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Hapalodectes leptognathus, dorsal view of left maxilla fragment, P.U.
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Phylogeny of 254 RHM N-terminals (the complete version of Figure 4A). More information about these proteins could be found in Table S4.
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... Описанный из Цаган-Хушу Hapalodectes dux Lopatin, 2001 основан только на голотипе -нижней челюсти с обоими рядами зубов [3,4]. H. dux был описан как древнейший представитель рода (фаунистический комплекс пачки жигден датируется поздним палеоценом -гашатием) [ Matthew, 1909; зоны Wa-4-Wa-7) [12][13][14][15][16]. ...
... nov. было достигнуто в том числе за счет переднего смещения вершины метаконида, которое уменьшило протокристидный угол (как и у H. leptognathus, см.[13,14]). Однако при этом новый вид сохранил некоторые примитивные для рода черты -относительно крупные дополнительные передние бугорки, наличие энтоконида и приблизительно одинаковую длину последнего и предпоследнего нижних моляров. По совокупности зубных признаковРис. ...
... paradux Lopatin, sp. nov., голотип ПИН, № 3104/775, фрагмент правой нижнечелюстной кости с M 2 -M 3 ; верхний палеоцен, свита наран-булак, пачка жигден.Таблица 1. Сравнение длины M 2 и М 3 (средние значения в скобках, в мм) у Hapalodectes (данные для ранее известных видов по [3,5,6,9,11,[14][15][16]) ...
Hapalodectes paradux sp. nov. (Hapalodectidae, Mesonychia) is described on the base of the dentary fragment with m2–m3 from the Tsagan-Khushu locality in Mongolia (Upper Paleocene, Naran Bulak Formation, Zhigden Member). The m2 and m3 are approximately the same size, with a high protoconid, anteriorly displaced reduced metaconid, anterolingually directed protocristid, very deep posterior notch, narrow talonid, and distinct hypoconid, entoconid and hypoconulid. Based on dental characters, the new species is presumably related to the base of the lineage of Hapalodectes that dispersed to North America at the beginning of the Eocene. Tsagan-Khushu is the only known locality where two species of Hapalodectes co-occur (larger H. dux Lopatin, 2001 and smaller H. paradux sp. nov.).
... The new species differs from the contemporaneous H. dux in smaller size (Fig. 3) and a number of features of the M 2 -M 3 (Fig. 4), including a reduced metaconid strongly shifted forward (with a ridge-like apex Table 1. Comparisons of the length of M 2 and M 3 (average values in parentheses, in mm) in Hapalodectes (the data on previously described species are given after [3,5,6,9,11,[14][15][16] H. paradux sp. nov. ...
... nov., suggests that the new species is close to this Hapalodectes lineage. This reduction was associated with a decrease in the width of the middle part of the Table 2. Comparisons of the structure of M 2 and M 3 in Hapalodectes (data on previously described species are given after [3,5,6,9,11,[14][15][16]; protocristid angle measured from images) lower molars (to enhance their shearing action) and occurred through the fusion of the metaconid base with the protoconid. The narrowing of the protoconid-metaconid region in H. paradux sp. ...
... nov. included the anterior displacement of the metaconid apex, decreasing the protocristid angle (also occurred in H. leptognathus, see [13,14] [6]. The scenario of the evolution of the genus in the Eocene includes the following assumptions. ...
Hapalodectes paradux sp. nov. (Hapalodectidae, Mesonychia) is described on the base of the dentary fragment with M2-M3 from the Tsagan-Khushu locality in Mongolia (Upper Paleocene, Naran Bulak Formation, Zhigden Member). The M2 and M3 are approximately the same size, with a high protoconid, anteriorly displaced reduced metaconid, anterolingually directed protocristid, very deep posterior notch, narrow talonid, and distinct hypoconid, entoconid and hypoconulid. Based on dental characters, the new species is presumably related to the base of the lineage of Hapalodectes that dispersed to North America at the beginning of the Eocene. Tsagan-Khushu is the only known locality where two species of Hapalodectes co-occur (larger H. dux Lopatin, 2001 and smaller H. paradux sp. nov.).
... An early Puercan age is also supported by the absence of the periptychid Ectoconus (Eberle et al. 2013), which defines the onset of middle Puercan (Pu2) time (Lofgren et al. 2004). Taylor (1984) and Szalay (1969). Dental measurements follow Archibald (1982). ...
An earliest Paleocene (Puercan) locality in the China Butte Member of the Fort Union Formation in the Great Divide Basin (GDB) of Wyoming contains a diverse mammalian faunal assemblage, including a number of ‘condylarth’ taxa. From UCM locality 2011035, we describe three new periptychid ‘condylarths’ and report first occurrences of Maiorana noctiluca, Ampliconus antoni and Conacodon harbourae from the GDB. The new genus and species Miniconus jeanninae is characterized by a ridge-like metaconid and incipient paraconid on p4, and a molar parastylid. Based on its similarity to M. jeanninae and differences from other species of Oxyacodon, O. archibaldi is placed within the new genus Miniconus. A second new genus and species Beornus honeyi is characterized by its large size with inflated premolars and molars, and small molar paraconid. A new species of Conacodon, C. hettingeri, is similar to other species of Conacodon but differs in its m3 morphology. To examine the relationships of the three new GDB taxa to each other and to other Puercan ‘condylarths’ from the Western Interior of North America, a phylogenetic analysis was performed using 28 Puercan periptychid and arctocyonid taxa as well as the eutherian outgroup taxon Procerberus formicarum and 64 dental characters. The resulting strict consensus tree of 210 steps confirms that the three new species from the GDB fall within Periptychidae. Beornus honeyi forms a polytomy with Mithrandir gillianus and Hemithlaeus kowalevskianus. Conacodon hettingeri is recovered as the basal member of a clade that includes the other species of Conacodon. Miniconus jeanninae is the sister to M. archibaldi. Additionally, the early Puercan Mimatuta spp. and Maiorana noctiluca fall within the Arctocyonidae, supporting the phylogenetic placement of these taxa by other recent analyses. The occurrence of the three new periptychids in the GDB indicates that mammalian diversity is higher than previously suggested for the early Puercan.
http://zoobank.org/urn:lsid:zoobank.org.pub:4F31F461-814D-4C4A-99A9-3D7ED5D6701C
... O'Leary and Rose (1995) also suggested the presence of sexual dimorphism in D. navajovius and D. willwoodensis, but they were not definitive on this topic due to an insufficient sample size. Szalay (1969c) additionally suggested that sexual dimorphism is present in the hapalodectid Hapalodectes leptognathus. Szalay (1969c) considered mandibular depth and differences in the relative compression of the molars as the primary markers of sexual dimorphism among mesonychians; however, he noted that these differences could be explained simply by intraspecific variability. ...
... Szalay (1969c) additionally suggested that sexual dimorphism is present in the hapalodectid Hapalodectes leptognathus. Szalay (1969c) considered mandibular depth and differences in the relative compression of the molars as the primary markers of sexual dimorphism among mesonychians; however, he noted that these differences could be explained simply by intraspecific variability. O'Leary et al. (2000) argued that differences in the depth of the mandible and size of the canines are the primary markers of sexual dimorphism among mesonychids (as for many carnivorous mammals). ...
The Mesonychia is a group of archaic carnivorous mammals of uncertain phylogenetic affinities with a Holarctic distribution during the Paleogene. Intensive fossil collecting efforts in the Bighorn Basin, Wyoming, have resulted in recovery of the largest sample and most complete specimens yet known of the mesonychid Dissacus praenuntius from the second biozone of the Wasatchian North American Land Mammal Age (Wa-0). The Wa-0 biozone corresponds to the body of the Paleocene-Eocene Thermal Maximum (PETM), a brief but intense global warming event that occurred ∼56 myr ago that significantly impacted terrestrial mammal faunas, including dwarfing in many mammal lineages. To evaluate the potential response of this lineage to climate change, we compared the PETM sample of D. praenuntius with those recovered from just before the PETM in the last biozone of the Clarkforkian North American Land Mammal Age (Cf-3) and just after the PETM in the Wa-1 biozone. While the sample size is still too small to say with certainty, tooth size (as a proxy for body weight) of D. praenuntius appears to be smaller during the late PETM than during either the pre-PETM Cf-3, or post-PETM Wa-1 biozones, suggesting the possibility of a muted dwarfing response to the PETM. However, the pattern observed for D. praenuntius differs from that of many other PETM mammals, as the shift to smaller body size is less pronounced and may have only occurred in late Wa-0.
... Paleontologists had long believed that mesonychians were the direct ancestors of Cetacea (i.e., whales; Van Valen 1966;Szalay 1969a;Gingerich et al. 1983;Thewissen et al. 1994), but recently discovered fossils (e.g., well-preserved hind limbs) have led paleontologists to root cetaceans within Artiodactyla (Gingerich et al. 2001;Gingerich 2003a;Thewissen et al. 2001Thewissen et al. , 2007Spaulding et al. 2009). ...
... The systematics and evolution of the mesonychians have been much enhanced by the works of F.S. Szalay in the 1960's (Szalay and Gould 1966;Szalay 1969aSzalay , 1969b. Mesonychids have been included in phylogenetic analyses dealing with relationships among mammals (e.g., Thewissen 1994;O'Leary 1998;Geisler 2001;Williamson and Carr 2007;Spaulding et al. 2009). ...
... The differences in depth of the mandibles and size of the canines have been considered as indications of sexual dimorphism for the mesonychid Ankalagon saurognathus (O'Leary et al. 2000). Szalay (1969a) also considered the existence of a sexual dimorphism in North American Hapalodectes leptognathus based on differences in mandible depth and in the relative compression of the molars. However, he also noted that these differences could be explained simply by intraspecific variability. ...
Here we review the fossil record of European mesonychids, which are known only through the genera Dissacus and Pachyaena from Thanetian and Ypresian localities (from MP6 to MP10 reference-levels). We describe two new species, Dissacus rougierae, sp. nov., and Dissacus raslanloubatieri, sp. nov., respectively from Palette (Ypresian, ≈MP7) and from La Borie (Ypresian, ≈MP8 + 9). We also describe new specimens of D. europaeus from Berru (Thanetian, ≈MP6). The evolution of the geographic distribution of the European mesonychids is characterized by three phases: (1) the mesonychid Dissacus appeared in Europe during the Thanetian (≈ 57–58 Mya), probably due to dispersal from North America; D. europaeus survived the PETM event (≈ 56 Mya) and possibly experienced a dwarfism; (2) the large mesonychid Pachyaena migrated into Europe shortly after the Paleocene-Eocene boundary (≈ 55 Mya), but it was restricted to northwestern Europe, while Dissacus is recorded at this time only in southwestern Europe (Palette); and (3) Pachyaena rapidly disappeared from European environments, while Dissacus subsequently dispersed into northwestern Europe (≈ 54–52 Mya). We performed phylogenetic analyses in order to identify the relationships of the new species among mesonychids. It seems that the mesonychids went through two radiative events: the first during the Paleocene, the second mostly during the early Eocene. The first one corresponds to the diversification of Dissacus, while the latter resulted in the appearance of the most specialized mesonychids, such as Pachyaena and Mesonyx.
... The present lower teeth (Figure 2) also show a typical morphology of the lower molariform teeth of the Mesonychidae in that the talonid is buccolingually compressed with only a single and mesiodistally oriented crest (cristid obliqua), and in that the cristid obliqua connects to the postprotocristid with a carnassial notch between them (Szalay and Gould, 1966;Geisler and McKenna, 2007). The present materials are distinguished from the cheek teeth of the Hapalodectidae in being distinctly larger, in having less transversely constructed lower teeth, and in lacking a hypocone (Szalay, 1969). morphological evidence. ...
... Species of Hapalodectes are small mesonychian mammals that range in age from late Paleo鄄 cene to middle Eocene ( Szalay, 1969a;Lopatin, 2001) . Like all mesonychians, Hapalodectes is distinctive in having buccolingually compressed lower cheek teeth with talonids that are sim鄄 plified to include little more than the cristid obliqua and the hypoconid ( Szalay, 1969b) . ...
... Such a basal phylogenetic position for Hapalodecti鄄 dae within Mesonychia implies that the group diverged from Mesonychidae no later than the ear鄄 ly Paleocene, well before its first appearance in the fossil record. Szalay (1969a) anticipated such an early divergence date for Hapalodectidae decades before Paleocene records of the group were actually discovered. ...
... The documented geographic range of Hapalodectidae includes China and Mongolia in east鄄 ern Asia ( Matthew and Granger, 1925;Li and Ting, 1987;Lopatin, 2001;Tong and Wang, 2006) and Wyoming and Colorado in western North America ( Matthew, 1909( Matthew, , 1915Gazin, 1962;Szalay, 1969a;Zhou and Gingerich, 1991; O爷Leary and Rose, 1995; Gunnell and Gin鄄 gerich, 1996;O爷Leary, 1998 ) . Hapalodectid mesonychians have never been reported from Europe. ...
A new species of the mesonychian mammal genus Hapalodectes is described from the Gashatan (late Paleocene) site of Subeng in Nei Mongol (Inner Mongolia). This is the first Paleocene record of Hapalodectes from China, and the second Gashatan species of Hapalodectes to be recorded from Asia. Available phylogenetic and biostratigraphic evidence supports an Asian origin for Hapalodectes (and Hapalodectidae). Hapalodectes apparently dispersed across Beringia coincident with PETM warming to colonize North America, thereby conforming to the “East of Eden” biogeographic pattern. Reconstructing the historical biogeography of Hapalodectes is facilitated by its restricted (i.e., non-European) geographic distribution. “East of Eden” dispersal such as that shown by Hapalodectes qualifies as an excellent example of geo-dispersal, whereby a major perturbation of the physical environment allows multiple clades to exhibit similar biogeographic and phylogenetic patterns. Purported examples of intercontinental mammalian dispersal at or near the Paleocene−Eocene boundary that conflict with the “East of Eden” pattern are critically examined and found to be wanting. The “East of Eden” biogeographic pattern adequately explains mammalian faunal turnover and Laurasian mammalian biogeography during the PETM.
... Species of Hapalodectes are small mesonychian mammals that range in age from late Paleo鄄 cene to middle Eocene ( Szalay, 1969a; Lopatin, 2001) . Like all mesonychians, Hapalodectes is distinctive in having buccolingually compressed lower cheek teeth with talonids that are sim鄄 plified to include little more than the cristid obliqua and the hypoconid ( Szalay, 1969b) . ...
... Szalay (1969a) anticipated such an early divergence date for Hapalodectidae decades before Paleocene records of the group were actually discovered. The documented geographic range of Hapalodectidae includes China and Mongolia in east鄄 ern Asia ( Matthew and Granger, 1925; Li and Ting, 1987; Lopatin, 2001; Tong and Wang, 2006) and Wyoming and Colorado in western North America ( Matthew, 1909 Matthew, , 1915 Gazin, 1962; Szalay, 1969a; Zhou and Gingerich, 1991; O爷Leary and Rose, 1995; Gunnell and Gin鄄 gerich, 1996; O爷Leary, 1998 ) . Hapalodectid mesonychians have never been reported from Europe. ...
... H. anthracinus and H. paleocenus are similar in size, but H. serus is significantly larger. The type species of Hapalodectes, H. leptognathus from the Wasatchian of Wyoming and Colorado, remains relatively poorly known (Szalay, 1969a; O爷Leary, 1998). H. leptognathus is substantially larger than H. paleocenus, but both species retain weakly developed metaconids on their lower molars. ...
... Within the last decade, the unanimous opinion among paleontologists was that the ancestors of cetaceans were Mesonychia, an extinct group of hoofed mammals (ungulates) living in the Northern Hemisphere during the Paleocene-Early Oligocene [about 60-30 million years ago (Ma)] (Van Valen 1966;Szalay 1969;Gatesy and O'Leary 2001) (Fig. 2.2). Cetaceanmesonychian affinities have been deduced principally from details of dentition and the ear region. ...
... The first cetaceans, the archaeocetes, originated in the early to middle Eocene, 52-42 Ma. For some 30 years (Van Valen 1968;Szalay 1969) interpretations of the fossil record held that cetaceans originated from a now extinct group of small terrestrial (presumably furred) ungulates (hoofed mammals), the mesonychian condylarths, which lived some 65 Ma. Evidence used was skull morphology, patterns of dentition, and vestigial hindlimbs of the early archaeocetes whose limb morphology bears a striking resemblance to mesonychians and to extant artiodactyls. ...
We address the developmental and evolutionary mechanisms underlying fore- and hindlimb development and progressive hindlimb reduction and skeletal loss in whales and evaluate whether the genetic, developmental, and evolutionary mechanisms thought to be responsible for limb loss in snakes "explain" loss of the hindlimbs in whales. Limb loss and concurrent morphological and physiological changes associated with the transition from land to water are discussed within the context of the current whale phylogeny. Emphasis is placed on fore- and hindlimb development, how the forelimbs transformed into flippers, and how the hindlimbs regressed, leaving either no elements or vestigial skeletal elements. Hindlimbs likely began to regress only after the ancestors of whales entered the aquatic environment: Hindlimb function was co-opted by the undulatory vertical axial locomotion made possible by the newly evolved caudal flukes. Loss of the hindlimbs was associated with elongation of the body during the transition from land to water. Limblessness in most snakes is also associated with adoption of a new (burrowing) lifestyle and was driven by developmental changes associated with elongation of the body. Parallels between adaptation to burrowing or to the aquatic environment reflect structural and functional changes associated with the switch to axial locomotion. Because they are more fully studied and to determine whether hindlimb loss in lineages that are not closely related could result from similar genetically controlled developmental pathways, we discuss developmental (cellular and genetic) processes that may have driven limb loss in snakes and leg-less lizards and compare these processes to the loss of hindlimbs in whales. In neither group does ontogenetic or phylogenetic limb reduction result from failure to initiate limb development. In both groups limb loss results from arrested development at the limb bud stage, as a result of inability to maintain necessary inductive tissue interactions and enhanced cell death over that seen in limbed tetrapods. An evolutionary change in Hox gene expression--as occurs in snakes--or in Hox gene regulation--as occurs in some limbless mutants--is unlikely to have initiated loss of the hindlimbs in cetaceans. Selective pressures acting on a wide range of developmental processes and adult traits other than the limbs are likely to have driven the loss of hindlimbs in whales.
