Known from a single tiny leg preserved in Myanmar amber Elektorornis chenguangi (Fig. 1; Xing et al. 2019; Late Cretaceous, 99 mya; HPG-15-2) has a remarkably long pedal digit 3.
The authors considered Elektornis a member of the clade Enantiornithes based on the following traits:
distal condyles of the tibiotarsus contacting medially
J-shaped metatarsal I
metatarsal IV mediolaterally reduced relative to metatarsals III and IV
metatarsal IV trochlea reduced to a single condyle,
None of the above traditional traits are scored in the large reptile tree (LRT, 1870+ taxa), where, nevertheless, all traditional enantiornithines nest together in a single clade using other tested traits.
The LRT was unable to resolve the nesting of Elektornis based on so few character traits. Three trees were recovered. Elektornis nested with a different taxon in each tree (Fig. 1). None have the iconic long pedal digit 3. Only the enantiornithine chick, STM 34-1 (Fig. 1), that nests close to Chiappeavis has similarly long penultimate phalanges (a trait not tested by the LRT). Neither of these taxa are listed in the analysis by Xing et al. 2019.
The PILs (parallel interphalangeal lines) that can be traced in Elektornis show an interesting pattern (Fig. 1). The lateral and medial line sets are continuous, showing how phalanges probably flexed and extended in sets. By contrast the transverse line sets are all interrupted by intervening bones. In other taxa that show an interrupted PILs pattern the manus or pes is stiffened, not as flexibile or extensible. Perhaps this confirms earlier interpretations that hypothesize the use of elongate pedal digit 3 as a bark probe, seeking insects in the manner of manual digit 3 in the aroboreal placental aye-aye (Daubentonia).
References Xing, L et al. (6 co-authors) 2019. A New enantiornithine bird with unusual pedal proportions found in amber. Current Biology. 29 (14): 2396–2401.
Motani and Geerat 2021 break down the ‘steps’ needed for terrestrial tetrapods to become marine tetrapods.
Unfortunately the authors are working from invalid traditional hypotheses of phylogenetic interrelationships that are still being taught by PhDs in college auditoriums.
From the abstract: “Marine reptiles and mammals are phylogenetically so distant from each other that their marine adaptations are rarely compared directly.”
This blanket statement is not true. In the large reptile tree (LRT, 1870+ taxa) several marine reptiles and mammals are indeed phylogenetically close. Others the authors think are close, indeed are not close (see below).
“We reviewed ecophysiological features in extant non-avian marine tetrapods representing 31 marine colonizations to test whether there is a common pattern across higher taxonomic groups, such as mammals and reptiles. Marine adaptations in tetrapods can be roughly divided into aquatic and haline adaptations, each of which seems to follow a sequence of three steps. In combination, these six categories exhibit five steps of marine adaptation that apply across all clades except snakes: “
“Step M1, incipient use of marine resources; Step M2, direct feeding in the saline sea; Step M3, water balance maintenance without terrestrial fresh water; Step M4, minimized terrestrial travel and loss of terrestrial feeding; and Step M5, loss of terrestrial thermoregulation and fur/plumage.”
This is a laudable attempt at focusing on this issue using logic, but it’s not a good idea to do this with an out-of-date family tree (see below). Not sure why avian taxa were excluded.
“Acquisition of viviparity is not included because there is no known case where viviparity evolved after a tetrapod lineage colonized the sea.”
Sea snakes. According to Wikipedia, “Except for a single genus, all sea snakes are ovoviviparous; the young are born alive in the water where they live their entire lives. … The one exception is the genus Laticauda, which is oviparous; its five species all lay their eggs on land.”
The abstract continues: “A similar sequence is found in snakes but with the haline adaptation step (Step M3) lagging behind aquatic adaptation (haline adaptation is Step S5 in snakes), most likely because their unique method of water balance maintenance requires a supply of fresh water. The same constraint may limit the maximum body size of fully marine snakes.”
So the authors DID look at snakes.
“Steps M4 and M5 in all taxa except snakes are associated with skeletal adaptations that are mechanistically linked to relevant ecophysiological features, allowing assessment of marine adaptation steps in some fossil marine tetrapods.”
This describes fingers turning into flippers. Snakes were exempt from this, naturally.
“We identified four fossil clades containing members that reached Step M5 outside of stem whales, pinnipeds, sea cows and sea turtles, namely Eosauropterygia, Ichthyosauromorpha, Mosasauroidea, and Thalattosuchia, while five other clades reached Step M4: Saurosphargidae, Placodontia, Dinocephalosaurus, Desmostylia, and Odontochelys.”
Here’s where things fall apart. The LRT documents separate origins for odontocetes and mysticetes, separate origins for seals and sea lions, separate origins for many sea turtles and protostegids, the origin of ichthyosaurs, mesosaurs and thalattosaurs from sauropterygians close to Wumengosaurus and the origin of sauropterygian from aquatic younginiforms, which include Saurosphargidae. Dinocephalosaurusis a lepidosaur derived from basal tanystropheids including the small lizard-like Huehuecuetzpalli in the LRT. Desmostylia are transitional taxa between mesonychids + hippos + anthracobunids and mysticetes in the LRT (Fig. 1). Odontochelysis a basal soft-shell turtle derived from a small horned pareiasaur, Sclerosaurus. Apparently the authors do not understand these interrelationships. Always work within a valid phylogenetic context, otherwise every word you type is a waste of time.
The abstract continues: “[several sentences skipped here] This makes it difficult to reconstruct the evolutionary history of marine adaptation in many clades.”
By contrast, the evolutionary history of every taxon in the LRT is readily revealed back to Ediacaran worms. This makes it easy to reconstruct the entire evolutionary history of marine adaptations in all tested clades. The LRT is free to use without citation because it’s online.
Recent housekeeping in the large reptile tree (LRT, 1870+ taxa; subset Fig. 4) and a new DGS tracing of the in situ skull of Martensius bromackerensis(Berman et al. 2020; Early Permian, 50cm; MNG 13814 adult holotype; MNG 14230 juvenile and smallest specimen; Figs. 1, 2) resulted in scoring changes that moved this former caseasaur next to ‘the odd one‘… Tetraceratops, a taxon not quite like any other reptile and known from a single iconic bumpy skull (Fig. 3).
Earlier I trusted the freehand reconstruction of Berman et al. 2020 (Fig. 1), rather than creating my own reconstruction using DGS methods based on the published photo of Martensius (Fig. 2). The differences are subtle, but enough to change scores. Note the wide occiput and narrow rostrum. The early presence of a large lateral fenestra, unrelated to other fenestrated taxa, will have to await a CT-scan of the skull. At present the cheek bones (i.e. jugals, post orbitals) are not visible beneath this disarticulated ‘roadkill‘ skull.
Martensius bromackerensis (Berman et al. 2020; Early Permian, 50cm; MNG 13814 adult holotype; MNG 14230 juvenile and smallest specimen) was originally considered a caseasaur, nesting betweenEocasea and Casea. Here Martensius is a sister to Tetraceratops, a taxon omitted by Berman et al. 2020. These two nest together at the base of the Lepidosauromorpha, a splinter from the larger traditional clade, Captorhinidae (Fig. 4). This is one node off from the earlier nesting of Tetraceratops.
Martensius was a caseasaur mimic. A small skull is present in Martensius, a trait typical of many caseasaurs. The feet are large and robust, as in caseasaurs.
This is the first postcranial material known for a tetraceratopsian.
Tetraceratops remains an odd taxon with several derived traits unlike those of any other tetrapod. By comparison, Martensius is more primitive and provides the first clues to the post-crania we should expect for the next Tetraceratops specimen to be recovered: short legs, long body, big feet (Fig. 1).
It’s worth remembering the LRT Lepidosauromorpha are largely herbivores at their genesis. This clade ultimately produced apex predators like mosasaurs and giant pterosaurs, while also producing snakes, turtles and pseudo-rib gliders.
The present housekeeping of the LRT is designed to ferret out bad scores, reduce the number of MPTs (most parsimonious trees) and so more closely model actual evolutionary events. As you might remember the fish and theropod/bird sections of the LRT had to be set apart from the main LRT because MacClade only permits 1500 taxa to be tested. At present the fish, theropod and now the lepidosauromorph sections are all fully resolved after housekeeping. The basal vertebrate and archosauromorph sections will follow after their own housekeeping.
References Berman DS, Maddin HC, Henrici AC Sumida SS, Scott D and Reisz R 2020. New primitive caseid (Synapsida, Caseasauria) from the Early Permian of Germany. Annals of the Carnegie Museum 86(1):43–75. Matthew WD 1908. A four-horned pelycosaurian from the Permian of Texas. Bulletin of the American Museum of Natural History 24:183-185. Sidor CA and Hopson JA 1998. “Ghost lineages and “mammalness”: Assessing the temporal pattern of character acquisition in the Synapsida”. Paleobiology 24: 254–273.
From the Pterosaur Heresies, August 19, 2013: “Stereophallodon (Earliest Permian) was described by Brinkman and Eberth (1986) as an ophiacodontid more primitive than Ophiacodon(Fig. 2), a taxon nesting at the base of the Therapsida in the large reptile tree. Raranimus (Early Middle Permian) was described by Liu, Rubidge and Li (2009) as a basal therapsid. Funny, they both had double canines, a trait not present in other basal therapsids, or ophiacodontids.”
“Liu et al. (2009) reported, “While sphenacodontid synapsids are considered the sister-group of therapsids, the place of origin of therapsids is an enigma, largely because of a long standing morphological and temporal gap (Olson’s Gap) in their fossil record.” Unfortunately, Liu et al. (2009) did not recognize the basal nesting of Stenocybus, but did nest Tetraceratopsin their tree, not realizing it nests more parsimoniously with the diadectomorph, Tseajaia. Liu et al. (2009) did not include Ophiacodon (Fig. 2) or Stereophallodon in their taxon list. Taxon exclusion is the problem once again.”
Getting back to the present, Duhamel, Benoit, Rubidge and Liu 2021 report, “The non-mammalian therapsids comprise a paraphyletic assemblage of Permian-Jurassic synapsids closely related to mammals that includes six major clades of largely unresolved phylogenetic affinity.”
Duhamel, Benoit, Rubidge and Liu 2021 report, “Understanding the early evolutionary radiation of therapsids is complicated by a gap in the fossil record during the Roadian (middle Permian) known as Olson’s gap. Because of its early stratigraphic occurrence and its primitive features, Raranimus dashankouensis, from the Dashankou fauna (Rodian), Qingtoushan Formation (China), is currently considered the best candidate to fill this gap. However, it is known from only a single specimen, an isolated snout, which limits the amount of usable phylogenetic characters to reconstruct its affinities.”
Understood. The LRT had the same problem, but resolved it 8 years ago.
Duhamel, Benoit, Rubidge and Liu 2021 report, “In addition, understanding of the stratigraphy of the Qingtoushan Formation is poor. Here, we used CT scanning techniques to digitally reconstruct the bones and trigeminal canals of the snout of Raranimus in 3D. We confirm that Raranimus shares a high number of synapomorphies with more derived therapsids and is the only therapsid known so far to display a “pelycosaur”-like maxillary canal bearing a long caudal alveolar canal that gives off branches at regular intervals. This plesiomorphic feature supports the idea that Raranimus is basal to other therapsids.”
‘Olson’s Gap’ is no longer a gap. Wikipedia reports, “The ‘Gap’ was finally closed in 2012 when Michael Benton confirmed that the terrestrial fossil record of the Middle Permian is well represented by fossil localities in the American Southwest and European Russia and that the gap is not an artifact of a poor rock record since there is no correlation between geological and biological records of the Middle Permian.”
Click HERE to see an enlargement of the graphic above (Fig. 3).
References Benton MJ 2012. No gap in the Middle Permian record of terrestrial vertebrates. Geology. 40 (4): 339–342. Bibcode:2012Geo….40..339B. doi:10.1130/g32669.1. Brinkman D and Eberth DA 1986. The anatomy and relationships of Stereophallodon and Baldwinonous (Reptilia, Pelycosauria). Breviora 485: 1-34. Duhamel A, Benoit J, Rubidge BS and Liu J 2021. A re-assessment of the oldest therapsid Raranimus confirms its status as a basal member of the clade and fills Olson’s gap. The Science of Nature 108, Article number: 26 DOI: https://doi.org/10.1007/s00114-021-01736-y https://link.springer.com/article/10.1007/s00114-021-01736-y Liu J, Rubidge B and Li J-L 2009. New basal synapsid supports Laurasian origin for therapsids. Acta Palaeontologica Polonica 54(3): 393-400.
The chordate sense of smell, the ability to detect trace amounts of chemicals in water, first appeared prior to the Early Cambrian. This is documented by the genesis of a single narial opening above the oral cavity on the extant hagfish (genus: Myxine, Fig. 1). Outgroup nematodes, like Enoplus (Fig. 1), do not have a single opening that can be labeled a naris, nose or olfactory cavity.
The subsequent migration of the naris to the top of the head occurred with the elongation of the rostrum, as demonstrated in the living lamprey, Pteromyzon (Fig. 1).
The subsequent division of the dorsal naris into an anterior incurrent opening and a more posterior excurrent opening is demonstrated in Jaymoytius (Fig. 1), a finless descendant of the lamprey.
The subsequent second division of the naris into a left and right set of incurrent and excurrent narial openings is demonstrated in Birkenia (Fig. 1). This taxon also nests the nares close to the snout tip.
The Birkenia narial pattern of four openings (two left and two right nares some distance from the snout tip) is retained by sharks and bony fish, including the sturgeon,Acipenser (Fig. 1).
Early in the Devonian both excurrent narial openings migrated first to the jaw rim and then inside the mouth in Gorgonasus (Fig. 1) and its descendants, the tetrapods, including air-breathing humans. The internal narial opening in the roof of the mouth is called a choana, or choanae for both internal nares. The incurrent narial openings also migrated to the jaw rims in basal tetrapods, like Panderichthys (Fig. 2), but in later taxa migrated higher on the skull.
Thereafter the external naris and internal choana took on several shapes and often fused to form a single opening. A flexible trunk extends the external naris on some mammals. Soft tissue and muscles developed over the external naris in some marine mammals to prevent water from entering.
Much of the above is well known and taught in college textbooks. However the hypothesis of a transition from a single dorsal naris to the first median incurrent-excurrent naris to the first pair of incurrent-excurrent nares is presented here for the first time. If not, please provide a citation so I can promote it here.
Subsurface paired eyes first appear in our vertebrate lineage in the hagfish (genus: Myxine, Fig. 1). Hagfish ancestors that must have appeared earlier than the Early Cambrian (Fig. 3).
Dong and Allison 2020 report “Hagfish eyes are markedly basic compared to the eyes of other vertebrates, lacking a pigmented epithelium, a lens, and a retinal architecture built of three cell layers – the photoreceptors, interneurons & ganglion cells.”
This is what one would expect given a completely blind outgroup taxon, Enoplus, the roundworm (Fig. 2) a benthic nematode.
Dong and Allison 2020 wrote: “Hagfish eyes represent either a transitional form in the early evolution of vertebrate vision, or a regression from a previously elaborate organ.”
In the large reptile tree(LRT, 1870+ taxa; subset Fig. 3) hagfish eyes represent an early evolution of vertebrate vision. More primitive taxa (nematodes and lancelets) do not have paired surface eyes. Lancelets have a single primitive ‘frontal eye‘ with putative photoreceptors oriented dorsally. In Pikaia there is no fossil evidence of eyes.
Dong and Allison needed a valid phylogenetic analysis, like the LRT, that minimizes taxon exclusion. Then phylogenetic bracketing can recover an hypothesis of ocular genesis in chordates.
Dong and Allison 2020 wrote: “Here we show the hagfish retina is not extensively degenerating during its ontogeny, but instead grows throughout life. The epithelium that encompasses these photoreceptors lacks the melanin pigment that is universally associated with animal vision; notwithstanding, we suggest this epithelium is a homolog of gnathosome Retinal Pigment Epithelium (RPE).”
The authors report the eyes of hagfish do not have lenses that can resolve images. The skin over the eyes are the only part of the hagfish that has no pigment. This is step one toward permitting light to come into the hagfish retina.
Dong and Allison 2020 wrote: “We infer that the hagfish retina is not entirely rudimentary in its wiring, despite lacking a morphologically distinct layer of interneurons.”
Taxa following hagfish in the LRT have eyeballs more typical of vertebrates. The first of these include Middle Cambrian Metaspriggina (Fig. 3 with a pair of eyeballs on either side of its single dorsal naris (= nostril), but this time completely anterior to the rest of the body.
Metaspriggina is basal only to other fin-less taxa with eyes located at the extreme anterior of the torso and atrium. These taxa include the wide, armored lancelets, Arandaspis,Poraspis and Drepanaspis (Fig. 5).
On another branch of the LRT, (Fig. 3) the extant lamprey (Pteromyzon, Fig. 6) and Early Silurian Jamoytius (Fig. 6) retain the eyeball near the middle of the skull, preserving the olfactory rostrum observed in Myxine, the hagfish (Fig. 1). The rostrum is missing in Metaspriggina and its armored jawless kin (Fig. 5).
In adult lampreys the eyeball has an iris, lens and breaks the surface of the skin. In young lampreys the eyes are poorly developed and buried under the skin, as in adult hagfish. Lampreys undergo a metamorphosis during maturity that brings well-developed eyes to the surface.
We know the above taxa are late survivors of earlier radiations (Fig. 3) because the basal galeaspid, Haikouichthys (Fig. 7), is from the Early Cambrian.
Descendants of these basal vertebrate taxa, including primates and humans, further refined the eyeball to their individual needs, but the basics were all present by the start of the Early Cambrian.
Certain subterranean taxa have become secondarily blind through evolution. The extant electric eel (Electrophorus) and banded knifefish (Gymnotus) are derived from blind cave fish and remain largely blind, now depending on electric impulses to sense their environment.
We’re going to expand a definition today Tree shrew-like taxa are all related to one another (Fig. 1). The traits they share are inherited, not convergent. They form traditionally overlooked links between more familiar clades. That’s because ultimately some of these tree shrew-like taxa evolve to other shapes and sizes, like bats, giraffes, kangaroos, killer whales and humans. It’s about time we understood just exactly where we humans and we placentals came from.
Unfortunately, O’Leary et al. 2013is the current standard and doggone it, that crew had to invent a hypothetical ancestor for placentals because they chose to exclude pertinent taxa… and they relied on genomic testing. Two major sins.
Caluromys also precedes a clade of largely carnivorous marsupials (traditional creodonts) in the LRT (Fig. 6).
The large tree shrew-like Virginia opossum (Didelphis) precedes a clade of largely herbivorous marsupials in the LRT (Fig. 6). This opossum can be thought of as a large tree shrew if you have the smallest inkling of imagination.
A mouse-like marsupial, Monodelphys, the extant gray short-tailed opossum (Fig. 2) is a good climber, but is more at home closer to the ground. As might be expected for a placental proximal outgroup taxon, Monodelphis females have a transitional open pouch.
As you might imagine, taking care of growing, hungry Monodelphis youngsters can be quite a chore for the mom (Fig. 3) especially in Late Jurassic and throughout the Cretaceous when this scene was common if you knew where to look (with night vision goggles). One of life’s mysteries is how this sort of maternal care was selected for. It looks extremely debilitating, but somehow it worked! This is why we celebrate Mother’s Day.
The last common ancestor of all placentals in the LRT, Early Eocene Vulpavus palustris (Fig. 2), is basically a large tree shew. We’ll all be looking for its little sister in Jurassic formations.
The two extant taxa the dictionary considers tree shrews, Ptilocercus (Fig. 3) and Tupaia (Fig. 3) are basal to two different clades of placentals, Volitantia and Glires. This breaks tradition, which nests these two in a traditional clade, Scandentia. In the LRT that clade name is a junior synonym for Placentalia.
Taxa with a tree shrew morphology are common along the backbone of the mammal cladogram (Fig. 1). All basal marsupial and placental clades have either a tree shrew-, squirrel-, mouse- or phalanger-like morphology, with sizes up to the Virginia opossum. Thereafter some become bats (Fig. 7). Others become primates. Still others become rodents, mulittuberculates and tenrecs.
Monotremes appear to have rarely climbed trees. Most of these mouse-like invertebrate-eaters don’t have any obvious arboreal traits. Long-limbed, Late Jurassic Juramaia might be the exception. Extant monotremes do not attempt climbing. Late surviving, Late Cretaceous Ukhaatherium, the basalmost therian in the LRT, has a supple backbone and long limbs, ideal for a tiny tree climber. In the LRT, Ukhaatherium is the basalmost member of Theria (Parker and Haswell 1897), aka Marsupialia (Illiger 1811).
Genomic analyses do not recover a similar tree topology for mammals. None provide transitional taxa between monotremes and marsupials and placentals. Some indicate that hyraxes, elephants and armadillos are basal placental taxa. Avoid deep time genomic analyses. Through no fault of their own, genes become corrupted by epigenetic interactions with continental viruses. The majority of paleontologists have not yet embraced that crack in the glass.
“Whenever you find yourself on the side of the majority, it is time to pause and reflect.” – MARK TWAIN
References O’Leary, MA et al. 2013. The placental mammal ancestor and the post-K-Pg radiation of placentals. Science 339:662-667. abstract
Contra traditional genomic studies, the origin of placental mammals occurred between the extant mouse-like marsupial without a pouch, Monodelphis (Fig. 1), and the larger, late surviving, Early Eocene arboreal placental, Vulpavus palustris (Fig. 2). Evidently both had their genesis in the Early Jurassic based on chronological bracketing.
According to Wikipedia, “Vulpavus (“fox grandfather”) is an extinct genus of Miacidae. It measured 60–90 cm in length and had an estimated weight over 1.19 kg (in V. palustris).” That is all Wikipedia has to say about this largely overlooked, yet important basal placental.
Vulpavus palustris (Marsh 1871) Bridgerian (Early to Middle Eocene) was a primitive miacid, a mink-like basal member of the Placentalia. Here Vulpavus was derived from a sister to Monodelphys (Fig. 1) and phylogenetically preceded Middle Paleocene Protictis and the extant coatimundi, Nasua. Both are basal members of the basal placental clade Carnivora.
A second traditional Vulpavus specimen, Vulpavus (Phlaodectes) ovatus (Fig. 3), does not nest with the first, according to the large reptile tree (LRT, 1870+ taxa). Here it nests with Onychodectes and other more terrestrial taxa at the base of the larger herbivorous placentals that give birth to precocial young (able to walk and follow their mother shortly after birth). Note the longer premaxilla and smaller teeth.
re: Vulpavus (Phlaodectes) ovatus (Middle Eocene; 12cm skull length) Matthew 1909 wrote: “An incomplete skeleton including a well preserved skull, represents a species very distinct from V. palustris and pro/ectus but presenting throughout the same general characters of teeth, skull and skeleton, and referable to the genus Vulpavus as a fairly distinct subgenus.”The orbits are wide apart, but the braincase is small. The squamosal glenoid is large. Matthew compared this specimen to carnivores, but this placental with small molars nests at the base of largely herbivorous taxa. Matthew wrote, “There is no indication of an osseus bulla.” That’s the ossified sphere that shields the middle ear bones in placentals.
Vulpavus and Onychodectes are traditionally considered miacids and taeniodonts.
According to Wikipedia,“Miacidae as traditionally conceived is not a monophyletic group; it is a paraphyletic array of stem taxa. Traditionally, Miacidae and Viverravidae had been classified in a superfamily, Miacoidea. Today, Carnivora and Miacoidea are grouped together in the crown-clade Carnivoramorpha, and the Miacoidea are regarded as basal carnivoramorphs. Some species of the genus Miacis are closely related to the order Carnivora, but only the species Miacis cognitus is a true carnivoran, as it is classified in the Caniformia.”
Traditional members of the Taeniodonta nest in far flung clades within Theria in the LRT. Taeniodon itself is a bivalve mollusc, so we should probably forget this clade and never mention it again.
In the LRT, (subset Fig. 4) Miacis nests within the Carnivora, at the base of the clade that ultimately produces sea lions. So Vulpavus and Onychodestes are not related to Miacis in the LRT.
References Marsh 0C 1871. Notice of some new fossil mammals and birds from the Tertiary formations of the West. American Journal of Science, Series 3, 2: 120-127. Matthew WD 1909. VI. – The Carnivora and Insectivora of the Bridger Basin, Middle Eocene. Memoirs of the American Museum of Natural History. 9(6):576pp.
Known from Early Paleocene fossils in Bolivia, with a phylogenetic genesis in the early Jurassic, Pucadelphys andinus (Figs. 1-3), nests in the large reptile tree (LRT, 1870+ taxa) just prior to the extant arboreal didelphid, Caluromys (Figs. 3-4). These taxa nest as omnivores between the largely herbivorous marsupials and the largely carnivorous marsupials, not far from the omnivorous ancestors of placentals.
35 partial skeletons are known from mouse-like Pucadelphys, dying en masse within ten feet of each other, perhaps during a flash flood. This was originally considered odd because usually marsupials are territorial and isolated from one another (kangaroos are exceptions to this trend). Twelve are female. Six are male with larger heads and larger canines. Five were juveniles. Ladeveze et al. 2011 concluded, “the early Palaeocene P. andinus population at Tiupampa was a socially interacting group, characterized by gregariousness, male–male competition and polygyny.”
Later, Astúa et al. 2015 reported the first evidence of gregarious denning in didelphids supported by photos (Fig. 2).
Surprisingly Pucadelphys phylogenetics are rather difficult to find. Pucadelphys is al so close to Caluromys geographically. Prepubes are present on both taxa.
While adding Pucadelphys to the LRT a review revealed a new last common ancestor for the Placentalia. Caluromys (Figs. 3, 4) used to hold that honor. Now it returns to mouse-like Monodelphis (Fig. 5), one of the few extant marsupials without a marsupium.
Kraus and Fadem 1987 report on Monodelphis: litter size ranged from 2 to 13 with a m:f gender ratio of 1:1. Females typically have 13 teats that can be retracted into her body. After a 14-day gestation, 1cm young emerge and attach to a teat. The young grow hair after 3 weeks, open their eyes a week later, and are weaned at eight weeks. Sexual maturity occurs after 5 months of age and live to 4 years old.
References Astúa D et al. 2015. First evidence of gregarious denning in opossums (Didelphimorphia, Didelphidae), with notes on their social behaviour. Biol. Lett. 11: 20150307. http://dx.doi.org/10.1098/rsbl.2015.0307 Kraus DB and Fadem BH 1987. Reproduction, development and physiology of the gray short-tailed opossum (Monodelphis domestica). Lab Anim Sci 37(4):478–482. Ladeveze S, de Muizon C, Beck R, Germain D and Cespedes-Paz R 2011. Earliest evidence of mammalian social behaviour in the basal Tertiary of Bolivia Nature, 474, 83-86 DOI: 10.1038/nature09987 Marshall LG and De Muizon C 1988. The Dawn of the Age of Mammals in South America. National Geographic Research 4:23-55. Marshall LG, de Muizon C and Sigogneau-Russsell D 1995. Pucadelphys andinus (Marsupialia, Mammalia) from the early Paleocene of Bolivia. Part I: The locality of Tiupampa: age, taphonomy and mammal fauna. Mémoires du Muséum national d’histoire naturelle 165: 11–20.
Anna Krahl 2021 brings us her thoughts on swimming methods used by turtles and plesiosaurs.
From the abstract: “The terrestrial origins of the diapsid Sauropterygia and Testudines are uncertain, with the latter being highly controversially discussed to this day.”
Not true. The large reptile tree (LRT, 1869+ taxa) clearly shows the terrestrial origins of both clades. The traditional Testudines is an invalid clade because it is diphyletic with parallel origins of softshell and hardshell turtles from two small horned pareiasaurs (Fig. 1). The larger pareisaur, Bunostegos, is their last common ancestor.
Krahl 2021 wrote: “For only 15 Ma, Nothosauroidea lived in shallow-marine seas of the Triassic. Contrastingly, the pelagic Plesiosauria evolved in the Late Triassic, dispersed globally, and inhabited the oceans of the Jurassic and Cretaceous for approximately 135 Ma.”
Krahl omits the hind-limb flipper only taxa, Yunguisaurus (Fig. 2) and Thalassiodracon. and does not consider the vertical orientation proposed for plesiosaur feeding.
Krahl 2021 wrote: “Since the Cretaceous (~100 Ma), Chelonioidea, the modern sea turtles, have populated the oceans.”
Krahl is not aware that the traditional clade Cheloniodea is polyphyletic. at least three clades of sea turtles evolved independently (Fig. 1). Always start from a valid phylogeny.
Krahl 2021 wrote: “All three groups evolved aquatic paraxial locomotion. Nothosaurs swam with their foreflippers, supported by the swimming tail. Plesiosaurs are the only tetrapods to have ever evolved four hydrofoil-like flippers.”
Did Krahl forget ichthyosaurs here? Especially the Triassic giant, Shonisaurus. Other ichthyosaurs also emphasize the limbs/flippers. Cartorhynchus is a pachpleurosaur with large fore flippers.
Krahl 2021 wrote: “The plesiosaur flipper beat cycle has been debated for nearly two centuries. The different proposed locomotory styles (rowing, rowing-flight, underwater flight) are discussed in this review.”
I will leave locomotory styles to the experts. When done well, ancestors will show precursor styles.
Krahl 2021 wrote: “A fourth gait that is employed by Carettochelys insculpta, which combines rowing and flying, is introduced.”
We looked at Carettochelys earlier here. It looks like it was just learning how to swim with new flippers (Fig. 3).
Krahl 2021 wrote: “The osteology of the locomotory apparatus of nothosaurs and plesiosaurs is reviewed and compared to that of extant underwater-flying Chelonioidea.”
Krahl publishes crude drawings of generic taxa. Probably not the best way to go about doing this.
“In conclusion, underwater flight remains the favoured locomotory style for plesiosaurs. Also, the review reveals that nothosaur locomotion has largely remained unstudied. Further, our understanding of joint morphologies and mobilities of the foreflipper in nothosaurs, plesiosaurs, and even recent sea turtles, and of the hindflipper in plesiosaurs, is very limited. It is crucial to the discussion of locomotion, to find out, if certain limb cycles were even possible, as evidence seems to point to the improbability of a rowing motion because of limited humerus and femur long axis rotation in plesiosaurs.”
Krahl presented 11 small suprageneric cladograms from prior authors, to show her lack of certainty with regard to phylogeny. I’ll say it again, don’t start your studies without a valid phylogenetic context on which to base your studies. This is essential.
Krahl compares “a spectrum of gradual adaptations” in sauropterygians to the traditional clade ‘Cetacea’ unaware that this clade has been invalid for several years.
Functionally Krahl compares sauropterygians to sea turtles, explaining, “Chelonioidea were chosen as functional analogue because they fly underwater. Sea turtles were given the favor over penguins because they do not have a reduced digital number and because they do not have the highly derived avian flight mechanism (i.e., the acrocoracohumeral ligament and the osteological complex that resolves around it) that penguins and other birds have.”
Krahl reiterates recent hypotheses that ‘prove’ the pliosaur/ plesiosaur dichotomy invalid. The LRT does not confirm that dichotomy invalid. That issue came under review a few days ago here.