“…The differentiation of the Bolivia group from all other Astronotus is potentially explained by the presence of the series of rapids on the Madeira River. These series of rapids are thought to delimit the geographic distributions of such diverse taxa as Inia geoffrensis and I. boliviensis [48, 49], Cichla monoculus and C. pleiozona [50], or they act as barriers, restricting gene flow in Colossoma macropomum [13] and Podocnemis expansa [51]. The physiochemical composition of the Negro River has also been suggested to act as a barrier between and within species [16, 17, 52, 53].…”
The neotropical cichlid genus Astronotus currently comprises two valid species: A. ocellatus Agassiz, 1831 and A. crassipinnis Heckel, 1840. The diagnosis is based on color pattern and meristics counts. However, body color pattern is highly variable between regions and the meristic counts show a considerable overlap between populations differing in color patterning. They do not represent true synapomorphies that diagnose species. Purportedly the only truly diagnostic character is the presence or absence of one or more ocelli at the base of the dorsal fin, diagnosing A. ocellatus and A. crassipinnis, respectively. Using the 5′ portion of the mitochondrial COI gene and EPIC nuclear markers, the validity of the dorsal ocelli as diagnostic character was tested in individuals sampled from ten localities in the Amazon basin. Analyses rejected the hypothesis that dorsal ocelli are diagnostic at the species level. However, they revealed the existence of five hypothetical, largely allopatrically distributed morphologically cryptic species. The phylogeographic structure is not necessarily surprising, since species of the genus Astronotus have sedentary and territorial habits with low dispersal potential. The distribution of these hypothetical species is coincident with patterns observed in other Amazonian aquatic fauna, suggesting the role of common historical processes in generating current biodiversity patterns.
“…The differentiation of the Bolivia group from all other Astronotus is potentially explained by the presence of the series of rapids on the Madeira River. These series of rapids are thought to delimit the geographic distributions of such diverse taxa as Inia geoffrensis and I. boliviensis [48, 49], Cichla monoculus and C. pleiozona [50], or they act as barriers, restricting gene flow in Colossoma macropomum [13] and Podocnemis expansa [51]. The physiochemical composition of the Negro River has also been suggested to act as a barrier between and within species [16, 17, 52, 53].…”
The neotropical cichlid genus Astronotus currently comprises two valid species: A. ocellatus Agassiz, 1831 and A. crassipinnis Heckel, 1840. The diagnosis is based on color pattern and meristics counts. However, body color pattern is highly variable between regions and the meristic counts show a considerable overlap between populations differing in color patterning. They do not represent true synapomorphies that diagnose species. Purportedly the only truly diagnostic character is the presence or absence of one or more ocelli at the base of the dorsal fin, diagnosing A. ocellatus and A. crassipinnis, respectively. Using the 5′ portion of the mitochondrial COI gene and EPIC nuclear markers, the validity of the dorsal ocelli as diagnostic character was tested in individuals sampled from ten localities in the Amazon basin. Analyses rejected the hypothesis that dorsal ocelli are diagnostic at the species level. However, they revealed the existence of five hypothetical, largely allopatrically distributed morphologically cryptic species. The phylogeographic structure is not necessarily surprising, since species of the genus Astronotus have sedentary and territorial habits with low dispersal potential. The distribution of these hypothetical species is coincident with patterns observed in other Amazonian aquatic fauna, suggesting the role of common historical processes in generating current biodiversity patterns.
“…The virtual cranial endocast of Prospaniomys was compared with natural and virtual caviomorph endocasts from the literature (Pilleri et al, 1984; Dozo, 1997a, b; Dozo et al, 2004; Madozzo-Jaén, 2019; Ferreira et al, 2020, 2021; Fig. 5).…”
Section: Methodsmentioning
confidence: 99%
“…All graphs were obtained using the free software PAST v4.10 (Hammer et al, 2001). Figure 6.Boxplots showing the following comparisons: ( 1 ) olfactory bulbs volume with respect to total endocast volumes of Prospaniomys , the fossil cavioid Neoreomys , extant caviomorphs, and noncaviomorph rodents; ( 2 ) neocortical surface with respect to total endocast surfaces of Prospaniomys , extant caviomorphs, and Paleogene noncaviomorph rodents; ( 3 ) paraflocculi volume with respect to total volumes of endocasts of Prospaniomys and Paleogene noncaviomorph rodents.Figure 7.Regression plots of ( 1 ) log 10 (olfactory bulbs volume, in mm 3 ) versus log 10 (endocranial volume, in mm 3 ); ( 2 ) log 10 (olfactory bulbs mass, in g) versus log 10 (body mass, in g); ( 3 ) log 10 (neocortical surface, in mm 2 ) versus log 10 (endocranial surface, in mm 2 ); ( 4 ) log 10 (paraflocculi volume, in mm 3 ) versus log 10 (endocranial volume, in mm 3 ); ( 5 ) log 10 (paraflocculi mass, in g) versus log 10 (body mass, in g).Figure 8.( 1–3 ) Encephalization quotients of Prospaniomys , the fossil cavioid Neoreomys , the fossil chinchilloid Neoepiblema , extant caviomorphs ( Phyllomys , Myocastor , Capromys , Cavia , Dolichotis , Dinomys , and Lagostomus ), and fossil noncaviomorph rodents ( Paramys , Ischyromys , Cedromus , Pseudotomus , and Rapamys ): ( 1 ) based on Jerison's (1973) equation; ( 2 ) based on Eisenberg's (1981) equation; ( 3 ) based on Pilleri et al's (1984) equation; ( 4 ) regression plot of log 10 (endocranial mass, in g) versus log 10 (body mass, in g). 1 = Prospaniomys priscus ; 2 = Phyllomys dasythrix Hensel, 1872; 3 and 4 = Myocastor coypus Kerr, 1792; 5 = Capromys pilorides (Say, 1822); 6 and 7 = Coendou spinosus Cuvier, 1823a; 8 = Erethizon dorsatum (Linnaeus, 1758); 9 = Neoreomys australis Ameghino, 1887; 10 = Dolicavia minuscula Ameghino, 1908; 11 = Cavia sp.…”
Section: Methodsmentioning
confidence: 99%
“…Paleoneurological information for rodents in general and caviomorphs in particular is scarce. The oldest and most representative works are those of Dechaseaux (1958) and Pilleri et al, (1984) who included brief descriptions of a few fossil rodents. Dozo (1997b) and Dozo et al, (2004) described natural endocasts of Cephalomyidae gen. indet.…”
Section: Introductionmentioning
confidence: 99%
“…The basal phylogenetic position of Prospaniomys within Pan-Octodontoidea (Fig. 1) sheds light on the earlier endocranial anatomy of the group, and allows anatomical comparisons with other extinct and living caviomorphs (Pilleri et al, 1984; Dozo, 1997a, b; Dozo et al, 2004; Madozzo-Jaén, 2019; Ferreira et al, 2020, 2021), as well as other fossil rodents (e.g., Dechaseaux, 1958; Pilleri et al, 1984; Bertrand and Silcox, 2016; Bertrand et al, 2016b, 2017, 2018, 2019). We also describe and mention different aspects of the cranial circulatory system and cranial foramina.…”
The study of the cranial endocast provides valuable information to understand the behavior of an organism because it coordinates sensory information and motor functions. In this work, we describe for the first time the anatomy of the encephalon of an early Miocene pan-octodontoid caviomorph rodent (Prospaniomys priscus Ameghino, 1902) found in the Argentinean Patagonia, based on a virtual 3D endocast. This fossil rodent has an endocast morphology here considered ancestral for Pan-Octodontoidea and other South American caviomorph lineages, i.e., an encephalon with anteroposteriorly aligned elements, mesencephalon dorsally exposed, well-developed vermis of the cerebellum, and rhombic cerebral hemispheres with well-developed temporal lobes. Prospaniomys Ameghino, 1902 also has relatively small olfactory bulbs, large paraflocculi of the cerebellum, and low endocranial volume and degree of neocorticalization. Its encephalization quotient is low compared with Paleogene North American and European noncaviomorph rodents, but slightly higher than in several late early and late Miocene caviomorphs. Paleoneurological anatomical information supports the hypothesis that Prospaniomys was a generalist caviomorph rodent with terrestrial habits and enhanced low-frequency auditory specializations. The scarce paleoneurological information indicates that several endocast characters in caviomorph rodents could change with ecological pressures. This work sheds light on the anatomy and evolution of several paleoneurological aspects of this particular group of South American rodents.
The brain of the La Plata dolphin, Pontoporia blainvillei, was studied with methods of quantitative morphology. The volumes and the progression indices of the main brain structures were determined and compared with corresponding data of other Cetacea, Insectivora and Primates. In Pontoporia, encephalization and neocorticalization are clearly greater than in primitive ("basal") Insectivora. The indices are in the lower part of the range for simian monkeys. The paleocortex is regressive in accordance with the total reduction of the olfactory bulb and olfactory tract. In contrast to the situation in primates, the septum, schizocortex and archicortex are not progressive in Pontoporia. The striatum and cerebellum are strongly progressive, corresponding to the efficiency and importance of the motor system in the three-dimensional habitat. The diencephalon, mesencephalon and medulla oblongata show considerable progression. Obviously, this is correlated with the extensive development of structures of the acoustic system. The superficial correspondence of the brains of dolphins and primates in relative size and in the degree of gyrencephaly is rather a rough morphological convergence than a sign of functional equivalence. It is coupled to a strongly divergent development of the various functional systems in the two mammalian orders according to their specific evolution.
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