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Mesomyzon mengae gen. et sp. nov.a, A complete fish (IVPP V14718A) in left view. b, Holotype (IVPP V14719) in right view. c, Drawing of the holotype, with the dorsal fin and caudal region reconstructed on the basis of IVPP V14718A. d, Photograph of head and anterior part of body of the holotype. e, Drawing of the same part as in d. Scale bars, 10 mm (a–c) and 5 mm (d, e). Abbreviations: a., anus; br.b., branchial basket; c.f., caudal fin; d.f., dorsal fin; d.t.?, possible digestive tract; g., gonads; g.a., gill arches; g.f., gill filaments; l., liver; l.e., left eye; l.ot., left otic capsule; ms., myosepta; nc., notochord; or.d., oral disk; p.c.?, possible piston cartilage; pc.c., pericardial cartilage; r.e., right eye; r.ot., right otic capsule.
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Widespread nowadays in freshwater and coastal seas of the cold and temporal zones, lampreys are a jawless vertebrate group that has been in existence for more than 300 million years but left a meagre fossil record. Only two fossil lamprey species, namely Mayomyzon pieckoensis and Hardistiella montanensis, have been recognized with certainty from No...
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... two specimens of the new lamprey Mesomyzon are nearly of the same size. The body is elongated and eel-shaped (Fig. 1a-c). The anterior portion of the body is rounded, whereas the tail is more compressed laterally and tapers posteriorly. The body length measured in the holotype of Mesomyzon V14719 (with the tail missing) is about 83.5 mm, whereas in V14718B (without the tip of the snout) it is 85 mm. Thus, the specimens of Mesomyzon are longer than those ...
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... complete one of the three known Hardistiella specimens ("which does not exceed 10 cm in total length" 5 ) from Montana, and much shorter than most recent lampreys 7,8 . Its ratio of body length to body depth is about 12 (on the basis of both V14718B and V14719). The corresponding ratio is 8 to 9 in Mayomyzon 1 , 10 in Hardistiella (inferred from Fig. 1A of ref. 2) and 12-20 in the recent lampreys from China 8 and elsewhere in the world 7 . Mesomyzon is thus obviously slenderer than the two Carboniferous lampreys and closer in body proportion to the living ones. In the holotype in which the head is well preserved, the ratio of body length to head length (measured from the tip of the ...
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... holotype lies, for the most part, on its flank but with its head and anterior portion of the body rotated (along its axis) slightly towards its left so that the right side of the head is turned somewhat upwards. As a result of the rotation, the right eye, as a round dark stain (l.e., Fig. 1d, e), is situated near the top line of the head, whereas the left eye, as a faint circle with rough interior (r.e., Fig. 1d, e), is situated under, and partly overlapped by, the right eye. A small circle in the middle of the bigger circle of the right eye may indicate the presence of the lens. The left and right otic capsules (l.ot. and ...
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... head and anterior portion of the body rotated (along its axis) slightly towards its left so that the right side of the head is turned somewhat upwards. As a result of the rotation, the right eye, as a round dark stain (l.e., Fig. 1d, e), is situated near the top line of the head, whereas the left eye, as a faint circle with rough interior (r.e., Fig. 1d, e), is situated under, and partly overlapped by, the right eye. A small circle in the middle of the bigger circle of the right eye may indicate the presence of the lens. The left and right otic capsules (l.ot. and r.ot., Fig. 1d, e) are just behind the eyes and displayed in the same way as the eyes. The nasohypophysial opening was not ...
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... 1d, e), is situated near the top line of the head, whereas the left eye, as a faint circle with rough interior (r.e., Fig. 1d, e), is situated under, and partly overlapped by, the right eye. A small circle in the middle of the bigger circle of the right eye may indicate the presence of the lens. The left and right otic capsules (l.ot. and r.ot., Fig. 1d, e) are just behind the eyes and displayed in the same way as the eyes. The nasohypophysial opening was not seen in either of the specimens because of the state of ...
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... parts or imprints of the endoskeleton of the cranium could be observed because it was neither calcified nor ossified. However, it is extremely fortunate that, on the holotype, a subterminal sucking oral disk (or.d., Fig. 1d, e) is clearly shown in the form of depressed rectangular areas divided by ridges, arranged in radiating rows around the oral opening. This is somewhat similar to the mouth structure of the enigmatic lamprey-like Pipiscius (see Figs 3-5 in ref. 9) from the Carboniferous period of Illinois 10,11 . We could count four or five such areas ...
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... usually cartilaginous visceral skeleton in the form of the branchial basket (br.b., Fig. 1d, e) shows its distinct general outline and structure in light-grey stain on the holotype. The branchial basket of lamprey has not previously been observed in fossils, although elongated branchial baskets with many branchial units have been seen in the Late Devonian anaspid-like form Euphanerops longaevus from Miguasha, Québec, Canada 5,10 ...
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... in light-grey stain on the holotype. The branchial basket of lamprey has not previously been observed in fossils, although elongated branchial baskets with many branchial units have been seen in the Late Devonian anaspid-like form Euphanerops longaevus from Miguasha, Québec, Canada 5,10 . Not only are the outlines of the seven gill pouches (g.p., Fig. 1d, e) clearly visible but the impressions of the gill filaments (g.f., Fig. 1d, e) can also be traced in many places posterior to the vertical bars (gill arches, g.a., Fig. 1d, e) of the branchial basket. The length of the branchial apparatus obviously exceeds that of the preorbital region, whereas the gill pouches in Mayomyzon and ...
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... previously been observed in fossils, although elongated branchial baskets with many branchial units have been seen in the Late Devonian anaspid-like form Euphanerops longaevus from Miguasha, Québec, Canada 5,10 . Not only are the outlines of the seven gill pouches (g.p., Fig. 1d, e) clearly visible but the impressions of the gill filaments (g.f., Fig. 1d, e) can also be traced in many places posterior to the vertical bars (gill arches, g.a., Fig. 1d, e) of the branchial basket. The length of the branchial apparatus obviously exceeds that of the preorbital region, whereas the gill pouches in Mayomyzon and Hardistiella are closely set and the branchial apparatus is hardly longer than the ...
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... have been seen in the Late Devonian anaspid-like form Euphanerops longaevus from Miguasha, Québec, Canada 5,10 . Not only are the outlines of the seven gill pouches (g.p., Fig. 1d, e) clearly visible but the impressions of the gill filaments (g.f., Fig. 1d, e) can also be traced in many places posterior to the vertical bars (gill arches, g.a., Fig. 1d, e) of the branchial basket. The length of the branchial apparatus obviously exceeds that of the preorbital region, whereas the gill pouches in Mayomyzon and Hardistiella are closely set and the branchial apparatus is hardly longer than the preorbital region 4,10 . The first gill pouch is situated posteroventral to the otic capsule, as in ...
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... nately, no distinct gill openings could be detected on the specimens, although we believe there should be seven separate ones because in other respects Mesomyzon is too similar to the extant lamprey. Posterior to the last gill pouch, faintly visible are the upper and lower parts of the anterior portion of the pericardial cartilage (pc.c., Fig. 1d, e). Two thin lines, stretching forwards from the anterior part of the branchial apparatus, seem to enclose a rod-like structure. Conceivably, it could be interpreted as the piston cartilage (p.c.?, Fig. 1d, e) that supports the rasping tongue. Behind the anterior part of the pericardial cartilage, the outline of the liver (l., Fig. 1d, e) ...
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... Posterior to the last gill pouch, faintly visible are the upper and lower parts of the anterior portion of the pericardial cartilage (pc.c., Fig. 1d, e). Two thin lines, stretching forwards from the anterior part of the branchial apparatus, seem to enclose a rod-like structure. Conceivably, it could be interpreted as the piston cartilage (p.c.?, Fig. 1d, e) that supports the rasping tongue. Behind the anterior part of the pericardial cartilage, the outline of the liver (l., Fig. 1d, e) can also be traced. As judged from the situation in recent lampreys, the liver might be longer than that in our illustration. The digestive tract (d.t.?, Fig. 1d, e) is probably represented by a thin ...
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... (pc.c., Fig. 1d, e). Two thin lines, stretching forwards from the anterior part of the branchial apparatus, seem to enclose a rod-like structure. Conceivably, it could be interpreted as the piston cartilage (p.c.?, Fig. 1d, e) that supports the rasping tongue. Behind the anterior part of the pericardial cartilage, the outline of the liver (l., Fig. 1d, e) can also be traced. As judged from the situation in recent lampreys, the liver might be longer than that in our illustration. The digestive tract (d.t.?, Fig. 1d, e) is probably represented by a thin dark band that extends backwards from the end of the branchial basket, along the upper border of the liver, to an area below the dorsal ...
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... be interpreted as the piston cartilage (p.c.?, Fig. 1d, e) that supports the rasping tongue. Behind the anterior part of the pericardial cartilage, the outline of the liver (l., Fig. 1d, e) can also be traced. As judged from the situation in recent lampreys, the liver might be longer than that in our illustration. The digestive tract (d.t.?, Fig. 1d, e) is probably represented by a thin dark band that extends backwards from the end of the branchial basket, along the upper border of the liver, to an area below the dorsal fin, where it bends down to the probable anus (a., Fig. 1c). However, the interpretation of the thin dark band as the dorsal aorta is not ruled ...
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... situation in recent lampreys, the liver might be longer than that in our illustration. The digestive tract (d.t.?, Fig. 1d, e) is probably represented by a thin dark band that extends backwards from the end of the branchial basket, along the upper border of the liver, to an area below the dorsal fin, where it bends down to the probable anus (a., Fig. 1c). However, the interpretation of the thin dark band as the dorsal aorta is not ruled ...
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... with coarse sediments, lined in a row and situated in the posterior half of the abdomen are eight or nine circular spaces, here interpreted as gonads (g., Fig. 1c), although they might alternatively be interpreted as gut. They are not arranged metamerically. Lamprey females have a single horseshoe-shaped ovary, whereas the testis of males consists of leaf-like lobes 7,13,14 . The appearance of the gonads in the new form seems similar to that in the latter. Numerous myosepta (ms., Fig. 1c) are ...
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... as gonads (g., Fig. 1c), although they might alternatively be interpreted as gut. They are not arranged metamerically. Lamprey females have a single horseshoe-shaped ovary, whereas the testis of males consists of leaf-like lobes 7,13,14 . The appearance of the gonads in the new form seems similar to that in the latter. Numerous myosepta (ms., Fig. 1c) are distinctly visible in the holotype. About 80 or more trunk myomeres can be counted. Under the dorsal margin of the body and parallel to the margin is the notochord (nc., Fig. 1c), a dark-stained thick band that stretches from the head region back to the end of the body. The traceability of the notochord in the fossils of many ...
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... the testis of males consists of leaf-like lobes 7,13,14 . The appearance of the gonads in the new form seems similar to that in the latter. Numerous myosepta (ms., Fig. 1c) are distinctly visible in the holotype. About 80 or more trunk myomeres can be counted. Under the dorsal margin of the body and parallel to the margin is the notochord (nc., Fig. 1c), a dark-stained thick band that stretches from the head region back to the end of the body. The traceability of the notochord in the fossils of many soft-bodied animals is certainly due to the more decay- resistant characteristic of its sheath 15 . The myoseptum that crosses (d, e). Abbreviations: a., anus; br.b., branchial basket; ...
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... left otic capsule; ms., myosepta; nc., notochord; or.d., oral disk; p.c.?, possible piston cartilage; pc.c., pericardial cartilage; r.e., right eye; r.ot., right otic capsule. the notochord in each segment made it difficult to observe the shape of arcualia, if any is preserved there. Paired fins and anal fin are absent. The dorsal fin (d.f., Fig. 1a) is seen in V14718B above the posterior portion of the body. It most probably merges with the caudal fin (c.f., Fig. 1a). Very faint impressions of rays are occasion- ally seen in the dorsal fin in V14718B (r.?, Fig. 1c). The tail seems diphycercal rather than hypocercal on the same ...
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... cartilage; r.e., right eye; r.ot., right otic capsule. the notochord in each segment made it difficult to observe the shape of arcualia, if any is preserved there. Paired fins and anal fin are absent. The dorsal fin (d.f., Fig. 1a) is seen in V14718B above the posterior portion of the body. It most probably merges with the caudal fin (c.f., Fig. 1a). Very faint impressions of rays are occasion- ally seen in the dorsal fin in V14718B (r.?, Fig. 1c). The tail seems diphycercal rather than hypocercal on the same ...
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... to observe the shape of arcualia, if any is preserved there. Paired fins and anal fin are absent. The dorsal fin (d.f., Fig. 1a) is seen in V14718B above the posterior portion of the body. It most probably merges with the caudal fin (c.f., Fig. 1a). Very faint impressions of rays are occasion- ally seen in the dorsal fin in V14718B (r.?, Fig. 1c). The tail seems diphycercal rather than hypocercal on the same ...
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... of a specific suctorial, parasitic mode of life. The material of Mesomyzon was collected from the freshwater shale deposits of the Yixian Formation. The new locality is not far from the famous Jehol Biota 16 localities in Liaoning with its present latitude of about 418 N, which is within the range of the palaeolatitude of the Jehol Biota (40-458 N (ref. 17)) during the Early Cretaceous. Associated with the new lamprey are abundant fossils commonly found in the Jehol Biota, including insects, a teleost Lycoptera davidi (Osteoglossomorpha), a salamander, a lizard and an unidentified fossil bird. All of these animals are terrestrial or freshwater dwellers. There is also no indication ...
Citations
... 1g-i, 2h-j). This lamina is thus proportionally much larger than its counterpart in living lampreys [10][11][12]20 , whereas this structure is likely much less developed, if present, in all other known fossil lampreys 3,8,9,[21][22][23][24][25][26][27] . Despite the variations in the relative size and the shape of the ventral part, the general morphology of this key feeding structure is similar in both Yanliaomyzon species. ...
Lampreys, one of two living lineages of jawless vertebrates, are always intriguing for their feeding behavior via the toothed suctorial disc and life cycle comprising the ammocoete, metamorphic, and adult stages. However, they left a meager fossil record, and their evolutionary history remains elusive. Here we report two superbly preserved large lampreys from the Middle-Late Jurassic Yanliao Biota of North China and update the interpretations of the evolution of the feeding apparatus, the life cycle, and the historic biogeography of the group. These fossil lampreys’ extensively toothed feeding apparatus differs radically from that of their Paleozoic kin but surprisingly resembles the Southern Hemisphere pouched lamprey, which foreshadows an ancestral flesh-eating habit for modern lampreys. Based on the revised petromyzontiform timetree, we argued that modern lampreys’ three-staged life cycle might not be established until the Jurassic when they evolved enhanced feeding structures, increased body size and encountered more penetrable host groups. Our study also places modern lampreys’ origin in the Southern Hemisphere of the Late Cretaceous, followed by an early Cenozoic anti-tropical disjunction in distribution, hence challenging the conventional wisdom of their biogeographical pattern arising from a post-Cretaceous origin in the Northern Hemisphere or the Pangean fragmentation in the Early Mesozoic.
... B 290: 20230333 indicating there may also be some influence of decay on these specimens. The specimen of Mesomyzon, a Cretaceous lamprey that was previously interpreted as a late metamorphic stage lamprey [81,82], is instead recovered here as being morphologically similar to early decay stage adult lampreys, while the 'adult' fossil specimen (labelled Mesomyzon_CJ) could also be considered as close to the extant late metamorphic stages. This was not expected, and potentially indicates some overlap in the tissues lost during decay and those developed during the final stages of metamorphosis, suggesting that taphonomic factors could have been conflated with ontogeny-derived change. ...
Exceptionally preserved fossils of soft-bodied organisms provide unique evidence of evolutionary history, but they are often contentious; different approaches frequently produce radically different reconstructions of taxa and their affinities. Conflict arises due to difficulties in disentangling the three non-independent factors that underlie all morphological variation within and between fossils: ontogeny, taphonomy and phylogeny. Comparative data from extant organisms can be extremely powerful in this context, but is often difficult to apply given the multi-dimensionality of anatomical variation. Here, we present a multivariate ordination method using discrete morphological character data from modern taxa at different ontogenetic and taphonomic stages (semaphoront and 'semataphonts'). Analysing multiple axes of morphological variation simultaneously allows us to visualize character combinations that are likely to exist in fossil specimens at intersecting stages of growth and decay, and thus constrain interpretation of fossils. Application to early vertebrates finds variation in fossil specimens to be accounted for by all three axes: primarily decay in Mayomyzon, ontogeny in Priscomyzon and phylogeny in 'euphaneropoids' and Palaeospondylus. Our demonstration of empirical multi-factorial variation underscores the power of multivariate approaches to fossil interpretation, especially non-biomineralized taxa. As such, this conceptual approach provides a new method for resolving enigmatic taxa throughout the fossil record.
... K 1 b 2 presents abundant fossils of the Jehol Biota, which is a well-known regional biota that was distributed in East Asia in the middle of the Early Cretaceous (Li et al., 2016). It is defined as a large number of well-preserved multi-phylum fossils, represents the bestpreserved terrestrial biota in the Cretaceous, and provides valuable information for understanding Mesozoic terrestrial ecosystems (Zhou et al., 2003;Chang et al., 2006;Zhou and Wang, 2017). In addition, geophysical data show that during the development of the Early Cretaceous rift basin, effective magma channels formed in the basement of the basin, resulting in the continuous rise of hydrothermal fluids (Chen et al., 2018). ...
The Early Cretaceous palaeoclimate was characterized by arid-humid alternation and accompanied by a series of short-term extreme environmental events, resulting in significant disturbances to the terrestrial ecosystem. However, the discontinuity of terrestrial geological records leads to a lack of detailed research on the coevolution mechanism of organisms and the environment. This study aims to investigate the response of the late Barre-mian-early Aptian subtropical lake biome structure to the hydroclimate crisis in the Yin'e Basin based on palynology, macropalaeontology, and geochemistry (i.e., major and trace elements, organic carbon isotopes, and biomarkers). The warm and semihumid climate promoted an increase in the abundance and degree of divergence in the vegetation, and the brackish-oxic conditions of the water column were conducive to the prosperity of aquatic organisms. The early aridification of the climate led to a decline in the lake level and a salinity crisis. The saline-suboxic conditions of the water column triggered the first aquatic crisis, while bacterial populations increased gradually. Cooling and continuous aridification led to a significant reduction in the types and amount of vegetation. The insufficient supply of nutrients and the continuous shrinking of the lake caused a second aquatic crisis, and several macroscopic organisms disappeared. The multivariate correlation analysis based on geochemical parameters showed that the palaeoclimate was the key driving factor for the evolution of palae-olakes and their conditions in the water column, and there was a close relationship among the ecological environmental indicators. The petrological and geochemical parameters suggest the existence of lacustrine hy-drothermal activity, which could also have a direct impact on the ecological environment of the lake. This study of the Bayingebi Formation palaeolake in the Yin'e Basin provides a strong example of the close coupling changes in the palaeoclimate and lake ecosystem to understand the continental sedimentary response to Early Cretaceous palaeoclimate warming events.
... 1g-i, 2h-j). This lamina is thus proportionally much larger than that in living lampreys 10,11 , whereas this structure is likely much less developed, if present, in all other known fossil lampreys 4,8,[15][16][17][18][19][20][21] . This toothed lamina is convexly curved and characterized by a prominent central cusp anked by two slightly smaller lateral cusps like in Geotria 9,10 . ...
Lampreys, the oldest living jawless vertebrates, represent an iconic model in evolutionary biology and are always intriguing for their bizarre feeding behavior of sucking blood or gouging out tissues from their victims. They seemingly underwent few changes in morphology and feeding habit since their first appearance in the Late Devonian. However, their evolutionary history is not so simple, as demonstrated by two superbly preserved large lampreys from the Middle-Late Jurassic Yanliao Biota of North China. These fossils present radical changes in the feeding apparatus, body size, and life-history strategy of their group during the Jurassic era and paved the way for the origin of living lampreys. Their extensively toothed feeding structures are radically different from the simply structured dentition of their unusually small-sized and probably non-predatory Palaeozoic relatives but surprisingly resemble the Southern Hemisphere pouched lamprey, which foreshadows an ancestral flesh-eating habit for modern lampreys. In the petromyzontiform timetree recalibrated on the basis of these stem lampreys, the evolutionary increase of lampreys’ body size accompanied the establishment of the modern-type three-phased life cycle, which was likely triggered by the concurrent evolutionary thinning of the body integument of their most significant piscine hosts in the Early Jurassic. Our study also places modern lampreys’ origin in the Southern Hemisphere of the Late Cretaceous, followed by an early Cenozoic anti-tropical disjunction in distribution, hence challenging the conventional wisdom of their biogeographical pattern arising from a recent origin in the Northern Hemisphere or the tectonic fragmentation of Pangean supercontinent as far back as 200 million years ago.
... Yet, the record of Mesozoic and Cenozoic jawless fishes has proven elusive. 12,25,26,42 Only one hagfish and one lamprey species are known for the entirety of the Mesozoic, the former of which is based on a single specimen. 12 The paucity of the post-Paleozoic jawless vertebrate fossil record necessitates a greater reliance on molecular phylogenetics to provide insights into the recent evolutionary history of the jawless vertebrate radiation. ...
... 68 Tip dates and codings were inputted for the three extinct genera included in the dataset (yMayomyzon, yMesomyzon, yPriscomyzon) based on the literature. [25][26][27]42 An origin prior of 439 million years ago with bounds of 600 and 400 million years ago was set based on the age of the oldest definite gnathostome, yFanjingshania renovata, from the early Silurian (439 Ma) of China (Andreev et al. 69 ). The use of this gnathostome as a prior age was to account for uncertainties surrounding the interrelationships of early jawed and jawless vertebrates, 27 and predates the oldest fossil lampreys and hagfishes. ...
The development of a movable jaw is one of the most important transitions in the evolutionary history of animals.1 Jawed vertebrates rapidly diversified after appearing approximately 470 million years ago. Today, only lampreys and hagfishes represent the once dominant jawless grade2,3,4 and comprise less than 1% of living vertebrate species. Their relationship to other vertebrates ranks among the more contentious problems in animal phylogenetics.5,6,7,8,9,10,11,12 Further, the phylogenetic relationships within lampreys and hagfishes remain unclear,13,14,15 and the ages of their living lineages are largely unexplored.16,17 Because of their importance for the genomic and developmental changes that prefigured jawed vertebrate diversity,18,19,20,21 the evolutionary history of lampreys and hagfishes is a major frontier of organismal biology. Of these two clades, lampreys22 are more ecologically diverse, exhibiting freshwater, anadromous, and fully marine forms, as well as parasitic and nonparasitic species.23,24 Here, we present a new phylogeny and historical biogeographic reconstruction of all living lampreys. Whereas the early diversification of this clade tracks Pangaean fragmentation, lampreys also rapidly radiated in the northern hemisphere during the mid-Cretaceous and directly after the Cretaceous-Paleogene extinction. These radiations mirrored concurrent ones in other animals and plants and coincided with changes to lamprey ecology and feeding behavior. Our results suggest that 80% of living lamprey clades appeared in the last 20 million years of Earth history. Rather than gradually accumulating since the oldest stem-group forms appeared in the early Paleozoic, living lamprey biodiversity results from diversifications extending from the Cretaceous to present.
... Discovered in the beginning of this century, the Liutiaogou locality is a text book example of the diversity and faunal assemblages found in the Jehol biota. It yielded very rich fossils including fossil insects, crayfishes, spiders, vertebrates (e.g., lampreys, fishes, bird feathers), and plants (e.g., Chang et al., 2006;Liu & Huang, 2019). The fossil insects are abundant and diverse. ...
Rudiaeschna jarzembowskii sp. nov., the second species of the small aeshnopteran family Rudiaeschnidae, is described from the Lower Cretaceous Yixian Formation at the Liutiaogou locality, Ningcheng County, Inner Mongolia, NE China. The new species differs from the type species of the family, namely Rudiaeschna limnobia, in possessing less cells and crossveins in nearly all parts of forewing. It also shows a distally forked vein RP2, a character that was previously only known in taxa of the much more recent and derived aeshnopteran family Aeshnidae.
... These biota fossils are a well-known regional biota distributed in East Asia in the middle of the Early Cretaceous (Zhou et al., 2003). Many beautifully preserved multi-phylum fossils have been collected, representing one of the best-preserved terrestrial biotas in the Cretaceous, providing valuable information for understanding the Mesozoic terrestrial ecosystem (Chang et al., 2006;Zhou and Wang, 2017). A large number of conchostracans Eosestheria sp. were observed in the lacustrine sediments ( Fig. 8A), which is a typical representative of the second stage of Jehol Biota evolution (Zhou, 2006). ...
Rapid changes in paleoclimate in the Early Cretaceous had profound impacts on the global ecosystem, which is recorded not only in marine sediments but also in coeval sediments deposited in continental lake systems. This study performed the lake sedimentary characteristics and paleontological data of the upper member of Bayingebi Formation (K1b²) of Lower Cretaceous in the Yin'e Basin (North China) and revealed the paleoclimate disturbances and the evolution of paleovegetation and paleoenvironment recorded in the continental lake. The sediments of K1b² can be divided into 10 kinds of lithofacies according to grain size, sedimentary structure and overall lithofacies. The three lithofacies associations are nearshore subaqueous fan, semi-deep lake/deep lake and shallow lake respectively. Seventy-eight palynomorph genera and two hundred and thirty-one palynomorph species were identified in the K1b² samples, which allowed to distinguish 3 palynozones. The sporopollen spectrum and the ecological characteristics of sporopollen parent plants indicate that there was abundant temperate coniferous forest vegetation during the deposition of Bayingebi Formation. The mixed phenomenon of a few cold-loving molecular spores and pollen such as spruce, cedar and fir with tropical and subtropical spores and pollen suggest vertical zoning of plants. It is inferred that the ground shape and height difference around Yin'e Basin in Early Cretaceous is large, and there may be paleogeomorphic features of high mountains, and the paleoclimate has vertical zoning. The K1b² depositional period was mainly in the warm temperate-temperate paleoclimate background, and oil shale was mainly developed in the semi-humid warm temperate climate. The suitable paleotemperature and the sedimentary environment of semi-deep lake/deep lake provide rich organic matter sources and good preservation conditions for the formation of oil shale. The dropstone structures commonly found in the lower strata of the oil shale member of the Bayingebi Formation in the study area were deposited in a semi-humid temperate climate and were inferred to be ice-rafting deposits, which may be related to a brief climatic cooling event or seasonal freezing during the Early Cretaceous in northern China. The typical East Asian paleontological fossils (Jehol Biota) and lacustrine hydrocarbon source rocks developed in the Early Cretaceous in the study area were affected by the paleoclimate warming in the early Aptian, which was closely related to the increase of global CO2 concentration in this period.
... Despite this, they still have some features, e.g., the extremely small body equipped with a teeth-bearing oral disc and prominent eyes, which suggest an ancestral life history pattern without the larval stages and hence distinct from that of their living counterparts (Miyashita et al. 2021). Mesomyzon, the only Mesozoic representative of this group, reduces the gap between the Paleozoic and modern lampreys (Chang et al. 2006). It shows not only a fairly modern look in external morphology, but also a three-phased (larva, metamorphosis and adult) life cycle interposed with a stage of radical metamorphosis (Chang et al. 2006(Chang et al. , 2014, a particular adap-tive strategy well known in living lampreys (Hardisty 1979). ...
... Mesomyzon, the only Mesozoic representative of this group, reduces the gap between the Paleozoic and modern lampreys (Chang et al. 2006). It shows not only a fairly modern look in external morphology, but also a three-phased (larva, metamorphosis and adult) life cycle interposed with a stage of radical metamorphosis (Chang et al. 2006(Chang et al. , 2014, a particular adap-tive strategy well known in living lampreys (Hardisty 1979). However, since only a young adult specimen was used in the original description of Mesomyzon (Chang et al. 2006) and the subsequent study merely focused on the larvae and transformers (Chang et al. 2014), the knowledge of the morphology of this fossil lamprey is still limited. ...
... It shows not only a fairly modern look in external morphology, but also a three-phased (larva, metamorphosis and adult) life cycle interposed with a stage of radical metamorphosis (Chang et al. 2006(Chang et al. , 2014, a particular adap-tive strategy well known in living lampreys (Hardisty 1979). However, since only a young adult specimen was used in the original description of Mesomyzon (Chang et al. 2006) and the subsequent study merely focused on the larvae and transformers (Chang et al. 2014), the knowledge of the morphology of this fossil lamprey is still limited. Inspired by the collection during the past ten years of dozens of exquisitely-preserved specimens, we present here an extensive morphological investigation of Mesomyzon. ...
Lampreys, one of the remaining two living jawless vertebrates, carry great weight in the study of vertebrate evolution. They have a long history dating back to the Devonian but left a scarce fossil record. So far, only five unequivocal fossil lampreys have been described, of which four are Paleozoic. Mesomyzon Chang, Zhang & Miao, 2006, the only known Mesozoic lamprey bridging the Paleozoic and extant relatives, was originally considered similar in morphology and life history to modern forms. Although being repeatedly referred to in early vertebrate phylogeny, the morphology of Mesomyzon is far from adequately known. Based on extensive investigations on numerous new and well-preserved specimens, we present herein more details of the morphology of this fossil lamprey, thereby releasing a package of new information of the cranial nerves, some associated structures of the oral disc, and the naso-hypophysial complex, which are barely preserved in previously known fossil lampreys. Mesomyzon shows peculiarities in having an extremely long anterior dorsal fin and a ribbon-like preanal skin fold, and hence being restored in a distinct profile from the formerly claimed look. Additionally, it shares with some Southern Hemispheric species the widely separated dorsal fins, posteriorly positioned cloaca and enlarged oral papillae. In the light of these new data, the feeding ecology of Mesomyzon was tentatively discussed and this fossil lamprey was considered a likely blood feeder, judging from the reinforcement of the attachment and sensory structures on the periphery of the oral disc.
... Lampreys have a slightly different caudal fin morphology. In many species, the tail is diphycercal, meaning it has dorsal and ventral fold symmetry as in the hagfish, but has a notochord that extends to the very tip of the tail with no dorsal or ventral bending (Chang et al. 2006). The fin folds tend to be either completely rounded or rhomboid, where maximal fold height is in the middle of the caudal fin and then tapers to a pointed end ( Fig. 2; Naseka et al. 2009). ...
Fishes are the longest persisting living vertebrates and as such, display an incredible array of diversity. Variation in the tail, or caudal fin, is often a reflection of a fish's environment, and affects movement, predation, defense, and reproduction. Previous literature has discussed many aspects of caudal fin form and function in particular taxonomic groups; however, no previous work has synthesized these studies in order to detail how the caudal fin is structured, and what purpose this structure serves, throughout the phylogeny of fishes. This review examines the caudal fin throughout the main lineages of fish evolution, and highlights where changes in shape and usage have occurred. Such novelties in form and function tend to have far-reaching evolutionary consequences. Through integration of past and present work, this review creates a coherent picture of caudal fin evolution. Patterns and outliers that demonstrate how form and function of this appendage are intertwined can further inform hypotheses that fill critical gaps in knowledge concerning the caudal fin.
... The cyclostomes include two extant taxa, hagfishes (Myxinoidea or Hyperotreti) and lampreys (Petromyzontida or Hyperoartia), and a small number of fossil taxa that are only preserved in Konservat-Lagerstätte, essentially of Devonian (Gess et al. 2006), Carboniferous (Bardack and Zangerl 1968;Bardack and Richardson 1977;Bardack 1991;Janvier 1996a), and Cretaceous (Chang et al. 2006(Chang et al. , 2014 ages (369-, 300and 110-My-old, respectively). The early fossil lampreys are clearly identified by their oral disk (or "sucker") strengthened by an annular cartilage, but generally lack clear evidence of keratinous teeth, which may, however, be preserved sometimes in the form of impressions (Gabbott et al. 2016;Janvier and Sansom 2015) (Figure 15.3C, D). ...
