Eoconstrictor barnesi, Palci & Onarv & Lee & Smith & Wings & Márton & Georgalis, 2024

Palci, Alessandro, Onary, Silvio, Lee, Michael S. Y., Smith, Krister T., Wings, Oliver, Rabi, Márton & Georgalis, Georgios L., 2024, A new booid snake from the Eocene (Lutetian) Konservat-Lagerstätte of Geiseltal, Germany, and a new phylogenetic analysis of Booidea, Zoological Journal of the Linnean Society 202 (2), pp. 1-27 : 4-16

Eoconstrictor barnesi sp.nov.

( Figs 2–1 0, Supporting Information, File S1: Figs S1 , S 2 )

Zoobank registration: This published work and the nomenclatural act it contains have been registered in ZooBank, the official registry of zoological nomenclature for the International Code of Zoological Nomenclature (ICZN). The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix ‘https://zoobank.org/’. The LSID for this publication is: urn:lsid:zoobank.org:pub:7EA0164B-217B-49AD-88FC-20F231060251 , while the LSID for the new species Eoconstrictor barnesi is: urn:lsid:zoobank.org:act:75DD1A6B-57F4-4DFF-9883-E7A684294FFF

Etymology: Species epithet honouring Ben Barnes, who pioneered palaeontological excavations and research in the brown coal deposits of Geiseltal in the 1920s, as part of his Ph.D. studies at the Geological Institute of Halle (Saale).

Holotype: GMH XXXVIII-20-1964 , a partial skull and partially disarticulated skeleton missing only the most anterior precloacal region, the cloacal region, and most of the tail ( Figs 2–5 , Supporting Information, File S1: Fig. S1 ).

Paratype: GMH LIX-3-1992 , a moderately complete and only slightly disarticulated skull and skeleton preserving the anterior half of the body ( Figs 6–10 , Supporting Information, File S1: Fig. S2 ) .

Type locality and age: The Konservat-Lagerstätte of Geiseltal , located about 30 km west of Leipzig and 20 km south-east of Halle, in the state of Saxony-Anhalt, Germany ( Barnes 1927, Krumbiegel et al. 1983). The fossils were recovered from fossil sites within coal mines identified by Roman numerals (e.g. LIX, XXXVIII). Both fossil specimens come from fossil sites in the upper middle coal seam (obere Mittelkohle). The age of the deposits is broadly estimated as late early or middle Eocene (~Lutetian, i.e. anywhere between 41 and 48 Mya) ( Georgalis et al. 2021).

Diagnosis: Eoconstrictor barnesi sp. nov. can be distinguished from E. fischeri based on the presence of a single labial foramen in the maxilla (four in E. fischeri ), the different position of the mental foramen, which is located ventral to the 4 th tooth position (ventral to the 5 th tooth position in E. fischeri ), and based on the lateral offset of the mandibular cotyle relative to the rest of the compound bone (offset absent in E. fischeri ). Eoconstrictor barnesi shares the presence of a single labial foramen in the maxilla with E. spinifer , but can be distinguished from the latter based on: its more elongated maxilla (length/height ratio between 7.5 and 7.9 vs. a ratio of ~ 4.68 in E. spinifer ; the maxilla of E. spinifer is slightly damaged posteriorly, but based on its posterior tapering no more than two tooth positions are missing); a quadrate ramus of the pterygoid that is gently curved laterally (forming a distinct ~120° angle in E. spinifer ); the presence of a median tubercle on the zygosphene (absent in E. spinifer , at least in the anterior precloacal vertebrae, more posterior vertebrae are unknown in that species); an almost straight anterior margin of the zygosphene (excluding lateral projections) [crenate sensu Auffenberg (1963) in E. spinifer ]; and presence of prezygapophyseal accessory processes throughout the precloacal vertebral column (absent at least in the anterior precloacal vertebrae in E. spinifer ). Eoconstrictor barnesi differs from both E. fischeri and E. spinifer in the presence of small paracotylar foramina on at least some of its vertebrae and in the anterior margin of the foramen for the exit of the mandibular branch of the trigeminal (V3), which is gently rounded instead of sharply pointed. Although E. fischeri and E. spinifer share a ventromedian crest on the basioccipital ( Scanferla and Smith 2020a, Georgalis et al. 2021), this element is currently unknown in E. barnesi .

Description

Cranial material of GMH XXXVIII-20-1964 (holotype)

Based on the relative length of the lower jaw, the skull of this specimen is about 35% larger than that of the paratype ( GMH LIX-3-1992 ) but unfortunately far less complete ( Figs 2B , 3 ). The only bones that are present and not too badly crushed are the frontals, parietal, left jugal, right supratemporal, right maxilla, left palatine and pterygoid, most of the left lower jaw (missing only the angular), and the right dentary.

The frontals are fairly well preserved, except ventrally, where the descending flanges and medial pillars are broken off ( Fig. 4A–D ). However, a portion of the medial frontal pillars is still preserved dorsally, indicating that these were present. In dorsal view each frontal has an almost semicircular outline, with a distinct lateral flange above the orbit. In lateral view, the frontals show distinct articular surfaces for the prefrontals and the parietal, and the descending flanges, although partially damaged, were clearly deeper posteriorly.

Unlike the paratype, this specimen also preserves the ventral portion of the left jugal (sensu Palci and Caldwell 2013). The dorsal part that articulated between the frontal and the parietal is missing ( Figs 3 , 4E–F ). The preserved part of the element has a claw-shaped profile, with a broad dorsal end (incomplete) and a tapering descending ramus that is recurved posteriorly. The element closely resembles the ventral half of the jugal in E. fischeri SMF-ME 11 398.

The right supratemporal is very similar to that of the paratype, has the same dorsomedial curvature, expanded and gently rounded anterior end, and thick posterior end bearing a broad facet for articulation with the quadrate ( Fig. 4G ).

The parietal is nearly complete and very robust ( Fig. 4H–K ). Compared to the parietal of the paratype it is relatively broader anteriorly, and more triangular in dorsal view. A distinct mid-sagittal crest is present on the posterior half of this bone and is replaced anteriorly by a round crest that merges into a subtriangular mound just posterior to the frontoparietal suture. The frontoparietal suture appears straighter in the holotype compared to the paratype, where it is clearly U-shaped (i.e. distinctly concave anteriorly). This difference is unlikely to be an artefact of poor preservation of the anterior margin of the parietal, since the only gently curved posterior margin of the frontals matches the anterior margin of the parietal, indicating that this is the genuine morphology present in the holotype.

The right maxilla is quite robust but still relatively elongate (length to height ratio = 7.5). Its ventral margin is straight and bears 17 tooth positions, whereas the dorsal margin has a distinctive sigmoidal curvature in lateral view ( Fig. 4L–O ), which is absentintheparatypeGMHLIX-3-1992(notethatthissigmoidal curvature is not the same as that observed in Messelopythonidae, where the curvature affects the lateral margin of the maxilla and is observed in dorsal view; Smith and Scanferla 2022). However, as in the paratype, the maxilla of GMH XXXVIII-20-1964 also bears an anterior superior alveolar foramen that is located dorsal to the third maxillary tooth position, and has two foramina for the entry of the maxillary division of the trigeminal nerve (V2). The main, larger entrance of the trigeminal nerve in the maxilla is located on the medial end of the palatine process, whereas a foramen for a secondary smaller branch is located just posterior to this process, near its base. The palatine process is quadrangular in shape and anteromedially long. As in the paratype, the maxilla of GMH XXXVIII-20-1964 also has a thin medial crest running along the posteromedial margin, where this bone would articulate with the ectopterygoid. In dorsal view the maxilla is relatively straight posteriorly, and gently curved medially in the anterior region.

The left pterygoid is relatively well preserved and only lacks the distal half of the quadrate ramus and a small fragment just posterior to the dentigerous portion ( Fig. 4P–S ). The dentigerous ramus preserves 10 tooth positions and has a concave medial margin. An additional tooth may have been present at the end of the dentigerous ramus, where the bone is damaged.The pterygoid is broadest at the level of the ectopterygoid process, which is quite robust and terminates in a broad sub-elliptical facet for articulation with the ectopterygoid. The longitudinal axis of this facet is tilted anterodorsally. On the opposite side of the ectopterygoid process, the pterygoid expands into a broad rounded flange (basipterygoid flange). The quadrate ramus is relatively deep, at least anteriorly where it is preserved, and bears a deep medial longitudinal groove for the m. protractor pterygoidei.

The left palatine bears six tooth positions and a distinct maxillary process posterolaterally ( Fig.4T–W ). This process is short and square in shape, and slightly damaged distally. The choanal process lies on the opposite side, and appears to be very short. There is the possibility that the process may be broken off distally, but its similarity to the same process in the paratype suggests that this may in fact be the actual morphology of the bone. A distinct ridge runs dorsally along the anteromedial edge of the choanal process and merges anteriorly with the dorsal surface of the dentigerous process of the palatine.A distinct concave facet for a tongue-in-groove articulation with the pterygoid is visible at the posterior end of the palatine in ventral view. In medial and lateral views, the palatine is deeper at mid-length and its dorsal margin slopes gently anteriorly and posteriorly. There is no foramen for the passage of a branch of the trigeminal nerve. This palatine is overall very similar to an isolated palatine (YPM-VPPU 12281) from the Phosphorites du Quercy, France, figured in Georgalis et al. (2021: fig. 105).

Lower jaw of GMH XXXVIII-20-1964 (holotype)

The lower jaw of this specimen is reasonably complete, missing only the angular ( Fig. 5 ). The left dentary is the better preserved of the two elements ( Figs 3B , 5A–C ). It is fairly robust, slightly arched in lateral view and mostly straight in dorsal view, except towards its anterior end, where it bends medially to a small degree. A relatively small mental foramen is located ventral to the fourth tooth position. There is a distinct posterodorsal ramus, deeper and twice the length of the posteroventral ramus. The two rami are separated by a deep notch where the surangular process of the compound bone articulates. The Meckelian groove is shallow, runs along the ventral margin of the dentary and extends anteriorly to its far end. The dentary bears 18 tooth positions.

The compound bone ( Fig. 5E–G ) is slightly longer than the dentary and bears a prominent rounded coronoid process with an anterior margin that forms almost a 90° angle with the straight dorsal margin of the surangular process. At the base of the coronoid process, where this meets the surangular process, lies the anterior surangular foramen. A tall surangular crest slopes posteroventrally from the coronoid process and delimits the adductor fossa laterally. The prearticular crest is somewhat damaged, but appears to be much lower than the surangular crest. Posteriorly, the mandibular cotyle is delimited anteriorly by a distinct transverse crest, which laterally merges with the crest for the insertion of the m. adductor externus superficialis. This latter crest slopes anteroventrally from its position near the cotyle until it approaches the ventral margin of the compound bone halfway toward the coronoid process, then gently rises again until it reaches a point ventral to the coronoid process.

The left splenial is preserved and appears to be missing only its most posterodorsal portion ( Fig. 5D, H ). It is an elongate, subtriangular element, with a distinct longitudinal medial keel that fits into the Meckelian groove. A foramen for the anterior intermandibularis nerve is only partially preserved, the portion of the bone framing the foramen dorsally being lost due to breakage. The articular surface for the angular is only partially preserved (dorsal portion missing).

The left coronoid is complete, and has a distinct hockeystick shape, with a strap-like ascending process expanding anteroventrally into a broader, mediolaterally flat anteroventral portion ( Fig. 5I, J ). The angle between the posterior ascending ramus and the horizontal portion is about 120°.

Postcranial material of GMH XXXVIII-20-1964 (holotype) The postcranial skeleton of this specimen is partially disarticulated into a series of segments, but a large part of the body is preserved, with the exception of the most anterior precloacal, the cloacal, and most of the caudal regions. Only about 10 distal caudal vertebrae remain ( Fig. 2 ; Supporting Information, File S1: Fig. S1 ). This snake has at least 189 vertebrae preserved, but if we consider that the most anterior elements, the cloacal region, and most of the tail are missing (and possibly also the posterior end of the precloacal series), then the total number of vertebrae must have been much higher. In fact, the number of precloacal vertebrae in specimens of E. fischeri varies between 246 and 303 (see Remarks above), so it is plausible that E. barnesi had a similar number, with some variability among individuals.

The average centrum length of the largest vertebrae in GMH XXXVIII-20-1964 is 12.8 mm, and the vaulting ratio (sensu Georgalis et al. 2021) is 0.33 (averages from 4 among the largest mid-trunk vertebrae).

The overall vertebral morphology of this specimen is mostly consistent with that observed in members of Boidae (see Szyndlar and Georgalis 2023). The anterior trunk vertebrae have distinct hypapophyses that decrease in height posteriorly and eventually turn into low but distinct haemal keels on the mid-trunk vertebrae. Posteriorly in the trunk region, the haemal keel grades into a gently rounded surface with a small posteroventral tubercle. The most posterior precloacal vertebrae have a very narrow, mediolaterally compressed, mid-sagittal portion of the centrum that is delimited laterally by deep subcentral fossae. There are only 10 posterior caudal vertebrae that can be confidently identified, four preserved in dorsal view and six in left lateral view ( Fig. 2 ; Supporting Information, File S1: Fig. S1 ). These vertebrae are anteroposteriorly elongate, bear low neural spines, small but distinct prezygapophyseal accessory processes, and well-developed subtriangular haemapophyses that point posteroventrally.

All vertebrae possess a pair of small subcentral foramina, at least in all those where this feature can be ascertained. The neural spines of the mid-trunk vertebrae are trapezoidal in lateral view, dorsally flat and with an anterior edge that is well posterior to the zygosphene roof. Posteriorly they slightly overhang the condyle, which is robust and hemispherical and otherwise exposed in dorsal view in disarticulated vertebrae. Prezygapophyseal accessory processes can be observed in all of the preserved regions of the body. Parasagittal ridges sensu Hsiou et al. (2014) are present on the most robust mid-trunk vertebrae, and at their posterior end sometimes is a small, rounded tubercle, likely marking the insertion of a tendon from the transversospinalis muscle complex.

The zygosphene on mid-trunk vertebrae is relatively thin (width to height ratio = 3.2, where width is measured between the dorsolateral corners of the zygosphene and height is measured in the middle of the zygosphene) and bears a median tubercle. The median tubercle is subtriangular in dorsal view and dorsoventrally thin (lamellar). The anterior margin of the zygosphene is almost straight (excluding lateral projections).

Based on microCT scan images, paracotylar foramina appear to be present on at least some of the vertebrae, but due to the small size of the foramina and the numerous fractures affecting most of the vertebrae it is unclear how frequent this feature is across the vertebral column. Note that paracotylar foramina are present in some (but not all) members of Boidae (see Szyndlar and Georgalis 2023).

The ribs are distinctly curved, with a posterodorsal tubercle and a small foramen on the shaft distal to the articular head.

Cranial material of GMH LIX-3-1992 (paratype)

The skull of this specimen is well preserved albeit not complete ( Fig. 6B ). Most bones could be segmented from the microCT scan data and visualized digitally in three dimensions ( Figs 7 , 8 ). The premaxilla, basioccipital, supraoccipital, otoccipitals, parabasisphenoid, right prootic, vomers, septomaxillae, right maxilla, and right palatine are absent or too fragmentary to be digitally isolated.

Both nasals are partially preserved in this specimen ( Fig. 8A–C ). The dorsal horizontal lamina is best preserved in the right nasal and has a triangular shape. The descending flange of the nasals is deeper anteroventrally. There is no indication of a process that may have contacted the frontals posteroventrally, and the contact must have been exclusively posterodorsal.

Both prefrontals are preserved ( Fig. 7 ), but the left element is somewhat better preserved ( Fig. 8D–F ). The prefrontal bears a broad subtriangular lateral lamina, which extends dorsally into a tongue-shaped dorsomedial lappet. The well-developed medial and lateral foot processes delimit a lacrimal foramen that is open ventrally.

Both frontals are present in this specimen, and preserved only slightly offset relative to one another ( Fig. 8G–K ). In dorsal view they have a subrectangular to trapezoidal outline with a flat dorsal surface. Anteromedially they bear a protruding process for articulation with the nasals. Ventrally the frontals are in contact to fully enclose the space for the olfactory bulbs. Distinct frontal medial pillars are present and meet the lateral flanges to fully enclose the olfactory tracts ( Fig. 8I ). In lateral view articular facets for the prefrontals and parietal are visible anteriorly and posterodorsally, respectively. The frontals are much deeper posteriorly, where they articulated with the missing parabasisphenoid.

The parietal is very well preserved ( Fig. 8L–O ). Anteriorly it bears a U-shaped sutural margin for the frontals and has greatly expanded anterolateral processes for articulation with the jugals (sensu Palci and Caldwell 2013), which unfortunately are not preserved in this specimen (note that there is some disagreement about the presence of jugals in modern snakes, with the elements in this position behind the orbit interpreted as postfrontals by Zaher et al. (2023); however, see Segall et al. (2023). In dorsal view the parietal tapers posteriorly forming an almost triangular outline. A distinct mid-sagittal crest is present on the dorsal surface and extends along the posterior half of the bone. In the anterior half the crest is replaced by a low ridge, which appears to extend anteriorly up to the fronto-parietal suture; however, this could be artifactual because the feature is not observed in the holotype (GMH XXXVIII-20-1964) and the anterior region of the parietal presents some fractures.

Both left and right supratemporals are preserved, with the former in slightly better condition ( Fig. 8P, Q ). In dorsal view the supratemporals are slightly curved, with the concavity facing dorsomedially. The supratemporals are flattened and expanded anteriorly, where they articulate with the prootic and parietal, and taper and thicken posteriorly. The anterior margin of the better preserved supratemporal is gently rounded. A distinct broad facet for articulation with the dorsal condyle of the quadrate is present posterolaterally.

The left prootic is fairly well preserved ( Fig. 8R ). This bone shows the two openings for the exit of the maxillary (V2) and mandibular (V3) divisions of the trigeminal nerve, separated by a laterosphenoid ossification (‘ophidiosphenoid’ sensu Gauthier et al. 2012). The opening for cranial nerve V3 has a rounded anterior margin, unlike that of E. spinifer and E. fischeri , where the margin of the foramen is pointed anteriorly ( Georgalis et al. 2021). The opening for the maxillary branch is not closed by the prootic anteriorly but by the parietal. A foramen for the exit of the hyomandibular branch of the facial nerve (cranial nerve VII) is visible just posterior to the exit of the mandibular branch of the trigeminal. Just ventral to this exit is a foramen for the palatine branch of the facial nerve. Foramina for the exit and re-entry of the nerve that innervates the constrictor internus dorsalis muscle complex (‘cid nerve’ of Rieppel 1979) are visible along the anteroventral margin of the prootic. This margin slopes anterodorsally and forms the sutural contact with the missing parabasisphenoid. Posteroventrally the margin of the prootic slopes at a 45° angle and dorsally forms the anterior margin of the fenestra ovalis in a distinct crista prootica (part of the crista circumfenestralis). The dorsal margin of the prootic is subhorizontal and posterodorsally a shallow excavation marks the articular surface for the supratemporal.

Both left and right quadrates are preserved ( Fig. 7 ), but the left quadrate is fractured at the middle of the shaft, and the two halves are slightly displaced relative to one another. The right quadrate is preserved in much better condition ( Fig. 8S–T ). In lateral view, the right quadrate has a narrow, subtriangular outline, with a straight anterior margin and a short dorsal margin that slants posteroventrally. In posterior view the bone is constricted mediolaterally just above the ventral condyle, which is distinctly expanded and has a saddle-shaped articular surface for the compound bone. There is no clear indication of the presence of a stylohyal process, but this could be because of poor preservation and/or scan resolution.

The left maxilla is well preserved ( Fig. 8U–X ). It is an elongate bone (length to height ratio = 7.9) bearing 16 tooth positions, but only seven teeth are preserved in position. There is no facial process, and the maxilla simply increases in depth anteriorly quite gently. In dorsal view an anterior superior alveolar foramen is clearly visible above the third tooth position. Three distinct foramina are present medial, anterior, and posterior to the palatine process. The anterior foramen (variably present in snakes) is here interpreted as the exit of a nerve and/or blood vessel, whereas the other two foramina are for the entry in the maxilla of branches of the maxillary division of the trigeminal nerve (cranial nerve V2). The palatine process is almost triangular in dorsal view, with a long anteromedial edge. Laterally the maxilla bears a single labial foramen located above the fourth tooth position. The ventral margin of the maxilla is straight. In dorsal and ventral views, the anterior end of the maxilla is gently bowed medially. There is no distinct ectopterygoid process, but a thin medial shelf extends along the posterior quarter of the bone.

Both palatines are preserved, but the right element is very badly crushed and could not be segmented. The left palatine, on the other hand, is nearly complete ( Fig. 8Y, Z , A’). The palatine lacks a foramen for the suborbital branch of the maxillary division of the trigeminal nerve and appears to have a short and thin choanal process. This could be due to poor preservation, and part of the process may be missing, but the same condition is also observed in the holotype. The anterior edge of the choanal process merges with the dorsal surface of the palatine along a thin crest. The maxillary process is complete, subrectangular in dorsal view, and slightly bent posterolaterally. There are six tooth positions. In lateral view the palatine is deeper at the level of the maxillary process, and its dorsal margin slopes down anteriorly and posteriorly from that point.

The ectopterygoid could be identified only on the left side ( Fig. 8 B’). It is a flat, V-shaped bone, with distinct medial and lateral processes for articulation with the maxilla. The medial process is much broader than the lateral one and convex in shape. The notch separating the two processes is likely artifactual. The posterior end of the bone is damaged and a surface for articulation with the pterygoid cannot be recognized.

Although both pterygoids are preserved, they lie on top of each other, which complicates the interpretation of their morphology ( Fig. 8 C’). The right pterygoid is the better preserved of the two. While an accurate tooth count is difficult to obtain on the right pterygoid due to the numerous fractures in this element, 11 tooth positions can be identified on the left pterygoid. The dentigerous portion is fairly straight, whereas the quadrate ramus arches posterolaterally, is blade-like in shape and has a distinct longitudinal groove for the attachment of the musculus (m.) protractor pterygoidei. A distinct and stout ectopterygoid process is present lateral to the posterior half of the tooth row; this process has a broad medial base and tapers into a laterally facing sub-elliptical articular facet for the ectopterygoid.

Lower jaw of GMH LIX-3-1992 (paratype)

The left lower jaw of this specimen is very well preserved ( Figs 6 , 7 ). The left dentary ( Fig. 9A–C ) is a robust element that bears 17 tooth positions, with 11 teeth still in place. In dorsal view this bone is broader posteriorly than anteriorly and is gently curved mediolaterally. A single mental foramen is present ventral to the fourth tooth position. The posterodorsal ramus of the dentary is deeper and about twice the length of the posteroventral ramus. In medial view, a shallow Meckelian groove extends all the way from the posterior notch between posterodorsal and posteroventral rami to the anterior end of the dentary. A medial subdental shelf is absent.

The compound bone ( Fig. 9D–F ) is slightly longer than the dentary and bears a distinct surangular process that fits between the posterodorsal and posteroventral rami of the latter bone. The dorsal margin of the surangular process slopes posterodorsally into a distinct coronoid process. Anteroventral to this process, in lateral view, an anterior surangular foramen is visible. The adductor fossa is deep, well defined, and bordered medially and laterallybytheprearticularandsurangularcrests, respectively.These crests are subequal in height. The mandibular cotyle is slightly offset laterally relative to the rest of the compound bone, because of a gentle bend in the posterior quarter of this bone (this offset is absent in E. fischeri , where the cotyle is in line with the main body of the compound). A distinct mediolateral crest marks the anterior margin of the mandibular cotyle. There is effectively no retroarticular process, but a blunt ending of the compound posterior to the cotyle. The ventral margin of the compound bone is relatively straight, with only a gentle sigmoidal curvature. Along the ventrolateral margin of the compound bone is a longitudinal crest, presumably for the insertion of the m. adductor externus superficialis ( Fig. 9E ). This crest starts anteriorly in the middle of the ventral margin of the compound and extends posteriorly up to the anterior margin of the mandibular cotyle.

The splenial and angular are not preserved on the left side, but fortunately their right counterparts are ( Fig. 9G–H ). The right angular is complete, while the right splenial is missing the most anterior portion, but is preserved well enough that most details are visible. The intramandibular joint is clearly visible between the angular and the splenial, with a convex surface on the former fitting into a concave facet on the latter. Both elements are subtriangular, although the angular is much deeper at mid-length and slightly longer anteroposteriorly. A foramen for the exit of a branch of the intermandibularis nerve is visible on each element (i.e. anterior and posterior mylohyoid foramina).

The left coronoid is well preserved, although a small portion of its anteroventral end may be missing due to breakage ( Fig. 9I, J ). This element is comma shaped and strap like and articulates with the medial side of the well-developed coronoid process on the compound. Both the coronoid bone and the coronoid process of the compound are subequal in height when articulated.

Postcranial material of GMH LIX-3-1992 (paratype)

The postcranium of this specimen is preserved almost in articulation, with very little distortion and displacement ( Fig. 6A ). Only the cloacal and caudal regions cannot be identified. There are at least 113 preserved precloacal vertebrae. The largest mid-trunk vertebrae are 10.8 mm long (average centrum length of four among the largest mid-trunk vertebrae).

As in the holotype described above, the vertebral morphology of the paratype is consistent with that of Boidae (see Szyndlar and Georgalis 2023). The anterior precloacals have long and slender hypapophyses, strongly projecting posteriorly, and equally long neural spines ( Fig. 10 ). Their synapophyses project ventrally below the ventral margin of the small and subcircular cotyle. The mid-trunk vertebrae ( Fig. 10F–J ) lack hypapophyses, but have a distinct mid-sagittal keel; the midventral keel disappears in the most posterior precloacals ( Fig. 6C ). The ‘vaulting ratio’ (sensu Georgalis et al. 2021) of the two segmented vertebrae is 0.55 for the anterior precloacal ( Fig. 10A–E ) and 0.32 for the mid-trunk vertebra ( Fig. 10F–J ). The centra are robust, subtriangular in shape, and bear a pair of small subcentral foramina, features that are similar to those of other booids. The condyles are robust and hemispherical, exposed in dorsal view in disarticulated vertebrae. The neural spines are anteroposteriorly short with the anterior edge well posterior to the zygosphene roof. In lateral view the neural spines are trapezoidal, with a slanting anterior margin and a straight dorsal margin. Parasagittal ridges (sensu Hsiou et al. 2014) are present on the most robust mid-trunk vertebrae. Distinct small prezygapophyseal accessory processes are consistently present on all precloacal vertebrae. In dorsal view the anterior margin of the zygosphene is almost straight (excluding lateral projections) and is marked by the presence of a distinct sub-triangular median tubercle. The tubercle is broad mediolaterally at its base, but fairly thin dorsoventrally (lamellar tubercle sensu Georgalis et al. 2021). The zygosphene of the mid-trunk vertebrae is relatively thin (width to height ratio = 3.5). The two vertebrae that were segmented both have small paracotylar foramina (Supporting Information, File S1: Fig. S2 ).

The ribs are typical for alethinophidians, well curved, with a posterodorsal tubercle and a small foramen on the shaft just distal to the articular head.

Figures

Figure 1. Map of Germany, with close-up on the locality of Geiseltal, in Saxony-Anhalt.The stars mark the two fossil sites that yielded GMH XXXVIII-20-1964 and GMH LIX-3-1992.

Figure 2. Eoconstrictor barnesi, GMH XXXVIII-20-1964, holotype. A, View of the specimen as preserved, insets show clusters of vertebrae that are preserved on the same slab but a few centimetres away from the rest of the body; (B) close-up of the skull in dorsal view and disarticulated left lower jaw in lateral view; (C) close-up of three mid-trunk vertebrae in ventral view; (D) close-up of two posterior trunk vertebrae in ventral view; (E) close-up of four mid-trunk vertebrae in left lateral view; (F) close-up of four mid-trunk vertebrae in dorsal view.

Figure 3. Eoconstrictor barnesi, GMH XXXVIII-20-1964, holotype, digital renderings of the segmented skull. A, skull in dorsal view and disarticulated left lower jaw in lateral view.B, skull in ventral view and disarticulated left lower jaw in medial view. Abbreviations: c, coronoid; co, compound; d, dentary; f, frontal; j, fragment of jugal?; ma, maxilla; p, parietal; pa, palatine; pt, pterygoid; sp, splenial; st, supratemporal.

Figure 4. Eoconstrictor barnesi, GMH XXXVIII-20-1964, holotype, digital renderings of the segmented skull bones.A–D, frontals in dorsal (A), ventral (B), anterior (C), and left lateral (D) view; E–F, possible fragment of left jugal in lateral (E) and medial (F) view; G, right supratemporal in lateral view; H–K, parietal in dorsal (H), ventral (I), left lateral (J), and anterior (K) view; L–O, right maxilla in dorsal (L), lateral (M), medial (N), and ventral (O) view; P–S, left pterygoid in dorsal (P), ventral (Q), lateral (R), and medial (S) view; T–W, left palatine in dorsal (T), ventral (U), lateral (V), and medial (W) view.Abbreviations: asaf, anterior superior alveolar foramen; bv, blood vessel; chp, choanal process; ep, ectopterygoid process of pterygoid; flf, frontal lateral flange; fmp, frontals median pillars; malf, maxillary labial foramen; mp, maxillary process; mgqr, medial groove on quadrate ramus; mV2, maxillary foramen for maxillary branch of trigeminal nerve (V2); mV2a, accessory foramen for maxillary branch of trigeminal nerve (V2); pmc, parietal midsagittal crest; pmmc, posteromedial maxillary crest; pp, palatine process of maxilla; mV2, maxillary foramen for maxillary branch of trigeminal nerve (V2); qr, quadrate ramus of pterygoid.

Figure 5. Eoconstrictor barnesi, GMH XXXVIII-20-1964, holotype, digital renderings of the segmented lower jaw bones.A–C, left dentary in dorsal (A), lateral (B), and medial (C) view; (D) left dentary in medial view with associated splenial in articulation; (E–G) left compound bone in dorsal (E), lateral (F), and medial (G) view; (H) splenial in medial view; (I–J) left coronoid in medial (I) and lateral (J) view. Abbreviations:aesc, crest for attachment of adductor externus superficialis muscle on compound bone; af, adductor fossa; asf, anterior surangular foramen; cp, coronoid process; pdp, posterodorsal dentary process; mc, mandibular condyle; mf, mental foramen; mg, Meckelian groove; sac, surangular crest; sap, surangular process; sp, splenial.

Figure 6. Eoconstrictor barnesi, GMH LIX-3-1992, paratype.A, View of the specimen as preserved; (B) close-up of the skull in left lateral view; (C) close-up of three precloacal vertebrae in ventral view; (D) close-up of five precloacal vertebrae in left dorsolateral and dorsal views.

Figure 7. Eoconstrictor barnesi, GMH LIX-3-1992, paratype, digital renderings of the segmented skull.A, skull in left lateral view; (B) skull in dorsal view; (C) skull in right ventrolateral view.Abbreviations:a, angular; c, coronoid; co, compound; d, dentary; ec, ectopterygoid; f, frontal; ma, maxilla; n, nasal; p, parietal; pa, palatine; pf, prefrontal; pr, prootic; pt, pterygoid; q, quadrate; sp, splenial; st, supratemporal.

Figure 8. Eoconstrictor barnesi, GMH LIX-3-1992, paratype, digital renderings of the segmented skull bones. A–C, nasals in dorsal (A), lateral (B), and anterior (C) view; (D–F) left prefrontal in dorsal (D), lateral (E), and posterior (F) view; (G–K) frontals in dorsal (G), ventral (H), anterior (I), posterior (J), and left lateral (K) view; (L–O) parietal in dorsal (L), ventral (M), anterior (N), and left lateral (O) view; (P–Q) supratemporals in dorsal (P) and left lateral (Q) view; (R) prootic in left lateral view; (S–T) right quadrate in lateral (S) and posterior (T) view; (U–X) left maxilla in dorsal (U), lateral (V), medial (W), and ventral (X) view; (Y–Z, A’) left palatine in dorsal (Y), lateral (Z), and ventral (A’) view; (B’) ectopterygoid in dorsal view; (C’) overlapping pterygoids, right pterygoid in ventrolateral view obscuring most of left pterygoid lying underneath (in dorsolateral view). Abbreviations: alp, anterolateral process of ectopterygoid; amp, anteromedial process of ectopterygoid; asaf, anterior superior alveolar foramen of maxilla; bv, foramen for blood vessel; chp, choanal process of palatine; cid, foramina for exit (posterior) and re-entry (anterior) of nerve that innervates the constrictor internus dorsalis musculature; df, descending flange of nasal; dl, dorsal lappet of prefrontal; ep, ectopterygoid process of pterygoid; fmp, frontals median pillars; fpf, facet for articulation with prefrontal; fp, facet for articulation with parietal; fq, facet for articulation with quadrate; fst, facet for articulation with supratemporal; hl, horizontal lamina of nasal; lf, lacrimal foramen; ll, lateral lamina of prefrontal; malf, maxillary labial foramen; mp, maxillary process of palatine; mV2a, maxillary foramen for accessory branch of maxillary division of trigeminal nerve (V2); mV2, maxillary foramen for maxillary division of trigeminal nerve (V2); pmc, parietal midsagittal crest; pmmc, posteromedial maxillary crest; pp, palatine process of maxilla; qr, quadrate ramus of pterygoid; V2, exit for maxillary branch of trigeminal nerve (cranial nerve V); V3, exit for mandibular branch of trigeminal nerve; VIIh, exit for hyomandibular branch of facial nerve (cranial nerve VII); VIIp, exit for palatine branch of facial nerve.

Figure 9. Eoconstrictor barnesi, GMH LIX-3-1992, paratype, digital renderings of the segmented lower jaw bones. A–C, left dentary in dorsal (A), lateral (B), and medial (C) view; (D–F) left compound bone in dorsal (D), lateral (E), and medial (F) view; (G) right splenial and angular in medial view; (H) right splenial and angular in lateral view (i.e. showing sutural contacts with dentary and compound, respectively); (I–J) left coronoid in medial (I) and lateral (J) view.Abbreviations:a, angular; aesc, crest for attachment of adductor externus superficialis muscle on compound bone; af, adductor fossa; aif, anterior intermandibularis nerve foramen; asf, anterior surangular foramen; cp, coronoid process; mc, mandibular condyle; mf, mental foramen; mg, Meckelian groove; pac, prearticular crest; pdp, posterodorsal process of dentary; pif, posterior intermandibularis nerve foramen; sac, surangular crest; sap, surangular process; sp, splenial.

Figure 10. Eoconstrictor barnesi, GMH LIX-3-1992, paratype, digital renderings of the segmented precloacal vertebrae.A–E, anterior precloacal in anterior (A), posterior (B), left lateral (C), dorsal (D), and ventral (E) view; (F–J) middle precloacal in anterior (F), posterior (G), left lateral (H), dorsal (I), and ventral (J) view.