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Scientific Reports Volume 11, Article Number: 21818 (2021) Cite this article

The Middle Triassic Luoping Biota in southwestern China represents the beginning of modern marine ecosystems. Arthropods, fish, and marine reptiles are rich and diverse, indicating a recovery from the Permian-Triassic mass extinction. Here, we report a new specimen of the predatory marine reptile electrictonosaurus based on an almost complete skeleton. This specimen is larger than most other known pachysaurus. The size, canine-shaped teeth, protruding clavicle, and the flat distal end of the anterior ribs show its relationship with Electrosaurus cuspidate, while the new specimen is approximately pointed. Three times the size of the toothed dragon. Positive model. The morphological characteristics indicate that the new specimen is an adult of D. acutidentatus, allowing individual genetic variation. The fang-like teeth and huge size confirm that it is a predator, but the amputated hind limb on the right indicates that it was preyed by an unknown hunter. The predation of such a large predator indicated that the predation pressure in the early Mesozoic was very strong, which may be an early sign of the Mesozoic ocean revolution.

The first large marine reptiles evolved in the Early Triassic and Middle Triassic 1,2, forming part of the "modern style" marine ecosystem, as life went from the Permian-Triassic Mass Extinction (PTME)3 Appeared during the recovery. This can also be said to be the time when the Mesozoic Marine Revolution (MMR) began4,5,6, which is a long-standing ecological transformation, and the marine ecosystems related to the arms race between predators and prey are more productive. New groups of mollusks and arthropods provide food for predatory gastropods, crustaceans, fish and reptiles. Here, we report a relatively large predatory pachysaurus that was preyed by larger predators, providing direct evidence for the MMR arms race.

Triassic marine restoration has a series of marine fauna in southern China, including the Nanzhang-Yuan'an, Chaohu, Panxian, Luoping, Xingyi and Guanling faunas. In particular, the Luoping Biota in the Middle Triassic produced nearly 20,000 large fossils, providing an extraordinary record of very early marine reptiles8,9. Contrary to modern marine ecosystems, super carnivores that feed on other four-legged animals were common in the Mesozoic oceans, confirming the different nutritional structure at that time.

Here, we report and describe a new large-scale marine pachysaurus species from the Luoping Biota, deciphering its role in the evolution of the first dragon, and its role in the restoration of ecosystems and the predation of giant animals in the early Mesozoic oceans. Ecological significance.

The Luoping Biota from the quarry near Daozi Village, Luoping County, Yunnan Province, China includes a variety of arthropods, conodonts, foraminifers, molluscs, echinoderms, brachiopods, fish, marine reptiles, plants and trace fossils 8, 10, 11, 12, 13. The fossil layer appears in the second member of the Guanling Formation. It contains about 16 m of dark micrite limestone in the Daozi section. The bedding is thin to moderately thick, indicating a semi-closed intra-platform environment10,11. The common conodont combination is mainly composed of Cratognathodus sp. And Nicoraella kockeli, indicate that the Luoping biota belongs to the Pelsonian Substage of the Middle Anician, and the U-Pb age of the volcanic tuff at the bottom of the I section is 246.6 ± 1.4 Ma, confirming this age of 10, 14.

Diandong dragon belongs to Shang, Wu, and Li, 2011.

Sharp Tooth Electric Dragon Shang, Wu & Li, 2011.

Small and medium-sized protosaurus with the following unique combination of characteristics: the anterior maxilla has long and pointed teeth; the upper jaw has single enlarged teeth and smaller teeth; the parietal hole is approximately flush with the front edge of the superior temporal window; Super temporal is smaller than the orbit; the interorbital bridge is wider; the frontal lobe is excluded from the orbit; the posterolateral process of the frontal lobe extends to the anterior edge of the supratemporal fenestra; through the contact between the cheek and the squamous part, from the temporal The posterior orbit is excluded from the inferior fenestra; there is an outer wing; the spine is composed of about 38 anterior sacrums, 3 sacrums, and more than 30 coccyx; The middle condyle foramen does not exist; the acetabular process of the pubic bone is strongly offset from the main body.

With WIGM SPC V 1105, an almost complete skeleton is exposed on the ventral side (Figure 1).

The complete skeleton of WIGM SPC V 1105 viewed from above. Note the missing left foot. Scale bar = 10 cm.

Daozi Village, Luoping County, Yunnan Province, China; the second member of Guanling Formation, Ani Stage, Middle Triassic.

WIGM SPC V 1105 is a large pachytrasaurus with a length of 88.6 cm from the tip of the snout to the end of the tail vertebral column (Figure 1). The specimen is exposed on the ventral surface, and the skull is exposed on both the ventral and dorsal sides. In the model, the skull accounts for 7.8% of the total length, the neck 22.9%, the trunk 32.4%, and the tail 36.9% (Table 1).

The skull of WIGM SPC V 1105 is exposed in both the dorsal and ventral views, and is compressed on the dorsal and ventral side (Figure 2). The outer nostril and the supratemporal window are oval in shape, and the orbits are nearly round.

WIGM SPC V 1105 photo and explanatory drawing of the skull. (a, b) dorsal view; (c, d) ventral view. Ang angle, at.c atlantoaxial vertebrae, at.nar atlantoaxial nerve arch, ax.c central axis, ax.nar central axis neural arch, bo occipital bone, d tooth, outer wing, eo-op exoccipital-opistotic, f Frontal lobe, hd hyoid bone, j jugal, m maxilla, n nasal cavity, p parietal bone, pat proatlas, pl palatine, pm premaxilla, pob postorbital, pof postfrontal, prf prefrontal, pt pterygoid, q quadrate, qrp , rap posterior joint process, sang surangular, so supraoccipital, spleen, square scales, vomer bone. The scale division in (a) = 1 mm. The scale bar in (b–d) = 2 cm. This image was generated using CorelDRAW X7 (https://www.coreldraw.com/en/pages/coreldraw-x7/).

In the dorsal view (Figure 2a, b), the anterior maxilla of the anterior maxilla is partly protruding, defined by the nose contraction of the anterior maxilla, which is different from the reported specimens of D. acutidentatus17,18. The anterior maxilla forms the anterior and medial edges of the outer nostril. The nasal process extends and narrows back along the posterior medial side of the nose, reaches the anterior edge of the orbit, and contacts the cusp line of the prefrontal lobe. The anterior maxilla touches the maxilla on the outside of the outer nostril.

The maxilla is slender, the anterior part is wide laterally, and the posterior process gradually becomes thinner. Its anteromedial border forms the posterolateral boundary of the outer nostril and overlaps the posterior anterior maxilla on the outside. The anterior nose contraction is mainly defined by the strong medial curvature of the anterolateral maxillary rim. On the inside, the maxilla is in direct contact with the back of the outer nostril, and the forehead is at the back; the nasal contact time may be longer. In the back, the maxilla borders the anterolateral edge of the orbit. The posterior process of the maxilla is in contact with the neck bone on the outside of the orbit. The bridge of the nose is broken. They are separated on the medial side by the anterior maxilla and contribute little to the posterior and outer nostrils. The outer nostrils are sub-circular.

The forehead is an arched bone that merges with the lacrimal gland. Its dorsal part expands back, and its ventral part forms the anterior dorsal edge of the eye socket. In the back, the prefrontal lobe overlaps the posterior frontal lobe obliquely at the midpoint of the dorsal edge of the orbit. The posterior frontal bone is a small trapezoidal bone that forms the dorsal edge of the orbit and is wider than Dianopachysaurus dingi19. In the back, it meets the posterior orbital bone in front of the supratemporal fenestra and has a small medial contact with the parietal bone, separating the posterior frontal lobe from the supratemporal fenestra. Both the prefrontal and posterior frontal lobes touch the frontal lobe on the dorsal side to prevent it from entering the orbit.

The frontal lobe merges medially into a dorsal butterfly shape, which expands obliquely in four directions. Previous contact with the nasal cavity is uncertain, but it may be extensive. The central contact with the anterior maxilla is narrow and irregular. The frontal lobe is horizontally connected with the prefrontal and posterior frontal lobe along the arc of the dorsal orbital edge to prevent it from entering the orbit, such as Spiked Electric Dragon 17, but different from Huikunlong and Ding's Pneumocystis19,20. The frontal lobe does not enter the supratemporal fenestra. Like D. acutidentatus, it is narrowly excluded by the parietal and posterior orbital lobe. In Dianopachysaurus dingi19, the contact between the posterior frontal lobe and the parietal lobe excludes the frontal lobe from the supratemporal fenestra. Backward, the frontal lobe slightly expands, laterally toward the supratemporal fenestra, and bifurcates into a narrow fork around the parietal protuberance, separating them from the posterior frontal lobe.

The parietal bone is partially fused, showing only sutures in front of the pineal foramen. The front protrusion is inserted between the rear frontal margin and has an arched border. Viewed from the side, the parietal lobe is on the anterior edge of the supratemporal fenestra, behind the posterior frontal lobe, and intersects the posterior orbital bone at a narrow point of contact. This is different from K. hui and Dianopachysaurus dingi19,20, where the parietal lobe is in contact with the anterolateral side of the posterior frontal lobe. The bone forms the medial edge of the supratemporal fenestra. The narrow posterolateral process is inserted by the dorsal process of the squamous body. The foramen of the pineal gland is sub-circular, aligned with the front edge of the supratemporal fenestra, more forward than K. hui20, and not as elongated as Dianopachysaurus dingi19.

The posterior part of the orbit is roughly three-radial, developing in three processes: anterior ventral, anteromedial and posterior. The anterior abdominal protrusion outlines the posterior edge of the orbit and overlaps the jugular vein laterally. The narrow anteromedial protrusion extends dorsally to form the anterior edge of the supratemporal fenestra and intersects the posterior frontal and parietal lobe in front of the supratemporal fenestra. This is different from the reported specimens of D. acutidentatus, K. hui and Dianopachysaurus dingi 17,19,20, more like nothosaus21,22. It overlaps extensively with the posterior frontal lobe. The posterior process is triangular and extends almost to the posterolateral edge of the supratemporal fenestra, forming the boundary of most of its lateral part. After that, the tip of the process is inserted into squamous cells.

The cheeks are in the shape of a boomerang and form most of the lateral edges of the eye socket. It touches the maxilla at the anterior abdominal rim of the orbit and overlaps with the maxilla on the dorsal side. In the back, the jugular vein forms the anterior edge of the infratemporal fenestra. Its kyphosis is wide front to back, extending to the dorsal side, and overlaps the posterior orbit at the abdominal rim of the posterior orbit. In D. acutidentatus 17, there is a small contact between the posterior cervical process and the dorsal side of the squamous protrusion.

Squamous bone is a large bone that expands in four directions. The protrusion forms most of the supratemporal strip, extending forward to the level of the front edge of the supratemporal fenestra, and partially overlaps the posterior orbital bone on the medial side, except for the squamous bone that holds the last point of the posterior orbital bone. At the foremost part of the squamous body, there is a small lateral contact with the kyphosis. The medial process of the squamous bone forms almost the entire posterior edge of the supratemporal fenestra, and the posterolateral process of the parietal bone is inserted medially. The posterolateral descent process is firm and expands to the ventral side, forming a sheet-like structure on the posterior edge of the skull, and touching the square outside part on the posterior medial side. However, the posterior process is the shortest of the four processes, and it is not as obvious as the reported sabertodon specimens. acutidentatus or K. hui17,20. The supratemporal fenestra is round, smaller than the orbit, and has straighter lateral edges. Its slenderness is not as good as Dianopachysaurus dingi and K. hui19,20.

Quadratojugal is not exposed. The superior occipital bone is a diamond-shaped bone inserted into the ventral side of the parietal bone, but has been basically broken; it forms the dorsal edge of the foramen magnum. exoccipital-opistothotic forms the lateral edge of the foramen magnum, while the basal occipital bone forms the ventral side; these elements are also destroyed.

In the ventral view (Figure 2c, d), the inner nostrils are roughly round. The vomer is a long bone with the posterior bifurcation along the midline of the upper jaw, forming the medial edge of the inner nostril. In the front, the bone meets the maxillary part of the anterior maxilla and contacts the maxilla anteriorly. In the back, the posteromedial process of the two vomeres is separated by the front process of the pterygoid process, with little contact with the back of the palate, such as D. acutidentatus18,22 but different from K. hui20.

The palatine bone is a band-shaped bone. It forms the posterolateral edge of the inner posterior nostril. On the anterolateral side, it touches the maxilla and meets the vomerine on the inside. On the posterior medial side, there is a highly irregular oblique suture between the palatine bone and the pterygoid bone.

The wing bone is one of the largest bones in the skull, forming most of the upper jaw at the back. The two wing bones fuse along the midline, leaving a straight groove in the front, which becomes more irregular in the back. Unlike D. acutidentatus, it has neither a central opening nor a rear cavity18. The tapered pterygoid protrusion is inserted between the two vomeres, and in K. hui20 it overlaps, and the anterior and outer sides of the pterygoid have a great oblique contact with the palate. Viewed from the side, the transverse process of the wing process extends ventrally and behind the rear edge of the outer wing. The pterygium forms almost the entire edge of the infratemporal fenestra in the front, middle and back. The elongated rectangular branch of the wing-shaped bone extends posteriorly to the rear edge of the square, and is in contact with the square wing-shaped branch.

The outer wing bone is roughly a small square bone, sutured to the transverse process of the wing bone. It is not as prominent as in Nozosaurus (such as Nozosaurus 21, Larrysaurus 22), but is relatively larger than in the specimens reported in D. acutidentatus 18,23, and in K. hui and Dianopachysaurus dingi19,20 It is uncertain whether there is an external pterosaur. The outer pterygoid bone touches the palatine bone forward, excluding the palatine bone from the infratemporal fenestra. In the back, it contributes little to the edge of the infratemporal fenestra outside the transverse process of the pterygoid process. The square part is exposed, contacting the square branch of the wing-shaped bone and its wing-shaped branch. The two rod-shaped hyoid bones are ossified and well-preserved, located below the wing bones. They are elongated and slightly expanded at both ends.

The mandible is mainly exposed on the ventral surface and partly on the dorsal side (Figure 2). The tooth is a long bone that occupies more than half of the anterior maxilla and has a wider joint backbone than D. acutidentatus or K. hui18,20,23. In the dorsal view, the mandible is partially exposed on the dorsal edge of the mandible and extends to the ventral side of the squamous bone. The horn bone is a long ribbon-shaped bone that meets the teeth at the front and the posterior joints at the back. The joint is sutured on the dorsal side of the horn, with an obvious kyphosis, extending backward, and the end is gradually tapering.

In the ventral view (Figure 2c, d), 9 upper anterior teeth and 7 lower teeth can be seen, which are prone, canine-like and have apical lines. Compared with other teeth, the 2nd and 3rd from the right and the 1st, 3rd, and 5th maxillary anterior teeth from the left are fully grown, elongated and less curved. However, the reported specimens of Spinosaurus and Fethosaurus have five teeth on each anterior maxilla17. The space between the 2nd and 3rd right front teeth indicates that there may be one or two missing teeth. Each upper jaw has a canine with small tapered teeth around it, and the lower jaw has five to six corresponding teeth. Canine teeth also have apical stripes like anterior maxillary teeth. A row of teeth is restricted to the level before the posterior edge of the eye socket.

There are 38 anterior sacral vertebrae, 3 sacrum and 33 coccygeal vertebrae (Fig. 1); these counts are roughly the same among contemporary Eriobotrya 19, 24, and 25. The atlas and shaft are exposed on the dorsal side (Figure 2a, b). The atlas is leaning forward, and its nerve spine does not intersect with its counterpart. Proatlas is a pentagonal bone, out of touch with the atlas. The axis has rotated laterally, but it is still connected to the map.

There are 19 cervical vertebrae, and Dianopachysaurus dingi19 has 20/21. The central cylinder is rhombus in ventral view, increasing in length backwards, and the vertebrae are tightly connected. The epiphyseal joint on the cervical rib (CR), visible in the ventral side view, is strong and offset from the long axis of the rib by about 90°, defined between the main body and the protruding protrusion. The lengths of these extensions and extensions are roughly equal, until about CR14, when the extensions begin to extend strongly. Starting from CR16, the protrusion is significantly reduced.

There are approximately 19 thoracolumbar vertebrae, most of which are covered by the abdominal vertebrae (18 segments are in the Slim Electron 25); an estimated count is made from two stomachs corresponding to one vertebra. The central joint is not as tight as the cervical spine. The transverse process faces backward. The dorsal rib is a single-head arched bone, the proximal flat end is slightly expanded, but it maintains a constant diameter along its entire length, and the distal end is a flat short column. The dorsal ribs DR1-6 are exposed on the ventral side, while the remaining ribs are mostly covered by the stomach. The stomach body has 24 rows, indicating that there are 12 more dorsal vertebrae covered, and each stomach body is composed of a medial element and four lateral elements (Figure 4a).

Three sacral vertebrae can be identified in the dorsal view (Figure 4b), which are the same as Dianmeisaurus gracilis, Dianmeisaurus dingi and K. hui19,24,26. The sacrum has a slender cylindrical shape with a thicker distal end, closely connected to the vertebral body, and may overlap the ribs behind each proximal end. At the distal end, the sacrum expands back into a small triangular protrusion that overlaps the next sacrum back. The sacrum SR2 and SR3 may be connected to the ilium, while other ribs cover the pubis and ischia (Figure 3c, d).

WIGM SPC V 1105 Photographs and explanatory diagrams of the chest girdle, forelimbs, pelvic girdle, and hind legs of the ventral side view. (a, b) Chest strap and forelegs. (c, d) The pelvic girdle and hind limbs. Such as astragalus, calcaneus, cl clavicle, coracoid, cr1 tail rib 1, cr19 cervical rib 19, cv1 coccyx 1, cv19 cervical vertebra 19, dc2 distal carpal 2, dc3 distal carpal 3, dc4 distal carpal 4, drrib 2 , dv2 dorsal vertebra 2, dr19 dorsal rib 19, dv19 dorsal vertebra 19, f femur, fibula, hu humerus, interclavian, il iliac, in the middle, is the ischia, mc1 metacarpal 1, 5 mc5 metacarpal mt5 metatarsal 5, pu pubis , Radius, sc scapula, sr1 sacrum 1, ti tibia, ul ulna, uln ulnare. (a, b, d) = scale in 2 cm. The scale division in (a) = 1 mm. This image was generated using CorelDRAW X7 (https://www.coreldraw.com/en/pages/coreldraw-x7/).

There are 33 rhomboid tail vertebrae, and their size gradually decreases towards the rear end of the tail. The caudal vertebra CV13-21 has a band-shaped nerve spine. The tail ribs are present in CV1-11. They are flat, arched bones, slightly backwards. The size of the ribs is about the same as CR1-5, but suddenly decreases from CR6-11 (Figure 4c). The distal end of CR3-8 is flat, while more posterior ribs have pointed ends.

Select the posterior part of WIGM SPC V 1105. (b) The dorsal sacrum area; (c) A part of the caudal area in the ventral side view. cr5 caudal rib 5, cv5 caudal vertebra 5, cv15 caudal vertebra 15, dr19 dorsal rib 19, dv16 dorsal vertebra 16, dv17 dorsal vertebra 17, dv19 dorsal vertebra, 1 pubic bone 1 pubic bone 1 pubic bone, sr3 sacrum 3, sv1 sacral vertebra 1, sv1 sv2 sacral vertebra 2, sv3 sacral vertebra 3. Scale bar = 5 cm. This image was generated using CorelDRAW X7 (https://www.coreldraw.com/en/pages/coreldraw-x7/).

The chest strap is exposed in the ventral side view (Figure 3a, b). Unlike D. gracilis, which is more like a diamond shape, the interclavian bone is an arrow-shaped bone with a strongly concave posterior edge and two lateral processes pointing to the posterior and lateral sides. Its tip points forward, but it does not reach the front edge of the chest strap between the collarbone. The clavicle is an L-shaped ribbon-like bone with characteristic protrusions on the anterolateral side, such as D. acutidentatus and larger than D. gracilis17,24. The clavicle forms a tiny posterolateral protrusion that covers the back of the scapula. The tapering medial process expands to intersect its counterpart, forming the front edge of the chest strap. The scapula is exposed in the ventral view, so the back edge is covered. In this view, it is sub-rectangular, with a rounded anterior edge and two posterior facets of the clavicle and humerus, inclined and separated by a small ridge. The coracoid process is a widened band of bone at the proximal and distal ends, and is the largest element in the chest belt. The front medial edge is more concave than the back medial edge. At the proximal end, the beak is flat suddenly and meets the contralateral element in a straight midplane. The distal coracoid process is stronger and expands forward into a broad circular protrusion on the front edge. The distal edge is straight and connects to the scapula in the front, and there is a smaller joint behind the humerus on the smaller triangular posterior distal process. There is a small hole near the anterior and distal edge of the scapular facet, which is 24 larger than that of the electric eyebrow dragon.

The forelimbs are almost intact, with the ventral side exposed, accounting for about 13.7% of the body length (Figure 3a, b). The humerus is strongly curved (40°) and shorter than the femur (Table 1). The proximal articular surface is round, the small articular surface of the scapula is larger than the coracoid process, while the distal articular surface is convex. Two straight oblique small articular surfaces are used to contact the radius and ulna. These aspects cancel out more strongly than D. acutidentatus17. There is no evidence of the presence of medial condyle 20,24. Compared with the humerus, the ulna and radius are almost equal in length and relatively slender (Table 1). The two ends of the ulna are of equal width, and the two ends of the radius are not significantly expanded, slightly to the medial side.

There are more than four wrists, and the ventral surface is round and flat. The intermediate is slightly larger than the ulna (Table 1), which is different from D. acutidentatus17, and there are joints on the inside and inside of the ulna. The distal carpal bone 2 is the largest of the distal carpal bones, and there is a joint distally between the middle and the ulna. Distal carpal bones 3 and 4 are present, but extremely reduced. The metacarpal bones are elongated and shaped like an hourglass. Metacarpal 1 is the shortest of the five, while metacarpals 2-4 are almost equal in length, while metacarpal 5 is slightly shorter. All fingers point to the ulnar side of the limb. The bone gap between the 4th and 5th metacarpal bones is the widest. The phalanx element is well preserved, but the fifth position on the right hand shows unusual preservation, which will be discussed further in the discussion. The fourth and fifth phalanx on the left are small and round, and the fifth phalanx on the right is missing. In view of this, the forelimbs are likely to have a phalange formula of 2-3-4-4-3.

The pelvic girdle is exposed on the ventral side (Figure 3c, d). The pubic bone is a large plate-shaped bone. The front and back edges of the bones are concave near the distal end (approximately one-third of the full length), forming a "waist" shape that is narrower than that of a slender electric dragon. The ischium is large and irregular in shape. On the inside, it expands into a large, square, plate-like part that meets the opposite element along a straight central joint. Viewed from the anterior distal side, the ischium is waist-shaped, separating the large and strong anterior distal protrusion from the broad rounded end that contacts the distal pubic bone and the ilium to form the acetabulum. Compared with the slender electric dragon, the anterior distal process is narrower and deviates from the main body more strongly. There is a wider extension in the backward direction. The thyroid window is large and rectangular, bounded by the posterior part of the pubic bone and the anterior part of the ischia on both sides. Viewed from the ventral surface, the iliac bone is covered by the pubis and ischia.

The left hind limb is well preserved and exposed in the ventral side view (Figure 3c, d). The amputation of the right femur will be discussed below. The femur is long and round, and the epiphysis is slightly waist-like; it is larger and thinner than the humerus (Table 1). The proximal end is wider than the distal end, but it is damaged in this specimen. The tibia and fibula are also elongated bones. The tibia is stronger than the D. acutidentatus model specimen, but more similar in size. Both have slightly expanded proximal and distal ends, but the proximal end of the fibula is hidden under the distal femur. The stronger waist on the fibula gives it a stronger curved appearance and forms a large interosseous window.

Astragalus and calcaneus are the only components of tarsal bones. Astragalus is larger than the calcaneus, located between the distal tibia and fibula, with a sharp proximal edge (Table 1). The small face of astragalus in contact with the tibia and fibula is straight. The calcaneus is sub-round. The length increases from metatarsals 1-4, and then decreases at metatarsals 5; metatarsals 1 is the shortest. All metatarsals have an elongated hourglass shape. pes is not well preserved because the numbers 1 and 2 are pressed together. Except for the 5th phalanx, the phalanx is not as long as the metatarsal and has a lumbar cylindrical shape; therefore, other fingers may lose some nails. The toe phalanx style cannot be determined due to preservation.

We added WIGM SPC V 1105 to the branch matrix of Lin et al. 27 and copied their analysis method in PAUP* version 4a169. Our branch analysis produced the four most parsimonious trees (tree length = 485 steps, CI 0.388, RI 0.622). The strict consensus of these trees (Figure 5) is consistent with the results of previous studies, that is, Diandonglong and Dianmeilong24 are closely related.

The strict consensus tree of the four most parsimonious trees (TL = 485 steps, CI = 0.388, RI = 0.622), proving the phylogenetic position of WIGM SPC V 1105. Bootstrap support values ​​≥ 50% (1000 repetitions) are marked. This image was generated using Adobe Illustrator 2021 (https://www.adobe.com/products/illustrator.html).

Diandongsaurus has some similarities with Keichousaurus and Dianopachysaurus18,19, but there are many morphological differences. Keichousaurus and Dianopachysaurus have small cone-shaped teeth 19,20, while Diandongosaurus has elongated canine-shaped teeth. Taking into account the size of the orbit, the supratemporal window of Diandongsaurus is elliptical and larger than the other two taxa. The tail ribs of Dianopachysaurus form a tapered distal end, which is different from Diandongosaurus, whose tail ribs have a flat distal end17,20.

Diandongsaurus is also different from other Triassic protosaurus dinosaurs. Strong anterior teeth distinguish it from pistosaauroids with erect anterior teeth. The size of the supratemporal fenestration is significantly larger than Qianxilong 28, while the unique tapered nose and nose of Umonglong 29 is different from the blunt mouth of Diandonglong. Its collarbone formed a protrusion, which does not exist in European pachysaurus. Dianyinlong's superior temporal window is smaller than that of Laryngosaurus and Nozosaurus, and in some species, its eye sockets are almost twice as large.

WIGM SPC V 1105 is roughly similar to D. acutidentatus, but differs in several characteristics, including being quite large, and the contracted nose of WIGM SPC V 1105 is a novel species of Pachysaurus. These morphological differences between WIGM SPC V 1105 and D. acutidentatus can be considered as evidence for the establishment of a new species. Or, WIGM SPC V 1105 has no wing bone opening in the two reference specimens of D. acutidentatus18,23 (specimen NMNS-000933-F03498 and BGPDB-R0001), and other differences, such as larger size and roundness of humerus and femur The shaped end may be caused by individual genetic variation or even preservation problems. According to previously recorded specimens, there is an interspecies variation in the phalangeal formula in D. acutidentatus, because the pedal formula counts 2–3–4–5–4 in the orthomodel, but it counts 2–3–4 in the reference specimen BGPDB –6–4 -R000123. In this case, WIGM SPC V 1105 may be an adult of D. acutidentatus. Taking these factors into consideration, we designated WIGM SPC V 1105 as meeting the standard of D. acutidentatus (see).

The skeleton of WIGM SPC V 1105 shows an amputation of the right hind limb (Figure 1, 3c, d), which indicates an attack from a top predator (Figure 6). The evidence has the following three points: (1) the right femur snapped off sharply from the middle, and no trace was found in the distal half of the blade; (2) the rest of the bone was articulated well, and there was no sign of water interference after death; (3) Luoping There are two types of potential predators in the biota: the quaginozosaurus 9 with a right mandibular branch of about 65 cm, and the mixed archer of the dragon crocodile 30 with a length of more than 3 m and equipped with dagger-shaped serrated teeth. In addition, WIGM SPC V 1105 may not be an agile fast swimmer, as shown by its large size, jagged abdomen, and flat chest strap.

The artist's restored WIGM SPC V 1105 was attacked by a predator and died. Illustrator: Yang Tinglu.

The unnaturally distorted fifth finger of the manual phalanx seems to be additional evidence of predation behavior, especially when it is noted that the other phalanx and the last coccyx bone remain in their original position, indicating a low-energy environment. However, burial factors cannot be ruled out because no bite marks were found on the manual phalanx.

This is consistent with the species richness of the Luoping biota, including sauropods, ichthyosaurs, sauropods and protosaurus as top predators8. Except for the accidental herbivorous marine reptile Atopodentatus unicus31,32, the seven saurioptera species in Luoping (Table 2) are all predators. Further predators include two ichthyosaurs, Mixosaurus. panxianensis33 and Phalarodon atavus34, turtle sauropod dinosaurs Sinosaurosphargis yunguiensis35 and Lagocephalosaurus polycarpon36, as well as protosaurus Dinocephalosaurus orientalis37 and protosaurus Kianosuchus mixtus30. Non-reptile fossil groups such as arthropods, molluscs, echinoderms, brachiopods, fish and plants are also quite diverse8,10.

More broadly, predatory marine reptiles are the main new animal component. When the predators are mainly sharks and some bony fish, there is no evidence that any of these groups existed in the Permian. The acceleration of life in the "modern fauna" of the Triassic 40 is marked by a wealth of new invertebrates and fish fauna, including new orthopedic fishes (neopterygians) and sharks (neoselachians). Reptiles include ichthyosaurs, plagiodonts, and protosaurus, all of which appeared in the Olenician (late Early Triassic), within 5 Myr after PTME. Ichthyosaurs were originally small snake-shaped swimmers, and there was a huge diversity in the Middle Triassic, some of which reached huge sizes in the late Triassic. Placodonts flourished in the Middle Triassic and Late Triassic with their special mollusk broken dentition. Among the first dragons, the pachysaurus first appeared in the Early Triassic and Yuan’an Kaichosaurus 41, and reached the peak of diversity in the Middle Triassic, especially records from southern China and Europe, and in the late Triassic. The world has decreased and disappeared. Nosoronke is mainly represented by Nothronosaurus and Larrysaurus, among which the Three Gorges of Larrysaurus first appeared in the Early Triassic 42. The Middle Triassic reached the maximum diversity of more than 20 species9,43. The last record is that 44 Pistosauroidea from the Carnian stage in Spain, such as Augustasaurus 45 and Cymatosaurus 46, were discovered in the Middle Triassic. The clade survived into the Jurassic and Cretaceous periods such as Plesiosaurus and Shanglong47. The size of these Triassic protosaurus species ranged from 5 cm long and 48 pachysaurus like Keichousaurus to 5-7 m 9 of Lophosaurus Nothosaurus.

Such a developed nutritional structure reflects the complete recovery after PTME3 and the early stages of MMR2. Based on the high level of boredom predation markers on the shells of bivalves in the Early Jurassic, it has been recommended to start MMR as soon as possible. This drilling is evidence of a new gastropod predation pattern, also from Triassic 49. Sturdy shell sculptures have also been reported in Triassic gastropods and bivalves, which are interpreted as an anti-predatory feature and are typical of MMR7. All this shows that MMR began in the Triassic, and this early beginning is likely to be related to two consequences of PTME. The first is that extinction cleared the ecological space and allowed new taxa to dominate the Triassic ecosystem. These new taxa established new life patterns and arms races that were faster than the Paleozoic. The second is the more direct aspect of ocean turbulence after PTME, when harsh environmental conditions interfered with recovery and forced some strong ecological interactions. In the Early Triassic and Middle Triassic, new clades with new adaptability appeared, including new anti-predation strategies, such as thickened shells and cementation of oysters and mussels, rapid escape of scallops, active crinoids, Prominent sculptures of gastropods and bivalves, as well as many taxa of deep burrows, as well as new hunting modes, including shell cutting of Malakostella, gastropods using chemical and mechanical methods to drill holes, And the hard food of various fish and reptiles.

The evidence of predation shown in our WIGM SPC V 1105 specimen is consistent with the broader evidence of the Triassic predator-prey arms race. Although Neusticosaurus edwardsii from the Middle Triassic of Mount Saint George can reach 120 cm in length51, the pachysaurus are generally small pterosaurs, many less than 50 cm, such as K. hui and Neusticosaurus peyeri48, 52. Therefore, WIGM SPC V 1105 is relatively large for this group. Pachypleurosaurians are small enough to be eaten by fish: According to reports, specimens from the Middle Triassic of Monte San Giorgio are 32 cm long Saurichys and gastric contents in fossil feces53,54. In addition, the Hubei alligator specimen from the Nanzhang-Yuan'an Biota showed abnormal preservation of its left forelimb, and nearly half of the hand was torn off before burial, indicating predation55. However, these are relatively small marine reptiles that feed on low nutrient levels56. In the Cretaceous mosasaur associated with shark teeth, direct fossil evidence of predation of medium to large carnivorous marine reptiles has been reported, but such discovery was limited in the Triassic. The Macocnemus Protosaurus from the Middle Triassic of the Eastern Swiss Alps may be preyed by some marine predators, but it may be a land-based coastal reptile rather than a marine predator54,58. Nonetheless, a related Tanystropheus reported from the same location with a severed neck provides indirect evidence of predation59. A more direct case is the 5-meter-long Guizhou ichthyosaur from the Xingyi Biota of the Middle Triassic, with a sea dragon skeleton 60 found in its stomach. The predation of this super carnivore is relatively rare in modern oceans. Although top predators such as leopard seals and killer whales sometimes prey on other quadrupeds, they usually feed on low-trophic prey over time1,61,62 .

The specimen is WIGM (Wuhan Institute of Geology and Mineral Resources) SPC V 1105, which is a nearly complete skeleton joined by the Wuhan Center of the China Geological Survey (WGSG) in Wuhan, Hubei Province, China. It was collected from the second member of the Guanling Formation in the quarry near Daozi Village, Luoping City, northeastern Yunnan Province, China. Use fine needles and mechanical dental drills to remove excess rock from around the bone. We use the binocular microscope Olympus SZ61 to prepare and observe specimens.

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We thank Grant nos for his support. National Natural Science Foundation of China 41972014, 42030513 and 41661134047, British Natural Environment Research Council NE/P013724/1, European Research Council 788203 (Innovation) Fund, China Geological Survey DD20190811.

State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430078

Liu Qiling & Li Tian

School of Earth Sciences, East China University of Science and Technology, Nanchang 330013, Jiangxi, China

Hubei Provincial Key Laboratory of Paleontology and Geological Environment Evolution, Wuhan Center, China Geological Survey, Wuhan 430023, Hubei, China

Liu Qiling, Long Cheng, Yan Chunbo, An Zhihui

School of Earth Sciences, Life Sciences Building, Tyndall Avenue, University of Bristol, Bristol, BS8 1TQ, UK

Michael J. Benton & Benjamin C. Moon

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LC designed the study; QL, CY, and ZA collected data; QL and BM did specimen description; QL and LT performed phylogenetic analysis; TY contributed ancient art; QL, MB, LC, and LT were based on all co-authors The comments were written in the manuscript.

Correspondence with Longcheng or Li Tian.

The author declares no competing interests.

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Liu, Q., Yang, T., Cheng, L. etc. The injured Diapsida (Diapsida: Sauropterygia) from the Luoping Biota of the Middle Triassic indicates the predation pressure of the Mesozoic. Scientific Report 11, 21818 (2021). https://doi.org/10.1038/s41598-021-01309-z

DOI: https://doi.org/10.1038/s41598-021-01309-z

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