Another look at the O’Leary et al. hypothetical ancestor of placentals

This post takes another look at
O’Leary et al. (2013) who created a hypothetical ancestral placental. Now that several dozen mammals have been added to the LRT (including the extant basal placental, Monodelphis), hopefully now we can look at the situation with more insight. Let’s see how close to Monodelphis O’Leary’s team got in creating their own hypothetical ancestor. Comparisons can be made both in the bones and soft tissues between the LRT ancestor, Monodelphis, and the imagined ancestor of the O’Leary team (see below).

BTW, the O’Leary team nested Didelphis and Monodelphis as sisters without descendants using nucleotide data. The LRT found that both were good plesiomorphic models for as yet undiscovered ancestors to the Metatheria and the Eutheria (=Placentalia) respectively.

Figure 1. The purported marsupial without a pouch, Monodelphis domestica, nests as the most primitive tested placental in the LRT.

O’Leary et al. (2013) sought to bring new insight into the earliest radiation of placental mammals by creating a hypothetical ancestor to all placentals. They reported this happened in a great radiation of clades right after the K-T extinction event. This counters earlier claims that undiscovered placentals may have been present during the Cretaceous based on data mentioned below. Monotremes and metatherians, the ancestors of today’s egg-laying and marsupial mammals, were present during the Cretaceous. Other lineages of mammals, like Morganucodon, were present as far back as the Triassic. So the O’Leary et al. hypothesis requires relative stasis throughout much of the Mesozoic for mammals, followed by an explosive radiation in the first third of the Paleocene following the K-T extinction event.

Figure 2. Hypothetical ancestor to placental mammals as imagined by O’Leary et al. 2013.

The O’Leary et al. abstract reports: “To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.”

Figure 3. Monodelphis skull in three views. Note the supra occipital is narrower than the exoccipitals, like other mammals, not like the data from the figure previously used. From Digimorph.org and used with permission.

What the O’Leary team imagined vs what the LRT recovered:

1. Molecular clock analyses indicate crown Placentalia were present by the late Early Cretaceous, 100 mya. The LRT confirms that.
2. Fossil evidence does not corroborate the presence of early primates and early rodents in the Late Cretaceous. The LRT recovered an Early Cretaceous carnivore, Vinceletes and a Late Jurassic rodent precursor, Shenshou, a sister to the extant Solenodon clade that includes moles and shrews, and a Late Triassic sister to multituberculates, Haramiyavia, which nest as derived rodents in the LRT. 
3. Phenomic phylogenies incorporating fossils have placed ordinal and intraordinal speciation of Placentalia after the K-Pg (K-T) extinction event. The LRT found two raditions: small arboreal basal mammals in the Triassic and Jurassic, larger Tenreccetaceans and Condylarthra (ungulates and kin) in the Cenozoic. 
4. Ukhaatherium, Mailestes and Zalambdalestes, all from the Late Cretaceous, nest outside the Placentalia. In the LRT the first two nest with Leptictis a basal Tenreccetacean. The last one indeed does nest outside with wombats in the Marsupialia. So, one out of three. 
5. The first members of modern placental orders began appearing 2 to 3 million years (My) later during the Paleocene.All recent clock-based estimates for the ages of key clades, with few exceptions, are substantially older than indicated by the fossil record.  The first placentals in the LRT appear in the Late Triassic, which agrees with the clocks, not O’Leary et al.
6. We recognize Protungulatum donnae as the oldest undisputed species within crown Placentalia (Fig. 1), and this species dates to the earliest Paleocene. Haramiyavia (Late Triassic) was tested in the LRT, but later deleted due to its low number of traits.
7. We find with 100% jackknife support that Eomaia falls outside of Eutheria as a stem taxon to Theria. So does the LRT.

Figure 4. Entire skeleton of Monodelphis from Digimorph.org and used with permission.

O’Leary et al. reconstructed the placental ancestor.
Let’s see how well it conforms to the LRT placental ancestor, Mondodelphis (M).

 

1. It weighed between 6 and 245 g – M: 58 (f) to 95(m) grams
2. insectivororous – M: omnivorous – gives rise to carnivores and insectivores, notably it holds prey with its hands, which is the fast track toward the primaries
3. scansorial – M: scansorial
4. single young born hairless, eyes closed – M: 6-11 young, hairless, eyes closed
5. uterus with two horns – M:?
6. placenta with trophoblast – M:?
7. sperm with flat head – M:?
8. abdominal testes just caudal to kidneys M: scrotum after 24 days; several placental clades do not produce a scrotum (see below)
9. brain has corpus callosum, encephalizatin quotient >0.25 – M:?
10. facial nerve fibers passed ventral to the trigeminal sensory column – M:?
11. gyrencephalic cerebral cortex – M:?
12. separate olfactory bulbs – M: single bulb
13. hemichorial placenta – M: a rudimentary placenta develops then disappears
14. separate openings for anus and urogenitalia – M: single cloaca
15. triangular perforated stapes – M: perforation triangular, externally rectangular
16. lacked epipubic bones – M: epipubes present, as in other basal placentals
17. internal carotid artery present, but did not leave its mark on bones – M:?
18. seven post canine teeth, four premolars and three molars – M: four molars, also in Asrioryctes, Leptictis and other Tenreccetaceans.
19. premolar 3 is lost in Theria, so:p1,2,4,5, m1,2,3 – M: 3 premolars, 4 molars; in many other placentals: 3 premolars, 3 molars (2-4). Pachygenelus has 6 post canine teeth. Morganucodon has 4 premolars, 4 molars. Juramaia has 5 premolars, 3 molars. Amphitherium has 5 premolars and 6 molars. So did certain mammals add teeth? Or did most lose teeth? Depends on where you start counting…

Look again at #4 above. 
Consider the survival advantage that Monodelphis presents: Six to eleven young born at a time feeding on up to 13 retractable nipples without a pouch, versus one joey in a pouch, the marsupial constraint. Female opossums, including Didelphis, often give birth to very large numbers of young, most of which fail to attach to a teat.

Paleogeography
O’Leary et al. state: “Our relatively younger age estimate for Placentalia means that there is no basis for linking placental interordinal diversification to the Mesozoic fragmentation of Gondwana [thus] Afrotheria did not originate in Africa.” The LRT provides a chronology by which placentals could spread worldwide before the breakup of Pangaea and Gondwana.

The O’Leary et al. cladogram
(Fig. 5) does not resemble the LRT. Gradual accumulations of derived traits are hard to find in the O’Leary et al. cladogram. They found the anteaters and sloths were the most primitive placentals and nested whales with hooved mammals, among other odd pairings.

Figure 5. Simplified version of the O’Leary et al 2013 cladogram showing placental relations exploded after the K-T boundary.

The LRT provides
a gradual accumulation of derived traits unmatched by the O’Leary et al topology. This is the best test of tree topology validity as it echoes actual evolutionary events, micro step by micro step.

O’Leary et al. taxa not validated by the LRT

1. Epitheria – all placentals sans Xenarthra.
2. Sundatheria – (= Scandentia + Dermoptera)
3. Afrotheria 
4. Paenungulata
5. Tethytheria
6. Boreoeutheria
7. Laurasiatheria
8. Euarchontoglires
9. Euarchonta

A postscript on testicles
According to slate.com, “Platypus testicles, and almost certainly those of all early mammals, sit right where they start life, safely tucked by the kidneys. Nearly all marsupials today have scrotums, Marsupials’ testicles hang in front of their penises.” In the opossum they are about where the ovaries are in females. In some placentals like “elephants, mammoths, aardvarks, manatees, and groups of African shrew- and mole-like creatures…retain their gonads close to their kidneys. Scrotums bounce along between the hind limbs (behind the penis) of primates, cats, dogs, horses, bears, camels, sheep, and pigs. Hedgehogs, moles, rhinos and tapirs, hippopotamuses, dolphins and whales, some [wait a minute, only some?] seals and walruses, and scaly anteaters have gonads inside and away from the kidneys.” You can read the various hypotheses of why testicles descend or not the slate website.

References
Wible JR, Rougier GW, Novacek MJ, Asher RJ 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary Nature 447: 1003-1006
O’Leary, MA et al. 2013. The placental mammal ancestor and the post-K-Pg radiation of  placentals. Science 339:662-667. abstract

ArchibaldEtAl.pdf
protungulatum-donnae website

Better data on Protictis shifts it from bats to carnivores

Updated January 06, 2016 based on additional taxa.

This is what happens
when you get data more directly. In this case data that used to come from a freehand drawing (Fig. 1) now comes from a photo of Protictis (Cope 1883, Mac Intyre 1966; middle Paleocene; Fig. 1). As everyone knows, in Science, you have to be willing to let go of any pet hypotheses of relationships whenever better data recover different results. And this is how you do it: You just do it!

Figure 1. Protictis skull based not on a free hand drawing, but on this published photo from Mac Intyre 1966. Note all difference with the original freehand drawing, also from Mac Intyre 1966. Preserved elements about 5 cm in length.

More than five years ago,
before ReptileEvolution.com was first created with about 260 taxa in the large reptile tree (now 915 taxa), Protictis was not included in that data matrix. Rather it nested in a separate ‘bat’ cladogram between Chriacus and bats based on data gleaned from the line art reconstruction in Mac Intyre 1966  Now Protictis joins the LRT with data based on a published photo (Fig. 1) in Mac Intyre 1966. Now it nests with Vulpavus, Deltatherium and the carnivore specimen of Ectocion. all within the Carnivora. That makes sense based on several traits, including the very large canine teeth.

That early Palaeocene date
along with the rather derived node occupied by Protictis anticipate (currently without much evidence) a wider radiation of the Carnivora during the Jurassic and Cretaceous than prior workers surmised. An early member of this clade, Vincelestes, is found in Early Cretaceous strata, yet even at that early date, already shows distinctly derived traits. Phylogenetic and chronological bracketing predict that mongoose- and civet-like carnivore taxa will be found in Jurassic and Cretaceous strata.

I’ll have to go back and update
any figures that have not yet been updated. Here (Fig. 2) is the latest on bat origins (now sans Protictis). And there’s more here. It’s the same topology, only without Protictis now.

Palaechthon has been added today
but it nests, as it did before, with the dermopteran, Cynocephalus.

Figure 2. Known bat ancestors to scale. Click to enlarge. Protictis is no longer among them. It is likely that bat ancestors never got as large as Chriacus, but it is the only representative of that morphology, between Ptilocercus and bats.

And we can still use Ptilocercus as a pretty good model
for bat origins. It nests close to their ancestry without showing signs of great deviation.

Figure 3. Ptilocercus, Icaronycteris and a hypothetical transitional taxon based on the ontogenetically immature wing of the embryo Myotis. If you’re going to evolve wings it looks like you have to stop using them as hands early on. Note in the bat embryo there is little indication of inter-metacarpal muscle. That area looks identical to the web.

 

References
Cope ED 1882. Synopsis of the Vertebrata of the Puerco epoch. Proceedings of the American Philosophical Society 20:461-471.
Mac Intyre GT 1966. The Miacidae (Mammalia, Carnivora) Part 1. The systematics of Ictidopappus and Protictis. Bulletin of the American Museum of Natural History 131(2):115-210.

The weird skull and affinities of Brachydectes

Before you read any further, check out Jason Pardo’s letter below. He’s the expert. I’m only a freshman when it comes to this very unusual taxon and its kin. 

This post was updated February 8, 2017 with new identifications of several skull bones. This did not change the nesting of Brachydectes with Eocacilia. 

Further updated March 18, 2017 with new skull bone identities for Brachydectes. 

Brachydectes newberryi (Cope 1868, AMNH 6941; latest Carboniferous; 300 mya; Fig. 1-4) was long considered a lysorophian amphibian with a tiny skull, an extremely long snake-like torso, vestigial limbs and a very short tail. You find them in eastern Kansas.

Figure 1. Brachydectes overall and skull in four views.

A recent PlosOne article
by Pardo and Anderson (2016) studied the skull of Brachydectes (Fig. 3) using micro CT scanning. They report, “Contra the proposals of some workers, we find no evidence of expected lissamphibian synapomorphies in the skull morphology in Brachydectes newberryi, and instead recognize a number of derived amniote characteristics within the braincase and suspensorium. Morphology previously considered indicative of taxonomic diversity within Lysorophia may reflect ontogenetic rather than taxonomic variation.” Later they wrote, “an expansive phylogenetic analysis is outside the scope of this study and will appear elsewhere.” 

Earlier
in the large reptile tree (LRT), Brachydectes nested between Adelospondylus and Eocaecilia, which also has a long snake-like torso, but composed of far fewer and individually much longer vertebrae and a distinct skull architecture. A large, but not exhaustive, selection of basal amniotes was tested and none attracted Brachydectes as much as the two lissamphibians listed above, given the prior data of a line drawing of the skull (Fig. 2) by Marjanovic and Laurin 2013 derived from Wellstead C F 1991.

Figure 2. Brachydectes skull data from a line drawing produced by Marjanović and Laurin 2013. Most leposponysls have a very narrow parasphenoid process and large interptyergoid vacuities, but eocacaecilians expanded this bone and reduced the vacuities like Brachydectes did.

Figure 1. Brachydectes newberryi has some difficult to identify bones just aft of the orbit due to fusion and reduction. Brachydectes (Laysorophus) elongatus (Fig. 2) provides Rosetta Stone clues as to what is happening in this clade.

The new data 
(Figs 2,3 ) are not too far off from the Wellstead C F 1991 data. Notably the tabular no longer extends ventrally alongside the squamosal as it does in the larger specimen. Does this represent a break? or fusion? Or phylogenetic difference? Below (Fig. 3) is the new data on KUVP 49541, plus a reinterpretation of skull sutures based on the micro CT scans. The nesting of the new Brachydactes does not shift in the LRT. It is still a lissamphibian close to microsaurs and caecilians. That’s a broad range, indicative of a long list of yet to be found taxa.

Pardo and Anderson’s reconstruction
(Fig. 3) does not include the coronoid or lateral exposure of the splenial.  Pardo and Anderson note the single supraoccipital compares well with that of various basal reptiles, and indeed it does.  The occipital arch of other lissamphibians consists of only paired exoccipitals,.. until you include microsaurs.

More on supraoccipital homologies
According to Pardo and Anderson, “the presence of a well-developed median supraoccipital is restricted to the amniote crown and recumbirostran ‘microsaurs’. Although the supraoccipital of Brachydectes and ‘microsaurs’ has traditionally been considered convergent with the amniote supraoccipital, new data from μCT have demonstrated that the ‘microsaur’ supraoccipital shares a number of morphological details with early amniotes, and early eureptiles in particular, and is likely homologous with the amniote element. This homology does not extend far down the amniote stem, as seymouriamorphs lack a supraoccipital and ‘anthracosaurs’ generally exhibit paired elements within the synoptic tectum.” 

Noteworthy:
In the LRT, microsaurs are sisters to the clade that includes Adeospondylus, Brachydectes and Eocaeceila. That’s a great deal of phylogenetic distance, but not as great as any other pairing in the LRT. Perhaps more taxa will fill the apparent gaps someday.

Figure 4. Four sizes of Brachydectes in situ. Here, unfortunately, the authors have penned in the sutures, negating any possibility of any reviewer to judge whether they were drawn correctly or not.

Pardo and Anderson also report
“neurocranial morphology does not support a close relationship between Brachydectes and lissamphibians.” Admittedly, Brachydectes is indeed quite different from its sisters…yet it is not closer to other tested taxa in the LRT. If you look at various microsaurs and other lissamphibians, you get a wide range of morphologies at every node.

By noting various key features in contention with the traditional relationship. Pardo and Anderson essentially ‘put the cart before the horse.’ They waited to do the phylogenetic analysis, when they should have done that analysis before publishing. Homoplasy is rampant in tetrapods. I think they fell prey to yet another example. Only analysis, at present, settles all issues.

Pardo and Anderson then report, 
“Morphology of the braincase of Brachydectes suggests a close relationship with the brachystelechid ‘microsaurs’ Carrolla craddocki  and Quasicaecilia texana, within the Recumbirostra.” These two are new to me and untested in the LRT. Wikipedia nests them with Batropetes, which has long legs, and a horned-lizard type body, only distantly related to Brachydectes in the LRT. The skull of Quasicaecilia is shown here, but no post-crania is shown. Recumbirostran microsaurs, are considered the earliest known example of adaptation to head-first burrowing in the tetrapod fossil record. I wish the sister candidates offered by Pardo and Anderson were long and snake-like, but they are not. Deletion of post-cranial traits from the LRT does not shift the placement of Brachydectes within the LRT.

Figure 5. Original interpretation of Brachydectes, KUVP 49541, by Pardo and Anderson. Colors added for clarity and to match micro CT scan.

References
Carroll RL 1967. An Adelogyrinid Lepospondyl Amphibian from the Upper Carboniferous: Canadian Journal of Zoology 45(1):1-16.
Carroll RL and Gaskill P 1978. The order Microsauria. American Philosophical Society, Philadelphia, 211 pp.
Cope ED 1868. Synopsis of the extinct Batrachia of North America. Proc Acad Nat Sci 20: 208–221. doi: 10.5962/bhl.title.60482
Jenkins FA and Walsh M 1993. An Early Jurassic caecilian with limbs. Nature 365: 246–250.
Jenkins FA, Walsh DM and Carroll RL 2007. Anatomy of Eocaecilia micropodia, a limbed caecilian of the Early Jurassic. Bulletin of the Museum of Comparative Zoology 158(6): 285-366.
Marjanović D and Laurin M 2013. The origin(s) of extant amphibians: a review with emphasis on the “lepospondyl hypothesis”. Geodiversitas 35 (1): 207-272. http://dx.doi.org/10.5252/g2013n1a8
Pardo JD and Anderson JS 2016. Cranial Morphology of the Carboniferous-Permian Tetrapod Brachydectes newberryi (Lepospondyli, Lysorophia): New Data from µCT. PLoS ONE 11(8): e0161823. doi:10.1371/journal.pone.0161823. online here.
Wellstead C F 1991. Taxonomic revision of the Lysorophia, Permo-Carboniferous lepospondyl amphibians. Bulletin of the American Museum of Natural History 209: 1–90.

wiki/Eocaecilia
wiki/Brachydectes
wiki/Adelospondylus

Acristatherium is not a eutherian. Maybe not even a therian.

Hu et al. 2016
recently published on Acristatherium yanensis (IVPP V15004, Fig. 1), which they described as a new basal eutherian mammal from the Early Cretaceous Jehol biota, Liaoning, China. The specimen includes most of the skull. They noted the presence of an unexpected septomaxilla (other eutherians do not have that bone). They tested 70 taxa and 408 characters. They nested “A. yanensis as the most basal eutherian in the selected group. The morphological differences between Acristatherium and Eomaia indicate that eutherians already had a significant degree of generic diversification ca 125 Ma (mya).”

Figure 1. Acristatherium nests with Cronopio, between monotremes and metatherians in the LRT, not with eutherians.

Unfortunately they did not include
Cronopio, Monodelphis and Didelphis among their 70 taxa. In the large reptile tree Acristatherium nested with Cronopio and together they nested between monotremes and metatherians. The septomaxilla is commonplace around that clade. In both the original and LRT cladograms, Acristatherium nested just primitive to Eomaia. However, Hu et al nested the basal carnivoran eutherian, Vincelestes more primitively than Acristatherium + Cronopio for reasons unknown.

Figure 2. Cronopio is a basal mammal nesting between Juramaia and Didelphis, a basal marsupial. Scale bar = 1cm.

Cronopio dentiacutus (Rougier et al. 2011, early Late Cretaceous, 98 mya, MPCA PV 454) was originally described as a dryolestid mammal. Tradtionally dryolestids nest outside of the Theria. That is also so in the large reptile tree as Cronopio nests between Juramaia and Didelphis. Here we see yet another diastema, a trait found in many diverse and often unrelated mammals. Acristatherium has no diastema and so was likely more primitive. The two nest as late survivors of an earlier Late Triassic radiation and were probably both commonplace in their time.

Therians do not lay eggs,
but give birth to live, often underdeveloped young. At present, it is not possible to determine via phylogenetic bracketing if Acristatherium laid eggs or produced underdeveloped young, but I would lean toward the latter given its tiny size.

PostScript:
Dr. Darren Naish recently praised online for SciAm the 1854 prehistoric Crystal Palace restorations by BW Hawkins (Fig. 3) as, and I quote, “Among the Most Accurate Renditions of Prehistoric Life Ever Made….Often derided, and today somewhat neglected and forlorn, the famous prehistoric animal models of Crystal Palace in London have a lot to teach us…”

Figure 3. One of the Victorian London dinosaurs crafted by BW Hawkins for the Crystal Palace exhibit, that Dr. Naish reports, “have a lot to teach us.”

You might remember Dr. Naish was also the harshest and most vocal critic of the blog you are reading and the website it promotes, ReptileEvolution.com. He and others blackwashed the entire project as something “the world has to ignore,” despite every attempt at accuracy and transparency. Several years later, Dr. Naish is still wondering “When are you going to stop?”

Let us all remember, it is human nature to embrace and extol the overlooked nuances we believe we are the first to appreciate and talk about. That’s why scientists take such delight in the process of discovery, no matter how little it interests the rest of society. That’s why whenever we parents congregate we laud our own children. And that’s why 1995 hipsters embraced the Hush Puppies shoe just as the brand was hitting the nadir of its popularity.

Likewise, because we all have egos, it is also human nature to denigrate and disparage overlooked nuances that others were the first to appreciate and talk about, especially when those others do not have ‘hipster’ status and are metaphorically ‘swimming in the same pond’. That last factor is very important. That’s why alternate views of Christianity were exterminated for 15 centuries — even though they all followed the ‘Prince of Peace’. That is also why American females were not allowed to vote, become Mercury astronauts or run for president until alpha male attitudes relaxed — even though we males still loved American females as wives, daughters and mothers.

Perceived menace makes people kinder to their kin (race, gender, income level, religion, nationality, baseball team), but nastier to outsiders (see SciAm online article here). That’s why it is always better to convince others you share common values and origins. A century ago the Irish in America went through their own ‘freshman hazing’ and came out with an annual holiday. Gaining acceptance in the scientific community for the large reptile tree should not be that difficult since it likewise offers no threat, but helps test away many enigmas and misfits.

For more on primate status behaviors, according to Jane Goodall, click here.

References
Hu Y-M, Meng J, Li C-K and Wang YQ 2016. New basal eutherian mammal from the Early Cretaceous Jehol biota, Liaoning, China. Proceedings of the Royal Society B.
doi:10.1098/rspb.2009.0203 Published online
Rougier GW, Apesteguía S and Gaetano LC 2011. Highly specialized mammalian skulls from the Late Cretaceous of South America. Nature. 479: 98–102. doi:10.1038/nature10591.

The geologically oldest Archaeopteryx (#12)

Updated November 10, 2016 with higher resolution images of the specimen. The new data moved the taxon over by one node. 

Not published yet in any academic journal,
but making the news in the popular press in Germany to promote a dinosaur museum (links below) is the geologically oldest Archaeopteryx specimen (no museum number, privately owned?). Found by a private collector in 2010, the specimen has been declared a Cultural Monument of National Significance. It is 153 million years old, several hundred thousand years older than the prior oldest Archaeopteryx. It is currently on  display at a new museum, Dinosaurier-Freiluftmuseum Altmühltal in Germany, about 10 kilometers from where the fossil was found.

Figure 1. The new oldest Archaeopteryx in situ with color tracings of bones. The ilium has been displaced to the posterior gastralia, or is absent. I cannot tell with this resolution.

Figure 1b. Archaeopteryx 12 in higher resolution.

So is it also the most primitive Archaeopteryx?
No. But it nests as the most primitive scansioropterygid bird. As we learned earlier, the Solnhofen birds formerly all considered members of the genus Archaeopteryx (some of been subsequently recognized by certain authors as distinct genera) include a variety of sizes, shapes and morphologies (Fig. 3) that lump and separate them on the large reptile tree. The present specimen has been tested, but will not be added to the LRT until it has a museum number or has been academically published (both seem unlikely given the private status). Given the additional publicity the specimen is now in the LRT.

The fossil is wonderfully complete and articulated
and brings the total number of Solnhofen birds to an even dozen.

This just in
Ben Creisler reports, “The fossil specimen was originally found in 2010 in fragmented condition and took great effort to prepare and piece together as it now appears.”

Figure 2. Reconstruction of the geologically oldest Archaeopteryx, now nesting at the base of the Scansoriopterygidae. Note the large premaxillary teeth and short snout on a relatively small skull.

Compared to other Archaeopteryx specimens
you can see the new one is among the smallest (Fig. 3) and has a distinct anatomy.

Figure 2. Several Archaeopteryx specimens. The geologically oldest one, (at bottom) is among the smallest and most derived, indicating an earlier radiation than the Solnhofen formation.

References
Spektakulaerer-Fund-kommt-in-Ausstellung-article
originalskelett-eines-archaeopteryx-zu-sehen.html
auf-zum-archaeopteryx

Website

Eomaia needs a makeover

With the recent nesting
of Eomaia (Ji et al. 2002) closer to Thylacinus (Fig. 1) than to eutherians (click here). Thylacinus is the longn-legged marsupial wolf AND it’s a basal marsupial with an unspecialized dentition. So maybe that slinky rat-like appearance originally given to Eomaia (Fig. 1) needs an update. I mean, look at those long legs! (Then again, the proximal sister, Didelphis, (Fig. 2) also has long legs, but you’d never know it the way it slinks around.

Maybe the carriage of Eomaia was a bit more upright,
like Thylacinus, despite the great size difference. The morphology was similar enough to nest the two together to the exclusion of all other 783 taxa. The metacarpals and metatarsals appear to trend toward digitigrade, as in so many marsupials, not flat-footed as originally reconstructed. The PILs align either way.

Let’s see what happens
when we let the bones and phylogenetic bracketing tell another tale.

Figure 1. Eomaia in situ, as originally reconstructed, as reconstructed here and compared to Thylacinus. This is what this blog and ReptileEvolution.com really do best. Show sister taxa together to scale and not to scale to drive home their similarities with a strong visual impression. You can always ask for the data matrix later.

 

I note
long neural spines in Eomaia around the shoulders. The tibia and fibula appear to be able to be closely appressed, despite their disturbance post-mortem. The slender cervicals are unlike those of Didelphis (Fig.2). The lumbar region appears to be more supple, like Thylacinus, built for galloping.

Figure 2. Didelphis, the extant opossum, a slinky marsupial more primitive than Eomaia.

I’d like to see original data
for the reflected process of the dentary on Eomaia. Sister taxa don’t have a ventral protrusion, but they do have a sharp little ascending curl of bone, and I don’t see it in the fossil.

References
Ji et al 2002. The earliest known eutherian mammal, Nature 416:816-822.m online here.

wiki/Eomaia

Eomaia and Monodelphis switch places and wombats are added to the LRT

Updated February 21, 2019 with a new cladogram of the Metatheria including many more taxa. 

Today
I added Vombatus (Geoffroy 1803; 98 cm long; extant) and Thylacoleo (Owen 1859; 114 cm long; <2mya;  ) to the large reptile tree (now 783 taxa). Here (subset Fig. 1) they nested together as they do traditionally and share with Macropus protruding dentary incisors that are only incipient in Anebodon.

While rummaging around the marsupials…
I checked data for Monodelphis (Burnett 1830) based on newly found Digimorph.org photos. Previously I had relied on drawings. The differences in data got rid of several autapomorphies and shifted Monodelphis closer to traditional placentals and Eomaia (Ji et al. 2002) closer to Thylacinus, with which it apparently shares a digitigrade manus and pes. You might remember Monodelphis has no pouch. Eomaia was hailed as the basalmost eutherian. That I’ll have to look into further and will report when the dust has settled. I have not updated the online pages yet for these taxa.

Figure 2. Monodelphis skull in three views. Note the supra occipital is narrower than the exoccipitals, like other mammals, not like the data from the figure previously used.

References
Burnett GT 1830. Illustrations of the Quadrupeda, or Quadrupeds, being the arrangement of the true four-footed Beasts indicated in outline. Quarterly Journal of Science, Literature and Art, July to December, 1829, 336–353.
Ji et al 2002. The earliest known eutherian mammal, Nature 416:816-822.
Pine RH, Flores DA and Bauer K 2013. The second known specimen of Monodelphs unistriata (Wagner) (Mammalia: Didelphimorphia), with redescription of the species and phylogenetic analysis. Zootaxa3640 (3):425-441.

wiki/Monodelphis
wiki/Eomaia

Microsaurs in the Viséan and Middle Devonian footprints

Figure 1. Which came first? The tracks or the trackmakers? In this case the tracks came first, strong indications that the variety of Devonian trackmakers we have found were all commonplace in the Late Devonian. The variety of basal reptiles and microsaurs found in the Visean must also reflect a wide radiation of derived taxa, pointing to an earlier origin.

The earliest known microsaur,
Kirktonecta milnerae (Clack 2011, UMZC 2002, Viséan, 330 mya), is not the basalmost microsaur, nor is it a basalmost lepospondyl, the parent clade. In the large reptile tree, Kirktonecta nests with Tuditanus, phylogenetically nesting much more recently than the Utegenia(Lepospondyl) /Silvanerpeton (stem-reptile) split.  That means what we have as taxa in the Visréan represents these taxa when they were commonplace, long after their origination and radiation.

On a related note,
the earliest known tetrapod trackways, the early Middle Devonian Zachelmie trackways, precede all known Devonian trackmakers in the Late Devonian. That means we no longer have to wait for the Late Devonian taxa to begin to evolve the earliest reptiles, but we can still use their morphologies. Now we can begin to evolve reptiles earlier, likely during the Tournasian, the first part of Romer’s Gap, a time for which there are (strangely) few to no fossils during the first 15 million years of the Carboniferous. This time succeeded a major extinction event, the Hangenberg event, in which most marine and freshwater groups became extinct or reduced, including the Ichthyostegalia. Evidently the places where these rare survivors were radiating are currently unknown in the fossil record. These survivors include basal temnospondyls and lepospondyls that also include basal microsaurs.

Fortunately,
the Ichthostegalia had already given rise to a wide range of stem-amphibians and stem-reptiles that ultimately produced all the post-Devonian tetrapods. Those Zachelmie trackways dated 10-18 million years earlier, give more time for reptilomorphs and reptiles to have their genesis and radiation. Post-extinction events traditionally produce new clades. So it appears to be with the genesis of the Reptilia (= Amniota).

The Early Devonian
is where we find Meemannia eos, an early ray-finned fish that was originally classified an early lobe-finned fish. So it didn’t take long after the origin of such fish to develop fingers and toes and move onto land.

This just in:
Recent work by Sallan and Galimberti 2015 showed that only small fish survived the Devonian / Carboniferous extinction event. Read more here. And a paper on Late Devonian catastrophes, impacts and glaciation here.

References
Clack JA 2011. A new microsaur from the early Carboniferous (Viséan) of East Kirkton, Scotland, showing soft tissue evidence. Special Papers in Palaeontology. 86:1–11.

Sallan L and Galimberti AK 2015. Body-size reduction in vertebrates following the end-Devonian mass extinction. Science, 2015; 350 (6262): 812 DOI: 10.1126/science.aac7373

Anebodon: another symmetrodont or marsupial mole sister?

Updated March 09, 2018 with the nesting of this taxon with the golden mole, Notoryctes.

Bi et al. 2016
reported on “Anebodon luoi (STM 38-4, Tianyu Museum of Nature, Shandong Province, China, Fig. 1) a new genus and species of zhangheotheriid symmetrodont mammal from the Lujiatun site of the Lower Cretaceous Yixian Formation, China. The fossil is represented by an associated partial skull and dentaries with a nearly complete dentition.”

Figure 1. Anebodon luoi subjected to DGS tracing and phylogenetic analysis nests with Macropus, the extant kangaroo, not with Zhangheotherium. The kangaroo kink is just starting here with a concave/convex maxilla. The canines are present, but tiny. The anterior dentary teeth extend anteriorly, the first step toward the kangaroo’s ‘tusks’.

Bi et al. noted
Anebodon lacked the high molar count typical of derived symmetrodonts. Their diagnosis focused on dental differences compared to Maotherium and Kiyatherium.

By contrast
the large reptile tree (LRT) nested Early Cretaceous Anebodon with the the golden mole Notoryctes (Fig. 1). A septomaxilla was identified in Anebodon.

The clade
Symmetrodonta is considered paraphyletic at Wikipedia. The clade is based on teeth characterized by the triangular aspect of the molars when viewed from above and the absence of a well-developed talonid. Perhaps such teeth were common to basal placentals.

References
Bi S-D, heng X-T, Meng J, Wang X-L, Robinson N and Davis B 2016. A new symmetrodont mammal (Trechnotheria: Zhangheotheriidae) from the Early Cretaceous of China and trechnotherian character evolution. Nature Scientific Reports 6:26668 DOI: 10.1038/srep26668

Zhangheotherium: a Maotherium sister

Updated July 06 2022 with a revised nesting for Zhangheotherium.

Today we’ll look at
Zhangheotherium quinquecuspidens (Hu et al. 2009; Late Jurassic/Early Creteacous; dentary length 3 cm; IVPP V7466; Fig. 1). It was originally described as a symmetrodont mammal, an ‘archaic’ taxon typically represented by only tooth and dentary scraps. Here (Fig. 1) a complete skeleton provided new insight to the original authors. They reported Zhangheotherium did not travel in a parasagittal posture and the cochlea (an organ of the inner ear) was not fully coiled.

Figure 1. Zhangheotherium reconstructed. The tail is unknown. The high scapulae indicate great strength in the pectoral region, likely for arboreal locomotion in a taxon of this size. Zhangheotherium nests as a basal pangolin. It was preserved in ventral view. Here the epipubes are identified as pubes, which is otherwise not shown.

Figure 2. Hu et al. nested Zhangheotherium basal to the Placental/Marsupial split, contra the results of the large reptile tree.

Hu et al. reported\, 
Zhangheotherium radiated before the divergence of living marsupials and placentals. Here, in the large reptile tree (LRT) Zhangheotherium nests with Maotherium, prior to the origin of mammals.

Hu et al note:
“A mobile clavicle–interclavicle joint that allows a wide range of movement of the forelimb has an ancient origin in the mammalian phylogeny.” This is quite visible in the fossil and interesting with regard to Zhangheotherium’s.

In Zhangheotherium, Hu et all note

1. The cervical ribs were unfused.
2. The caudal transverse processes were wide
3. Three or four sacrals were present [suggesting stress in this area, perhaps for balance].
4. The pisiform is very large
5. Only the dorsal acetabulum is preserved
6. Zhangheotherium has an external pedal spur, as in Ornithorhynchus [not sure about this disarticulated bone, perhaps not a spur, but a simple spindle-shaped ankle bone similar to one seen in Manis, see Fig. 4]
7. The interclavicle is triangular and the sternal manubria are only three in number.
8. It is more primitive than Henkelotherium and Vincelestes in retaining the interclavicle in its pectoral girdle/sternal manubrium
9. These new data suggest that the mobility of the clavicle and scapula has a more ancient origin than the more parasagittal posture of the forelimbs
10. The mobile and pivotal clavicle evolved before the divergence of multituberculates and therians. [in the LRT multituberculates are therians and placentals]

Hu et al. report, “It has been argued that dental characters are as homoplasic as non-dental characters and the reliability of dental characters for inferring the relationships of major lineages of mammals has been questioned. Zhangheotherium has provided more extensive basicranial and postcranial evidence to corroborate the traditional hypothesis that symmetrodonts represent a part of the basal therian radiation.” [Zhangheotherium has five or more molars, as in Maotherium].

Figure 5. Henkelotherium, a traditional pantothere, nests as a Late Jurassic pre-rabbit in the LRT. Note how tiny it is.

Hu et al. link
Zhangheotherium to Henkelotherium (Krebs 1991; Late Jurassic, Kimmeridgian; Figs. 5, 6).

In the large reptile tree
Henkelotherium and Zhangheotherium do not nest together. Rather Henkelotherium nests with rabbits.  Wikipedia considers Henkelotherium a paurodontid dryolestid (formerly considered a eupantothere) and similar in locomotion patterns to tree shrews and opossums. Key to Henkelotherium are the enlarged dentary incisors (premaxilla remains unknown). This represents the first step toward the larger incisors found in plesiadapiformes, Tupaia-like tree shrews, apatemyids and rodents + multituberculates.

Back to Zhangheotherium, you’ll note
the dentary condylar process curves dorsally and no post-dentary bones are present. That dorsal curve removes most of the ability to resist jaw dislocation often caused by struggling large prey and or small pieces of even larger prey are working against large canines, which were also not present in Zhangheotherium. These traits point to a tiny prey diet, likely of insects.

References
Hu Y-M, Wang YQ, Luo Z and Li CK 1997. A new symmetrodont mammal from China and its implications for mammalian evolution. Nature 390:137-142.
Krebs B 1991. Skelett von Henkelotherium guimarotae gen. et sp. nov. (Eupantotheria, Mammalia) aus dem Oberen Jura von Portugal. Berl Geowiss Abh A.: 133:1–110.

wiki/Zhangheotherium