The Carnian Age - 3

Erpetosuchus granti is a small (about 60 cm ion length) crocodylomorph known from four specimens from the latest Carnian Lossiemouth Sandstone Formation [Benton and Walker 2002]. A related but somewhat later (?early to mid Norian) species has more recently been found in the New Haven Formation of the Newark Supergroup, Connecticut Valley [Olsen et al 2000]. It can be assumed that these little animals had a wide distribution over much of northern Pangea at the time.
The Erpetosuchids were lightly built, fast running (cursorial) animals with a fully erect dinosaur-bird-mammal type stance. They may have been either bipedal or (as illustrated above) lightly built quadrupeds. It is difficult to say more, as only the head and the front part of the body is known from the incomplete remains. In any case, these little animals were the "greyhounds" of the Triassic. In proportions of the skull, neck and forelimbs Erpetosuchus is very similar to the later facultatively bipedal Rhaetian age sphenosuchian crocodylomorph Terrestrisuchus, as well as to the tiny ornithodiran Scleromochlus (also found at Lossiemouth), the Middle Triassic lagosuchid dinosauromorphs Lagerpeton and Marasuchus, and basal dinosaurs. All these animals represent an important element in the late Triassic terrestrial ecosystem as small active insectivores and predators of microvertebrates, and continued in this niche until the middle or late Jurassic, when they were replaced by coelurosaurian dinosaurs.

References/Links:  Jeff Poling - Fossil of crocodile with erect stance found; Benton and Walker 2002

Saltopus elginensis is an enigmatic ornithodiran known from a single partial but still fairly complete skeleton from the Lossiemouth Sandstone of Elgin, Scotland. In life, this was a gracile, long-legged cat-sized animal about 60 or 70 cm long, with jaws equipped many small sharp teeth indicating a mostly insectivorous diet (although microvertebrates were also on the menu).

The fossil has not been adequately reexamined since its discovery in 1910, and the extremely poor preservation of the specimen makes it impossible to interpret unambiguously. So where Saltopus fits on the evolutionary tree is still debatable. It may be a non/pre-dinosaurian ornithodiran, such as a lagosuchid or a pterosaur relative like Scleromochlus, or a very early theropod dinosaur (the original reference to four sacral vertebrae (source of much confusion as dinosaurs have three and more basal archosaurs two) would seem to be an error, with the animal having the normal compliment of three), perhaps a primitive ceratosaur (It is similar in proportions to small Norian and later coelophysids), which makes it more advanced than Herrerasaurus. It may even be a juvenile of a larger animal. Whatever the case, the existence of this animal and others like it shows that the Carnian undergrowth was alive with many kinds of small active archosaurs.  

References/Links:  Mickey Mortimer - What is Saltopus?;   DinoData - Saltopus; Paul 1988

Pisanosaurus is a small dinosaur, about a meter in length, known from a single partial skeleton from the Ischigualasto Formation, San Juan Province, Argentina. One of the earliest known and most primitive of the ornithischian dinosaurs (Order Ornithischia), it is usually included under the family Fabrosauridae (a mostly early Jurassic group best known from South Africa) but is too poorly known to be place there with any certainty. The Fabrosauridae in fact are something of a garbage taxon for any basal or very primitive ornithischian dinosaurs.

Recent microvertebrate collecting in the Upper Triassic Chinle Group of Texas, New Mexico and Arizona has shown that ornithischian dinosaurs were much more common and diverse during the Carnian than previously believed, with prosauropods. Carnian ornithischians of west and central equatorial and low latitude northern Pangea include a possibly carnivorous ornithischian of Chinle Otischalkian age, and a the following somewhat younger (Adamanian age - Latest Carnian) taxa: Tecovasaurus murryi (Chinle, the most widespread form); Pekinosaurus olseni, and Galtonia gibbidens (known from the Newark Supergroup but also from teeth in the Chinle) [Heckert & Lucas, 2001]. It seems that ornithischians originated during the early or middle part of the Carnian, and diversified rapidly during the late Carnian. All these animals were pretty similar; small, gracile, fast-running, and apart from the one curious exception, herbivorous.

Herrerasaurus ishigualastensis, known from the Ischigualasto Formation, San Juan Province, Argentina (Southwest Pangea), is a very primitive and early member of the theropod dinosaur clade, and the eponymous representative of the family Herrerasauridae. Since Herrerasaurus was found, other herrerasaurs have turned up or been relocated in this group. These include Staurikosaurus from the (slightly earlier?) Santa Maria Formation, Brazil, which Paul 1988 considers a more primitive animal, the Norian Chindesaurus, and the poorly known Caseosaurus, the two latter from North America. At one time it was thought that the herrerasaurs lay outside the rest of the dinosaur lineage [Benton 1990], but they were later (following publication of several papers by Sereno and Novas) considered pre-ceratosaurian theropods proper. These were all medium to large and active terrestrial carnivores, which were distinguished from the contemporary rauisuchians by their efficient bird-like digitigrade (standing on toes) stance. Herrerasaurus was one of the largest Carnian dinosaurs, with an estimated overall length of around 3.9 metres, and an adult weight of about 210 kg [Paul 1988]. Yet both early dinosaurs and pseudosuchians (Ornithosuchids, rauisuchids, and poposaurids) co-existed happily for many millions of years. It is likely that the slower and more heavily built pseudosuchians were ambush predators that fed on large or slow animals; and the more lightly built and fast-running herrerasaurs and Coelophysids were pursuit predators of small to medium-sized animals

During the Late Carnian, the megaherbivore niche was still dominated by large kanneymeriid dicynodonts, as it had been throughout almost the entire Triassic (from the Olenekian age onwards). And although by the late Carnian they were still common, they were reduced in diversity, with only one species found in each local fauna. The best known species are Placerias hesternus (= Placerias gigas) of the Chinle Formation, Arizona, and south in the Ischigualasto local fauna of Argentina, has been found the related Ischigualastia jenseni (known only from the Lower Third of the Ischigualasto Formation [Bonaparte, 1970]). both members of the placerine tribe. Placerias is also reported from Morocco (which shares a number of points of similarity with the west North America fauna), and a "large dicynodont" is described from India [Lucas 1998].

The Placerines were sturdy animals, with an overall length of about 3.5 metres; a height of around 1.3 to 1.6 metres, and a short deep skull about 55 cm long, these stocky animals were the size of a modest hippopotamus, which they vaguely resembled. They easily massed over a tonne each. Some Placerias (presumably males) had tusks which were used for intraspecific display and combat, and also for digging through the soil in search of roots and tubers, as indicated by the wear facets (worn down tooth edges). [King & Cluver 1991]

Large numbers of Placerias have been found at a single quarry, which indicates, like the Jurassic and Cretaceous sauropod dinosaurs and the Cenozoic elephants, these large herbivores lived and traveled in herds, and they must have had a huge impact on the local environment.

Even though the Carnian dicynodonts are not as abundant as the contemporary traversodontids and rhynchosaurs, or even the Ladinian dicynodonts, the three groups together characterize the herbivore dynasty of the Middle and Early late Triassic, and supported a number of large carnivorous types, such as the prestosuchids, rauisuchids, and poposaurids. These large pseudosuchians, which reached 4 to 5 meters and more in length, were the only terrestrial predators strong enough to bring down a full-grown dicynodont, and even they would have had a difficult time of it.

References/Links:
 BBC - Walking with Dinosaurs - Fact Files - Placerias
 Paleo Photos - Placerias (mounted skeleton)

One of the most common animals of the Carnian age was the large herbivorous traversodontid cynodonts of the genus Exaeretodon; known from the Gondwanan biogeographic province (Argentina, Brazil, India, and more recently [Depuydt 1998] Madagascar; with smaller and more distantly related forms from western Laurasia). These were the largest of the Traversodontidae, reaching nearly 2 meters in length, and probably weighing around 80 kilos live. They were also among the most mammalian of the group, with a mammalian hip indicating a more erect posture and limbs under the body; possibly also some steps towards coupling of locomotion and breathing [Hunt 1994-1997].

In the Ischigualasto Formation, San Juan Province, Argentina, Exaeretodon frenguellii Cabrera 1944 and the similar and comtemporary Exaeretodon argentinus Bonaparte 1962 (could these two species be sexual dimorphs?), along with the rarer and even larger Ischignathus were large, advanced herbivorous cynodonts and the most common members of the local fauna. [Bonaparte, 1970, Bonaparte, 1982] E. argentinus is not mentioned in more recent literature such as the papers by Lucas [e.g. Lucas 1998] and others, so perhaps it is a synonym of E. freguelli. In any case, these animals, like the contemporary rhynchosaurs, seem to have been abundant across Gondwana (southern Pangea), but strangely not in the north of the supercontinent, where smaller forms like Arctotraversodon plemmyridon and Boreogomphodon jeffersoni are found. E. statisticae Chaterjee is known from the Lower Maleri (early part of the Late Carnian) of India, and may be a junior synonym of E. freguelli.  

List of species:
Exaeretodon Cabrera, 1943
?E. argentinus Bonaparte, 1962 (= E. frenguellii?)
?E. vincei (Bonaparte, 1963) [Proexaeretodon Bonaparte, 1963; = E. frenguellii?]
?E. major (Huene) Barbarena, 1974 [Traversodon? major Huene, 1935-42]
E. frenguellii Cabrera, 1943
?E. statisticae Chatterjee, 1982 (= E. frenguellii?)
E. riograndensis Abdala, Barbarena & Dornelles, 2002
E. sp. Madagascar

Links: Exaeretodon frenguellii (info sheet); Triassic Gomphodonts (more info), Digimorph - Exaeretodon (University of Texas CT Facility).

Dromatherium sylvestre and Microconodon tenuirostris were tiny rat or shrew-like animals known from a few jaws and teeth from the Latest Carnian (Adamanian stage) of the Newark Supergroup of Eastern North America (North Carolina, Virginia, and Pennsylvania). Originally (during the 19th century) considered among the earliest and most primitive mammals, they were reinterpreted in the 1920s by G.G. Simpson. Their several supposedly unique mammalian features are shared by tritheledontids and other advanced cynodonts, and they are now best regarded as advanced or derived eucynodonts of uncertain affinities. [Sues 2001] A dromatherid has been reported from the Tiki Formation, India, and several problematic taxa known only from isolated teeth from the Late Triassic and Early Jurassic of Europe are also usually placed in the Dromatheridae [Luo et al 2002]

Links/References: Trevor Dykes 2001-2003 Chiniquodontoidea,

Adelobasileus cromptoni, known from a partial skull from the Latest Carnian (Adamanian) Tecovas Formation, West Texas, USA, is the most primitive and perhaps the earliest known mammal, intermediate condition between non-mammalian cynodonts and true Early Jurassic mammals. It also predates the earliest known tritylodontids and trithelodontids, unless the partial dentary called Pachygenelus milleri, from the contemporary (or earlier?) strata of the Dockum Formation, Texas [Chaterjee 1986], turns out to be a genuine trithelodontid. Gondwanadon tapani from the Tiki Formation, South Rewa Gondwana basin, Madhya Pradesh, India (?early Late Carnian). Claimed to be the earliest mammal, this specimen is based on a single tiny molar. Its attribution as a morganucodontid is very dubious, but it does seem to indicate that as early as the late Carnian there were tiny animals on the borderline between reptile and mammal scurrying through the undergrowth or in trees. The name means "Gondwana tooth". Exact systematical relationships of both these tiny animals are uncertain.

Links/References: Trevor Dykes 2001-2003 Basal Mammaliaformes, Morganucodontidae and Hadrocodium