Another Triassic turtle enters the LRT

This turned out to be a somewhat ‘ho-hum’ event,
but a good opportunity to review turtle origins, still suffering from taxon exclusion and inappropriate taxon inclusion, as determined by the LRT (subset Fig. 4), which tests all contenders.

Sterli, de la Fuente and Rougier 2007 described
“a complete cranial and postcranial anatomy and a phylogenetic analysis of Palaeochersis talampayensis (Rougier, de la Fuente and Arcucci 1995), the oldest turtle from South America, is presented here.”

Figure 2. Palaeochersis skull from Rougier et al. 1995 with colors and new bone labels added.

Figure 1. Palaeochersis skull from Sterli et al. 2007 with colors and new bone labels added.

Figure 2. Palaeochersis overall reconstructed from elements in Sterli, de al Fuente and Rougier 2007. This Triassic turtle nests in the LRT with Proganochelys in figure 3.

Figure 2. Palaeochersis overall reconstructed from elements in Sterli, de al Fuente and Rougier 2007. This Triassic turtle nests in the LRT with Proganochelys in figure 3.

Unfortunately
taxon exclusion and bone misinterpretation mar this description, published before the genesis of ReptileEvolution.com and a distinctly different take on turtle origins based on including more taxa. Palaeochersis (Figs. 1, 2; PULR 68; Late Triassic, Norian-Rhaetian) is the third Triassic turtle to enter the LRT after Proganochelys and Proterochersis (Fig. 3).

Proganochelys and Proterochersis, two Traissic turtles.

Figure 3. Proganochelys and Proterochersis, two Traissic turtles.

Sterli, de la Fuente and Rougier 2007 report,
“Palaeochersis talampayensis has primitive character states in the skulllike the presence of lacrimal and supratemporal bones, the presence of a quadrate pocket, a foramen trigemini partially enclosed, middle ear limits partially developed, presence of an interpterygoid vacuity, presence of a cultriform process and a high dotsum sellae. However, Palaeochersis talampayensis also has derived character states like the absence of vomerine teeth, basipterygoid articulation sutured, processus paraoccipitalis tightly articulated to quadrate and squamosal, and cranioquadrate space partially enclosed in a canal. The postcranial description was based on Palaeochersis holotype (PULR 68) and on specimen PULR 69 represented by an almost complete skeleton and a hindfoot, respectively.” 

Figure 1. Carbonodraco enters the LRT alongside another recent addition, Kudnu, at the base of the pareiasaurs + turtles.

Figure 4. Subset of the LRT focusing on turles. Palaeochersis is not listed here, but nests with Proganochelys, as shown in the LRT, which has been updated.

According to the LRT
Proganochelys, Proterochersis and Palaeochersis were terminal taxa, leaving no descendants. Instead, according to the large reptile tree (LRT, 1740+ taxa, subset Fig. 4), a Late Permian/Early Triassic sister to Niolamia gave rise to a Late Permian/Early Triassic sister to Meiolania (Fig. 5) gave rise to a Triassic hornless Kallokibotion, otherwise known only from the Latest Cretaceous and later. More derived taxa include Kayentachelys (Early Jurassic) filling in the temporal gap. In turtles the cranial horns are primitive. The loss of cranial horns is a derived trait. That’s something turtle workers have yet to appreciate.

Figure 4. Bunostegos and Elginia at the base of hard shell turtles in the LRT, where late-surviving Niolamia and Meiolania are basal hardshell turtles more primitive than Proganochelys and Palaeochesis. Not all colors here match those in figure 1. Note the labels.

Figure 5. Bunostegos and Elginia at the base of hard shell turtles in the LRT, where late-surviving Niolamia and Meiolania are basal hardshell turtles more primitive than Proganochelys and Palaeochesis. Not all colors here match those in figure 1. This sequence was submitted for publication, but rejected. 

Taxon exclusion mars all prior basal turtle studies.
In the LRT Palaeochersis nests with another Triassic turtle, Proganochelys. Given their overall and detailed morphology, that was expected and comes as no surprise.

Not much else to report here,
other than the identities of cranial bones in hard-shell turtles need to be reconsidered in light of their ancestry from the late-surviving, giant-horned turtles, Niolamia and Meiolania and before that, ancestral pareiasaurs like Elginia and Bunostegos (Fig. 4). These are taxa traditionally omitted from recent turtle ancestry studies. The LRT omits no putative ancestral turtle candidates. Rather the LRT tests them all. And for new readers, note (Fig. 4) soft-shell turtles had their own parallel origin and ancestry from different small horned pareiasaurs.

Longtime readers may notice:
Several of the older turtle skull illustrations (Fig. 5) were recolored to match an emerging standard pattern (e.g. bright green for supratemporals). My fault that I did not do this from the very beginning ten years ago. More work for me, but lookout for different colors in older blogposts.


References
Rougier GW, de la Fuente and Arcucci AB 1995. Late Triassic turtles form South America. Science 268:855–858.
Sterli J, de la Fuente MS and Rougier GW 2007. Anatomy and relationships of Palaeochersis talampayensis, a Late Triassic turtle from Argentina. Palaeontographica Abt. A 281:1–61.

wiki/Palaeochersis (Spanish)

Inside an odd Triassic ichthyosaur: an odd embryo, not a meal

Summary for those in a hurry:
A new 5m adult ichthyosaur displays reversals (limb-like fins, a deep pelvis and a long neck) that went unnoticed, until it came to the embryo, which was misidentified as an incomplete thalattosaur meal.

Jiang et al. 2020 brought us news
of a “4m Triassic thallatosaur” swallowed by a 5m ‘megapredator’ ichthyosaur (Fig. 1; (XNGM-WS-53-R4). “The prey is identified as the thalattosaur Xinpusaurus xingyiensis based on close similarities of appendicular skeletal elements in both shape and size. The similarity is most characteristically seen in humeral morphology—it is a robust bone with a limited shaft constriction, and with an expanded proximal extremity.”

“The skull, mandible, and tail of the prey are unlikely to be present in the bromalite (= fossil of digested or digestible remains, i.e. coprolite), given that no isolated elements from these body regions are mixed in with what is preserved.”

Figure 1. Guizhouichthyosaurus ate a Xinpusaurus

Figure 1. Images from Jiang et al. proposing their hypothesis of a thalattosaur, Xinpusaurus, as stomach contents within the much larger Guizhouichthyosaurus. This hypothesis is based on several errors.

From the Jiang et al. abstract:
“Here we report a fossil that likely represents the oldest evidence for predation on megafauna, i.e., animals equal to or larger than humans, by marine tetrapods—a thalattosaur (∼4 m in total length) in the stomach of a Middle Triassic ichthyosaur (∼5 m). The predator has grasping teeth yet swallowed the body trunk of the prey in one to several pieces.”

After tracing published photos:

  1. The larger specimen is distinct from the holotype Guizhouichthyosaurus tangae (Fig. 4; Cao & Luo, 2000; IVPP V 11853) and reconstructions (Figs. 2, 3) are distinct from the Jiang et al. reconstruction. The limb-like fins of the adult were not reported. Several bones were misidentified in the embryo.
  2. Phylogenetic analysis (Fig. 9) nests the XNGM-WS-53-R4 specimen with Shonisaurus popularis (Fig. 5), two nodes away from Guizhouichthyosaurus.
  3. The embryo is folded in thirds and surrounded by an oval membrane. The unfolded morphology of the embryo matches the adult (Fig. 3).
  4. The size of the 1m embryo is much smaller than the estimated 4m prey item.
  5. The location of the embryo is in the posterior half of the abdomen near the uterus, distinct from the location of the more anterior stomach.
Figure 8. The skull of the new specimen wrongly assigned to Guizhouichthyosaurus by Jiang et al. 2020.

Figure 2. The skull of the new specimen wrongly mistakenly assigned to Guizhouichthyosaurus by Jiang et al. 2020.

Figure 1. The XNGM-WS-53-R4 specimen does not nest with Guizhouichthys but with Shonisaurus and has a distinct morphology.

Figure 3. The XNGM-WS-53-R4 specimen does not nest with Guizhouichthys (Fig.4). but with Shonisaurus (Fig. 5) and has a distinct morphology. Note the long neck and limb-like flippers/

Figure 2. Two closely related ichthyosaurs, Guizhouichthyosaurus tangae and "Cymbospondylus" buchseri, one with large flippers, one with small.

Figure 4. Two closely related ichthyosaurs, Guizhouichthyosaurus tangae and “Cymbospondylus” buchseri, one with large flippers, one with small.

The original diagram of the far from complete ‘stomach contents’
(Fig. 6) overlooked the skull, mandible, tail and many other bones here (Figs. 3, 4) here reconstructed (Fig. 7) as a complete skeleton of an embryo folded into a soft and pliable egg-like shape. Even the kink of the ichthyosaur tail is preserved. Both ends of the embryo were overlooked by those with firsthand access to the specimen (Fig. 1).

Figure 5. Shonisaurus popularis is a larger relative of the XNGM WS 53 R4, but retains the long slender flippers of Guizhouichthyosaurus.

Figure 5. Shonisaurus popularis is a larger relative of the XNGM WS 53 R4, but retains the long slender flippers of Guizhouichthyosaurus.

According to Laura Geggel, writing for LiveScience.com
“About 240 million years ago, one giant sea monster ate another, and then died with chunks of the beast in its belly. Researchers in China have now discovered and analyzed the fossilized corpses of these beasts, which they are calling the oldest evidence of megapredation — when one large animal eats another — on record.”

“The ichthyosaur may have attacked and killed the thalattosaur before eating it, but it’s also feasible that the ichthyosaur was simply scavenging the thalattosaur’s remains, the researchers said.”

Figure 8. Photo from Jiang et al. 2020. The XNGM-WS-53-R4 embryo in situ. Colors added.

Figure 6. Photo from Jiang et al. 2020. The XNGM-WS-53-R4 embryo in situ. Colors added. Note the posterior mandible was misidentified as a humerus. The distal humerus was tentatively misidentified as an interclavicle. One ilium is another jaw element .The other ilium is an ulna.

Figure 7. The XNGM embryo traced, unfolded and reconstructed from the tracing using DGS methods, as in the adult.

Figure 7. The XNGM embryo traced, unfolded and reconstructed from the tracing using DGS methods, as in the adult.

The IVPP holotype of Guizhouichthyosaurus
has much longer fins with more phalanges than the Jiang et al. adult and embryo specimens.

In the large reptile tree
(LRT, 1737+ taxa) thalattosaurs and mesosaurs are sister clades to ichthyosaurs. Why is this important? This XNGM specimens have long proximal limb element proportions and short digits. They also have more cervical vertebrae creating a longer neck. This odd morphology is more similar to those of thalattosaurs, mesosaurs and basal ichthyopteryigians like Wumengosaurus and Thaisaurus (Fig. 7) than to the XNGM specimen’s closer ichthyosaur relatives (Fig. 9), like Shonisaurus.

Phylogenetic reversals like this are rare.
Now we have one more example to add to that list.

Figure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

Figure 7. Basal Ichthyosauropterygia. The limb-like flipper and additional cervicals in the XNGM-WS-53-specimen are reversals to these more primitive taxa.

Figure 2. Guizhouichthyosaurus tangae skull preserved in three dimensions.

Figure 8. Guizhouichthyosaurus tangae skull preserved in three dimensions.

Figure 9. Subset of the LRT focusing on ichthyosaurs.

Figure 9. Subset of the LRT focusing on ichthyosaurs.

Displaying an unexpected limb/fin reversal,
a deep pelvis and a long neck, the XNGM adult and embryo were not typical of closely related ichthyosaurs. This odd morphology was originally overlooked in the adult and only partly observed in the embryo. This resulted in an incorrect assessment of the embryo as a thalattosaur meal. Tracing, reconstruction and phylogenetic analysis of both adult and embryo corrected the relationship and revealed the overlooked reversals in this unusual ichthyosaur. The XNGM specimen needs a new generic name because it is not congeneric with the holotype of Guizhouichthyosaurus.


References
Cao and Luo 2000. Published in: in Yin, Zhou, Cao, Yu & Luo, 2000. Geol Geochem 28 (3), Aug 8, 2000.
Jiang D-Y et al. (7 co-authors) 2020. Evidence supporting predation of 4-m marine reptile by Triassic megapredator. online
Maisch M et al. 2015. Cranial osteology of Guizhouichthyosaurus tangae (Reptilia: Ichthyosauria) from the Upper Triassic of China. Journal of Vertebrate Paleontology 26(3): 588-597.

Publicity
https://www.livescience.com/triassic-sea-monster-ate-huge-reptile.html
https://www.livescience.com/24031-ancient-sea-monsters-predator-x.html

Pre-pterosaur skull evolution

Pterosaurs are chiefly known by their post-cranial traits.
Here (Fig. 1) a diagram is presented of pterosaur ancestor skulls in phylogenetic order. Alongside this diagram is a list of general trends documented from the tritosaur lepidosaur, Huehuecuetzpalli (at top), to Macrocnemus to Cosesaurus to Longisquama and culminating with the basal pterosaur, Bergamodactylus (at bottom).

Figure 1. Skulls of pterosaur ancestors from Huehuecuetzpalli through Macrocnemus, Cosesaurus, Longisquama and the pterosaur Bergamodactylus.

Figure 1. Skulls of pterosaur ancestors from Huehuecuetzpalli through Macrocnemus, Cosesaurus, Longisquama and the pterosaur Bergamodactylus.

Huehuecuetzpalli never fits well
into traditional squamate cladograms because it is not a member of the Squamata.

Earlier we looked at the gradual evolution
of the manus in these taxa (Fig. 2). You won’t find evidence like this ‘out there’ in the academic literature where PhDs continue to say, “We still don’t know the ancestors to pterosaurs.” This is rather embarrassing for them, if not now, then someday.

pterosaur wings

Figure 2. Click to enlarge. The origin of the pterosaur wing and whatever became of manual digit 5?

Addendum: originally published online on Facebook yesterday:
For my paleo friends… this is Cosesaurus (Fig. 3), a lepidosaur, not closely related to living lizards, that was able to run bipedally, like some living lizards do by convergence. It had sprawling limbs, but created a narrow gauge trackway matching Early to Middle Triassic Rotodactylus footprints found from Europe to North America. Lateral toe (#5) uniquely bent back to imprint dorsal side down behind the other four regular toes.

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

Figure 3. Click to enlarge and animate. Cosesaurus flapping – fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.

The curved, stem-like, immobile coracoid is an indicator of flapping (birds share this trait), matched to a strap-like scapula (birds share this trait). The interclavicle overlaps the sternum and clavicles to create a pre-sternal complex, as in pterosaurs. A tiny pterosaur-like prepubis is present. So is an anterior projection of the ilium (top pelvic bone) typically found only in bipeds. Two wrist bones migrated to the thumb side of the wrist to create a pteroid and preaxial carpal, otherwise only found in pterosaurs (but similar, by convergence, to the panda’s ‘thumb’). The tail is extremely narrow and stiff.

Extradermal membranes extend from the crest of the skull to the back of the pelvis. Fibers (pre-wings) trail the forelimbs. A membrane trails each hind limb. These and many other traits are shared with pterosaurs, the flying reptiles of the Mesozoic.

Like birds, pterosaur ancestors used their decorative traits (feathers, membranes) for display, including flapping prior to being able to fly. Running bipedally enabled breathing while running (something quadrupedal undulating lizards cannot do). Bipedal locomotion increased stamina and warmed up the metabolism. So secondary sexual traits (decorations and behavior for display) helped create both birds and pterosaurs.

I studied the one-of-a-kind fossil, a hand-sized mold of such exquisite detail that it also preserved a small jellyfish, in Barcelona in the 1990s where it was inappropriately wrapped in a few layers of toilet paper. In 2000 I described Cosesaurus as an ancestor to pterosaurs, and did so by adding it to four previously published phylogenetic analyses.

Unfortunately, that peer-reviewed and academically published paper has been ignored ever since, for reasons I still cannot fathom other than I have no science degree, let alone a PhD. To this day paleontologists repeat the phrase, “We still don’t know where pterosaurs come from.” Frustrating, but I’ve gotten used to it. I guess this posting is just a chance to vent.

For more exquisite Cosesaurus details, click here: http://reptileevolution.com/cosesaurus.htm

The origin of endothermy triggered by the P-Tr extinction event?

Benton 2020 reports,
“the emergence of endothermy in a stepwise manner began in the Late Permian but accelerated in the Early Triassic. The trigger was the profound destruction wrought by the Permian-Triassic mass extinction (PTME).”

Two more abbreviations found in Benton 2020 that will be making the rounds:

  1. Mesozoic Marine Revolution (MMR)
  2. Triassic Terrestrial Revolution (TTR).

According to Benton 2020:
“Among tetrapods, both synapsids and archosaurs survived into the Triassic, survivors were marked by the acquisition of endothermy, as shown by bone histology, isotopic analyses, and the acquisition of insulating pelage. Both groups before the PTME had been sprawlers; after the event they adopted parasagittal (erect) gait.”

Actually lots of other clades lacking endothermy, a pelage or a parasagittal gait also survived into the Triassic, as everyone knows.

Actually, none of these traits appeared in any of the above-named groups until the Middle Triassic and then tentatively. Even so, that was just a few million years after the extinction event.

Actually, one group of lepidosaurs also produced endotherms with insulating pelage: fenestrasaurs (including pterosaurs; Fig. 1). This has been a thorn in Benton’s side since Peters 2000–2009. Benton and his colleagues have ignored and omitted these peer-reviewed contributions to the literature for the last twenty years to preserved some sort of status quo.

As everyone knows., crocs returned to a sprawling gait and ectothermy. Hmmm…

Figure 3. The origin of pterosaurs now includes Kyrgyzsaurus, nesting between Cosesaurus and Sharovipteryx.

Figure 1. The origin of pterosaurs now includes Kyrgyzsaurus, nesting between Cosesaurus and Sharovipteryx.

Benton continues making classic mistakes by

  1. including pterosaurs with dinosaurs.
  2. omitting the bipedal basal crocodylomorphs that are essential to the dinosaur origins story.
  3. omitting the basal bipedal fenestrasaurs that are essential to the pterosaur origins story.
  4. omitting Repenomamus and other mammal mimics.

Benton claimed
“there is now substantial evidence that dinosaurs originated in the Early Triassic following several discoveries in 2010 and 2011. Asilisaurus, from the Manda Formation (Anisian, Middle Triassic, 247–242 Ma) of Tanzania, and postulated that this was a representative of a new group called the silesaurids, close to dinosaurs.”

Unfortunately, adding taxa reveals
the poposaur Silesaurus and Asiliisaurus are poposaurs, dinosaur mimics not close to dinosaurs.

Another Middle Triassic poposaur with erect limbs,
Lotosaurus
, would have supported Benton’s claims, but was not mentioned. The origin of the poposaurs (Turfanosuchus (Fig. 2) certainly could go back to the Early Triassic.

Figure 1. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

Figure 2. Poposauridae revised for 2014. Here they are derived from Turfanosuchus at the base of the Archosauria, just before crocs split from dinos.

Benton perpetuates the myth
of the Pseudosuchia, an invalid clade in the LRT.

Benton employs too few taxa
to realize the basal dichotomy between Euarchosauriformes and Pararchosauriformes that preceded the extinction event.

Likewise, Benton employs too few taxa
to realized the basal reptile split between lepidosauromorphs (including pterosaurs and rhynchosaurs) and archosauromorphs (including synapsids, non-lepidosaur diapsids and archosauriformes) goes back to the Early Carboniferous).

Key taxa,
like Euparkeria, Youngosuchus, Decuriasuchus, Turfanosuchus, Pseudhesperosuchus, Gracilisuchus and PVL 4597 (Fig. 2), are not mentioned in the Benton text.

The Middle Triassic is when archosauriformes radiated widely,
perhaps with Early Triassic and Late Permian roots, but everyone knew this already.

In short,
there is little to nothing new here and lots of mythology. I think everyone knew animals on planet Earth essentially picked themselves up and started all over again after the end Permian extinction event which wiped out 95% of all species.

Figure 1. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

Figure 3. The origin of dinosaurs in the LRT to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.  Note the phylogenetic miniaturization at the origin of Archosauria (Crocs + Dinos).

More taxon inclusion would have saved this paper.
You may remember Benton and Hone 2007, 2009 also deleted taxa and citations to achieve the end they sought, based on Benton’s 1999 paper on pterosaur origins, featuring the tiny bipedal croc with tiny hands, Scleromochlus. Sadly, Benton’s latest cherry-picking and machinations are destroying any good reputation earlier work may have earned him.


References
Benton MJ 2020. The origin of endothermy in synapsids and archosaurs and arms races in the Triassic, Gondwana Research (2020), https://doi.org/10.1016/j.gr.2020.08.003
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330

http://reptileevolution.com/pterosaur-wings.htm

https://pterosaurheresies.wordpress.com/2012/04/13/a-supertree-of-pterosaur-origins-hone-and-benton-2007-2009/

Adelobasileus restored: NOT ‘the oldest mammal’

When Lucas and Hunt 1990
and Lucas and Luo 1993 described the cranium (all that is known) of Adelobasileus (Fig. 1) they concluded it was, ‘the oldest mammal’. 

Figure 1. Adelobasileus restored like Therioherpeton after first nesting together in the LRT.

Figure 1. Adelobasileus restored like Therioherpeton after first nesting together in the LRT. Line drawing for Adelobasileus from Lucas and Luo 1993.

By contrast
the large reptile tree (LRT, 1707+ taxa, subset Fig. x) nests Adelobasileus with the low and wide mammal-mimic cynodont, Therioherpeton (Fig. 1), despite the very few characters that could be scored here. Both also nest with Sinocodon and Haramiyavia in the LRT. Thus Adelobasileus in not the oldest mammal. It is not even a mammal.

Therioherpeton
Fig. 1) was originally described by Bonaparte and Barberena 1975 as ‘a possible mammal ancestor’.

Later
Oliveira 2006 reevaluated Therioherpeton“Therioherpetidae are distinguished from all other probainognathians by upper teeth with the imbrication angle increasing in the posterior postcanines. In addition, upper and lower postcanine teeth are labio-lingually narrow.” This author did not include Adelobasileus in his cladogram. Oliveira nested Therioherpeton with Riograndia.

Figure 1. Megazostrodon skull in several views. Drawings from Gow 1986. Colors applied here.

Figure 2. Megazostrodon skull in several views. Drawings from Gow 1986. Colors applied here. This is the last common ancestor of all mammals in the LRT.

The last common ancestor of all mammals
in the LRT (subset Fig. x) continues to be Megazostrodon (Fig. 2), from the early Jurassic. Other, more derived mammals, like Morganucodon, are found in the Late Triassic, indicating an earlier origin and radiation.

Figure x. Subset of the LRT focusing on therapsids, like Repenomamus, leading to mammals.

Figure x. Subset of the LRT focusing on therapsids leading to mammals. Adelobasileus nests with Therioherpeton in this older cladogram that does not list Adelobasileus.

The most recent paper on basal mammals
and their immediate ancestors, King and Beck 2020, shows just how different cladograms can be when taxa are excluded (Fig. 3, click to enlarge). King and Beck mix non-mammals with prototherians, metatherians and eutherians in a mish-mash as compared to the LRT (Fig. x). At least they nest Adelobasileus outside their Mammalia (which should include only Prototherians, Metatherians and all descendants of their last common ancestor, Megazostrodon, Fig. 2).

Figure 3. Click to enlarge. Stem mammal cladogram from King and Beck 2020 showing how different their topology is to the LRT (color overlays, key at left) which has a wider gamut of included taxa. Arrow points to Adelobasileus near top.

Figure 3. Click to enlarge. Stem mammal cladogram from King and Beck 2020 showing how different their topology is to the LRT (color overlays, key at left) which has a wider gamut of included taxa. Arrow points to Adelobasileus near top.

Add taxa 
and multituberculates nest with rodents, Fruitafossor nests with xenarthrans and other taxa nest appropriately with prototherians, metatherians and eutherians as shown in the LRT (subset Fig. x).

The nesting of Adeolbasileus with Therioherpeton
is not quite an original hypotheses. Google the two keywords, “Adelobasileus, Therioherpeton” and you’ll find someone tweeted these two as possible ancestor-descendant taxa, but unfortunately, still considered Adelobasilesus ‘the oldest mammal.’


References
Bonaparte JF and Barberena MC 1975. A possible mammalian ancestor from the Middle Triassic of Brazil (Therapsida–Cynodontia). Journal of Paleontology 49:931–936.
King and Beck 2020. Tip dating supports novel resolutions of controversial relationships among early mammals. Proceedings of the Royal Society B 287: 20200943.
http://dx.doi.org/10.1098/rspb.2020.0943
Lucas SG and Hunt 1990. The oldest mammal. New Mexico Journal of Science 30(1):41–49.
Lucas SG and Luo Z 1993. Adelobasileus from the upper Triassic of west Texas: the oldest mammal. Journal of Vertebrate Paleontology 13(3):309–334.
Oliveira EV 2006. Reevaluation of Therioherpeton cargnini Bonaparte & Barberena, 1975 (Probainognathia, Therioherpetidae) from the Upper Triassic of Brazil. Geodiversitas 28 (3): 447-465.

http://reptileevolution.com/sinoconodon.htm
wiki/Adelobasileus
wiki/Therioherpeton

Triassurus: a tiny Triassic salamander?

Summary for those just skimming:
Including more taxa and using DGS to gather more data from fossils upsets academic results again.

Shoch et al. 2020 discuss the origin of salamanders
by directing their attention to a tiny juvenile Triassic tetrapod, Triassurus (PIN-2584/10, skull length 3.8 mm; Ivakhnenko 1978; Figs. 1–3). The discovery of a larger referred specimen (FG 596/V/20), provided Schoch et al. a reason to reexamine the type.

Science first learned about tiny Triassurus
from Ivakhnenko 1978 (here reproduced in a book, Fig. 1). Not much detail back then.

Figure 1. Illustration and description Triassurus (Ivakhnenko 1978).

Figure 1. Illustration and description Triassurus (Ivakhnenko 1978). Little more than the outline of the skull was illustrated back then.

The Schoch et al. tracing of the tiny holotype
(Fig. 2) likewise offers few details. DGS colors (Fig. 2) provide more and different details.

Figure 3. Triassurus in situ with tracing from Schoch et al. 2020 and DGS color tracing.

Figure 2. Triassurus in situ with tracing from Schoch et al. 2020. DGS color tracing added here. See figure 3 for a reconstruction.

Pushing those DGS details around
to create a reconstruction (Fig. 3) helps one understand the anatomy of Triassurus, enough to score it.

Figure 4. The type specimen of Triassurus in situ and reconstructed.

Figure 3. The type specimen of Triassurus in situ and reconstructed.

Scoring the Middle Triassic Triassurus type
nests it with Early Permian Gerrobatrachus (Fig. 4), one node away from extant salamanders in the large reptile tree (LRT, 1690+ taxa; subset Fig. 5). So, if Triassic Triassurus is the earliest known salamander (as Schoch et al report), then Early Permian Gerobatrachus is one, too. And it is tens of millions of year older. If Gerobatrachus is not a salamander, then both are not salamanders.

Figure 5. Gerrobatrachus adult.

Figure 4. Gerrobatrachus adult.

The LRT tree topology
is distinctly different than the cladogram published by Shoch et al. 2020 (Fig. 6).

Figure 5. Subset of the LRT focusing on basal tetrapods including Triassurus, type and referred specimen FG 596 V 20.

Figure 5. Subset of the LRT focusing on basal tetrapods including Triassurus, type and referred specimen FG 596 V 20.

Unfortunately,
the cladogram employed by Schoch et al. 2020 (Fig. 6) needs more taxa. Currently it nests Proterogyrinus as the outgroup taxon. That creates problems. Relative to the LRT (Fig. 5) one branch of the Schoch et al. cladogram is inverted such that the basalmost tetrapods, Siderops and Gerrothorax, nest as highly derived terminal taxa. The other branch with caecilians, frogs and salamanders is not inverted relative to the LRT, but in the LRT caecilians do not nest with frogs and salamanders. Caecilians nest with microsaurs in the LRT.

Figure 6. Cladogram from Schoch et al. 2020 nests both specimens of Triassurus close to salamanders. Colors match colors in figure 5.

Figure 6. Cladogram from Schoch et al. 2020 nests both specimens of Triassurus close to salamanders. Colors match colors in figure 5.

Schoch et al. 2020 reported on Triassicus,
“to reconstruct crucial steps in the evolution of the salamander body plan, sharing numerous features with ancient amphibians, the temnospondyls. These finds push back the rock record of salamanders by 60 to 74 Ma and at the same time bridge the wide anatomic gap among salamanders, frogs, and temnospondyls.”

In the LRT the salamander body plan goes back to the Early Permian, at least.

From the abstract:
“The origin of extant amphibians remains largely obscure, with only a few early Mesozoic stem taxa known, as opposed to a much better fossil record from the mid-Jurassic on.”

In the LRT the origin of extant amphibians can be traced in detail over several dozen taxa (Fig. 5) back to Cambrian chordates.

Figure 2. Cladogram from Schoch et al. 2020. They insert Eocaecilia here derived from Doleserpeton. The LRT nests Eocaecilia with microsaurs. Note how the morphology does not fit here. Where is Apteon in this cladogram?

Figure 7. Cladogram from Schoch et al. 2020. They insert Eocaecilia here derived from Doleserpeton. The LRT nests Eocaecilia with microsaurs. Note how the morphology does not fit here. Where is Apteon in this cladogram?

From the abstract:
“Yet the most ancient stem-salamanders, known from mid-Jurassic rocks, shed little light on the origin of the clade.Here we report a new specimen of Triassurus sixtelae, a hitherto enigmatic tetrapod from the Middle/Late Triassic of Kyrgyzstan, which we identify as the geologically oldest stem-group salamander.”

“The new, second specimen is derived from the same beds as the holotype, the Madygen Formation of southwestern Kyrgyzstan. It reveals a range of salamander characters in this taxon, pushing back the rock record of urodeles by at least 60 to 74 Ma (Carnian–Bathonian). In addition, this stem-salamander shares plesiomorphic characters with temnospondyls, especially branchiosaurids and amphibamiforms.”

FIgure 8. The FG 596 V20 specimen that Schoch et al. referred to Triassurus does not nest with Triassurus in the LRT. See Figure 9 for reconstruction.

FIgure 8. The FG 596 V20 specimen that Schoch et al. referred to Triassurus does not nest with Triassurus in the LRT. See Figure 9 for reconstruction.

Speaking of that second specimen…
a reconstruction of the narrow-snouted FG 596 V20 specimen (Fig. 8) does not look like the wide-mouth type of Triassurus. In the LRT the second larger FG 596 V20 specimen nests with the CGH129 specimen of the legless microsaur, Phlegethontia (Fig. 9) far from Triassurus and other salamanders.

Figure 9. Reconstruction of the specimen referred to Triassurus, which does not nest with Triassurus in the LRT.

Figure 9. Reconstruction of the specimen referred to Triassurus, which does not nest with Triassurus in the LRT.

What Schoch et al. identified as a large horizontal quadrate (q)
in the FG 596 V20 specimenn(Fig. 8) is re-identified here as a large humerus, larger than the ones they identified. The forelimb goes into the left mouth. The left maxilla is displaced back to the occiput.

Figure 10. Phlegethontia longissima skull (CGH 129) has relatively large temporal plates, a wide flat cranium and a long pointed rostrum.

Figure 10. Phlegethontia longissima skull (CGH 129) has relatively large temporal plates, a wide flat cranium and a long pointed rostrum.

In conclusion, the tiny Triassurus type
nests close to salamanders, but closer to Early Permian Gerobatrachus (Fig. 4). The larger referred FG 596 V20 specimen with legs (Fig. 9) nests with legless Late Carboniferous Phelgethontia (Fig. 10), far from salamanders. Adding taxa and getting deeper into the details using the DGS method upsets the simpler and inaccurate Schoch et al. tracings, tree topology and conclusions.


References
Ivakhnenko M 1978. Tailed amphibians from the Triassic and Jurassic of Middle Asia. Paleontological Journal 1978(3):84-89.
Schoch RR et al. 2020. A Triassic stem-salamander from Kyrgyzstan and the origin of salamanders, Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2001424117

https://phys.org/news/2020-05-triassurus-sixtelae-fossil-kyrgyzstan-oldest.html

Taxonomic problems? Go back to the holotype.

Sometimes taxa are mislabeled.
Such is the case with Pholidophorus? radians (Figs. 1–3), a ‘herring-like’ Jurassic (Solnhofen Fm.) fish with ganoid scales, tiny fins and a large forked tail. This specimen (Fig. 1) was identified as Pholidophorus in The Rise of Fishes (Long 1995) and at the Wikipedia entry for Pholidophorus.

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Compare the one on the left to figure 2. No tested fish in the LRT is closer to Robustichthys than Pholidophorus.

Figure 1. Pholidophorus in situ and two skulls attributed to this genus from Long 1995. Neither diagram matches this specimen, despite overall similarities.

The images in the diagrams above
(Fig. 1) are indeed variations on Pholidophorus (Fig. 4). However, the specimens in the photographs (Figs. 1–3) nest with Elops, the ladyfish (or tenpounder) in the large reptile tree (LRT, 1668+ taxa) on the other branch of bony fish.

Figure 2. Another specimen of Pholidophorus? radians

Figure 2. Another specimen attributed to Pholidophorus? radians

Figure 3. DGS tracing of Pholidophorus? radians along with a reconstruction moving the crushed bones to their invivo positions.

Figure 3. DGS tracing of Pholidophorus? radians along with a reconstruction moving the crushed bones to their invivo positions.

Yesterday
I found the Pholidophorus latiusculus holotype in the literature (Arratia 2013; Late Triassic; Fig. 4). The LRT recovered it apart from the Solnhofen (Late Jurassic) specimen identified as Pholidophorus in Long 1995 and Wikipedia.

The Late Triassic holotype of Pholidophorus
nests with Osteoglossum, the extant arrowana of South America and spiny-finned Bonnerichthys, from the Niobrara Sea of the Cretaceous. All likely had their genesis in the Late Silurian based on their close-to-the-base phylogenetic node.

Figure 4. Pholidophorus holotype from Arratia 2013, overlay drawing from Agassiz 1845.

Figure 4. Pholidophorus holotype from Arratia 2013, overlay drawing from Agassiz 1832.

It is easy to see how later specimens
were allied with the holotype, but this turns out to be yet another case of convergence. A wide gamut phylogenetic analysis that minimizes taxon exclusion minimizes phylogenetic errors like this one. Earlier I made the mistake of combining the data from the diagram (Fig. 1) and the photo (Fig. 2) creating a chimaera. Best to just find the holotype and work from that.


References
Agassiz L 1832. Untersuchungen über die fossilen Fische der Lias-Formation. Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde, 3, 139–149.
Arratia G 2013. Morphology, taxonomy, and phylogeny of Triassic pholidophorid fishes (Acinopterygii, Teleostei). Journal of Vertebrate Paleontology 33:sup1:1–138.
Sallan LC 2012. Tetrapod-like axial regionalization in an early ray-finned fish. Proceedings of the Royal Society B 279:3264–3271.

wiki/Pholidophorus

Meet Seazzadactylus, the newest Late Triassic pterosaur

Dalla Vecchia 2019 introduces us to
Seazzadactylus venieri (Figs. 1–3; MFSN 21545), a small Late Triassic pterosaur known from a nearly complete, disarticulated skeleton (Fig. 2). The tail is supposed to be absent, but enough is there to show it was very gracile. The gracile feet are supposed to be absent, but they were overlooked. The rostrum was artificially elongated, but a new reconstruction (Fig. 3) takes care of that. A jumble of tiny bones in the throat (Fig. 4) were misidentified as a theropod-like curvy ectopterygoid, but the real ectopterygoid fused to the palatine as an L-shaped ectopalatine was identified (Figs. 3,4). 

Figure 1. Seazzadactylus nests between the two Austriadactylus specimens in the LPT.

Figure 1. Seazzadactylus (at far right) nests between the two Austriadactylus specimens in the LPT.

Seazzadactylus is a wonderful find,
and DGS methodology (Fig. 1) pulled additional data out of it than firsthand observation, which was otherwise quite thorough (with certain exceptions).

Figure 2. Seazzadactylus in situ and tracing from Dalla Vecchia 2019. Colors added here.

Figure 2. Seazzadactylus in situ and tracing from Dalla Vecchia 2019. Colors added here.

Dalla Vecchia reports

  1. The premaxillary teeth are limited to the front half of the bone. Dalla Vecchia did not realize that is so because, like other Triassic pterosaurs, the premaxilla forms the ventral margin of the naris, dorsal to the maxilla (Fig. 3).
  2. A misidentified theropod-like ectopterygoid and pterygoid. Dalla Vecchia should have known no pterosaur has an ectopterygoid shaped like this. Rather the curvy shape represents a jumble of bones (Fig. 4). The real ectopalatine in Seazzadactylus has the typical L-shape (Figs. 3, 4) found in other pterosaurs.
  3. The scapula is indeed a distinctively wide fan-shape.
  4. The proximal caudal vertebrae are present, as are several more distal causals. All are tiny.
Figure 3. Seazzadactylus reconstructed using DGS methods.

Figure 3. Seazzadactylus reconstructed using DGS methods. No such reconstruction was produced by Dalla Vecchia. This is a primitive taxon precocially and by convergence displaying several traits found in more derived taxa.

Figure 4. Seazzadactylus bone jumble, including the L-shaped ectopalatine (orange + tan).

Figure 4. Seazzadactylus bone jumble, including the L-shaped ectopalatine (orange + tan). No pterosaur has a theropod-like ectopterygoid. That’s a loose jumble of bone spurs and shards.

It is easy to see how mistakes were made.
Colors, rather than lines tracing the bones, would have helped. Using a cladogram with validated outgroup taxa and more taxa otherwise were avoided by Dalla Vecchia for reason only he understands.

Figure 5. Seazzadactylus pectoral girdle.

Figure 5. Seazzadactylus pectoral girdle.

Phylogenetically Dalla Vecchia reports,
Macrocnemus bassaniiPostosuchus kirkpatricki and Herrerasaurus ischigualastensis were chosen as outgroup taxa.” (Fig. 6)

Funny thing…
none of these taxa are closely related to each other or to pterosaurs (Macrocnemus the possible distant exception) in the large reptile tree (LRT, 1549 taxa) where no one chooses outgroup taxa for pterosaurs. PAUP makes that choice from 1500+ candidates.

Figure 5. Cladogram by Dalla Vecchia 2019 showing where Seazzadactylus nests

Figure 6. Cladogram by Dalla Vecchia 2019 showing where Seazzadactylus nests. Their is little to no congruence between this cladogram and the LPT (subset Fig. 7), exception in the anurognathids. This cladogram needs about 200 more taxa to approach the number in the LPT.

Within the Pterosauria,
Dalla Vecchia nests his new Seazzadactylus between Austriadraco and Carniadactylus within a larger clade of Triassic pterosaurs that does not include Preondactylus, Austriadactylus or Peteinosaurus. Dalla Vecchia’s cladogram includes 27 taxa (not including the above mentioned outgroup taxa). In the large pterosaur tree (LPT, 239 taxa) Austriadraco (BSp 1994, Fig. 8) is a eudimorphodontid basal to all but two members of this clade. Carniadactylus (Fig. 8) is a dimorphodontid closer to Peteinosaurus. So there is little to no consensus between the two cladograms.

Figure 7. Subset of the LPT focusing on Triassic pterosaurs.

Figure 7. Subset of the LPT focusing on Triassic pterosaurs and their many LRT validated outgroups.

Publishing in PeerJ may cost authors $1400-$1700 (or so I understand).
Dalla Vecchia asked his Facebook friends for monetary help to get this paper published. I offered $900, but only on the proviso that the traditional outgroup taxa (listed above and unknown to me at the time) not be employed. You can understand why I cannot support those invalidated (Peters 2000) outgroups. Dr. Dalla Vecchia’s rejected my offer with a humorless invective of chastisement that likened my offer to one traditionally made by the Mafia. A more polite, ‘no thank-you,’ would have sufficed. Just today I learned of Dalla Vecchia’s ‘chosen’ outgroups (see list above). Kids, that’s not good science.

Figure 6. Seazzadactylus sister taxa in the Dalla Vechhia 2019 cladogram to scale.

Figure 8. Seazzadactylus sister taxa in the Dalla Vechhia 2019 cladogram to scale.

Bottom line:
A great new Triassic pterosaur! We’ll hash out the details as time goes by.


References
Dalla Vecchia FM 2019. Seazzadactylus venieri gen. et sp. nov., a new pterosaur (Diapsida: Pterosauria) from the Upper Triassic (Norian) of northeastern Italy. PeerJ 7:e7363 DOI 10.7717/peerj.7363
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

Saurichthys: a Triassic ‘tuna’ close to the last of the lobefins

Saurichthys (Fig. 1) looks like a Triassic barracuda, but here in the large reptile tree (LRT, 1535 taxa, subset Fig. 5) nests between the last of the Devonian putative lobefins, Strunius (Fig. 2)  and the extant tuna (Thunnus, Figs. 3,4).

Figure 1. Saurichthys, shaped like a barracuda, sister to the tuna.

Figure 1. Saurichthys, shaped like a barracuda, sister to the tuna. Note: the diagram, from Gregory 1938, lacks teeth. More complete specimens have teeth.

Saurichthys sp. (Agassiz 1834; up to 1m in length; Early Triassic to Mid Jurassic) is a predatory tuna sister with a long pointed snout and a long, barracuda-like body. Traditionally considered a member of the Saurichthyformes, that clade now appears to be a junior synonym for the previously named Scombridae. Only one dorsal fin appears here. More than 30 species are known. Several taxa are junior synonyms.

Figure 2. Strunius skull enlarged to show detail. Inset shows the second origin of the dual external naris as the original apparently splits by the addition of a skin bridge creating two openings. Compare to figure 1.

Figure 2. Strunius skull enlarged to show detail. Inset shows the second origin of the dual external naris as the original apparently splits by the addition of a skin bridge creating two openings. Compare to figure 1.

Strunius walteri (Jessen 1966; originally Glyptomus rolandi Gross 1936; 10 cm in length; Late Devonian) was considered a lobe-fin fish with ray fins. Here it nests with Cheirolepis, a traditional and transitional ray fin fish. The origin of the double naris in this lineage appears here as a split dividing the original single in two. The palate and possible choana are not known.

Figure 3. Thunnus, the tuna, skeleton and skin.

Figure 3. Thunnus, the tuna, skeleton and skin. More primitive than traditional cladograms recover it.

This appears to be a novel hypothesis of interrelationships
that links previously unlinked taxa. If I missed a citation that predates this one that supports this hypothesis of interrelationships, please send me the citation.

Figure 2. Thunnus, the tuna, nests with some of the most basal bony fish, like Strunius and Pholidophorus.

Figure 4. Thunnus, the tuna, nests with some of the most basal bony fish, like Strunius and Pholidophorus.

Thunnus thyrnnus (Linneaus 1758; 4.6m long) is the extant Atlantic tuna. Traditionally it is considered a member of the perch family. Here it nests with Triassic Pholidopterus. The jugal is retained. The squamosal is a vestige. The intertemporal, supratemporal and tabular are disconnected from one another. The maxilla is toothless. Note the lacrimal contacts the ventral jugal, creating an orbit not confluent with a lateral temporal fenestra. The tip of the premaxilla rises to produce procumbent teeth, but the rest extends posteriorly beyond the maxilla.

Figure 4. Subset of the LRT focusing on basal vertebrates (fish) and the tuna clade.

Figure 5. Subset of the LRT focusing on basal vertebrates (fish) and the tuna clade.

The LRT continues to bring diverse clades of fish together,
reducing the number of clades and illuminating interrelationships.

Figure 1. Pholidophorus in situ + two skull drawings relabeled with tetrapod names.

Figure 6. Pholidophorus in situ + two skull drawings relabeled with tetrapod names, looks more like a tuna than the other clade sisters.

Pholidophorus sp. (Agassiz 1832; Middle-Late Triassic; 40cm long) was a herring-like fish with primitive ganoid scales and poorly ossified spine. Traditionally considered an early teleost, with large eyes, here it nests with Late Devonian Strunius, but lacks the central process of the tail. Here the skull bones are re-identified with tetrapod labels. The pectoral and pelvic fins were similar in size. Earlier we looked at the connection between Pholidophorus and Strunius.


References
Agassiz L 1832. Untersuchungen über die fossilen Fische der Lias-Formation. Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde, 3, 139–149.
Agassiz JLR 1835. Recherches sur les Poissons fossiles, 5 volumes. Imprimerie de Petitpierre et Prince, Neuchaatel, 1420 pp.
Agassiz JLR 1835. On the fossil fishes of Scotland. Report of the British Association for the Advancement of Science, British Association for the Advancement of Science, Edinburgh.
Gross W 1933 1936 Die Fische des baltischen Devons, Palcteontographica A 79:1-74.
Jessen 1966. in Piveteau (Ed.). Traite de paleontologie. Tome 4. L’origine des Vertebres, leur expansion dans les eaux douces et le milieu marin. Vol. 3. Actinopterygiens, Crossopterygiens, Dipneustes. Masson & Cie, Paris
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Wu F-X, Sun Y-L and Fang G-Y 2018. A new species of Saurichthys from the Middle Triassic (Anisian) of Southwestern China. Vertebrata PalAsiatica 56(4):287–294. pdf

wiki/Strunius
wiki/Pholidophorus
wiki/Thunnus
wiki/Saurichthys

Mesozoic mammals: Two views

Smith 2011 reported,
at the beginning of the Eocene, 55mya, “the diversity of certain mammal groups exploded.” These modern mammals”, according to Smith, ‘ consist of rodents, lagomorphs, perissodactyls, artiodactyls, cetaceans, primates, carnivorans and bats. Although these eight groups represent 83% of the extant mammal species diversity, their ancestors are still unknown. A short overview of the knowledge and recent progress on this research is here presented on the basis of Belgian studies and expeditions, especially in India and China.’

Contra the claims of Smith 2011
in the large reptile tree (LRT, 1354 taxa, subsets Figs. 2–4) prototherians are known from the late Triassic (Fig. 1). Both metatherians and eutherians are known from the Middle Jurassic. Many non-mammal cynodonts survived throughout the Mesozoic. In addition, the ancestors of every included taxon are known back to Devonian tetrapods.

Noteworthy facts after an LRT review (Fig. 1):

  1. All known and tested Mesozoic mammals (Fig. 1) are either small arboreal taxa or small burrowing taxa (out of sight of marauding theropods).
  2. All Mesozoic monotremes are more primitive than Ornithorhynchus and Tachyglossus (both extant).
  3. All Mesozoic marsupials are more primitive than or include Vintana (Late Cretaceous).
  4. All Mesozoic placentals are more primitive than Onychodectes (Paleocene).
Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Given those parameters
we are able to rethink which mammals were coeval with dinosaurs back on phylogenetic bracketing (= if derived taxa are present, primitive taxa must have been present, too).

Smith reports, “The earliest known mammals are about as old as the earliest dinosaurs and appeared in the fossil record during the late Trias around two hundred and twenty million years ago with genera such as Sinoconodon (pre-mammal in the LRT), Morganucodon (basal therian in the LRT) and Hadrocodium (basal therian in the LRT). However, the earliest placental mammals (Eutheria) were not known before the Early Cretaceous. Eomaia scansoria (not eutherian in the LRT) from the Barremian of Liaoning Province, China is the oldest definite placental and is dated from a hundred and thirty million years ago.”

Mesozoic Prototherians

  1. All included fossil taxa are Mesozoic. Two others are extant (Fig. 2).
Figure 2. Mesozoic prototherians + Megazostrodon, the last common ancestor of all mammals. Only two taxa (gray) are post-Cretaceous.

Figure 2. Mesozoic prototherians + Megazostrodon, the last common ancestor of all mammals. Only two taxa (gray) are post-Cretaceous.

Mesozoic Metatherians (Marsupials)

  1. Derived Vincelestes is Early Cretaceous, which means Monodelphis and Chironectes were present in the Jurassic.
  2. Derived Didelphodon is Late Cretaceous, which means sisters to Thylacinus through Borhyaena were also present in the Mesozoic.
  3. Derived Vintana is Late Cretaceous, which means sisters to herbivorous marsupials were also present in the Mesozoic.
Figure 3. Mesozoic metatherians (in black), later taxa in gray. Whenever derived taxa are present in the Mesozoic (up to the Late Cretaceous) then ancestral taxa, or their sisters, were also present in the Mesozoic. Didelphis is extant, but probably unchanged since the Late Jurassic/Early Cretaceous.

Figure 3. Mesozoic metatherians (in black), later taxa in gray. Whenever derived taxa are present in the Mesozoic (up to the Late Cretaceous) then ancestral taxa, or their sisters, were also present in the Mesozoic. Didelphis is extant, but probably unchanged since the Late Jurassic/Early Cretaceous.

Mesozoic Eutherians (= Placentals)

  1. Rarely are placental mammals identified from the Mesozoic, because many are not considered placentals.
  2. Placentals (in the LRT) are remarkably rare in the Mesozoic, but sprinkled throughout the cladogram, such that all taxa more primitive than the most derived Mesozoic taxon (Maelestes and derived members of the clade Glires, Fig. 4, at present a number of multituberculates) must have had Mesozoic sisters (Carnivora, Volitantia, basal Glires). 
Figure 4. Mesozoic euthrerians (placentals, in black). Later taxa in light gray. All taxa more primitive than Mesozoic taxa were likely also present in the Jurassic and Cretaceous. None appear after Onychodectes. Madagascar separated from Africa 165-135 mya, deep into the Cretaceous with a population of tenrecs attached. No rafting was necessary. 

Figure 4. Mesozoic euthrerians (placentals, in black). Later taxa in light gray. All taxa more primitive than Mesozoic taxa were likely also present in the Jurassic and Cretaceous. None appear after Onychodectes. Madagascar separated from Africa 165-135 mya, deep into the Cretaceous with a population of tenrecs attached. No rafting was necessary.

The above represents what a robust cladogram is capable of,
helping workers determine the likelihood of certain clades appearing in certain strata, before their discovery therein, based on their genesis, not their widest radiation or eventual reduction and extinction. In other words, we might expect sisters to basal primates, like adapids and lemurs, to be present in the Mesozoic, but not sisters to apes and hominids. We should expect sisters to all tree shrews and rodents to be recovered in Mesozoic strata. We should expect to see sisters to Caluromys, Vulpavus and other small arboreal therians/carnivorans in Mesozoic strata, but not cat, dog and bear sisters.

References
Smith T 2011. Contribution of Asia to the evolution and paleobiogeography of the earliest modern mammals. Bulletin des séances- Académie royale des sciences d’outre-mer. Meded. Zitt. K. Acad. Overzeese Wet.57: 293-305