Ancient marine predator had a built-in float

About 240 million years ago, when reptiles ruled the ocean, a small lizard-like predator floated near the bottom of the edges in shallow water, picking off prey with fang-like teeth. A short and flat tail, used for balance, helps identify it as a new species, according to research published in the Journal of Vertebrate Paleontology.

An illustration of Brevicaudosaurus [Credit: Tyler Stone]

Paleontologists at the Chinese Academy of Scientists and Canadian Museum of Nature have analysed two skeletons from a thin layer of limestone in two quarries in southwest China. They identified the skeletons as nothosaurs, Triassic marine reptiles with a small head, fangs, flipper-like limbs, a long neck, and normally an even longer tail, probably used for propulsion. However, in the new species, the tail is short and flat.

"Our analysis of two well-preserved skeletons reveals a reptile with a broad, pachyostotic body (denser boned) and a very short, flattened tail. A long tail can be used to flick through the water, generating thrust, but the new species we've identified was probably better suited to hanging out near the bottom in shallow sea, using its short, flattened tail for balance, like an underwater float, allowing it to preserve energy while searching for prey," says Dr Qing-Hua Shang from the Chinese Academy of Sciences, in Beijing.

The scientists have named the new species Brevicaudosaurus jiyangshanensis, from the Latin 'brevi' for 'short,' 'caudo' for 'tail,' and the Greek 'sauros' for 'lizard.' The most complete skeleton of the two was found in Jiyangshan quarry, giving the specimen its species name. It's just under 60cm long.

Brevicaudosaurus jiyangshanensis, gen. et sp. nov., skeletons in dorsal view. A, IVPP V 18625,
 holotype; B, IVPP V 26010, referred specimen [Credit: QING-HUA SHANG,
XIAO-CHUN WU and CHUN, Journal of Vertebrate Paleontology]

The skeleton gives further clues to its lifestyle. The forelimbs are more strongly developed than the hind limbs, suggesting they played a role in helping the reptile to swim. However, the bones in the front feet are short compared to other species, limiting the power with which it could pull through the water. Most of its bones, including the vertebrae and ribs, are thick and dense, further contributing to the stocky, stout appearance of the reptile, and limiting its ability to swim quickly but increasing stability underwater.

However, thick, high-mass bones act as ballast. What the reptile lost in speed, it gained in stability. Dense bones, known as pachyostosis, may have made it neutrally buoyant in shallow water. Together with the flat tail, this would have helped the predator to float motionless underwater, requiring little energy to stay horizontal. Neutral buoyancy should also have enabled it to walk on the seabed searching for slow-moving prey.

Highly dense ribs may also suggest the reptile had large lungs. As suggested by the lack of firm support of the body weight, nothosaurs were oceanic nut they needed to come to the water surface for oxygen. They have nostrils on the snout through which they breathed. Large lungs would have increased the time the species could spend under water.

Brevicaudosaurus jiyangshanensis, gen. et sp. nov., IVPP V 18625, photographs and outlines
of the skull and the mandible in dorsal view. A,B, IVPP V 18625, holotype, in dorsal view;
C, D, IVPP V 26010, referred specimen, snout portion of the skull. Zigzag lines indicate
broken areas.Abbreviations: art, articular; bo, basioccipital; cqp, cranio-quadrate passage;
d, dentary; ec, ectopterygoid; eo, exoccipital; f, frontal; j, jugal; m,maxilla; n, nasal;
 op, opisthotic; or, orbit; p, parietal; pf, prefrontal; pl, palatine; pm, premaxilla;
po, postorbital; pof, postfrontal; pt, pterygoid; q, quadrate;qj, quadratojugal;
 rap, retroarticular process; sa, surangular; so, supraoccipital; sq, squamosal;
st, stapes [Credit: QING-HUA SHANG, XIAO-CHUN WU and CHUN,
Journal of Vertebrate Paleontology]

The new species features a bar-shaped bone in the middle ear called the stapes, used for sound transmission. The stapes was generally lost in other nothosaurs or marine reptiles during preservation. Scientists had predicted that if a stapes was found in a nothosaur, it would be thin and slender like in other species of this branch of the reptilian family tree. However, in B. jiyangshanensis it is thick and elongate, suggesting it had good hearing underwater.

"Perhaps this small, slow-swimming marine reptile had to be vigilante for large predators as it floated in the shallows, as well as being a predator itself," says co-author Dr. Xiao-Chun Wu from the Canadian Museum of Nature.

Source: Taylor & Francis [October 28, 2020]

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Evolutionary pattern of genus Cribroconcha reveals survival strategy of ostracods from late Paleozoic

Ostracods are microcrustacea that first appeared in the Ordovician and are still developing today. Although tiny, they are the most abundant fossil records of the Arthropod phylum, and the most diverse species of Crustaceans, with about 65,000 living and fossil species.

Distinct species of Cribroconcha Cooper, 1941
[Credit: NIGPAS]

Ostracods offer special insights into the characteristics of Devonian bio-environmental events. The ostracode genus Cribroconcha Cooper, 1941, is characterized by distinct morphological features, rapid evolutionary rates and wide geographical distribution, making it a potential index fossil for stratigraphic correlation and palaeoecological changes.

Recently, Dr. SONG Junjun from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGPAS) and her colleagues made a thorough analysis of the evolutionary pattern of Cribroconcha lineages and the established biozones.

To date, 37 species and two subspecies (36 species plus one species that with two subspecies) of the ostracode genus Cribroconcha Cooper, 1941, have been reported worldwide, ranging in age from the Middle Devonian to the Early Permian with an acme during the Carboniferous.

Based on the geographical distribution and morphological characteristics of Cribroconcha, two evolutionary lineages (i.e., Lineage 1 and Lineage 2) were identified, which originated in the European and the Kazakhstan plates, respectively. Lineage 1 can be subdivided into three types: 1-A (stable type), 1-B (reshaped type) and 1-C (spiny type).

Distribution of Cribroconcha species from the Late Devonian
to the Early Permia [Credit: NIGPAS]

The researchers found that 1-A stable type species inherited the characteristics of the early species totally. The 1-B reshaped type had elongate carapaces with subrectangular outline and subquadrate posterior border. Compared with the early species, species of this type only changed in the outline. The 1-C spiny type had the longest stratigraphic range and most species of this type had two sharp spines in the posterior border.

Most species of the 1-A and 1-B are benthic and living in a shallow marine environment. Some species of 1-C are nektonic and appeared in the deep cold waters from the shelf to the basin.

Only 1-C type species extended to the Early Permian, which implies the survival strategy of spiny type was successful. The morphological variability of spiny type is also related to the glacial event across the Devonian-Carboniferous boundary in the northern Gondwana, which generated cold deep water currents invading the palaeotethysian basins.

The research results were published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

Author: Li Yuan | Source: Chinese Academy of Sciences [October 26, 2020]

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Tracking the Himalayan history from the evolution of hundreds of frogs, lizards and snakes

The Himalaya are among the youngest and highest mountains in the world, but the exact timing of their uplift and origins of their biodiversity are still in debate. Generally, there are two hypotheses about the uplift process of the Himalaya. The "Stepwise Hypothesis" states that the Himalaya rose slowly from 1000-2500 m during 56-23 million years ago (Ma), before an additional rapid uplift to 4000 m during 23-19 Ma, and a final rise to the current average elevations (~5000 m) at around 15 Ma. Alternatively, recent hydrological and thermal evidences support that this region was probably not elevated to current elevation till mid-Pliocene ("Late Orogeny Hypothesis").

The Himalaya and representative amphibians and reptiles
[Credit: Science China Press]

Time-based records of biological processes can be informative about montane histories and environmental changes. Various hypotheses about Himalayan origins can be tested using phylogenetic information and estimates of the timing of biological speciation events. To address the question about the timing of the Himalaya uplift, we carried out field work across the Himalaya to collect samples of amphibians and reptiles. The Himalayan region encompasses multiple countries and has many access challenges, so sampling across the entire region is difficult, which has inhibited integrative studies of the origin of the Himalayan biota.

Combining 14 time-calibrated phylogenies of Himalayan-associated amphibian and reptile families involving 85 genera and 1628 species, we estimated times of divergence among 183 species that occur in the Himalaya. We identified 230 biogeographic events related to the Himalayan species. The dynamics of in situ diversification and dispersal rates remained essentially parallel across the Cenozoic. Both the in situ diversification rate, as well as the dispersal rate into the Himalaya, fit the Stepwise Hypothesis for the origin of this mountain range. In contrast, our estimates of origination and peak diversification are not consistent with the late-uplift hypothesis.

Biotic assembly through time of herpetofauna in the Himalaya. (a): The rates of in situ diversification
 and dispersal of the Himalayan herpetofauna through time (smoothed across 5 Ma windows).
Dispersal indicates "dispersal into the Himalaya." MDivE = maximal number of observed
 in situ diversification events per Ma. MDisE = maximal number of observed dispersal events
per Ma. Ambiguous events are separately listed. (b): Dispersal events from adjacent regions
 into the Himalaya (smoothed across 5 Ma windows). MDisE = maximal number
of observed dispersal events per Ma [Credit: Science China Press]

The rapid Himalayan uplift and associated intensified South Asia Monsoon not only promoted a pulse of uplift-driven in situ diversification, but also affected the rates of biotic interchange. Biotic interchange was restricted by the lack of a moist environment that is required by many reptiles and amphibians. In contrast, an expanded tropical forest belt is thought to have persisted between the Himalaya and Southeast Asia since the middle Miocene, which likely accounts for the high dispersal rates between these two regions.

This work has important implications about the assembly process of Himalayan herpetofauna and its conservation. Our analyses show a deep-rooted origin of Himalayan herpetofauna originating in the Paleocene, but with rapid diversification in the Miocene.

The study is published in the National Science Review 2020.

Source: South China Press [October 26, 2020]

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