''Diodorus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of silesaurid

dinosauriform Dinosauromorpha is a clade of avemetatarsalian archosaurs (reptiles closer to birds than to crocodilians) that includes the Dinosauria (dinosaurs) and some of their close relatives. It was originally defined to include dinosauriforms and lager ...

s (relatives of

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s) from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

(

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

)

Timezgadiouine Formation The Timezgadiouine Formation, sometimes spelled as the Timesgadiouine Formation, is a Triassic geological formation in the Argana Basin of Morocco. It is a succession of red bed sediments spanning from the Olenekian to at least the Carnian, encomp ...

of the Argana Basin of

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to ...

Discovery

The first fossils of this

taxon In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

were discovered by a team from

Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher le ...

in the northeastern Argana Basin, east of Imziln, Morocco, with support from the

National Geographic Society The National Geographic Society (NGS), headquartered in Washington, D.C., United States, is one of the largest non-profit scientific and educational organizations in the world. Founded in 1888, its interests include geography, archaeology, and ...

and permission from the Moroccan Ministry of Energy and Mines. The remains were found in a quarry at of the Irohalene Mudstone Member of the

, as part of a layer of disarticulated specimens that included fossils of

phytosaurs Phytosaurs (Φυτόσαυροι in greek) are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. Phytosauria and Phytosauridae are often considered to be equivalent g ...

, prolacertiforms, fish, and

temnospondyls Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carb ...

. In 2012, the paleontologists Christian F. Kammerer,

Sterling J. Nesbitt Sterling Nesbitt (born March 25, 1982, in Mesa, Arizona) is an American paleontologist best known for his work on the origin and early evolutionary patterns of archosaurs. He is currently an associate professor at Virginia Tech in the Department of ...

, and

Neil H. Shubin Neil Shubin (born December 22, 1960) is an American paleontologist, evolutionary biologist and popular science writer. He is the Robert R. Bensley Professor of Organismal Biology and Anatomy, Associate Dean of Organismal Biology and Anatomy and ...

scientifically described A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...

the remains, and identified them as representing the first body fossil record of the group

Silesauridae Silesauridae is an extinct family of Triassic dinosauriforms. It is most commonly considered to be a clade of non-dinosaur dinosauriforms, and the sister group of dinosaurs. Some studies have instead suggested that most or all silesaurids compr ...

from northern Africa. Based on these fossils, they named the new

and species ''Diodorus scytobrachion''; the generic name refers to Diodorus, a legendary king of the

Berber people , image = File:Berber_flag.svg , caption = The Berber flag, Berber ethnic flag , population = 36 million , region1 = Morocco , pop1 = 14 million to 18 million , region2 = Algeria , p ...

and son of

Sufax Sufax, Syphax, Sufaqs or Sophax (Ancient Greek: Σόφακος ''Sophaxus'') was a hero or demigod from the Traditional Berber religion, Berber and Greek mythology, Greek mythologies. Family According to the myth, Sufax was the son of goddess ...

, the founder of

Tangier Tangier ( ; ; ar, طنجة, Ṭanja) is a city in northwestern Morocco. It is on the Moroccan coast at the western entrance to the Strait of Gibraltar, where the Mediterranean Sea meets the Atlantic Ocean off Cape Spartel. The town is the cap ...

, and also in honors

Diodorus Siculus Diodorus Siculus, or Diodorus of Sicily ( grc-gre, Διόδωρος ; 1st century BC), was an ancient Greek historian. He is known for writing the monumental universal history ''Bibliotheca historica'', in forty books, fifteen of which su ...

, a 1st-century

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

historian who wrote about

North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in ...

. The specific name is

ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

for "leathery arm", in reference to the possible

integument In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, shell, germ or rind. Etymology The term is derived from ''integumentum'', which is Latin for "a covering". In a transferred, or ...

of the animal, and also honors

Dionysius Scytobrachion Dionysius Scytobrachion ( grc, Διονύσιος ὁ Σκυτοβραχίων) (Scytobrachion meaning 'leather arm'), also known as Dionysius of Mytilene (the capital of Lesbos), was the author of a series of stories set in the region now known a ...

, a classical

mythographer Myth is a folklore genre consisting of narratives that play a fundamental role in a society, such as foundational tales or origin myths. Since "myth" is widely used to imply that a story is not objectively true, the identification of a narrat ...

who chronicled the mythical history of North Africa. The very delicate

holotype specimen A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

is the front part of a right

dentary bone In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

(the tooth-bearing front part of the lower jaw) missing the front tip and preserving six

tooth sockets Dental alveoli (singular ''alveolus'') are sockets in the jaws in which the roots of teeth are held in the alveolar process with the periodontal ligament. The lay term for dental alveoli is tooth sockets. A joint that connects the roots of the ...

with four teeth (three with

tooth crowns In dentistry, crown refers to the anatomical area of teeth, usually covered by enamel. The crown is usually visible in the mouth after developing below the gingiva The gums or gingiva (plural: ''gingivae'') consist of the mucosal tiss ...

), and is cataloged as specimen MHNM−ARG 30 at the Museum d’Histoire Naturelle de Marrakech. Assigned specimens include the much better preserved isolated teeth MHNM−ARG 31, 32, and 33, the two

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) MHNM−ARG 34 and 35, the

metatarsal 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 med ...

(a foot bone) MHNM−ARG 36, and the

femur 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 ...

(thigh bone) MHNM−ARG 37, which is crushed from front to back. While these elements were not associated with each other, and probably represent different individuals, the describers assigned them all to ''Diodorus'' based on comparison with the holotype (the isolated teeth), or on the silesaurid or

features of the bones. The latter was based on the assumption that there would only be one silesaurid present in this member of the Timezgadiouine Formation, as is probably the case for other localities where silesaurids are known.

Description

''Diodorus'' is estimated to have been around long, and has been described as being a "small" silesaurid. The holotype dentary bone of the lower jaw has a lateral ridge slightly above mid-height on its outer surface, which is well-developed at the hind end of the bone fragment, at the level of the sixth tooth position, which weakens frontwards until it disappears under the second tooth position. This lateral ridge, running parallel to the tooth socket margin, is only known from ''Diodorus'' among silesaurids, and is therefore considered an

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

(a distinguishing or diagnostic feature) of this genus. There is a row of nutrient foramina between the tooth socket margin of the dentary and the ridge on the side. As in all silesaurids except ''

Asilisaurus ''Asilisaurus'' ( ); from Swahili, ''asili'' ("ancestor" or "foundation"), and Greek, (, "lizard") is an extinct genus of silesaurid archosaur. The type species is ''Asilisaurus kongwe.'' ''Asilisaurus'' fossils were uncovered in the Manda Beds ...

'', the

Meckelian groove The Meckelian groove (or Meckel's groove, Meckelian fossa, or Meckelian foramen, or Meckelian canal) is an opening in the medial (inner) surface of the mandible (lower jaw) which exposes the Meckelian cartilage.Sacisaurus'' and ''

Silesaurus ''Silesaurus'' is a genus of silesaurid dinosauriform from the Late Triassic, of what is now Poland. Discovery Fossilized remains of ''Silesaurus'' have been found in the Keuper Claystone in Krasiejów near Opole, Silesia, Poland, which is al ...

''. The Meckelian groove does not extend in front of the second tooth position, unlike in ''Sacisaurus'' and ''Silesaurus'' where the groove extends frontwards through the dentary symphysis (where the two halves of the lower jaw connect). The Meckelian groove is distinct from that of other silesaurids in that it expands in height towards the back, and reaches 40% of the dentary's height by the fourth tooth position. The dentary is distinct in being bowed at the underside. The

roots A root is the part of a plant, generally underground, that anchors the plant body, and absorbs and stores water and nutrients. Root or roots may also refer to: Art, entertainment, and media * ''The Root'' (magazine), an online magazine focusing ...

of the four preserved teeth are firmly fused to their sockets (the ankylothecodont condition), like in all silesaurids except possibly ''

Lewisuchus ''Lewisuchus'' is a genus of archosaur that lived during the Late Triassic (early Carnian). As a silesaurid dinosauriform, it was a member of the group of reptiles most commonly considered to be the closest relatives of dinosaurs (possibly tr ...

'' and in non-

archosauriform Archosauriformes (Greek for 'ruling lizards', and Latin for 'form') is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Latest Permian (roughly 252 million years ago). It was defined by Jacques Gauthier ...

archosauromorphs Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, liz ...

, but unlike other members of Archosauria. The three preserved tooth crowns are triangular with denticles (serrations) on the front and back edges, as in all silesaurids except ''Lewisuchus'' and ''Asilisaurus'', narrow, and tilted forwards. The forwards tilt of all the frontmost teeth (at an angle of about 20 degrees from the root) is a distinct feature of ''Diodorus'', but the frontmost tooth of ''Sacisaurus'' has a similar angle. The three crowns decrease in size towards the front of the dentary (the crown height of the first tooth is about 66% of the second tooth, which is about 60% of the fourth tooth), as is also the case for ''Sacisaurus''. The assigned isolated teeth are very similar to the fourth tooth of the holotype, but more bulbous at their bases and larger overall, which indicates they were either from further back in the jaw or from a larger individual. The teeth of ''Diodorus'' have 4–5 denticles per , which is coarser than the 6–7 denticles per 5 mm of ''Silesaurus'', are proportionally broader and lack longitudinal striations. The tooth crowns are generally similar in proportions to those of ''

Technosaurus ''Technosaurus'' (meaning "Tech lizard", for Texas Tech University) is an extinct genus of Late Triassic silesaurid dinosauriform, from the Late Triassic Cooper Canyon Formation (Dockum Group) of Texas, United States. For about 20 years after ...

'' and ''Sacisaurus'', but can be distinguished from the former in lacking an accessory cusp, and from the latter in lacking a cingulum and in that the crown base is more abruptly expanded and spade-shaped. The humerus of ''Diodorus'' was elongated and rather featureless apart from the distinct ectepicondyle and entepicondyle (the projections on each side of the

condyle of the humerus The Condyle of humerus is the distal end of the humerus 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 thr ...

) that are separated by a prominent furrow at the lower side. The shaft of the humerus is very straight, and the long sides of the upper and lower ends are in the same plane when viewed from above and below. The head of the humerus is weakly developed and asymmetrical, with the inward portion expanding. The upper and lower ends of the humerus are weakly expanded in relation to the shaft, similar to ''Silesaurus'' among archosaurs on the line leading to birds. The deltopectoral crest extends extends one third of the humerus' length, but its top is located at the upper tip of the humerus similar to ''Silesaurus'', and unlike the condition in

dinosaurs Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

, where the top of the crest is about 30% down the shaft. The one known femur assigned to ''Diodorus'' measures in length. The head of the femur is triangular when seen from above, with rather straight edges as in ''Sacisaurus'' and ''Silesaurus'', instead of rounded like in most other archosaurs. As in silesaurids, but unlike all other archosaurs, there is a distinct notch below the femur's head. A straight groove runs across the upper surface of the femur's head. The anterior trochanter is small and projects upwards, and there is a distinct, blade-shaped dorsolateral trochanter next to it. A "finger-shaped" anterior trochanter, the lack of a trochanteric shelf, and a blade-like dorsolateral trochanter is also seen in ''Sacisaurus'' and ''Silesaurus''. The fourth trochanter of ''Diodorus'' is in a position similar to ''Silesaurus'' and further up the femur than in ''Sacisaurus'', though less developed than in either, is crescent-shaped, and has a sharp rim. The lower end of the femur is only slightly more expanded than the rest of the shaft, and the lower surface has a rounded depression. The crista tibiofibularis and the medial and lateral condyles are rounded on their backsides, and the side of the lateral condyle is rounded like in other dinosauriforms. The ridges that extend upwards from the crista tibiofibularis and the medial condyle extend for more than 1/4 of the femur's shaft, like in ''Sacisaurus'', ''Silesaurus'', and ''Asilisaurus''. The metatarsal is elongated and as in ''Silesaurus'' has a robust rim for attachment of

extensor muscles In anatomy, extension is a movement of a joint that increases the angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extendin ...

. It is unclear which digit it belonged to, but it was possibly the third, based on its rectangular profile when viewed from the lower end and its symmetry from side to side.

Classification

Only fragmentary specimens of non−dinosaurian dinosauromorphs (basal members of the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

that includes dinosaurs) from Argentina were recognized until the 21st century, when their taxonomic diversity, and geographic and stratigraphic range expanded. Significantly, a widespread group was first recognized upon the discovery of ''Silesaurus'' from Poland, similar features of which were later identified in new and previously discovered taxa from the Americas and Africa. Features suggested to unite this group include long necks, long limbs, quadrupedality, dentary "beaks " on the lower jaw, and leaf-shaped front teeth that indicate herbivory or omnivory. Based on these shared features, Nesbitt and colleagues named the new clade Silesauridae in 2010, as an early

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

of Dinosauria. In their 2012

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

, Kammerer, Nesbitt, & Shubin both coded the ''Diodorus'' holotype alone and the holotype and the assigned specimens together, with the results of both analyses being identical, which indicates the inclusion or exclusion of the assigned material does not alter the classification of this taxon significantly. They found ''Diodorus'' to be well-supported as a member of Silesauridae, a clade that includes taxa more closely related to ''Silesaurus'' than to dinosaurs or more basal dinosauromorph groups, such as

Lagerpetidae Lagerpetidae (; originally Lagerpetonidae) is a family of basal avemetatarsalians. Though traditionally considered the earliest-diverging dinosauromorphs (reptiles closer to dinosaurs than to pterosaurs), fossils described in 2020 suggest that ...

. They found ''Diodorus'' to be deeply nested within this group, in a clade with ''Sacisaurus'' and ''Silesaurus'', with the former as sister taxon. ''Diodorus'' and ''Sacisaurus'' share the frontwards decrease in dentary tooth size and the frontmost tooth being tilted forwards). While the Meckelian groove extends to the front of the dentary, through its beak-like tip, that of ''Diodorus'' does not even reach the front of the toothed part of the dentary, which the describers considered an

evolutionary reversal Devolution, de-evolution, or backward evolution (not to be confused with dysgenics) is the notion that species can revert to supposedly more primitive forms over time. The concept relates to the idea that evolution has a purpose (teleology) and ...

. The describers of ''Diodorus'' stated that the discovery of a silesaurid in Morocco demonstrates that the group continued to be present in Africa during the Late Triassic (the earliest known African silesaurid is ''Asilisaurus'' from the early

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

of Tanzania). While footprints had earlier indicated the presence of dinosauromorphs in the Timezgadiouine Formation, ''Diodorus'' is the first definitive silesaurid record, which supports that this group had a

cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of the world in appropriate habitats. Such a taxon, usually a species, is said to exhibit cosmopolitanism or cosmopolitism. The ext ...

in the Middle−to−Late Triassic. They suggested that basal dinosauromorphs were widespread, temporally long-ranged, and common rather than rare and restricted in time and space in Triassic fossil assemblages, and that this pattern had only been recently recognized due to specimens being misidentified as true dinosaurs and the rather low potential of these small-bodied, delicate animals being preserved. The following cladogram shows the placement of ''Diodorus'' among Silesauridae according to Martz and Small, 2019: Silesaurid distribution

Paleobiology

It is debated whether silesaurids were quadrupedal or bipedal.

Paleoenvironment

''Diodorus'' is known from the base of the Irohalene Mudstone Member (designated as t5) of the Timezgadiouine Formation in Morocco, a diverse assemblage of Triassic tetrapod animals (ancestrally four-limbed animals). While this assemblage was previously thought to be of late Carnian age based on

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictiona ...

, detailed age data is lacking for the Triassic of North Africa. As the faunal assemblage of the Timezgadiouine Formation is complex and conflicting, it may be either Carnian or

in age according to Kammerer, Nesbitt, & Shubin. The Timezgadiouine Formation is part of the

Argana Group The Argana Group is a Permian to Triassic geological group in the western High Atlas northeast of Agadir, Morocco. Sometimes known as the Argana Formation, it contains eight geological members often divided into three formations. They include the ...

, a long succession of

red bed Red beds (or redbeds) are sedimentary rocks, typically consisting of sandstone, siltstone, and shale, that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain th ...

sediments deposited in the Argana Basin. The Argana Basin is a northeast-to-southwest oriented valley extending for about 85 km (53 miles) in the western part of the High Atlas.

References

Silesaurids Late Triassic reptiles of Africa Fossils of Morocco Fossil taxa described in 2012 Taxa named by Christian F. Kammerer Taxa named by Sterling Nesbitt Taxa named by Neil Shubin {{paleo-archosaur-stub