and Hadrocodium for examples. [Well, those are all bad examples as they are all Early Jurassic, but consider the small earliest Triassic cyndont, Thrinaxodon (Fig. 1).]

Figure 1. Thrinaxodon, a burrowing synapsid from the Early Triassic was similar in size and proportion to the Late Permian ancestor of all archosauriformes, Youngoides (Fig. 2). These similar basal taxa were the genesis for all later mammals, dinosaurs and birds. 

Figure 1. Thrinaxodon, a burrowing synapsid from the Early Triassic was similar in size and proportion to the Late Permian ancestor of all archosauriformes, Youngoides (Fig. 2). These similar basal taxa were the genesis for all later mammals, dinosaurs and birds.

On the diapsid/archosauriform side, the likely aquatic proterosuchids cross the Permo-Triassic boundary, then give rise to all the familiar archosauriformes. In the water niche larger tetrapods, like crocs, are supported. As Malcolm Gladwell documented so well [in his book Outliers], an initial minor advantage can accelerate or become emphasized over time.

So, again guessing here, the largely nocturnal denizens of the burrows and leaf litter apparently played to their environment and stayed small yielding the otherwise unoccupied largely diurnal aquatic-grading-to-terrestrial taxa the larger size as they played to their niche. Maybe the diapsids just got to the outdoors/daylight niche first.

Figure 2. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa. Youngoides and the earliest proterosuchids were Late Permian. Others were Early Triassic and later.

Figure 2. Updated image of various proterosuchids and their kin. When you see them all together it is easier to appreciated the similarities and slight differences that are gradual accumulations of derived taxa. Youngoides and the earliest proterosuchids were Late Permian. Others were Early Triassic and later.

Along the same lines, the lepidosaur diapsids stayed relatively small and unobtrusive except for the Late Triassic sea-going tanystropheids and Late Cretaceous sea-going mosasaurs, perhaps following the same niche rules and regs as above. Pterosaur lepidosaurs also experienced much greater size in the Late Cretaceous.

Just a thought/opinion supported by what I can recall at the moment. Let me know your thoughts if you’d like to continue this thought journey. [END]

And then beyond that exchange…
I note that EarlyTriassic synapsid taxon list also includes the large dicynodont, Kanneymeira and a number of small therocephalians. Burrowing taxa are pre adapted to a nocturnal existence. The big dicynodont must have survived in some sort to refuge niche.

The standard story
includes the notion that dinosaurs and other archosauriform predators were snapping up every little synapsid they saw, so the survivors became invisible by becoming nocturnal and or really tiny… and that probably continued throughout the Mesozoic, with both clades improving generation after generation.

erythrosuchid

Figure 3. Basal archosauriforms from the Early Triassic,  including Euparkeria, Proterosuchus and Garjainia.

The twist brought to you by
the large reptile tree is the outgroup for the Archosauriforms, Youngoides, is a small, Thrinaxodon-sized terrestrial younginiform diapsid (Fig. 1). Perhaps an early affinity for rivers and lakes was the key to survival among proterosuchid archosauriforms when the P-Tr problems escalated. But also note that the small ancestors to dinosaurs, the euparkeriids, (Fig. 3) ALSO survived the P-Tr boundary as small terrestrial forms alongside the much larger terrestrial erythrosuchids, otherwise known as giant younginids.

Maybe we’ll never know…
but it’s interesting to put at least some of the puzzle pieces together.

 

 

Why Pterosaurs Are Extinct Today

The K/T Extinction Event
Everyone knows that pterosaurs, dinosaurs and a host of other prehistoric reptiles died out at the K/T (Cretaceous/Tertiary) boundary ~65 mya. But SOME birds, lizards, turtles, crocs and mammals survived. So, why did ALL pterosaurs die out?

Phylogenetic Analysis 
As in dinosaurs, the pterosaurs we know from the latest Cretaceous were not the same pterosaurs living in the Triassic, Jurassic or Early Cretaceous. All of these earlier pterosaurs became extinct, but a few genetic lines survived by evolving into the Late Cretaceous forms we know and love. Phylogenetic analysis indicates that certain lucky Middle Jurassic Dorygnathus specimens ultimately evolved (via several transitional taxa) into Quetzalcoatlus, Pteranodon, Nyctosaurus, Tupuxuara and any other Late Cretaceous pterosaurs I’m forgetting (the current list is not much longer than this).

The Example of Dorygnathus
Analysis illustrates how the descendants of Dorygnathus changed in size and shape as they evolved into the above Late Cretaceous taxa. Therein, l think, lies the answer to why pterosaurs were not able to continue evolving into the modern day.

The Azhdarchidae.

Figure 1. The Azhdarchidae. Click to enlarge.

Size Matters
If we were to follow the lineage of Dorygnathus through Quetzalcoatlus (Fig. 1) we would meet the following taxa in order: Dorygnathus (SMNS 50164), Pterodactylus? spectabilis (TM 10134), Beipiaopterus, No. 44, No. 42, Jidapterus, Chaoyangopterus, Zhejiangopterus and finally the two species of Quetzalcoatlus. Setting aside the huge size differences between the two Qs and their phylogenetic predecessor, Zhejiangopterus, note that tiny TM 10134 and two other tiny pteros, No. 42 and No. 44, are in this line-up.

Tiny Survivors
In the Late Jurassic the genetic lineage of Dorygnathus, of the Middle Jurassic, was represented by a tiny version of itself, TM 10134. There were no other full-size Dorygnathus present in the Late Jurassic. Something killed every other one over a certain size. Only tiny dory descendants somehow survived. Was it because of their size?

Major Morphological Changes in Tiny Taxa
As mentioned above (Fig. 1) other Late Jurassic tiny dorygnathids also include No. 42 and No. 44, both of which evolved a slender elongated neck, a low trostrum, smaller teeth and longer more gracile limbs. These traits were retained in all later and larger azhdarchids and huanhepterids (Fig. 1). (Pterorhynchids, scaphognathids and ctenochasmatids were also Dorygnathus descendants you can read about here, here and here).

Good Times
When the threat of extinction did not loom over pterosaurs, they tended to become bigger. Evidently this was especially true during the latest Cretaceous because pterosaurs reached their greatest sizes right at 65 million years ago.

Not Being Small Is What Killed Late Cretaceous Pterosaurs
Just as being small saved many pterosaur lines earlier, being small saved many other vertebrates following the K/T mass extinction event. Big vertebrates did not survive. Unfortunately the giant pterosaurs of the latest Cretaceous could not breed small enough to save themselves, as their ancestors had done. We don’t find any pterosaurs smaller than Nyctosaurus in the Late Cretaceous.

Serial Size Reduction and How It Happens
ln pterosaurs phylogenetic size reduction from Dorygnathus to TM 10134 was made possible by reaching sexual maturity at half their final size (Chinsamy et al. 2008). Smaller pelves would have passed smaller eggs, smaller hatchlings and an even smaller second generation in serial fashion. Smaller vertebrates typically have a relatively faster maturation process, creating more tiny hatchlings earlier and at a faster clip. This increase in reproductive rates raised the odds that whatever was killing the larger, slower-to-breed individuals could be overcome by an acceleration in breeding, producing an acceleration in genetic variation and mutation. Such a serial size reduction pattern occurred at the base of nearly every major clade within the Pterosauria. When the same process is observed about a dozen times that verifies its veracity.

Phony pterosaur.

Figure 2. Phony pterosaur.

If only some tiny pteros existed at the Late Cretaceous, we might have some “thunderbirds” flying around today (Fig. 2).

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
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.