Hallensia
| Hallensia | ||||||||||||
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Fossil of Hallensia matthesi |
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| Temporal occurrence | ||||||||||||
| Lower to Middle Eocene | ||||||||||||
| 50.7 to 44.7 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Hallensia | ||||||||||||
| Franzen & Haubold , 1986 | ||||||||||||
Hallensia is a now extinct genus from the group of equine species (Equoidea) within the odd ungulate (Perissodactyla). It is mainly known for two more or less complete skeletons from the Messel pit and the Geiseltal ; other isolated finds come from France. The animals lived in the Lower and Middle Eocene 49 to 45 million years ago. They were smaller animals thatshowedsimilarities to Propalaeotherium , but were built more compactly. A precise allocation to a specific family within the Equoidea cannot be givenfor Hallensia . In terms of dentition and skeleton construction, it shows features of both horses and Palaeotheriidae as their closest related group. Thegenus was first described in 1986, but at that time it was regarded as a representative of the extinct, ungulate-like condylar , and only later was a position within the Equoidea recognized.
features
Hallensia was a rather small representative of the early equine species, an almost complete, articulated skeleton had a head-torso length of more than 50 cm and a height in the area of the arched back of around 40 cm. In general, the representatives were characterized by a quite robust physique, which still had the arched trunk spine typical of early higher mammals . The skull was 17 to 17.5 cm long in two complete specimens and had a very slender structure. His forehead was slightly arched. What was particularly striking was the extremely small nasal space between the nasal bone and the median jawbone , which only reached roughly to the rearmost incisor . When viewed from above, the nasal bone was elongated and narrow, slightly triangular in front. It reached far forward, almost to the tip of the snout. The zygomatic arches were only weakly wedged laterally and developed slender overall. There was a distinctive crest on the parietal bones . At the occiput , the skull already protruded slightly backwards, so that it looked somewhat elongated. The eyepiece was compared to other early equine, about Propalaeotherium forward very much about over the first molars cm, reaching a diameter of 2 to 2.5. There was also a very large and deep infraorbital foramen just in front of the eye window, roughly above the last and penultimate premolars .
Two lower jaws were between 13.7 and 16.3 cm long. The symphysis was noticeably flat, the front end of the jaw was very narrow, analogous to the skull, which suggests a narrow snout. The height of the bone behind the last molar was around 4 cm, the articular branch protruded up to 8 cm. The dentition involved, as with most early equine complete tooth number of higher mammals with the following dental formula : . The incisors are not fully known, but were designed in the shape of a shovel. The canine was shaped like a dagger and raised and separated from the rear dentition by a short diastema , which could sometimes be completely absent. All molars had low crowns ( brachyodont ). The row of teeth was mostly closed, only between the two anterior premolars a brief additional diastema occurred. The chewing surfaces of the molars were marked by rounded enamel cusps , some of which formed parallel rows ( bunolophodont ). However, there were also individual smaller minor cusps between the main cusps, so that there were six cusps per tooth. The length of the molars increased towards the back, and the molars in the upper jaw became more and more trapezoidal in outline and rectangular in the lower jaw. The length of the molars varied from 0.9 to 1.1 cm.
The body skeleton has not been passed on in full, and only a few features can be recognized due to the preservation. 7 cervical, 19 thoracic, 5 lumbar and 5 sacral vertebrae of the spine are known, the exact number of caudal vertebrae is missing. The cervical spine was typically extremely short for early equines. It only reached 46% of the length of the thoracic spine (80% in today's horses). The humerus was about 11 cm long. On the forearm, the ulna, which was 12 cm long, was much stronger than the spoke , which was only 8.6 cm long, and had an extensive upper joint ( olecranon ). The femur had a pronounced, rounded third trochanter on the shaft. With a length of up to 17 cm, it was the longest bone. In contrast to the thigh bone, the shin appeared short and compressed. It was 13 cm long and was not attached to the fibula. Typically for early unpaired ungulates, the front legs ended in feet with four rays (II to V), the hind legs in feet with three (II to IV). The outermost ray of the forefoot was clearly reduced in length. The metacarpal and metatarsal bones of the strong central ray (III) were 5.2 and 5.6 cm in length, respectively. Overall, the rear foot was made stronger than the front.
Fossil finds
Finds from Hallensia are rare and limited to Central and Western Europe . The most extensive finds come from the Geiseltal southwest of Halle in Saxony-Anhalt . A complete skeleton from the area of the lower carbon, albeit severely detached from the bandage, should be emphasized. In addition to this, a good three dozen other skull and dentition fragments were found here. An almost complete skull comes from the lower mid-charcoal, a few other bits of dentition came to light from the upper mid-charcoal. The finds date to the Middle Eocene and are around 47 to 45 million years old. A nearly complete skeleton was recovered from the Messel pit near Darmstadt in Hesse . The only thing missing is the anterior part of the skull, but the bones are badly damaged by pyrite deposits . However, the find is characterized by an extraordinarily good preservation of the soft tissue . In old age it corresponds roughly to the fossil remains from the lower coal of the Geiseltal. The oldest find of Hallensia was reported from France. It is a right upper jaw from Epernay in the Paris Basin , which dates to the Lower Eocene and is therefore around 50 million years old.
Paleobiology
In its overall habit, Hallensia resembled the well-known Propalaeotherium , typical of both is the upturned spine. The tracing of the soft tissue caused by bacteria in the Messel find reproduces the entire body and points to a clumsier structure than is the case with Propalaeotherium . Food residues in the back of the body indicate that they were digested in the intestines (rectal fermenter), as in today's horses . Due to the large amount of leftover food, the location of the colon and the appendix is well traced. These correspond in shape to those of today's horses, but are smaller. Furthermore, bacterial colonies were found in this area of the body, which suggests that the food of the earliest odd-toed ungulates was processed with the help of such microorganisms. The leftover food consists of numerous plant material, mainly stem material, but few leaves. In addition, a lot of coarse clastic material could be detected, such as sand and smaller pebbles up to 8 mm in size. This suggests that Hallensia sought its food at least partially on the ground and swallowed these sediments as "bycatch".
Systematics
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Internal systematics of the Equoidea according to Remy et al. 2019
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Hallensia is a now extinct genus from the order of the odd-toed ungulates (Perissodactyla). Within this it is placed under the subordination of the Hippomorpha and the superfamily of the Equoidea , which unites today's horses (Equidae) and the extinct Palaeotheriidae . For a position in the Hippomorpha and Equoidea, the deep and backward position of the foramen opticum opposite the Tapiromorpha as another large group of odd ungulates speaks for itself. It can Hallensia currently been put in a closer family and is considered incertae sedis . It probably acts as a mediator between the two families. Hallensia connects the palaeotheria with the short, postcanine diastema that is clearly longer pronounced in the horses, with the horses again the structure of the pelvis and here especially the ischium , the design of which in the palaeotheria did not allow a fast run. In this sense, some phylogenetic analyzes, such as those from 2013 and 2019, classify Hallensia as a primitive representative of the Equoidea. Other studies see Hallensia but rather as a basal odd ungulate, which, together with Cambaytherium, belongs to a "core group" of the order.
The following types are recognized today:
The first scientific description of Hallensia was in 1986 by Jens Lorenz Franzen and Hartmut Haubold . The holotype (copy number GMH XXXVI / 285) includes an almost complete, but strongly disarticulated skeleton from the Geiseltal . In the first description, both authors referred the genus to the condylarthra , primitive ungulates . Only later was it recognized that Hallensia clearly belongs to the unpaired ungulates due to the complete reduction of the first forefoot ray and the saddle-shaped lower joint end of the ankle bone , features that do not occur in the condylarthra. Already in 1977 Horst Werner Matthes had referred two upper jaw fragments from the Geiseltal to Propachynolophus within the Equoidea, but without giving reasons. The generic name Hallensia refers to the city of Halle in Saxony-Anhalt , near which the Geiseltal is located and where the Geiseltal collection is kept.
Individual evidence
- ↑ a b c d e f Jens Lorenz Franzen and Hartmut Haubold: A new Condylarthre and a Tillodont animal (Mammalia) from the Middle Eocene of the Geiseltal. Palaeovertebrata 16 (1), 1986, pp. 35-53
- ↑ a b c d e f g h Jens Lorenz Franzen: Hallensia (Mammalia, Perissodactyla) from Messel and the Paris basin as well as supplements from the Geiseltal. Bulletin de L'Institut Royal des Sciences Naturelles de Belgique 60, 1990, pp. 175-201
- ^ A b Jean A. Remy, Gabriel Krasovec, Éric Lopez, Bernard Marandat and Fabrice Lihoreau: The Palaeotheriidae (Equoidea, Perissodactyla, Mammalia) from the Eocene fauna of Aumelas (Hérault department, France). Geobios 41 (13), 2019, pp. 525-585, doi: 10.5252 / geodiversitas2019v41a13
- ↑ David J. Froehlich: Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla). Zoological Journal of the Linnean Society 134, 2002, pp. 141-256
- ↑ Laure Danilo, Jean A. Remy, Monique Vianey-Liaud, Bernard Marandat, Jean Sudre and Fabrice Lihoreau: A New Eocene Locality in Southern France Sheds Light on the Basal Radiation of Palaeotheriidae (Mammalia, Perissodactyla, Equoidea) Journal of Vertebrate Paleontology 33 (1), 2013, pp. 195-215
- ↑ Sunil Bajpai, Vivesh Kapur, JGM Thewissen, Debasis P. Das and BN Tiwari: New Early Eocene cambaythere (Perissodactyla, Mammalia) from the Vastan Lignite Mine (Gujarat, India) and an evaluation of cambaythere relationships. Journal of the Palaeontological Society of India 51 (1), 2006, pp. 101-110
- ↑ Lisa Noelle Cooper, Erik R. Seiffert, Mark Clementz, Sandra I. Madar, Sunil Bajpai, S. Taseer Hussain and JGM Thewissen: Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls. PLoS ONE 9 (10), 2014, p. E109232
- ↑ Horst Werner Matthes: The equids from the Eocene of the Geiseltal. In: Horst Werner Matthes and Burchard Thaler (eds.): Eocene vertebrates of the Geiseltal. Martin Luther University Halle-Wittenberg Scientific articles 1977/2 (P 5), Halle (Saale), 1977, pp. 5–39