Jinchuanloong niedu: A new species of Eusauropod Dinosaur from the Middle Jurassic of Gansu Province, China.

Sauropod Dinosaurs first appeared around the begining of the Jurassic, undergoing an extinction event at the end of the Early Jurassic, which has been linked to a period of intense global warming, which only a single lineage, the Eusauropods, survived. All subsequent Sauropod groups diversified from this single lineage. One group of Eusauropods, the Neosauropods, would eventually radiate and become the dominant Sauropods through the Late Jurassic and Cretaceous, but in the Middle Jurassic a variety of non-Neosauropod Eusauropods could still be found, particularly in East Asia.

In a paper published in the journal Scientific Reports on 23 May 2025, Ning Li of the School of Earth Sciences and Resources at the China University of Geosciences, Xiaoqin Zhang of Chuxiong Normal University, Xinxin Ren of the Key Laboratory of Stratigraphy and Paleontology of the Ministry of Natural Resources at the Institute of Geology of the Chinese Academy of Geological Sciences, Daqing Li of the Institute of Vertebrate Paleontology at the Gansu Agricultural University, and Hailu You of the Key Laboratory of Vertebrate Evolution and Human Origins at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, and the College of Earth and Planetary Sciences at the University of the Chinese Academy of Sciences, describe a new species of non-Neosauropod Eusauropod from the Middle Jurassic Xinhe Formation of Gansu Province, China.

The Xinhe Formation is a 120 m thick sequence exposed in the Jinchuan District of Jinchang City, which starts at its bottom with a succession of conglomerates, sandstones, and siltstones, becoming finer further up where it becomes a sequence of interbedded shales and mudstones. It is thought to have been laid down in an ancient lake environment, roughly 166-165 million years ago. the specimen from which the new species is described was found in the lower part of this formation.

The new species is named Jinchuanloong niedu, where 'Jinchuanloong' means 'Jinchuan-dragon', and 'niedu' means 'Nickel-city', in reference to the abundant nickel resources in Jinchang, where the metal is mined extensively. It is described from a single specimen, comprising an almost intact skull, lateromedially compressed on its left side, along with the five anteriormost cervical (neck) vertebrae, and, separately, a section of twenty nine articulated caudal (tail) vertebrae. These were confirmed to be from the same animal by impressions of the pelvic girdle and sacral vertebrae, which connect them to the cervical vertebrae. These caudal vertebrae have not been excavated, but remain in place with a protective fence around them.

Skull of Jinchuanloong niedu (JCMF0132) in left lateral view. Abbreviations: a, aperture; an, angular; aof, antorbital fenestra; d, dentary; en, external naris; f, frontal; fo, foramen; inf, infratemporal fenestra;j, jugal; l, lacrimal; m, maxilla; n,nasal; o, orbit; p, parietal; pf, prefrontal; pm, premaxilla; po, postorbital; pop, paraoccipital process; q, quadrate; qj, quadratojugal; sa, surangular; snf, subnarial foramen; sq, squamosal. Li et al. (2025).

A phylogenetic analysis recovered Jinchuanloong niedu as a non-Neosauropod Eusauropod outside the two major non-Neosauropod Eusauropod clades, the Mamenchisauridae and the Tauriasauria, forming a sister taxon to the Tauriasauria plus the Neosauropoda. Li et al. suggest that the status of Jinchuanloong niedu as an apparently separate lineage outside of any of the major clades lends support to the idea that East Asia was a significant centre for Sauropod diversification in the Middle Jurassic.

Phylogenetic relationships of Jinchuanloong niedu. Li et al. (2025).

Li et al. further note that the dentition of Middle Jurassic Sauropods from East Asia, and in particular taxa from western China, is extremely variable, which they take as a sign of niche partitioning (i.e. different species having different diets), which in turn could have driven a high rate of taxonomic diversification.

Caudal vertebrae of Jinchuanloong niedu (JCMF0132). Li et al. (2025).

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Apolithabatis seioma: A new species of stem-group Ray from the Late Jurassic Solnhofen Limestone.

Chondrichthyans, or Cartilaginous Fish, are among the most numerous Vertebrate fossils in the geological record, but almost all these fossils are of isolated teeth. Whole-body fossils of Chondrichthyans, in contrast are extremely rare, limiting our understanding of the morphology and biology of ancient members of this group. 

The oldest known body fossils of Batomorphs, or Rays, date back to the Jurassic Period, considered to be an important interval in Shark and Ray evolution, and come from a series of  'Konservat-Lagerstätten',  the most notable of which is the Solnhofen Limestone, of southern Germany, which records a series of deposits laid down in the Kimmeridgian-Tithonian (i.e. between 154.8 and 143.1 million years ago) in a series of islands, known as the Solnhofen Archipelago, on the edge of the Tethys Sea with many enclosed, placid, lagoons that had limited access to the open sea and where salinity rose high enough that the resulting brine could not support life. The Solnhofen Limestone records a range of Vertebrate fossils in exquisite detail, including Holocephalians (Chimeras), Hybodont Sharks, Selachimorph Sharks, and at least two genera of Batomorphs.

Until fairly recently, all Batomorphs from the Solnhofen Limestone were refered to the genera Asterodermus and Spathobatis, but recent studies have suggested that none of the Solnhoffen specimens can be assigned to Spathobatis, a genus originally described from French specimens, with the German specimens assigned to Spathobatis reassigned to a new genus, Aellopobatis. All known specimens of Asterodermus and Aellopobatis from the Solnhoffen Limestone are thought to be of Tithonian age, although many specimens were collected decades ago from working quarries, and may not be dated accurately.

In a paper published in the journal PLoS One on 23 January 2025, Julia Türtscher and Patrick Jambura of the Department of Palaeontology and the Vienna Doctoral School of Ecology and Evolution at the University of Vienna, Frederik Spindler of PALAEONAVIX, and Jürgen Kriwet, also of the Department of Palaeontology and the Vienna Doctoral School of Ecology and Evolution at the University of Vienna, deescribe a new species of Batomorph from the Kimmeridgian Painten site within the Franconian Alb of central Bavaria.

Geographical setting and stratigraphy of Painten. (A) Geographical map of the ’Solnhofen Archipelago’ and Nusplingen. (B) Stratigraphic section of the Upper Jurassic (upper Kimmeridgian to lower Tithonian) sediments of the ’Solnhofen Archipelago’ (southern Germany), the sequence exposed at Painten is indicated by a bracket. Note that the new Batomorph fossil is from the Ulmense rebouletianum-horizon within the Lithacoceras ulmense Subzone of the Kimmeridgian (highlighted). Türtscher et al. (2025).

The new species is described from a single specimen, DMA-JP-2010/007, and is named Apolithabatis seioma, where 'Apolithabatis' means 'Fossil Ray' in Greek, while 'seioma' derives from the Greek 'seismós', meaning 'shake', in reference to the way in which the fossil was extracted from the rock. The single known specimen of Apolithabatis seioma is at least 120 cm in length, with a heart-shaped disc and a long narrow tail. It has two dorsal fins, both behind the pectoral girdle (i.e. on the tail).

Overview of DMA-JP-2010/007, the holotype of Apolithabatis seioma. (A) Photograph of the specimen. (B) Illustration of the specimen showing the skeletal morphology. Abbreviations: ac, antorbital cartilage; bp, basipterygium; br, branchial arches; c, vertebral centra; cf, caudal fin; d1, first dorsal fin; d2, second dorsal fin; hs, haemal spine; mk, Meckel’s cartilage, ms, mesopterygium; mt, metapterygium; nc, nasal capsule; ns, neural spine; pb, puboischiadic bar; pp, propterygium; pq, palatoquadrate; r, ribs; ra, pectoral fin radials; rap, pelvic fin radials; ro, rostrum; sc, scapulocoracoid; syn, synarcual. The scale bar equals 10 cm. Türtscher et al. (2025).

Previous phylogenetic studies have recovered Jurassic Batomorphs as a part of the crown group (i.e. descended from the last common ancestor of all living members of the group), with the Torpediniformes (Electric Rays) forming the sister group to all other members of the group. However, Türtscher et al. recovered Apolithabatis seiomai, along with the other Jurassic genera Aellopobatis, Asterodermus, Belemnobatis, Kimmerobatis, and Spathobatis, in a distinct clade which has a sister group relationship to all extant Batomoph groups (including the Torpediniformes). Since this implies that this group is not descended from the last common ancestor of all living Batomorphs, Türtscher et al. regard this group, which they name the Order Apolithabatiformes, to stem group Batomorphs.

Majority-rule consensus tree with bootstrap and jackknife frequencies (jackknife values in parentheses). Daggers before taxon names indicate extinct taxa. Türtscher et al. (2025).

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Simoniteuthis michaelyi: A new species of Vampire Squid from the Early Jurassic of Luxembourg.

The modern Vampire Squid, Vampyroteuthis infernalis, is considered to be a relict species, having a mosaic of features associated with the Octobrachia (Octopus) and Decabrachia (Squid, Cuttlefish, and the extinct Belemnites). Notably, it has a well-developed gladius (mineralised internal support equivalent to the pen of Squid or the cuttlebone of Cuttlefish), and a rudimentary tenth pair of arms, both features of the Decabrachia, leading to the common name 'Vampire Squid', although molecular studies have placed this Cephalopod firmly within the Octobrachia. Vampyroteuthis infernalis is therefore considered to be the sole living member of the Order Vampyromorpha. This order has a fossil record dating back to the Mesozoic, and has been divided into two suborders, the Vampyromorphina, which contains the living Vampire Squid and a single Oligocene species, Necroteuthis hungarica, and the Loligosepiina, which contains 13-14 genera from the Jurassic and Early Cretaceous.

In a paper published in the Swiss Journal of Palaeontology on 14 February 2024, Dirk Fuchs of the Bayerische Staatssammlung Für Paläontologie Und Geologie, and Robert Weis and Ben Thuy of the Musée National d’histoire Naturelle Luxembourg, describe a new species of Vampyromorph Cephalopod from the Early Jurassic Schistes Carton of Luxembourg.

The new species is described on the basis of a single specimen from a bituminous black shale exposed in Bascharage, southeast Luxembourg, which is considered to be of equivalent age to the better known Posidonia Shale of southwest Germany. These deposits are thought to have been laid down in a shallow part of the northwestern peri-Tethys, close to the London-Brabant landmass. The shales lack any sign of bioturbation or benthic fauna, have a high organic carbon content, and contain fossils of pelagic Animals with articulated skeletons and soft tissue preservation, leading palaeontologists to interpret the environment as being a shallow, enclosed sea with sheltered conditions and an oxygen-depleted seafloor.

The new species is named Simoniteuthis michaelyi, where 'Simoniteuthis' Jo Simon, a volunteer palaeontologist at the Musée National d’histoire Naturelle Luxembourg, who skilfully and patiently cleaned the fossil in the nodule and unveiled the soft part preservation (the sufix '-teuthis' means 'Squid'), and 'michaelyi' honours Patrick Michaely, the director of the museum.

The specimen is preserved as part and counterpart on a split shale slab, and consists of the gladius and head-arm complex, including the proximal and middle parts of the arms, and the eyeballs. The remains of two small Fish can be observed within the tentacle area. Seen under UV light, the musculature of the arms can be observed. Like other members of the Suborder Loligosepiina, Simoniteuthis michaelyi has only eight pairs of arms, lacking the rudimentary tenth pair found in the living Vampyroteuthis infernalis. Details of the gladius are largely obscured by leaked ink, but it is  23 cm in length, and has distinct lateral wings, a diagnostic feature of Vampyromorphs.

Simoniteuthis michaelyi, holotype (MNHNL TI024), Lower Toarcian, Serpentinum Chronozone, Exaratum Subchronozone, Bascharage. (A)–(D) slab; (E)–(G) counter-slab. (A) overview; (B) camera lucida drawing of (A); (C) close-up of the head–arm complex; (D) same under UV-light showing the weakly illuminating arm musculature; (E) overview; (F) close-up of the preyed Fish, red colour Specimen 1 (op, opercle; sop, subopercle), blue colour Specimen 2 (caud, caudal fin; sop, subopercle; centra, central vertebra); (G) same under UV-light. Scale bars are 10 mm. Fuchs et al. (2024).

The number of arms in Vampire Squid remains somewhat of a puzzle. The common ancestor of all Coleoid Cephalopods is thought to have had five pairs of arms, a state retained in the living Squid and Cuttlefish. Members of the Octobrachia, including Octopus and the Mesozoic Loligosepiina, appear to have lost one pair of arms, leaving them with four. The living Vampire Squid, however, retains a rudimentary fifth pair of retractable, filamentous arms. Since it is unlikely that the species would have re-evolved a fifth pair of arms, it is assumed that it is a member of a lineage that has never lost the fifth pair of arms, implying that the Octopus and Loligosepiina lineages lost their fifth pair of arms separately. Confusingly, the extinct Suborder Prototeuthina, variously thought to be the ancestor of all Octobrachians, the ancestor of Vampyromorphs but not Octopus, or Octopus but not Vampyromorphs, also appear to have had only four pairs of arms. Possible filamentous arms have been reported on two Jurassic Vampyromorphs; a specimen of Mastigophora brevipinnis from Wiltshire, England (though other members of the same species appear to lack these extra arms), and possibly a specimen of Jeletzkyteuthis coriaceus from the Posidonia Shale. Niether of these species are thought to be closely related to the Vampyromorphina, nor to one-another, which, combined with the uncertainty as to whether they have a tenth pair of arms at all, provides palaeontologists with little help in unravelling the history of the fifth pair of tentacles.

Gladius morphology of Simoniteuthis michaelyi, holotype (MNHNL TI024), Lower Toarcian, Serpentinum Chronozone, Exaratum Subchronozone, Bascharage. (A) Overview of the slab; (B) close-up of the anterior hyperbolar zone showing the course of growth increments; (C) schematic morphology and measurements; (D) overview of the counter-slab; (E) close-up of the posterior gladius showing the course of growth increments. Scale bars are 10 mm. Fuchs et al. (2024).

The presence of two small Fish associated with the head-arm complex of Simoniteuthis michaelyi has implications for the taphonomy of the Schistes Carton. The most logical explanation for Fish being found in this location is predation by the Mollusc, and such small Fish are known to have been an important part of the diet of many Early Jurassic Cephalopods. Cephalopods with captured prey Fish have been found in several other deposits where the bottom waters are thought to have been anoxic, which has led to the suggestion that they may have been distracted by the capture of the Fish, causing them to drift into anoxic waters and die.

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Ceoptera evansae: A new species of Darwinopteran Pterosaur from the Middle Jurassic of the Isle of Skye.

Pterosaurs first appear in the fossil record in the Late Triassic, and persist till the end of the Cretaceous. During this time three basic morphotypes are found. The Rhamphorhynchoids are present from the Late Triassic till the Late Jurassic, and are considered to be a paraphyletic group from which all non-Rhamphorhynchoid Pterosaurs are descended. The highly derived Late Jurassic-End Cretaceous Pterodactyloids, are assumed to be a monophyletic group. Between these lie the Late Jurassic Darwinopterans; the Darwinopterans and Pterodactyloids are thought to comprise a single monophyletic clade, the Monofenestrata, although it is unclear if the Darwinopterans are a polyphyletic group of basal Monofenestratans from which the Pterodactyloids are descended, or whether they are a monophyletic group forming a separate branch of the Monofenestratan family tree.

Pterosaurs had delicate skeletons, made up of numerous elongate, thin bones. This is an excellent morphology for a flying Animal, but hampers the chances of that Animal's remains from being fossilised. Thus, the majority of known Pterosaur fossils come from a small number of Konservat Lagerstätten. The excellent preservation found at these sites has given us a good understanding of Pterosaur anatomy, functional morphology, and reproduction, but because their distribution in time is rather uneven, give us a rather limited perspective on the group's evolution and history. The majority of Konservat Lagerstätten date from two periods, the Late Jurassic and Middle Cretaceous, leaving us with some large gaps in which little is known about the diversity of Pterosaurs. This includes the late Early and Middle Jurassic, an interval of about 20 million years on which almost no Pterosaurs are known. The most abundant deposit from this period is the Taynton Limestone Formation of Oxfordshire, England, but the remains extracted from this deposit comprise almost exclusively isolated, and often fragmentary, bones, telling us little more than that Pterosaurs were present. Isolated Pterosaur bones are also known from the Oxford Clay, albeit in lower abundance. Fragmentary remains are also known from Kyrgyzstan, Mongolia, and China during this interval, though deposits from Argentina and China previously thought to have been of Middle Jurassic origin, from which a number of Pterosaur have been described. have recently been re-evaluated as being younger or older. 

In 2022 a Middle Jurassic Rhamphorhynchine Pterosaur, Dearc sgiathanach, was described from the Isle of Skye, Scotland, and in 2023 a partial non-Pterodactyloid Pterosaur was described from the same location. These, along with a possible Aurognathid from Mongolia, are currently the only known articulated Pterosaur skeletons from the Middle Jurassic.

In a paper published in the Journal of Vertebrate Paleontology on 5 February 2024, Elizabeth Martin-Silverstone of the Palaeobiology Research Group at the University of Bristol, David Unwin of the Centre for Palaeobiology and Biosphere Evolution and School of Museum Studies at the University of Leicester, Andrew Cuff of the Human Anatomy Resource Centre at the University of Liverpool,  Emily Brown of the Fossil Reptiles, Amphibians, and Birds Section at the Natural History Museum and the School of Geography, Earth & Environmental Sciences at the University of Birmingham, Lu Allington-Jones of the Conservation Centre  at the Natural History Museum, and Paul Barrett, also of the Fossil Reptiles, Amphibians, and Birds Section at the Natural History Museum, describe a new species of Darwinopteran Pterosaur from the Middle Jurassic of the Isle of Skye.

The new species is named Ceoptera evansae, where 'Ceoptera' derives from 'cheò' or 'ceò' (pronounced ‘ki-yo’) the Gaelic word for 'mist', in reference to the Gaelic name for the Isle of Skye, Eilean a’Cheò, or Isle of Mist, and '-ptera' the Greek for 'wing', and 'evansae' honours Susan Evans of University College London, 'for her many years of anatomical and paleontological research, in particular on Skye', and for introducing Martin-Silverstone et al. to the locality where the specimen from which the species is described was found.

HMUK PV R37110, the holotype of Ceoptera evansae, approximately as it was found (top) and by CT reconstruction with elements (bottom). Abbreviations: c, coracoid; cv, caudal vertebra; dsc, distal syncarpal; dv,  dorsal  vertebra; fe,  femur; m,  manual-phalanx; mc,  metacarpal; mt,  metatarsal; p, pedal-phalanx; pe, pelvis; ph, phalanx; psc, proximal syncarpal; r, rib; ra, radius; s, scapula; st, sternum; tf, tibia +fibula; ul, ulna; v, vertebra; w, wing-phalanx. Martin-Silverstone et al. (2024).

Ceoptera evansae can be distinguished from all other Pterosaurs by two features: (1) the presence on the distal (sternal) portion of the coracoid shaft of a well-developed, elongate, narrow, sub-rectangular bony flange (probably a site for insertion of the sternocoracoideus muscle) with an irregular ‘wavy’ free margin, which extends proximally for almost one-quarter of the length of the coracoid; and (2) the lateral surface of the posterior, dorsally expanded, portion of the post-acetabular process of the ilium bears a prominent depression divided in two by a low, rounded vertical ridge.

Reconstruction of the right scapulocoracoid of Ceoptera evansae (NHMUK PV R37110), made from CT scans in (A) lateral and (B) medial views. (C) Reveals a close-up of the expanded sub-triangular brachial flange of the coracoid, one of the diagnostic characters of this taxon. Abbreviations: acc, acrocoracoid process; afs, articular facet for sternum; bf, brachial flange; c, coracoid; cf, coracoid flange; gl, glenoid; s, scapula; sde, distal expansion of scapula. The top scale bar is for (A) and (B). Martin-Silverstone et al. (2024).

Ceoptera evansae is calculated to have had a wingspan of about 1.6 m. Determining the maturity of Pterosaurs can be difficult, as the order in which the fusion of bones occurred seems to have been highly individualistic, often not following the same pattern in members of the same species. Nevertheless, the pelvic plates, syncarpals, and tibia-fibula of Ceoptera evansae are fully fused, probably indicating that this was a mature individual.

Skeletal  of Ceoptera  evansae (NHMUK PV R37110), showing the material that is present (top, with greyed bones indicating partially preserved elements) and an artist’s  impression of what the entire skeleton would have looked like if complete. Mark Witton in Martin-Silverstone et al. (2024).

A phylogenetic analysis was carried out including Ceoptera evansae along with previously described Pterosaurs. This recovered the Darwinoptera as a monophyletic clade, forming a sister group to the Pterodactyloids, although this is not yet sufficiently statistically strong to assume that later discoveries will not change this reconstruction.

Reduced strict consensus tree of 2890 most parsimonious trees (tree lengths = 553; Retention Index = 0.779, Consistency Index = 0.360, with bootstrap/Bremer support values for each node) showing Ceoptera evansae as a basally branching Monofenestratan (M) Pterosaur within Darwinoptera (D). Silhouettes from top to bottom of: Preondactylus; Jeholopterus; Rhamphorhynchus; Darwinopterus; Ctenochasma; Nyctosaurus; Germanodactylus; and Quetzalcoatlus. Martin-Silverstone et al. (2024).

Ceoptera evansae is the fourth known articulate Pterosaur from the Middle Jurassic, and the second described species. The interpretation of Ceoptera evansae as a member of the Darwinoptera shows that this group was not, as was implied by the previously available evidence, restricted to the Late Jurassic of East Asia, but had a much wider distribution both geographically and chronologically. Furthermore, the addition of Ceoptera evansae to the Pterosaur phylogenetic tree implies that the Darwinoptera are not simply a polyphyletic basal group of Monofenestratans, but rather a distinct clade forming a sister taxon to the Pterodactyoidea.

Life reconstruction of Ceoptera evansae. Mark Witton in Martin-Silverstone et al. (2024).

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Lampreys from the Jurassic of northeast China, and their implications for the history of the group.

As one of only two groups of living jawless Vertebrates, Lampreys (Petromyzontiformes) have an important place in our understanding of the history of the group. They have a unique feeding style, with a sucker mouth which they use to attach to their prey, before either detaching a chunk of tissue to be consumed or remaining attached and draining their host's blood. Fossil Lampreys are known from the Carboniferous, showing that they have been around for at least 360 million years, but unfortunately the post-Carboniferous fossil record of the group to-date comprises only two species from the Cretaceous Jehol Biota of China. These Jehol Lampreys are apparently little different from their modern relatives, implying that some significant changes had taken place between the Carboniferous and the Cretaceous, including a re-arranging of the arrangement of the keratinous teeth, the appearance of a worm-like ammocoete larval stage, the invasion of fresh-water environments, and the adoption of an anti-tropical distribution (i.e. being found outside the tropics in both hemispheres, but being absent from tropical areas). 

In a paper published in the journal Nature Communications on 31 October 2023, Feixiang Wu of the Key Laboratory of Vertebrate Evolution and Human Origins at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, Philippe Janvier of the Muséum national d’Histoire naturelle, and Chi Zhang, also of the Key Laboratory of Vertebrate Evolution and Human Origins at the , Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, describe two new species of Lamprey from the Middle Jurassic Yanliao Biota Lagerstätte of northeastern China, and discuss the implications of these for the evolution of Lampreys as a group.

Both of these Jurassic Lampreys have a feeding apparatus which includes well-developed movable biting plates on the tongue-like piston, something known in the living Pouched Lamprey, Geotria australis, which is found in New Zealand, Chile, Argentina, the Falkland Islands, South Georgia and the southwest and southeast corners of Australia, but which has not previously been seen in any fossil Lamprey. The discovery of this trait in Jurassic Lampreys has important implications for the history of the group, suggesting that this may be a lost ancestral trait in the group, not an advanced development in the Pouched Lamprey, as had previously been assumed.

Both new species are placed in a new genus, Yanliaomyzon, meaning 'Yanliao sucker' in reference to the Yanliao Biota and the feeding apparatus of Lampreys. Both members of the genus have oral discs with well-toothed anterior and lateral fields, the teeth on these fields are closely arranged, dorsally truncated, and spatulate in shape with the slightly concaved under-surface of the free edge protruding as a shallow blade. 

The first new species is named Yanliaomyzon occisor, where 'occisor' means 'killer' in reference to the presumed hunting habit of the species. The species is described from two specimens, the first being complete and coming from the Daxishan locality in Jianchang County, Liaoning Province, and the second comprising a head and the forepart of the body, and coming from the Nanshimen Village locality in Hebei Province. Both are from the Tiaojishan Formation, which is thought to be between 160 and 158.58 million years old. Yanliaomyzon occisor has a supraoral lamina which completely spans the lateral rims of the oral aperture, the central cusps of which are flanked immediately by two smaller projections. It has 16 circumoral teeth, and a tail which takes up 28% of its bodylength.

Jurassic Lamprey from the Yanliao Biota, China, Yanliaomyzon occisor (a) Photograph of holotype (IVPP V 15830); (b) Line drawing of the oral disc and dentition of (a); (c), (d) Paratype (IVPP V 18956B), photograph (c) and line drawing (d); (e) Restoration. Abbreviations: adf, ‘anterior dorsal fin’ (dorsal fin); af, anal fin fold; ba, branchial apparatus; ca, cloaca (anus); cot, circumoral teeth; da, dorsal aorta; dcf, dorsal lobe of caudal fin; dt, oral disc teeth; cf, caudal fin; e, eyes; dt, disc teeth; go, external gill openings; gp, gular pouch; ic, intestine contents; io, infraoral lamina; ll, longitudinal lingual lamina; ll.l, left longitudinal lingual lamina; ll.r, right longitudinal lingual lamina; lv, liver; ns, olfactory organ (nasal sac); oc, otic capsule; od, oral disc; of, oral fimbriae; op, oral papilla(e); paf, precloacal skin fold; pdf, ‘posterior dorsal fin’ (anterior part of caudal fin); pt, piston cartilage; so, supraoral lamina; tl, transverse lingual lamina; vcf, ventral lobe of caudal fin; V1?, ophthalmic ramus of trigeminal nerve? Wu et al. (2023).

The second new species is named Yanliaomyzon ingensdentes, where 'ingensdentes' means 'large teeth', in reference to the large cuspid laminae on the gouging piston of this species. This species is described from a complete specimen and a separate preserved oral disk, both from the Daohugou Beds at Wubaiding Village in Reshuitang County, Liaoning Province, a locality dated to about 163 million years ago. Yanliaomyzon ingensdentes has a supraoral lamina occupying roughly one-third of the rim of the oral aperture; as well as a transverse lingual lamina which almost equals the supraoral lamina in width. It has about 23 circumoral teeth, and a tail which makes up about 40% of its bodylength.

Jurassic Lamprey from the Yanliao Biota, China, Yanliaomyzon ingensdentes (f) Photograph of holotype (IVPP V 16715B), white arrow pointing to the skeletal relics in gut content; (g) Oral disc and dentition; (h) Restoration. Abbreviations: adf, ‘anterior dorsal fin’ (dorsal fin); af, anal fin fold; ba, branchial apparatus; ca, cloaca (anus); cot, circumoral teeth; da, dorsal aorta; dcf, dorsal lobe of caudal fin; dt, oral disc teeth; cf, caudal fin; e, eyes; dt, disc teeth; go, external gill openings; gp, gular pouch; ic, intestine contents; io, infraoral lamina; ll, longitudinal lingual lamina; ll.l, left longitudinal lingual lamina; ll.r, right longitudinal lingual lamina; lv, liver; ns, olfactory organ (nasal sac); oc, otic capsule; od, oral disc; of, oral fimbriae; op, oral papilla(e); paf, precloacal skin fold; pdf, ‘posterior dorsal fin’ (anterior part of caudal fin); pt, piston cartilage; so, supraoral lamina; tl, transverse lingual lamina; vcf, ventral lobe of caudal fin; V1?, ophthalmic ramus of trigeminal nerve? Wu et al. (2023).

Both species of Yanliaomyzon are large, with the complete specimen of Yanliaomyzon occisor measuring 642 mm; among extant Lampreys this is exceeded only by the Anadromous Sea Lamprey, Petromyzon marinus (maximum adult length 1200 mm), Pacific Lamprey, Entosphenus tridentatus (850 mm), Pouched Lamprey, Geotria australis (788 mm), and Arctic Lamprey, Lethenteron camtschaticum (790 mm). 

The most distinctive feature of these Lampreys is the extensively toothed oral disc and tongue-like piston, which is similar in morphology to that of the extant Poached Lamprey, a species with a Southern Hemisphere distribution, which is capable of delivering a powerful bite and removing large chunks of flesh from its prey. 

Feeding apparatus of Yanliaomyzon and the Pouched Lamprey, Geotria australis. (a)–(d) Oral disc and dentition of Yanliaomyzon ingensdentes, (a) Photograph (IVPP V 16716B) and (b) Line drawing; (c) Photograph (IVPP V 16716A), whitened with ammonium chloride, the white arrow pointing to the imprints of the wrinkles of the gular pouch; (d) Restoration. (e), (f) Oral disc and dentition of Yanliaomyzon occisor, (e) Photograph (IVPP V18956A), whitened with ammonium chloride; (f) Restoration; (g) Oral disc and dentition of Geotria australis. Abbreviations: cot, circumoral teeth; dt, oral disc teeth; gp, gular pouch; ic, intestine contents; io, infraoral lamina; ll, longitudinal lingual lamina; ll.r, right longitudinal lingual lamina; od, oral disc; of, oral fimbriae; op, oral papilla(e); so, supraoral lamina; tl, transverse lingual lamina. Wu et al. (2023).

Both species of Yanliaomyzon have gular pouches, a feature seen in 12 species of living Lamprey, as well as the Cretaceous Mesomyzon mengae, but unknown in other fossil Lampreys. This feature has been suggested to be connected to courtship displays in male Lampreys, or serving as an energy reserve during anadromous (sea-to-freshwater) migrations; seven of the extant species in which this feature is found undertake such migrations.

Also seen in both species of Yanliaomyzon is a long dorsal fin extending anteriorly until the level of the fourth gill pouch, and a a long precloacal skin fold, which extends anteriorly to the anterior branchial region.

A phylogenetic analysis recovered Yanliaomyzon as stem group Lampreys (i.e. more closely related to living Lampreys than to any other living group, but not decended from the last common ancestor of all living Lampreys). Notably, including Yanliaomyzon in the analysis led to Mesomyzon mengae also being recovered as a stem group Lamprey, where previous studies had recovered it as a member of the crown group. In this analysis all fossil Lampreys lie outside the crown group (the crown group comprises everything descended from the last common ancestor of all living members of a group), which now comprises only living species. 

In this new analysis, Geotria australis, the only member of the family Geotriidae, is recovered as the outgroup to all other Lampreys, with the genus Mordacia, with two species forming the family Mordaciidae, forming the sister group to the family Petromyzontidae (Northern Hemisphere Lampreys), which includes all other living Lampreys. This is another new interpretation, with previous analyses having suggested either that the Geotriidae and Mordaciidae are sister groups, on a separate branch to the Petromyzontidae, or that the Petromyzontidae and Geotriidae are sister groups, with the Mordaciidae being sister to the pair.

Time-calibrated phylogeny of the Cyclostomes and Lampreys. The time-tree is the all-compatible consensus tree summarized from the Bayesian total evidence dating analysis on the partitioned data. The node ages in the tree are the posterior medians, and the error bars at the nodes denote the 95% highest posterior density intervals. The shade of each circle represents the posterior probability of the corresponding clade. The colour of the branch represents the median relative evolutionary rate of the feeding mechanism characters at that branch. Abbreviations: C., Caspiomyzon; Cam., Cambrian; Carbon., Carboniferous; Dev., Devonian; En., Entosphenus; Eu., Eudontomyzon; G., Geotria; I., Ichthyomyzon; La., Lampetra; Le., Lethenteron; M., Mordacia; Ord., Ordovician; P., Petromyzon; Perm., Permian; Sil., Silurian; T., Tetrapleurodon; Y., Yanliaomyzon. Wu et al. (2023).

Yanliaomyzon occisor is the largest fossil Lamprey known to science, and would be large for a modern Lamprey. Among living Lampreys large size is associated with longer migrations, a wider range, larger clutches of eggs, and a greater tolerance for salt water. Many small Lamprey species do not feed at all after metamorphosing from their ammocoete larval stage. Based upon this, and the prevailance of anadromous migrations among Lampreys recovered as basal within the crown group by Wu et al.'s phylogenetic analysis, Yanliaomyzon occisor appears likely to have been an anadromous migratory species with a triphasic life cycle (this is known to have been the case in Mesomyzon mengae, a Cretaceous species found to be less closely related to the crown group than Yanliaomyzon occisor in the phylogenetic reconstruction).

The long dorsal fin and ribbon-like precloacal skin fold seen in both species of Yanliaomyzon also suggest that these Lampreys were powerful swimmers. Similar arrangements are seen in the European Eel, Anguilla vulgaris, and African Knifefish, Gymnarchus niloticus, both of with are capable of swimming against powerful currents, something likely to be useful in a Lamprey migrating upstream to reproduce.

Lampreys appear to have switched from a simple non-migratory life cycle lacking a separate larval stage to the modern three stage, anadromous migratory life cycle some time after the Carboniferous, and the discovery of Yanliaomyzon spp. strongly suggests that this had occurred by the Middle Jurassic. This change in lifestyle appears to have also been connected to a sharp increase in the body size of Lampreys, probably as a result of the interactions between Lampreys and a changing prey-community.

Lampreys first appeared in the Devonian, and have generally been assumed to have been either carnivorous or predatory from the outset. However, Wu et al. point out there is little evidence for such behaviour in Palaeozoic Lampreys, which are very small, lack an ammocoete larval stage, and have simply structured and tiny dentition and a small buccal cavity (the space where the glands which secrete anticoagulants are found in modern Lampreys). The oral disks of these Palaeozoic Lampreys were capable of attaching, but had little biting capacity. Furthermore, the majority of Palaeozoic Fish were covered with thick scales or amoured plates, which it is unlikely even a modern Lamprey could penetrate, and which it is highly unlikely that the much smaller and less well armed Palaeozoic Lampreys could have overcome. As an alternative, Wu et al. suggest that early Lampreys may have specialised in scraping Algae from the bodies of larger Animals, using their oral disks to stay attached when their hosts moved about. Adopting a specialist niche such as this would have enabled Lampreys to flourish in an environment where they faced competition from a large number of other Jawless Fish species, notably the Conodonts from which they are thought to have derived, and which were armed with similar feeding apparatus. This evolutionary jump could help to explain the rapid range expansion of Palaeozoic Lampreys, which were restricted to the southern polar region in the Devonian, but which had reached equatorial regions by the Late Carboniferous. 

Wu et al.'s phylogenetic reconstruction suggests that the ancestors of Mesomyzon mengae diverged from the ancestors of Yanliaomyzon spp. and modern Lampreys in the Early Jurassic, suggesting that more powerful oral disks associated with predation and parasitic behaviour had evolved by this point. This may have been linked to the rise of Teleost and Acipenseriform fish in the Early Jurassic, which typically have much thinner scales than the Gannoid Fish they supplanted, as well as the disappearance of potential competitors such as the Conodonts in the Permian and Triassic extinctions, which would have created new opportunities for Lampreys, leading to the development of more the specialized feeding apparatus and the increase in size seen in later members of the group. This increase in size would have facilitated the invasion of freshwater environments and the development of a migratory reproductive cycle.

The feeding apparatus and gut of Yanliaomyzon spp. appear similar to that of the modern carnivorous Pouched Lamprey, Geotria australis, indicating that this lifestyle had appeared by the Middle Jurassic. Wu et al. hypothesise that carnivory is the ancestral state for crown group Lampreys, and that parasitism arose as specialization derived from this, the reverse of the previously assumed scenario. The adaptation to a carnivorous lifestyle would have provided Lampreys with a high energy diet, enabling the evolution of larger body sizes, and longer migrations.

Modern Lampreys have an anti-tropical distribution, found in temperate and sub-arctic waters in both hemispheres, north and south of the 30° parallel and the 20°C isotherm. This preference for cool waters was also seen in the earliest Lampreys, and while the group have at times moved into more equatorial waters, this appears to have coincided with cooler intervals in the geological record. 

Timetree of the Petromyzontiformes projected with paleotemperature curve since the Devonian and biogeographic reconstructions of the group. Wu et al. (2023).

Lampreys were present in palaeoequatorial regions of Euramerica during the Late Carboniferous Ice Age, and all known Mesozoic fossils are restricted to temperate regions of the Northern Hemisphere. The size and morphology of these Mesozoic Lampreys suggests that they were probably stronger swimmers than even the most widespread current species, such as the Pouched Lamprey, Geotria australis, and Pacific Lamprey, Entosphenus tridentatus. Both of these predatory Lampreys are capable of following shoals of Fish for long distances, and reaching considerable depths; Pacific Lampreys are typically found at depths of 0-500 m, but the maximum depth at which the species has been recorded is 1485 m. A Lamprey capable of sustained swimming at such depths would be capable of migrating across the equator without ever having to enter warm water.

Crown group Lampreys were assumed to have arisen in the Southern Hemisphere between 280 and 220 million years ago, before the breakup of Pangea, and then Gondwana, leading to the anti-tropical distribution of the group. Wu et al.'s study suggests that the crown group is younger than previously thought, and probably arose in the Southern Hemisphere, with a subsequent migration of some groups back into the Northern Hemisphere. Wu et al. suggest that the crown group may have appeared around the end of the Cenomanian-Turonian Thermal Maximum, an event likely to have wiped out the stem group Lampreys, with the subsequent migration of Lampreys back into the Northern Hemisphere having occurred before the Palaeocene-Eocene-Thermal-Maximum, an event which would have excluded from lower latitudes. 

Crown group Northern Hemisphere Lampreys, Petromyzontidae, are thought to have arisen in the late Oligocene in western North America, and subsequently spread around the hemisphere following the development of ice caps in Greenland and the Arctic Sea, enabling them to spread to eastern North America and then Europe. The absence of such cold water close to the major landmasses of the Southern Hemisphere has led to the uneven species richness in the two hemispheres.

Wu et al. suggest that the morphology and lifestyle of Lampreys is not as conservative as previously thought, and that the group underwent a major evolutionary leap in the Jurassic, including a significant increase in size and swimming ability and the modification of the feeding apparatus into a more modern configuration. Crown group Lampreys are suggested to be much younger than previously hypothesized, and to have arisen in the Southern Hemisphere rather than the Northern Hemisphere, as previously thought.

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