''Besanosaurus'' (meaning "

Besano Besano is a town and ''comune'' located in the province of Varese, in the Lombardy region of northern Italy. Paleontological site The fossils of Besano In 1993 the fossil of a Triassic aquatic reptile dating back to about 235 million years wa ...

ombardy,_N._Italy.html" ;"title="Italy.html" ;"title="ombardy, N. Italy">ombardy, N. Italy">Italy.html" ;"title="ombardy, N. Italy">ombardy, N. Italylizard") is a genus of large ichthyosaur (a marine reptile, not a dinosaur) that lived during the middle Triassic period, approximately 235 million years ago. This marine reptile came from its own family Besanosauridae and was named by Dal Sasso and Pinna in 1996. The type of species is ''Besanosaurus leptorhynchus'' meaning "long-beaked reptile from

Discovery

The bones of ''Besanosaurus'' were first discovered in "Sasso Caldo" quarry in the spring of 1993 by the volunteers of the paleontological group of

, a small town in the

Lombardy Lombardy ( it, Lombardia, Lombard language, Lombard: ''Lombardia'' or ''Lumbardia' '') is an administrative regions of Italy, region of Italy that covers ; it is located in the northern-central part of the country and has a population of about 10 ...

region of north

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...

. The fossil was almost completely embedded in the rock and could be first seen only through

x-rays An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, ...

; to detect the content of the 38 slabs of stone enclosing the skeleton, 145

radiograph Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography ("diagnostic" and "therapeut ...

s were necessary. The skeleton of ''Besanosaurus'' came to light in the paleontological laboratory of

Museo Civico di Storia Naturale di Milano The Museo Civico di Storia Naturale di Milano (Milan Natural History Museum) is a museum in Milan, Italy. It was founded in 1838 when naturalist Giuseppe de Cristoforis donated his collections to the city. Its first director was Giorgio Jan. ...

after 16500 hours of preparation. The preparators removed the rock enclosing the fossil step by step, working under a

stereo microscope The stereo, stereoscopic or dissecting microscope is an optical microscope variant designed for low magnification observation of a sample, typically using light reflected from the surface of an object rather than transmitted through it. The instr ...

with chisels, needles and pins. The 38 slabs were reassembled and a silicon rubber matrix was made, from which a cast of the original specimen was obtained.

Description

While later ichthyosaurs developed fish-shaped body plans, ''Besanosaurus'' was less fish-shaped, bearing a small skull, long trunk and tail, and elongated flippers. Although it was once considered that it did not have a half-moon shaped tail fin and lacked a dorsal fin, at least more primitive ''

Mixosaurus ''Mixosaurus'' is an extinct genus of Middle Triassic (Anisian to Ladinian, about 250-240 Mya) ichthyosaur. Its fossils have been found near the Italy–Switzerland border and in South China. The genus was named in 1887 by George H. Baur. The ...

'' had dorsal fin. ''Besanosaurus'' is a large ichthyosaur. The holotype specimen measures long from its snout tip to tail tip. The specimen PIMUZ T 4847 was estimated by Bindellini and colleagues in 2021 to have a total length of , and is the largest known specimen of ''Besanosaurus''. The smallest known specimens of ''Besanosaurus'' represent animals about long.

Skull

The skull of ''Besanosaurus'' is proportionately small, making up less than 10% of the animal's total length. 67% of the skull's length is occupied by a long, narrow snout, which is strongly demarcated from the rear part of the skull. This elongated snout resembles those of

gavials The gharial (''Gavialis gangeticus''), also known as gavial or fish-eating crocodile, is a crocodilian in the family Gavialidae and among the longest of all living crocodilians. Mature females are long, and males . Adult males have a distinct b ...

and

river dolphins River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...

. All of the teeth of ''Besanosaurus'' are small, cone-shaped, and set into sockets, with the exception of the rearmost 30% of the teeth in the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

e (back upper tooth-bearing bones), which are set into a short groove. The tooth crowns bear prominent ridges while the

tooth root Dental anatomy is a field of anatomy dedicated to the study of Tooth (human), human tooth structures. The development, appearance, and classification of teeth fall within its purview. (The function of teeth as they contact one another falls elsewh ...

s bear even stronger ridging. The

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

e (front upper tooth bearing bones) of ''Besanosaurus'' are very long, and extend behind the external nares (nostril openings), where they form part of their border and block the

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...

s from reaching these openings. In addition to the premaxillae, the borders of the external nares are also formed by the maxillae and

lacrimals The lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the Orbit (anatomy), orbit. It has two surfaces and four borders. Several ...

. The maxillae and the prefrontals (a pair of skull roof bones) contact each other. The maxillae do not extend far behind the external nares. The cheek region of ''Besanosaurus'' is short, occupying only 13% of the total skull length. The jugals (bones beneath the

eye sockets In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is , o ...

), are approximately L-shaped. The postorbitals are visible towards the rear of the top of the skull. The frontals (bones in the skull roof) are long, broad, and flat. While the frontals enter the temporal fossae (depressions on top of the skull), they are not involved in the borders of the

temporal fenestrae The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

(openings on top of the skull). The front ends of the frontals overlap the nasal bones. The frontals intrude between the parietals and

postfrontal The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

s (two other pairs of skull roof bones). The quadrates (cranial bones that articulate with the mandible) each bear a triangular projection on their lower inner sides. ''Besanosaurus'' has a convex

occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape, and their anteri ...

(the part of the skull that connects to the

vertebral column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordata, ...

). The stapedes (bones in the lower part of the back of the skull) are long, slender, and bear expanded lower ends. The

surangular The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular The articular bone i ...

s (rear lower jaw bones forming the upper edge of the mandible) bear prominent emarginations, known as coronoid processes, rising above the rest of their upper edges.

Vertebrae and ribs

''Besanosaurus'' has 60 vertebrae located in front of its hips (presacrals); 11 of these are neck vertebrae. In addition to these vertebrae, there are 2 hip and 139 tail vertebrae. Both the front and back faces of the vertebral bodies (

centra Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees. The chain has three different f ...

) are concave, sloping inwards to a very thin layer of bone if not an opening. The neck vertebrae have prominent zygapophyses (bony projections of the vertebrae) and large, robust

neural spines The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

(the blade-like part at the top) with roughly round cross-sections. The roughly rectangular neural spines of the trunk vertebrae are also tall, and are more than half as wide from side to side as they are from front to back. The centra of the trunk vertebrae are at most half as long as tall. The frontmost cervical ribs (those attached to the neck vertebrae) are double-headed, unlike the other, single-headed cervical ribs behind them. The dorsal (trunk)

rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...

s bear grooves along their shafts. The heavily built

gastralia Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these ...

(belly ribs) are united along the animal's midline. About half of the total length of ''Besanosaurus'' is composed of its tail. The tail lacks a prominent bend. The neural spines of the tail vertebrae slope backwards, except near its end, where they instead slope forwards. The articular faces of the centra of the tail vertebrae vary in shape; the front ones are roughly triangular, the middle are hexagonal, and the rear are elliptical. The

chevrons Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * ''Eulithis testata'', a moth * Chevron (geology), a fold in rock lay ...

(bones beneath the tail vertebrae) are not very long. When viewed head-on, they appear Y-shaped.

Appendicular skeleton

The

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...

e (shoulder blades) of ''Besanosaurus'' are wide and shaped like

sickle A sickle, bagging hook, reaping-hook or grasshook is a single-handed agricultural tool designed with variously curved blades and typically used for harvesting, or reaping, grain crops or cutting succulent forage chiefly for feeding livestock, ei ...

s. Their front lower edges are short and mildly bowed inwards while their upper edges are heavily enlarged. The

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

s (additional shoulder bones below the scapulae) are shaped like

axe An axe ( sometimes ax in American English; see spelling differences) is an implement that has been used for millennia to shape, split and cut wood, to harvest timber, as a weapon, and as a ceremonial or heraldic symbol. The axe has many for ...

heads, with their upper margins heavily expanded and their lower ends fan-shaped. The coracoids do not bear openings. The

clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the rig ...

s (collarbones) of ''Besanosaurus'' are thin and broadest at their middles. ''Besanosaurus'' does not appear to have an

interclavicle An interclavicle is a bone which, in most tetrapods, is located between the clavicles. Therian mammals ( marsupials and placentals) are the only tetrapods which never have an interclavicle, although some members of other groups also lack one. In th ...

, an additional shoulder bone between the clavicles. The ilia (upper hip bones) of ''Besanosaurus'' are rather wide. The upper ends of the ilia are enlarged and directed inwards, though the lower ends are more heavily expanded. The

pubic bones In vertebrates, the pubic region ( la, pubis) is the most forward-facing (ventral and anterior) of the three main regions making up the coxal bone. The left and right pubic regions are each made up of three sections, a superior ramus, inferior r ...

(front lower hip bones) are vaguely circular in shape. They each bear a well-developed

foramen In anatomy and osteology, a foramen (;Entry "foramen"
in

that extends to the edge of the bone, forming a notch. The foreflippers of ''Besanosaurus'' are about 15% longer than its hindflippers. Each flipper bears three primary digits (those originating from the

wrist In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...

ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular join ...

) and one accessory digit (a digit not originating from the wrist or ankle), for a total digit count of four. The

humeri The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a round ...

(upper arm bones) are very short, being wider than they are long and rounded. Both the front and back edges of the humeri are bowed inwards, though this is stronger and more notch-like on the front edges. The lower arm bones as wide as the are long. The

radii In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

(front lower arm bones) have constricted middles and are roughly quadrangular, the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

e (rear lower arm bones) are rounded and smaller than the radii. The carpals (wrist bones),

metacarpals In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeleton, skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpa ...

, and manual

phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

(finger bones) are rounded. The

femora The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with t ...

(thigh bones) are 1.22 times as long as wide, narrower than the humeri but still very wide and short. The femora have constricted middles, with the midshaft width being somewhat smaller than the breadth of the upper end. The lower leg bones (

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

e and

fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...

e) have constricted middles and are more elongate than the radii and ulnae. The tibiae are the longer of the two pairs of lower leg bones. The lower ends of the fibulae are heavily expanded. The tarsals (ankle bones),

metatarsals The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...

, and phalanges of the hindflippers are thinner than the corresponding bones of the foreflippers. The pedal phalanges (toe bones) have constricted middles and are shaped like

ellipse In mathematics, an ellipse is a plane curve surrounding two focus (geometry), focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant. It generalizes a circle, which is the special ty ...

Paleobiology

It was an eel-like swimmer with moderate speed along with rapid acceleration and good maneuvering, and lived in tropical seas, in coastal, and

Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...

-like environments. Besanosaurs were

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...

and fed mainly on small fish,

cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...

, and marine reptiles. The reptile's reproduction was

ovoviviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...

, meaning the eggs incubated inside the body and hatched at birth.

References

External links

Besanosaurus at Gigadino
Middle Triassic ichthyosaurs Fossils of Italy Middle Triassic reptiles of Europe Ichthyosauromorph genera {{triassic-reptile-stub