Palaeoxonodon: a Stem Therian Mammal From Bathonian Jurassic Isle of Skye (or Lumper Attack!)

A lower jaw of Palaeoxonodon from the Middle Jurassic of the Isle of Skye, Scotland, sheds new light on the diversity of British stem therians

Authors:

Close et al

Abstract:

The Middle Jurassic was a key interval of mammalian evolutionary history that witnessed the diversification of the therian stem group. Great Britain has yielded a significant record of mammalian fossils from this interval, represented by numerous isolated jaws and teeth from the Bathonian of Oxfordshire and the Isle of Skye. This record captures a key period in early cladotherian evolution, with amphitheriids, peramurans and ‘stem zatherians’ displaying intermediate talonid morphologies that document the evolutionary assembly of tribosphenic molars. We present a mandible with near-complete dentition from the late Bathonian (c. 167.4–166.5 Ma) Kilmaluag Formation, near Elgol, Skye, representing the amphitheriid Palaeoxonodon ooliticus, previously known only from isolated teeth. The specimen sheds new light on the taxonomic diversity of British Middle Jurassic stem therians, as the morphological variation within the preserved tooth row encompasses that previously ascribed to three distinct species within two genera: Palaeoxonodon ooliticus, P. freemani and Kennetheridium leesi. Thus, both P. freemani and K. leesi are subjective junior synonyms of P. ooliticus. The dental formula of P. ooliticus (i4:c1:p5:m5) is intermediate between the primitively larger postcanine count (p5:m6–7) of Amphitherium and the reduced number in peramurans and tribosphenidans (p5:m3). Phylogenetic analyses of P. ooliticus generally confirm a close affinity with Amphitherium, but highlight the lack of strong empirical support for hypothesized patterns of divergences among early cladotherians.

 pop sci write up.

Three Oldest Known Snake Fossils Found From Jurassic Bathonian Jurassic Britain, Kimmeridgian Jurassic Portugal

Fossilized remains of four ancient snakes have been dated between 140 and 167 million years old - nearly 70 million years older than the previous record of ancient snake fossils - and are changing the way we think about the origins of snakes, and how and when it happened. The findings have been published in the prestigious peer-reviewed journal Nature Communications.

"The study explores the idea that evolution within the group called 'snakes' is much more complex than previously thought," says lead author and professor Michael Caldwell in the Faculty of Science at the University of Alberta. "Importantly, there is now a significant knowledge gap to be bridged by future research as no fossils snakes are known from between 140 to 100 million years ago."

The oldest known snake, from Southern England, near Kirtlington, Eophis underwoodi, is known only from very fragmentary remains and was a small individual, though it is hard to say how old it was at the time it died. The largest snake, Portugalophis lignites, from coal deposits in Portugal, near Guimarota, was a much bigger individual at nearly a meter or more in length. Several of these ancient snakes (Eophis, Portugalophis and Parviraptor) were living in swampy coastal areas on large island chains in western parts of ancient Europe, while the North American species, Diablophis gilmorei, is found in river deposits from some distance inland in Western Colorado.

This new study makes it clear that the sudden appearance of snakes, some 100 million years ago, reflects a gap in the fossil record, not an explosive radiation of early snakes. From 167 to 100 million years ago, some 70 million years, snakes were radiating and evolving towards the elongate, limb-reduced body plan characterizing the now well known, ~100-90 million year old, marine snakes from the West Bank, Lebanon, and Argentina, that still possess small but well developed rear limbs. As is always the case, the distribution of these newer oldest snakes, and the anatomy of the skull and skeletal elements, makes it clear that even older snake fossils are waiting to be found.

"Based on the new evidence and through comparison to living legless lizards that are not snakes," explains Caldwell, "the paper explores the novel idea that the evolution of the characteristic snake skull and its parts appeared long before snakes lost their legs."

link.

paper link.

First Continental Biota (Inclusive of Cladotherian Mammals!) From Bathonian Jurassic Morocco Found

Guelb el Ahmar (Bathonian, Anoual Syncline, eastern Morocco): First continental flora and fauna including mammals from the Middle Jurassic of Africa

Authors:

Haddoumi et al

Abstract:

We report the discovery in Mesozoic continental “red beds” of Anoual Syncline, Morocco, of the new Guelb el Ahmar (GEA) fossiliferous sites in the Bathonian Anoual Formation. They produced one of the richest continental biotic assemblages from the Jurassic of Gondwana, including plants, invertebrates and vertebrates. Both the sedimentological facies and the biotic assemblage indicate a lacustrine depositional environment. The flora is represented by tree trunks (three families), pollen (13 species, five major clades) and charophytes. It suggests local forests and humid (non-arid) conditions. The vertebrate fauna is dominated by microvertebrates recovered by screening-washing. It is rich and diverse, with at least 29 species of all major groups (osteichthyans, lissamphibians, chelonians, diapsids, mammals), except chondrichthyans. It includes the first mammals discovered in the Middle Jurassic of Arabo-Africa. The GEA sites yielded some of the earliest known representatives of osteoglossiform fishes, albanerpetontid and caudate amphibians, squamates (scincomorphans, anguimorphan), cladotherian mammals, and likely choristoderes. The choristoderes, if confirmed, are the first found in Gondwana, the albanerpetontid and caudatan amphibians are among the very few known in Gondwana, and the anguimorph lizard is the first known from the Mesozoic of Gondwana. Mammals (Amphitheriida, cf. Dryolestida) remain poorly known, but are the earliest cladotherians known in Gondwana.The GEA biotic assemblage is characterized by the presence of Pangean and Laurasian (especially European) taxa, and quasi absence of Gondwanan taxa. The paleobiogeographical analysis suggests either a major fossil bias in Gondwana during the Middle Jurassic, and an overall vicariant Pangean context for the GEA assemblage, or alternatively, noticeable Laurasian (European) affinities and North-South dispersals. The close resemblance between the Bathonian faunas of GEA and Britain is remarkable, even in a Pangean context. The similarity between the local Anoual Syncline Guelb el Ahmar and Ksar Metlili faunas raises questions on the ?Berriasian age of the latter.

Palaeobiogeography of the Bajocian/Oxfordian Jurassic Sinai

Palaeobiogeography of the Bajocian–Oxfordian macrofauna of Gebel Maghara (North Sinai, Egypt): Implications for eustacy and basin topography

Authors:

Abdelhady et al

Abstract:

Based on newly collected material from the Bajocian–Oxfordian rocks of Gebel Maghara (North Sinai, Egypt) and available published information, the palaeobiogeographic pattern and the dispersal potential of the macrofauna including bivalves, ammonites, corals, and brachiopods are investigated. Both clustering methods and ordination techniques were applied and evaluated. During Bajocian times, G. Maghara occupied an intracratonic setting and was isolated from the main ocean by islands and shallows. These barriers may have limited the dispersal potential of the macrofauna and impeded the faunal exchange with even nearby areas. Although these barriers had disappeared by rejuvenation of faults during an active rift stage in Bathonian times, the same biogeographic patterns continued, which may be related to the global sea level lowstand. By Callovian times, a time of global sea level highstand, in contrast, the fauna of the study area became very similar to that of northeastern Africa. Similarly, diversity and extinction rates increased from the middle Bathonian onward, which may reflect intrusion of cosmopolitan taxa due to the newly established open marine setting and the global sea level highstand. Towards the Oxfordian, lowering of temperature may have limited the dispersal ranges of the macrofauna within the Ethiopian Province. As a result, a southeastern subprovince (Indo–Malagasy) including Tanzania, Madagascar, and India became established. Although the geographic patterns of the different faunal groups exhibit some similarities resulting from abiotic factors such as sea level, climate, and basin topography, biotic characteristics such as life habits and larval development played the dominant role in shaping the distribution pattern. The dispersal potential was highest for ammonites, followed by that of corals and then bivalves. Brachiopods had the lowest dispersal potential.

Anthracolestes sergeii: a new Dryolestid Mammal From Bathonian Jurassic Siberia

The oldest dryolestid mammal from the Middle Jurassic of Siberia

Authors:

Arerianov et al

Abstract:

Anthracolestes sergeii, gen. et sp. nov., based on three isolated lower molars and several edentulous dentary fragments from the Middle Jurassic (Bathonian) Itat Formation at Berezovsk Quarry in Krasnoyarsk Territory, Russia, is the oldest and most basal representative of Dryolestidae. It shows four unambiguous synapomorphies of Dryolestidae: lower molars with unilaterally hypsodont crowns, unequal roots, and pronounced precingulid instead of cusp f, and dentary with unequal alveolar borders. The dental formula of the new taxon is i1–4, c (double-rooted), p1–4(?), and m1–4(?). Anthracolestes sergeii, gen. et sp. nov., is plesiomorphic relative to more derived and geologically younger dryolestids in having possibly fewer lower molars, less pronounced mesiodistal compression of lower molars, oblique protocristid, short mandibular symphysis, and shallow mandibular ramus of the dentary. Asia is most likely the place of origin for Dryolestidae, but this group is so far not known from that continent after the Middle Jurassic.

Stem Therian Amphibetulimus From Bathonian Jurassic Siberia

Stem therian mammal Amphibetulimus from the Middle Jurassic of Siberia

Authors:

Alexander Averianov, Thomas Martin, Alexey Lopatin and Sergei Krasnolutskii

Abstract:

Amphibetulimus krasnolutskii is known from the Middle Jurassic (Bathonian) Itat Formation of Krasnoyarsk Territory, West Siberia, Russia, by several edentulous and three dentigerous dental fragments, preserving p1, antepenultimate, and ultimate lower molars, and by an upper molar. It is unique among stem therians by widely open trigonids on the posterior lower molars, paraconids that are higher than the metaconids and have keeled mesiolingual vertical crests, pronounced unilateral hypsodonty of the lower molars and correlated unequal alveolar borders of the dentary ramus, and a linear Meckelian groove that is not connected to the mandibular foramen and extends along the pterygoid ridge. Amphibetulimus differs from more derived stem therians by a simple unicuspid talonid without an incipient talonid basin and a distinct labial cingulum on the upper molars. The lack of an ectotympanic facet and the long linear Meckelian groove extending onto the pterygoid ridge suggest that Amphibetulimus had a derived state of the transitional mammalian middle ear, where the ear ossicles were connected to the dentary not by a thick “ossified” Meckelian cartilage, but by a thin Meckelian cartilage, as in prenatal and early postnatal stages of some modern therians.

Megaconus mammaliaformis: A Fuzzy Therapsid (Haramiyid, Mammaliaform) From Bathonian Jurassic China

A newly discovered fossil reveals the evolutionary adaptations of a 165-million-year-old proto-mammal, providing evidence that traits such as hair and fur originated well before the rise of the first true mammals. The biological features of this ancient mammalian relative, named Megaconus mammaliaformis, are described by scientists from the University of Chicago in the Aug 8 issue of Nature.

"We finally have a glimpse of what may be the ancestral condition of all mammals, by looking at what is preserved in Megaconus. It allows us to piece together poorly understood details of the critical transition of modern mammals from pre-mammalian ancestors," said Zhe-Xi Luo, professor of organismal biology and anatomy at the University of Chicago.

Discovered in Inner Mongolia, China, Megaconus is one of the best-preserved fossils of the mammaliaform groups, which are long-extinct relatives to modern mammals. Dated to be around 165 million years old, Megaconus co-existed with feathered dinosaurs in the Jurassic era, nearly 100 million years before Tyrannosaurus Rex roamed Earth.

Preserved in the fossil is a clear halo of guard hairs and underfur residue, making Megaconus only the second known pre-mammalian fossil with fur. It was found with sparse hairs around its abdomen, leading the team to hypothesize that it had a naked abdomen. On its heel, Megaconus possessed a long keratinous spur, which was possibly poisonous. Similar to spurs found on modern egg-laying mammals, such as male platypuses, the spur is evidence that this fossil was most likely a male member of its species.

"Megaconus confirms that many modern mammalian biological functions related to skin and integument had already evolved before the rise of modern mammals," said Luo, who was also part of the team that first discovered evidence of hair in pre-mammalian species in 2006.

A terrestrial animal about the size of a large ground squirrel, Megaconus was likely an omnivore, possessing clearly mammalian dental features and jaw hinge. Its molars had elaborate rows of cusps for chewing on plants, and some of its anterior teeth possessed large cusps that allowed it to eat insects and worms, perhaps even other small vertebrates. It had teeth with high crowns and fused roots similar to more modern, but unrelated, mammalian species such as rodents. Its high-crowned teeth also appeared to be slow growing like modern placental mammals.

The skeleton of Megaconus, especially its hind-leg bones and finger claws, likely gave it a gait similar to modern armadillos, a previously unknown type of locomotion in mammaliaforms.

Luo and his team identified clearly non-mammalian characteristics as well. Its primitive middle ear, still attached to the jaw, was reptile-like. Its anklebones and vertebral column are also similar to the anatomy of previously known mammal-like reptiles.

"We cannot say that Megaconus is our direct ancestor, but it certainly looks like a great-great-grand uncle 165 million years removed. These features are evidence of what our mammalian ancestor looked like during the Triassic-Jurassic transition," Luo said.

"Megaconus shows that many adaptations found in modern mammals were already tried by our distant, extinct relatives. In a sense, the three big branches of modern mammals are all accidental survivors among many other mammaliaform lineages that perished in extinction," Luo added.

Paper link.

Significant Climate Change From Bajocian to Bathonian Jurassic in Negev

Jurassic flora of the Negev Desert: Plant taphonomy, palaeoecology and palaeogeographic inference

Authors:

1. Valentin Krassilov (a)
2. Alex Berner (b)
3. Sophia Barinova (a)

Affiliations:

a. Institute of Evolution, University of Haifa, Mount Carmel, Haifa 31905, Israel

b. Israel Institute of Technology, Haifa, 32000, Israel

Abstract:

Jurassic fossil plants of Makhtesh Ramon, the northern Negev, are collected from the Early Bajocian paralic Inmar Formation conformably overlain with the marine Mahmal Formation, which contains ammonite markers of the Middle–Upper Bajocian age. Plant remains occur in the thin ferruginous layers traceable all over the questa exposures, composed of re-deposited sand at the base and the fine-grained ferro-alumosilicate lamella on top. Plants are preserved as ferruginous molds of leafy shoots and reproductive material, buried by turbid run-over sand flows and embedded in the back-wash clayey deposits as calcified plant debris. On account of their peculiar taphonomy and elementary composition, the fossiliferous horizons are interpreted as tsunamites. The coastal plant assemblages are endemic at the syntaxonomic level, with Gondwana affinities extended to insular landmasses north of the Tethys. The abundance of bennettitalean plants and the inferred proximity of Araucaria-like brachyphylls gives the Bajocian Inmar flora a thermophilic paratropical aspect, while the Bathonian flora of Sinai is of a more temperate aspect, suggesting a major mid-Jurassic climate change.