New palaeothentid marsupials (Paucituberculata) from the middle Miocene of Quebrada Honda, Bolivia, and their implications for the palaeoecology, decline and extinction of the Palaeothentoidea

<p>Paucituberculatan marsupials, particularly members of the family Palaeothentidae, were important components of South American mammal communities during much of the Cenozoic. However, after the late early Miocene, palaeothentid remains are rare in the fossil record, and the group is last recorded at late middle Miocene sites in Colombia, Bolivia and possibly Argentina. Here, we describe new specimens of palaeothentids from one of these late middle Miocene sites, Quebrada Honda, Bolivia, which include: (1) the first described lower dentitions of <i>Acdestis maddeni</i>, which exhibit distinctive features such as a greatly elongated paracristid and a single-rooted m4; (2) the first described late middle Miocene palaeothentines, representing two new species of <i>Palaeothentes</i>, <i>P. serratus</i> sp. nov. and <i>P. relictus</i> sp. nov., distinguished from other species of <i>Palaeothentes</i> by the presence of an anterobasal cingulid and reduced anterior trigonid crest, among other features; and (3) remains of a third new species, <i>Chimeralestes ambiguus</i> gen. et sp. nov., distinguished from other palaeothentids by its combination of a labially positioned cristid obliqua, reduced m4, and sharply curved entocristid. Phylogenetic and palaeoecological analyses show that Quebrada Honda palaeothentids were taxonomically and morphologically diverse and likely spanned a wide range of ecological niches. Combined with the wide geographical distribution of palaeothentoids during the late middle Miocene, this suggests that the disappearance of these marsupials was preceded by an abrupt rather than gradual decline in taxonomic and ecological diversity as well as geographical range.</p> <p><a href="http://zoobank.org/urn:lsid:zoobank.org:pub:DA7E10BA-7203-4F5A-A3AB-F0E7352B101C" target="_blank">http://zoobank.org/urn:lsid:zoobank.org:pub:DA7E10BA-7203-4F5A-A3AB-F0E7352B101C</a></p

Eomakhaira molossus Engelman & Flynn & Wyss & Croft 2020, gen. et sp. nov.

&lt;i&gt;Eomakhaira molossus&lt;/i&gt;, gen. et sp. nov. Figures 3&ndash;4, 6&ndash;16; tables 1&ndash;2 &lt;p&gt;HOLOTYPE: SGOPV 3490, a partial rostrum of a senescent individual preserving the right maxilla with C-P3, alveoli and partial roots of M1&ndash;2, and part of M3; left maxilla with C-P3, anterior root of M1, and M3&ndash;4; left and right horizontal rami of the mandible, including both lower canines and most of the postcanine dentition, as well as parts of the coronoid processes; the entire left and parts of the right nasal; parts of the palatine; and the orbital process of the left lacrimal.&lt;/p&gt; &lt;p&gt; DIAGNOSIS: A member of Borhyaenoidea based on its short, robust rostrum, presence of lingual median canine sulci, extremely small protocone, small and unicuspid talonid on m4. Differs from all other borhyaenoid sparassodonts in the following combination of features: small size (smaller than most other borhyaenoids; length of m1&ndash;4 = 37.3 mm, comparable to &lt;i&gt;Fredszalaya hunteri&lt;/i&gt; or the extant dasyuromorphian &lt;i&gt;Sarcophilus harrisii&lt;/i&gt;); maxilla very deep and maxillary &ldquo;cheeks&rdquo; absent; mandibular symphysis unfused and anteroposteriorly narrow; two mental foramina present; length/width ratio of palate&gt;1.5; palate extending to level of M4; presence of postpalatine tori (shared only with &lt;i&gt;Arminiheringia&lt;/i&gt; and possibly &lt;i&gt;Callistoe&lt;/i&gt; among borhyaenoids); absence of postpalatine torus foramen; sphenorbital foramen opening dorsal to M4; large canines; absence of longitudinal striations on the canine roots (shared only with other thylacosmilines and possibly &lt;i&gt;Lycopsis viverensis&lt;/i&gt;); median keel on the labial face of upper canines; medial sulcus on lingual face of upper and lower canines; short lower canine roots; presence of three premolars with no diastemata between them; premolars large and robust but not globular; asymmetric protoconid of P1 (shared only with &lt;i&gt;Arminiheringia&lt;/i&gt; and &lt;i&gt;Callistoe&lt;/i&gt;); P3 significantly longer than p3 (possibly autapomorphic for this taxon); bulbous roots only on p3; preparacingulum absent; M3 with narrow stylar shelf and prominent ectoflexus; M4 extremely narrow anteroposteriorly (only comparable to &lt;i&gt;Patagosmilus&lt;/i&gt; among borhyaenoids), subequal or greater in width to M3, and with three roots; protocone vestigial (at least on M4); absence of an anteriorly projecting ventral keel of paraconid (which only occurs in proborhyaenids among sparassodonts); protoconid of m4 posteriorly salient; metaconid absent on m4 and probably m2&ndash;3; posterolabial cingulid present; talonid of m4 almost absent; and p1&ndash;3 short relative to m1&ndash;4 (shared with &lt;i&gt;Paraborhyaena&lt;/i&gt; among borhyaenoids with three premolars). Canines more mediolaterally compressed than in borhyaenoids other than &lt;i&gt;Patagosmilus&lt;/i&gt;, &lt;i&gt;Thylacosmilus&lt;/i&gt;, and possibly &lt;i&gt;Proborhyaena&lt;/i&gt;. P/p3 labiolingually narrower than in &lt;i&gt;Fredszalaya&lt;/i&gt;, &lt;i&gt;Plesiofelis&lt;/i&gt;, &lt;i&gt;Acrocyon&lt;/i&gt;, &lt;i&gt;Arctodictis&lt;/i&gt;, &lt;i&gt;Australohyaena&lt;/i&gt;, &lt;i&gt;Borhyaena&lt;/i&gt;, and &lt;i&gt;Callistoe,&lt;/i&gt; but wider than in &lt;i&gt;Prothylacynus&lt;/i&gt; and some individuals of &lt;i&gt;Pharsophorus&lt;/i&gt;, comparable in relative proportions to &lt;i&gt;Arminiheringia&lt;/i&gt;, &lt;i&gt;Paraborhyaena&lt;/i&gt;, and &lt;i&gt;Proborhyaena&lt;/i&gt;.&lt;/p&gt; &lt;p&gt;TYPE LOCALITY: Cachapoal locality, west side of Estero Los Llanos of the upper R&iacute;o Cachapoal drainage, Libertador General Bernardo O&rsquo;Higgins Region, central Chile (fig. 2).&lt;/p&gt; &lt;p&gt;STRATIGRAPHIC OCCURRENCE: Abanico Formation. Most specimens from Estero Los Llanos were recovered from talus cones at the SE nose of a roughly N-S running ridge of ~ 1,500 m relief. This ridge roughly parallels the strike of the steeply west-dipping beds. The thickness of the Abanico Formation in the Cachapoal region has not been measured in detail but is on the order of 2000&ndash;4000 m. Within this thick succession, the exact horizon that produced SGOPV 3490 is not known, as the specimen was collected from talus. For additional geological context of the Cachpaoal locality see Flynn and Wyss (2004), Hitz et al. (2006), and West et al. (2014).&lt;/p&gt; &lt;p&gt; AGE: Probably early Oligocene,?Tinguirirican SALMA. Fossils from the Cachapoal locality are likely at least 29.3 &plusmn; 0.1 million years old (at least in part), based on an unpublished date for a volcanic tuff that is thought to either correlate with or overlie the fossil-producing horizons at Los Llanos (Charrier et al., 1997; Flynn and Wyss, 2004). It must be cautioned, however, that this date is from ~ 5 km to the south, in the neighboring Las Le&ntilde;as drainage, and that the units involved have not been traced directly between the two locations due to precipitous intervening topography. The only radioisotopic date for the Cachapoal Valley itself is an 40 Ar/ 39 Ar date of 11.1 &plusmn; 1.8 Ma reported by West (2017) from levels far above the fossil-producing strata, which does little to precisely constrain the age of the fossils. The presence of the polydolopid &lt;i&gt;Kramadolops&lt;/i&gt; (&lt;i&gt;Polydolops&lt;/i&gt; in Flynn and Wyss, 2004) and the archaeohyracid &lt;i&gt;Archaeotypotherium&lt;/i&gt; (Croft et al., 2008a) suggest a pre-Deseadan age, and the presence of the interathere &lt;i&gt;Johnbell hatcheri&lt;/i&gt;, otherwise known only from the Tinguirirican type locality (Hitz et al., 2006), suggests that fossils from the Cachapoal locality are probably similar in age to those of the Tinguiririca Fauna (~33&ndash;32 Ma; Flynn et al., 2003).&lt;/p&gt; &lt;p&gt; ETYMOLOGY: The name of the genus derives from the Greek root &lt;i&gt;Eo&lt;/i&gt; s, meaning &ldquo;dawn,&rdquo; and &lt;i&gt;makhaira&lt;/i&gt;, a type of short sword or large knife (often translated as &ldquo;carving knife&rdquo;), in reference to the bladelike canines of thylacosmilines. The specific epithet comes from the Greek &lt;i&gt;molossus&lt;/i&gt;, a term used to refer to short-snouted, robust-skulled dog breeds such as mastiffs and bulldogs and refers to the short, robust snout of this species. Gender is masculine.&lt;/p&gt;Published as part of &lt;i&gt;Engelman, Russell K., Flynn, John J., Wyss, André R. &amp; Croft, Darin A., 2020, Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (? Tinguirirican) Cachapoal Locality, Andean Main Range, Chile, pp. 1-76 in American Museum Novitates 2020 (3957)&lt;/i&gt; on pages 8-10, DOI: 10.1206/3957.1, &lt;a href="http://zenodo.org/record/5370642"&gt;http://zenodo.org/record/5370642&lt;/a&gt

Eomakhaira molossus, a new saber-toothed sparassodont (Metatheria: Thylacosmilinae) from the early Oligocene (?Tinguirirican) Cachapoal locality, Andean Main Range, Chile. (American Museum novitates, no. 3957)

75 pages : illustrations (chiefly color), maps ; 26 cm.Thylacosmiline sparassodonts (previously recognized as thylacosmilids) are among the most iconic groups of endemic South American Cenozoic mammals due to their distinctive morphology and convergent resemblance to saber-toothed placental carnivores. However, the early evolution of this group and its relationship to other sparassodonts remains poorly understood, primarily because only highly specialized Neogene taxa such as Thylacosmilus, Anachlysictis, and Patagosmilus are well known. Here, we describe a new Paleogene sparassodont, Eomakhaira molossus, from the Cachapoal locality of central Chile, the first sparassodont reported from early Oligocene strata of the Abanico Formation. Eomakhaira shares features with both Neogene thylacosmilines and Paleogene “proborhyaenids,” and phylogenetic analyses recover this taxon as sister to the clade of Patagosmilus + Thylacosmilus. This broader clade, in turn, is nested within the group conventionally termed Proborhyaenidae. Our analyses support prior hypotheses of a close relationship between thylacosmilines and traditionally recognized proborhyaenids and provide the strongest evidence to date that thylacosmilines are proborhyaenids (i.e, the latter name as conventionally used refers to a paraphyletic group). To reflect the internestedness of these taxa, we propose use of Riggs’ (1933) original name Thylacosmilinae for the less inclusive grouping and Proborhyaenidae for the more inclusive one. Saber teeth arose just once among metatherians (among thylacosmilines), perhaps reflecting a developmental constraint related to nonreplacement of canines in metatherians; hypselodonty may have relaxed this potential constraint in thylacosmilines. The occurrence of Eomakhaira in strata of early Oligocene age from the Chilean Andes demonstrates that the stratigraphic range of thylacosmilines spanned almost 30 million years, far surpassing those of saber-toothed placental lineages

Figure S1 and Tables S1-12 from Diversity and disparity of sparassodonts (metatheria) reveal non-analogue nature of ancient South American mammalian carnivore guilds

This study investigates whether terrestrial mammalian carnivore guilds of ancient South America, which developed in relative isolation, were similar to those of other continents. We do so through analyses of clade diversification, ecomorphology and guild structure in the Sparassodonta, metatherians that were the predominant mammalian carnivores of pre-Pleistocene South America. Body mass and 16 characters of the dentition are used to quantify morphological diversity (disparity) in sparassodonts and to compare them to extant marsupial and placental carnivores and extinct North American carnivoramorphans. We also compare trophic diversity of the Early Miocene terrestrial carnivore guild of Santa Cruz, Argentina to that of 14 modern and fossil guilds from other continents. We find that sparassodonts had comparatively low ecomorphological disparity throughout their history and that South American carnivore palaeoguilds, as represented by that of Santa Cruz, Argentina, were unlike modern or fossil carnivore guilds of other continents in their lack of mesocarnivores and hypocarnivores. Our results add to a growing body of evidence highlighting non-analogue aspects of extinct South American mammals and illustrate the dramatic effects that historical contingency can have on the evolution of mammalian palaeocommunities

New mammal faunal data from Cerdas, Bolivia, a middle-latitude Neotropical site that chronicles the end of the Middle Miocene Climatic Optimum in South America

We provide new and revised identifications of mammals from the early middle Miocene (Langhian age, Colloncuran South American Land Mammal Age [SALMA]) of Cerdas, Bolivia. We also formally name a new typothere notoungulate, Hegetotherium cerdasensis, sp. nov., that can be distinguished by the absence of an external talonid sulcus on m3 and its small size (15–25% smaller than Hegetotherium mirabile). We refer several typothere specimens from Nazareno, Bolivia, to H. cerdasensis, which suggests that the two sites are of similar age. We report the first sparassodont and astrapothere remains from Cerdas. Sparassodont remains include an associated basicranium and mostly complete mandible; the species appears to represent a new, small-bodied borhyaenoid. Astrapothere remains consist of many tooth fragments from a new species of the subfamily Uruguaytheriinae. A partial sloth dentary from Cerdas likely pertains to the subfamily Megatheriinae and is the first report of the family Megatheriidae from the site. A newly discovered peltephilid armadillo specimen includes a partial articulated carapace that supports recognition of the Cerdas taxon as a new species. The two dasypodids of Cerdas (one Euphractini, one Eutatini) represent two new species closely related to undescribed species from the late middle Miocene (Serravallian age, Laventan SALMA) of Quebrada Honda, Bolivia. The mammals of Cerdas indicate that (1) the middle latitudes (southern tropics) contributed significantly to the diversity of Miocene mammal communities in South America; and (2) the Middle Miocene Climatic Optimum was a key factor in the differentiation of South American mammal assemblages. Citation for this article: Croft, D. A., A. A. Carlini, M. R. Ciancio, D. Brandoni, N. E. Drew, R. K. Engelman, and F. Anaya. 2016. New mammal faunal data from Cerdas, Bolivia, a middle-latitude Neotropical site that chronicles the end of the Middle Miocene Climatic Optimum in South America. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1163574.Fil: Croft, Darin A.. Case Western Reserve University; Estados UnidosFil: Carlini, Alfredo Armando. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ciancio, Martin Ricardo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Brandoni, Diego. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Drew, Nicholas E.. Case Western Reserve University; Estados UnidosFil: Engelman, Russell K.. Case Western Reserve University; Estados UnidosFil: Anaya, Federico. Universidad Autónoma Tomás Frías; Bolivi

Chlorocyon phantasma, a late Eocene borhyaenoid (Mammalia, Metatheria, Sparassodonta) from the Los Helados locality, Andean Main Range, central Chile. (American Museum novitates, 0003-0082 ; no. 3918)

22 pages : illustrations (some color), map ; 26 cm.Sparassodont metatherians were the dominant terrestrial mammalian predators during South America's long Cenozoic isolation. This group's early fossil record is very poor, however, particularly for the late Eocene and early Oligocene. Here, we describe a new sparassodont, Chlorocyon phantasma, gen. et sp. nov., based on a specimen from Los Helados, a new locality within the Abanico Formation of the Andean Main Range of central Chile. New ⁴⁰Ar/³⁹Ar dates at Los Helados bracketing the fossil-bearing level constrain the age of this specimen to 37-36 Ma (late Eocene), indicating that this new taxon likely pertains to the Mustersan South American Land Mammal "Age." Chlorocyon is the first Paleogene sparassodont reported from Chile and the first sparassodont described from the Abanico Formation. Distinctive features, including a p3 with an anterior edge that is more curved than the posterior edge and the lack of a hypoconulid on m4, suggest that Chlorocyon is a borhyaenoid closely related to Pharsophorus or Plesiofelis, although much smaller. Chlorocyon represents a welcome addition to the sparse record of late Eocene sparassodonts and indicates that the diversity of non-proborhyaenid borhyaenoids prior to the late Oligocene was greater than previously thought

Chlorocyon phantasma, a late Eocene borhyaenoid (Mammalia, Metatheria, Sparassodonta) from the Los Helados locality, Andean Main Range, central Chile /

no. 391

Structure, Growth and Histology of Gnathal Elements in <i>Dunkleosteus</i> (Arthrodira, Placodermi), with a Description of a New Species from the Famennian (Upper Devonian) of the Tver Region (North-Western Russia)

A new species of Dunkleosteus, D. tuderensis sp. nov., is named based on an infragnathal from the Famennian of the Tver Region, Russia. CT scanning of the holotype revealed two high-density bony constituents comparable in position and interrelations to components described for coccosteomorph arthrodires, supported by the presence of at least two clusters of large vascular canals marking separate arterial supplies. Coccosteomorph and dunkleosteid pachyosteomorphs exhibit similar growth patterns including labio-basal depositions of vascularized bone in the infragnathals and basally in the supragnathals. In contrast to coccosteomorphs, dunkleosteid reinforcement of the occlusal margins occurred via the formation of dense osteonal bone, in parallel with resorption forming extensive lingual fossae. Active bone remodeling proceeded without a complete reworking of the primary osteonal bone structure and the original arrangement of vascular canals. Due to inconsistent anatomical terminology in gnathal elements of dunkleosteid arthrodires, a revised terminology is suggested and new terms are introduced