Palæos:		Unit 400: Therapsida
The Vertebrates		300: Dinocephalia

Therapsida: Dinocephalia

SYNAPSIDA
|
Therapsida
|--Biarmosuchia
`--+--Dinocephalia
   |  |--Estemmenosuchidae
   |  |  |--Anoplosuchus
   |  |  `--+--Estemmenosuchus
   |  |     |--Molybdopygus 
   |  |     `--Zopherosuchus
   |  `--+--Anteosauria
   |     `--Tapinocephalia
   `--+--Anomodontia
      |  |--Venyukovioidea
      |  `--Dicynodontia   
      `--Theriodontia
         |--Gorgonopsia
         `--+--Therocephalia
            `--CYNODONTIA

Taxa on This Page

1. Anoplosuchus X
2. Dinocephalia X
3. Estemmenosuchidae X
4. Estemmenosuchus X
5. Molybdopygus X
6. Zopherosuchus X

Dinocephalia

Titanophoneus potens.  Late Wordian epoch.  Length 6 m.  Image © Kelly Taylor -- reproduced with permission.

A number of writers have included the dinocephalians in the suborder Anomodontia, but it is now acknowledged they constitute a separate group. The dinocephalians are divided into three main groups, the mostly carnivorous Anteosauria (which included giants up to 6 meters and more in length), and the medium to very large herbivorous estemmenosuchids and Tapinocephalia.  The tapinocephalians are again divided into two branches, the titanosuchids, which were large ponderous herbivores or omnivores, and the tapinocephalians, which were equally large and ponderous but more specialized as purely herbivores, both of which reached the size of an ox or even a rhinoceros in the larger species. The tapinocephalians also have the dubious distinction to be -- almost without dispute -- the ugliest vertebrates that nature has ever produced.  The anteosaurs clearly preyed largely on their estemmenosuchid and tapinocephalian cousins.

The Dinocephalians are an ancient group and their ancestry is not clear. It is assumed that they must have evolved during the earlier part of the Ufimian/Roadian, or even Kungurian epoch, but no trace has been found; the fauna described by Olson of this age has turned out, on reinspection, to be not therapsid but misinterpretation of caseid remains [ref. pers. communication Christian Kammerer]. Even the earliest members, the estemmenosuchids and early brithopodids of the Russian Ocher fauna, (late Roadian or early Wordian age) were already a diverse group of herbivores and carnivores.

All Dinocephalians are distinguished by the interlocking incisor (front) teeth. Correlated features are the distinctly downturned facial region, deep temporal region, and forwardly rotated suspensorium. The way the jaw mechanism works is shown in the figure.  

The later dinocephalians improved on this system by developing heels on the lingual sides of the incisor teeth which met against one another to form a crushing surface when the jaws were shut.  

The dinocephalians were originally carnivorous, as represented by the anteosaurs, but even the earliest Estemmenosuchids, and then the somewhat later titanosuchids and tapinocephalids adapted to a herbivorous life-style, replacing the big Caseid pelycosaurs as the dominant vertebrate plant eaters. In all dinocephalians the synapsid opening for attachment of jaw muscles remained relatively small, and it is assumed that the power of the bite was provided by the sheer mass of the animals' jaw and muscles. This was a less efficient system than that developed by the anomodonts and theriodonts, but it clearly worked well, because these creatures dominated the large herbivore and large carnivore niche for some millions of years.

At the end of mid-Permian time (mid or late Capitanian age) all the dinocephalians became extinct. The reason for this extinction is not clear, and the conventional explanation -- that they were out-competed by the more efficient herbivorous anomodonts and carnivorous theriodonts -- is about as persuasive as the old idea that the mammals out-competed the dinosaurs. Possibly disease, sudden climatic change, or other factors of environmental stress brought about their end. With their passing some of the most interesting prehistoric creatures this Earth has seen disappeared; they were replaced by much smaller dicynodonts and theriodonts. MAK000809.

Estemmenosuchidae

With the decline of the Kungurian and Ufimian caseids, the herbivorous Estemmenosuchidae took over the role of top herbivore. These were massive, clumsy-looking animals, with a sprawling posture, reaching the size of an adult bull, although some types were smaller.

The skull is high and massive. The creature is equipped with several bizarre set of large horns projecting both upwards and outwards, probably used for intra-specific display. There are five large teeth on the maxillae (upper jaw bone), rather short canines, and at least twenty small and uniform post-canines. Each tooth has a swollen crown and a sharp, laterally compressed at the apex. There are also numerous small teeth on the palate (vomers, palatines and pterygoids). The reduced side teeth, with a bulky body for digesting volumes of plant food, indicate a herbivorous lifestyle, despite the large canines. Vegetable matter was grasped with the strong front teeth and swallowed without chewing, as the weak and thin side teeth only served to keep food in the mouth. These animals would nevertheless have taken carrion when they could find it, as the great force exerted by the chisel-like front teeth could cut up meat quite easily.

As with the tapinocephalids of the early Capitanian epoch, a number of types are known, and it seems that, for a short time, the estemmenosuchids constituted a successful evolutionary radiation. Connections are sometimes suggested with Styracocephalus, but in the estemmenosuchids the 'horns' are situated on the frontals and directed dorsally. In Styracocephalus the 'horns' are formed by the tabular and directed posteriorly. Otherwise their features very similar to those of Styracocephalus. It is not possible to say therefore whether the relationship is one of ancestor- descendent or simply evolutionary convergence due to similar lifestyle, although difference in the bones forming the horns would suggest the latter.

The remains of Estemmenosuchus have been found in a channel flood deposit, indicating that they probably frequented lowland and marshy areas.  MAK000725.

Dinocephalia: Medium to large (1-3 m) big-bodied, short-legged "dog-faced" forms.

Range: Middle Permian to Late Permian of Russia & South Africa. 

Phylogeny: Eut herapsida: Neotherapsida + *: Estemmenosuchidae + (Anteosauria + Tapinocephalia). 

Characters: Skull usually massive, $ nares not terminal [RS01]; bone horns on maxillae or skull table; orbits small; temporal opening fairly large; some saggital crest; some with conspicuously thickened crania (head-butting?); highly integrated; no secondary palate; $ premaxilla vomerine process absent (vomer contacts body of premaxilla directly) [RS01]; $ pterygoid transverse process anterior to orbit [RS01]; $ reflected lamina of angular smooth, without ridges or fossae [RS01]; $ foramen on medial jaw, between angular and prearticular [RS01]; incisors interdigitate; canines sometimes long; cheek teeth small; tail very long; hindlimb posture somewhat upright, but forelimbs sprawl; metapodial V at least as long & robust as Mp IV [RS01]; phalangeal formula 23345 / 23333; carnivores (early) or herbivores (later). 

Links: Early Mammal-like Reptiles; Schnellbestimmung anhand von typischen Schädelmerkmalen (in German); Notes From Other Vertebrates (go down to Christian Kammerer's comments); dinosaurs- titanophoneus potens; More Titanophoneus potens; BPI Palaeontology (includes life reconstruction); The first Karoo Reptiles and their origin; Early Mammal-like Reptiles; therapsid3a; therapsid4b (Best on the Web). 

References: Rubidge & Sidor (2001) [RS01].

Image: Titanophoneus potens courtesy of mathematical.com. ATW020219.

Estemmenosuchidae: Parabradysaurus?

Range: Middle Permian (uppermost Kazanian) to Late Permian (lower Tatarian) of Russia

Phylogeny: Dinocephalia: (Anteosauria + Tapinocephalidae) + *: Anoplosuchus + (Estemmenosuchus + Molybdopygus + Zopherosuchus)

Characters: medium to large size; skull with heavy pachyostosis [BS00]; often with numerous knob-like or horn-like protuberances [BS00]; teeth on vomers [BS00]; tail short; herbivorous. 

Links: dinosaurs-estemmenosuchus uralensis; Gondwona Studios; Estemmenosuchus Printout - Enchanted Learning Software.  

References: Battail & Surkov (2000) [BS00]. ATW020522.

Anoplosuchus: A. tenuirostris Tchudinov 1968b

Range: Middle Permian (uppermost Kazanian) to Late Permian (lower Tatarian) of Russia (Ocher District)

Phylogeny: Estemmenosuchidae: (Estemmenosuchus + Molybdopygus + Zopherosuchus) + *.

Characters: medium-sized [BS00]; skull narrow; preorbital region long, low & broad; outer edge of jaw in region of canine bears weak boss; preorbital skull without excrescences or thickening [BS00] except in posterior nasal region (?); postorbital (skull?) short, weak, broad & high; incisors more or less equal in size to canines [BS00]; numerous small post-canine teeth [BS00].

Links: paleng2_0p189abs (abstract of Ivakhnenko article stating that Anoplosuchus is synonymous with Estemmenosuchus & Zopherosuchus); RepTherapS.pdf;

References: Battail & Surkov (2000) [BS00]

Note: known from an incomplete skeleton and skull plus referred skull & jaw fragments.  ATW020522, MAK000725.

Estemmenosuchus: E. uralensis Tchudinov, 1960; E. mirabilis Tchudinov, 1968.

Range: Middle Permian (uppermost Kazanian) to Late Permian (lower Tatarian) of Russia (Ocher District).

Phylogeny: Estemmenosuchidae:: Molybdopygus + Zopherosuchus + *.

Characters: bull-sized; massive skull [BS00]; rather spectacular "horns;" anterior nasal form unpaired boss on dorsal snout [BS00]; jugal & squamosal form massive lateral outgrowth (see image at right) [BS00]; long, curved incisors [BS00]; canines short & thick [BS00]; at least 20 weak marginal teeth [BS00]; note the typically herbivorous teeth in image at left. 

Links: dinosaurs-estemmenosuchus uralensis; Estemmenosuchus Printout - Enchanted Learning Software; therapsid3b. 

Note: E. uralensis is larger, with a longer skull in proportion to width.  The postorbitals & postfrontals form a pair of partially fused horn-like protuberances on the skull table just posterior to the orbits.  E. mirabilis is smaller, with a shorter skull.  The horn pair is shorter, well-separated and the horns extend more laterally.  Note that the image at right is a mirabilis.  [BS00].  

References: Battail & Surkov (2000) [BS00].  ATW020522.

Molybdopygus: (= Deuterosaurus) M. arcanus Tchudinov 1964

Range: Late Permian of Russia, Bolshoi Kitiak, Malmych, Kirov.  Lower Tatarian Substage.  

Phylogeny: Estemmenosuchidae: Estemmenosuchus + Zopherosuchus + *.

Characters: known only from pelvic bones.  Smaller than Estemmenosuchus, but perhaps more massively built [BS00]; flat facets at posterior end of acetabulum; high pubo-ischiadic symphysis. 

References: Battail & Surkov (2000) [BS00].  ATW020523

Zopherosuchus: Z. luceus Tchudinov 1983.

Range: Middle Permian (uppermost Kazanian) to Late Permian (lower Tatarian) of Russia (Ocher District).

Phylogeny: Estemmenosuchidae:: Estemmenosuchus + Molybdopygus + *.

Characters: small-bodied [BS00]; no cranial horns [BS00]; frontals & parietals particularly thick; temporal fenestrae short, but very tall [BS00]; relatively small number of postcanine teeth [BS00].

References: Battail & Surkov (2000) [BS00].  ATW020524.

checked ATW031025