[PaleoIchthyology • 2021] Mawsonia sp. • The First late Cretaceous Mawsoniid Coelacanth (Sarcopterygii: Actinistia) from North America: Evidence of A Lineage of Extinct ‘Living Fossils’

Reconstruction of Mawsonia sp. roaming in the brackish or fresh water costal environment of Texas during the Cenomanian.

in Cavin, Toriño, Van Vranken, ... et Winkler, 2021. 

DOI: 10.1371/journal.pone.0259292 

 twitter.com/PabloTorino4

Original artwork by Zubin Erik Dutta.

Abstract

Today, the only living genus of coelacanth, Latimeria is represented by two species along the eastern coast of Africa and in Indonesia. This sarcopterygian fish is nicknamed a "living fossil", in particular because of its slow evolution. The large geographical distribution of Latimeria may be a reason for the great resilience to extinction of this lineage, but the lack of fossil records for this genus prevents us from testing this hypothesis. Here we describe isolated bones (right angular, incomplete basisphenoid, fragments of parasphenoid and pterygoid) found in the Cenomanian Woodbine Formation in northeast Texas that are referred to the mawsoniid coelacanth Mawsonia sp. In order to assess the impact of this discovery on the alleged characteristic of "living fossils" in general and of coelacanths in particular: 1) we compared the average time duration of genera of ray-finned fish and coelacanth in the fossil record; 2) we compared the biogeographic signal from Mawsonia with the signal from the rest of the vertebrate assemblage of the Woodbine formation; and 3) we compared these life traits with those of Latimeria. The stratigraphical range of Mawsonia is at least 50 million years. Since Mawsonia was a fresh, brackish water fish with probably a low ability to cross large sea barriers and because most of the continental components of the Woodbine Fm vertebrate assemblage exhibit Laurasian affinities, it is proposed that the Mawsonia’s occurrence in North America is more likely the result of a vicariant event linked to the break-up of Pangea rather than the result of a dispersal from Gondwana. The link between a wide geographic distribution and the resilience to extinction demonstrated here for Mawsonia is a clue that a similar situation existed for Latimeria, which allowed this genus to live for tens of millions of years.

Systematic paleontology

Actinistia Cope, 1871.

Latimerioidei Schultze, 1993.

Mawsoniidae Schultze, 1993.

Genus Mawsonia Woodward in Mawson and Woodward, 1907

Mawsonia sp.

‘Mid’-Cretaceous paleogeographical map of western Laurasia and western Gondwana showing biogeographical affinities of vertebrates from the woodbine formation (red circle).
Brown areas indicates continental vertebrates and the blue areas indicate brackish and marine vertebrates. Orange dots indicate approximate locations of records of Mawsonia.

Comparison of the geographical distributions of the two extant Latimeria species and their supposedly common ancestor 30 to 40 million years ago (left) with those of Mawsonia in the mid-cretaceous, about 100 million years ago and in the Late Jurassic–basal Cretaceous, about 145 million years ago (right).

Lionel Cavin, Pablo Toriño, Nathan Van Vranken, Bradley Carter, Michael J. Polcyn, Dale Winkler. 2021. The First late Cretaceous Mawsoniid Coelacanth (Sarcopterygii: Actinistia) from North America: Evidence of A Lineage of Extinct ‘Living Fossils’ PLoS ONE. 16(11): e0259292. DOI: 10.1371/journal.pone.0259292 

 twitter.com/PabloTorino4/status/1458976004886732805

[Mammalogy • 2012] ‘Ninh Cùng’ (Annamite Rat) | The first record of living “Fossil” species Laonestes aenigmanus in Phong Nha - Ke Bang, Quang Binh province, Vietnam

Laonastes aenigmamus | Truong Son Rat (Annamite Rat) 
or  Laotian Rock Rat. To locals it is known as ‘Ninh Cùng’.

Laotian Rock Rat Laonastes aenigmamus was first discovered in Hin Nammo NBCA, Khammoune Province, Lao PDR in 2005 by Jenkins et al. (2005). This species was later recognized as living species of the ancient family Diatomyidae which was thought to be extinct since the Miocene, about 11 millions years ago. Conservation of this species is recommended at the highest priority not only due to its limited range but also due to its status as the single living representative of an ancient family.

During biodiversity survey on small mammals in Phong Nha - Ke Bang National Park, Quang Binh Province, Central Vietnam, we obtained 4 specimens of un-usual small animals in Thuong Hoa Commune, Minh Hoa District, Quang Binh Province. Based on analysis of appearance, body measurements and skull charasters of these specimens, we confirm that they belong to Laotian Rock Rat Laonastes aenigmamus which was described in 2005 based on specimens collected in Hin Nam No National Biodiversity Conservation Area, Khammoune Province, Lao PDR. Morphological features and some ecological attributes of this species are provided. This species is proposed to be included in the Checklist of wild mammal species of Vietnam under name as Truong Son Rat (Annamite Rat).

Main threats to Annamite Rat in Vietnam are wildlife hunting/snaring and forest destruction. Snaring small mammals for food and for trade is common habit of local residents in Thuong Hoa and nearby communes. Urgent conservation actions and further studies on population genetics and ecology of this elusive species are recommended.

Keywords: Laonestes, Laotian Rock Rat, đa dạng sinh học, Ne Cung, Phong Nha - Ke Bang

The first record of living “Fossil” species Laonestes aenigmanus in Phong Nha - Ke Bang, Quang Binh province, Vietnam

http://vjs.ac.vn/index.php/vjbio/article/view/668

Rare ancient rock rats found in Quang Binh

http://talkvietnam.com/2012/10/rare-ancient-rock-rats-found-in-quang-binh/

http://www.phongnhakebang.vn/Vn/default.aspx?Cat=3&Group=13&Item=439

http://khoahoc.baodatviet.vn/Home/KHCN/Chuot-da-Lao-Con-nhieu-bi-an-cho-kham-pha/20121/186143.datviet

http://talkvietnam.com/2011/09/species-believed-extinct-11-million-years-found-in-vietnam/

[Mammalogy • 2007] Laonastes aenigmamus | Kha-nyou | Laotian Rock Rat • Multiple molecular evidences for a living mammalian fossil

Fig. 1. A juvenile Laonastes aenigmamus, captured and released after photography, provides evidence that this species is, indeed, very much alive. Known locally as Kha-nyou, the Laotian rock rat possesses a rat-like head with long whiskers and a furry squirrel-like tail. It lives in the limestone rock outcroppings of central Lao People's Democratic Republic. (Photo by Uthai Treesucon, David Redfield 2006 Lao expedition).
doi: 10.1073/pnas.0701289104 

Abstract Laonastes aenigmamus is an enigmatic rodent first described in 2005. Molecular and morphological data suggested that it is the sole representative of a new mammalian family, the Laonastidae, and a member of the Hystricognathi. However, the validity of this family is controversial because fossil-based phylogenetic analyses suggest that Laonastes is a surviving member of the Diatomyidae, a family considered to have been extinct for 11 million years. According to these data, Laonastes and Diatomyidae are the sister clade of extant Ctenodactylidae (i.e., gundies) and do not belong to the Hystricognathi. To solve the phylogenetic position of Laonastes, we conducted a large-scale molecular phylogeny of rodents. The analysis includes representatives of all major rodent taxonomic groups and was based on 5.5 kb of sequence data from four nuclear and two mitochondrial genes. To further validate the obtained results, a short interspersed element insertion analysis including 11 informative loci was also performed. Our molecular data based on sequence and short interspersed element analyses unambiguously placed Laonastes as a sister clade of gundies. All alternative hypotheses were significantly rejected based on Shimodaira–Hasegawa tests, supporting the idea that Laonastes does not belong to the Hystricognathi. Molecular dating analysis also supports an ancient divergence, ≈44 Mya ago, between Ctenodactylidae and Laonastes. These combined analyses support the hypothesis that Laonastes is indeed a living fossil. Protection of this surviving species would conserve an ancient mammalian family. 

Keywords: Laonastes aenigmamus, molecular phylogeny, rodent, retroposons

Fig. 3. Molecular time scale for the order Rodentia.

Fig. 4. Phylogenetic affiliations of Laonastes based on presence/absence patterns of retroposed SINEs. The phylogenetic tree indicates the three major rodent clades: the mouse-related clade, the Ctenohystrica, and the squirrel-related clade.

Huchon, D., Chevret, P., Jordan, U., Kilpatrick, C.W., Ranwez, V., et al. 2007. Multiple molecular evidences for a living mammalian fossil. PNAS Proc Natl Acad Sci USA 104 (18): 7495–7499. doi: 10.1073/pnas.0701289104 

[Mammalogy • 2012] A Remarkable Case of Micro-Endemism in Laonastes aenigmamus (Diatomyidae, Rodentia) Revealed by Nuclear and Mitochondrial DNA Sequence Data

Abstract

Laonastes aenigmamus is endemic to the limestone formations of the Khammuan Province (Lao PDR), and is strongly specialized ecologically. From the survey of 137 individuals collected from 38 localities, we studied the phylogeography of this species using one mitochondrial (Cyt b) and two nuclear genes (BFIBR and GHR). Cyt b analyses reveal a strong mtDNA phylogeographical structure: 8 major geographical clades differing by 5–14% sequence divergence were identified, most of them corresponding to distinct karst areas. Nuclear markers display congruent results but with a less genetic structuring. Together, the data strongly suggest an inland insular model for Laonastes population structure. With 8 to 16 evolutionary significant units in a small area (about 200×50 km) this represents an exceptional example of micro-endemism. Our results suggest that L. aenigmamus may represent a complex of species and/or sub-species. The common ancestor of all Laonastes may have been widely distributed within the limestone formations of the Khammuan Province at the end of Miocene/beginning of the Pliocene. Parallel events of karst fragmentation and population isolation would have occurred during the Pleistocene or/and the end of the Pliocene. The limited gene flow detected between populations from different karst blocks restrains the likelihood of survival of Laonastes. This work increases the necessity for a strict protection of this rare animal and its habitat and provides exclusive information, essential to the organization of its protection.

Introduction

Eroded limestone outcrops form a prominent part of the landscape in Southeast Asia. Because of high limestone weathering erosion in these areas resulted in scattered, isolated limestone hills with steep flanks called karsts towers. Despite a high diversity of habitat specialists and endemic taxa, these limestone karsts remain among the least studied ecosystems in Southeast Asia. Between 1985 and 2004 they contributed only to 1% of the global and regional biodiversity research output from terrestrial and freshwater ecosystems, while they cover around 10% of the land area in Southeast Asia. However, in the Khammuan Province of Lao PDR, several new endemic vertebrate species were recently described: a bird, Pycnonotus hualon, a bat, Hipposideros scutinares, a gymnure, Hylomys megalotis, and a murid rodent, Saxatilomys paulinae.

Laonastes aenigmamus, recently described from this region by Jenkins et al., is of special interest. Using comparative morphological and molecular data, this new species was initially described as a member of a new genus and ranked within the Hystricognathi rodents in a new family: the Laonastidae. But, further studies demonstrated: first, that L. aenigmamus is a member of the Diatomyidae, a fossil family known from early Oligocene to late Miocene in Pakistan, India, Thailand, China, and Japan; second, that the Diatomyidae are the sister group of the Ctenodactylidae, a family of small rodents found in rocky deserts across the northern parts of Africa; third, that together with the Hystricognathi, the Diatomyidae and the Ctenodactylidae form the suborder Ctenohystrica.

In a previous study we presented a preliminary analysis of the genetic diversity of L. aenigmamus: 52 specimens were sampled and the population structure was surveyed by sequencing 887 base pairs of the Cytochrome b (Cyt b) gene. Phylogenetic and haplotypic network reconstructions revealed three well-supported and rather divergent lineages, suggesting that L. aenigmamus populations are geographically structured. However, altogether these samples represented a limited part of the estimated range of the species; most of them were sampled in local markets and their exact geographic origin was impossible to determine; this study was based on a fragment of a single mitochondrial gene.

Before its scientific discovery, the kanyou was considered as a kind of game, trapped and eaten by the villagers. Since 2008, the conservation of L. aegnimamus is regulated in Lao PDR and since 2009 this species is listed as «Endangered» on the IUCN Red List. During the last four years we add the unique opportunity to accompany local officers in the field when they explained this change to local populations, and to sample for molecular analyses the last specimens that were captured by traditional hunters. We were able to sample 137 individuals for which the exact locality of collect was known. It represents 38 localities probably spanning the whole geographical range of the species. Thus, the sampling obtained for this study is exceptional both in terms of number of individuals and number of localities sampled and will not be able to be carried out again. In the present study we: (1) improve evaluation of the genetic diversity and delineation of the phylogeographical structure of L. aenigmamus, by sequencing both nuclear and mitochondrial markers of a larger number of geographically referenced individuals; (2) obtain a better definition of the geographical distribution of the species; (3) highlight the spatial and temporal history of the limestone formation of the Khammuan Province, using the evolutionary history of this species as a guide. Our analysis strongly underlines the necessity for a strict protection of this rare animal and its habitat and provides exclusive information, essential to the organization of its protection.

 Nicolas V, Herbreteau V, Couloux A, Keovichit K, Douangboupha B, et al. 2012. A Remarkable Case of Micro-Endemism in Laonastes aenigmamus (Diatomyidae, Rodentia) Revealed by Nuclear and Mitochondrial DNA Sequence Data. PLoS ONE 7(11): . doi:10.1371/journal.pone.0048145